0

Equipment of Ceramic Plants

Study Support

Dalibor Jančar

Ostrava 2015

VYSOKÁ ŠKOLA BÁŇSKÁ – TECHNICKÁ UNIVERZITA OSTRAVA

FAKULTA METALURGIE A MATERIÁLOVÉHO INŽENÝRSTVÍ

1

Title: Equipment of Ceramic Plants

Code: 635-3006/01

Author: Ing. Dalibor Jančar, Ph.D.

Edition: first, 2015

Number of pages: 54

Academic materials for the Metallurgical Engineering study programme at the Faculty of

Metallurgy and Materials Engineering.

Proofreading has not been performed.

Execution: VŠB - Technical University of Ostrava

1

TABLE OF CONTENTS

TABLE OF CONTENTS ............ CHYBA! ZÁLOŽKA NENÍ DEFINOVÁNA.

1 INTRODUCTION .......................................................................................... 5

2 RAW MATERIAL EXTRACTION ............................................................. 7

2.1 Excavators ........................................................................................................... 7

2.1.2 Bucket chain excavator ........................................................................................... 7

2.2 Loaders ................................................................................................................ 8

3 RAW MATERIAL TRANSPORT ............................................................. 10

3.1 Conveyors .......................................................................................................... 10

3.1.1 Belt conveyors ....................................................................................................... 11

3.1.1.1 Cable belt conveyor ........................................................................................ 11

3.1.1.2 Steep belt conveyor ........................................................................................ 11

3.1.2 Bucket elevator ...................................................................................................... 11

3.1.3 Threaded conveyor ................................................................................................ 11

3.1.4 Rollway ................................................................................................................. 11

3.1.4.1 Driven ............................................................................................................ 12

3.1.4.2 Gravity roller .................................................................................................. 12

3.1.5 Transport slides and chutes ................................................................................... 12

3.1.6 Suspended bench conveyors.................................................................................. 12

3.2 Pneumatic transport equipment ........................................................................ 13

3.2.1 High-pressure pneumatic transport ....................................................................... 14

3.2.1.2 Cell feeders ..................................................................................................... 14

3.2.2 Pneumatic transport of (medium-pressure) mixers ............................................... 15

3.2.3 Pneumatic transport of aerating chutes ................................................................. 15

3.3 Inter-object transport ........................................................................................ 15

3.3.1 Rail and automobile transport ............................................................................... 15

3.3.2 Interoperational transport ...................................................................................... 15

3.4 Liquid transport equipment (dredge) ................................................................ 16

3.4.1 Single-acting piston pump ..................................................................................... 17

3.4.2 Rotary pump .......................................................................................................... 17

3.4.5 Dredge pump ......................................................................................................... 17

4 BATCHERS, FEEDERS ............................................................................. 19

4.1 Belt feeder ......................................................................................................... 20

4.2 Apron feeder ...................................................................................................... 20

2

4.3 Roll feeder ......................................................................................................... 20

4.4 Vibration feeder................................................................................................. 20

4.5 Disc feeder ......................................................................................................... 20

4.6 Rotary-gate (flight) feeder ................................................................................. 21

4.7 Chain (screen) feeder ........................................................................................ 21

4.8 Feeding screw feeder ........................................................................................ 21

5 SIZE REDUCTION ..................................................................................... 22

5.1 Jaw breaker ....................................................................................................... 23

5.2 Cone crusher ..................................................................................................... 23

5.3 Roll crusher and breaker .................................................................................. 24

5.4 Antifriction crusher and breaker ....................................................................... 24

5.4.1 Weight crusher and breaker................................................................................... 24

5.4.2 Centrifugal breakers .............................................................................................. 24

5.5 Rotory crushers and breakers ........................................................................... 25

5.5.1 Rotory crushers and breakers with swinging mixing devices ............................... 25

5.5.2 Rotory crushers and breakers with fixed mixing devices ..................................... 25

5.6 Gravity roller breakers ..................................................................................... 28

5.6.1 Ball breakers .......................................................................................................... 28

5.7 Bar breakers ...................................................................................................... 29

5.8 Autogenousbreakers .......................................................................................... 30

5.9 Centrifugal(planetary) breakers ....................................................................... 30

5.10 Vibration breakers........................................................................................... 30

5.11 Míxer breakers (attritors) ............................................................................... 31

5.12 Colloid breakers .............................................................................................. 32

5.13 Jet spray breakers ........................................................................................... 33

6 SEPARATION .............................................................................................. 35

6.1 Sorting ............................................................................................................... 36

6.1.1 Mechanical sorting ................................................................................................ 36

6.1.2 Water (hydraulic) sorting ...................................................................................... 36

6.1.3 Air separation sorting ........................................................................................... 37

6.2 Separating ......................................................................................................... 38

7 MIXING AND HOMOGENIZATION ...................................................... 40

7.1 Prehomogenisation............................................................................................ 41

7.2 Míxers ................................................................................................................ 41

3

8 FORMING .................................................................................................... 43

8.1 Pressing ............................................................................................................. 44

8.1.1 Dry and semi-dry pressing .................................................................................... 45

8.1.1.1 Granulation ..................................................................................................... 45

8.1.1.2 Single-action compression ............................................................................. 46

8.1.1.3 Double-action compression ............................................................................ 46

8.1.1.4 Isostatic pressing ............................................................................................ 47

8.2 Plastic forming .................................................................................................. 48

8.2.1 Drawing ................................................................................................................. 49

8.2.1.1 Drawing worm presses ................................................................................... 49

8.2.2 Thowing ................................................................................................................ 50

8.3 Casting .............................................................................................................. 51

9 RECOMMENDED LITERATURE ........................................................... 54

4

STUDY INSTRUCTIONS

Ceramic works equipment

You have obtained study material for the part-time study of the second semester subject Gas

Engineering from the study branch Thermal Equipment and Ceramic Materials.

Prerequisites

The subject doesn´t have any prerequisites.

Subject objective and learning results

The objective of the subject is to be made acquainted with the technological flow of ceramic

material production from the extraction of basic raw materials up to the resultant forming of

final shapes.

After studying the subject a student should have:

knowledge results

Knowledge of equipment for mining, loading, transporting, processing and treating raw

materials

Knowledge of the machines presently used for forming ceramic products.

skills results

The capability of independently choosing certain equipment (machines) for an individual

technology, kinds of materials and the final properties of products.

When studying each chapter we recommend the following procedure:

To read chapter categorization.

To study a chapter through to understand the principle of given technological equipment.

The method how to communicate with the teacher:

It is possible to communicate with a teacher using the email address: dalibor.jancar@vsb.cz

or telephone number: 597 321 537.

Subject guarantor: Ing. Dalibor Jančar Ph.D.

Lecturer: Ing. Dalibor Jančar Ph.D.

5

1 INTRODUCTION

Chapter sections:

equipment selection and design for ceramic works;

technological procedures of ceramic works production;

raw material extraction - excavators;

loading raw materials - loading machines.

Study time: 30 minut

Objective: After studying through these chapters

you will know the technological operation of ceramic works from

deposit exploration to the final product;

you will be acquainted with basic extractions and loading machines;

Lecture

When selecting and designing equipment for ceramic works it is necessary to

proceed mostly from the raw material basics, which we have available. This means that the

selection of various types of equipment is subordinated to the method of processing extracted

raw materials and their properties (fragility, adhesiveness, etc.). It is necessary to take into

consideration that raw materials can sometimes change their own character, and that is why it

is necessary to carry out a proper survey of deposits.

Technological procedure for ceramic works production:

raw material extraction (excavators, loaders),

raw material transport (conveyor belts, ropeways, automobile transport and

other ways),

feeders

6

reduction equiment (crushers, breakers),

raw material separation (meshes, grills, sorters),

blending and homogenisation (mixers, smoothing),

forming

It is necessary to be aware that the limiting element of a ceramic works is its

oven. It is the most expensive equipment, it is difficult to exchange, and creates the final

product. That is why in selecting individual equipment before final processing, we always

have to have a capacity reserve for individal equipment. During such a procedure we cannot

then have an interruption of production for the individual sections of continuous raw material

processing.

7

2 RAW MATERIAL EXTRACTION

In this area there is found equipment for the mining and loading of raw materials

which are known as excavators and equipment for loading raw materials by equipment known

as loaders.

2.1 EXCAVATORS

An excavator is mechanical equipment, which is used for separating lightly

disconnected rock (soil, gravel, sand, brick clay) and for loading heavy disconnected rock,

which has already been broken up and is found in landfills or directly in a quarry. The

performance of this equipment is recorded in [m3/hour] or in [t/hour].

2.1.1 Single-bucket excavators

They are used for mining rocks of various hardness, of dry and plastic, lumpy rocks

broken up by blasting. The basic part is the bucket, according to which it they can be divided

into buckets with the upper or lower bucket.

Excavators with upper buckets are used for loading broken-up rock (limestone) for

earth work above the terrain level or for mining gravel, sand and clay rock.

Excavators with lower buckets are used when deepening pits of smaller dimensions, in

building constructions and for the mining of soil under the water surface level, for treating

terrain, etc.

The operational performance of single-bucket excavators depends mostly on the bucket

dimension (m3), the loosening-up of soil co-efficients, the soil density (t.m

-3), the working

cycle (s).

A forward shovel (bucket) has a tilted bottom, through which it is emptied and

produces a volume of 0,15 m3 to 4 m

3, even exceptionally more.

There are used most often with belt or bucket-wheel undercarriages, rarely with rail

undercarriages or walking undercarriages.

2.1.2 Bucket-ladder excavators

They are used for excavating lightly disconnected materials (gravel sand, clays, brick

clay), for terrain treatment, for excavating sand from the bottom of the water surface, at the

level at the bottom of the river, for material handling at landfills, for raw material

homogenization, and other areas. They have a high output, as their operation is uninterrupted.

The working parts are wheel buckets. They are hollow vessels with a content of 25 to

150 l, and with a big excavator up to 250 l. The wheel buckets are fastened to a linked chain

which circulates in the bucket ladder. Guiding pulleys guide the linked chain. An excavator

has a self-propelling undercarriage, for which it is necessary to construct a rail track. Before

activating the machine it is necessary to treat the terrain for excavation.

8

The operational output of bucket-ladder excavators depends mostly on the dimension

of the bucket wheel (m3), the bucket wheel spacing (m), the chain speed (m.s

-1), and the co-

efficient of the loosened-up soil.

The biggest excavators are over 200 meters long and have a height of 100 meters.

Bucket-ladder excavators can deepen a pit the length of a football pitch at a depth of

over 25 meters in one day. At top speed they can travel along a highway at one kilometer per

hour, of course it lasts a while.

2.2 LOADERS

Loaders are machines which scoop up soft, broken-up rock, and also other granular

material and load them onto a transport container. They are simple structurally and lighter in

operation than excavators.

Loader categoriation:

1. Cyclically working with buckets - front-loader

- overhead

- rotating

- tunnel maker

2. Continually working a) bucket-wheel - with rotating conveyor belt

b) worm (screw) - stroking

c) bucket

d) plate

e) scraper loader

Summary concept:

After studying this chapter through the following concepts should be clear

for you:

selection of ceramic works design;

the selection of suitable technology for excavating and loading raw

materials according to the type of raw material

Questions:

1. What is necessary to occur during selecting and designing equipment for

ceramic works ?

9

2. What is the general technological procedure for ceramic works

production? What is the limiting factor in ceramic works?

3. What do we select suitable technological equipment for mining and

loading according to?

4.

What are the most known types of equipment for excavating and loading

raw materials?

5. What does the operational output of wheel bucket and bucket ladder

excavators mostly depend on?

10

3 RAW MATERIAL TRANSPORT

Chapter sections:

basic raw material transport categorization:

conveyor belt categorization;

loose and lumpy raw material transport.

Study time: 35 minutes

Objective: After studying through this chapter

you will know the basic types of mechanical conveyor belts.

Lecture

Transport and material handling only passively share in the production process.

because it does not directly influence their own technological activity.

Categories:

Fluent (conveyor belts, chutes, pneumatic and hydraulic transport, etc).

Interrupted (ropeways, cranes, lifts, ships, rail and non-rail vehicles, etc.)

3.1 CONVEYOR BELTS

Conveyor belt categories:

1. Mechanical with a drawing component

2. Mechanical without a drawing component

3. Hydraulic (using rollerways)

4. Pneumatic

11

3.1.1 Belt conveyors

Belt transport is one of the most economical and efficient means of transport for short

and middle distances. It is possible to divide belt transport into:

Transport for short distances (4 - 20 m).

Transport for large distances (100 - 5000 m)

It is used for the transport of powder, loose and non-adhesive granular materials. The

conveyor belt slope angle determines the material angle of discharge, which is the root angle

of the straight surface line of the discharge taper of loosely poured non-coherent material. The

smaller the angle of discharge, the more material caving in from the belt. It can be up to 24°.

The drawing component of the conveyor belt is a belt. It can be made of textile, rubber, or be

reinforced or with steel. It is placed on load-bearing rollers.

3.1.1.1 Cable belt conveyor

It is used for distant transport. A rubber belt with a profiled edge bears a pair of non-

metallic cables, which are also drawing cables. The suspended belt conveyor removes the

resistance of the rubber belt when shifting to load-bearing rollers (the rubber belt is not

burdened by the force of traction), which enables it to be used even for several kilometers of

long transport.

3.1.1.2 Steep conveyor

It is determined for transporting material in a soft state and adhesive, partially pre-

crushed earth under a slope of 80°. It consists of a load-bearing belt conveyor and a forced-

down belt, which copies the shape of the load-bearing conveyor. The drawing profile of the

load-bearing belt is partially trough-shaped. The material on the load-bearing belt is loaded by

a hopper, where it is caught after its release by a forced-down belt. The transport speed of

both belts is the same, so that material is carried away almost vertically towards a drive pulley

and it proceeds on for further technological treatment. It saves using a built-up area.

3.1.2 Bucket elevator

It is used for the vertical transport of loose, lightly-granular and non-adhesive

materials. It continuously works and solves spatial problems.

3.1.3 Threaded conveyor

Material is transported in a steel chute along a helix.

The transport chute is closed with a cover against dust and it is possible to empty the

chute in any location. It can also have reserve functioning. It is used for loose materials. The

maximum temperature of transported material is up to 70 °C, for conveyors produced from

special alloys they can reach a temperature up to 300 °C.

It must not be used for sharp or adhesive material!

3.1.4 Rollerway

12

It is used for lumpy products (bricks, linings, panels, glass, cases, boards, etc).

Categories: 1 Driven - by cogwheels, by chains, towing

2. Gravity roller (an inclination from 5 to 15°).

3.1.4.1 Driven

Lumpy material is transported along rollers driven most often by an electrical motor.

For the roller drive there is used tapered cogwheels or a roller chain. The spacing of rollers is

selected so that a transported piece lies on at least three rollers at the same time.

3.1.4.2 Gravity roller

Material moves along small rollers. It is used for short distances. It has an inclination

of 5 to 15°. It sometimes can be horizontal, and then the transported material has to be pushed

manually.

3.1.5 Transport slides and chutes

It is used for granular and non-adhesive materials. It uses gravitation (the chute

inclination has to be greater than the material angle of discharge) + shedding.

3.1.6 Suspended bench conveyors

It basically concerns a chair lift cableway closed in a circuit. It is used for transporting

pressings, slabs, dry bricks and other products in ceramic works. It can go through an oven, in

which enamelled products are placed. It then has to be made of high-grade, creep-resistant

steel.

Concept summary:

After studying through this chapter the following concepts should be clear to

you:

the selection of a suitable conveyor for loose and lumpy materials

according to the kind of material and transport location.

Questions:

1. What is the angle of discharge and how is it determined?

2. What is the maximum angle of discharge of transported material for

transport using a belt conveyor?

3. What suitable belt conveyor adjustment is used to overcome transport

13

steepness?

4. From what material do we select a belt conveyor belt for sharp-edged

materials and materials with high temperatures?

5. What conveyor is most suitable for vertical transport?

6. What kinds of rollerways can we encounter?

3.2 PNEUMATIC TRANSPORT EQUIPMENT

Chapter sections:

powder raw material transport - pnuematic transport;

pneumatic transport categories;

high-pressure pneumatic transport;

medium-pressure pneumatic transport;

pneumatic transport using aeration channels;

interobject transport.

Study time: 45 minutes

Objective: After studying through this chapter

you will know the basic types of pneumatic transport for transporting

powder raw materials.

you will know the basic types of interobject transport

Lecture

14

In plants for the production of building materials on the basis of the silicate transport

of powder materials compressed air is being used more and more. Especially in the transport

of non-adhesive powder or lightly-granular materials, for example cement, ash, limestone,

koalin, foundry sand, and similar materials. As a complementary part of separating air

equipment systems, they are used to shift captured solid particles for the storage and

depositing of waste, or for the transport of separated products for further treatment. We can

divide pneumatic transport into mobile and stationary transport. Among mobile pneumatic

transport we can count loose materials of the most various mobile media - containers, crates,

trailers. Stationary pneumatic transport is thought of as solidly built-in equipment in a certain

location. Material is transported through a tube to distances from 1000 m up to a height of 40

m [1].

Stationary pneumatic transport categories:

Low-pressure

Medium-pressure

High- pressure

Transport using pneumatic chutes

3.2.1 High-pressure pneumatic transport

It is mostly used to fill in cement reservoirs and to empty them. Compressed air is

used for transport with a pressure 0,23 up to 0,8 MPa. The trasport pipeline is a seamless steel

tube with diameters 70, 80, 100, 125, 150 up to 200 mm. For the transport of solid abrasive

materials there is used a steel pipeline lined with basalt. A cyclone and hose filter is used for

separating the transported material from the load-bearing air. The most important part of the

pneumetic system is the equipment for supplying powder material and for mixing with load-

bearing air, that is feeding equipment (Fuller pump, chamber feeder).

3.2.1.1 Fuller pump

The principle of a cantilevered Fuller pump is maybe this: The pump is made of two

chambers (pressure and mixing) separated by a valve. Powder material in measured dosages is

fed into the mixing chamber. If the pressure of the powder material grows to a prescribed

level, the valve opens and the material falls into the mouthpiece spaces, which are in the

lower parts of the mixing chamber. A helix is used for pushing the air out of the powder

material, and to prevent it from going into the mixing chamber.

3.2.1.2 Chamber feeders

Differing from the Fuller cantilever pump, it work interruptedly. And it is in two

phases. In the first phase there is the filling of pressure vessels with the powder material and

their closing. In the second phase there is the joint opening of the valve for supplying

compressed air and the emptying of the opening into the pipeline.

If we want to have a continuous supply, we use two pumps. Thus always in the first

phase there is the filling of one pump and in the other the emptying, and in the second phase

the opposite.

15

3.2.2 Pneumatic mixing transport (medium-pressure)

The pneumatic material transport sysyem using a mixer is suitable for dry, loose, non-

adhesive materials continually transported in smaller amounts for further production or

storage, for example for the transport of separated ash in boiler houses.

The separated material falls from the discharge chute to the rotating feeder, under

which a mixer is placed, ensuring the mixing of air with the material. The source of the

pressure air is a ventilator or blower. Aerating the operational (storage) resevoir is carried out

using filtering equipment located on the resevoir. Its regeneration is ensured by the blow of

pressure air [2].

3.2.3 Pneumatic transport using aeration chutes

In some cases it is suitable to use transport using pneumatic transport chutes instead of

high-pressure pneumatic transport. Especially when transporting short distances, where

favourable conditions are created for it, and where a space is available for the necessary

inclination of pneumatic transport chutes. In this case transport equipment is composed of the

source of pressure air (most often a ventilator station), the intake of pressure air with a

regulating body, the transport chutes themselves including material inlets, branches,

ventilation valves, discharges and aeration. It basically can be said that the only fundamental

difference is that this transport doesn´t have a mixer.

3.3 INTEROBJECT TRANSPORT

It is used for transporting building materials (quarry stone, clays, gypsum, brick clay,

flour, crushed stone, final products). It is necessary to transport this material into the

production process and shift it using an individual production operation. And after treatment

to move it to shipping and to transport it to the place of consumption.

3.3.1 Rail and automotive transport

Rail transport moves mainly raw materials and fuel and takes final products away.

Automotive transport in industry for the production of building materials and fire-resistant

materials transports up to 60 % of the volume of all materials. Lorries are the most wide-

spread means of transport in the silicate industry for shorter and longer distances when

transporting raw materials.

3.3.2 Interoperational transport

It is used for the transport of pressings into drying rooms, the transport of dried

products to ovens and final products from ovens to the storage of goods. For example, there is

a deck-convoy vehicle, which moves along rails, furthermore electric car traversers and

various kinds of convoy lorries. Deck-convoy lorries are used for the mechanized transport of

ceramic products between convoy lorries and drying room chambers. Car traversers are rail

transport machines with low platforms for transporting convoy vehicles or oven vehicles on

permanent tracks.

16

Concept summary:

After studying this chapter through the following concepts should be clear to

you:

pneumatic transport;

what a Fuller pump is;

what chamber feeders are used for;

which types of transport fall under interobject transport.

Questions:

1. What are the most important parts of high-pressure pneumatic transport?

2. What are chamber feeders used for?

3. Where is it possible to use raw material transport using aeration channels?

3.4 EQUIPMENT FOR FLUID TRANSPORT ( DREDGE)

Chapter sections:

dredge transport - kinds of pumps:

pump output;

Necessary study time: 10 minutes

Objective: After studying through this chapter

you will know the basic types of pumps used for dredge transport

Lecture

17

At cermaic works plants it is sometimes necessary to transport the dredge from

separation into gypsum forms to higher locations than those which this dredge was prepared

in. For these purposes there are used:

3.4.1 Single-acting piston pump

A liquid is transported through them using pressure brought about by the piston

motion in a cylinder.

A crank mechanism introduces it into activity. A liquid enters into a cylinder using the

suction opening, on which the suction pipeline is fixed. The liquid leaves the cylinder through

the outlet opening, onto which the discharge pipe is fixed.

Regulation:

by changing the rotation

using a water accumulator

The piston pump does not have a large transport output, but reaches high pressure up

to 40 MPa.

3.4.2 Rotary centrifugal pump

For transporting liquids and dredge with a large output a rotary pump is used. This

deals with a high-speed machine of relatively small dimensions, which favourable is shown in

its mass and price. The most important parts of the pump are the rotor made of a shaft with a

rotor wheel and the pump case.

Regulation:

by changing rotation

by throttling the discharge pipe

Total efficiency: 85 – 88%.

3.4.5 Dredge pump

It is used for transporting water with rough mixtures (dredge, etc.). It has a large

clearance and reaches low pressures.

Concept summary:

After studying this chapter through the following concepts should be clear

to you:

what kinds of pumps are possible to use for transporting dredge;

what the efficiencies of individual pumps are;

18

Questions:

1. What kinds of pumps are possible to use for dredge transport?

2. Can you explain the principle of the piston pump?

38

19

4 BATCHERS, FEEDERS

Chapter sections:

supplying raw materials - batchers, feeders;

Time necessary for study: 20 minutes

Objective: After studying through this chapter

you will know the basic kinds of equipment for the uniform supply of

materials,

Lecture

They are used for supplying exactly measured amounts of loose, granular and non-

adhensive elements into mixing equipment or for the uniform supply of various materials into

crushers and breakers not to lead to their clogging up.

Categories:

For dry granular material: 1. Movable a) belt

b) apron

c) vibration

d) chain

e) roll

f) disc

g) rotary gate

2. Rotary

For adhesive material 1. roll

2. cased

3. roll with a feeding thread

For opening material 1. helixical

20

4.1 BELT FEEDER

A belt feeder is used for feeding dry, powder and granular non-adhesive material

(max. to the grain dimension of 100 mm). If a rubber belt is used, the temperature of the feed

material must not exceed 80 °C.

Regulation

using a closing slide (a change in flow profile)

a speed change in the fed material

4.2 APRON FEEDER

It precisely is concerned with a form of a belt feeder. Instead of a belt there is a chain,

which enables the transport of material under an angle up to 20°. It is used in the civil

engieering and ceramic industries for loose and rough-grained materials.

4.3 ROLL FEEDER

It is used for feeding light and lumpy materials (max. granulity of 150 mm). The main

part is a rotating cylinder, which can be cylindrical or multi-edged. With the turning of the

cylinder, material is brought out to the surface by friction. The amount of fed material is

regulated by a closing slide or by speedily rotating the cylinder.

4.4 VIBRATION FEEDER

The working part of the machine is a suitably formed chute, produced from a steel

sheet. An electrical magnetic vibrator is connected to the chute and material begins to be fed

along the chute through vibration. A form of transport slide.

.

If the feeder has to sort as well, it has to have two meshes. It is used for dry, non-

adhesive materials up to a size of 150 mm and a maximum temperature up to 70 °C. It has

small energy consumption, simple service and minimal wear of its functional surface.

4.5 DISC FEEDER

Disc feeders are derived from disc batchers. Material falls in them through a vertical

mouthpiece onto a coaxial plate, which is screwed onto the flange of a threaded wheel placed

in the housing of the drive mechanism coming from a drive screw. It is possible to regulate

the height of their layer of material either by a telescopic membrance under the disc (that is a

collector) or by regulating the size of its diameter at a dimension 630 up to 250 mm, or if need

be by the height of the filling cylinder (using a screw) In regards to requirements to constantly

regulate the peripheral speed on the disc diameters, the number of rotations is to the extent of

0,33 až 0,85 s-1

In its basic technical perimeters the disc feeder reaches a transport efficiency

of 0,033 do 0,825 m3.s

-1 The given technical design enables the feeding of all loose and

granular materials with various speeds up to a granule size of 200 mm (for example, sand,

21

crushed stone material, gypsum and cement. The working part is a horizontal disk. Material

is collected from the disk by an adjustable colletor.

4.6 ROTARY GATE (FLIGHT) FEEDER - ROLL

They are made up of a bladed wheel which rotates in a roller with inlet (upper) and

outlet (lower) openings. In the state of rest the wheel blades prevent the flow of material.

When the wheel turns material pours into the upper chamber, which slightly turns to the lower

position enabling its emptying out. The working part is then a gate (rotor) which has 6 to 12

blades. The size of the gate gives the grain size of the supplied material, which can be 12 - 50

mm. The amount is regulated by changing the rotation of the closing slide or gate. It is

suitable only for dry materials with small granulity.

4.7 CHAIN (SCREEN) FEEDER

Chain (screen) feeders consist of sets of linked chains, which are loosely suspended on

a roll beside each other. In a state of rest hanging linked chains prevent material from falling

out of the reservoir. After putting the chain into operation in the arrow direction in a

changeable number of rotations at a dimension 0,25 - 0,5 s-1

the material is passed on for

further transport.

4.8 FEEDING SCREW FEEDER

Feeding screw feeders, working on the principle of worm conveyors, are mentioned in

the chapter about plastic forming.

Concept summary:

After studying through this chapter the following concepts should be clear

to you:

for what reasons feeders are used;

what kinds of feeders are used in ceramic works;

Questions:

1. What kinds of feeders are used in ceramic works?

2. With what is it possible to regulate the amount of fed material for a roll

feeder? What materials are suitable for rotary gate feeders?

3. What is the biggest advantage of a disc feeder?

4. What is a chain (screen) feeder used for?

22

5 SIZE REDUCTION

Chapter sections:

the purpose of size reduction;

granular system characteristics;

size reduction machine categories;

crushers and breakers with directly driven mechanisms.

Necessary study time: 120 minutes

Objective: After studying these chapters

you will know the concepts of specific surface, the milling curve;

you will know basic kinds of crushers and breakers;

you will know the difference between a crusher and a breaker.

Lecture

Is it one of the main operations. It deals with reducing, which is carried out for the

purpose of:

1. separating valuable minerals

2. it is assigned for products of a certain size

3. it is assigned for products with larger surfaces- fine

It deals with very energy demanding operations.

An important numerical characteristic of a granular system is special surface S (or also

surface density Sv), which is the parameter of the average (mean) values of the roughness of

the entire granular system. When the same mass of the solid phase system grows, the surface

size, reducing the size of the particles hyperbolically, that is the specific surface, is the

indirectly specific size of the particles.

23

WITH SIZE REDUCTION DEVICES

I. Crushers and breakers directly driven by devices

5.1 JAW BREAKERS

They are used for crushing large pieces of raw materials.

They are made up of two jaws, one moveable and the other fixed. It concerns a

pendulum with the moveable jaw, driven by an eccentric shaft. For a single-toggle crusher the

sense of rotation is important for the pulling-in of material into the groove between the jaws.

.A single-toggle crusher is used as a secondary crusher for example for the production

of gravel into concrete.

A double-toggle crusher is used as a primary crusher for crushing quartz, limestone,

magnesite, burnt clay, shale, glass cullets, fire clay fragments and for crushing various rocks

in the gravel industry

The advantage of jaw breakers is that they have little dust nuisance, of course in

comparison with impact crushers (viz Chapter 5.5.2). They have a lower reduction ratio,

meaning input material contains less fine particles.

5.2 CONE CRUSHERS

They are similar to jaw breakers, but their wedge-shaped mouth is round. It is again

used for hard, fragile and non-lubricated materials. As opposed to jaw breakers, the advantage

is their fluent running with shaking, smaller energy consumption and greater production

capacity.

Categories: a) acute-angle

b) obtusangular

c) with a fixed shaft

Acute-angle cone crushers have an apex angle of an acute crusher cone cca 20°. The

shaft axis is slanted (an inclination of 1 – 2°) as opposed to a notional cone axis, whose cone

copies the conical surface and there is crushing between the cone and fixed jaws. The

crushing cone is solidly set on the axis. It is used for rough crushing.

The principle an obtusangular cone crusher is the same as an acute-angular one, the

precise apex angle of the crusher cone is obtuse (cca 100°). It is used for light crushing.

Cone crusher with a fixed shaft (that is a gyratory crusher) has a fixed axis

eccentrically set by the driving body, which bears the crusher cone. The axis is parallel with

the slope axis - it copies the roll surface.

A.

24

5.3 ROLL CRUSHERS AND BREAKERS

Size reduction is carried out by reducing the pressure between two parallel rolls

turning against each other. The size of the output granule determines the goove between the

rollers. One of the rollers is pressed towards the second roller using a spiral spring or

hydraulically. They are used for medium-size and light crushing, or is need be grinding hard,

fragile material, such as quartz, feldspar, fireclay and magnesium scar. The peripheral speed

of both rolls is mostly the same, only for the reduction and spread of plastic components, is a

more economic diffterental speed of rolls, that is the roll differencial. The same effect is

reached when there is the same rotation with various roller diameters.

For soft and medium-size hard materials (chalk, limestone, magnesite) a toothed-roll

is used. In processing soft materials (brick clays) there knife rolls are used, which are slotted

or toothed type, or of a "hedge-hog" and "wolf" type.

5.4 ANTIFRICTION CRUSHERS AND BREAKERS

Reduction machines fall into this group, which is equipment on which material is

forced between two joint rolling surfaces: a grinding body, that is a cylindrical or conical

tread ( tread breakers) or balls (circulating crushers) and a grinding path, which is ringed (ring

crushers) and it is either even, dish-like, conical or cylindrical.

5.4.1 Weight crushers and breakers

Among the most know types of weight crushers and breakers there are Edge crushers,

which are either for wet grinding (extrusion) or for dry grinding (screening).

Treads on the wet-grinding crushers rotate and material is pushed through across a

static bowl. Central moistening is located on the main shaft. It is used for the wet processing

of brick clays.

Conversely, for dry-grinding crushers the bowls rotate and the treads stand. It is used

for the continuous grinding of dry mixtures in fire protection industries. The entire crusher is

closed and connected to a dust exhaust.

5.4.2 Centrifugal breakers

These breakers have a fixed ring grinding track and circulating grinding bodies, treads

or balls, pressed onto a ground stock by a centrifugal force. The crushers are high-speed,

working from 100 to 200 rotations per minute. The main group are Pendulum crushers, less

often there are Circulation crushers.

Pendulum breakers are machines with a vertically driven shaft connected by a frame,

on which a pendulum hangs, carrying a rotationally set tread, that are pulleys. During rotation

pendulums space out and press treads with centrifugal force on the vertical ringed mixing

tracks.

25

5.5 ROTATING CRUSHERS AND BREAKERS

Rotating machines have various impact tools, be they pivoted, that is a hammer or pin

or fixed, blades, or crosses. Its job is to impact material and knock it out. As opposed to

crushers and breakers with slow loaded material between a pair of active components it

concerns loading with high speeds and this is mostly on one working surface.

Categories: a) swinging with a grinding tool

b) fixed with a grinding tool

5.5.1 Rotating crushers and breakers with swinging grinding tools

What mostly belongs here are Hammer crushers, Hammer breakers and Pestle

(piston) crushers.

Hammer crushers and breakers have one or two rotors, on which are pivotally hung

hammers which are in a radical impact position during operation. The supplied material is

reduced under impact, shock or shear. In the lower part of the working area there are mostly

meshes preventing the outlet of excessive granules into a product. They are used for crushing

and grinding soft and medium-hard materials with grindability with not too much moisture

and toughness, such as limestone, gypsum, chalk, slate, coal, clay, bauxite and marl. They

have a simple structure, moderately small dimensions and high production capacity. The

reduction level is from 40 to 50.

Twin-rotor hammer crusher has two high-speed shafts rotating against each other,

bearing a pair of straps, between which a hammer is hung in a pivot. The material moves

upwards. crushed material falls through onto a drop screen, on which a second degree of

crushing is set.

Single-rotor hammer crusher mostly has instead of two straps a rotor, on which

hammers are hung on rolling pins. They are used for crushing fragile materials, such as

limestone, fireclay, cinder and clays

Hammer crushers for adhesive materials are constructed with a roll or with a scaled,

circulating mesh. The roll motion has a cleaning effect (it prevents pasting over of the

working areas), and even a transport effect. Crushers are used in cement factories for crushing

brickwork raw materials.

Hammer breakers work similar to hammer crushers, but they have a greater number of

lighter hammers, and the construction is less robust. The peripheral speed of hammer breakers

is 20 až 50 m.s-1

, and hammer crushers over 50 m.s-1

.

5.5.2 Rotor crushers and breakers with fixed grinding tools

For bladed breakers the ground stock is fed into the air flow (or the hot air flow) and

in the rotor between the blades and housing, that is in the grinding chamber between the

blades, turbulence is caused by pressure changes and vibrations, which leads to particles

colliding together, to "self-rubbing". The product is transferred by the airflow into a cyclon.

The air then goes out through a filter to the surroundings. The centrifugal unground product

returns from the upper area of the rotor back to the final grinding. The diameter of the rotor is

250 to 1000 mm. The gap between the stator and rotor is 5 to 12 mm. The peripheral speed of

26

the blade is 60 to 100 m.s-1

. It is used for grinding fireproof and ceramic clays, kaolin,

bergmeal, bauxite and talc. It grinds at a medium fineness 300 m or at a big fineness 50 m.

Bolt breakers are also called basket or cage breakers or disintegrators, and they have

peg bolts caught on one side on a circular panel, that is a stator or rotor, and on the other side

along the individual circular rows in ringed flanges of a semi-cicular shape, so that they create

a cage or basket. The material is reduced by impacts between the bolts by two rotating rotors

moving in a counterdirection (with a peripheral speed of 20 to 40 m.s-1

). They are used for

light crushing or rough grinding of soft and fragile materials with small abrasivity, for

grinding chalk, gypsum, coal and dry clays (with moisture less than 11 %). The imput granule

is up to a size 20 to 40 mm. The output product has a max.granule of 4 mm.

Peg breakers - impact breakers with loose-ended tools. have on the rotor either on one

or both sides a tool sticking out in the shape of a peg, a nib or a cross. They are also often

called attritors (the same name is used even for mixer breakers, Chap 5.11). They are used for

the light grinding of soft up to medium-hard materials (limestone, talc, chalk, graphite). It is

possible to control product granulity by rotation selection and by the number of pegs.

Impact crushers and breakers reduce material not only by impact in a rotor with a

solidly anchored blade, but also by the sudden impact of cast off pieces on the impact amour

plates or grills. They are able to process big boulders and give a good isometric shape to a

product. They have one or two cylindrical rotors, provided with 2,3 or 4 interchangeable

blades, which knock material out, and cast it off against the armour plate or grill impact walls.

Pieces are sorted on it and fragments or whole pieces are regularly taken away along the

arising cracks and fly back against the rotor. New material is thrown against it, it crashes into

it - causing autogenous crushing. Some impacted pieces are again involved and cast off by the

blades again against the impact walls. A series of such impacts continues as long as there is a

sufficiently light product, on which a lesser centrifugal force works. It finds a gap between the

impact wall and the rotor or the impact grill. The size of the output product granule is 40 mm

It is possible to control the granulity to a certain measure by revolution. They are used for

grinding limestone, cement sintered clay, fireclay, ore, coal, coke, basalt, granite and gravel to

concrete. They can even process pieces over 1 m in diameter!

For mechanical sweeping crushers and breakers material is cast off using the

centrifugal force of radical blades axially sticking out from a horizontal sweeping disk - the

rotor against the peripheral armour plate ring, where it shatters. The crusher can be a single-

rotor or dual-level with two disks. It is suitable for the selective crushing of brittle and

abrasive materials, limestone, cement sinter clay. Max. granulity of the output granule is

100 mm. In breakers of this type of air resistance plays a role on light particles. That is why

special vacuum sweeping breakers were developed.

Pneumatic swepping breakers which give the material speed by air flow from jets. The

material falls into the space betwen the mouth of the air jets (400 m.s-1

) and cast-off tubes,

which are channeled on the impact wall, with which it shatters. A product is carried out by the

air into the separator, In this way SiC can be processed.

Concept summary:

After studying this chapter the following concepts should be clear to you:

27

specific surface;

grinding cruve;

the purpose of size reduction;

the difference between a crusher and a breaker;

the selection of suitable reduction tools for certain kinds of

materials.

Questions:

1. What is the purpose of size reduction?

2. Can you explain the concept specific surface?

3. What are basic size reduction machine categories?

4. What´s the difference between a crusher and a breaker?

5. What is a single-toggle crusher used for?

6. Can you explain the diffrence between a conical crusher with a

swinging axis and with a fixed axis.

7. What types of cylinders exist for cylindrical crushers and for what

materials are the individual types used for?

8. Can you explain the principle of an impact crusher?

II. Crushers and breakers indirectly driven by tools

Chapter sessions:

the principle of crushers and breakers indirectly driven by tools;

crushers and mixers indirectly driven by tools;

gravity roller breakers, principles, kinds;

gravity roller breakers, filled with ground stock and grinding bodies

- equations;

centrifugal, vibration and mixer breakers

28

Necessary time for study: 120 minutes

Objective: After studying this chapter

you will know the most important breakers used in the ceramic

industry;

you will know the equation to calculate the filling of a ball breaker

with ground stock and by grinding bodies

Lecture

In the second group there are breakers with size reduction grinding tools, and these

breakers with grinding tools do not move on tracks of a precisely determined structure, but are

usually made up of a great number of "tools" ((balls, bars, rolls, flints – pebbles, rough grain

ground stock) called grinding bodies and they loosely move in a closed grinding area. These

are called breakers indirectly driven by tools or also breakers with loose grinding bodies.

Grinding in these breakers takes place by the impact of bodies on the ground

stock or the friction between the grinding bodies, and even joint friction and impact

between particles

The frequency and intensity of impact and friction depends on the number of rotations

or oscillations per time unit, but it is the same for the number of grinding bodies, on their size

and mass (the density of material from which they are created).

5.6 GRAVITY ROLLER BREAKERS

Size reduction is carried out by the impact, pressure and friction of falling and the

effect of gravity of the loose grinding bodies. Most examples of gravitational breakers are ball

breakers.

5.6.1 Ball breakers

It concerns one of the most often used breakers in traditional light ceramics and in

cement production

29

Ball breakers are basically hollow barrels or cylinders. They turn around a horizontal

axis and they are partially filled inside with loose grinding bodies - most often iron or ceramic

balls. During breaker rotation the grinding bodies create a centrifugal force which is carried

upwards and falls after reaching a certain height. The material is falling and bodies are rolling

over, and are ground by hits (impacts) pressure and rubbing. In the cement industry ground

raw materials are consequently stored in homogenious strengths.

Roll breaker in ceramics is used most often for wet grinding. It can also be to mix raw

materials, but they do not have too different grindabilities. The filling and emptying takes

place through an opening with a closing and releasing (with a stopcock) lid. That is why they

have is an "aerating" opening. Emptying can occur with overpresure up to 0,3 MPa.

Single-chamber tube breakers have a length 3 to 8 times greater than their diameter.

They grind a passage in it. Ground stock enters into the breaker by a hollow pin and the

product is tightened by the outlet pin. They are used mainly in the cement industry for the dry

grinding of sintered clay and the wet grinding of raw materials.

Multi-chamber breakers. that is combined breakers, have individual chambers filled

with various big grinding balls

Tube breakers with a external separation between chambers that is multi-level

breakers, are divided with inaccessible barriers at 2 separate chambers, with every intake of

material from outside and through the peripheral output of a product.

For these types of breakers we grind in an opened or closed cycle.

Opened cycle: Ground stock is ground in one chamber, its product enters into an elevator and

it is carried into a sorter. The rough part from the sorter goes for final

grinding into the second chamber of the breaker. Its product is connected

to the fine fraction, then it is taken with it from the sorter

Closed cycle: Ground stock is ground in one chamber, its product enters into an elevator and

it is carried into a sorter. . The rough part from the sorter goes for final

grinding into the second chamber of the breaker. Its product enters again

into the sorter and all sorts of output leaves the sorter.

The difference is then only in that in the closed cycle the product ground from the

second chamber is also sorted

Grinding body material: steel, flint, porcelain, steatite, korund, etc..

Breaker brickwork material: silex, porcelain, steatite, corundum, rubber

5.7 BAR BREAKERS

The grinding bodies are cylindral bars with a diameter 35 to 125 mm, a length of 25 to

50 mm (shorter than the length of the internal breaker area). l:D = 1,5 to 2,5. It is used for wet

or dry flow reduction on the interface between fine crushing and rough grinding.

Filling degree f = 35 až 45 %,

Maximal entry grain -25 mm (with greater granules a bigger bar spacing)

30

Size of product granule - 1 to 3 mm,

Rotations 55 to 65 % of ball breakers

They grind hard and brittle material (only a few fine parts arise, which make

treatment more difficult, they give a more regular granule)

5.8 AUTOGENUOUS BREAKERS

They are distinguished in that they have no (or only very few) grinding bodies. Rough

pieces grind material more finely. They grind in a short roll with a large size (4 to 9 m), so

that to impact energy is sufficient. Material enters and exits through a hollow pin. For

example, it is used for grinding limestone.

5.9 CENTIFUGAL (PLANETARY) BREAKERS

In addition to gravitational acceleration, these breakers also use centifugal

acceleration, which is made in high frequencies for intensive size reduction.

They are used mainly for very fine grinding and the mechanical activation of hard

materials. They grind a mixture of big grinding bodies. Fine grinding is carried out wet.

Laboratory breakers work with a speed up to 10 g, which means a considerable shortening of

grinding time.

Grinding corundum: Ball breaker 150 hours

Planetary breaker 1 hour

5.10 VIBRATION BREAKERS

Vibration breakers grind using grinding bodies introduced into the vibration motion of

grinding vessels. The vessels consist of elastic or rubber blocks.

The oscillation amplitude is very small, only several millimeters. Grinding vessels

have a circular oscillation at a frequency 1500 or 3000 cycles a minute, which is the

frequency of a network(50 Hz) or half of it.

The grinding bodies are usually balls with a diameter 10 to 30 mm, for big breakers

even 60 mm. Bars or rolls can be used as well (the production waste from antifriction

bearings) suitable for grinding using friction. They can grind wet as well as dry.

Filling degree - f = 70 až 80 %,

Maximal input granule - 5 mm,

Product granule size - 0,1 to 0,04 mm,

Production rate - 1000 to 2000 kg.h-1

,

They can grind medium-hard up to hard materials, not too abrasive

31

5.11 MIXER BREAKERS (ATTRITORS)

. The principle of mixer breakers is grinding using the impact and friction of loose

grinding bodies introduced into motion by a míxer. It grinds in the dredge! The mixer can be

in the form of a frame, a peg, a ring, or a disk and screw. Such grinding bodies use sand (sand

breakers), glass balls (pearly breakers) or steel or ceramic balls with a diameter of several

tenths to several millimeters. The peripheral speed is 8 to 12 m.s-1

(high-speed breakers), 0,5

up to 3 m.s-1

(slow-speed breakers). Circulation for big breakers helps by using a valveless

pump (p), which sucks at the bottom through a special divided valve (v) and by a lid forcing

the dredge back into the dish.

A sand breaker uses a sand grain with a diameter 0,5 to 0,9 mm and a mixer with 1700

to 2000 rot.min-1

. The breakers are used in oxidic ceramics, the grinding of porcelain matter,

and in glazure grinding. It is important to observe the viscosity of the dredge, which

considerably increases product fineness.

Concept summary:

After studying the chapter through the following concepts should be clear

to you:

grinding bodies;

ground stock;

breaker filling;

opened and closed cycle.

Questions:

1. Can you explain the principle of breakers with loose grinding bodies?

2. Can you name the basic types of breakers with loose grinding bodies?

3. How do we categorize ball breakers according to grinding environment?

4. Can you explain the principle of the opened and closed cycle?

5. What material is the whole brickwork of a ball breaker from?

6. What are the most common shapes of the grinding bodies of ball

breakers?

7. From what materials are grinding bodies for ball breakers?

8. What does autogenous grinding mean?

9. What grinding bodies do we use for vibration and planetary breakers?

32

WITHOUT REDUCTION GRINDING TOOLS

Chapter sections:

the principle of breakers without reduction tools;

basic categories;

non-mechanical methods of size reduction.

Necessary study time: 90 minutes

Objective: After studying these chapters

you will know special kinds of breakers for very fine grinding;

you will know non-traditional methods of size reduction.

Lecture

This deals with a group of breakers without size reduction tools. They are mostly

used for very fine grinding, founded on the principle of particles colliding together, which are

loaded with a high gradient speed in a fluid or liquid environment.

Categories:

1. Fall breakers (autogenous)

2. Colloid breakers

3. Jet spray breakers (pneumatic)

4. Sweeping breakers

5.12 COLLOID BREAKERS

. Very fine grinding in dredge in high-speed rotary equipment is called colloid

grinding. For size reduction it takes place in a narrow gap between the stator and rotor

B.

33

causing skid tension in the load-bearing media with a high drop speed, they disperse, emulsify

and homogenize together. The dredge is forced in under pressure. The gap between the stator

and rotor is setable. On the surface of the stator and rotar various strong adhesive layers arise,

according to the viscosity of the environment, between which there takes places during high

speeds then the formation of thin whirling layers. For micometric particles such quick rotation

can take place so that a certain tension leading to their interruption arises.

Size of grain product - up to 0,5 m.

A grooved colloid breaker with a rotor conically embedded into a stator can be built

with toothing. The rotor has 3000 rot.min-1

. The gap is adjustable.

The grinding bodies are from single-grain corundum disks.

Vibroactive breaker has cavational hollows made between the stator and rotor.

Note.: Cavitation is the formation of a cavity in liquids when the local temperature

drops, following their implosion (by collapsing). The pressure drop can be a consequence of a

local increase in speed (called hydrodynamic cavitation), or the passage of intensive acoustic

waves in period dilutions (acoustic cavitation). Cavitation is initially filled in by a vacuum,

later a gas from the surrounding liquids can diffuse into it.. When underpressure vanishes,

which creates cavitation, its bubbles collapse during the foundation of impact waves,by the

destructive effects of the surrounding material. Cavitation arises for example on the blades of

ship screws, turbines, on pumps and other equipment, which move at great speeds in liquids.

Cavitation causes noise, reduces the efficiency of machines and can cause their mechanical

damage as well.

Cavitation takes place, if there is a drop of underpressure under water steam pressure.

It leads to the tearing off of small water layers from the rotor´s walls, to the release of

absorbed air, to hydraulic impacts and shaking - an intensive pulsation of high frequencies. In

25 cavities with 3000 rot.min-1

the impact frequency is 75 000 min-1

. Equipment works in a

closed cycle with the use of rotor suction effects. It grinds or disperses less solid materials,

such as MgO, CaCO3, graphite, bergmeal, kaolin, benonite and other elements.

5.13 JET SPRAY BREAKERS

The intensive whirling and joint collision of particles in a gaseous environment, that is

a dry one, is possible to bring about with a jet system. It is possible to reach a flow speed of

500 to 1200 m . s-1

. The internal space is arranged so that it works together as a centrifugal

pneumatic sorter, so that particles gradually grind together in internal multiple cycles.

Jet spray crusher with a flat chamber (micronizer – spiral jet breaker) has a cylindrical

surface chamber into which 6 to 20 jets are tilted in the mouth along the periphery in a

tangential chamber at an angle 30 to 75°.

Compressed air with a pressure 0,5 to 1,5 MPa (or smoked gases) is lead into the

separation ring of the surrounding grinding chamber, which is forced in by the feeding ground

stock injector. The particle path and pressure media cross inside the chamber and particles

with speeds from 100 to 150 m.s-1

(in air), 200 to 250 m.s-1

(in steam) meet in the arising

whirl below acute angles and grind together. The centrifugal force presses the biggest

34

particles in the direction of the periphery of the grinding chamber, particles circulate as long

as they are not so fine that they are transported by the wider tubes in the chambers bottom

into cyclon parts where the separation of air takes place and its consequent dedusting in a

filter. Ground stock remains in the working chamber for about 10 to 20 s, and load-bearing

medium is only a hundreth of this value. The equipment iteslf is small, but appropriate for a

compressor station.

Grinding degree - up to 6000 (colloid breakers: 600, ball

breakers: 60),

Grain product size - 0,1 up to 6 m,

Production rate - 5000 kg.h-1

,

For the very fine grinding of talc, graphite, barite, Al2O3.

Counterflow jet breakers work on the principle of two jets lying against each other,

leading to a frontal collision of particles.

Fluid counterflow jet breakers have 3 to 6 Laval jets with supersonic speed media,

which introduces ground stock into a fluid state. Size reduction takes place by particles

crashing together and through friction. The material practically doesn´t come into contact

with the jets nor with the walls of the grinding area and that is why there is not abrasion

purification. The breaker is suitable for reducing strongly abrasive materials such as SiC,

wolfram, Al2O3, ZrO2, corundum, quartz, but also for materials of a foliated character, such

as mica, graphite and talc.

Summary concept:

After studying this chaper through the following concepts should be clear

to you:

the principle of cavitation;

jet spray breakers;

Questions:

1. For what is grinding without reduction tools used?

2. Can you explain the principle of a breaker with a flat chamber?

3. Can you name other kinds of breakers and their principles?

35

6 SEPARATION

Chapter sections:

kinds of dressing;

mechanical sorting;

water sorting;

air sorting;

separating- according to density, magnetic separation

Necessary study time: 110 minutes

Objective: After studying these chapters

you will know the principle of mechanical sorting using meshes and

grills;

you will know the principle of water sorting on the basis of gravitation

and centrifugal speed and the kinds of sorters;

you will know the principle of air sorting on the basis of graviation and

centrifugal speed and the kinds of sorters

you will know the principle of magnetic separation.

Lecture

Dressing with separation is understood as a series of operations carried out with

particle systems, which is possible to divide into three basic groups:

1. Sorting that is separation according to particle size into two or more groups,

classes, fractions or categories. For example, sand fractionation.

36

2. Separating that is particle separation according to kind, which is supported by

various material properties, such as density, physical properties (mechanical,

eletrical, chemical, etc.)

3. Parting or segregation, that is separation according to grouping. Solid particles

are segregated from a liquid (filtration) or gaseous environment (dedusting)

6.1 SORTING

In these operations the sorting symbols are the geometric dimensions of particles. It is

carried out on various types of mesh grills and other sorters in various types of environments

(water, air), using the gravitational and sedimentary speed of particles.

6.1.1 Mechanical sorting

It is carried out on standardized meshes or grills for both wet and dry conditions.

The screens are perforated or meshed. Laboratory meshes of a size in the order of

micrometers are produced electrolically. Operational meshes from wire or man-made fibre

have hole sizes 0,1 up to 100 mm. Grills are systems of uniform bars of various profiles

oriented and titlted in the direction of material progress. They can be solid or moveable.

Material is screened through a mesh or grill and the result is a rough (overmeshed) and

fine (undermeshed) product. Sorting is never carried out perfectly, both products contain

defective grains. In rough products a defective undermesh that is the non-separation of

fine components and in fine products defective overmeshing, that is the non-separation

of a rough component.

It can be generally said that the success of technical sorting, whether it be through

screening or non-meshed sorting depends on these factors:

The granular composition, density or moisture of a sorted material,

Method of sorting (dry or wet)

The sorters parameters (rotations, amplitude) and the sorting parameters

(period, volume concentration)

6.1.2 Water (hydraulic) sorting

A sediment tank or settling tank works either periodically or in combination, when

fine dredge constantly flows through and sediment sometimes collects as at the sediment

channels.

Taken from: Hanykýř, V., Kutzendörfer, J. Technologie keramiky. Hradec Králové: Vega,

2002. 287 s. ISBN 80-900860-6-3.

Funnels are created by a series of pyramids, groutings by a series of cones with a

closed internal cone. They work continually as settling cones.

Mechanical sorters have a space for sediment made from inclined channels, from

whose bottom the sediment is continuously dug out, while fine fraction flow across a fire

bridge.

37

The sorting limit is 50 to 500 m. It is used in the grinding circuit. The digging out is

carried out by a system of rakes and a transport worm.

Among centrifugal sorters there is mostly hydrocyclons used also for densifying and

separating.

The dredge rotation is achieved through its being put under a pressure from 30 to 400

kPa in a tangental direction to the cylindrical parts. It is achieved so that the peripheral speed,

even several 10ths m.s-1, of the centrifual force is many times more than the gravitational

one. The rough and heavy fractions settle in the lower end parts and densely flow out the

lower outlet jet. The sorting limit can be in a range of 2 to 250 m, exceptionally up to 500

m. For a narrow sorting limits there is used higher pressures, narrow cones with acute apex

angles, (10 up to 15° instead of 20°), more diluted dredge and a smaller outlet jet.

For a big capacity with small hydocyclones they gather together in a multicyclone.

For example for a sorting limit under 10 m there is used 72 hydrocyclones with a diameter

15 mm.

For reducing abrasion there is used lining rubber (for washing koalin) or abrasion-

proof plastics. They are built in the same way as tri-product hydrocyclones with two coaxial

tribitory tubes carrying the finest and roughest fractions. Turbocyclones are also constructed

(centricyclones), in which the dredge is accelerated by a blade wheel placed in the lower part

of the cylindrical area (it is used in the grinding of cement raw material sludge).

6.1.3 Air (wind) sorting

Air sorting is mainly suitable for separating fine fractions. It is best to sort by particle

systems with a 10 % to 30 % of fine parts.. Surface moisture cannot be more than 6%.

The sediment speed in the air is much greater than in water (about 65 times). The

acuity of sorting depends considerably on the time, during which the sorting is carried out,

that is the length of the particle track. It should be the greatest, that is why it is introduced in

sorting houses which have a spiral track of air

The sorting limits are from hundreds of m to 3 mm for them.

Sorting in a zig-zag sorter mainly takes place in the fractures of canals - the number of

fractures corresponds to the degree of sorting, in which repeated resorting takes place. The

sorting limit is from 0,1 to 10 mm.

In the first case it concerns an inclined vibrating mesh with a high frequency of air

being blown through, in the second case about a non-moveable mesh with air pulses being

blown through, brought about by rotating valves. This sorter is suitable for dedusting dry

roughly granular materials.

Among the most common sorters is a circuit sorter with an internal circulation of air

and with a rotating sweeping plate, on which material arrives.

Closely related to air sorting is the separation of dust from the air flow, by which dust

is understood the majority of specks from 0,1 m up to 1 mm. This is in the sedimentary

particle in the gravitational field (of the dust chamber) in the centrifugal field (cyclones) or in

the electrostatic field (that is the electrofilters) A good separation is achieved even in the

filters (dry or wet).

38

6.2 SEPARATION

The task of separation or the enriching of the particle system according to

mineralogical composition, which is carried out on the basis of various material properties,

firstly according to various physical properties, such as density, magnetic and electric

properties, surface absorption properties, elasticity modules, colour, but also according to

chemical behaviour, for example cyanide infusion, amalgamation (connecting metal with

mercury).

The oldest method is wet separation according to density. Among basic equipment for

this method of mechanical separation there are separators. Separation is carried out in the

conditions of disturbed settlement on the basis of stratifying the loosening system. Grains

with greater densities create a lower layer - it reduces the system´s area of gravity, the

potential energy drops, so that separation is carried out as well on equal-falling grains.

Separators are usually made up of 2 connected dishes, in one is the mesh with material, in the

other a piston (with a quick movement downwards and slow movement upwards), which

loosens the grain system in the water. Stratification takes place in the mesh, the heavy parts

(with greater density) gather below , the lighter parts above - under the mesh is water in the

base and heavy particles are distributed, for example by a groove at a certain depth under the

surface, they lightly flow across.

Separation on the basis of magnetic properties which is carried out exclusively by

electromagnets, is often connected to enriching raw materials on the basis of electrical

properties under the joint name of electrical separation. These separators are mostly of a

barrel shape. Material comes to the rotating barrel and the magnetic components are peeled

off by the barrel and they fall from it later than non-magnetic components.

Separation on the basis of electric properties. A non-conductive grain in an electrical

field is polarized, an opposite charge arises in it, before it is in the supporting electrode. The

polarization force depends on the strength of the electrical field and on the permitivity of the

material. How quickly a body charges depends on its surface conductivity (for example in

separating limestone and quartz).

Separation on the basis of surface force - foam decantation. Material dredge, after a

small feeding of the flotation of chemical agents, which cling to small, wetable particles,

whirl through the air. In the phasal interface a whole series of possible physical-chemical

processes are carried out. On the surface there arises foam with a mineral compound, which

constantly fades away, the rest of the compounds stay in the dredge.

Concept summary:

After studying this chapter the following concepts should be clear to you:

basic sorting groups;

mesh sorting;

water sorting;

air sorting;

magnetic separation.

39

Questions:

1. What is sorting used for?

2. Can you explain the concepts of overmeshed and undermeshed?

3. Can you explain the principle of sediment tanks and mechanical

sorters?

4. Can you explain the principle of hydrocyclones and what they are used

for?

5. What is the technological procedure for washing kaolin?

6. What is the principle of a gravitational sorter?

7. What is the principle of magnetic separation?

40

7 MIXING AND HOMOGENIZATION

Chapter sections:

the purpose of blending and homogenization;

pre-homogenization;

separating dumps;

mixers - gravitional, mechanical, pneumatic and static

Necessary study time: 25 minutes

Objective: After studying through this chapter

you will know the types of homogenization;

you will you the types of mixers

Lecture

Mixing or mixing and homogenization is a process in which the local distribution of

components changes during the reduction of concentrated gradients inside a system. It is very

often an original process carried out together with a main process, as for example during

grinding. It is covered in all production coming from at least 2 components.

Mixing particle matter takes place by moving individual particles or their groups into

different areas. They are distinguished into:

1. Conventional mixing – it takes place with the transfer of groups of adjacent particles

from one place in a system to another. It is done by the work

of shearing force in certain areas of a material, for example, an

2. intervening mixer, through macromixing

3. Diffuse mixing – it takes place by moving individual particles, usually by small

individual motions caused by random forces, which arise

41

secondarily caused by shear, tension or pressure stress. It takes

place in micromixing.

7.1 PREHOMOGENIZATION

Prehomogenization is mostly used in cement works and in the production of rough

ceramics. In cement works it is in such a way only the main raw material is prepared, that is

limestone. It is reasonable in such a way also to prepare blast furnace slag.

The procedure requires raw material at a maximal grain size of about 25 mm.

The quality of the mixing bed depends on the kind of method of pouring. Storage is

usually carried out in the form of longitudinal dumps drawing crosswise. If there is not

enough room, there is ringed filling, which is more expensive.

Categories of dumps:

1.Perpendicular dumps

a) Roofed dumps that is the Chevron method which is the most wide-spead method, in

which material is dispersed in individual layers along the entire length of a dump on its

ridge.

b) Line dumps according to the Winrow method, in which material is layered in

longitudinal strips beside each other and between each other. The previous method

disadvantageously prevents the mixing of rough parts at the periphery of the

embankment, that is at the bottom of the dump.

2. Ringed dumps are built in circular halls, in which the centre acts as a rotating

storage transporter and taking away scrapper.

Dump collection is carried out most often by an excavating excavator (scrapper).

Dumps are taken away from the front side in sliced layers. Every batch taken away

corresponds to an average composition.

The dump height at a given width depends on the poured coal material. The length

ratio to the width has to be at the biggest, at least 5:1. In fluent production the conical end of

the landfill is usually not taken away, so that it is possible to avoid fluctuation of the required

raw material composition.

7.2 MIXERS

The course of mixing in a mixer does not depend only on its structure, but very

fundamentally on the mixing composition. A mixer does not have any dead spots, in which

material could stay without movement and the course of mixing from the point of view of

mixers is influenced mostly by the speed of a mixer, its filling level and its dimensions and

shape.

Mixer clasification:

1. Gravitational – they have rotating dishes of a barrel or other various shape.

2. Mechanical – they have rotating mixing tools

42

a) Worm mixers have a worm as a mixing tool, used together for transport

b) Paddle and gate mixers. have a paddle or worm shape on a blade shaft

c) Disk mixers – for these mixers mixing in a flat dish (a plate or bowl) takes place,

usually rotating around a vertical axis. They are used in the preparation of working

mixtures forming using a dry or semi-dry method, for example for preparing a tiles

mixture, in the production of fire-resistant materials for mixing fireclay, etc.

d) Circular mixer – it is in the form of a circular breaker and it is also used for grinding

3. Pneumatic– mixing is reached by auxilary medium (through air)

4. Static– mixing is reached by solid in-building, which suitably regulates material

flow. It is usually used for mixing gases and liquids.

Concept summary

After studying this chapter through the following concept should be clear:

conventional and diffuse mixing;

prehomogenization;

dumps;

gravitational and mechanical mixers, pneumatic and static mixers.

Questions

1. Can you explain the concepts conventional and diffuse mixing?

2. Can you explain the concept prehomogenization?

3. What are the main advantages of line dumps?

4. Can you explain the principle of a circular mixer?

43

8 FORMING

Chapter sections:

individual kinds of forming according to water content;

pressing;

dry and semi-dry pressing;

granulation;

isostatic pressing.

Necessary study time: 225 minutes

After studying this chapter:

you should know all kinds of forming;

the principle of granulation;

the concept of a spray drier;

the principle of single-action and double-action compression;

the backfill mixture for pressing;

pressing at a constant height and constant pressure;

isostatic pressing.

Lecture

Forming is a production operation given by working material, working mixture and a

systematically given geometry.

We can divide material for forming into:

Dredge - forming by casting (little viscosity and a low flow limit) (thixotropy)

Pastes - shaping, plastic forming

44

Mixtures - they have no bonding agent

It is possible to divide forming according to water content:

Pressing – water content 0 to 25 %

Plastic forming – water content 15 to 25 %

Casting – water content 26 to 40 %

The methods of pressing, plastic forming and casting are methods which work on

material in the long-term: Among the methods of short-term forming using acting forces there

are:

Ramming and press-ramming

Vibration and vibration pressing

Forming using pressure waves

By working with forces we can rank these methods in the short-term into pressing

techniques

8.1 LISOVÁNÍ PRESSING

Pressing in ceramics is understood as the forming and thickening of particle systems,

power and granular systems, crumblings and granulates up to plastic paste by working with

external forces (pressure) Moisture moves at about 0 to 25 % and pressing pressures are from

3 to 200 MPa, exceptionally up to 500 MPa.

The main advantages of pressing:

The dimensional accuracy of pressings effected by small amounts of shinkage

Energy savings during drying

Very good thickening

A small amount of waste during production

The possibility of automation

A suitable content of water for a given pressing pressure is such, during which the

pressing has the smallest shrinkage, that is the content of water in the pressing is only such to

fill in gaps between grains. The entire volume of these gaps and pores determines the critical

moisture. It depends on the granulity (the distribution of particle sizes and particle shape and

their layout, shrinkage, which is dependent on the pressing method). Critical moisture drops

with increasing pressing pressure. A higher content of moisture than critical moisture

increases the pressing volume, which is shown in its higher porosity.

The content of water determines the pressing pressure and dimentional tolerance of

pressings. In moisture up to 40 it usually presses a pressure 20 to 200 MPa (a dimensional

45

tolerance of 1 %). For 10 to 15 % water there is selected a pressing pressure of 20 MPa (a

dimensional tolerance 2 %) and the total shrinkage is 12 to 15 %.

8.1.1 Dry and semi-dry pressing

It is used for thickening powder and granular systems with moisture up to 8%,

pressure 20 to 200 Mpa, and sometimes 500 MPa.

8.1.1.1 Granulace Granulation

The direct pressing of fine, soft powders is unsuitable, because air is pressed as well,

which leads to the cracking of pressings. That is why at first there is only prepared granulates

of a grain size 0,2 to 1 mm, which have a good pressability. Granulation is carried out using

these various methods:

Prepressing, that is rough pressings (by briquetting, by pelleting), which is crushed,

the crushed material is screened, a suitable fraction is mixed for the pressing mixture

in order to achieve a big pouring mass. A granulate is angular and sometimes it is

badly running.

Pelletization on a plate (conical or barrel) granulator, where fed powder scrapes, it

piles up into little water drops or dredge - it carries out piling-up granulation. The

granulate is a round grain of approxiately the same size.

Mixing granulation in granulation mixers with raking mixing bodies. They are fed

towards an agglomeration of a certain powder into a vertical cylindrical chamber with

a vertical shaft (1000 to 3000 rot/min) with a resetable blade upwards and it sprays an

agglomeration liquid. In high turbulent flow, particles are moistened and wrapped into

the growing agglomerate, which drops spirally and exits the bottom of the cylinder.

the granulate is circular.

Spray drying the dredge in the flow of hot drying media (air, combustibles). Drying

takes place is several seconds, it is cheap, thermally efficient and has little working

force need. The size and granulity and the granulate are setable, The spraying is

carried out in pressure jets or by a spraying disk. The temperature of hot air on entry is

cca 240 °C, on exiting cca 90 °C, according to operation.

o The drying room with a pressure jet has a high drying tower of a moderately

small diameter. The hot air is transferred overarm, the mixture upwards

(counterflow) , the final drying is concurrent. The product is gathered in the

lower part where like in the cyclone moist air is led out

o Drying rooms with spray disks work on the principle of centrifugal spraying.

They have a drying tower with a greater diameter and a moderately small

height. Dying is concurrent.

Factors influencing granulate quality:

the size of the jet outlet opening,

the outlet speed of dredge flow from a jet

the physical properties of the spraying dredge (mostly viscoscity, furthermore volume

mass and surface tension)

46

jet rotation

size of the drying room chamber

8.1.1.2 Single-action compression

Pressing is carried out using a stamping tool only from one side (from above). It is

suitable only for pressings of low shapes - the compactness of the pressings drops with the

distance from the stamping tool press

After pressing there is the problem of pressing out the pressing from a mould.

Pressing is either with a contant pressure, when a constant pressing compactness is

achieved, of course the height can drop ( suitable for products, which are still machined

before burning) or with a constant height (the punch enters the mould with the same depth) -

the compactness for the pressing fluctuates according to filling, but the height is constant (it is

necessary to maintain the amount of filling and it properties (moisture, ´). From the above

mentioned it consequently follows that the dosage and filling of pressing tools which after all

is valid for all kinds of pressing:

Volume the dosage of a supposed homogenous well-filled pressing

mixture with a constant moisture, it is used in pressing tiles

and slabs, it is quick and suitable for automation

Mass it is more precise and for pressing fire resistant building

materials, because it is possible to keep exact dimensions even

for big products

8.1.1.3 Double-action compression

For more even pressing it is neccesary to carry out pressing from two sides. we have

these kinds of two-sided pressings:

Simultaneous

Non-simultaneous

With a spring-loaded mattress

Simultaneous pressing is just double-sided pressing, that is working with the same

force at the same time, the same speed from both sides. It is possible only on special hydraulic

presses.

Non-simultaneous pressing – there is pressing first from one side and then the other

during the use of suvný coating and setable impact screws, which are upper stamping tools

along the sides

Pressing with a spring loaded mattress.– the spring-loading is prestressed by springs or

hydraulics across a relief valve

In pressing complicated shapes with different pressing heights there has to be a multi-

part stamping tool

47

The moulds are made from tool steel or alloyed carbides

8.1.1.4 Isostatic pressing

It is a forming method in which a liquid is used for pressure transfer (less often than

gas). For pressing there is used granulates of a moisture 5 to 10 %. Pressure works on the

pressing closed in an elastomeric (rubber) mattress uniformly in all directions.

The advantages of isostatic pressing

The possibility to evenly gain pressings of a moderately large

dimension regardless of the size/diameter ratio and without a great

amount of plastifiers

For obtaining the same volume mass a pressure 2-3x smaller is enough

A greater strength due to homogenous pressing

The possiblity of pressing crucibles, tubes and other complicated

shapes.

Concept summary:

Aft:er stuying through this chapter the following concepts should be clear

to you

mixture, paste, dredge;

pressing, plastic forming, casting;

critical moisture;

granulation;

spray drying room;

simultaneous and non-simultaneous pressing;

isostatic pressing.

Questions:

1. Can you explain the main difference between pressing, plastic forming

and casting?

2. What is granulation?

3. What is the principle of spray drying rooms and what are they used for?

4. What are the main advantages of pressing?

5. Can you explain the principle of single-action compression?

6. Can you explain the principle of double-action compression?

7. Can you explain the difference between pressing at a constant pressure

48

and at a constant height?

8. What is dosage mixture?

9. What is the principle of isostatic pressing?

10. What are the advantages of isostatic pressing?

8.2 PLASTIC FORMING

Chapter sections:

paste forming - drawing, throwing

the presence of air in paste

clipping paste

Necessary study time: 45 minutes

Objective: After studying this chapter

you will know the principle of drawing, - horizontal, vertical, with a

vacuum and without one.

you will know the principle of throwing - manual and mechanical

using a template.

Lecture

Plastic forming is the oldest method of forming. It processes a heterogenous multi-

phase mixture of a pastelike consistency with a moisture usually15 up to 25%. It is used in the

technology of building ceramics (bricks, gravel) and fire-resistant materials (fireclay), and in

fine ceramic technology (porcelain)

Categories:

1. Drawing

worm

49

piston

cylinder

2. Rotating

loose

mechanical

8.2.1 Drawing

Drawing, more correctly extrusion, is forming by drawing a pastelike mixture through

a profiled aperture. Individual formings (bricks, bars, tubes) are cut off from it, and if

necessary further shaped. A continuous flow of material comes out of it. The working

pressure for a usual press is perhaps up to 3MPa. A zone is cut off into:

a) Handled pieces indicated as blooms, loaves, packages. In this form the material is

left to mature for further processing (plates, cups) or it is burnt (opening material)

b) Semi-products for pre-pressing (steel casting tubes, vents) or for hardening for

machining.

c) Final products - bricks, beams, tiles, tubes

8.2.1.1 Drawing worm presses

The main part of a worm press is a worm, which homogenizes a mixture, and also

transports and presses it. It rotates in a cylindrical chamber and a paste is pressed out through

the aperture. It is categorized according to position.:

Horizontal

Vertical

Both mentioned types can further be:

Usual (without a vacuum)

With a vacuum

The presence of air in the paste worsens it formability, it shows itself as

opening material:

1) It reduces plasticity

2) It reduces cohesiveness, binding propoerties and strength

3) It reduces cubic mass (´)

4) It causes the expansion of paste coming out of the press, which is shown in

elasticity and elastic recovery

.Aeration causes an improvement of the forming properties of the paste, increasing its

plasticity, increasing its continuity and by it the moveability of liquid phases by disturbing the

50

hydrophobia and by facilitating particle hydration. Of course, it increases the entire energy

consumption.

Reducing worm rotations can increase aeration!

Underpressure is 70 to 90% čli 30 to 50 kPa. Vacuuming is carried out most often by

a water air pump, that is by a vacuum rotation pump.

If the length and mass zone do not safely allow drawing horizontally, a vertical press.

is used.

8.2.2 Throwing

Throwing is a traditional method of forming ceramics, in which plastic paste is in a

rotating direction and it is done manually or with a tool of a rotating shape.

Free turning (with a free hand) happens without the use of a plaster mould on a

potter´s wheel (man-made pottery)

Mechanical turning is carried out most often using a plastic mould and a flat, most

often today, rotating roller template. In forming flat products (plates, saucers, etc.) it forms a

mould in the internal surface and a template externally – that is throwing out or throwing in.

In forming hollow products (cups, etc.) the mould gives a more external shape, the template

forms a cavity - – that is throwing out or in

Concept summery:

After studying the chapter through the following concepts should be clear

for you:

drawing

throwing

a worm press

a piston press

throwing in and throwing out

Questions:

1. How mich water does paste contain for plastic forming?

2. What is the principle of a worm press?

3. What causes the presence of air in the paste and how is it possible to

reduce its presence?

4. How is it possible to draw products too long?

5. What is used to cut off paste?

6. Can you explain the concepts of throwing out and throwing in?

51

8.3 CASTING

Chapter sections:

the principle of casting

lití na střep; casting for body

lití na jádro. casting for the core

Necessary study time: 35 minutes

Objective: After studying this chapter

the principle of casting

the requirements for dredge casting

what liquification is

the formation of plastic moulds and their lifetime

Lecture

Casting is a ceramic method of forming for current drainage from fluid dredge, in

which a body is formed in a cut absorbent, most often a plastic mould.

Categories:

1. Casting for body

2. Casting for core

In casting for body a dredge mould is filled usually from a distribution pipeline,

where it is led to a circulation pump. During mould filling, it is useful to rotate and to

gradually uncouple the jet from the bottom upwards. The casted dedge is left to sit before a

testing time in a mould, so that the required strength of a body is created. Many times it is

necessary to completely pour the dredge to completely fill the mould. And then emptying it

52

by roatating the mould, it pours out, excess dedge flows back to the tank, a casted body stays

on the walls of the mould. This sits for a certain time, hardens, it strengthens by other water

drainage it drys, its contraction is carried out and it is separated from the mould.

In casting for a core a plastic core (J) is inserted into a mould. The dredge is poured

into the gap between the core and a mould determining the body strength, which is created in

the mould and in the core. The dredge has to be completely poured until the time both bodies

are connected. In this way, massive products are casted, for example some sanitary ceramics,

big isolators, glass pots, etc.

Complicated shapes, which are spilled out of the form, have a two-part shape.

Requirements for casting dredge:

1. If possible a low content of water, it shortens the downtime in body formation

and in drying.

2. A high speed in body formation and thickening, time and space savings

3. Low and constant viscosity, minimal flow limit. Tixothropy facilitates the

casting out of excessive dredge, in forming a casting is easily deformed

4. A low content of liquidification and its corrosive effects

5. Easy separation from the mould and sufficient casting strength

Water in the dredge is partially replaced by liquidifications (water glass, Na2CO3,

Na3PO4), which increase the electro-kinetic potential of dispersed particles and cause an

apparent reduction of dredge viscosity. This leads to quicker body formation.

The mass casting of oval bowls, lids, handles column casting is used. that is, battery casting.

Moulds are placed next to each other, the lower side of a mould (for example, for bowls)

creates the interior surface, the upper side the exterior surface.. It is casted for a full body. The

handle is casted in the same way.

Concept summary:

After studying this chapter the following concepts should be clear to you:

casting for body and casting for core

what liquidifications are

the production of plaster moulds

the formation of complicated products by casting

Questions:

1. What is the difference in casting for a body and for a core?

2. What are the requirements for casting dredge?

3. What are liquidifications and which materials belong among them

53

4. Can you explain the concept of electro-kinetic potential?

5. Can you explain the concept of dredge viscosity?

54

9 RECOMMENDED LITERATURE

[1] KUNEŠ, K., ŠPIČÁK, K. Procesy a zařízení v keramice I; II, Částičové soustavy I,

Tvarování II.

[2] PROKEŠ, J. Stroje zařízení – Průmyslová výroba hrubé keramiky. Brno: VUT.

[3] PROKEŠ, J. Strojní zařízení: průmyslová výroba maltovin a hrubé keramiky.