TYPES OF MOULD

TYPES OF MOULD (JENIS ACUAN)There are two major types of molds: 1.Two plate mold

2.Three plate mold1.Two Plate Mold

A two plate mold is the simplest type of mold. It is called a two plate mold because there is one parting plane, and the mold splits into two halves. The runner system must be located on this parting plane; thus the part can only be gated on its perimeter.

1.1 Direct Gate Method:

Figure 1 shows a simplest structure only for a single impression (parts) mould.

Figure 1: Direct Gate Method

1.2 Side Gate Method

Figure 2 shows the structure of side gate method for a multi-impression mould in general. This method is also used for a single-impression mould in special shape.

Figure 2: Side Gate Method1.3 Side Gate with stripper plate Method

Figure 3 shows the structure of side gate method with stripper plate. Figure 3: Side Gate with stripper plate method2.Three Plate Mold

A three plate mold differs from a two plate in that it has two parting planes, and the mold splits into three sections every time the part is ejected. Since the mold has two parting planes, the runner system can be located on one, and the part on the other. Three plate molds are used because of their flexibility in gating location. A part can be gated virtually anywhere along its surface.

2.1 Pin Point Gate Method:

Figure 4, illustrates the structure for a single impression mould. In general, this method is taken for a multi- impression mould and for a multi-point gate.

Figure 4: Pin Point Gate Method2.2 L type Runner Method;

STANDRD MOULD BASE (2 PLATE MOULD):

1. TOP CLAMPING PLATE.

2. LOCATING RING.

3. CAVITY PLATE.

4. CORE PLATE.

5. SUPPORT PLATE.

6. BOTTOM CLAMPING PLATE.

7. PARELLELS / SPACER BLOCK

8. EJECTOR RETAINER PLATE.

9. EJECTOR PLATE.

10. STOP BUTTON / STOP PIN.

11. PILLAR.

12. SPRUE BUSHING.

13. SPRUE PULLER PIN.

14. RETURN PIN / EJECTOR RETAINER PIN

15. GUIDE PIN.

16. GUIDE BUSH.Function of Mold Base Parts ( FUNGSI BAHAGIAN-BAHAGIAN ACUAN) I. T0P CLAMPING PLATE:

Memegang bahagian pegun/tetap acuan untuk plat pegun/tetap daripada

mesin suntikan.(Holds the stationary part of the mold to the stationary platen of the

injection machine). 2. LOCATING RING OR SPRUE RUSHING RETAINER RING:

Di pasang ke dalam counterbore pada plat pengapit atas( top clamping) dan digunakan untuk menempatkan acuan pada platen fix half, muncung dan sprue bushing adalah sejajar/selaras.

(Fits into a counterbore in the top clamping plate and is used to locate the mold on the platen of the press so the nozzle and sprue bushing are aligned). 3. CAVITY PLATE:

Sebahagian daripada bahagian bergerak acuan yang ke dalamnya peneraju atau pemandu pin dipasang. Juga digunakan untuk memegang teras, blok rongga, dan spru sesendal.(Part of the stationary section of the mold into which the leader or guidepins are mounted. Also used to hold core, cavity blocks, and sprue bushing.)4. CORE PLATE:

Plat bahagian atas pada acuan seksyen moveable . Merupakan garis perpisahan daripada acuan dengan plat rongga penahan. Digunakan untuk memegang sesendal pin peneraju dan juga teras dan rongga blok.

(Top plate of the movable section of the mold. Forms the parting line of the mold with cavity retainer plate. Used to hold the leader pin bushings as well as core and cavity blocks.)5. SUPPORT PLATE:

Dipasang di belakang plat teras penahan untuk menjaga plat ini dari lenturan dibawah tekanan yang tinggi digunakan dalam pengacuan suntikan.

(Mounted behind the core retainer plate to keep this plate from bending

under the high pressure used in injection molding).

6. BOTTOM CLAMPING PLATE:

Memegang bahagian bergerak acuan untuk platen boleh alih itu daripada

mesin suntikan.

(Holds the moving portion of the mold to the moveable platen of the injection machine).

7. PARALLELS/SPACER BLOCK:

Dipasang pada plat pengapitan bahagian bawah di bawah plat sokongan untuk membentuk ruang yang membolehkan bar lenting untuk bergerak apabila bahagian produk adalah di tolak keluar.(Mounted on the bottom clamping plate under the support plate to form a

space which allows the ejector bar to move when the piece parts are ejected.)8. EJECTOR RETAINER PLATE (Knockout pin plate):

Counterbore untuk kepala pin lenting, pelenting pin balasan, dan

pin alat untuk mengeluarkan spru.

(Counterbore for the heads of ejector pins, ejector return pins, and sprue puller pin).

9. EJECTOR PLATE (Knockout bar ):

Diperketatkan bersama-sama dengan plat pelenting penahan untuk membentuk satu unit. Bertindak sebagai plat belakang untuk pin dalam plat pelenting penahan.

(Bolted together with the ejector retainer plate to form a unit. Acts as a back up plate for the pins in the ejector retainer plate).

10. STOP BUTTONS/STOP PIN:

Dipasang pada bahagian bawah clamping plate, ia adalahuntuk plat pelenting.

(Pressed into the bottom clamping plate, they are lands for the ejector plate).

11. PILLARS:

Bar bulat diletakkan di antara plat sokongan dan pengapitan bahagian bawah

plat. Ketinggian sama seperti persamaan. Diperketatkan untuk plat pengapitan bawah, ia digunakan sebagai sokongan tambahan bagi plat penahan teras.

(Round bars placed between the support plate and the bottom clamping plate. The same height as the parallels. Bolted to the bottom clamping plate, they are used as additional support for the core retainer plate.)12. SPRUE BUSHING:

Mencelah menentang muncung mesin suntikan. Mempunyai kon-lubang berbentuk melalui mana bahan dipaksa ke pelari acuan.

(Butted up against the nozzle of the injection machine. Has a conical-shaped hole through which the material is forced into the mold runner).

13. SPRUE PULLER PIN:

Pin terletak secara langsung di bawah pembukaan spru itu. Digunakan untuk menarik spru dibentuk daripada sesendal selepas tembakan telah dibuat.

(Pin located directly under the opening of the sprue. Used to pull the

molded sprue out of the bushing after a shot has been made).

14. RETURN PINS (Ejector return pins) (Safety pins) (Push backs):

Terletak di plat pelenting penahan. Daya plat lenting dan pelenting

plat penahan, dan oleh itu pin lenting, pada kedudukan bawah seperti

yang ditutup acuan.

(Located in the ejector retainer plate. Force the ejector plate and ejector

retainer plate, and therefore the ejector pins, to the bottom position as

the mold closes)l5. GUIDE PINS:

Keras dan pin keluli bawah ditekan ke dalam salah satu plat. menyelaraskan

kedua-dua bahagian asas acuan.

(Hardened and ground steel pins pressed into one of the plates. Align

the two halves of the mold base).

16. GUIDE BUSH:Sesendal keluli keras dan bawah yang ditekan ke dalam salah satu

plat. Bertindak sebagai permukaan yang mengandungi untuk pin pemimpin.

(Hardened and ground steel bushings which are pressed into one of the

plates. Serve as bearing surfaces for the leader pins).

BAHAGIAN CORE DAN CAVITY

Cavity:It is female part of the mould, which gives the external shape of the Component. Pockets, Slots, holes are considered as Cavities. These are highly polished to a mirror finish, requires better finishing appearance on the outer surface of the componentCore:It is male part of the mould, which gives the internal shape of the Component. All Projections are considered as Cores. These are not required high polish as the Component is to be sticks on to core.

Parting Surface:That part of the mould plate, adjust to the impression, which butt together to form a seal and prevent loss of plastic material from the impression.EJECTOR SYSTEM

EJECTION SYSTEM Plastic material shrinks on solidification this property compels plastic components to sit tightly on the core and makes the removal difficult. The mechanism of removal of moulded part from the core is called ejection system.

Injection moulding machines are provided with an automatic activation of an ejector system which is situated behind the moving platen.

Ejector Grid:

Ejector grid is the portion of the ejection system which provides a space into which the ejector plate assembly is mounted. This grid allows to and fro movement of the ejector plate assembly within the grid.

The grid normally consists of back plate and spacersTYPES OF EJECTOR GRIDIn line Ejector grid:-

Inline type of grid consists of two support block and a back plate. Usually on top of spacers core back plate is mounted.

This type of system is suitable for small mould when the distance between two riser blocks increase additional block may be incorporated in between in stead of increasing the thickness of core plate or core back plate. Sometimes additional local support pillars may be used

Frame type ejector grid:

Some times grid is made by enclosing all the four sides which is called frame type ejector grid.

It prevents foreign particles to enter and there by ensures smooth and accurate functioning of ejector assembly movement.

It provides better support than inline grid.

Circular support pillar grid: Ejection grid can be made by mounting circular support pillars on to the back plate and enclosing these circular pillars by thin metal plates to prevent foreign particles in ejection system used for large moulds.

Ejector plate assembly:-

It consists of retainer plate which holds ejector elem-ent like pins, sleeve etc and ejector plate, which supports the ejector pin etc and helps in actuating pins.

An ejector rod is screwed with ejector plate and other end of ejector rod is free which is pushed by the actuating rod of the injection moulding mach-ine.

This assembly system shall depend mainly on the size of the mould. For smaller mould and ejector rod bush is fitted into the back plate in which the ejector rod slides.

For heavy moulds two or four bushes are fitted in the ejector plate assembly itself. This assembly with the help of guide pillars mounted on the back plate is made to slide to eject the component.

Length of the ejector rod depends on the ejection stroke which is again dependant on the max depth of hole of the plastic component.

After placing the ejector elements in the retainer plate, ejector plate is placed at the back of retainer plate and screwed together tightly.

Thickness of retainer plate is governed by the thickness of head of ejector elements length and breadth depends on the distance between ejector element placed at max distance in the direction of x and y.

Thickness of ejector plate depends on the ejection force required to eject component. Length and breadth is same as retainer plate.Ejector plate assembly return system: - In general two systems are used for the purpose of returning of ejector plate assy. For the next shot.

One is push back system and other spring return system.

In push back pin system four pins called push back pin are fitted at four corners in the ejector plate assy. Just opposite to these pins four more pins called returning pins are fitted in the fixed half of the mould. When mould starts closing these returning pins pushes the push back pins there by the ejector plate assy. Returns to rear most position. In spring return system the spring is fitted to the ejector rod supported by cap or washer screwed at rear end of ejector rod so that it is slightly at compression between ejector back plate and cap or washer. This system is used for smaller mould. For larger mould more than one spring are used between retainer and core back plate.Push Back Return System: Push back pins (return pins) are basically large diameter ejector pins fitted close to the four corners of the ejector plate assembly. A cross section through part of a mould which illustrates a push back pin is shown in Figure 5-13. In the molding position as shown at (a) the push back pins are flush with the mould plate surface. In the ejected position the push back pins protrude beyond the mould plate surface (b). Thus when the mould is in the process of being closed, the push back pins strike the fixed mould plate and progressively return the ejector plate assembly to its original position (a). Push-back return system push-back return system

in close condition(a)

in open condition(b)

Spring Return System:For small mould, where the ejector assembly is of light construction, a spring or stack of Belleville washers can be used to return the ejector plate assembly. A typical arrangement of the spring actuating method is shown in Fig. 5-14. In this design the spring is fitted on the ejector rod. A cap is attached to the end of the ejector rod to hold the spring in position under slight compression. In operation when the ejector assembly is actuated, the spring is compressed further. Immediately the mould closing stroke commences, the spring applies a force to return the ejector assembly to its rear position.The Basic Ejection Techniques:- Pin ejection

- Stepped pin ejection

- D shaped ejection

Sleeve ejection

Blade ejection

Stripper plate ejectionDESIGN OF PIN EJECTION SYSTEM: Cut = Thickness of plastic component

Dep = Diameter of ejector pin

Cd = Depth of hollow portion of plastic component.

Bs = Bearing surface of plastic component for

Where,

Cid = Inside diameter of component = core diaFor every 100sqcm of bearing surface are 1sqcm of ejector pin is recommended

Total area of ejector pins = Bs . 100

Max. Diameter of pin = Thickness of plastic component.

Nep = Number of ejector pins required = Bs4 = Bs .

100 ((Dep)2 25 ((Dep)2Ejector pin should be placed at thicker portion of the plastic component and should be placed in such a way that they do not get bend during ejection.

PIN EJECTION:This is the most common type of ejection as in general it is the most simplest incorporated in a mould with this particular technique the moulding is ejected by the application of pressure a circular rod called as ejector pin. The ejector pin headed to its attachment to ejector plate assembled, the working diameter of ejector pin is must be good slide fit. In matching hole in the mould plate, if it is not the plastic material with creep through the clearance and the mass of material will progressive of build of bending the mould plate. The rare part of ejector pin is fitted into a suitable hole which is bored and counter-bored in retainer plate. The rare case of ejector pin is back up of the ejector plate. The accommodation provides must allow the ejector pin float way the feature is necessary. As taken above, the ejector pin must be slide fitted in the hole in the mould plate. The direction of movement of ejector pin is therefore controlled by this hole should not be bored absolutely in right angle when the ejector unity assembled.

STEPPED EJECTOR PIN Consider the case of where the small diameter (3mm) ejector pin are required the stepped ejector pins, now slender long length diameter ratio in ejector pin have the tendency to construct in use. It is desirable to keep the working length to such as ejector pin to minimum this is achieved by designing ejector pins. A stepped ejector pin manufactured from a solid rod, alternating. It could have to be steel. The small diameter portion being fitted as suitable hole matching in large diameter portion. The two parts will brazed together .this later method has advantages that should the ejector pin break only the smaller diameter portion be remade. The stepped ejector pin is normally used face pin for ejection of moulded bushes and ribs, note that the main ejection is provided the standard plain type ejector pin. The length should be kept as short as possible. This length is need only equal length in contact with the mould plate is kept into minimum by in corpora ting a clearance diameter hole in the mould plate .A suitable length the small diameter ejector pin is 5 to 6 times the diameter.D- SHAPED EJECTOR PIN This is the name given to a flat sided ejector pin. It is the made quite simply by machining. A flat on to a standard ejector pin. It is used primarily for the ejection for the thin walled box type the procedure adapted for producing D shaped hole as shown in figure.

Mark required position of ejector pin.

Bore the required diameter hole in the bolster.

Machining out the recess to accommodate the insert.

Fit the inserts and hold back with screws.BLADE EJECTION The main purpose of blade ejector is for the ejection of vary slender such as ribs and other projection. Which can not satisfactorily be ejected by the standard type of ejector? The blade is basically a rectangular ejector pin, while the blade ejector is machined solid rods

It is more usually fabricated the element in which case a blade of steel is inserted into a slot machine into a standard type of ejector pin.

The blade may be pinned or alternated it may be brazed .the advantage of two part construction is that the blade can easily replaced should become damaged.

The blade ejector element is fitted to the ejector assembled in a manner to that described for the standard ejector pin. The rectangular plate ejector accommodated in a completely shaped hole in the mould part.The sleeve ejection

The sleeve ejector is mounted into the ejectors pin plate like a conventional ejector pin. The core pin which fits into the sleeve is mounted into the clamping plate. As the ejector unit is activated, the sleeve pushes the piece part off the core pin. Sleeve ejectors are used to push bosses and knob-like piece parts off core pins. It is undesirable to allow the sleeve to be in contact with the core pin over its entire length. To reduce frictional wear, to facilitate fitting and to lesson the possibility of scoring, the surface contact between the two parts is kept to a minimum.

Stripper Plate Ejection:

Stripper plate ejection is generally used where ejector pin marks would be objectionable on the piece parts and where maximum ejection surface is required. Stripper plates are used on single and multiple cavity moulds. An angle of approximately 5 is machined in the stripper plate and on the plunger, as shown in fig. 5-18. This prevents scoring of the plunger as the stripper plate moves in and out over the plunger. The illustration shows two methods of keeping the stripper plate from coming completely off the plungers and out of the mould. View at shows the use of a stripper bolt to limit the travel of the stripper plate. View at B shows the return pin held to the stripper plate by a screw. This allows the stripper plate and ejector plate to operate as a unit. In more complicated designs, pull rods mounted in the stationary portion of the mould are used to activate the stripper plate.DESIGN OF KNOCK-OUT ROD L = Length of the ejector rod.

= Height of ejector rod bush + Ejector stroke length +10mmEjection stroke length = Max. Depth of component +8mmH = Thread diameter length

= Ejector plate thickness 3mm

= 15 to 20mm in general

D = Ejector rod diameter (Table-1)

d = Threaded diameter (Table-1)

Design of Knock-Out Rod & BushTableL in mmD in mmd in mm

Up to 15015M10

150-20020M12

250-30025M16

DESIGN OF KNOCK-OUT BUSH: H = Height of the ejector rod bush = Thickness of back plate

H = Thickness of collar = 4to 5mm

D1 = Internal diameter of bush= Outside diameter of ejector rod.

D2 = outside diameter of bush = D1 + 8 to 10mm

D3 = Diameter of collar of bush =D2 + 6 to 8mm

TYPES OF LAYOUT OF CAVITIES Cavities should be placed in such a way that when they are connected with sprue through runner and gate will ensure the uniform filling of impressions.

In general multi-cavity mould having same shape and size of impressions are connected through runners and gates of similar cross sectional area and length and cavity should be placed at equidistance from the centre of the sprue.

For multi cavity mould having differently shaped impressions should be connected through following system:

SYMMETRICALLLY AT SAME PCD LAYT-OUT OF A FOUR IMPRESSIONS MOULD.

R= Distance between sprue centre and cavity insert or distance at which cavity insert to be placed from the centre of cavity holding plate

R = (CLd+5)/ (2Sinx/2)

CLd = Collar dia. of cavity insert.

C I = I.D. of cavity insert. GL = Gate length (0.5 1mm) CE = External dia of cavity insert.

X = 360/Number of cavities.

L = Runner length = R-(CI/2+GL)

Runner of different cross-sectional area but same length.

Gate should have similar cross-sectional area.

It is required when dissimilar cavities are placed at equidistance from the centre of the sprue.

It is called runner balancing. Runners of same cross sectional area and length.

Gate should have different cross sectional area

This is done when dissimilar cavities are placed at equidistance from the centre of the sprue.

This is called gate balancing. Runners of different cross sectional area and length.

Gate should have same cross sectional area.

When cavities not placed at equidistance from sprue centre.

SELECTION OF RUNNER Runner is a channel in the mould which connects the spur with gate

For a single day-light mould runner is made on the parting surface.

Runner may also be placed below the parting surface for complex mould.

Runner cross sectional shapes should be so design that it provide maximum cross sectional area from the pressure transfer point of view and at the same time it should have minimum contact on the periphery from maximum heat transfer point of view.

Out of this round runner is most efficient from heat transfer point of view, but cutting half of the runner in fixed half and other half in movable half matching of two halves to get full round runner is difficult.

Instead of round runner if half-round runner is used it leads to problem of ejection of component and feed system.

Round and Modified Trapezoidal runners are mostly used. Runner length is kept as short as possible for rapid filling of cavity & to reduce pressure loss. Corners formed at the junction of main & secondary runner should be rounded off to reduce flow resistance.

CALCULATION OF RUNNER DIAMETER = W X 4L

3.7

Where, w = wt. of comp. in gm, (volume X density)

L = runner length in mmRunner efficiency =Area / Perimeter

Area is important to ensure the delivery of particular volume molten plastic material into the cavity in specific time duration i.e. within injection time.

Perimeter of the runner profile is important as less perimeter is preferred for less heat loss from the molten plastic material . There by maintaining proper melt condition for smooth flow of the molten plastic through spure, runner , gate and finally into the impression

Size of runner depend on flowing factors

Runner length

Wt. of moulding

MFI of the mouldingFor high viscose material the runner size will be higher than the calculated value. As the behavior of the plastic material has the restriction for easy flow .in addition to the this care May taken in the flow path to maintain high surface finish there by reducing the frictional flow restriction during the filling of the cavity

RECOMMENDED MAIN AND SECONDARY RUNNER DIAMETERWeight of component

in gmRunner length

in mmRunner Dia

in mm

Up to 15Under 502.5

Up to 15Over 504

15-50Under 505

15-50Over 506

50-200Under 806

50-200Over 808

Over 200Under 1002

Over 200Over 10010

SELECTION OF GATES

Rectangular edge gate The cross section being simple cheap to machine.

Gate dimensions can easily be modified.

All common moulding materials can be moulded by this.

Witness mark is left on the visible surface of component. For polystyrene, acetal; it is more clear.

Use of soap case, Instrument box etc.

Normal size is (3 X1) mm Approx. for components up to 30gm wt.

Large components with hard flow material size may (10 X 8) mm.

Components can be de gated at machine by operator.

If, h = Depth of gate in mm Then, A = Surface area of cavity (mm)

t = Thickness of component.

Lg = Land length in mm. (1mm to 1.5mm).

n = Material constant

MaterialValue of n

Polyethylene, Polystyrene0.6

Poly acetal, Polycarbonate,

Polypropylene

0.7

Cellulose acetate,Acrylic Nylon0.8

Pvc0.9

Overlap gate In this type of gate the material coming from the gate is forced to impinge on an opposing face of the impression and then the material progressively fills the impression displacing the air.

If a gate is provided at the centre of on end of a solid rectangular block then the material will enter the cavity with a jet form and will be solidified when comes in contact of cool mould walls. After this the material required for filling the4 cavity will flow around the original jetted material giving rise to a flow line.

It is used for block type component, radio knob etc.

Land length L1 = 0.5 - 0.75mm Gate width W = nA/30 (n = Material constant)

Gatelength L2 = n+W/2 Gate Height h = nt (t = component thickness)

Fan gate This is a modified rectangular edge gate.

The width of the gate increases with the decrease of depth towards impression to get a constant cross sectional area through out the gate length.

Land length is little more than rectangular gate.

Used for the component having large volume and thin wall thickness like scale, jeweler box etc. Width of gate at bigger end, W = nA 30

Minimum depth of gate, h1 = nt Maximum depth of gate, h2 = Wh1

D Land length, L = 1.3 mm

Where,

N = Material constant

A = Area of cavity surface (mm)

t = Thickness of component (mm)

Diaphragm gate

It has a circular runner which is connected with the sprue centrally.

A gate is cut to connect the impression with runner.

If bore is not important gate is cut in the core which is easy to cut.

This is used for tubular shaped moulding in a single cavity mould (baby cycle wheel, lamp shade).

Ring gate In this case as usual runner is used with a gate all round the external periphery of the component.

It ensures uniform feeding around the core pin.

Ring gated components are normally provided with stripper plate ejection.

The gate is in the form of a concentric film between the runner and impression. Used in producing tubular mouldings like body of a float valve, water gun, plastic bangles with multi impression two-plate mould. L= Length of gate

h= Depth of gate

n= Material constant

t= Thickness molding

Film gate

Long rectangular type edge gate is called film gate.

Due to longer length wrap age of the component reduced.

Depth of gate is kept lesser than rectangular edge gate.

Runner is extended beyond the end of component.

Where,

h=Depth of gate, L= Land length of gate, n= Material constant

t= Thickness of component Subsurface/Tunnel/submerged gate When a gate is provided below the parting line is called a subsurface gate

It is a circular or oval gate

The runner is terminated at distance X from impression.

A secondary runner usually of conical form is machined at an angle to the impression wall and is stopped short of the impression wall by a distance L.

It is used for moldings of injection syringe L(Land length) = 1.9mm (minimum)

= 30 - 45 Angle subtended by centre line of Secondary runner and impression wall

Pin-point gate

TAB GATE A projection or tab is moulded on the side of the component.

At right angle a rectangular gate is provided to join the tab and runner.

This is an alternative to overlap gate.

This was designed specifically for use with acrylic material to obtain stress free high optical clarity.

This is used for solid block or thick type job where mark is allowed on side of the component only, like clock glass, lens etc.

COOLING SYSTEM One of the most important acceptation of mould design is the provision of suitable and adequate cooling arrangement in all injection moulding. Even though it involves having a heated mould, the purpose of mould is to cool the molten plastic. The means of cooling and insulated to prevent any escape of heat by conduction or radiation. It would quickly cool the material will be mould and would no longer fulfill its function. The cooling system is an essential mould feature, requiring special attention in mould design. It should ensure rapid and uniform cooling of the moulding. In design of mould component and layout of the guides and ejectors. The allowance should be proper size and position of the cooling system. Rapid cooling improves process economy, while uniform cooling product by different shrinkage, internal stresses and mould will relies problem. In addition uniform cooling ensure a shorter moulding cycle. A rapid and uniform cooling is achieved by a sufficient number of properly located channels. The location of this channel should be consist with shape of moulding and should be as close as cavity will allowed by strength and rigidity of the mould. Increasing the depth of cooling line from the moulding surface reduces the heat transfer efficiency and to wide a pitch gives a non-uniform surface. A straight drill line are preferred to bubblers they should be designed so that cross-sectional area remains constant for entire circuit for tube bubblers area in the both side of the tube should be equal material with higher thermal conductivity should be used. If all the heat cannot be removed with a steel mould. The described location of this heating-cooling phase is the mould close to where most of the heat decapitated that is where the most of the material is located.

DESIGN OF COOLING HOLE: dT= Diameter of cooling hole

C = Distance between centre of the cooling hole and the surface

of the plastic compo-

nent. = 2 to 3 dt

t = Thickness of the plastic component

b = Centre distance between two adjac-

ent holes = max. 3dt t in mmdT in mm

Up to 28-10

2-410-12

4-612-15

STRAIGHT SECTION STROKE ROUND FLOW These are the most common cooling channels found in the mould.

They are normally in series of drilling package of series and that are round in diameter.

STROKE STRAIGHT SECTION RECTANGULAR FLOW

This type of cooling is used commonly found in backup plate rushed in mould cooling. These are the usually series of package but a rectangular shape that compromises the cross-sectional area. CIRCULAR SECTION ROUND FLOW

Circular sections are used to cool round plate, cylindrical stroke, cone shape cores and cavity, etc. this arrangement, when properly interfered makes it possible to follow close radius of the round core or cavity so that the distance of channel is kept as a uniform depth.

CIRCULAR SECTION RECTANGULAR FLOW

These have the rectangular cross-section area for easy of machining.

BUBBLERS

This channel component are normally connected with straight section round flow. They are used in cooling of pins, cores and deep draw area. Epical two channels are parallel the surface of the back plate of the different depth. In bottom channel tubes are screwed go to that top area to be cooled (pin and core) the inlet water groove & lower channel fills the tube, and then overflow of the outlet each core tube receives same cooling with maximum velocity.

BAFFLES These constitute an alternating method for cooling pins, cores, and deep draw areas, unlikely baffles they are tied together in series triple straight section stroke the coolant extruded section that intersect with all of the baffles of the channels, each baffle is a round drill section, with blade to divided in cross-section area in half. The coolant flowing in straight section runs baffles blades, and makes it bends to the baffles. In as much as the blade does not extend all the way of the end of the baffle. If they run blow the back side of the plate, make another so turn back into straight into as goes next baffle. This is an expectable method for smaller number of cavity from side to side or very large diameter channels and baffles.

METHOD OF CONSTRUCTION OF MOULDInteger MethodWhen core and cavity is made in a single block of steel without any bolstering is called integer method. In these method two halves contains two solid blocks only.USE

Single impression mould.

For more strength.

Big component.

Disadvantages: Difficult to make multi-cavity mould because even if one part of cavity and core becomes misaligned then the total block is rejected.

Higher machining cost because big machine with high accuracy is required.

High material cost.

INSERTED METHODIn this method core and cavity is made from a small block of steel Known as core insert and cavity insert respectively and fitted in core holding cavity holding plate.

USE

Multi impression mould.

Small components.

Replacement of insert easy.DISADVANTAGES;

To machine recess for collar of insert machining cost increases and mould become little weak.

DETERMINATION OF NUMBER OF CAVITIES By Shot capacity Ns = 0.85 W

m

By Plasticizing capacity Np = 0.85 X P X Tc 3600m By clamping capacity Nc = C .

Pc X AmWhere,

Ns, Np & Nc = Number of cavities based on shot, plasticizing and clamping capacity respectively.W = Rated shot capacity for polymer in gm

m = Moulding wt per cavity in gm. (Volume* Density)

P = Rated plasticizing capacity for polymer (gm/hr)

Tc = Over all cycle time (sec)

C = Rated clamping capacity in tons

Pc = Clamping pressure in Tons/cmof projected area (0.630T/cm)

Am = Projected area of moulding including runner (cm)

Molding Wt (g)FactorMolding Wt(g)Factor

0.3-0.51.55-101.15

0.5-1.01.410-201.10

1.0-3.01.3Above 201.05

3.0-5.01.25

DESIGN OF GUIDE PILLAR

Diameter of guide pillar to be used depends on the size of the mould and side thrust. Mould having deep and heavy cross sectional cores exerts more side thrust.

Ps = Stem. dia of pillar ( P0 + 7 to 8mm)

Pc = Collar dia of pillar (Ps +2 tcp)

Tcp = Width/thickness of collar of pillar (from table)

Pillar stem. Dia .(mm) PsCollar thickness/Width(mm) tcp / Wcp

Up to 203

20-404

40-605

60-1006

100-2008

SIZE OF MOLD

(Length x Width)WORKING DIA. OF PILLAR

(In mm)

100x10010

100x15013

150x20016

200x25019

250x30022

300x40025

400x60032

600x70038

DESIGN OF GUIDE BUSH

Bi = Guiding dia of bush = Guiding dia of pillar Po

Bo = Outside dia of bush = stem dia of pillar Ps.

BC = Collar dia of bush = collar dia of pillar Pc

Bl = Length of bush = Thickness of mounting plate.

DESIGN OF LOCATING RING

D1d8 = Fixed platen hole dia 0.1mm (say 125)

d1 = Dsp = Collar dia of sprue bush +0.1mm

D2 = 7mm (for M6 screw)

D3 = Dia of screw head (10mm)

= 20, = 45

H1 = 10mm for small and 12mm for big mould

PCD = 70 90mm

H = 6 8mm

h = 4mm

K = 6mm

Types of locating rings and its uses Reduced diameter type

Constant diameter type

Increased diameter type

Increased depth type

DESIGN OF SPRUE BUSH The pact of mould having the tapered channel, connecting the cavity and machine nozzle is known as sprue bush.

The taper channel is called as sprue.

Where,

Dsp= Collar dia. of spur bush (From table 1)

dsp= Outside dia. of spur bush based on spur dia (From table1)

tsp =Collar thickness of spur bush based on spur Dsp (From table 1)

Lsp= Length of sprue bush As minimum as possible.

Normally 45 to 100mm

Equal to height from top surface of cavity plate to the top surface of top plate. d = Depth of radius (1.5 - 4mm) Approx R = Nozzle sitting radius (From table II)

= Nose radius of machine nozzle + 2mmDy = Smaller dia. of sprue (Nozzle orifice dia + 0.5-1mm) di = Bigger dia. f sprue (calculate) (table II)

Di = 2 LSP tan/2+dyWhere,

TABLE 1

d i (mm)d sp (mm)Dsp (mm)t sp (mm)d i (mm)

2.5 - 3.51224162.5 - 3.5

3.5 - 5.51632183.5 - 5.5

5.5 - 7.52040225.5 - 7.5

TABLE 2Machine capacity

In tons.Nozzle orifice Dia

In mm.Nozzle Radius

In mm.

30310

80310

130510

180510

300510

TYPES OF LAYOUT OF CAVITIES Cavities should be placed in such a way that when they are connected with sprue through runner and gate will ensure the uniform filling of impressions.

In general multi-cavity mould having same shape and size of impressions are connected through runners and gates of similar cross sectional area and length and cavity should be placed at equidistance from the centre of the sprue.

For multi cavity mould having differently shaped impressions should be connected through following system:

SYMMETRICALLLY AT SAME PCD LAYT-OUT OF A FOUR IMPRESSIONS MOULD.

R= Distance between sprue centre and cavity insert or distance at which cavity insert to be placed from the centre of cavity holding plate

R = (CLd+5)/ (2Sinx/2)

CLd = Collar dia. of cavity insert.

C I = I.D. of cavity insert. GL = Gate length (0.5 1mm) CE = External dia of cavity insert.

X = 360/Number of cavities.

L = Runner length = R-(CI/2+GL)

Runner of different cross-sectional area but same length.

Gate should have similar cross-sectional area.

It is required when dissimilar cavities are placed at equidistance from the centre of the sprue.

It is called runner balancing. Runners of same cross sectional area and length.

Gate should have different cross sectional area

This is done when dissimilar cavities are placed at equidistance from the centre of the sprue.

This is called gate balancing. Runners of different cross sectional area and length.

Gate should have same cross sectional area.

When cavities not placed at equidistance from sprue centre.TWO PLATE MOULD

TYPE OF MOULD

THREE PLATE MOULD

HOT RUNNER

CONVENTIONAL SPURE

COLD RUNNER

HOT RUNNER

COLD RUNNER

VALVE

SLEEVE

AIR

RING/PLATE

STRIPPER

PIN

TYPE OF EJECTION

Side wall contact on the core.= (Cid Cd (cm2) Thumb rule

Based on 85%of rated shot capacity

Based on 85%of rated plasticizing capacity

*Moulding weight m is to be multiplied with a factor to add up spur and runner weight

Pl= Length of pillar (can be found out from assembly drawing i.e. Perpendicular distance from guide pillar holding plate to guide bush holding plate)

Lsp= 60mm usually

= 2 to 5

Normally di is kept equal to dia of runner.

Keeping the above in view the following cross section of runner

are usually used:

- Round

- Trapezoidal

- Modified Trapezoidal.

Direct Sprue Gate

Application: for temperature-sensitive & high viscose materials, high-quality parts and those with heavy section.

Advantage : results in high quality & exact dimensions.

Disadvantage: post-operation for sprue removal, visible gate mark

h = nt

W = nA

30

It is used for thin walled large components like compact disc cover, motor Cycle wind screen etc

Application: primarily for smaller parts in multy-cavity molds and for elastic materials.

Advantages: automatic gate removal.

Disadvantage: for simple parts only because of high pressure loss.

Application: for multi-cavity moulds & center gating.

Advantage: automatic gate removal.

Disadvantage: large volume of scrap & higher mould cost.

Tab width: Y= D

Tab depth: X = 0.9t

Tab length: Z = 1.5D

Where,

D = Runner diameter,

t = Wall thickness of plastic component

Application: for high-quality technical parts, independent of cycle time, also suitable for material difficult to process

Advantage: no material loss from runner system & automatic gate separation.

Disadvantage: expensive moulds especially due to control equipment.

Application: for materials with large softening & melt temperature range& rapid sequence cycles

Advantage: automatic separation material loss from only after shut down

Disadvantage: danger of cold material gating into cavity after interruption

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