CRYOGENIC GRINDING

SEMINAR REPORT

Submitted byRAJESH.S

S7 MECHANICALREG NO; 08401042

ToThe University of Kerala

In partial fulfillment of the requirements for the award of the degreeOf

Bachelor of Technology in Mechanical Engineering

Department Of Mechanical Engineering Government Engineering College, Barton Hill, Thiruvananthapuram -35

OCTOBER 2011

DEPARTMENT OF MECHANICAL ENGINEERINGGOVERNMENT ENGINEERING COLLEGE

BARTON HILL, THIRUVANANTHAPURAM – 35

CERTIFICATE

This is to certify that the report entitled “CRYOGENIC GRINDING”, submitted by “RAJESH.S, S7 MECHANICAL, REG NO; 08401042” to the university of Kerala in partial fulfillment of the requirements for the award of the Degree of Bachelor of Technology in Mechanical Engineering (stream) is a bonafide record of the seminar presented by him.

GUIDE COORDINATOR

Mr. GOPAKUMAR Mrs. VINEETHA S DAS

HEAD OF THE DEPT.

Mr. SUNEESH

CONTENTS PAGE NO:

ABSTRACT 1

ACKNOWLEDGEMENT 2

NOMENCLATURE 3

INTRODUCTION 4

THE BEGINNINGS 5

ABOUT CRYOGENIC GRINDING 6

CRYOGENS AND IT’S APPLICATIONS 7

EXPERIMENTAL STUDY 8

CONVENTIONAL Vs CRYOGENIC GRINDING 10

CRYOGENIC GRINDING SYSTEM FOR SPICES 11

CRYOGENIC GRINDING OF PLASTICS 13

MAIN FACTORS INFLUENCING GRINDING 16

OPTIMIZED TECHNOLOGIES 19

NEW TECHNOLOGY 22

APPLICATIONS 26

ADVANTAGES 27

DISADVANTAGES 28

CONCLUSION 29

REFERENCES 30

ABSTRACT

Cryogenic grinding has been the development in the field of ultrafine

grinding of plastics, especially the ones with low softening temperature. The

word ‘Cryogenics’ originates from the Greek word ‘cryo’, which means cold.

Temperatures as low as -180ºC are attained in cryogenic systems. The

extremely low temperatures are produced by using substances called ‘cryogens

‘such as liquid nitrogen and liquid helium. Cryogens are used in various

machining operations such as cryogenic deburring, cryogenic deflashing,

cryogenic tempering and cryogenic grinding.

Cryogenic grinding, also known as freezer milling/ freezer grinding/

cryomilling is the act of cooling or chilling a material and then reducing it

to smaller particle size. Almost all materials embrittle when exposed to low

temperature. Cryogenic size reduction utilizes the cooling effect of liquid

nitrogen to embrittle materials prior to and or during the grinding process.

Materials which are elastic in nature, which have low melting points,

which have low combustion temperatures and which are sensitive to

oxygen can be ideally machined by cryogenic grinding process.

A cryogen like liquid nitrogen is applied mostly in the form of a

jet. At a low temperature of -196ºC of the cryogen, the temperature is

effectively controlled and embrittles the work piece. This enables the

grinding of the work piece.

ACKNOWLEDGEMENT

With profound respect and immense gratitude I wish to thank

Mrs. VINEETHA, Mr. GOPAKUMAR & Mr. SATHEESH Lecturers of

Mechanical Engineering, GECB for guiding me to take up this subject and also

helping me to successfully complete the seminar.

I am grateful to Prof. SUNEESH, Head of the Department of

Mechanical Engineering who has supported me with very useful suggestions

for improvement throughout the seminar.

I would like to express my deep sense of gratitude to Smt. GEETHA,

Principal GECB for providing all the facilities needed during the course of this

seminar.

Above all I thank almighty for all His blessings showered upon me and

giving me strength and presence of mind in successfully completing my

seminar.

RAJESH.S

NOMENCLATURE

D : Particle Size

Er : Relaxation Module

Wm : Specific Work of Comminution

N : Standardized Distance to Symmetric Centre

H : Standardized Temperature

EVA : Ethylene Vinyl acetate

LN2 : Liquid Nitrogen

LD-PE : Low Density Poly Ethylene

PP : Polypropylene

INTRODUCTION

Almost all materials embrittle when exposed to low temperature.

Cryogenic size reduction utilizes the cooling effect of liquid nitrogen to

embrittle materials prior to and or during the grinding process. Materials

which are elastic in nature, which have low melting points, which

have low combustion temperatures and which are sensitive to oxygen can

be ideally machined by cryogenic grinding process.

A cryogen like liquid nitrogen is applied mostly in the form of a

jet. At a low temperature of -196 ºC of the cryogen, the temperature is

effectively controlled and embrittles the work piece. This enables the grinding

of the work piece.

Cryogenic grinding usually starts with chips. This is cooled using a

chiller. The final product is a range of particle sizes which are sorted and

either used as it is or passed on and further size reduction is performed.

THE BEGINNINGS

An exact history of cryogenic grinding technology is not easily

determined. The history is unclear for reasons such as the secrecy

involved in research as this technology could prove to be very

profitable.

What is known is that the technology is derived from conventional

grinding and is used in the grinding of elastic materials.

CRYOGENIC GRINDER

ABOUT CRYOGENIC GRINDING

Cryogenic grinding , also known as freezer milling/ freezer grinding/

cryomilling is the act of cooling or chilling a material and then

reducing it to smaller particle size.

A cryogen like liquid nitrogen is applied mostly in the form of a

jet. At a low temperature of -196 ºC of the cryogen, the temperature is

effectively controlled and embrittles the work piece. This enables the

grinding of the work piece.

CRYOGENS AND IT’S APPLI CATIONS

The word ‘cryogenics’ originated from Greek word ‘cryo’, which means

cold. Temperatures as low as -180 ºC are attained in cryogenic systems. The

extremely low temperature are produced by using substances called

‘cryogens 'such as liquid nitrogen and liquid helium. Cryogens are stored in

vessels called as Dewar flask which provides good insulation.

Cryogenic fuels such as liquid hydrogen are used as rocket fuels and

propellants. Cryogens are used to achieve superconductivity in metals such as

tin and aluminium. These are also used for the preservation of bodies of animal

and humans, this process is called as cryopreservation. Cryogens are used in

food industry for food handling and processing.

Cryogenic substances are used in various machining operations

such as cryogenic tempering and cryogenic grinding. Cryogens like liquid

nitrogen are mainly used in special chilling and freezing applications.

EXPERIMENTAL STUDY

Conventional versus Cryogenic grinding

There are several processes used to produce ground rubber crumb. Two of

the most common are conventional grinding and cryogenic grinding. The

ambient process uses a high powered cracker mill and rubber is sheared and

ground into a small particle.

RUBBER GRINDER

Conventional grinding

Metal is separated using a magnetic separator. The process produces a

material with an irregular shape. In addition the process generates a significant

amount of heat. Excess heat can degrade the rubber.

Cryogenic grinding

Cryogenic grinding of rubber usually starts with chips. This is cooled

using a chiller. The final product is a range of particle sizes which are

sorted and either used as is or passed on and further size reduction

performed .The cryogenic process produces fairly smooth fracture surfaces.

No heat is generated in the process. This results in less degradation of the

rubber.

In addition, the most significant feature of the process is that almost

all fiber or steel is liberated from the rubber resulting in a high yield of usable

product and little loss of rubber.

CONVENTIONAL Vs CRYOGENIC GRINDING

Existing Grinding System Cryogenic Grinding System

The heat is developed inside the

grinding mill.

Temperature below 0 ºC inside the grinding mill.

This heat, which developed during grinding, leads on the one hand to evaporation of the essential oils and on the other hand, heat- sensitive fats are melted. This is turn can lead to the grinding elements become grassy (oily) and clogged or even to machine blockages.

Minimal loss of volatile components.

Air pollution due to evaporating essential oil into the atmosphere.

No, evaporation of essential oil into the atmosphere.

Existing grinding equipments more than two times recycle into the mill for required particle size.

Approx. 2 - 3 times higher grinding capacity.

Low throughput . High throughput.

High energy consumption. Low energy consumption.

No control on particle size. Particle size under control.

CRYOGENIC SYSTEM FOR HERBS

Cryogenic grinding of spices is a method of powdering spices/herbs at sub

zero temperatures ranging from 0 to minus 196 ºC. The spices are frozen with

liquid nitrogen, as they are being ground. This process does not damage or alter

the chemical composition of the spices in any way. Normal grinding process

which does not use a cooling system can reach up to 200 ºC temp. This high

temperature can reduce volatile components and heat sensitive constituents in

spices.

The Process:

The material is feed into a feeder hopper and dropped into a conveyor.

When the material to be processed enters the pre-chilled conveyor; liquid

nitrogen is sprayed and blended directly onto the material. The material is

conveyed via a stainless steel special design auger. The auger not only

transports the grinding media, but also mixes with liquid nitrogen for greater

cooling efficiencies.

The liquid nitrogen, a cryogenic fluid with a boiling temperature of -196 ºC

absorbs heat from the material and vaporized to a gaseous state.

Liquid nitrogen is added until the temperature of the material is reduced to

a

Predetermined set point. This set point is the glass transition temperature of

the material. Finally the brittle material enters an impact (pin) mill where it is

ground to a desired particle size. Computer controls the entire process of

cryogenic grinding system.

Pin Mill

Pin mills are high-speed machines working without screen. Pin rows which

are concentrically fixed on the rotor and stator discs, crush the particles,

interchangeable pins in different sizes can be delivered. According to the size

reduction problem, the concentrically spaces between the pins can be adapted to

the material.

Cryogenic grinding of plastics with air turbine

refrigeration system

Plastics after being grounded not only maintain intrinsic

properties, but also enhance the plasticity, formability,

solubility, etc. Therefore, it enlarges a great deal of application in the

area of reuse. There is a steady increase in the demands of fine powder in

powder molding, hot melt adhesive and plastics modification.

Refrigeration principle:

The working principle of air turbine refrigerator is to

convert the pressure potential energy of compressed air

released from the compressor to the kinetic energy of high-

speed airflow through the nozzle ring.

Recooling system

The cold airflow from the apparatus for utilizing cooling

energy is sent to recooling heat exchanger to cool the airflow

coming from the aftercooler with high pressure and ambient

temperature. Therefore, the airflow temperature at turbine inlet

is effectively reduced to lower temperature airflow at turbine

outlet.

Turbo expander

The turbo expander is composed of turbine blades, compressor blades,

nozzle ring, rotating shaft, bearing, outer shell, etc. As the rotational speed is up

to 50,000 rpm/min, bearing is the key component affecting the service life. Air

bearing and oil-lubricated bearing are the most common choice in engineering

practice.

Recooling heat exchanger

High compactness and high heat transfer efficiency are the main design

targets, thus plate-fin heat exchanger is chosen for its good heat transfer effect.

For the fine refrigeration effect, countercurrent flow mode is used to enhance

the refrigeration.

Precooling and cooling chamber

The design of the precooling and refrigeration chamber is

the important means to ensure grinding effect. In this study,

the spiral rotation of spiral propeller is used to increase the

dispersion of particles, making the cold air and particles to mix

well, and achieve proper heat transfer. At the same time, the

problems of particle transportation and arch forming are solved

with optimal cooling effect.

Vortex mill

Impact mechanical field is the most effective grinding means in

cryogenic grinding. In consideration of the comprehensive factors such as

material properties, grinding method, production capacity, energy

consumption a vortex mill is adopted as the grinder. The

rotating component of vortex mill consists of four stages. Each

stage is composed of blades and multiple cells, which are

formed by blades and their side conjunctive clapboard. There is

a lining with many grooves inside the outer shell. Moreover, the

clearance between blades and the lining is adjustable.

Improvement on vortex mill

Free path denotes a movement interval, within which a

particle moving in suspension with a certain concentration does

not collide with other particles. When a particle entering the

grinding area, if its distance to the blade is equal to or less than

the free path, it would collide with blades or lining first before

meeting other particles. According to the grinding mechanism,

the mutual collision between particles and blades or lining is

the most effective way of grinding in vortex mill. Therefore, the

probability of such collision is expected to be as big as possible.

So if the free path is too short, a particle entering the vortex

mill would collide with other particles first. Hence, the average

free path of particles is preferably raised to a certain extent by

appropriately increasing the blade number of each stage, which

would improve the grinding effect.

MAIN FACTORS INFLUENCING GRINDING

1. Material properties: Three kinds of plastic particles are grinded in the

same experimental equipments and condition. Mechanical property is the most

important factor in influencing the grinding effect. The output and reduction

ratio of PVA-2488 particles with the smallest elongation at break are higher.

However, for the NBR and EVA particles, there is little difference in elongation

at break.

2. Feeding particle size: The distribution of product particle size is related

to that of feeding particle size. Usually, too big particle size is very easy to

escape from the vortex field, while the opposite although increases the heat

exchange surface, but the size effect raises its anti-destructive capability,

leading to low product quality.

3. Cooling temperature: Theoretically, when the thermoplastic particles,

such as EVA and rubber are refrigerated into brittle state, the particles would

be easier to be ground by brittle fracture. However, comparing the ground

product from embrittled samples with the experimental results at room

temperature, although there is obvious difference in the particle shape, the

particle size of the former may not be finer.

4. Clearance between blades and lining: When the clearance becomes

smaller, the particle size is also smaller and the range of distribution is narrow.

5. Collision speed: As the vortex mill rotates faster, the impact speed

towards EVA particles increases, and correspondingly the fracture probability.

However, the rotating speed of rotor is restricted by the bearing load, strength of

rotor components, and machining accuracy, it is favorable to appropriately raise

the rotating speed of rotor to improve efficiency. The tangential speed of vortex

mill is selected as 105 m/s in this study.

Assumptions for calculation

1. The observed particles have the shape of a sphere.

2. The material properties are independent of location and temperature.

3. The particles have a homogeneous temperature in the calculation.

4. The flow, heat capacity, and heat transfer coefficient of particles and cold

air are invariant in the lateral spiral propeller.

5. Heat transfer among screw, cylinder wall, and cold air is considered to

reach a balance.

6. Only the heat transfer between particles and cold air is taken into

account.

Heat transfer calculation

Under the above assumptions, heat transfer between particles and cold

air could be simplified. The calculation diagram , lateral spiral propeller is

divided into n stages.

In the first stage, heat transfer of gas–solid is given by

Q = h × tm × S

CONCLUSIONS

1. Experiments show that adopting the cryogenic grinding system

refrigerated by air turbine refrigerator to process fine EVA powders is feasible.

Compared with liquid nitrogen, the energy consumed in this system is much

lower. Moreover, compared with the common refrigeration methods such as

freon, lithium bromide, and ammonia, this system possesses advantages of low

refrigeration temperature, simple equipments, and easy maintenance. And

compared with grinding at room temperature, the value of Ki in this system is

three times as large as that of the latter. Furthermore, another important

advantage is that introducing cold air into the grinding plant avoids overheating

of powder and dust explosion without any additional security equipment. In

addition to grinding EVA, this system could also be used as a kind of general

technology to grind other kinds of plastics by adjusting the related parameters.

Therefore, it owns a good commercial value. In other words, the cryogenic

grinding system refrigerated by air turbine refrigerator creates a new way of

recycling renewable plastics in a large scale, with high quality and low energy

consumption.

2. Material properties, feeding particle size, collision speed, etc. are the

main factors that affect the grinding effect. The selection principle of

refrigeration temperature is to ensure that the particles could maintain a

reasonable condition of low temperature. Moreover, experiments have proved

that it is not necessary to refrigerate EVA particles to the brittle condition. The

cooling energy is mostly used to counteract the grinding heat, ensuring that the

grinding process could be running for a long time at high quality and low

energy consumption.

3. Vortex mill is regarded as the research object in this study. An

engineering calculation and analysis approach is introduced from the energy

conservation law during the grinding process, aiming to guide the practical

application. These analytical results confirm the rationality of the experimental

results, which is beneficial to the improvement of equipments and evaluation of

multiple correlated parameters.

Optimized technologies for cryogenic grinding

Fine grinding or comminution gains increasing importance. This is

reflected in the extensive trend towards fine structuring of solid materials and

the rapid spreading of research disciplines like micro, nano, and surface

technologies. In addition to the target particle size, the specific comminution

work is substantially affected by the material properties. This work is 10 to

hundred times higher for the comminution of plastic than for minerals. The

theoretical background of cryogenic grinding and a new technology based on an

alternative cooling equipment are presented. With the alternative technology,

the operation costs during cold grinding will be drastically reduced. At the end,

experimental results show effects of the variation of different running

parameters.

1. Material properties

In addition to the target particle size, the specific comminution work is

substantially affected by the material properties. This work is 10 to hundred

times higher for the comminution of plastic than for minerals. Differences in the

specific work of comminution may be attributed to losses during the

deformation of the particle which does not result in a fracture. Whereas in brittle

materials, the imported comminution energy is saved in elastic deformation by

high stress fields, major part of plastic materials are being deformed

viscoplastically. This deformation behaviour is largely dependent on

temperature and time and is defined with the relaxation module. This module

describes the stress relief of a sample of constant expansion by plastic

deformation.

2. Heat transfer at a particle

The heat transfer at particles with a different diameter should be taken

into consideration before a calculation of the theoretical lowest demand on lN2

may be performed, due to the multiply stress of particles that is necessary to

achieve the desired particle size.

Relaxation of plastics at different temperatures.

3. Calculation of lN2 consumption

The heat to be discharged at cryogenic grinding is composed of heat,

which has been introduced by the product (Q feed) and the heat introduced by

the drive capacity of the mill (Q mill), provided that the grinding air flow required

for the operation of the mill is met by the condensing nitrogen alone.

Qtotal =˙Qfeed +Qmill

4. Economic aspect of cryogenic grinding

The utilization of liquid nitrogen (lN2) has undoubtedly numerous

advantages in application. However, these advantages have to be

counterbalanced against the high energy consumption, and thus investment cost

for the supply of the cold agents which considerably affects the operation cost

of a cryogenic grinding plant. For the grinding of 1 kg viscoelastic material an

amount ranging between 0.6 and 4 kg liquid nitrogen is required in optimized

mills Liang and Hao, 2000. In-house measurements at various contract grinding

companies yielded even consumptions of up to 6 kglN2/ kg solid material.

Provided a nitrogen price of approximately 0.10 /kgln2/kg solid material, the

cost of nitrogen alone would amount to more than 100 per ton material used (at

1 kgln2/kg solid material), thus representing over 40% of the cost of cryogenic

grinding.

New technology developed by Fraunhofer

UMSICHT

Measurements at production plants showed that the real consumption is

sometimes much higher than the theoretical calculated consumption. To relate

the theoretical to the practical consumption, the efficiency factor glN2 is

defined as

Ef = (theoretical consumption/ practical consumption)*100 %

At a cryogenic grinding plant in the chemical industry, this efficiency

factor varies from 25% to 75%. That shows that there is a demand of

optimization.

1. Optimized process design

In addition to increasing the efficient factor by optimizing the operation of

conventional plants, Fraunhofer UMSICHT has developed an innovative

technology which allows to avoid the use of lN2 partially or completely,

depending on the material. This technique is based on the employment of a

refrigeration plant. This plant has a cooling power of 40 kWth which is equal to

360 kglN2/h. The heat is transported by a cooling medium, which is still liquid

at temperatures below _1008C. This allows to cool the grinding material and the

grinding air separately in special heat exchangers down to a temperature of

about _608C. For many materials, this temperature is sufficient to become

brittle. Should this temperature be not sufficient, the material may be exposed

to further cooling in a cryoscrew with lN2 In order to perform the optimization

described, a pilot plant has been erected at the technical laboratory of

Fraunhofer UMSICHT. Planning did in particular focus on a high flexibility of

the plant. This made it possible to test both according to the traditional method

and according to the new method, as well as by combining both methods.

Injection options of nitrogen at different places of the grinding air circulation

allow cooling of the mill, independent of the cooling of the material. A number

of applicable grinding aggregates with different grinding principles may be

applied for different milling functions. The plant has a throughput performance

of 300 kg/h (depending on the material), so that the results achieved may be

readily transferred to large scale plants. To allow detailed estimates, extensive

measuring technology was included.

2. Comparison between conventional and alternative cooling technique

The supply of cold at a temperature of -196 8C is not necessary for many

plastic materials. In many cases, temperature levels noticeably above -80 8C are

sufficient to make plastics brittle. Characteristic for a process of cold generation

is the performance coefficient ‘e’ Nesselmann, 1957:

e= Q0/ W

Where ‘Q0’ represents the cold quantity, and W the required mechanical

capacity.

Process design of the cryogenic grinding facility at Fhl

UMSICHT

Cold amount of thermal energy (Qth) may be generated at a temperature

level of -80 *C utilizing one-sixth of energy input compared to a temperature

level of -196 *C. The connection between the performance coefficient of the

Carnot process eC and the parameter of the real process e is formed by the

efficiency factor ‘g’.

This plant configuration would yield a break-even point of 2676 h/a,

indicating the threshold for a cost-efficient application of the alternative

technology. For plants with lower operating hours, the conventional technology

is more efficient cost. However, the increased investment input for the

acquisition of a cold generation plant comprising the necessary equipment has

to be considered on the other hand.

Efficiency factor ‘g’ of different process

The Fig. shows the factor of four different processes (cold steam, Philips,

Thomson–Joule and adiabatic isothermal).

The connection between the performance coefficient of the Carnot process

eC and the parameter of the real process e is formed by the efficiency factor ‘g'.

This efficiency factor depends on the used cold generation process. With respect

to the temperature range between -80T C and 0T C, the cold steam process is the

efficient process

In comparison to the use of lN2, the reduced energy input of the

alternative cold technology is reflected in lower operation cost. However, the

increased investment input for the acquisition of a cold generation plant

comprising the necessary equipment has to be considered on the other hand. As

a consequence, a plant based on the alternative technology will be cost efficient

only after a certain operation time.

APPLICATIONS OF CRYOGENIC GRINDING

Cryogrinding of steel:- The large amount of heat generated during

grinding at high speed raises the temperatures at cutting zones excessively.

Cryogens such as liquid nitrogen will help in reducing the effect of heat on tool

and work piece, thereby increasing the life of the tool.

Thermoplastics: - Nylon, PVC, Polyethylene, Polypropylene are usually

machined using cryogenic grinding to form powders.

Thermo sets: - Synthetic and natural vulcanized rubber and materials

such as bakelite can be economically machined with cryogenic grinding and

recycled.

Adhesives and waxes :- Sticky materials such as adhesives and

waxes are difficult to machine using the conventional grinding methods. By

using cryogenic grinding, they can be embrittled easily and machined into fine

particles.

Explosives :- Explosive materials explode when their temperature

increases to ignition temperature in the presence of oxygen. By using

cryogens the ignition temperature can be reduced effectively and then be

machined.

Spices :- Spices like pepper ,cinnamon can be powdered by

cryogenic grinding which helps in the preservation of the taste and aroma.

ADVANTAGES OF CRYOGENIC GRINDING

Higher material removal rate can be achieved.

Tool wear and tear is minimized to a great extent.

Grinding forces are reduced.

Cryogens act as coolant and hence the effects of overheating of the tool

and work piece are reduced.

Materials which are soft and elastic in nature such as rubber can be easily

machined with this process.

Smaller particle size can be achieved.

Better surface finish and dimensional accuracy can be achieved.

Temperature below 0 0C inside the grinding mill.

Minimal loss of volatile components.

Low energy consumption.

Approx. 2 - 3 times higher grinding Capacity.

No Fire Risk.

Low capacity motors are required to grind the material.

No, evaporation of essential oil into the Atmosphere.

Particle size under control.

High throughput.

DISADVANTAGES OF CRYOGENIC GRINDING

1. Grinding system is very complex. It consists of large number of equipments

like dewar flask, grinder, nozzle, compressor, silica gel container.

2. Very costly. It need high capital cost. (For cryogenic grinding, compression

system, moisture adsorption system and grinding system are necessary.

3. Formation of ice around delivery nozzle. Silica gel absorbs moisture and

this moisture cause the formation of ice around delivery nozzle. It cause

blockage inside of the valve.

4. Large area requirement. Cryogenic grinding system includes compression

system, moisture adsorption system and grinding system.

5. Not economic. Chemicals such as silica gel & liquid nitrogen produce

unwanted products, which cause pollution.

6. Material specific. Cryogenic grinding can be used only for Materials which

are elastic in nature, which have low melting points, which have low

combustion temperatures and which are sensitive to oxygen .

CONCLUSION

Cryogenic grinding , also known as freezer milling/ freezer grinding/

cryomilling is the act of cooling or chilling a material and then reducing

it to smaller particle size. Cryogenic size reduction utilizes the cooling

effect of liquid nitrogen to embrittle materials.

The main advantages are higher material removal rate, tool wear and tear

is minimized to a great extent, and grinding forces are reduced. Cryogens act as

coolant and hence the effects of overheating of the tool and work piece are

reduced. Materials which are soft and elastic in nature such as rubber can be

easily machined with this process.

The application of cryogen in moist atmosphere may cause formation

of ice around the delivery nozzle and the piping system carrying the cryogen.

Cryogenic grinding improves product quality by controlling thermal

effects. Oxidation and surface burning are eliminated. Surface damage is

eliminated. Finer particle size is achieved. Material removal rate is high. The

process is economical in the long run.

REFERENCES

Michael, Jurgen & Damian,(2004) “Optimized technologies for

cryogenic grinding.” Int. J. Mineral Process.

Journal of “Process Mechanical Engineering”-2011. Fraunhofer

Institute for Environmental, Savety and Energy Technology UMSICHT,

Oberhausen, Germany

E-book of Spectra Cryogenic Systems Private Limited(2005 ) Cryogenic

equipment manufacturers and consultants “Cryogenic Grinding System for

Spices & Herbs” Kota 324005, Rajasthan, India

APPENDICES

Crackermill 11

Cryogenics 8

Cryopreservation 10

Dewar flask 10

Ethylene vinyl acetate 15

Freezer milling 9

Gas solid separator 11

Low density polyethylene 23

Magnetic separator 11

Pin mill 15

Polypropylene 23

Spices 29

Theoretical consumption 25

Vortex mill 18