Shoe Sole Manufacturing Tech

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Shoe Sole Manufacturing Tech.

INTRODUCTION

Now a days shoes are meant as basic requirement of our day to day

life. Through out the life we come across various types of shoes according to the

scenario we are going to face. Throughout the globe various foot wear

manufacturers came forward to full fill the customers requirements.

Basically shoe is consisting of upper part and sole part n upper part

manufacturing is expansive as its associated with skillful labour. It provides

identity, shape, look to a shoe of particular kind. Sole manufacturing iscomparatively less expansive as its associated with less skillful labour as compare

to upper.

Welt construction shoes are traditional design, with the upper stitched

to welted inner sole and the outer sole sewn to inner. Variation of this traditional

construction include the adhesive bonding of various parts in place sewing in which

the upper is turned out wards instead of inwards. This allows an appearance similar

to welted shoe but at a much lower manufacturing cost. The advantages of sheet

materials are essentially those of flexibility of design fashion and it is easy to supply

a large number of size variations.

Generally rubber, PVC, PU and EVA are used as raw material for sole

manufacturing. Each of above mentioned material has got specific characteristics

which promotes availability of different kinds of foot wear in the market to full fill

the various kinds of customer requirements.

Footwear industry is also unable to keep it self away from modern

technique. Traditionally compression-molding machines are used for sole

manufacturing, as manufacturers did not have any alternative other than rubber as a

raw material. Later on modern science suggested that PVC, EVA. and PU are the

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materials other than rubber can be used as raw materials with introduction of

injection molding, cold flow molding and R.I.M. concept in the fool wear industry.

Presently new techniques are adopted which provides cycle timereduction from 35-45 records with increase in number of cavities from two to four.

Production efficiency has been improved with the help of new and improved mold

design for longer mold life and better quality parts, improved cooling system.

Location of gale, separate core inserts to improve ventilation, reduced thickness of

parts without any compromise on quality.

The new techniques allows significant cost saving intelligence,

process innovation, increase productivity. Preventive maintenance quality control,

employment enrichment and site house keeping.

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1) Accelerator ( Mercapto benzthiazole)

2) Activator ( Stearic Acid, Zinc oxide )

FillersProcessing aids ( white oil )

Special purpose agents

Sulphur ( Vulcanization )

Vulcanization

Overriding and predominant in the technology of the industry,

particularly with the emphasis on higher production rates and new techniques is the

control of chemical reactions leading to cross linking to bonding to metal and

fabrics and rubber break down.

The final step in the manufacturing sequence in the vulcanization or

curing of the formed product. Basically, the process is that of applying heat at a

certain temperature for certain time. Vulcanization is most often combined with

forming. Method of molding.

Vulcanization process lead to improve the following characteristics.

Property Raw Rubber Vulcanized Rubber

1) Tensile strength (kg/cm2) 200 2000

2) Percentage elongation 1200 800

3) Water absorption capacity Good Very good

4) Tackiness More Very small

5) Working temp 10 600C - 40 to 1000C

6) Chemical Resistance Very poor excellent

7) Elasticity Very much lower much higher

8) Resistance to oxidation

abrasion wear and tear

Very much lower much higher

Machinery Used for Rubber Compounding

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Banbury mixer : The mixer consist of a completely enclosed mining chamber in

which two spiral shaped rotors operated a hopper to receive the material for mining

and a door for discharging the batch. Revolving in opposite directions and atslightly different speeds the two rotors keep the stock in constant circulation. The

ridge between the two cylindrical chamber sections helps force mixing and the

accurate convergence of the rotors and the chamber walls imparts shearing. This

combination of intensive working produces a highly homogeneous batch. The

batch is confined within the sphere of mixing action by an air-operated ram in the

feeding neck. The ram also greatly facilitates the flow between the blade tip and

shell where shearing is most extensive.

Two Roll mill : The two roll mill consist of opposite rotating parallel rollers placed

close to one another with the roll axes lying in a horizontal plane so that a relatively

small space or nip between the cylindrical surfaces exists. Material reaching the nip

is deformed by friction force between itself and the rollers and made to flow

through the nip in the direction of roll motion. Liquid plasticizers or finely divided

solid ingredients also are placed in the nip and are used to cut ribbons of shock from

the roll for feeding to a cooling tank and dicer. Usually by adjusting the roll temp

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FeedHo er Door

Cored rotors for

circulation ofcooling water or

steam

Drilledsides

WeightC linder

Floatingwei ht

Banbury Mixer


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the compound can be made to adhere to one of the rolls as a relatively thin sheet.

The rolls are heated or cooled by a heating or cooling medium introduced into their

hallow cores. They usually are rotated at different speeds to facilitate the formationof a sheet or hand frequently is cut and manually pulled loose from the roller. The

gap between the rollers generally may be adjusted manually by means of hand

driven or motor driven screw.

Process description of Rubber sheet manufacturing

Fresh batch is prepared and sent to the banbury mixer. The banbury

mixer are employed in the compounding section for compounding of rubber with

additives. The equipment under batch process with batch time 10 mins. A dust

collector is provided for dust collection. When compounding is completed the

obtained product is dropped over the open mill which masticate the compounded

rubber with shippy white powder. The masticated rubber compound is passed over

endless belt for coating the compounded rubber. The cooling operation is done with

deeping the compound in cold water and then exposed to the series of fans. Then

shippy white is sprayed over it to avoid sticking dusting storage.

Machineries used for compounding

Banbury mixer

Open mill

Cutter

Flow sheet of Rubber compounding

Fresh Batch

Banbury Two Roll Mill CoolingMixture

To pressing section Powder Spraying

Lab testing

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Vertical Injection Molding Machine

Molds of varying capacity may be used in any one run since the

volume of compound injected into each mold is determined by the backpressure

developed in the mold. Effective flash- free molding are not produced from this

type of m/c but by designing the molds for tear timing minimum speed waste can be

achieved.

Each station carries individual temperature controls, so that cure

temperature for moldings of different sole and heel thickness can be achieved.

EVA AS MATERIAL

Ethylene Vinyl Acetate ( EVA) as material copolymer of ethylene and

vinyl acetate (V.A.) colloquially termed EVA and are elastomeric in the 40-60%

VA range, commercially available grades containing usually 40-50%. The

copolymer is substantially amorphous at 40 % V.A. content but retains some of the

thermo plasticity of polyethylene.

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Commercial grades of EVA are marketed by Bayer or Levapren and

by U.S. inducter as Vynthene variation being confined by V.A. content and

viscosity. Ethylene vinyl acetate is characterized by good dry heat, ozone andweather resistance. Heat resistance is similar to A.C.M. and resistance to swelling in

oils and solvents is inferior to C.R. and N.B.R. vulcanized EVA. Copolymers with

stand 120oC continuously or 140-150% with a useful life of up to one year at 180-

200 oC life can be measured in weeks.

Physical Properties

Tensile strength ( in M.Pa.) 25Percentage elongation 200-600%

Hardness ( Shore -A ) 60-85

Compression set resistance over

temp range ( in oC )

100-180

Compounding sequence

1) Polymer 2) Pigment

3) Chemical 4) Fillers5) Blowing agent.

E.V.A. Compounding

Sr.No

.

Additives used Type of material Purpose

1 Fillers Calcium Carbonate Dimension stability and

cost reduction.2 Plasticizer Dioctylpthalate Aids the process operation

of mixing

3 Activator Stearic acid, Zinc oxide Activates the processing

rate.

4 Blowing agent Fomacin Micro Provides foam like

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structure

5 Pigments Carbon black Coloring

Machinery used

1) Kneaders 2) Two roll mill 3) Calendaring device z type blade

Kneaders: It is basically consist of a rotating and a square like container. Both the

container and the Z type blade, screw is made of stainless steel. The cover of the

container is opened and closed by hydraulic system. The fresh batch is introduced

to the device for compounding. Digital indicators provided to show the parameters

of the processing. The kneading action of blades produces a high viscosity product

in 10-15 minutes. The feed material is under gone heavy shearing action enables

the formation of product.

Calendaring device: The calendaring roller are usually chambered and not parallel

to compensate for variation in thickness across the sheet whilst this is an ideal

solution for a calendaring which produces one gauge of sheet from one compound a

change in either of these parameter gives a departure from the desire crown. Whilst

calenders can be chambered in a few hours to accommodate a permanent compound

change or to table up wear of rolls if more than are compound is processed then

some other device for resetting the crown will be needed if the amount of change of

crown needed is small then roll bending device can be installed. Calendaring for

rubber compounding normally produce sheet of thickness of in range 0.1 to 1.5 mm.

Both these dimensions however are very dependent upon the quality of sheeting

required and the characteristics of compound.

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Flow sheet of EVA. sheet manufacturing

Fresh

Batch kneader 1st Two roll mill

Cutting calendaring 2nd two roll mill

Weighted

Process description of EVA. Sheet manufacturing.

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Two Roll Mill

Calendaring Device

Kneaders


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Manual C. M. machines : It is hydraulically operated. Instead of oil, water can be

also used for production of pressure. But manual molding machines produces 4-8

pairs of role (rubber) in each cycle. Each cycle is completed in 10 mins. Tempmaintained at 1600C.

Automatic compression molding M/c : This type of Machines are used for

manufacturing of soles and insoles (EVA/rubber). All operations are hydraulic in

one cycle 6 sheets are produced. Each cycle is completed in 10-13 mins.

Temperature regulator is provided to regulate. The supply temperature which is

generally obtained from thermo Pac(180-185). The temp maintained at 170-1750C.

Cold flow Molding : It is generally applicable to EVA. Compounds. The EVA.

Compound is preheated then placed over a cold chamber at 50C. After that pressure

is applied to obtain desire sole. The EVA.sheet are heated at 90-1000C by passing

over a header. The objective of heating to activate the molecules of EVA

compound and softening the compound. The soften compound is molded in a cold

cavity to restrict the flow of vinyl molecule to obtain the desire shape and size.

Lab testing

Temp in C 160 1750C

Pressure in kg/cm2 1 1.5

Time in mins : 10

BATCH CLEANING PROCESS FOR MOLDS

i) fill the batch th with orion 355 and water 70 : 30.

ii) Open steam and air line

iii) Warm the solution uniformly.

iv) Hang the molds for cleaning with hooks and arrangement.

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v) Pull and drag the molds by chain with control switch system and dip the

mold totally inside the hot solution 12 molds to be dipped at the time

keep the molds dipped inside the solution for 4 hrs.vi) Take out the molds after 4 hrs with the control switch and clean with

plain cold water jet system.

vii) Clean and dry the water from the mold.

viii) Supply the clean mold to pressing section to use.

POLYVINYL CHLORIDE AS A MATERIAL

It is an interesting paradox that one of the least stable of commercially

available polymers should also be in terms of tonnage consumption at least one of

the two most important plastic materials available today. Yet this is the unusual

position held by polyvinyl chloride a material whose commercial success has been

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to a large extent due to the discovery of suitable stabilizer and other additives which

has enabled providing useful properties like as follows:

Electrical properties, weight, transparency or opaqueness, chemical,resistant, hardness, dimension stability. PVC is also available in adequate amount

and relatively at cheaper price.

Physical Properties

Specific Gravity 1.4

Tensile strength (M.Pa) 58

Elongation at break 5

Vicate softening (o

C) 80

Significance of k value

The value of k based on modular weight and having different physical

properties. It could be transparent, series transparent to opaque and in addition may

or may not require for food grade nontoxic stabilizes and can be blow-molded

injection or extrusion stretched blow molded.

Determination of k value.

C3150

Zlog5.1Zlog5.01C

20011Zlog5.1

k+

++++

=

Z relative viscosity

C concentration in grams/100 ml

ZCxt

tt

0

0

t time of flow in seconds

t0 time of flow in seconds of redistilled cycle.

C Concentration in grams of resin per milliliter of solution.

Compounding Sequence

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1. Polymer

2. Stabilizers

3. Plasticizers4. Extenders

5. Lubricants

6. Fillers

7. Pigments

8. Polymeric processing agents

9. Impact Modifier

Compounding of PVC

Name Type of material Purpose

Stabilizer Lead base, Beryllium cadmium Prevent degradation

Plasticiser Di-octylpthalate Di-iso octyle pthalate Aids the processing

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Operation of mixing

Lubricants Metallic stearates, stearic acid, oleic acid aids easier

procesibility and

effects the M.F.I.

Filler Forcal, clay, talc dolomite Provides hardness,

Dimension stability

& cost reduction.

Pigment Red ion oxide, carbon black coloring agents

Special agents

Blowing agent Azo-die compound Provides foam like

structure

Fire resistance Antimony trioxide Resistance to fire

Enhances.

Ultra-violet

stabilizer

Ranypol, Thinpol resistance to u.v

increases.

INJECTION MOLDING

Poly vinyl chloride material is injection molded to obtain solid soles

and blown soles.

Solid soles are commercially termed as sole pack.

General injection cycle of sole pack

Curing time 1.3 mins

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Compression 135oC

Melting 135.5 oC

Mold pressure 135.5

o

CAir pressure 700-800psig

Injection pressure 100 psig

Back pressure 8-10 kg/cm2

Machine Description

The machine is basically consists of two sections. One section clamps

and holds the mold halves together under pressure during the injection of the

material into the mold. The other section, the plasticising and injection unit includes

feed hopper the hydraullic cylinder which forces the screw an the heated barrel

which encloses the screw. The barrel is heated with the help of series of heaters.

Molds are provided with cooling system is chillers. Temp and pressure of varies

parts are indicated by indicators along with regulators with the help of which one

can easily fluctuate the temp and pressure at desire according to the requirement of

the product quality.

Process Description

A fresh batch of 100 parts of PVC compound +3 parts of pigments

+10-15% of recycled product is fed to the hopper. The feed material is initially

preheated in a preheated to remove moisture.

The feed material moves forward by the action of flights of the screw.

As it passes through the barrel the plastic picks up conduction heat from the heating

element on the barrel and frictional heat from the rotation of screw. The

compression ratio of screw is 2.5. As the material moves forward in the barrel it

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changes from granular to semi viscous continuously and it forces the screw

backward in the band against a preset hydraulic pressure. This backpressure is an

important processing variable. The screw stops turning when proper amount ofmaterial has reached the barrel sensed by vernier set limit switch. The material at

the nozzle end charged into the cavity at certain pressure cooling by the forward

motion of screw 1900 inches per minute by hydraulic pressure on the plastic. The

hot melt is forced through nozzle of barrel, through the sprue of the mold and into

the runner system and gates and mold cavity. The temperature of material sizes

from the barrel temperature to mold temperature and aids faster crosses linking

using the parts for 1.3 minutes. After that chillers are come to action for cooling the

part for a definite time interval after chilling screw moves backwards. After another

cycle the mould is opened hydraulically and the sole is ejected automatically with

the help of ejector pins. Example Flex point, N' Delio, Falton.

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Hooper

Chiller

MoldHeater

Carria eFT: feed zone temp

CT: Compression Zonetemp


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Injection Molding Machine for Solid Sole Manufacturing

General Injection cycle of Air blown

Injection 1st Pressure 4.2 seconds

Injection 2nd pressure 15 seconds

Prepare mold down 4.2 seconds

Prepare screw turn 12 seconds

Feed zone temperature 1650 CCompression zone temperature 1800 C

Metering zone temperature 1850 C

Nozzle temperature 1900 C

Machine Description

The machine is basically consists of two section. One section clamps

and holds mold halves together under pressure during the ejection of material into

the mold. The other section is the plasticizing and injection unit includes feed

hopper, the hydraulic cylinder which pushes the screw forward to the inject material

into the mold, a motor to rotate the screw and heat the barrel with the help of series

of heaters.

Here an air pump provided along with indicator and suitable piping

which is responsible for formation of blowing compounds. Chiller provided for

chilling operation. There are 18 workstation at present in this machine. A digital

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Preheater

MT: Metering zonetem

MP: Mold pressure

IP: Injection pressure

BP: Back pressure


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controller is provided in which all temperature, pressures of various zones are

indicating of corresponding workstation. After each cycle the workstation changes

their places by motor arrangement.Process Description

The feed material i.e. a fresh batch of 100 parts of PVC + 15-18 of

ADCL +10-19% of recycled product are being fed to the hopper after sufficient

preheating. The preheated material is conveyed inside the barrel by the screw

rotation. The conductive heats of the heaters are taken by the material along with

shear heat, which converts the material from solid state to semi viscous form. This

screw rotation stops when sufficient amount material reach the barrel. The screw

then moves forward to transfer the desire amount of molten material from nozzle to

cavity through sprue, runner and gate.

After sufficient of material injection the motion of screw is stopped.

The air pump starts working and supplies 6kg/cm2 air pressure to the cavity for

blowing of the injected material. After blowing cooling of the material is done with

the help of the chillers. After that screw moves backward. The workstation is

moved and another workstation comes under injection point. The cooled sole is

ejected out. Example Heritage, Seible, New Juliet.

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5. Hopper

6. Preheater 7. Screw

8. Heaters9. Nozzle

10. Gate11. Workstation12. Workstation bar 13. Piping for cooling

14. Chiller

1. Hydraulic operated air supplier

2. Air pressure indicator 3. Pump

4. Work station number indicator 15. Weight of material fed

16. Feed zone temperature17. Compression zone temperature18. Metering zone temperature19. Nozzle temperature

20. Pressure indicator

21. Timers


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Commercial development of polyurethane arose from the work of

German chemist attempting to develop the Du pont patent on Nylon-66. Polymers

by reacting aliphatic di-isocynates and aliphatic diols. Subsequent work resulted inproduction of useful product by using polymeric hydroxyl containing compounds

such as polyesters to give rubber, foam, coating and adhesives.

Physical Properties

Tensile strength 38 MPa

Percentage elongation 640

Resilience 56

Hardness (B.S.) 86

Tearing resistance 7.2

Abrasion resistance 15/cm3

Polyurethane compounding

Sr.

No.

Additives Types of materials Purpose

1 Catalyst Silicon , tertiary amines,

organo-metallic compounds

To speed up the reaction

2 Cross linking ,

chain extending

agents

Polyols, polyamines To give polymer cross

linking, to introduce

special polymer

segments

3 Blowing agent Water reacts with isocynates To produce foamed

structure

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4 Colorants Various pigments, carbon

black

To identify different

foam grades

5 Fillers Particulate, inorganic

material

To modify properties

( stiffness and fibre

properties )

6 Flame retardant Phosphorus and halogen

containing molecules

To reduce flammability

7 Smoke

suppressant

Particulate organic or

organic material,

polycarboxylates hydrates

oxides, borates

To reduce the amount

and slow down the rate

of smoke production

The RIM process

The reaction injection molding process is that in which the ingredientare injected into the closed mold where they react to give the molded product in the

required material. In the present case the ingredients are polyurethane foam and

simultaneously polymer formation and foaming occur in the mold.

Over the years three main variants have been tried in the RIM process.

It is usually to have two metered streams of reactants, which are intimately mixed

immediately prior to injection. In all cases to bring together for reaction polyols

compounds, isocynates, catalyst, chain extenders, cross linking agents, surfactant,

blowing agent and other additives such as colorants, ultra violet absorber. The

variants have been concerned with the way these ingredient and divided into two

streams.

RIM variants for PU systems for Shoe soles

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One shot system Prepolymer system Quasi prepolymer system

Polyols Polyhydroxyl Part polyhydroxyl compound

Cross linking agent -- --

Catalyst Silicones SiliconesBlowing agent Isocynates Blowing agent

Isocynates Cross linking agent Isocynates part polyhydroxyl

compound

In the one-shot system the isocynate forms one stream and all the

remaining components form the other.

In the prepolymer system the isocyanate is reacted, by the chemical

manufacturer, with all the other components except the cross linking agent. The

shoe-sole manufacturer then adds the cross linking agent (as the second stream ) to

the polyurethane prepolymer.

In the quasi-prepolymer the isocynate is reacted, by the chemical

manufacturer, with part of the polyhydroxyl compound, and this is used as one

stream. All other components are in the second stream.

Of these systems the quasi-prepolymer system is much the most

favoured. It has been found to give the optimum combination of processing

characteristics, storage stability and physical properties of the finished shoe sole.

Among the advantages if offers is a well matched flow-rate requirement from each

stream.

Processing description of P.U. sole manufacturing

The requirement in the plant is to store the ingredients for the two

streams of reactants, and then to meter them to the mixing chamber at the

appropriate rates, followed by injection of the reactive mixture into the mould, fig.

In the production head, each stream is in pumped circulation

continuously, to maintain uniformity of composition and temperature. When it is

time for an injection, valves interrupt the circulation to allow the required for an

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injection, valves interrupt the circulation to allow the required metered quantities

into the mixing chamber.

Notice that in this process relatively low pressures are used, andmixing is done in the high-speed (15 000 rpm) screw, compare this with the high-

pressure systems being developed for automobile parts, in which impingement

mixing is used.

The fundamental requirements for RIM equipment for this purpose may he listed as

follows :

a) The machine must accurately meter and dispense small shot sizes.

b) The components must be well mixed throughout the shot, lo minimize the

problem of variable performance in the finished product.

c) The temperature of the chemicals must be accurately controlled. PU foam

systems are sensitive to temperature variation and this foam systems are sensitive to

temperature variation and this requirement is therefore essential for consistent

products.

Molds

A number of procedures exist for the production of moulds, and

selection of the most appropriate will depend on cost and the number of mouldings

that will be required. Polyurethane forms foams at low pressures, so that it is often

practicable to use cheap cast moulds rather than expensive machined ones. Cast

moulds use an original model of the required moulded product/surface. This can be

made in various materials, e.g. wood. was. clay. The mould is then constructed by

applying the mould material to the model.

Molding Process

The machine tank. where accurate temperature control is applied, hold

I gallon of each stream component. One stream comprises the quasi-prepolymer i.e.

all the isocyanate reacted with part ofthe polyester. The other stream comprises the

other ingredient i.e. remainder of polyester (referred to as 'resin'). Surfactant cross

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linker, blowing agent (water). The machine tanks are supplied from holding tanks.

The prepolymer stream runs at 40C and the resin stream at 50C. These

temperatures are required to maintain appropriate viscosity for pumping and theyare also maintained in the holding tanks, which are stirred.

The circulating pumping rate is in the range 35-50 Cm3/sec.

The PU foam forming process is characterised by two stages, where

timing is important. These are 'cream time', which is the time taken for the Final

mixture of ingredients to become creamy in colour and consistency, as the

polymerization, cross linking and foaming begin to occur at an appreciable rate. The

induction time before creaming is observed is desirably short, because high

production rates are required. For PIJ shoe soles, cream times of 5-6 s are usual.

The second stage is the time required for full cure, and this is 2-3 min, giving a

remold time of perhaps 2 min.

COMPARISON AMONG RUBBER, PVC, EVA AND PU

BASED SHOE SOLES

Testing Rubber shoe

sole

PVC shoe sole EVA shoe sole PU shoe sole

Tensile

strength (Mpa)

2000 390-580 25 38

Percentage

elongation

1200 40 200-600 640

Tackiness Very small Optimum Large Optimum

Working temp.

(oC)

-40 to 100 150-190 100-180


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BIBLIOGRAPHY

PAGE NO.

1) Rubber Technology xxiii-xxv,

By : C.M. Blow 169,172,202,

218,231,243,

250,367, 451-462

2) Polymer Chemistry 212-214,264-289

By : B.K. Sharma

3) PVC Technology 10,11,228,229

By: A.S. Athalye

4) A Seminar Report On Polyurethane shoe sole 2,7-13, 17By : Sunil K. Goenka ( 1999-2000 )

5) www.google.com

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6) www.alstiva.com

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