Shoe Sole Manufacturing Tech

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 it’s associated with skillful labour. identity, shape, look to a shoe of particular kind.

It provides

Sole manufacturing is

comparatively less expansive as it’s 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

C.O.E.& T.,Akola

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Shoe Sole Manufacturing Tech.

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 time reduction 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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Shoe Sole Manufacturing Tech.

RUBBER AS A MATERIAL Rubber belongs to the class of substance termed as polymers high molecular weight compounds predominantly organic, consisting of long chain molecules made up of repeating units usually on a backbone of carbon atoms. These high molecular weight polymers have a lower temperature limit to their rubbery state. At the so-called glass transition temperature Tg there is a fairly abrupt change to a glassy state. Materials in the class of polymers, which are at normal temperature plastics, become rubber like as the temperature is raised above Tg. Types of Rubber Various types of rubbers used for sole manufacturing a) Natural Rubber

b) Synthetic Rubber

Natural Rubber i)

Ribbed smoke sheet

ii)

Pale crepe

Synthetic Rubber i)

Styrene Butadiene Rubber (S.B.R.)

ii)

Butadiene acrylonitrile

iii)

Poly chloroprene

iv)

Poly isoprene

v)

Poly butadiene Physical properties of Rubber a) Viscosity (stokes ) b) Ultimate tensile strength ( kg/cm2 ) c) Ultimate elongation Percentage d) Modulus Chemical Requirement of Rubber Specification

C.O.E.& T.,Akola

Max. 73 200 1200 96

Min. 14 160 800 25

Percentage by weight 3

Shoe Sole Manufacturing Tech.

1) Dirt content 2) Volatile matter 3) Total ash 4) Copper 5) Manganese 6) Nitrogen Rubber compounding

0.05 1.00 0.75 8.00 10.00 0.70

Compounding adapted to rubber with various additives to improve properties like mechanical, physical along with cost reduction. Additives used for rubber compounding Sr. Additives No. 1. Fillers 2.

Pigments

3.

Accelerator

4. 5.

Activator Antioxidant

6.

Plasticizer

7.

Blowing agent Stabilizer

8.

Type of material

Purpose

Carbon black, Activated silica, Activated magnesium carbonate, saw dust, calcium silicate Red ironoxide, Titan white, ultra marine blue, yellow iron oxide Mercapto benzthiazole, dibenzthiazyl disulphide Zinc oxide, stearic Acid Substituted phenyl group of pphenylene

Provides Reinforcements Reduction in cost Coloring

Dioctyl pthalate Di-Iso octyl pthalate Azo compounds foaming-N N-Nitroso compound White lead

9.

Vulcanizing Sulphur agent 10. Dusting Zinc stearate agent Sequence of additives used during compounding

Accelerates the vulcanization rate Activates the accelerator Provide moderate oxidant protection with min discoloration Aids the processing operation of mixing. Provides from like structure Prevents degration of rubber during processing Provides cross linking Avoids sticking of material.

Rubber + Peptizer ( Renasin ) Pigment +Tackifier (Rosin) Small chemicals C.O.E.& T.,Akola

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Shoe Sole Manufacturing Tech.

1) Accelerator ( Mercapto benzthiazole) 2) Activator ( Stearic Acid, Zinc oxide ) Fillers Processing 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 1) Tensile strength (kg/cm2) 2) Percentage elongation 3) Water absorption capacity 4) Tackiness 5) Working temp 6) Chemical Resistance 7) Elasticity

Raw Rubber 200 1200 Good More 10 – 600C Very poor Very much lower

8) Resistance to oxidation

Very much lower

Vulcanized Rubber 2000 800 Very good Very small - 40 to 1000C excellent much higher much higher

abrasion wear and tear Machinery Used for Rubber Compounding

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Shoe Sole Manufacturing Tech.

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 at slightly 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. Weight Cylinder

Feed Hopper Door

Floating weight

Cored rotors for circulation of cooling water or steam Drilled sides

Banbury Mixer 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 C.O.E.& T.,Akola

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Shoe Sole Manufacturing Tech.

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 formation of 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 Mixture To pressing section

Two Roll Mill

Cooling

Powder Spraying

Lab testing C.O.E.& T.,Akola

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Shoe Sole Manufacturing Tech.

Hardness in (Shore-A)

42 ± 2

Time (Dixon press)

8"

Temp

150 ± 20C

Shade

as per reference

Vertical Injection Molding of Rubber Injection molded rubber sole and heel units are produced on multipurpose molding machines. There machines are basically a rubber injector which consist of a reciprocating screw working within a pre-plasticising cylinder, the screw and cylinder being fitted with independent temperature regulators. The molding sections very depending upon the m/c design, but four, six and ten work station machines are commonly used, the mold station being carried on a rotary table. At the beginning of each cycle, the screw rotates and simultaneously moves to the back end of cylinder and the incurred compound in strip or pellet form is fed into the injection unit. The rotary action of the screw leaves hot plasticizes the compound in front of screw. The entire injection unit then advances to form a tight scal between the nozzle and the mold sprue. The screw acting as a ram moves forward without rotating forcing the compound through the nozzle into the closed mold. Pressure is maintained for several records after the mold is filled, to allow the compound to set up. The injection unit then reacts, the rotary table moves rent station prior to the injection paint opens, allowing the molded units to be removed from the mold cavity.

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Shoe Sole Manufacturing Tech.

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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Shoe Sole Manufacturing Tech.

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 and weather 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 180200 oC life can be measured in weeks. Physical Properties Tensile strength ( in M.Pa.) Percentage elongation Hardness ( Shore -A ) Compression set resistance over

25 200-600% 60-85 100-180

temp range ( in oC ) Compounding sequence 1) Polymer

2) Pigment

3) Chemical 4) Fillers 5) Blowing agent. E.V.A. Compounding Sr.No. Additives used 1 Fillers 2 3 4 5

Plasticizer Activator Blowing agent Pigments

C.O.E.& T.,Akola

Type of material Calcium Carbonate

Purpose Dimension stability and

Dioctylpthalate

cost reduction. Aids the process operation

Stearic acid, Zinc oxide

of mixing Activates the processing

Fomacin

rate. Micro Provides foam like

Carbon black

structure Coloring 10

Shoe Sole Manufacturing Tech.

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.

Kneaders C.O.E.& T.,Akola

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Shoe Sole Manufacturing Tech.

Calendaring Device

Two Roll Mill

Flow sheet of EVA. sheet manufacturing Fresh Batch Cutting Weighted

kneader

1st Two roll mill

calendaring

2nd two roll mill

Process description of EVA. Sheet manufacturing. A fresh batch of calcium carbonate and EVA. is prepared and being fed to a kneader it’s kept inside the kneader for 15 mins. The shearing action of blades enable the product formation. The product obtained from kneaders is fed to C.O.E.& T.,Akola

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Shoe Sole Manufacturing Tech.

the 1st two roll mill. The first two-roll mill is without cooling system, as this machine has to only preheat the material. Then the product is sent to the second two roll mill have the compound is refined and this sheeted. The output from the 2nd two roll mill is sent to the calendaring device for obtaining continuous stream of sheet of desire thickness. The sheets are being cut into smaller pieces send, then weighted and stored.

PRESSING SECTION This section deals with production of solid roles and insoles.

The

feed material required by this section is obtained from compounding section. Criteria of a compound to be sole Hardness of compound should be 50-60.

It should possess good

abrasion resistance. It should possess good tearing resistance. Machineries used : Manual and automatic compression molding machines 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

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Shoe Sole Manufacturing Tech.

pairs of role (rubber) in each cycle. Each cycle is completed in 10 mins. Temp maintained 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 5 0C. 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 ¾ 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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Shoe Sole Manufacturing Tech.

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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Shoe Sole Manufacturing Tech.

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 (oC)

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.  200  1.5 log Z − 1 + 1 +  + 1 + 0.5 log Z 1.5 log Z  C  k= 150 + 3C

Z  relative viscosity C  concentration in grams/100 ml Z

t − t0 t0 x C

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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Shoe Sole Manufacturing Tech.

1. Polymer 2. Stabilizers 3. Plasticizers 4. Extenders 5. Lubricants 6. Fillers 7. Pigments 8. Polymeric processing agents 9. Impact Modifier

Compounding of PVC Name Stabilizer Plasticiser

C.O.E.& T.,Akola

Type of material Lead base, Beryllium cadmium Di-octylpthalate Di-iso octyle pthalate

Purpose Prevent degradation Aids the processing

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Shoe Sole Manufacturing Tech.

Lubricants

Metallic stearates, stearic acid, oleic acid

Operation of mixing aids easier procesibility and

Filler

Forcal, clay, talc dolomite

effects the M.F.I. Provides hardness, Dimension stability

Pigment Special agents Blowing agent Fire resistance Ultra-violet

Red ion oxide, carbon black

& cost reduction. coloring agents

Azo-die compound

Provides foam like

Antimony trioxide

structure Resistance to fire

Ranypol, Thinpol

Enhances. resistance to u.v

stabilizer

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 C.O.E.& T.,Akola

1.3 mins 18

Shoe Sole Manufacturing Tech.

Compression

135oC

Melting

135.5 oC

Mold pressure

135.5 oC

Air 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 C.O.E.& T.,Akola

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Shoe Sole Manufacturing Tech.

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 of material 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.

Hooper

Heater

Mold

Carriage FT: feed zone temp

C.O.E.& T.,Akola

CT: Compression Zone temp

Chiller

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Shoe Sole Manufacturing Tech.

Preheater MT: Metering zone temp MP: Mold pressure IP: Injection pressure BP: Back pressure

Injection Molding Machine for Solid Sole Manufacturing General Injection cycle of Air blown Injection 1st Pressure Injection 2nd pressure Prepare mold down Prepare screw turn Feed zone temperature Compression zone temperature Metering zone temperature Nozzle temperature

4.2 seconds 15 seconds 4.2 seconds 12 seconds 1650 C 1800 C 1850 C 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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Shoe Sole Manufacturing Tech.

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. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14.

C.O.E.& T.,Akola

Hopper Preheater Screw Heaters Nozzle Gate Workstation Workstation bar Piping for cooling Chiller

1. 2. 3. 4. 15. 16. 17. 18. 19. 20. 21.

Hydraulic operated air supplier Air pressure indicator Pump Work station number indicator Weight of material fed Feed zone temperature Compression zone temperature Metering zone temperature Nozzle temperature Pressure indicator Timers

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Shoe Sole Manufacturing Tech.

Injection Molding Machine for Airblown Sole Manufacturing Lab Testing Surface blisters Flow marks Short shots Shrinkage Weld lines Internal voids.

POLYURETHANE AS A MATERIAL The particular polymer is fiber forming material although in many respect in many resembles the formation of polyesters and polyamides, it is not a condensation reaction but involves a transfer of a hydrogen atom and thus may be considered as an example of rearrangement polymerization. Several polymer currently used containing many linkages in addition to the urethane group. Because of this term polyurethane is now generally extended to cover all the complex reaction product of isocynates and polyols compounds.

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Shoe Sole Manufacturing Tech.

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 in production of useful product by using polymeric hydroxyl containing compounds such as polyesters to give rubber, foam, coating and adhesives. Physical Properties Tensile strength Percentage elongation

38 MPa 640

Resilience Hardness (B.S.) Tearing resistance Abrasion resistance

56 86 7.2 15/cm3

Polyurethane compounding Sr.

Additives

Types of materials

Purpose

No. 1

Catalyst

Silicon , tertiary amines,

To speed up the reaction

Cross linking ,

organo-metallic compounds Polyols, polyamines

To give polymer cross

2

3

chain extending

linking, to introduce

agents

special polymer

Blowing agent

Water reacts with isocynates

segments To produce foamed structure

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Shoe Sole Manufacturing Tech.

4 5

6 7

Colorants

Various pigments, carbon

To identify different

Fillers

black Particulate, inorganic

foam grades To modify properties

material

( stiffness and fibre

Flame retardant

Phosphorus and halogen

properties ) To reduce flammability

Smoke

containing molecules Particulate organic or

To reduce the amount

suppressant

organic material,

and slow down the rate

polycarboxylates hydrates

of smoke production

oxides, borates

The RIM process The reaction injection molding process is that in which the ingredient are 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 C.O.E.& T.,Akola

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Shoe Sole Manufacturing Tech.

One shot system Polyols Cross linking agent Catalyst Blowing agent Isocynates

Prepolymer system Polyhydroxyl -Silicones Isocynates Cross linking agent

Quasi prepolymer system Part polyhydroxyl compound -Silicones Blowing 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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Shoe Sole Manufacturing Tech.

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, and mixing is done in the high-speed (15 000 rpm) screw, compare this with the highpressure 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 C.O.E.& T.,Akola

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Shoe Sole Manufacturing Tech.

linker, blowing agent (water). The machine tanks are supplied from holding tanks. The prepolymer stream runs at 40°C and the resin stream at 50°C. These temperatures are required to maintain appropriate viscosity for pumping and they are 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

Tensile

sole 2000

shoe PVC shoe sole

EVA shoe sole

PU shoe sole

390-580

25

38

strength (Mpa) Percentage 1200

40

200-600

640

elongation Tackiness Very small Working temp. -40 to 100

Optimum 150-190

Large 100-180

Optimum <200

(oC) Resistance

Good

Good

Good

Optimum 78 Outstanding

Optimum 60-85 Good

less 86 Good

to Excellent

wear and tear Abrasion Hardness Dimensional C.O.E.& T.,Akola

Much higher 66 Least

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Shoe Sole Manufacturing Tech.

stability Cost

of Least

Less

More

more

production

CONCLUSION Yet after seeing the advantages and disadvantages of PVC, Rubber, EVA and PU base sole, we can conclude that if one wants shoe at cheaper price irrespective of the quality and dimension stability then rubber base sole are the right choice. If one wants shoe at relatively cheaper price along with dimension stability he should go for PVC based shoe. If one wants lightness, show and quality he should go for PU or EVA shoe sole. No doubt these two shoe soles are comparatively expensive than the Rubber and PVC based sole but they justify their corresponding price by providing suitable, outstanding properties. So above all this ultimate decision will be taken by the customer, who is going to purchase this sole base footwear.

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BIBLIOGRAPHY PAGE NO. 1) Rubber Technology By : C.M. Blow

xxiii-xxv, 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, 17

By : Sunil K. Goenka ( 1999-2000 ) 5) www.google.com

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Shoe Sole Manufacturing Tech.

6) www.alstiva.com

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