The Manufacturing Of Rubber Products Biology Essay

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Mixing equipment, calenders and extruders are the basic processing machines used in rubber production. Open roll or internal mixers break down the elastomers and incorporate selected ingredients.

Calenders are used for sheeting and combining with fabrics. Extruders shape rubber compounds for assembly with other components as in tire building, or in final form for curing in steam, dry heat, or by immersion in molten metal other heat transfer media.

Molded goods production may be by compression, transfer or injection techniques depending on equipment available in the press room. Specially designed presses, building and handling equipment are used in tire and mechanical goods with emphasis on automation in most modernplants.

A compounder should know handling methods, temperatures encountered and sequence of operations prevailing in his own plant. This is essential as a guide in developing practical trouble-free rubber stocks.

Breakdown

The overall objective in breaking down elastomers before compounding is to soften them and reduce nerve to a point where other ingredients may be added without difficulty. Natural rubber and copolymer elastomers respond somewhat differently during this processing step, but the general procedure and the equipment used is similar with both materials.

Rubber

In working with natural rubbers, it is considered good practice to blend different lots to assure uniform curing characteristics and physical properties in the resulting compounds. If an open roll mill is used, any one of three procedures may be followed to plasticize and soften the rubber: (a) a straight one-period breakdown, (b) two or more successive periods, or (c) a tight roll grinding operation in which the rubber is passed through a number of times without banding on the roll.

Internal mixers of the Banbury type are perhaps the most widely used for breaking down rubber in the modern factory. Current practice is to load them to the full capacity of the machine and operate on a short time cycle at an elevated temperature of 300 F, or higher. Rubber broken down in a Banbury is usually dropped on a sheeting mill and taken off in the form of "pigs" for storage until further use. In some of the larger factories, the Gordon Plasticator, a machine designed on the principle of a huge extended screw tuber is used to break down rubbers.

The difference between the operating speeds of front and back mill rolls, referred to as the "friction-ratio", will influence the degree of breakdown. This also holds true for rotors in internal mixers. The clearances, condition of the rotor surfaces as well as the ram shape and pressure al so influence the breakdown. Some internal mixers are designed to operate at several speeds, and the high speed is commonly used for breakdown purposes.

With both natural rubber and SBR, the breakdown cycles can be shortened and more satisfactorily performed by the use of chemical plasticizers.

Master-batching

Certain resinous or granular compounding materials such is the high styrene copolymers, high melting coumarone­ndene resins, shellac, glue, etc, may be conveniently master-batched and added in the desired proportions to the certain compound. Carbon blacks are frequently master-batched in certain operating shifts or in isolated areas to aid in cleanliness of the plant and to avoid contamination of stocks.

With SBR, it is possible to obtain black master-batches in which certain channel and furnace blacks are incorporated in slurry form prior to polymerization.

Organic accelerators, sulfur or other materials that are used in small quantities and must be completely dispersed in the final compound are also conveniently handled in master-batch form.

The Weighing Room

The weighing room or area continues to be an extremely important part of the well organized rubber factory. Cleanliness and accuracy are the main points for consideration so far as this step in compound building is concerned. Current practices may vary widely. Automatic or semi-automatic systems are used in some plants. Where such equipment is not available the weighing operations should be assigned to individuals who have been thoroughly impressed with the importance of the operations they perform.

Bulk ingredients are passed on to the mixing area in their original bags or "tote-boxes", oils or liquids in containers calibrated to assure transfer of the required amount into the batch without undue manipulation on the operator's part; and accelerators, antioxidants and other small quantity components in paper bags or other suitable containers.

Mixing

Mixing is the operation required to obtain a thorough and uniform dispersion in the rubber of ingredients called for by the formula. Whether done on the open-roll mill or in an internal mixer, a definite time, temperature and order-of-addition schedule should be followed for each batch. If poor dispersion is encountered, the cause of trouble should immediately be established and corrected. Faulty compounding materials, too short a mixing cycle, wrong order of addition, improper temperature control, or wrong batch size might be cited as factors to be investigated if troubles are noted.

The Scorch Problem

Compounds in process beyond the stage where part or all of the curing ingredients have been incorporated may suddenly, or gradually in some cases, become tough and unworkable. This phenomenon described as scorching, burning or precuring may be attributed to (1) faulty compound design (2) excessive processing temperature (3) Improper or insufficient cooling before storage between processing stages, or (4) faulty processing equipment.

Calendering

The rubber calender, originally consisting of three steel rolls but now available in a number of types and designs for specialized application, is essentially a device for forming rubber sheeting of various lengths and thicknesses which are used in subsequent building operations. It is also used extensively for fractioning or skim coating fabrics. Temperature control of calendar rolls is accomplished by the use of circulating water or steam. Gears are provided to permit operating the rolls at even or uneven speeds as the application requires.

Compounds to be run into liners as sheeting, or skim coated on fabrics should be designed with a full understanding of their processing requirements and the difficulties that may be encountered. They must be (a) free from excessive shrinkage, (b) not subject to becoming sticky at calendering temperatures, (c) possess sufficient tack for subsequent building operations or adhesion to the fabrics, and (d) scorch free. In running these compounds, one or more warm-up mills must be available to keep the feed stock uniform and plastic so that a uniform bank is maintained on the calender. Defects in the sheet or skim such as "crows feet" can be eliminated by temperature control, and blistering is generally eliminated by the use of "pricker" bars attached to the calender.

If smooth sheets thicker than can be run on the calender are desired, they may be built up by running the required number of plies on the bottom roll of the calender, or by the use of a doubling drum. Long lengths of sheet, thicker than can be smoothly run in a single pass, can be obtained by building up to the desired thickness in successive passes through the calender.

Compounds for frictioning must be tacky to conform to the processing requirements of sticking to or "running on" the center roll. Good tack is also required in the compounds for such applications as the building of a number of plies in belts, tires, footwear and other products. Proper temperature control contributes much to successful operation. Tack in the friction compound may be obtained by extra milling, by the use of resinous softeners such as pine tar or rosins, or by the use of mineral fillers recommended for this purpose. The problem of imparting sufficient tack to the compound is more difficult with SBR than it is with natural rubber. Calender roll pictures are given in the figure.

Extruding

The operation of extruding is widely used in the rubber industry both as an intermediate processing stage and in terming many articles for vulcanization directly after the process is completed. It is advisable that the compounder acquaint himself with the operating features of the tubers with which he is directly concerned, making note of the driving mechanism, the barrel diameter, length, and temperature control; the screws and their characteristics (single or double cut, depth and condition, etc.) the type of head and mechanical devices for holding and centering the cores and dies. Successful operation is a combination of the machine itself and the compounds that are used, and both play an important role.

Preparation for Vulcanization

Rubber stocks about to be assembled for vulcanization may be in a number of forms such as calendered strips or sheets, plied up slabs, extruded tubes and other cross sections, or partially combined with fabrics by the frictioning or skimming operations already performed. Tyres, tubes, hose, belts, footwear, rolls and many other articles are built to approximately finished forms before vulcanization. The various stocks that are combined to form such articles must be dimensionally stable, free from bloom, and possess the required building tack all of which depend upon proper compounding and processing.

The building tack in SBR and some heavily loaded rubber compounds can be improved to some extent by the use of pine tar, rosin esters and various coal tar or petroleum derivatives.

Curing Methods and Problems

Most natural and synthetic rubber articles require the application of heat to convert them to their finished form. This operation is broadly described as vulcanization or curing and may be done by a number of methods, depending on the compounds in process, the size, shape and overall structure of the finished article.

Press Curing

This includes the molding of articles by compression, transfer, or injection methods. Blocked-in articles which are cured directly between the press platens also come under this classification, as well as unblocked slabs. The heat source is generally saturated steam although other heat transfer media have been investigated in recent years. Electrically heated platens are also used in some installations. Radio frequency waves have been suggested as a means of curing or for preheating blanks to reduce the press time under other curing conditions.

Properties of Compounds

Compounds for press curing must be carefully designed to flow properly without scorching before the desired shape is reached, and to cure rapidly so that a maximum turnover is obtained with the equipment in use. They must be easily removable from the molds after cure and exhibit attractive appearing surfaces in the finished form. In addition to the handling requirement, these as well as all other compounds must possess the physical and aging properties required in the finished article.

The flow characteristics depend on the plasticity of the uncured stock as well as selection of the proper acceleration to permit complete filling of the cavity before the cure begins.

Porosity

Failure to obtain a dense finished structure may be caused by under curing or by insufficient external pressure during the initial stages of cure. The thickest part in the section of the molded article is the place to look for porosity and the curing cycle must be set up accordingly. If troubles are encountered, they can usually be corrected by use of a more suitable acceleration. Sudden development of porosity in stocks that have been running trouble free may be caused by moisture in the fillers or improper dispersion of the sulfur or accelerators in the compound. Improper mold design or the use of insufficient or improperly shaped stock to fill the mold cavity may also contribute to porosity.

Trapped Air

This common fault in some press cured article may be due to improper mold design, the use of too soft a compound, or unsuitable blanks for molding. In general the uncured stock should be shaped as near as possible to the form of the finished article before being placed in the mold. Injection or transfer molding operations used where applicable minimize defects of this type.

Removal from Mold

All molded articles must be easily removable after curing. Proper compound design and efficient mold lubrication can contribute much in this respect. In articles such as water bottles where the hot freshly cured part must be stretched in removal, low sulfur or sulfur- less compounds are found to possess the necessary mechanical strength at elevated temperatures to permit removal without tearing. In some cases where trouble is encountered, the addition of a plasticizer such as Reogen or Plastogen to the stock may serve as a suitable corrective measure.

Open Steam Curing

Open steam curing is used in the production of hose, wire and cable, and other extruded article such as tubing or channel stripping. With this method the article may be in direct contact with the steam, wrapped with fabric tape, encased in an extruded covering of lead, or supported by soapstone in a shielded pan. Equipment may consist of the standard autoclave, preferably with a heated jacket to cut down condensation and a closed chamber in which the articles are placed and the steam is introduced.

Another method of open steam curing is used in the production of insulated wire and cable. This method, known as the C.V. (continuous vulcanization) process utilizes jacketed tubes which may be 200 feet in length and operate under internal steam pressures upward of 200 psi as compared to the 30-80 pound operating range of the conventional steam vulcanizer.

In operating a closed chamber steam vulcanizer, the curing cycle consists of a rise to the predetermined pressure, a definite period at the required curing pressure, and a blowdown to atmospheric pressure. Too slow a rise or pressure fluctuations as curing conditions are reached may cause porosity. With some soft stocks the blowdown must also be carefully controlled.

Dry Heat Curing

Articles such as coated fabrics and footwear may be cured in heated dry air. Coated fabrics are generally festooned in heaters and cured at atmospheric pressure, although by the use of Butyl Eight acceleration, curing in the original roll as it comes from the calender can be accomplished at room or slightly elevated temperatures. Footwear heaters are generally operated at 30 pounds internal air pressure, and ammonia gas is sometimes used to produce a glossy surface on the finished article.

FOOTWEAR

INTRODUCTION

There are three general types of rubber footwear manufactured today:

Fabric top footwear, including athletic and casual shoes.

Waterproof, the designation applied to light rubber footwear for ordinary everyday use.

Heavy, used in industrial applications.

The above may be further classified into two groups hand made and machine made, otherwise known as direct vulcanized footwear.

Fabric tops are not limited to cotton ducks, black, white or brown. Today, patterns and colors of all descriptions in many of the new synthetic fibers are now utilized. Sneakers and casuals have gained widespread use in the replacing of leather shoes not only for summer wear, but for all seasons. The selection of last shapes and widths that are offered are similar to those of leather footwear. Orthopedic features such as rigid supporting counters, steel shanks, and arch supports, combined with lightness in weight and washability make them even more practical than leather for many uses, particularly in the field of women's footwear where this type offers better protection than the thin soled, low slung ballet type shoes.

In the waterproof and protective footwear field we have a similar diversification. The development of new polyesters and chemicals has enabled the industry to engineer their products for recreation, business wear and everyday living. The synthetics have produced footwear resistant to solvents, static cracking, heat and light. A full rainbow of colors are produced to meet the consumer requirements for style and utility.

One of the most recent developments in the footwear industry is the automatic rotary table rubber injection molding machine. This process is a combination of injection and compression molding.

At the beginning of each cycle, the whole injection unit moves forward axially, forcing the preheated compound through the nozzle. Simultaneously, the injection unit retracts so that a layer of compound is distributed over the length of the lasted shoe. The volume of compound

distributed in each part of the mold cavity is controlled by varying the speed of retraction. When the injection unit is sufficiently retracted, the sole mold is closed, and the clamp pressure is applied. The reciprocating screw then moves backward, masticating the amount of compound required for the next cycle, and the rotary table moves the next station in front of the injection unit. The cycle is from 2 to 5 minutes depending on the curing temperature. Although this machine was developed for PVC, it is being used with a variety of elastomeric compounds. The upper materials used include fabric, leather and plastic.

Compounding Requirements

The best polymer for handmade footwear is still Hevea rubber because of its excellent green tack and thermoplastic quality. These properties are most important since the lamination of parts is largely affected with hand rolling and a little plastic flow is needed to seal these joints to make them waterproof.

Since most of the parts of rubber footwear are not molded, the surface of the stock as it is calendered must be free from all defects and must be compounded so as to retain calender embossing in the operations that follow. Proper polymer combinations and filler selection, along with the correct balance of new gum to scrap will maintain this finish.

High styrene and other high melting point resins, organic colors, flock and some accelerators are often master batched in order to improve their dispersion when added to the final mix.

A proper balance maintained between the cure rate of the various parts of the shoe, particularly in heavy goods where there is a great variation in thickness between upper and outsole. "Started" soles will result if this rate

is not proper.

The acceleration system must permit cures at relatively low temperature and yet not cause scorching at processing or storage temperature. Thiazole type accelerators land themselves to footwear compounding since they yield safe cures with good plateau, Guanadines are effective secondary accelerators.

Processing

The manufacturing of rubber footwear involves the use of the same basic mill room equipment as in other rubber industries. Beyond this process however, there Is a multitude of operations such as fabric and rubber cutting, stitching, pre-cementing and fitting of various upper insole and outsole components. All of these parts in the various shoe sizes (a range generally from a child's 2 to men's 16) must arrive to the making conveyor in proper sequence for the final assembly.

Upper compounds are generally warmed up on feed mills along with cutting scrap. The ratio of new gum to scrap is determined by the plasticity requirements of the stock. Certain parts, such as unlined uppers can tolerate very little scrap, lest "sagging" take place during vulcanization. Soling stocks are warmed up on mills or in a Banbury along with cutting room scrap. All stocks are water cooled when calendered in order to obtain maximum shrinkage before the cutting operation. If shrinkage takes place after the cutting operation, distortion would result. In order to retain both surface clarity and tack, calendered upper stocks are run into hammocks, beaded reels and spools. Smaller parts such as toe caps, heel pieces and gum stays are cut using a toggle press cutting method. These parts are then laminated to fiber carrying boards or are booked. Soling is calendered and cut into three or four foot lengths and stored on cleated plywood or fiber boards in order to allow it to shrink completely before cutting. Larger gum parts such as boot legs are cut by hand with a hot knife at the time the rubberized lining fabric is laminated to it on a flat conveyor. Heavy parts such as outsoles are generally cut with a Wellman cutting machine.

This machine cuts a beveled edge so that the sole will lay at proper angle with the upper of the shoe with a minimum of strain at the edge. The soles are stored in special fabric leaved books to prevent distortion and pressing. All of these engraved gum parts are generally calendered on a (19"-30") four roll inverted L type calender in which the offset top engraved roll is removable to allow design changes. Foxings, bindings and other strips are cut into proper width at the calender using either a "self-cut" engraving roll or conventional wheel knives properly spaced, and are boarded or booked. Colored stripes are generally laminated to foxings at this point also. A 60" four roll lining calender is generally used to rubberize sheetings, ducks, net and fleece linings, friction coat fabrics, and also to sheet rag stock. Rag is a mixture of downgraded rubber stocks that are recompounded along with reclaim refined rubberized fabric scrap and whiting. This stock is stiff and is used for counters and insole parts.

Fabrics

Some of the basic fabrics used in footwear include, array, enameling, hose, boot and number ducks, osnaburgs, drills and twills, sheetings, nets and fleeces.

Additionally in the fabric shoes, we use various prints, corduroys, suedes, and hopsacking materials cotton, rayons, woolens, nylon, Dacron, sisal, hemp and many blends.

It is very important that these materials be free frcm copper and manganese and also that they have optimum amounts of sizing where required. Insufficient sizing in the backing fabrics will cause limpness and wrinkling when combined to the face fabric. An excess will cause lasting wrinkles in the making operation. An excess starch in the face fabric will also adversely affect the adhesion to the rubber foxing,etc.

The tennis upper fabrics are "combined" using SBR adhesive applied with a roller or doctor blade and subsequently laminated dry through a can dryer. Most uppers are two-ply although three-ply is also used to some extent in the direct molded tennis shoe. The amount and type of deposit will determine the hand of the upper. There must be a balance between adhesion and "breathability."

The face fabrics must be checked for wettability, crock resistance bleeding, washablity and adhesion. Some of these deficiencies can be compensated for by modification of foxing latex. Others like bleeding crocking and shrinkage can be remedied only by the fabric finisher Color stability in vulcanizing must be predetermined. Certain fabrics and braids cannot be vulcanized in an ammonia cure. Others may require lower than normal temperature.

Unlike waterproof uppers, tennis fabrics are plied up on a cutting table, generally 24 plies, 12 face down, 12 face up. These are cut with double arm clicker die presses so that each cut will produce 12 pair cuts. The cutting scrap is ground into flock for use as a stiffener in rag compounds.

Cements and Latices

Most rubber parts in both waterproof and term footwear are cemented at the calendaring operation with rubber cement. This cement is usually sheet rubber compounded with tackifiers and curatives, and dissolved rubber solvent. Tennis tops are machine cemented lasting. Lasted tennis shoes are dipped into compounded rubber latex to form a base on which to adhere the parts. Colo pigments, curatives, tackifiers and agents are used to obtain good adhesion and appearance.

Vulcanizing

Shoes arriving at the end of the making line are loaded onto monorai vulcanizer cars which are rolled into place after final inspection of the cure cycle.

Cure cycles will vary from 45 minutes to 1.5 hours depending on the type of footwear and the efficiency of the vulcanizer. In all cases 20 to 30 lbs. of compressed air is introduced to prevent blister formation from air entrapped between parts and also within heavy rubber part blowers circulate the air to minimize cold spots.

On heavy items like boots, a vacuum cure is run where air pressure is reduced inside the boot in order to compress parts and minimize the occurrence of pin holes at the seams.

If ammonia is to be used, three to five pounds of anhydrous ammonia is injected after the air has been introduced. Curing temperatures used vary from 260F to 300F. Ammonia cure produces a glossy tack free surface.

The advantage of "air" cures is that less pigmentation is required particularly for white compounds, as the ammonia has a yellowin effect. Shoes cured in this manner are slightly tacky to the touch. Multicolor braids and fabrics are often cured in air to retain brightness particularly if one or more of the colors react adversely with the ammonia.

FOOTWEAR COMPOUNDS

Synthetic Upper

Upper Compound

Natsyn

80

Air Dried sheets

80

Solprene 1205

20

SBR 1009

20

Hard Clay

60

Whiting

60

Whiting

60

Hard Clay

60

Light Process Oil

13

Pepton 22

0.25

Velsicol X-30

6

Process Oil

15

Zinc Oxide

5

Velsicol X-30

5

Stearic Acid

0.6

Zinc Oxide

5

Anthicheck Wax

0.15

Stearic Acid

0.5

AGERITE SUPERLITE

0.25

Anthicheck Wax

0.16

DOTG

0.5

AGERITE SUPERLITE

0.25

ALTAX

0.9

DOTG

0.5

Sulfur

2.15

ALTAX

1

 

 

ALTAX Sulfur

2.25

Total

248.55

Total

249.91

Sp.gr

1.43

Sp.gr

1.43

Top Grade Calender Sole

Calendered Sole

Brown Crepe

90

Brown Crepe

65

SBR 1009

10

High Styrene MasterbatcM 50%)

25

Hard Clay

85

SBR 1009

20

Pepton 22

0.1

Hard Clay

85

Process Oil

5.5

Whiting

80

Velsicol X-30

3.25

Process Oil

15

Zinc Oxide

5

Velsicol X-30

10

Stearic Acid

1.25

Zinc Oxide

5

Retarder

0.15

Stearic Acid

0.5

AGERITE SUPERLITE

0.3

AGERITE SUPERFLEX

0.25

DOTG

0.6

UN ADS

0.1

ALTAX

0.6

DOTG

0.75

Sulfur

2.95

ALTAX

1

 

 

Sulfur

2.7

Total

204.70

Total

310.3

Sp.Gr

1.35

Sp.Gr

1.46

Top Grade Molded Sole

Brown Crepe

70

SBR 1703

25

Solprene 1205

10

Hard Clay

80

Silene EF

25

Press Scrap (Ground)

30

Pepton 22

0.15

Process Oil

16

Velsicol X-30

10

Zinc Oxide

5

Stearic Acid

0. 75

Anticheck Wax

0.3

AGERITE SUPERLITE

0.3

DOTG

0.88

ALTAX

1.40

Sulfur

3.0

Soles and Heels

The last decade has witnessed revolutionary technical changes in the shoe industry. A result of this has been a gradual but persistent decrease in the production of old style conventional sole and heels.

Sole and heel producers, however, have not lost position as a result of this. Annual tonnage of their products has increased substantially due to the ingenuity of chemists and engineers in developing new materials and processes.

Today non-leather soles account for well over 70 per cent of shoe bottoms, as compared to 60 percent a decade ago. This increasingly high level of acceptance has been reached not only through demonstrated better service and comfort, but also through improved finished product appeal, a factor so essential according to current merchandising standards.

This steadily increasing acceptance of other than leather shoe bottoms indicates clearly how well the sole and heel industry has met challenge of these basic technological changes. The most important of these that need some elaboration are as follows:

Direct Molded Footwear

Unisoles - Nuclear and Polyvinyl Chloride

Printed Soling Sheets

Micro-Cellular Soling-Cushion-type and Firm (Leather­like)

A. Direct Molded Footwear (DMF)

This process involves the molding of rubber soles and heels directly to the shoe upper. Conceived in the early 1900's in Germany direct molded or vulcanized footwear did not reach actual production proportions until the depression of the 30s in Europe - in the United States in the mid '50's.

DMF production continues to show annual increases, in women's casuals, tennis, basketball shoes and sneakers. Also to some degree this process has been adopted by the U.S. Army.

Efficient, economical operation of expensive DMF equipment demands much faster curing cycles than conventional soles and heel. In addition to providing cycles of two minutes at 300 F. DMF compounds must be fast and free-flowing, without any incipient scorch which would preclude a strong permanent bond to the shoe upper.

Fast cures are obtained by a judicious combination of ALTAX and METHYL or ETHYL 21 MATE, or AMAX, CAPTAX and UNADS. Free flowing compounds require liberal amounts of oils and plastizers, such as light process oil, REOGEN and PLASTOGEN.

B. Unisoles

This is the term given to integrally-molded sole and heel combinations made in exact sizes and widths, once this unit is cemented to the shoe upper, it is ready for the shoe box, which eliminates many labour steps of finishing, heel attaching, inking, etc., for the shoe manufacturer.

Since these soles have to have the same "heft" or gauge on the edge as the sole, plus welting, of a stitched shoe they also result in a longer waring bottom. This means a higher quality shoe at lower cost, a tough combination to beat.

Unisoles, produced out of both rubber-resin compounds and polyvinyl chloride have been highly successful in juvenile shoes, and in men's shoes to a lesser degree.

Unisoles have become a highly significant, permanent fixture in the shoe industry, replacing a large amount of conventional soles and heels.

C. Printed Soling Sheets

Over the years, with steadily increasing labor costs in the sole and heel industry, there has been a trend to soling sheets rather than individually molded soles, in the thinner guages.

Since women's shoes constitute over 50% of shoe production and since soles for women's shoes are thin-gauge, this has meant a steadily increasing production of soling sheets .

Within the past few years, soling sheets, printed to give the appearance of a high-grade leather sole, have been imported from Germany. Acceptance by shoe manufacturers was immediate and sole and heel manufacturers procured equipment to duplicate these types of finishes.

The soling sheets are first printed pith rotogravur

rolls engraved to give a leather like pattern. In a continuous process, the sheet is then covered with a clear film of topcoat which can be formulated to give various levels of gloss. The topcoat is usually urethane or epoxy resin, which, when cured, makes the prints impervious to cleaning solvents used in the shoe factory.

This pre-finishing of soling sheets results in substantial savings to the shoe manufacturer, since the extra cost to hire for the pre-finished soling sheet is considerably less than his own cost of finishing the bottoms. The shoe manufacturer also ends up with a uniform, more pleasing appearance on his shoe bottoms.

D. Micro-Cellular Soling, Soft (Cushion-Like) and Firm (Leather-like)

Soft Cushion-Like

This type soling was first produced in the early '50's and gained immediate acceptance. Used in heavier gauges, this Micro-Cellular Soling gave a soft, cushiony, resilient walk to shoes of all types.

It was first predicted to be a more or less cyclical product but instead has become a permanent fixture it styling of shoes. It is estimated that 15% of all manufactured today carry these soft Micro-Cellular Soles.

Initially, this type soling was made only in sheet form but recently it has been produced in the heavier gauges in integrally molded sole and heel combinations which have become very popular on men's hunting and work boots.

This integrally molded shank effect results in a perfectly flat bottom usually with a rib design.

These soles are initally cured in design molds followed by oven treatment to eliminate residual shrinkage . Soles are then die-cut to a standard size.

Firm (Leather-Like) Micro-Cellular Soling

This type of soling has been a recent development in soling sheet and has been hastened by the desire of the shoe manufacturer for lighter weight in his shoe bottom.

Whereas the soft, cushion type is expanded to specific gravity of less than .70, the firm type is only partially expanded to a specific gravity range of 0.9 to 1.10.

There has been considerable usage of this firm cellular soling to date ,and it is predicted that it will continue to grow.

Heel formulas

 

Hi-Grade Tan

Standard N M Black

SBR 1507

50

55

Budene

50

---

SBR 1778

---

40

WH Tire Reclaim

---

17

Black MB 1805

---

11

Zinc Oxide

4

3

Zeo 45

68

---

Zeolex 23

---

85

DIXIE CLAY

---

40

Mapico Red

3

---

HAF Black

.50

---

Stearic Acid

2

1

Resinex 100

---

10

REOGEN

3

3

Panarez 6-210

15

---

Carbowax

2

---

AGERITE RESIN D

1

1

Light Process Oil

12

10

ALTAX

2

1.75

DOTG

1.50

1

Sulfur

2.50

2.50

Total

216.50

281.25

Sp.Gr

1.19

1.35

PNEUMATIC TYRES

Manufacturing

A pneumatic tyre structure can be broken down into the following basic parts.

Beads

The bead is a combination of multi-strand high tensile

steel wire, rubber insulation, fabric, wrapping, and flipper

strips - these forming the ring shaped unit that is

installed as the "bead" in tyre building. A suitable term

for this portion of the tyre, including this bead and the

surrounding rubber and fabric, would be "beaded edge". The

job of this beaded edge in a modern tyre is to hold

the casing on the rim by preventing the "beaded edges" from

stretching. Without the wire, the pressure of the air inside

the tyre would cause the edges of the casing to stretch until they slipped over the rim flanges. Obviously such a tyre would be worthless. The bead provides a fairly rigid, practically inextensible foundation supporting the tyre load, in turn, transferring this load to the flange edges of the rim. Compounds used in bead construction are:

Bead Insulation :

Its function is to adhere to the wire, give the finished bead the desired degree of rigidity and flexibility, and to insulate one steel strand from another.

Bead Cover and Wrap :

The compound used on the bead cover or wrap must have sufficient tack to insure good adhesion during assembly and cure, good flexibility after cure, and high heat resistance.

Bead Filler :

In passenger tyres the bundle of wires is small and there is sufficient stock and stock flow during cure that it is not necessary to use a bead filler. In truck tyres, and tyres with extremely large beads it is necessary to provide stock in addition to that insulating the wires and on a bead cover and wrap, to obtain a proper contour. This is usually a wedge shaped extrusion which is placed on top of the bead bundle before wrapping and should be a high quality flexible heat resistant stock.

Body : The body of a pneumatic tyre contains the following components :

Plies :

The plies form the skeletal component from which the tyre obtains its strength. This may be cotton, rayon, nylon, polyester, glass fiber, wire or any other material, which in the form of a strand or woven into a cord, has extremely high tensile strength and flexibility, and can be treated with an adhesive system to bond it tightly to a rubber compound. The fabric from which the individual ply is cut is a rubberized sheet of cords of selected dimension and number per inch. The rubberizing operation consists of impregnating or coating by immersion in a solution or emulsion of an adhesive, drying, and then by calendering applying an enveloping coat of compounded rubber. Since rayon and nylon are the two materials used in most volume at present, the compounds we talk about will be designed primarily for use with these two materials. The adhesive most commonly used with rayon and/or nylon is a latex-resin emulsion.

In order to ensure proper positioning of the cords in the calendered sheet, the cords before ruberizing are generally woven into a fabric held together by very light filler threads and the enveloping rubber sheet anchors the cords in their proper position.

The individual ply is cut from the fabric on a bias so that the cords will lie at a definite angle. In "radial" tyres this angle is approximately 90 deg to the length of the cut sheet. In "conventional" tyres this angle is approximately 38 deg to the length of the cut sheet. In "conventional" tyres the cut plies are assembled with cords essentially at right angles to each other in adjacent layers. The size of the tyre and' the service for which it is intended determine number of cords/plies applied to cords enhances their resilience.

b. Breaker, Cushion and Inserts

These body components contribute to load carrying capacity. Their use and positioning in tyre structure varies with anticipated service requirements.

The breaker is placed between the tread and top ply. Typical breaker consists of two plies of dipped and rubber coated cord fabric, applied at approximately right angles to each other. The breaker is slightly wider than the tread cap. Breaker fabric has a more open weave than is used in regular ply fabric construction, and the cords are somewhat larger. The coating is generally a high modulus ply compound, selected for good heat resistance, strength and ability to absorb road shock.

In some constructions these breaker plies are buried in the tyre between the plies and then in this position are called "cap plies" or "insert plies". Also buried in the plies, particularly between the cuter plies of truck tyres, are "cushions" or "inserts". These are calendered sheets of the same compound which is on the adjacent plies. These are generally used to provide better heat resistance and insulation of the cords in the crown area of the tyre. Passenger tyres generally do not contain breaker plies or "cushions" or "inserts".

During the past few years the tensile strength of cords has increased and as a result of this increase it has been possible to build tyres with a fewer number of plies and still retain the load carrying characteristics of the previous tyres. The standard tyre construction used on new automobiles is now a two ply tyre as compared to the previous four ply tyre. In truck tyres it is not uncommon to find four ply, six ply or eight ply construction. In using these "reduced ply" construction the compounder frequently must design a better quality stock than he has been accustomed to using in the full ply constructions. These stocks must have higher tensile strength, better tear resistance and improved heat resistance.

c. Tread

The Tread is the wearing surface of a tyre. It is applied as an extruded strip of compound, which, after vulcanization, must be fairly hard and very tough. Tyre treads, in addition to protecting the structure underneath, must exhibit maximum resistance to abrasion, tear, cracking, chipping, weathering and heat aging. In addition it must provide traction on wet, dry, cold, and hot road surfaces of various paving materials. Various tread patterns are shown in figure.

d. Sidewall :

The function and requirements of the sidewall are the same as those of the tread, except for traction, but the degree of which it must meet these requirements is not necessarily the sane. In some instances it is possible to use the same stock for tread and sidewall and in these instances the tread and sidewall are extruded as a single unit from a single barrel extruder. In other instances, for reasons of economy, or because the difference in service requirements demands it, a stock differing from that of the tread must be used. In some tyres there may be three stocks necessary; the cap stock to provide maximum wear, the base stock underneath the cap to develop low heat build-up and to resist heat build-up, and the sidewall stock to resist scuffing and weathering. The various tread components may be extruded and applied separately to a tyre. Generally3 however, two stocks are joined in a double barreled extruder and then applied as a single unit in tyre building. This dual extrusion also reduces the possibility of interface failures.

In passenger tyres more than half of the tyres made today have white sidewalls or, in some cases, colored sidewalls for decorative purposes. These generally are applied as a separate unit at the tyre building machine.

Chafer :

The chafer is a square woven fabric stock coated with an abrasion resistant compound. It is positioned over that area of the bead section which makes contact with the rim and it also extends for some distance between the sidewall and outer ply. Its function is to minimize chafing caused by contact with the rim end to add to the stability of the bead section of the tyre.

COMPOUNDING

Representative formulas listed suggest a practical approach to compounding for the required processing and physical properties essential in modern pneumatic tyre structure. Recommended uses of the various elastomers and carbons are based on present knowledge of industry practices.

Obviously, there are compounds in production which differ greatly in the use of the various polymers and/or black from these representative formulas. In preparing these representative formulas we have considered both quality and cost.

I have attempted to show a representative formula for each type of polymer.

In none of the passenger or truck body stocks do show the use of polymers other than SBR and natural rubber. Depending on the service requirements and economics polyisoprene can be used wholly or in part to replace natural rubber. Cis-4-polyburadiene and emulsion polybutadiene can also be used to replace SBR or natural rubber in moderate percentages. These polybutadienes improve the heat resistance characteristics of body stocks and the wear resistance of tread stocks.

Typical Truck Tyre Tread

 

Natural Rubber

Natural Rubber cis polybutadiene

Snaked Sheet

100

75

Cis-Polybutadiene

-

25

K-STAY G

1

2

Stearic Acid

2.5

3

Zinc Oxide

3.5

3.25

ANTOZITE 67 S

2

-

AGERITE SUPERFLEX SOLID

2

1

AGERITE HIPAR

-

1

Philrich 5

5

4

ISAF Black

50

45

Sulfur

2.3

2

AMAX

0.35

-

ALTAX

-

1

Total

168.65

162.25

Sp. Grav.

1.118

1.1

Truck tyre body plies

 

Breaker

Inner Ply

Outer Ply

Smoked Shefld

100

100

' 100

REOGEN

1

1

1

Stearic Acid

2

2

2

Zinc Oxide

5

5

5

AGERITE RESIN D

2

2

2

Pine Tar

4

2

2

Para Flux

3

-

--

Curoar P-25

2

1

1

FEF Black

30

15

10

SRF Black

10

10

10

Sulfur (Insoluble)

2.45

2.3

2.25

AM AX

0.5

0.4

0.4

Diphenylguanidine

0.2

-

0.1

Total

162.15

140.7

135.75

Sp. Grav.

1.10

1.06

1.04

Sample

 

Natural Rubber

SBR

Smoked Sheet

90

--

SBR 1500

-

95

Reclaim (Whole Tyre)

20

10

K.STAY G

2

2

Stearic Acid

1

1

Zinc Oxide

3.5

3.5

AGERITE SUPERFLEX SOLID

2

2

ANT0ZITE 67 S

5

7

Macrocrystalline Wax

2

2

Para Flux

6.4

6.4

GPF Black

70

60

Sulfur

2.5

1.8

AM AX

.35

1.2

Total

204.25

191.9

Sp. Grav.

1.18

1.1

Passenger Tyre Treads

 

Natural Rubber

SBR Cis-poly Butadiene

Smoked Sheet

100

-

SBR 1712

-

103.1

Cis-Polybutadiene

-

25

REOGEN

-

-

K-STAY G

-

5

Stearic Acid

2.5

2

Zinc Oxide

3.5

3

AGERITE RESIN D

1.5

1.5

AGERITE HP

0.5

0.5

ANTOZITE 67 S

4

4

Microcrystalline Wax

1

1

Philrich 5

5

7

HAF

50

-

ISAF

-

65

Sulfur

2.5

1.8

AMAX No. 1

0.5

__

AMAX

-

1.5

REDAX

0.5

-

Total

173.5

220.4

Sp. Grav.

1.12

1.13

Passenger Tyre Sidewalls

 

Black Natural rubber

Black SBR

Smoked Sheet

100

-

SBR 1500

-

50

SBR 1712

-

50

REOGEN

1

1

Stearic Acid

3

1.5

Zinc Oxide

5

3

ANTOZITE 67 S

4

4

Microcrystalline Wax

1.75

2

AGERITE SUPERFLEX SOLID

2

2

GPF Black

50

65

Sulfur

2.5

2.05

AMAX

0.5

1.1

Total

179.75

193.65

Sp. Grav.

1.15

1.16

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