+90 224 361 19 40

info@bursamak.com

CSS3 dropdown menu

Rubber Press - Silicone Press

We produce the rubber press that will speed up your business and production process. With the touch panel, every parameter from mold temperature to cycle time and waiting times is under your control. By recording the parameters for each mold, we ensure that you always produce products in the same time and level. We constantly keep the mold temperature under control with sensitive sensors and PLC. We provide very high energy savings by preventing unnecessary pump operation.

As a company specialized in high technology, we produce high-performance rubber presses that will speed up your rubber and silicone production and reduce your unit costs. With our heat control technology, you can use heating from the table or directly from the mold if you wish. With PID and direct control, you can control the heating performance completely at your discretion. With multi-point temperature measurement, PLC monitors heat distribution and resistance performances with continuous comparisons. It warns the operator in case of resistance failures and SSR relay failures.

With the automatic start feature, the machine can be started automatically by programming the desired days and hours. You can save 1000 patterns with their names and all parameters. Thanks to our high-performance hydraulic unit, you will not experience any loss of performance in long-term work.

With the shift tracking system, the production quantities of each shift are automatically recorded by the machine and can be monitored monthly. Thanks to the shift tracking system that cannot be reset by the operator, you can track your production much more effectively.

With our automation and production experience, we offer high technology and low cycle times in our rubber presses. We offer a cost advantage thanks to the low energy consumption and high production speed that comes with these. You can easily monitor the performance and production speed through your machine's operating system. If you wish, we also offer an integration service that instantly transfers the entire production process and requested data to your ERP software.

Vulcanization Press

MODEL	RP403	RP406	RP410	RP610	RP615	RP620	RP915	RP920	RP925
Table Dimension	400 X 400			600 X 500			900 X 600
Pressing Force (250 Bar)	40 Tons	80 Tons	125 Tons	125 Tons	200 Tons	250 Tons	200 Tons	250 Tons	300 Tons
Pressing Force (200 Bar)	30 Tons	60 Tons	100 Tons	100 Tons	150 Tons	200 Tons	150 Tons	200 Tons	250 Tons
Engine Power (kW)	3	5,5	7,5	7,5	11	15	11	15	18,5
Table Heating Power (kW)	15	15	15	25	25	25	35	35	35
Number of Cylinders	1	1	1	1	2	2	2	2	3
Cylinder Diameter	150	200	250	250	230	250	230	250	230
Stroke	200 mm			250 mm			300 mm
Maximum Clearance	250 mm.			300 mm.			350 mm.
Minimum Clearance	50 mm.			50 mm.			50 mm.
Table Movement	With hydraulic piston.
Closing Speed	10 mm/sn.
Auto Start	You can program the machine to work automatically and heat the mold by setting the days and hours you want.
Smart Resistance Technology	Automatically detects resistance breakdown and SSR relay breakdown thanks to multi-point temperature control.
Temperature Control	Heat control is provided with PID and Direct control options.
Safety Barrier	Available.
Control Unit	All functions and measurements are controlled by PLC.
Memory	1000 Molds can be saved with all their parameters.
Control Panel	7" Touch panel
Hydraulic Oil Cooling	Temperature controlled, separate pump prevents oil temperature from increasing.
Ventilation	Harmful gases and excess heat are removed from the operator with temperature-controlled automatic fans.
Heating from the mold	If desired, a heater can be added to the mold to shorten the heating time and save energy.
Automatic Lubrication	The machine automatically lubricates its columns and sliding table, eliminating the need for daily maintenance.
Middle and Side Scraper	There are hydraulic middle and side pushers. You can easily remove the products from the mold by moving the middle plate of the mold separately.
Shift Tracking	Records the production amount of 3 monthly shifts and stores it in its non-erasable memory.
Online Connection	It transfers data instantly to the server computer. It can be controlled remotely.
Consumption Tracking	It tracks the energy consumption amount of 3 monthly shifts. You can easily see the unit energy per product and the energy consumption of the machine.

Brochure

PRESS SELECTION

DETERMINING PRESSING FORCE

The main factors determining the pressing power are;

1-Mold size

2-Mold working system

3-Product thickness

4-Product hardness

The mold size is the most important factor in determining the required press force. The surface area of the mold determines the required force. In compression molds, an average of 15-20 kg force is required per cm². In transfer molds, the resistance increases as the dough passes through fine holes and 30-40 kg force is required per cm².

Compression Rubber Mold

Compression Rubber Mold

Transfer Rubber Mold

Transfer Rubber Mold

For example, if you have a mold size of 30cm X 30cm, you have 900cm² surface area.

If it is a compression mold, you need 900 X 15 = 13,500kg = 13.5 tons of force.

If it is a transfer mold, you need 900 X 30 = 27,000kg = 27 tons of power.

For presses to have a long life, it is more appropriate to operate at 150 bar pressure. Therefore, the press power that provides these forces we calculated at 150 bar pressure is suitable for you.

Machine manufacturers generally state the power they produce at 250 bar pressure. It is necessary to be careful about this. For example, a press that produces 60 tons of power at 250 bar pressure produces 36 tons of power at 150 bar pressure.

As the product thickness decreases, the force required will increase as it becomes more difficult to flow and move on thin walls. In this case, it is necessary to choose a press that is approximately 15% stronger than the calculated power.

As the product hardness increases, the yield strength will increase, so a higher press power will be needed. In this case, it is necessary to choose a press approximately 10% stronger than the calculated power.

DETERMINING HYDRAULIC CYLINDER DIAMETER

The first value you need to learn to know the power of a press is the cylinder diameter. The power of the press is the product of the cross-sectional area of the cylinder and the pressure. Press Power = π.r².p

PRESS POWER (kg.) = (Cylinder Radius (cm.))² X 3.14 X Pressure (bar)

If there is more than one cylinder in the press, it is necessary to calculate the powers of all cylinders and add them up.

When examined, it will be seen that many presses are far below the power stated on them.

DETERMINATION OF HYDRAULIC UNIT MOTOR POWER

There are two main factors to calculate the required motor power. One is the hydraulic cylinder size and the other is the press speed. You can easily calculate the required motor power with the formula below.

P = ( p x V x n) / 540.000

P : motor power (kW)

p : pump pressure ( bar )

V : Pump delivery volume (cm³ / cycle)

n : Speed of the electric motor used (rpm)

Here you can calculate the internal volume of the cylinder and how long it will take to fill the pump according to the delivery volume. This value will give you the closing speed of the press. As you can see from the formula, the required motor power is directly proportional to the speed of the press.

For example, to double the speed of a press, it is not enough to double the pump, it is also necessary to double the motor. Or vice versa. As the press slows down, the motor power requirement will decrease. The hydraulic unit motor power is a very important factor in the machine to be selected, because it is directly proportional to the speed of the press. When examined in this way, it will be seen that many presses cannot even manage to work one shift at maximum power.

RUBBER AND VULCANIZATION

VULCANIZATION

Vulcanization is the chemical process by which the physical properties of natural or synthetic rubber are improved; the finished rubber has higher tensile strength and resistance to swelling and abrasion, and is elastic over a wider temperature range. In its simplest form, vulcanization is accomplished by heating the rubber with sulfur.

The process was discovered in 1839 by the American inventor Charles Goodyear, who also noted the important role of certain additives in the process. Such a material, called an accelerator, causes vulcanization to proceed more quickly or at lower temperatures. The reactions between rubber and sulfur are not fully understood, but in the product, sulfur is not simply dissolved or dispersed in the rubber; it is often chemically combined in the form of cross-links or bridges between long-chain molecules.

RUBBER

Rubber, an elastic substance obtained from the exudates of certain tropical plants (natural rubber) or from petroleum and natural gas (synthetic rubber). Because of its elasticity, durability, and hardness, rubber is the primary component of tires used in automotive vehicles, aircraft, and bicycles. More than half of all rubber produced goes into automobile tires; the remainder goes into mechanical parts such as assemblies, seals, belts, and hoses, as well as consumer products such as shoes, clothing, furniture, and toys.

The basic chemical components of rubber are elastomers, or "elastic polymers", which are large chain-like molecules that can be stretched to great lengths and still return to their original shape. The first common elastomer was polyisoprene, from which natural rubber is made. Natural rubber, formed in a living organism, consists of solids suspended in a milky liquid called latex and circulates in the bark of many tropical and subtropical trees and shrubs, but predominantly Hevea brasiliensis, a tall, soft tree native to Brazil. Natural rubber was first scientifically described by Charles-Marie de La Condamine and François Fresneau following an expedition to South America in 1735. English chemist Joseph Priestley gave it the name caoutchouc in 1770 when he discovered that it could be used to erase pencil marks. Its major commercial success came after Charles Goodyear invented the vulcanization process in 1839.

Natural rubber continues to hold a significant place in the market today; its resistance to heat build-up makes it valuable for tires used on race cars, trucks, buses, and airplanes. However, it accounts for less than half of commercially produced rubber; the remainder is synthetically produced by chemical processes that were partially known in the 19th century but were not commercially used until the latter half of the 20th century, after World War II. The most important synthetic rubbers include butadiene rubber, styrene-butadiene rubber, neoprene, polysulfide rubbers (thiols), butyl rubber, and silicones. Synthetic rubbers, like natural rubbers, can be hardened by vulcanization and can be improved and modified for special purposes by reinforcing them with other materials.

NATURAL RUBBER PRODUCTION

Rubber Tree

Commercially, natural rubber is obtained almost exclusively from Hevea brasiliensis, a tree native to South America, where it grows wild to a height of 34 metres (120 ft). However, when grown on plantations, the tree grows only to about 24 metres (80 ft) because the carbon required for growth is also a major component of rubber. Since only atmospheric carbon dioxide can provide carbon to the plant, the element must be divided between the two needs when the tree is in active production. Furthermore, because the leaves are confined to the crown of the tree (to facilitate tapping), carbon dioxide uptake is less than in a wild tree. Other trees, shrubs and herbaceous plants produce rubber, but none are comparable in productivity to Hevea brasiliensis, so industrial botanists have concentrated their efforts on this species alone.

Rubber Tree

Latex collected from trees at a rubber plantation near Kuala Lumpur, Malaysia.

In Hevea cultivation, the natural contours of the land are followed and the trees are protected from the wind. Cover crops planted near rubber trees retain rainwater on sloping ground and help fertilize the soil by fixing atmospheric nitrogen. Standard horticultural techniques such as nursery cultivation of resistant rootstocks and grafting onto them, hand pollination, and vegetative propagation (cloning) to produce a genetically uniform crop are also used.

Hevea grows only in well-defined areas of the tropics and subtropics where frost never occurs. Heavy annual rainfall of about 2,500 mm (100 in), with a wet spring emphasis, is essential. As a result of these requirements, cultivation areas are limited. Southeast Asia is particularly well-positioned for rubber cultivation, as are parts of South Asia and West Africa. Hevea's native habitat in Brazil was almost completely wiped out by disease in the early 20th century.

Rubber Tree

Latex is extracted from the rubber tree.

When the bark of the Hevea tree is partially cut (stricken), a milky fluid oozes from the wound and dries to form a rubbery film. The biological function of this latex is still unclear: it may protect the inner bark and aid in wound healing, or it may serve other biochemical functions. Latex consists of an aqueous suspension of small particles, approximately 0.5 microns in diameter, of cis-polyisoprene, a high molecular weight linear rubbery polymer. The rubber content of the suspension is approximately 30%.

Rubber trees are tapped approximately once every two days, each time yielding a cupful of latex containing about 50 grams (1.7 ounces) of solid rubber. The standard method of tapping is to score the tree with a knife halfway around the trunk, starting at the highest point suitable for tapping and slanting the cut from left to right at an angle of 30°. Each subsequent cut is made just below the previous one. The trees are usually allowed to rest for a period after intensive tapping. Production begins when the tree is 5 or 6 years old; with care the useful life of the tree can be extended to over 20 years. With trees grown at a density of 375 per hectare (150 per acre), about 2,500 kg of rubber can be produced per hectare per year (i.e., approximately one tonne per acre per year).

After collecting the latex drawn from the tap, the rubber is recovered from the emulsion by coagulation with formic acid, creating crumbs that resemble milk curds. The crumbs are washed, dried between rollers, and compressed into blocks measuring 67 x 33 x 18 cm (26 x 13 x 7.5 in) and weighing 33.3 kg (73 lb). The blocks are then wrapped in polyethylene sheets and packed into one-ton crates for transport.

Latex

Passing sheets of natural rubber coagulated from latex through rollers, Krabi, Thailand.

The other production is smoked sheet, where the coagulated sheet is pressed into thin sheets, washed, and then dried over a smoky wood fire. The smoke contains natural fungicides that protect against mold growth and give it its characteristic amber color. The dried sheets are packed into 110 kg (250 pound) bales for transport.

About 10 percent of all natural rubber is shipped as latex, concentrated to a rubber content of about 60 percent and used to make dipped products such as surgical gloves, prophylactics and toys.

Development of the natural rubber industry

If the latex is allowed to evaporate naturally, the resulting rubber sheet can be dried and pressed into usable objects such as bottles, shoes, and balls. South American natives made such objects early on: rubber balls, for example, were used in an Aztec ceremonial game (called ollama) long before Christopher Columbus discovered South America and the Caribbean. Columbus is said to have seen natives in what is now Haiti playing a game with balls made from the gum of a tree during his second voyage to the New World in 1493–96. In 1615, a Spaniard described how Indians collected milk from cuts in various trees and smeared it on their cloaks, and also how they made crude shoes and bottles by covering them in clay molds and allowing them to dry.

The first serious accounts of rubber production and the primitive Native American production system were made in the 18th century by Charles-Marie de La Condamine, a member of a French geographical expedition sent to South America in 1735. La Condamine identified "caoutchouc" (the French spelling of the indigenous term "weeping wood") as the condensed juice of the Hevea tree and sent samples of rubber to Europe in 1736. At first, the new material was merely a scientific curiosity. A few years later, English scientist Joseph Priestley noted its usefulness for erasing pencil marks from paper, and thus the popular term rubber was coined. Other applications gradually developed, particularly for waterproofing shoes and clothing.

Significant progress toward a true rubber industry came from separate experiments in the early 19th century by Charles Macintosh, a Scottish chemist, and Thomas Hancock, an English inventor. Macintosh's contribution was the rediscovery of coal tar naphtha as a cheap and effective solvent in 1823. He placed a solution of rubber and naphtha between two fabrics, thus avoiding the sticky surfaces common in early single-weave rubber-treated garments. Production of these double-weave waterproof cloaks, known thereafter as "mackintoshes," began soon after.

Of even greater importance is the work of Hancock, Macintosh's colleague and collaborator. He first tried to dissolve rubber in turpentine, but his hand-coated fabrics were unsatisfactory in surface texture and odor. He then turned to the manufacture of elastic thread. Strips of rubber were cut from imported lumps and applied in crude form to clothing and shoes. In 1820, in an effort to make use of waste scraps, Hancock invented a chewing machine. Constructed from a hollow wooden cylinder fitted with teeth and turned by hand-operated, pointed cylinder, this tiny machine exceeded Hancock's wildest hopes by initially taking a load of two ounces of rubber. Instead of breaking the rubber into pieces, it produced sufficient friction to weld the rubber pieces into a coherent mass that could be used in later production.

Macintosh and Hancock's efforts solved the initial problem of processing the raw material, but there was a fundamental obstacle to the full use of natural rubber: it softened in heat and hardened in cold (especially annoying in North America, where the climate was more extreme than England's). It was also sticky, smelly, and perishable. These fundamental weaknesses were overcome in 1839 with Charles Goodyear's invention of vulcanization. By combining a compound of rubber, white lead, and sulfur, and developing a heat-treating (or curing) process, Goodyear created a product with impressive durability—at first called fireproof gum, later called vulcanized rubber.

Vulcanization made possible the modern rubber industry, allowing the substance to be used in machinery and bicycle tires, and later in automobiles. Although subsequent discoveries improved upon Goodyear's original techniques, the vulcanization process remained essentially the same as it had been in his time.

With the advent of the bicycle and, somewhat later, the automobile, and the invention of the solid and later pneumatic rubber tyre, the demand for rubber increased rapidly. By 1900, over 40,000 tonnes were being used each year, about half from Brazil and half from Central Africa, where it was obtained mainly from the Landolphia vine. However, as an important industrial material, rubber was needed in greater quantities than could be easily obtained from the wild and widespread trees of the Brazilian forests or from the African vines, which produced only about one kilogram per hectare and were destroyed to obtain rubber. In order to cultivate rubber trees elsewhere, in 1876 seeds of the Hevea brasiliensis tree from the Upper Orinoco basin were taken from Brazil to England, with the encouragement of the British India Office. Seedlings were grown at Kew Gardens and sent to Ceylon (Sri Lanka) and Singapore. These trees were the origin of the rubber plantation industry in Asia, which now produces more than 90 percent of the world's supply. The industry developed largely as a result of the work of Henry N. Ridley, director of the Singapore Botanical Gardens from 1888 to 1912. Ridley introduced horticulture and tapping methods still used today. Total world natural rubber production reached 3 million tonnes per year in the early 1970s, exceeded 4 million tonnes per year in the early 1980s, and reached 10 million tonnes per year in 2008. The major rubber-producing countries are Thailand, Indonesia, and Malaysia, followed by Asian producers China, India, the Philippines, Vietnam, and Sri Lanka, and the West African countries of Nigeria, Ivory Coast, Cameroon, and Liberia.

The automobile was established in Europe and North America in the first decades of the 20th century, and the automotive industry remained entirely dependent on natural rubber for its tires and other components until World War II. After Japan entered the war in 1941, Asian sources, except Sri Lanka, were cut off from the Allies. In response, the United States and the Soviet Union attempted to grow alternative sources of natural rubber, such as the guayule bush and the Russian dandelion. These attempts were not very successful, but they were much better than synthetic rubber. The United States, in particular, developed its synthetic rubber industry almost overnight, reaching an annual production of 800,000 tons. With the return of natural rubber to availability at the end of the war, the U.S. synthetic rubber industry went into sharp decline, but by the early 1950s, superior and more uniform synthetics were available. Exports of these materials spurred the development of the synthetic rubber industry in Europe. By the early 1960s, natural rubber production was surpassed by the production of synthetic elastomers.

SYNTHETIC RUBBER PRODUCTION

Polymerization methods

Synthetic elastomers are produced on an industrial scale by solution or emulsion polymerization methods. Polymers produced in solution generally have more linear molecules (i.e., less branching of side chains from the main polymer chain) and also have a narrower molecular weight distribution (i.e., greater length) and flow more easily. In addition, when polymerization is performed in solution, the arrangement of monomer units in the polymer molecule can be more precisely controlled. The monomer or monomers are dissolved in a hydrocarbon solvent, usually hexane or cyclohexane, and polymerized using an organometallic catalyst such as butyllithium.

In emulsion polymerization, the monomer (or monomers) is emulsified in water with a suitable soap (e.g. sodium stearate) used as a surfactant, and a water-soluble free radical catalyst (e.g. potassium persulfate, peroxides, a redox system) is added to initiate polymerization. After polymerization has reached the desired level, the reaction is stopped by adding a radical inhibitor. Approximately 10% of the synthetic elastomer produced by emulsion techniques is sold as latex. The remainder is coagulated with acidified brine, washed, dried, and pressed into 35 kg (77 pound) bales.

When emulsion polymerization of SBR is performed "hot" (i.e., at 50 °C or 120 °F), the polymer molecules are more branched. When polymerization is performed "cold" (i.e., at 5 °C or 40 °F), they are more linear and generally of higher molecular weight; these properties improve the rolling resistance and wear resistance of the tires. In some cases, polymerization is continued to obtain products with molecular weights that are normally difficult to dissolve. In these cases, approximately 30% heavy oil is added prior to coagulation to obtain "oil-expanded" elastomers with superior wear resistance.

The rise of synthetic rubber

The origins of elastomers, which form the basis of synthetic rubber, date back to the first half of the 19th century, when the goal was to elucidate the composition and structure of natural rubber and to reproduce the material. In 1838, the German F. C. Himly obtained a volatile distillate from the substance, and in 1860, the Englishman C. Greville Williams separated rubber by distillation into three parts: oil, tar, and "spirit." This last part was the more volatile part and the main component, which Williams named isoprene. The Frenchman Georges Bouchardat, with the help of hydrogen chloride gas and prolonged distillation, converted isoprene into a rubber-like substance in 1875, and in 1882, another Englishman, W. A. Tilden, produced isoprene by the destructive distillation of turpentine. Tilden also assigned the structural formula CH2=C(CH3)―CH=CH2 to isoprene.

The efforts outlined above were attempts to copy natural rubber. When the search for chemical equivalents to natural rubber was abandoned and the emphasis was on comparable physical properties, synthetic rubber emerged. The choice fell on butadiene (CH2=CH―CH=CH2), a compound similar to isoprene, as the basis for a synthetic product. Several important contributions came from Russia. In 1901, Ivan Kondakov discovered that dimethyl butadiene produced a rubber-like substance when heated with potassium, and in 1910, S. V. Lebedev polymerized butadiene from ethyl alcohol. During World War I, encouraged by the Allied blockade, Germany began to produce "methyl rubber" using Kondakov's process. This was an inferior substitute by today's standards, and after the war, German manufacturers returned to the cheaper and more satisfactory natural product. However, research and experimentation continued, and in 1926, G. Ebert of Germany succeeded in producing a sodium-polymerized rubber from butadiene. Over the next decade this material evolved into various types of "buna" rubber (which are derived from the first syllables of the two ingredients used to make them: butadiene and sodium [sodium]).

In the Soviet Union, production of polybutadiene using Lebedev's process began in 1932-33 using potatoes and limestone as raw materials. By 1940, the Soviet Union had the world's largest synthetic rubber industry, producing over 50,000 tons per year. Meanwhile, in Germany, the first synthetic elastomer that could replace natural rubber and produce satisfactory tires was developed at I.G. Farben by Walter Bock and Eduard Tschunkur, who synthesized a rubbery copolymer of styrene and butadiene using an emulsion process in 1929. The Germans called this rubber Buna S; the British called it SBR or styrene-butadiene rubber. SBR was in great demand during World War II, since styrene and butadiene could be made from petroleum, grain alcohol, or coal. It was produced in large quantities; up to 100,000 tons per year in Germany and the Soviet Union. Approximately 800,000 tons of SBR were produced annually in the United States, where it received the wartime name GR-S (government rubber-styrene). During the war, German chemical engineers perfected the low-temperature or "cold" polymerization of SBR, producing a more uniform product.

Other important synthetic elastomers were discovered in the decades before World War II, but none were suitable for making tires. These included polysulfides, synthesized in the United States by Joseph Patrick in 1926 and commercialized as oil-resistant thiocol rubbers after 1930; polychloroprene, a high-strength oil-resistant rubber, discovered by Arnold Collins in 1931 and commercialized as Duprene (later neoprene) by the DuPont Company in 1932; nitrile rubber (NBR), an oil-resistant copolymer of acrylonitrile and butadiene, synthesized by Erich Konrad and Tschunkur in 1930 and known in Germany as Buna N; and butyl rubber (IIR), a copolymer of isoprene and isobutylene, discovered by Americans R. M. Thomas and W. J. Sparks at the Standard Oil Company (New Jersey) in 1937.

After World War II, the increasing sophistication of synthetic chemistry led to many new polymers and elastomers. In 1953-54, two chemists, Karl Ziegler of Germany and Giulio Natta of Italy, developed a family of organometallic catalysts that could precisely control the arrangement and configuration of units along a polymer chain, thus producing regular (stereospecific) structures. Using such catalysts, isoprene was polymerized so that each unit in the chain was bonded to its predecessor in a cis configuration, which is almost identical to the structure of natural rubber. In this way, almost 100 percent cis-polyisoprene, or "synthetic natural rubber," was produced. In 1961, the same type of catalyst, containing butadiene as a monomer, was used to produce cis-1,4-polybutadiene, a rubber that was found to have excellent wear resistance, especially in tires subjected to harsh service conditions.

Several other developments characterized the postwar years. For example, block copolymers, in which a long sequence of one chemical unit is followed by a long sequence of another chemical unit in the same molecule, were made using many different units and sequence lengths. New oil- and heat-resistant elastomers were introduced, including styrene-acrylonitrile copolymers, polysulfides, and chlorinated and chlorosulfonated polyethylene. Some degree of control was gained over the wide range of molecular lengths found in most polymers, so that in many cases narrow or broad distributions with quite different viscous properties could be produced. In addition, polymers were synthesized with branched molecules, with many small branches along the main chain or a few long "arms" radiating from a central point, providing different flow properties and easier cross-linking.

World consumption of synthetic rubber reached nine million tons in 1993. Approximately 55% of all synthetic rubber produced is used in automobile tires.

Additives

A number of ingredients are added to both natural and synthetic rubber to achieve certain desired properties. Traditionally, blend formulations begin with the quantity of the specified elastomer—for example, natural rubber (NR), butadiene rubber (BR), or styrene-butadiene rubber (SBR)—given as 100 parts by weight. The quantity of each of the other ingredients is then expressed as parts by weight added per 100 parts by weight of elastomer. If two or more elastomers are used, they are expressed in the recipe as fractions of 100 parts—for example, "NR, 60 parts; BR, 40 parts." If the elastomer contains oil that has been pre-added by the manufacturer, allowance is made in the recipe for this dilution. For example, if SBR 1702 is used, the mix formulation might begin with “SBR 1702, 137.5 parts by weight” because this amount of SBR 1702 contains 37.5 parts by weight of oil and 100 parts by weight of SBR elastomer.

Cure package

The most important ingredients are the ingredients known as the cure package, which cause the bonding reactions to occur when the mixture is "cured." They are usually added at the end of mixing to minimize the risk of premature cure. The cure package usually consists of sulfur and one or more "accelerators" (e.g., sulfenamides, thiurams, or thiazoles) that cause the sulfur bonding reaction to occur more quickly and efficiently. When the sulfur to accelerator ratio is less than one, the recipe is known as an "active vulcanization" (EV) system and results in products with shorter lengths of sulfur bonds. EV products have improved flexibility but lower strength.

Two other components that play an important role in vulcanization chemistry are known as "activators," usually zinc oxide and stearic acid. These compounds combine and react with the accelerators to form a zinc sulfiding compound, which is the primary means of adding sulfur to the diene elastomer and forming sulfur linkages.

Other less commonly used bonding agents are sulfur compounds known as sulfur donors (e.g. tetramethylthiuram disulfide) which form monosulfur bonds between polymer molecules and peroxides, especially dicumyl peroxide. Peroxides decompose when heated to form radicals which abstract hydrogen from groups in the polymer molecules. The carbon radicals thus formed on different molecules then combine to form carbon-carbon bonds. Although the products with C―C bonds are more resistant to heat and oxidative attack, their strength is lower than those with sulfur bonds. Furthermore, monosulfur bonds give weaker products than polysulphide bonds. This paradoxical result (inherently strong C―C bonds give the weakest products, while inherently weak polysulphide bonds give the strongest products) is attributed to the fact that the weaker bonds will break under stress before the main chain, thus delaying the degradation of the elastomer molecule itself.

Fillers

Almost every conceivable material has been added to rubber to make it cheaper and tougher. Two particulate fillers are remarkable because they also strengthen elastomers to a remarkable degree. The most important, which is almost universally used, is finely divided carbon black, prepared by the incomplete combustion of petroleum or gas. Carbon black consists of small spherical particles, only 10–100 nanometers (10–100 billionths of a meter) in diameter, and composed of concentric layers of graphitic carbon. The surface of the particles also contains some oxygen and hydrogen. During manufacture, the particle chains fuse together to form extended open "structures" that are still very small in size.

Another reinforcing filler with particles of similar shape and size is finely divided silica (silicon dioxide, SiO2), prepared by burning silicon tetrachloride or acid precipitation from sodium silicate solution.

Both carbon black and silica, when added to a blend compound at a concentration of about 30% by volume, increase the elastic modulus of the rubber by a factor of two to three. They also impart considerable toughness, especially wear resistance, to weak materials such as SBR. If more is added, the modulus will increase further, but then the strength will begin to decrease. The disadvantages of reinforcement with carbon black or silica are lower springiness (elasticity) and a reduction in the initial high stiffness after flexing.

For a filler to be reinforcing, it appears that the primary particles must be small—say, 10–50 nanometers in diameter—and the elastomer must adhere well to them. If either of these conditions is not present, the reinforcing strength will be reduced. Indeed, the smaller the particle size (and therefore the larger the surface area), the greater the observed reinforcing effect. How fine particles can impart high strength and toughness to elastomer composites is still poorly understood. Reinforcement and hardening are probably related to the separation of highly stressed elastomer molecules from the filler particles, which reduces stress in the polymer chains and delays catastrophic fracture.

Preservative chemicals

Certain additives provide resistance to heat, sunlight, oxygen, and ozone. Amines, especially paraphenylene diamines, are powerful oxidation retarders or antioxidants. When added in small amounts (1-2 percent) to rubber compounds, they appear to disrupt free radical oxidation reactions that lead to molecular breakage and softening or increased bonding and hardening as the rubber ages. Another class of antioxidants, the hindered phenols, are less potent than the amines but have less tendency to stain light-colored rubber compounds. Small amounts of certain metals, especially copper, manganese, and iron, act as powerful oxidation catalysts; therefore, sequestering agents are used to inhibit the action of these elements if their presence is unavoidable.

Atmospheric ozone readily reacts with elastomers containing C=C double bonds, causing the molecules at the surface to break. As a result, small, deep cracks called ozone cracks form when the rubber is slightly stressed (more than about 10%). A typical outdoor ozone concentration, about 5 parts per 100 million, will cause cracks one millimeter long in unprotected rubber after only a few weeks of exposure. However, certain diamines (e.g., alkyl-aryl paraphenylene diamines) prevent cracking, presumably by competing with the C=C bonds in the rubber for reaction with ozone. These antiozonants "bloom" on the surface and react there, protecting the rubber. For this reason, a few percent of antiozonants are usually added to the blend formulation of rubber compounds based on unsaturated elastomers. An alternative protection method, often used simultaneously, is to add a few percent of microcrystalline paraffin wax to the blend formulation. Since the wax is incompatible with the elastomer, it will float to the surface and form a protective layer.

Plasticizers and processing aids

Liquids are added to elastomer blends to soften and plasticize the compound, which may occur during processing or later in use. For example, elastomers with high glass transition temperatures (and consequently slow molecular motion) can be improved by adding low-temperature plasticizers, i.e. compatible liquids that act as internal lubricants. Plasticizers must have low vapor pressure and high boiling points to be retained in the compound for long service periods. Examples include aliphatic esters and phthalates. Phosphate plasticizers also provide some flame resistance. Other liquids are added to rubber compounds as processing aids to facilitate mixing and extrusion. Typically, 5% of a petroleum oil is used.

Processing

Rubber processing consists of four basic steps: (1) mastication, where the elastomer is sheared and the molecules are broken down to allow easier flow, (2) mixing, which is usually carried out immediately after mastication and in which additives are incorporated, (3) shaping of the viscous mass, for example by extrusion or molding, and (4) curing, where the polymer molecules are bonded together and the shape is fixed.

Chewing

Mastication and softening are usually carried out in batches. The process is carried out in large closed mixing machines or rubber mills. The best example of a closed machine is the Banbury (trademark) mixer, which consists of heavy steel counter-rotating paddles in an hourglass-shaped chamber and can hold up to half a tonne of rubber. Rubber mills have two large horizontally opposed steel cylinders, up to 3 metres (10 ft) long, closely spaced, rotating slowly in opposite directions and at slightly different speeds. The rubber is sheared and softened in the space between the paddles and the wall of the Banbury mixer and in the space between the two cylinders in the roller mill.

To mix up

Mixing is sometimes carried out immediately after softening, in machines similar to those used in mastication. As described above, reactive materials, fillers, oils and various types of preservative chemicals are incorporated into the base elastomer by the combined action of shearing and mixing. A closed Banbury-type mixer can produce up to half a ton of mixed compound in a few minutes. The compound is then formed into sheets, coated with a separating agent to prevent sticking and stored until used on steel pallets capable of holding up to one ton of rubber.

Forming

There are several ways to shape the mixture into the desired shape. Extruders are used to produce long continuous products such as pipes, tire treads, and wire coverings. They are also used to produce various profiles that can then be cut to length. Multi-roll calenders are used to make large sheets. In transfer and injection molds, the rubber mixture is forced through channels into a mold chamber where it is cured under pressure to the required shape. Tires are made from several components: bead wire, sidewall compound, inner liner, cord layers, belt package, and rubber; these are brought together and assembled into a complete tire before being transferred to the curing press.

Curing

Curing is accomplished in pressure steel molds heated to temperatures where the bonding reaction occurs, either by steam or electricity. Typical curing conditions are a few minutes at 160 °C (320 °F). Thicker parts require longer cure times, up to several hours at lower temperatures, because heat penetrates the rubber slowly. Pressures of 1 megapascal (145 pounds per square inch) or more are typically applied to maintain the desired shape and to force trapped air to dissolve in the compound. Other methods of curing the rubber compound after it has been shaped include steam heating in autoclaves, microwave irradiation, and passing it through a heated bath or fluidized bed of molten metal salts. In these cases, curing is performed at a pressure close to atmospheric pressure.

BURSAMAK MACHINE LTD
Yaylacık mh. 44. sk. No:13 16280 Nilüfer / BURSA /TURKEY
+90 224 3611940-41 info@bursamak.com