Rubber Products

Rubber products are usually divided into three major classes: (1) tires, (2) industrial rubber goods used in motor-vehicle, aircraft, and ship construction, agricultural machine building, railroad transport, and construction, and (3) consumer goods, including footwear (the most important in this category), mats, bathing caps, inflatable inner tubes and rubber rings, gloves, and pacifiers.

Most rubber products are made from hard raw rubber, although some are made from latexes, for example, seamless gloves with thin walls, rubber thread, and foam-rubber seats for automobiles and furniture.

The technological process used in the production of rubber products from hard raw rubber consists of two major stages. In the preparation stage, rubber stock is produced by mixing raw rubber with the necessary ingredients in internal rubber mixers or in milling machines. In the final stage, the semifinished rubber product is vulcanized at temperatures of 140°-200°C and pressures of 0.3–20 meganewtons per sq m (MN/m²), that is, 3–200 kilograms-force per sq cm (kgf/cm²). Vulcanization equipment includes presses, boilers, and various types of apparatus for continuous action. The equipment used is determined by the type of rubber products manufactured. The textile materials and metals used in the production of rubber products are subjected to preliminary treatment in order to provide strong bonds between these materials and rubber under various operational conditions. Textile materials are impregnated in special machines with rubber cement or other adhesives and coated with rubber stock on calenders. Metals are degreased with organic solvents and coated with a layer of cement or brass; the latter process is called brass plating and is carried out in an electroplating bath.

The major types of industrial rubber goods and rubber footwear are considered below. The types of tires and the technology of their production are discussed in a separate article.

Industrial rubber goods. Industrial rubber goods are usually divided into the following major groups: molded goods, un-molded goods, conveyor belts, belts, and hoses. Practically all types of general-purpose and special-purpose raw rubber are used in the production of industrial rubber goods.

MOLDED INDUSTRIAL RUBBER GOODS. There are about 30,000 types of molded industrial rubber goods, including parts for packing, sealing, and shock absorption, such as gaskets, rings with various cross sections, dust-protection, moisture-protection, and oil-protection caps, and rubber and metal shock absorbers. These goods are produced by simultaneously molding and vulcanizing rubber stock in a compression mold mounted on a press or by injection molding.

UNMOLDED INDUSTRIAL RUBBER GOODS. There are about 12,000 types of unmolded industrial rubber goods, which are used mainly for sealing the windows and doors of motor vehicles, aircraft, and railroad cars and for hermetically sealing construction panels. These goods are made in the form of shaped cords of various lengths and cross sections by the extrusion of the rubber stock and the subsequent vulcanization of the semifinished product in apparatus for continuous action or in boilers by periodic batching. Seals may be either monolithic or porous.

CONVEYOR BELTS. Conveyor belts are elements of various types of conveyors and are designed for the transport of friable and other materials. The belts are reinforced mainly with fabrics made from synthetic fibers, cotton, or combined fabrics with a tearing stress of 65–300 kN/m, or 65–300 kgf/cm. Brass-plated steel line is used for reinforcing conveyor belts, which must be especially strong. The technology of the production of rubberized-fabric belts entails assembling the core of the fabric on duplicating units, coating the core with a layer of rubber stock of the required thickness on calenders, and vulcanizing the belt in a press having plates about 10 m long.

BELTS. Belts serve as the flexible element of the belt drive in the engines of automobiles, agricultural machines, and various industrial devices. A distinction is made between flat belts and V-belts. The technology used in the production of flat rubber belts, which are multilayered rubberized-fabric sheets, is similar to the technology of the production of conveyor belts; the sheet is cut into strips either before or after vulcanization in order to obtain belts having the required width. V-belts have a closed design and their cross section is trapezoidal.

The major parts of a V-belt include a central carrier layer made of rubberized cord fabric or cord, a rubber layer between the longer base of the trapezoid and the carrier layer (the tensile layer), a rubber layer between the carrier layer and the shorter base of the trapezoid (the compression layer), and an external fabric layer used as packing.

Belts are assembled on machines and then vulcanized in boilers, presses, or special rotary or diaphragm vulcanizers; the selection of vulcanization equipment depends on the length and cross section of the belt.

HOSES. Hoses are flexible tubes used for conveying liquids, gases, and friable materials under excess pressure (pressure hoses) or under vacuum (suction hoses). The general elements in the design of hoses are an inner sealing rubber layer, a heavy-duty carcass, and an outer rubber layer. The lining of a heavy-duty carcass designed for pressures reaching 2 MN/m²(20 kgf/cm²) consists of fabric. For hoses used at pressures reaching 10 MN/m²(100 kgf/cm²), the heavy-duty carcass is made of fiber braiding, and for hoses used at pressures reaching 70 MN/m²(700 kgf/cm²), of metal braiding.

Suction hoses have a possible vacuum of 80 kN/m²(600 mm Hg) and are constructed with a metal spiral in addition to the heavy-duty carcass. The inner and outer layers of a hose are made by extrusion, the lining carcass is applied on assembly machines, and the fiber or metal braiding is applied on special braiding machines. The assembled hose is either wrapped in a fabric band or molded with a lead shell and then vulcanized in a boiler; the band (or shell) is removed after vulcanization.

Rubber footwear. Depending on use, rubber footwear is divided into everyday, athletic, and industrial footwear. Industrial footwear is designed to protect the feet from the harmful effects of water, corrosive agents, low temperatures, and blows; examples are the boots used by fishermen, miners, and chemical workers, and dielectric rubber footwear.

Different types of rubber footwear are distinguished according to the production method used. Glued rubber footwear is assembled, or glued, from previously produced parts on conveyor lines and then lacquered and vulcanized in boilers. Stamped rubber footwear is mass-produced by impact stamping on special presses and subsequently lacquered and vulcanized in boilers; this method is used only in the production of galoshes. Molded rubber footwear is simultaneously pressed in a mold and vulcanized. This mechanized method is used in the production of various types of boots and footwear with fabric uppers.

A promising method in injection molding involves the use of compounds based on polyvinyl chloride and thermoelastic plastics alongside the traditionally used rubber stock; the rubber stock used includes mainly the butadiene-styrene and synthetic isoprene types of raw rubber. The most modern method is liquid molding, which entails the use of liquid oligomers, for example, polyurethanes, and of plastisols.