Rubber Processing

Vocabulary flashcards about rubber processing.

Rubber Processing Introduction

Production methods used for plastics are also applicable to rubbers, but rubber processing technology differs and the rubber industry is largely separate. Tires dominate the rubber industry.

Natural Rubber

Natural Rubber (NR) is tapped from rubber trees (Hevea brasiliensis) mainly in Southeast Asia. Consisting primarily of polyisoprene, most harvested latex is coagulated for the manufacture of dry rubber products, including tires.

Properties of Natural Rubber

NR's excellent tensile and tear strengths, and dynamical properties are offset by poor solvent, oil, and ozone resistance, which can be improved by epoxidation.

Synthetic Rubbers

Synthetic rubbers were invented to replicate natural rubber, produced from petroleum via polymerization. They are supplied as large bales, unlike TP and TS polymers.

Common Synthetic Rubbers

Butadiene rubber (BR), Nitrile rubber (NBR), Styrene-butadiene rubber (SBR), and Silicone rubber (SiR)

Silicone Rubbers

Silicone rubber is a synthetic elastomer containing silicon, carbon, hydrogen, and oxygen, with service temperatures ranging from −70 °C to 250 °C. Commonly used in pressure-sensitive adhesives.

Two Basic Steps in Rubber Goods

Rubber production (natural or synthetic) and Processing into finished goods through compounding, mixing, shaping, and vulcanizing.

Compounding

Rubber is always compounded with additives such as chemicals for vulcanization and fillers (reinforcing or non-reinforcing) to achieve desired properties, cost, and processability.

Vulcanization

Vulcanization is the process where viscoelastic polymers are cross-linked, preventing the rubber from taking other shapes and ensuring it returns to its original form.

Vulcanization Process

It involves heating the rubber to create chemical connections between molecules. The vulcanised rubber will always return to its original shape while unvulcanised rubber can be forced into a different shape

Reasons for Vulcanization

Vulcanization makes rubber stiffer and stronger while retaining extensibility by joining long-chain molecules. More cross-links increase stiffness.

Carbon Black in Rubber

It increases tensile strength and resistance to abrasion and tearing and provides protection from ultraviolet radiation

Filament Reinforcement in Rubber

Used to reduce extensibility while retaining desirable properties in products like tires and conveyor belts. Materials include cellulose, nylon, polyester, fiber-glass, and steel.

Other Fillers and Additives in Rubber

China clays, recycled rubber, antioxidants, coloring pigments, plasticizers, softening oils, blowing agents, and mold release compounds.

Shaping Processes for Rubber Products

Four categories include Extrusion, Calendering, Coating, and Molding/Casting. Some products require multiple processes and assembly.

Rubber Extrusion

Screw extruders with L/D ratios of 10 to 15 are used to reduce premature cross-linking. Die swell occurs in rubber extrudates before vulcanization.

Calendering

Rubber stock is passed through decreasing gaps by rotating rolls. Sheet thickness is slightly greater than the final roll gap due to die swell.

Roller Die Process

Combines extrusion and calendering for better quality products.

Molding Processes for Rubber

Compression molding, transfer molding, and injection molding. Curing (vulcanizing) occurs in the mold.

Moulded Rubber Products

Shoe soles, heels, gaskets, seals, suction cups, bottle stops, foamed rubber parts, and tires.

Tires and Other Rubber Products

Tires constitute about 75% of total rubber tonnage. The carcass contains plies of rubber-coated cords (nylon, polyester, fiber glass, or steel) for reinforcement.

Rubber Belts

Fabrics are coated by calendering, assembled, and vulcanized. Footwear uses molded parts from injection, compression, and special molding techniques.