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Extrusion Process of a Cold-Feed Rubber Extruder

Time：

2018-01-20

Rubber products come in a wide variety, yet their manufacturing processes are fundamentally similar. For rubber articles made from conventional solid rubber and raw rubber, the basic production sequence comprises six primary steps: mastication, mixing, calendering, extrusion, molding, and vulcanization. Of course, additional essential operations—such as raw material preparation, finished‑product finishing, and inspection and packaging—are also indispensable. The core of rubber processing lies in resolving the inherent contradiction between plasticity and elasticity. By employing various techniques, elastic rubber is transformed into a plastically deformable masticated compound; after incorporating multiple compounding agents to produce semi‑finished goods, further vulcanization converts these plastically workable intermediates into highly elastic materials with superior physical and mechanical properties.

Rubber products come in a wide variety, yet their manufacturing processes are fundamentally similar. For rubber articles made from conventional solid rubber and raw rubber, the basic production sequence comprises six primary steps: mastication, mixing, calendering, extrusion, molding, and vulcanization. Of course, additional essential operations—such as raw material preparation, finished‑product finishing, and inspection and packaging—are also indispensable. The core of rubber processing lies in resolving the inherent conflict between plasticity and elasticity. By employing various techniques, elastic rubber is transformed into a plastically deformable masticated compound; after incorporating multiple compounding agents to produce a semi‑finished product, further vulcanization converts this plastically workable intermediate into a highly elastic rubber article with superior physical and mechanical properties.

1. The primary raw material for rubber products is natural rubber, which is obtained by artificially tapping the bark of rubber trees grown in tropical and subtropical regions.

2. Various compounding agents are auxiliary materials added to enhance certain properties of rubber products;

3. Fiber materials—including cotton, hemp, wool, various man-made and synthetic fibers, as well as metallic materials such as steel wire—serve as the reinforcing skeleton in rubber products, enhancing mechanical strength and limiting deformation. During raw material preparation, ingredients must be accurately weighed according to the formulation. To ensure uniform mixing of the raw rubber with compounding agents, the materials require processing: the raw rubber should be softened in an oven at 60–70°C before being cut and milled into small pieces; block‑form compounding agents such as paraffin wax, stearic acid, and rosin must be crushed; powdered additives containing mechanical impurities or coarse particles should be screened out; and liquid additives like pine tar and coumarone need to be heated, melted, dehydrated, and filtered to remove impurities. Compounding agents must also be dried; otherwise, they tend to cake, and during mixing, uneven dispersion can lead to bubble formation, adversely affecting product quality.

Plasticizing

Raw rubber is highly elastic but lacks plasticity during processing, making it difficult to handle. To enhance its plasticity, raw rubber must undergo a plasticizing process. This ensures that compounding agents can be uniformly dispersed within the rubber during mixing and also improves the compound’s permeability—allowing it to penetrate fibrous fabrics—and its flow characteristics during calendering and molding. The process of breaking down the long-chain molecules of raw rubber to produce plasticity is called plasticization. There are two primary methods of plasticizing raw rubber: mechanical plasticization and thermal plasticization. Mechanical plasticization involves subjecting the rubber to mechanical compression and friction in a kneader at relatively low temperatures, which shortens the long polymer chains and transforms the material from a highly elastic state to a plastically deformable one. Thermal plasticization, on the other hand, entails passing hot compressed air through the raw rubber; under the combined action of heat and oxygen, the long-chain molecules are cleaved, resulting in reduced molecular weight and increased plasticity.