Basic Rubber Manufacturing Process

I. Basic Process Flow

Rubber products come in a wide variety, but the production process is basically the same. For rubber products made from general solid rubber—raw rubber as the raw material, the basic process includes six fundamental steps: plasticizing, mixing, calendering, extrusion, molding, and vulcanization. Of course, basic steps such as raw material preparation, finished product finishing, inspection, and packaging are also essential. The rubber processing process primarily addresses the contradiction between plasticity and elasticity. Through various process techniques, elastic rubber is transformed into plasticized rubber, then combined with additives to create semi-finished products. Finally, through vulcanization, plastic semi-finished products are converted into highly elastic rubber products with good physical and mechanical properties.

II. Raw Material Preparation

1. The main raw material for rubber products is raw rubber, which is obtained by collecting latex from rubber trees growing in tropical and subtropical regions through artificial tapping.

2. Various additives are auxiliary materials added to improve certain properties of the rubber products.

3. Fiber materials (such as cotton, hemp, wool, synthetic fibers, and metal materials like steel wire) serve as the framework for rubber products to enhance mechanical strength and restrict deformation. During raw material preparation, the ingredients must be measured accurately. To achieve uniform mixing of raw rubber and additives, materials need to be processed. Raw rubber should be softened in a 60–70°C drying room before being cut and broken into small pieces. Solid additives, such as paraffin, stearic acid, and rosin, must be crushed. Powders containing mechanical impurities or coarse particles need to be screened out. Liquid additives, such as pitch or gum rosin, need to be heated, melted, evaporated of moisture, and filtered to remove impurities. Additives must be dried; otherwise, they easily form lumps, which, if not uniformly dispersed during mixing, can create bubbles during vulcanization and affect product quality.

III. Plasticizing Raw rubber is highly elastic but lacks the plasticity needed for processing, making it difficult to work with.

To improve its plasticity, raw rubber is plasticized. This process allows additives to disperse evenly in the raw rubber during mixing and also helps enhance the penetration into fabrics and molding fluidity during calendering and forming. The process of breaking down long-chain molecules of raw rubber to form a plastic material is called plasticizing. There are two methods for plasticizing raw rubber: mechanical plasticizing and thermal plasticizing. Mechanical plasticizing involves low-temperature mechanical pressing and friction in a plasticizing machine, which degrades long-chain rubber molecules from a highly elastic state to a plastic state. Thermal plasticizing involves passing hot compressed air into the raw rubber. Under the effect of heat and oxygen, long-chain molecules are broken down to achieve plasticity.

IV. Mixing To meet different usage conditions, achieve various properties, improve rubber product performance, and reduce costs, different additives are added to raw rubber.

Mixing involves combining plasticized raw rubber with additives and using a rubber mixer to mechanically blend them, ensuring the additives are fully and evenly dispersed within the raw rubber. Mixing is a crucial step in the production of rubber products; if not done evenly, the rubber and additives cannot fully perform, affecting the product’s performance. The resulting material is called mixed rubber, which is the semi-finished material for making rubber products, commonly sold as a commodity. Buyers can directly process, mold, and vulcanize it into the desired rubber products. Depending on different formulations, mixed rubber comes in a series of grades and varieties, offering choices.

V. Molding In rubber product manufacturing, using a calender or extruder to pre-shape the material into various forms and sizes is known as molding.