Rubber is processed into rubber products through several key steps:
1. Raw material preparation
Selection of rubber types : Natural rubber is obtained from latex extracted from rubber trees. Synthetic rubbers like styrene-butadiene rubber (SBR) and butadiene rubber (BR) are produced through chemical synthesis. The choice of rubber depends on the desired properties of the final product. For example, natural rubber has good elasticity and strength, while SBR has better wear resistance.
Compounding : Rubber is mixed with various additives to achieve specific properties. Carbon black is a common filler that enhances strength and durability. For instance, adding 30 - 50 parts of carbon black per 100 parts of rubber can significantly improve the tensile strength. Antioxidants are used to prevent the rubber from degrading due to heat and oxygen. Plasticizers can make the rubber more flexible. The mixture is thoroughly blended in a mixer to ensure uniform distribution of the additives.
2. Shaping
Milling : The compounded rubber is passed through a milling machine. The machine has two large rollers that rotate in opposite directions. The rubber is fed between the rollers and is sheared and stretched. This process helps to further mix the rubber and break down any lumps. The milled rubber is then shaped into sheets or slabs of the desired thickness.
Extrusion : For products with complex shapes, such as hoses or profiles, the rubber is fed into an extruder. The extruder has a screw that pushes the rubber through a die. The die has the shape of the final product. For example, to make a rubber hose, the die would have a circular hole with the desired diameter. The extruded rubber comes out in a continuous shape and can be cut to the required length.
Molding : For products like rubber shoes or seals, the rubber is placed in a mold. The mold has two halves that are clamped together. Heat and pressure are applied to the mold. The rubber flows into the shape of the mold and takes on its form. The temperature and pressure depend on the type of rubber and the product. For example, natural rubber may require a temperature of around 140 - 160°C and a pressure of 10 - 15 MPa for vulcanization.
3. Vulcanization
Chemical reaction : Vulcanization is a crucial step that crosslinks the rubber molecules. Sulfur is a common vulcanizing agent. When the rubber is heated in the presence of sulfur, the sulfur atoms form crosslinks between the rubber polymer chains. This process transforms the rubber from a soft, pliable material into a strong, elastic product. The degree of vulcanization can be controlled by adjusting the amount of sulfur and the vulcanization time. For example, a higher sulfur content and longer vulcanization time will result in a harder and more durable rubber product.
Post - vulcanization treatment : After vulcanization, the rubber product may undergo some post - treatment processes. For example, it may be cooled to room temperature. In some cases, the product is subjected to a heat - aging test to check its stability and performance under long - term heat exposure.
Through these steps, rubber is transformed from a raw material into a wide range of rubber products with different shapes and properties, such as rubber tires, seals, hoses, and various industrial components.