The manufacturing process of bicycle inner tubes mainly includes core steps such as mixing, extrusion, vulcanization, and quality inspection. Butyl rubber or natural rubber is used as the main raw material, and a sealed rubber tube is produced through an automated process.
Mixing: Butyl rubber or natural rubber is mixed with carbon black, vulcanizing agents, antioxidants, and other additives according to the formula in an internal mixer to form a homogeneous rubber compound. This process is similar to "kneading dough," ensuring stable material properties.
Extrusion and Tubing: The mixed rubber compound is fed into an extruder and extruded into a hollow, continuous rubber tubular structure. It is then cooled and shaped using a coolant to form the basic shape of the inner tube.
Valve Installation: A hole is automatically punched in the cooled rubber tube, and a valve (i.e., the valve tip) is attached. This is a crucial component for inflation. Some production lines use interconnected equipment to achieve precise positioning and bonding.
Cutting and Joining: The continuous rubber tube is cut to the required size, and then the two ends are heated and fused to form a closed, annular inner tube. Joint strength directly affects safety during use, requiring strict control of process parameters.
Vulcanization:The formed "green tire" is placed in a mold and vulcanized under high temperature and pressure. Sulfur promotes cross-linking of rubber molecules, enhancing elasticity and durability, while also fixing the valve position.
Quality Inspection: After inflation, each inner tube is left to stand for a period of time to check for leaks; simultaneously, the tensile length is checked to ensure it meets specifications. Some factories use manual quality inspection to ensure that products leaving the factory are defect-free.
Packaging and Warehousing: Qualified inner tubes are deflated, folded, and then packed into cardboard boxes for final packaging.
