Industrial inner tubes are made by mixing rubber ingredients, then extruding the rubber into a long, hollow tube
The primary raw material for industrial innertubes is rubber, including both natural and synthetic rubbers. Butyl rubber, for example, is often chosen for its excellent airtightness. In addition to rubber, various additives are also required. For example, vulcanizers enhance the rubber's strength and elasticity, while antioxidants slow down rubber aging, enhancing the innertube's durability.
Mixing Process
Mixing is a critical step in thoroughly mixing the rubber raw materials with various additives to form a uniform mixture. First, the raw rubber and various compounding ingredients are accurately weighed according to the workshop's production plan and recipe. The weighing tolerance is controlled within specified limits. For example, the tolerance for medium-fine materials is 5 grams when weighed on a 5 kg scale, and the tolerance for bulk materials is 200 grams when weighed on a 50 kg scale.
Mixing is typically performed in an internal mixer. Plasticized rubber is added first, followed by small, medium, bulk materials, and oil. Mixing is performed under specific temperature, air pressure, and time conditions. During mixing in an internal mixer, the discharge temperature is generally no higher than 130°C. After mixing, the rubber compound is thinned on an open mill to a thickness of 1.5-2 mm. The thinned compound passes through rollers three times, with one 90-degree turn to ensure even mixing, before being rolled for subsequent processing.
Molding Process
Molding is the stage that gives the innertube its basic shape. The mixed rubber compound is fed into a molding machine, where the molding machine parameters are adjusted according to the desired innertube specifications. A common molding method is extrusion, where the rubber compound is extruded into a tubular shape. During the extrusion process, a small amount of talc is sprayed into the tubular to prevent sticking. Excess talc is recovered using negative pressure for environmentally friendly disposal.
The extruded tubular is cooled on an integrated line using circulating water sprays, followed by a blower to remove any surface moisture. Next, the tubular is punched to create holes for the valve. The valve is then automatically installed, and the installation area is compacted to ensure a tight bond between the valve and the tubular. Finally, the tubular is automatically cut to length according to product type. Vulcanization Process
Vulcanization is a key step in improving innertube performance. The formed innertube is placed in a vulcanizing mold in an autoclave or vulcanizer. Under high temperature (e.g., around 160°C) and high pressure, the rubber molecules react with the vulcanizing agent, imparting excellent elasticity, wear resistance, and strength. Vulcanization typically takes approximately 10 minutes, though the specific duration varies depending on factors such as the innertube's material, thickness, and vulcanization equipment.
Inspection and Packaging
Vulcanized innertubes undergo rigorous inspection. Inflating the tubes is performed to check for leaks, bubbles, and other quality issues to ensure product quality meets relevant standards. Passing inspections are placed in inner packaging bags, then sorted by specification and model into boxes. Finally, they are transported to the finished product warehouse for shipment.
The production of industrial innertubes is a complex, interlinked process, from the rigorous selection and preparation of raw materials, to precise control of key processes such as mixing, molding, and vulcanization, and finally to final inspection and packaging. Each step significantly impacts product quality. Only by strictly controlling each link in the production process can we produce high-quality industrial inner tubes to meet the needs of use in different fields.