General-purpose rubber machinery refers to the equipment used in the preparation of raw rubber or semi-finished rubber products. This includes a wide range of machines such as raw material processing equipment, rubber mixers, extruders, calenders, curtain fabric pretreatment devices, and cutting machines. These tools are essential for transforming raw materials into finished rubber products used in various industries, including automotive, construction, and manufacturing.
Rubber Mixing Machines
Rubber mixing machines are crucial in the rubber processing industry, and they are generally categorized into two main types: open-type and closed-type mixers. Both serve the purpose of blending and preparing rubber compounds, but they differ significantly in design and application.
Open Rubber Mixer
The open rubber mixer is one of the earliest and most widely used types of rubber mixing equipment. It is primarily used for heating, rolling, breaking down gels, plasticizing, and mixing rubber. The machine consists of two rollers that rotate at different speeds, along with components like roller bearings, roll gap adjustment systems, emergency braking mechanisms, frames, bases, transmission systems, and heating/cooling units. The working principle involves pulling the raw rubber into the gap between the two rotating rolls through friction, where it undergoes strong shearing and compression, increasing its plasticity. First introduced in 1826, this type of mixer remains popular due to its simple structure and reliability.
Closed Rubber Mixer
Unlike the open-type mixer, the closed rubber mixer is designed for more precise and efficient mixing. It features an enclosed mixing chamber, which allows for better control over the mixing process. After loading the raw rubber and additives into the chamber, the machine seals the opening, applies pressure using a top bolt, and rotates the rotors inside at varying or identical speeds. This process subjects the rubber to continuous folding, stirring, and kneading, promoting molecular chain scission and improving plasticity. The result is a well-dispersed and uniformly mixed rubber compound. The first closed-type mixer with an elliptical rotor was developed in 1916, leading to rapid advancements in the rubber industry. Modern versions can process up to 650 liters of material in just 2.5 to 3 minutes, making them highly efficient for large-scale production.
Extruder
Extruders play a vital role in shaping rubber into various forms such as treads, inner tubes, hoses, and rubber strips. They are also used for coating cables and wires. The most common type is the screw extruder, which works by rotating a screw inside a barrel to mix, plasticize, and compact the rubber. The material is then pushed toward the extrusion head, where it takes the desired shape through the die. For complex products, multiple extruders can be used together to achieve composite extrusion. Extruders are typically classified into hot-feed and cold-feed types. Hot-feed models use preheated rubber from an open mixer, while cold-feed models do not require prior heating, allowing for simpler and more flexible production setups.
Calender
Calenders are used mainly for applying adhesive or rubber coatings to fabrics, pressing rubber compounds, laminating layers, and embossing patterns. The core component is a series of rotating drums, usually three or more, arranged in a specific sequence. As the rubber enters the gap between the rotating drums, it is stretched and compressed under friction, forming the desired shape or texture. The first calender was introduced in 1857 and has since evolved significantly, especially after the 1950s with the growth of the plastics industry. Today's high-precision, high-speed calenders often include features like roller deflection compensation systems and automatic thickness control via computerized systems, ensuring consistent product quality and efficiency.
Low carbon USS flat washers, typically used with Grade 8 or hardened steel bolting, are used under bolt heads or nuts to increase the bearing surface area, or to offer protection so that the nut or bolt can be rotated without distortion of the bearing surface. Flat washers are also used to give tightness to a joint, to prevent leakage, and especially to distribute pressure under the head of a bolt or nut. Dimensional specifications are governed by ASME B18.21.1. USS (United States Standard) flat washers have a larger outer diameter than SAE (Society of Automotive Engineers) flat washers, and can be utilized in nearly any application. ASTM F844 covers the standard specifications for unhardened steel flat washers for general use. Available in zinc plated finish. Zinc plating sacrifices itself, corroding before the base material, offering added corrosion resistance.
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