What is a rubber compound? A rubber compound is like a formula that gives rubber its unique properties. It is made by mixing raw materials such as natural rubber, fillers and additives. The process is similar to cooking – choosing the right ‘ingredients’ according to the desired qualities. During the mixing process, these materials are blended into a rubber with specific properties. Depending on how it is mixed, the rubber can be flexible, heat-resistant, oil-resistant or abrasion-resistant.
Rubber compounds are used in many industries, such as automotive seals, tyres and aerospace parts. They can cope with challenges such as high temperatures and ageing. This makes them the material of choice for many tough jobs. Now, let’s take a closer look at the mixing process behind rubber compounds and see how they are made.
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Mixing process for rubber compounds
The mixing process is a key step in the production of rubber. In this process, different materials are mixed together to give the rubber the desired properties. Let’s take a look at the basic steps, the important equipment used and how the properties of rubber can be improved during the process.
Basic steps in rubber compounding
Compounding: First, natural or synthetic rubber is mixed with fillers, additives and vulcanising agents. Each material is added according to a specific formula to ensure the desired balance of properties is achieved.
Preliminary mixing: The rubber and fillers are mixed in a machine to ensure that the materials are evenly distributed.
Fine Mixing: The mixture is heated and pressed to fully mix the materials. At this point, the vulcanising agent is added carefully to avoid early reactions.
Plasticising and granulating: After mixing, the rubber compound is pressed into flakes or granules to facilitate processing and moulding.
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Key equipment in the mixing process
Rubber Mixing Mill: This machine mixes the raw materials at high temperature and pressure. Depending on the process, there are two types of mixers, open and closed.
Tablet press: This machine presses the rubber compound into tablets for subsequent steps.
Granulators: Granulators are used to make the rubber compound into granules, making it easier to store and transport.
Optimising rubber properties during compounding
The properties of rubber can be improved by controlling the temperature, time and sequence of mixing. For example, if the temperature is too high, the additives may react prematurely and affect the vulcanisation. If the mixing time is too long, the structure of the rubber may be damaged, reducing its quality. By carefully managing these factors, the flexibility, heat resistance and durability of rubber can be improved. Special additives can also be used to improve properties such as UV resistance or chemical resistance.
Common rubber compounds and their properties
Natural rubber/styrene-butadiene rubber/butadiene compound (NR/SBR/BR) is a widely used compound in the tyre industry. It combines the elasticity of natural rubber with the abrasion resistance of synthetic rubber, making it ideally suited to withstand the stresses of uneven road surfaces.
Styrene-Butadiene Rubber/Butadiene Blend (SBR/BR) is mainly used in products such as shoe soles, seals and rubber belts. Due to its good abrasion resistance, this compound is used in a wide range of everyday products.
Ethylene propylene diene monomer rubber (EPDM) is known for its superior heat and UV resistance. It is commonly used in car seals and electrical wire coverings because it can stand up to tough outdoor conditions.
Chloroprene rubber (CR) and chlorinated polyethylene rubber (CPE) are similar but used in different ways. CR is typically used in gaskets and wire insulation, while CPE is better for seals that need to resist high heat and be flame retardant.
Nitrile/Hydrogenated Nitrile Rubber (NBR/HNBR) is an oil- and chemical-resistant material used in a wide range of tubing and seals, especially in industrial and automotive manufacturing.
Silicone rubber and fluoroelastomer (FKM) offer excellent high-temperature resistance and chemical resistance. They are commonly used in high-end gaskets in the aerospace industry and other high-temperature resistant applications.
Additives to rubber compounds and their role
Additives in rubber compounds play a key role in improving the physical properties and durability of rubber. Here are some common types of additives and their functions:
Processing aids: These act like lubricants, helping the rubber flow smoothly during production. They prevent sticking and cracking, making the process faster and more efficient.
Antioxidants: Antioxidants are the ‘guardians’ of rubber. They protect rubber from air and sunlight and slow down the oxidation process. This property significantly extends the life of rubber products, especially in outdoor applications.
Fillers: Fillers like carbon black and silica not only reduce costs but also make the rubber stronger, harder, and more resistant to wear.. They provide a backbone that improves strength and durability.
Plasticisers: Plasticisers soften rubber and make it easier to mould. They keep rubber elastic at low temperatures, helping it to remain flexible and easy to process.
Vulcanising agents: Vulcanising agents, such as sulphur, are ‘reinforcing agents’ for rubber. They make rubber stronger and more elastic by cross-linking its molecular structure. They also enhance heat and chemical resistance, which is essential in many industrial applications.
Anti-Ozone Agents: Anti-Ozonants prevent ozone from creating cracks in rubber. Anti-ozonants protect rubber from this damage and extend its life in outdoor environments.
Each additive affects the hardness and elasticity of rubber as well as its chemical and heat resistance. Choosing the right additive is like tailoring rubber to meet different needs. This ensures that it performs well in harsh conditions such as extreme temperatures or chemical exposure.
Advantages of custom rubber compounds
Custom rubber compounds are like problem solvers. They are tailored to each project and their composition can be adapted to specific needs. Whether the goal is better heat resistance, greater flexibility or stronger chemical resistance, the formulation can be changed. This ensures that the rubber has the right properties for the job.
By customising formulations, rubber can meet unique challenges. For example, some industries require rubber that maintains its strength at high temperatures. Standard rubbers may not work under these conditions. But through customisation, rubber compounds can cope with extreme temperatures while maintaining strength. This results in more reliable, longer-lasting products.
One example is rubber made for high-temperature uses. In things like car shock absorbers or heat-resistant seals, customized rubbers are used. It include EPDM, which are designed to handle heat and stay flexible. This ensures equipment can run safely for a long time.
Application areas for rubber compounds
Rubber compounds are used in a wide range of industries, with each type meeting different needs based on its properties.
Automotive: Heat- and abrasion-resistant rubber is used in tires, seals, and systems that reduce vibration. Rubber compounds such as EPDM are often used for door seals to ensure protection against the elements.
Construction: Construction relies on rubber materials with durability and ageing resistance. Commonly, neoprene (CR) is used in seals and waterproofing systems to improve the durability of buildings.
Aerospace: Aerospace requires high-temperature, chemical-resistant materials. Fluoroelastomer (FKM) is used in aircraft seals and fuel lines to ensure stable operation in extreme environments.
Manufacturing: Manufacturers use elastic and abrasion-resistant rubbers, such as SBR for conveyor belts and seals, to ensure the efficient operation of machinery and equipment.
By adapting to the needs of different industries, rubber compounds play an important role in various fields, enhancing product performance and service life.
Summary
The versatility and flexibility of rubber compounds provide strong support for many industries. From automotive to aerospace, rubber materials drive a wide range of industries. By choosing the right ingredients and additives, rubber compounds can be carefully adapted This approach meets the specific needs of a wide range of applications. This not only improves the performance of the product, but also extends its service life.
As a supplier of rubber compounding equipment. Crowns Machinery can provide professional customised Rubber Mixing Mills according to different needs. Ensure that your production mixes the rubber compound according to the precise Provide more precise and efficient solutions for various industries.
