Secondary Sulfurization Heat Treatment: Methods, Precautions, and Suitable Ovens
Secondary Sulfurization Heat Treatment Method and Precautions
Secondary sulfurization, also known as post-vulcanization or two-stage sulfurization, is a process in which rubber products are further heated and vulcanized after reaching a certain degree of vulcanization, in the absence of heat sources. The goal of this process is to further crosslink the rubber products, thereby improving their mechanical properties and compression set performance. Secondary sulfurization is particularly important for peroxide-cured rubber products, such as nitrile rubber (NBR), ethylene-propylene rubber (EPDM), acrylic rubber, hydrogenated nitrile rubber (HNBR), silicone rubber, fluorine rubber, and fluoro-silicone rubber. This process can further enhance the mechanical properties and compression set performance of these materials.
1. Secondary Sulfurization Heat Treatment Methods
Secondary sulfurization heat treatment mainly involves the following steps:
Preheating: The rubber products are placed in a preheating oven for a preheating process. The purpose of preheating is to raise the temperature of the rubber products to a suitable level for better crosslinking reactions in the subsequent vulcanization process. The temperature and time for preheating are typically determined by the type and specifications of the rubber products, generally ranging from 100°C to 150°C, with a duration of 1-2 hours.
Vulcanization: After preheating, the rubber products are placed in a vulcanization furnace for the vulcanization process. The goal of vulcanization is to cause the rubber molecules in the products to crosslink, enhancing the performance of the rubber. The temperature and time for vulcanization also depend on the type and specifications of the rubber products, usually between 150°C and 200°C, with a duration of 2-4 hours.
Cooling: After vulcanization, the rubber products are cooled in water. The purpose of cooling is to quickly reduce the temperature of the rubber products, preventing deformation and aging at high temperatures. The cooling time typically depends on the type and specifications of the rubber products, generally lasting 10-20 minutes.
Post-treatment: After cooling, the rubber products undergo post-treatment processes such as trimming, polishing, and cleaning to improve their appearance, ensure more precise dimensions, and stabilize their properties.
2. Precautions for Secondary Sulfurization Heat Treatment
When conducting secondary sulfurization heat treatment, the following precautions should be taken into account:
Control of Temperature and Time: The temperature and time during preheating, vulcanization, and cooling must be strictly controlled. Excessive or insufficient temperature or time can negatively affect the performance of the rubber products.
Rate of Temperature Increase and Decrease: During the heating stage, the rate of temperature increase should be controlled to avoid the rubber products experiencing stress due to rapid temperature changes. Similarly, the cooling rate should be controlled to prevent cracking due to sudden temperature drops.
Equipment Maintenance: During the secondary sulfurization process, attention should be paid to the maintenance and upkeep of the equipment. Regular checks should be performed to ensure the equipment is operating properly, and any issues should be promptly addressed.
Proper Stacking of Products: Rubber products should be stacked properly during the secondary sulfurization process to avoid contact between non-working surfaces and separating boards, which could lead to the products sticking together.
Classification of Vulcanization: Rubber products of different types should not be mixed during vulcanization. Products of the same rubber type should be treated together in the secondary sulfurization process to prevent undesirable effects such as discoloration, corrosion, or aging caused by different vulcanization by-products.
Standard Operating Procedures: Operators should strictly follow operating procedures to ensure safety and standardization during the process. Precautions should be taken to prevent fire and explosion accidents.
Safety Measures: Safety should be a priority during secondary sulfurization to avoid fire and explosion risks. Environmental protection measures should also be taken to prevent the emission of harmful gases and wastewater.
3. Suitable Ovens for Secondary Sulfurization
Ovens are essential equipment in the secondary sulfurization heat treatment process. The following are types of ovens suitable for secondary sulfurization heat treatment:
High-Temperature Ovens: High-temperature ovens are suitable for rubber products that require higher vulcanization temperatures. These ovens typically offer a higher temperature range and better temperature control accuracy, which can meet the vulcanization needs of various rubber products.
Hot Air Circulation Ovens: These ovens use hot air circulation to ensure even heating of rubber products during vulcanization, improving the sulfurization effect. Hot air circulation ovens typically have adjustable temperature and time control systems, allowing operators to tailor the settings based on the rubber products' type and specifications.
Smart Constant-Temperature Ovens: Smart constant-temperature ovens use advanced temperature control systems to achieve precise control over the vulcanization temperature. These ovens offer advantages such as minimal temperature fluctuation, fast heating and cooling speeds, which significantly enhance vulcanization efficiency and product quality.
Dedicated Secondary Sulfurization Ovens: Manufacturers, such as Shenzhen Yihexing, produce ovens specifically designed for secondary sulfurization. These ovens are often customized based on the type and specifications of the rubber products, offering higher sulfurization efficiency and better product quality.
Cart-Type Ovens: Cart-type ovens are designed with carts and multi-layer racks, making it easy to load and unload rubber products. These ovens are ideal for large-scale production environments and can help improve production efficiency.
Custom Ovens: For rubber products with special shapes or unique vulcanization requirements, custom ovens can be designed and manufactured to meet specific sulfurization needs.
Conclusion
Secondary sulfurization heat treatment is a crucial process in the manufacturing of rubber products. Proper temperature control, time management, and selection of equipment are essential to enhance the performance and quality of rubber products. When choosing an oven, it is important to consider the type, specifications, and production needs of the rubber products to ensure optimal results. Additionally, safety, environmental protection, and equipment maintenance must be prioritized to ensure the smooth progress of production.