Preliminary preparations
Selection of raw materials and formula design
Selection of raw materials
The primary material for automotive sealing rubber strips is rubber, with common varieties including EPDM (ethylene propylene diene monomer), silicone rubber, and Neoprene. Among these, EPDM is the preferred choice for external sealing components due to its exceptional weather resistance and ozone durability.
Formula optimization
By considering the specific application areas of the sealing rubber strips-such as vehicle doors, windows, and engine compartments-and their performance requirements, including high and low-temperature resistance, oil resistance, and high tensile strength, we precisely regulate the weight ratios of raw materials through computer-controlled formulations to ensure optimal performance.
Raw material pretreatment
Solid raw materials must be ground and screened to ensure uniform particle size; liquid raw materials require filtration to remove impurities; rubber raw materials should be pre-softened to improve subsequent mixing efficiency. For reclaimed rubber, desulfurization treatment is also necessary to restore its elastic properties.
Core processing
Rubber compounding process
A batch of rubber compounding
Add the base rubber and auxiliary materials such as fillers, activators, plasticizers, and antioxidants into the machine in sequence. Under conditions of high pressure and temperature, the materials are mixed and vulcanized. The high-speed rotation inside the machinery ensures thorough blending of the raw ingredients, while maintaining the temperature between 120°C and 150°C to prevent premature vulcanization of the rubber due to excessive heat.
Two-stage rubber mixing
The initially processed semi-finished compound is then re-mixed with key additives such as accelerators and vulcanizing agents. During this stage, strict temperature and mixing time controls are essential to prevent premature decomposition and deactivation of the vulcanizing agents. Once blending is complete, the material is further processed through an open mill for mastication and cooling. The resulting compounded rubber is then cut into strips that meet extrusion specifications, ready for the next production step.
Molding and processing
Extrusion and vulcanization process
This stage involves processing the mixed rubber into rubber strips with specific cross-sectional shapes and vulcanizing them to achieve stable elastic properties. It comprises two main steps: extrusion molding and vulcanization curing.
Extrusion molding
Single extrusion: Is suitable for simple-sealed profiles, such as standard automotive window seals. In this process, compounded rubber is fed into a single-screw extruder. The screw's helical motion pushes the material forward, heating and plasticizing the rubber within the barrel. The softened material is then extruded through a die of specific shape to produce the preliminary profile of the rubber sealing component.
Composite extrusion: This technique is suitable for sealing strips with complex structures. It involves using a multi-screw extruder to concurrently feed different types of compounded rubber or a combination of compounded rubber and metal core into the extruder head. At the die, high-pressure co-extrusion is applied to produce a multi-functional composite rubber strip that seamlessly integrates various material properties.
Vulcanization curing
The extruded rubber strip remains in a thermoplastic state and requires vulcanization to induce cross-linking of the rubber molecules, thereby forming a stable elastic network. The vulcanization process demands precise control of temperature, pressure, and time: typically, temperatures range from 160°C to 200°C, pressure from 1 to 2 MPa, and duration from 4 to 8 hours. These parameters are adjusted according to the rubber formulation and product thickness. In the case of sponge rubber sealing strips, vulcanization also involves the decomposition of foaming agents, resulting in a uniform porous structure that enhances sealing elasticity and vibration damping performance.
Post-processing
Rapidly quench the vulcanized rubber strips in a cold water bath to stabilize the molecular structure and prevent deformation caused by gradual cooling. Once cooled, employ a hot air drying system to remove surface moisture, thereby preventing mold growth or surface defects during subsequent processing.
Cutting and trimming
Precisely cut and edge-trim rubber strips according to product size specifications after cooling:
- Cutting: Utilize multi-station integrated processing equipment to synchronize the cutting process with the rubber strip's movement, ensuring smooth, accurate cuts and consistent dimensions.
- Finishing: Remove burrs and flash generated during vulcanization.
For seal strips that require on-site assembly, such as door frame seals, joint treatment is necessary. The ends of the cut rubber strips are faced together and bonded through molded vulcanization to form a seamless ring, ensuring the joint strength matches that of the main body.
Based on the product functional requirements, some sealing strips require reprocessing:
- Velvet Lamination: Embedding nylon fibers onto the surface of the sealing strip to reduce friction against vehicle glass and enhance sound insulation; commonly used for window guide rail seals.
- Coating Treatment: Applying abrasion-resistant or waterproof coatings to improve durability and water resistance of the product.
- Deodorization: Spraying deodorizing agents onto rubber surfaces to eliminate residual odors from raw materials, thereby improving in-cabin comfort.
- Functional Integration: High-end vehicle sealing strips incorporate sensors to enable real-time monitoring of sealing performance.
Quality inspection and warehousing
The testing encompasses multiple aspects, including appearance, dimensions, physical properties, and functional performance. The key inspection criteria and standards are as follows:
- Appearance Inspection: No cracks, bubbles, burrs, or color inconsistencies; flocking or coating application should be uniform.
- Dimensional Inspection: Cross-sectional dimensions and length tolerances must meet design specifications, measured using precise tools such as calipers and optical comparators.
- Physical Property Testing: Tensile strength (in accordance with GB/T 528), compression set (per GB/T 7759), hardness (Shore A, following GB/T 531.1), and tear strength are evaluated using universal testing machines, Shore durometers, and similar equipment.
- Functional Performance Testing: Sealing effectiveness (leakage tests), weather resistance (simulated UV exposure and temperature-humidity cycling in aging chambers), oil resistance (immersion tests), low-temperature flexibility (bend tests), and high-temperature aging tests.
- Environmental Compliance Testing: Odor assessments (to control scent levels), volatile organic compound (VOC) emissions testing, ensuring standards for automotive interior environmental safety are met.
Qualified products are packaged using waterproof and dustproof materials such as polyethylene bags and cartons to prevent scratches or deformation during transit. The packaging is clearly labeled with the product model, specifications, and batch number. Storage is then carried out in temperature-controlled, dry, and well-ventilated warehouses, avoiding direct sunlight, high temperatures, and humid conditions to prevent premature aging of rubber components.
