Eight main causes and solutions for bubbling after vulcanization of rubber products

Rubber materials become damp during mixing, storage, or use, or moisture is not removed due to weather changes. During mixing, the moisture evaporates, forming bubbles. Batch differences in raw materials can also cause problems.

• Replace the batch of damp raw materials and test the suitability of different batches.
• Add a degassing agent (such as silicone oil) or a desiccant (such as calcium oxide) to the formula to absorb moisture from the rubber compound.
• Strictly control the humidity of the mixing and storage environment to avoid exposing the material to a humid environment.

Air is trapped inside the rubber compound during mixing. If the mold lacks venting channels or the venting process is incomplete, the gas cannot escape, forming bubbles or pores during vulcanization.

• Optimize the mixing process: Improve the mixing process on the open mill to reduce gas ingress; break air bubbles on the surface of the rubber compound before feeding; use rubber with higher Mooney viscosity (but a balance must be struck between processing performance and vulcanization strength).
• Mold improvements: Add venting channels and overflow channels to ensure timely gas discharge; perform vacuum treatment on the mold to reduce residual gas.
• Vulcanization process adjustments: Increase the number of venting cycles after mold closing and rationally arrange the venting time interval; improve injection pressure conditions to allow the rubber compound to slowly fill the mold cavity (avoiding insufficient rubber).

Improperly designed or blocked venting holes in the mold prevent gas from escaping during rubber compound flushing; complex mold structure leads to gas accumulation in dead corners.

• Redesign the mold venting system, increasing the number of venting holes or optimizing their location; clean the venting holes regularly to prevent blockage.
• Simplify the mold structure, reduce dead corners, and ensure smooth rubber compound flow.
• For thick product molds, adjust the vulcanization rate (e.g., choose low-temperature, slow vulcanization) to prevent internal gases from being trapped after the surface vulcanization.

Insufficient vulcanization (insufficient time or temperature), insufficient vulcanization pressure, excessive impurities in the vulcanizing agent, etc., leading to gas residue or premature decomposition.

• Vulcanization Time and Temperature: Extend the vulcanization time or increase the vulcanization temperature (within a reasonable range) to ensure sufficient vulcanization; cut open the product to check for a honeycomb structure inside; if present, increase the vulcanization time.
• Vulcanization Pressure: Increase the vulcanization pressure to promote gas expulsion; check the equipment pressure system to ensure stable pressure.
• Vulcanizing Agent Selection: Use a high-purity vulcanizing agent to avoid premature decomposition of small molecule impurities and the generation of gas; after 24 hours of rest, repressurize to reduce the impact of impurities.

Unreasonable material matching in the formula, lack of venting aids; improper use of reclaimed rubber or rubber powder leading to poor dispersibility.

• Adjust the formula: Add reclaimed rubber, rubber powder, or degassing agents (such as calcium oxide) to improve the degassing performance of the rubber compound.
• Add dispersing agents: Optimize the feeding sequence and the number of thin passes to improve material dispersibility.
• Reduce the Mooney viscosity of the compound: Select raw rubber or formulations with low air tightness to reduce gas entrainment.

Poor bonding between rubber and metal causes residual gas to shrink under pressure and diffuse to form bubbles after pressure is released.

• Improve the rubber-metal bonding process, such as surface treatment (sandblasting, applying adhesive), increasing the adhesive layer thickness, or using a specialized adhesive.
• When applying pressure to the bonding area, ensure uniform and continuous pressure to avoid gas residue.

• Pre-treatment of the rubber compound: Before vulcanization, perform several thin passes on the rubber compound, allow it to cure, and then apply pressure again to reduce internal stress.
• Environmental Control: Maintain a clean production environment to prevent impurities from contaminating the rubber compound; standardize the storage management of rubber sheets to prevent external contamination.
• Equipment Maintenance: Regularly inspect vulcanizing equipment (such as flat vulcanizing machines) to ensure precise temperature and pressure control.