What are the rubber molding solutions -2?

III. Process Operation Factors: If the formulation is a chemical problem, then the process is a physical problem—

how to allow the air entering the cavity and the generated gases to "escape" smoothly. 1. Insufficient or Unstable Vulcanization Pressure

Pressure is the direct driving force for venting gas. Insufficient pressure reduces the solubility of gas in the rubber compound,

 causing it to precipitate and form bubbles. Simultaneously, the rubber compound cannot tightly adhere to the mold cavity,

 leaving gas spaces. Solution: Ensure the vulcanization pressure is stable within a reasonable range

 (e.g., 1.4~3.4 MPa for general molding products, or 10~20 MPa based on equipment tonnage). 

Check the hydraulic system to avoid pressure fluctuations.

2. Improper Venting Operation (Most Critical)

When the mold closes, it acts like a piston. If it closes completely at once, 

the air in the cavity has no time to escape and will inevitably be compressed into the rubber compound.

 Many operators skip or shorten the venting process to speed up the process, which is the main cause of bubbles.

 Solution: Strictly implement multiple venting operations: When closing the mold, 

first use low pressure (or manually) to close it slightly, then immediately release it to allow the gas to escape; 

repeat 2-3 times, and finally increase the pressure to the rated pressure for vulcanization. For thick products, 

appropriately increase the number of venting operations and the venting time interval. 3. Vulcanization Temperature and Time

Excessive temperature will cause rapid cross-linking (scorching) of the rubber compound surface,

 forming a dense "skin" that blocks the escape channels for internal gas and moisture, 

thus creating high-pressure bubbles inside. Insufficient temperature or time will result in under-vulcanization,

 low rubber compound strength, and internal gas expansion pushing up the surface to form bubbles. 

Solution: Strictly follow the vulcanization curve of the rubber compound and avoid blindly increasing the temperature in pursuit of efficiency.

 For thick products, low-temperature, long-time vulcanization is recommended, 

or staged heating should be used to ensure synchronous internal and external vulcanization, 

allowing sufficient time for gas to escape before the rubber compound solidifies.

4. Pre-forming and Loading Process

The shape and weight of the semi-finished rubber compound directly affect venting.

 Too much rubber compound will cause turbulent flow during mold closing, trapping air; 

too little rubber compound will not be able to completely fill the mold, leaving space for bubbles or dents. 

If the pre-formed shape is complex or too large, it may directly block the specially designed venting channels. 

Solutions: 1. Control the weight of the rubber compound within a reasonable range

 (e.g., for a typical flatbed mold, a 15%~20% increase in rubber compound is needed to produce overflow, 

but more is not necessarily better). 

Pre-form the rubber compound into a "blank" shape similar to the mold cavity to prevent the rubber compound from flowing too far and trapping gas during mold closing.

IV. Mold Design and Rubber Molding Equipment Factors: The mold is the final "gateway" determining whether gas can escape. 

1. Defects in Venting and Overflow Channels: If the mold does not have venting channels, 

or if the venting channels are too shallow or blocked by contaminants, air will have nowhere to escape.

 The venting channels must be located at the end of the rubber compound flow (the last place to fill). 

Solution: Properly design venting channels. For high-precision products, 

venting channels with a depth of 0.01~0.03mm can be created on the parting surface. 

Ensure the overflow channel (escape hole) has sufficient capacity, typically 15-20 times the overflow volume, 

to facilitate pressure transmission and gas discharge. Clean the mold regularly to prevent venting hole blockage.

2. Mold Structure and Surface Condition

An overly complex mold structure with dead corners, or insufficient surface smoothness of the cavity, 

will hinder the flow of rubber and the expulsion of gas. Residual mold release agents or oil stains will also volatilize into gas at high temperatures.

 Solutions: Simplify the structure as much as possible, avoiding sharp dead corners. Keep the mold clean and polish it regularly.

 It is recommended to use internal mold release agents (added to the rubber compound) 

to reduce the amount of external mold release agents sprayed, 

preventing their volatilization and gas generation.

3. Lack of Auxiliary Equipment Functions

For high-precision or complex products, the natural venting of ordinary flat vulcanizing machines is often insufficient. 

Solutions: Use a vacuum flat vulcanizing machine. Before mold closing and vulcanization, evacuate the mold cavity to completely eliminate the gas source;

 this is currently one of the most thorough methods to solve the problem of trapped air. V. Special Case Analysis: 

When producing products containing metal parts such as skeleton oil seals and bushings, air bubbles often appear at the rubber-metal bonding interface. 

This is often not a simple venting problem, but rather a bonding failure or interface contamination. If the metal surface is not clean (with oil stains, rust), or the adhesive is not applied evenly,

 gas will accumulate in unbonded areas under vulcanization pressure. Once the pressure is removed, this compressed gas will expand, lifting the rubber layer and forming bubbles. 

Solutions: Strictly adhere to the metal surface treatment process (degreasing, sandblasting, phosphating, etc.). Control the adhesive coating thickness and drying time to avoid contamination. 

Add tackifiers to the formulation to ensure the adhesion between the rubber and the metal can resist the gas expansion force. Summary: For systemic risk management of bubble problems in molding, 

the following troubleshooting logic is recommended: Observe the morphology: Determine if it is random micropores, a single large bubble, or a central shrinkage cavity. Control the source: Check if the raw materials are damp, add calcium oxide if necessary; check if the volatile content of the formulation is too high. Check the channels: Clean the mold venting channels, confirm that the venting holes are not blocked, and that their positions are reasonable. Adjust the process: Slow down the mold closing speed, increase the number of venting cycles, and check if the temperature is too high, causing surface sealing. Modify the design: Optimize the preform shape to avoid the rubber clogging the air passages; consider vacuum equipment for complex parts. Through the above comprehensive adjustments from chemistry to physics, from design to operation, the bubble defects in molded vulcanized products can be systematically reduced or even eliminated.