The bubble problem in the cross-section of the insulation layer during applications for two-stage vacuum extruders is a common quality defect. It not only affects the appearance quality of the product, but also may reduce the insulation performance and mechanical properties of the product. Therefore, solving this problem is important for improving product quality and production rate. The following is a detailed analysis and treatment measures for the bubble problem in the cross-section of the insulation layer when applying for two-stage vacuum extruders.

I. Analysis of the Causes of Bubble Formation

Material issue:

Rubber materials may contain moisture or volatile substances during mixing, storage and use. These moisture or volatile substances evaporate and form bubbles when heated during the extrusion process.

Low-molecular-weight volatile substances in rubber materials are also prone to volatilization during the extrusion process, forming bubbles.

If the additives or fillers in rubber materials are not evenly dispersed, it may also lead to the formation of bubbles.

Mold design issues:

Improper setting or blockage of the exhaust holes in the mold leads to the inability of the gas generated during the extrusion process to be discharged smoothly.

Incorrect design of the mold runner causes the rubber to flow unsmoothly during the extrusion process, generating vortices or retention zones, thereby triggering bubbles.

Process issues:

Both excessively high and low extrusion temperatures may lead to the formation of bubbles. Excessively high temperatures will accelerate the volatilization of low-molecular-weight volatile substances in rubber, forming bubbles. If the temperature is too low, it will cause poor fluidity of the rubber and poor exhaust.

The extrusion speed is too fast, and the rubber's residence time in the extruder is insufficient, resulting in inadequate plasticization and exhaust.

Insufficient vulcanization time, improper vulcanization temperature or insufficient vulcanization pressure may also lead to the formation of bubbles.

Ii. Handling Measures

Material control

The quality of raw materials is strictly controlled. Rubber materials are dry and free of moisture before mixing, and the content of volatile matter meets the standards.

Select appropriate additives and fillers, and consider the impact of their dosage and dispersibility on bubble generation when designing in multiple regions.

Pre-treat rubber materials, such as vacuum drying or heat drying, to remove moisture or volatile matter from them.

Mold optimization

Correctly design the exhaust holes of the mold to ensure smooth exhaust. The location, quantity and size of the exhaust holes should be correctly designed based on the flow characteristics of the rubber and the performance of the extruder.

Optimize the design of the mold runner to avoid the generation of vortices or retention zones. The runner should be as smooth as possible without dead corners to ensure that the rubber flows smoothly during the extrusion process.

Regularly maintain and service the molds, clean the impurities and residues in the exhaust holes and flow channels to prevent blockage.

Process adjustment

According to the characteristics of the rubber material and the performance of the extruder, correctly set the process parameters such as extrusion temperature, speed and pressure. The extrusion temperature should be controlled within the plasticizing temperature range of the rubber to avoid being too high or too low.

Appropriately increase the rotational speed and back pressure of the extruder screw to enhance the plasticization degree of rubber and the exhaust effect.

Strictly control the vulcanization time, temperature and pressure to ensure that the rubber is fully vulcanized. The vulcanization time should be correctly set according to the thickness of the rubber and the vulcanization temperature. The vulcanization temperature should be controlled within the vulcanization temperature range of the rubber to avoid being too high or too low. The vulcanization pressure should be large enough to ensure that the rubber closely adheres to the mold during the vulcanization process.

Other measures:

A degassing device, such as a vacuum degassing device, is installed before the extruder to remove gases and volatile substances from the rubber.

Regularly maintain and service the extruder, clean impurities and residues from components such as the screw, barrel and hopper to prevent contamination of the rubber.

Increase employee training, enhance the skill level and quality awareness of operators, and ensure the stability of the production process and the consistency of product quality.

To sum up, solving the bubble problem in the cross-section of the insulating layer during applications for two-stage vacuum extruders requires approaches from multiple aspects such as material control, mold optimization, and process adjustment. By taking comprehensive measures, the generation of bubbles can be reduced, and the quality of products and production rate can be improved.

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