It is due to the presence of gas when the BMC substrate is pressurized, which leads to protrusions on the surface of the product.

Possible causes and corrective measures Possible causes and corrective measures Possible causes and corrective measures]:

1, The "dry glass fiber" in the BMC raw material causes voids in the molding compound layup, and the gas collected in these voids may expand into bubbles during molding. To completely correct it, it is necessary to change the process or reduce the glass fiber content when preparing BMC.

2. BMC raw material is contaminated by moisture, oil from the press, lubricating oil or external release agent. It may turn into steam and cause bubbles when it is heated during molding. Calcium carbonate and stearate are hydrophilic substances, so they are easy Contaminated with water.

3. The opportunity to capture air should be minimized. This opportunity depends on the area and location of the BMC paving material. In fact, reducing the area of the paving material is effective. It is effective to place it in the center of the mold like a pyramid, which can force the air to form. The middle ran ahead of the BMC stream and escaped.

4. When the mold is closed to the final size, the mold clamping speed should be reduced as much as possible. A lower mold clamping speed will reduce the agitation of the material and weaken the chance of trapping air.

5. The above-mentioned lower mold closing speed, if combined with a lower mold temperature, can lead to a flatter flow and less pre-gel, which also reduces the chance of trapping air, but the curing time must be lengthened.

6. It is effective to reduce the molding pressure, which can form a flatter material flow and reduce the chance of trapping air.

7. Check the parallelism of the mold installation and the parallelism of the press itself. Due to the mis-installation of the mold, the agitation of the material flow (uneven flow) will increase the chance of trapping air.

8. Excessive initiator or polymerization inhibitor can cause pregelation and uneven flow. Similarly, low shrinkage additives can also cause gas generation. At this moment, it is necessary to improve the BMC formulation.

9. The viscosity of the material greatly affects the material flow, so it is necessary to adjust it to an appropriate range, and usually pay attention to the extent to which different viscosity levels will affect the location and frequency of bubbles.

10. The variable cross-section and variable-thickness parts of the product can change the flat material flow, and the excessively thick cross-section cannot get sufficient heat and pressure during curing. For this reason, the product design can be reviewed.

11. Generally, the air trapped in the molding process will cause the product to suffer from lack of meat, spontaneous combustion and bubbles. Therefore, proper discharge flash is necessary to facilitate exhaust.

12. Excessively dry mass makes the material flow unstable, leading to pre-gelling, pinholes and air bubbles.