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Analysis of defects and causes of BMC products
Release time:
2023-07-01
The protrusion on the surface layer of the product is caused by the appearance of gas when pressurizing the BMC substrate.
Possible Causes and Corrective Measures Possible Causes and Corrective Measures Possible Causes and Corrective Measures]:
1. The "dry fiberglass" in the BMC raw material causes voids in the molded plastic layer, and the gas collected in these voids may expand into bubbles during molding. To completely correct the situation, it is necessary to change the process or reduce the content of glass fiber in the preparation of BMC.
2. BMC raw materials are contaminated by moisture, press oil, lubricating oil or external mold release agent, in the molding heat may be converted into steam and lead to bubbles, calcium carbonate and stearate are hydrophilic substances, so it is easy to be contaminated with water.
3. The opportunity to capture the air should be reduced to a minimum, this opportunity depends on the area and location of the BMC material, in fact, the use of reducing the area of the material, similar to the pyramid like laying on the central part of the mold is effective, can force the air in the molding to run in front of the BMC material flow and escape.
4. When closing the mold to the final size, should try to slow down the closing speed, lower closing speed will reduce the material agitation and weaken the opportunity to capture the air.
5. These lower closing speeds, if combined with lower mold temperatures, result in flatter flow and less pre-gel, also reducing the chance of air trapping, but the curing time must be increased.
6. Reducing the molding pressure is effective in creating a flatter flow and reducing the chance of air trapping.
7. Check the parallelism of the mold installation and the press itself. Because the mold installation is not level will cause the material flow of the churning (uneven flow) will increase the chance of trapping air.
8. Excessive amount of initiator or polymerization inhibitor can cause pre-gel and uneven flow, similarly, low shrinkage additives can also cause gas generation, at this moment, improve the formulation of BMC is necessary.
9. The viscosity of the material greatly affects the material flow, so it should be adjusted to the appropriate range, usually focus on the different viscosity levels will affect the extent to which the location and frequency of bubble occurrence.
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2023-07-01
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