Defects and Cause Analysis of BMC Products

1、 Bubble

It is due to the gas generated during the pressurization of BMC substrate, which causes protrusions on the surface of the product.

Possible reasons and corrective measures Possible reasons and corrective measures Possible reasons and corrective measures Possible reasons and corrective measures:

The "dry glass fiber" in BMC raw materials causes voids in the layer of molding compound, and the gas accumulated inside these voids may expand into bubbles during molding. To fully correct it, it is necessary to change the process or reduce the content of glass fibers during the preparation of BMC.

BMC raw materials may be contaminated by moisture, oil droplets from the press, lubricating oil, or external release agents. When heated during molding, they may transform into steam and form bubbles. Calcium carbonate and stearate are hydrophilic substances, so they are prone to moisture contamination.

3. The opportunity to capture air should be minimized, depending on the area and location of the BMC material. In fact, reducing the area of the material and placing it in the middle of the mold like a pyramid is useful to force air to run ahead of the BMC material flow during molding and escape.

4. Before closing the mold to the final size, the closing speed should be slowed down as much as possible. A lower closing speed will reduce the agitation of the material and weaken the opportunity to capture air.

5. If the above lower mold closing speed is combined with lower mold temperature, it can lead to smoother flow and less pre gel, and also reduce the opportunity to capture air, but the curing time must be longer.

Reducing the pressure of molding is useful as it can create a flatter material flow and reduce the chance of capturing air.

7. Check the parallelism of the mold installation and the parallelism of the press machine itself. Due to the uneven installation of the mold, it can cause agitation (uneven flow) of the material flow, which increases the chance of capturing air.

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

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

10. Changing the cross-section and thickness of the product can alter the flat material flow, while excessively thick cross-sections may not receive sufficient heat and pressure during curing. Therefore, product design can be reviewed.

11. Usually, the air captured during molding can cause meat shortage, spontaneous combustion, and air bubbles in the product, so appropriate trimming is necessary to facilitate exhaust.

12. The excessively dry and hard material mass causes the instability of the material flow, resulting in the feeding of gel, pinholes and bubbles.

Article source: BMC molded products http://www.jmlicheng.com