Why do pinholes appear on the surface
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This post was last edited by pop2000911 on 2015-7-17 at 19:35. While preparing epoxy AB adhesive, it was found that too much defoamer from BYK had been added to the formula. After making calculations to adjust the amount to that of a normal formula, it was observed that while the product made using the normal amount of the defoamer had a very smooth surface, the product made with the adjusted amount had many pinholes on its surface. I’m not sure how to resolve this issue; please **help me, thank you!
Mainly, the flow velocity is too high, exceeding the speed of sound; the pressure drop during venting is greater than the critical flow pressure drop, and the energy is converted into noise.
Bubbling occurs first and foremost because there is air inside. This situation arises when the instructions in the product formula are not followed properly. Another possibility is that the area to be repaired was not cleaned thoroughly, nor was it made rough by grinding it; environment and temperature also play a role. Generally, the product instructions will guide you on the proper mixing methods and processing times.
Maybe I didn’t explain it clearly. For example, in a normal formulation, the amount of defoamer is 1%; now I have increased this amount to 3%. So by reducing the volume of the current formulation by 3 times and then adjusting the amounts of the other ingredients back to 1% as in the normal formulation, pinholes will appear on the surface of the adhesive.
Under normal circumstances, as long as the proportions are followed strictly, pinhole defects generally do not occur. However, it is also necessary to take appropriate measures based on the environmental conditions and temperature at the time, such as applying heat or using thicker materials.