How do we get rid of the mess created from using fumed silica?
Dave Dunn's June 2017 column.
Question: Can you help us to get rid of the mess created from using fumed silica in our silicone and polyurethane adhesive manufacture? It is so lightweight that it covers the entire factory.
Answer: First, you can use vacuum extractors above your mixing tanks to minimize dust getting into the air. However, other methods of handling fumed silica can virtually eliminate dust. Some manufacturers of silicone sealants use completely closed mixing systems, and they can use vacuum to transfer the fumed silicone into these tanks. For the more common mixing systems using open tanks, fumed silica suppliers can provide handling systems that are usually based on using either vacuum or diaphragm pumps to transfer the material directly from large bulk sacks that avoid the use of simple paper sacks. They will often supply these to you as a customer at no charge.
Question: We bond borosilicate glass to stainless steel with an epoxy adhesive. Our production is very slow; we get very strong bonds, but sometimes see cracking of the glass. What can you suggest?
Answer: The problem with this combination of materials is first that you have widely differing coefficients of thermal expansion between the steel, the glass and the epoxy adhesive. The expansion coefficient of the glass is very low compared to the steel, and that of the adhesive is much higher than both. Furthermore, the adhesive shrinks in volume as it converts from liquid to solid. The combination of these factors can cause very large stresses in the bonded assembly, leading to the cracks in the glass, as you’ve seen. I have seen this in the bonding of stainless steel needles in glass syringes.
You can counter this problem by trying to make the adhesive more forgiving from a thermal expansion point of view. Using a glass-based filler might help, and a slightly more flexible epoxy might dissipate the stresses. However, the best way to improve your bonding might be to switch to a UV-cured acrylic adhesive. Toughened adhesives of this type have been used successfully for this type of application for many years. Not only will they give you strong, stress-free bonds, but they will cure in seconds at room temperature and dramatically improve your productivity. ASI
Any views or opinions expressed in this column are those of the author and do not represent those of ASI, its staff, Editorial Advisory Board or BNP Media.