Powder Particle Size

Q. We are currently using an epoxy powder and are considering purchasing powder sieves to determine what percentage of fines, and median and coarse material is present in our powder. We have had a company quote the shaker and the screens, but are unsure what size the screens should be. Are 10-, 35- and 55-micron screens sufficient, or do we need to consider other sizes?  –M.C.

A. You will have difficulty getting a detailed particle size analysis using a series of screens, as the particles will vary widely from top to bottom. You will have powder ranging from as small as 5 micron to as large as 120 micron. The percentage of small particles will likely be very small, and you may have difficulty getting them to work through the screen.

You could get a laser particle size analysis from the supplier to see the actual full range by percentage, or you could have an independent source do the analysis for you. The resulting graph will tell you far more than a series of screens. However, I understand that owning a machine for your own regular use is not practical. 

If you proceed with the screens, you should be looking primarily at the fines, particles below 20 micron and particles below 10 micron. You may also want to see how much coarse powder you have, so something around 60 micron would be useful to determine the material larger than that size. I would have 10-, 20- and 60-micron screens to separate the coarse and fine particles. If you want one additional size in the mix to better determine the mean, I would go with a 35-micron screen.