Q.
Recently we had a problem with too much moisture in our filler and we ended up scrapping a lot of product before the problem was caught. How can we prevent this from happening again?

A.
Although rare, too little moisture in the filler may cause static buildup when used with continuous casting machines. The result can be variable viscosities and feed rates (dry flow problems). When there is too much moisture in the filler, the matrix can be very sticky and difficult to process. The bigger problem is that the matrix won’t cure properly, and you are likely to have porosity problems. If you have large internal pores from moisture, you need to be concerned about the part’s strength. There will be cosmetic issues, too. These parts end up getting scrapped.

All of our products’ moisture content is measured prior to shipment to ensure it is spec. Two primary ways that fillers get out of spec are during transportation and in storage. Filler is not hydroscopic — it doesn’t absorb moisture — however it does have a surface area that water molecules can sit on. If your filler is delivered on a flatbed truck, make sure it has been covered with a tarp just in case the truck passed through a rain shower. The bag doesn’t have to be soaking wet for you to have problems. Store the product in a dry container in a temperature and humidity-controlled environment at your facility. There are expensive electronic tools you can buy to measure moisture content. Usually common sense and a few precautions are all that is necessary.

Bob Baker, Technical Service Director
Calcium Carbonate & Barium Sulfate Products
J.M. Huber Corporation