Drying of materials.

Within our industry we have certain materials referred to as hygroscopic material that absorb moisture and if not properly dried and handled will when processed in this condition destroy themselves physically.

Such materials are Polycarbonate, Polyurethane, PET, nylons…. Etc.

To review what we do in the drying of materials we take out any moisture that is in the pellet that it has absorbed while sitting around. So we shall start our discussion with virgin pellets, material. On this point you may wish to talk to your resin supplier and find out how the material is shipped, and what is the moisture level. Some suppliers ship their resin dry in foil lined, vacuumed sealed containers ready to be used directly out of the bag, box or other container. If that is the case your drying of the material may in fact be wasteful, both from an energy standpoint and also from the point that if the dryer is not correct and or working properly it may contaminate the material with moisture.

So the handling of the bags or containers of your resin now becomes a key issue, as we wish no holes in the bags and lids sealed on containers.

The drying process is based on the following:
a- Airflow over the  pellets,
b- Correct temperature of the pellets,
c- Dryness of the actual air going thorough our pellets (referred to as DEW POINT)
d- Proper residence time exposed to the previous 3 factors.

If we skimp or skip any of the 4 factors in anyway we may not dry our pellets correctly and end up wasting both time, and money.

The basics of drying are stated as:

We heat the pellets up to the proper temperature so as to thermally expand the pellet, this expansion than allows a pathway for internal moisture (H2O) to move. Than we pass air over the pellets that is dryer than the pellets (Dew Point) and the moisture (H2O) leaves the pellet and jumps into the air as it is attracted to this, the air being dryer (has less moisture content) than the resin pellet.

The above statement is what goes on, how you do that and with what types of equipment, maintenance on said equipment and all is how successful you will be.

Thanks for the time, more next time.

TA
Steven L Silvey
Silveys Plastic Consulting
silveysplastics@aol.com
360-882-3183