Last summer, the plant obtained a new process machine. A hopper pours plastic pellets in one end, a few pipes add metered amounts of specific chemical additives, and the “premixture” is heated in the mixing tank. Once the pellets are melted and mixed with the additives, the mix is extruded and then cut at precise intervals to make blanks. In the next section, the blanks are machined; out come the finished parts. These are very high profit, except when the parts come out bad.

Unfortunately, the parts have been coming out bad far too often lately. The production manager insists there is a problem in the heating section, but an electrician confirmed the heating elements run for the desired time and that the supply voltage is correct. No problems were found with how the additives are metered, and the mixer is operating properly. Can you solve this?

This could be a design problem. If the process heaters are also expected to overcome cold ambient air blowing onto the mixer, install a mechanical barrier.

Determine the temperature of the pellets as they sit in the hopper. It may be necessary to preheat them. Low winter humidity may trigger excess static electricity among the plastic particles. If this is the case, there are products that discharge static. You may suggest adding oil or water mist to the pellets or an additional heating system to the mixing tank.

Heating elements in contact with the mixture can become covered in precipitate, thus reducing transfer to the mixture. If that’s your setup, suggest they be pulled and cleaned. If they are dual element heaters, then check both elements.

Monitor for the desired temperature during the whole mix cycle.