Material handling continued

In the previous articles, we have taken the material through the entire system to the point of making parts. At this point it now becomes a choice, one do you have scrap, or two you make entirely good parts. If you do make entirely good parts, with no scrap than you are done until next month, but if you do have that occasionally product than how it is handled is of a concern.

Runners and the occasionally non-acceptable parts can be reground and in some cases, the material can be added back into the material stream. If the addition of regrind is on a continuous basis than a beside the press granulator is something that may be in service and hopefully feeds automatically into the material stream at a consistent amount.
In some cases if the material is hygroscopic and the material is ground immediately upon begin molded than the drying of the material may be avoided as it has not adsorbed any moisture, and may be added immediately to the material stream.

If the shop takes its scrap and than grinds later, it is important to try to keep it as clean as possible. In many shops, this is where the contamination of the material happens. Sprues, non-conforming parts are tossed into the cardboard box and than when the box is full they are stacked in an area to await granulation / size reduction and no one has covered or sealed the box / container. Upon time permitting, the material is ground and than stored in barrels, bags, or boxes, awaiting the time it will be reused.

Things to keep in mind;

1) Labeling of all containers with the product number and type/ grade of material. Possibly, even the customer, preprinted labels work. Both for scrap and ground materials.
2) The use of clean containers to hold the scrap and than upon granulation the lining of the container with a clean poly type bag will assist in minimizing the contamination and moisture absorption.
3)  The type of granulator that is used, looking at screen size, blade configuration, RPM, and through put. The other aspect is temperature of the product, if grinding beside the press the material is warmer and thus softer than having cooled completely, resulting in an easier cutting material.
4) Runners: sometimes the runners can entangle giving rise to added difficulties in grinding when done as a secondary approach thus a beside the press grinder if allowed is beneficial in saving time.
5) If parts are non-conforming due to internal contamination such as black specs and other such particulate, do not grind, but toss away.
6) Fine generation can be address with blade sharpness, screen size and temperature of the product being ground.

The above is only a short list of handling the scrap and non-conforming parts. Depending on the method used referring to earlier sections of this series should allow you to re-introduce the material.

As for the finished production, that topic will be address next month.  Thanks for the time.

Steven L Silvey
Sr. Technical Service
General Polymers Division
Ashland Distribution