Page 108 - Injection Molding Advanced Troubleshooting Guide
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10.3 Purging Compounds 93
9. Clean all hoppers and feed lines of any purging compound. Be sure to clean off
any shelves that can trap pellets, such as the edge of the magnet drawer.
10. Begin feeding new material to the machine.
11. Using screw rotate and inject forward to start purging the new color or material
through the barrel. Once any residual color swirls from the purging are gone
the press can be restarted.
12. If using a hot runner mold try raising the temperatures 30–50 °F to improve
cleaning. Use a hot runner safe purging compound to speed manifold cleanout.
13. Note that nozzles and tips can trap material for many shots and it is often faster
to remove the nozzle and tip and clean rather than relying on the purging
action.
10.3 Purging Compounds
There are many commercial purging compounds available on the market. Some
compounds rely on an abrasive scrubbing action, some rely on chemical reactions,
and some use a combination of the two. Experience says that they are well worth
evaluating for impact. To calculate the value of using a purging compound try the
following:
1. Purge with baseline method. Document the amount of time it took from the last
good part to the first good part of the next color. Also document the amount of
material used to make the color change. Finally document the scrap encoun-
tered during and after the color change.
2. After conducting step one, do the same with the purging compound being eval-
uated. Document time to changeover, weight of purging compound used, weight
of material used, and scrap during and after change.
3. Do the math. Even though a purging compound is expensive it may yield a much
cheaper material change.
Because a purging compound is costly, make sure that it is being used correctly. If
using a purging compound everyone must be familiar with the correct procedure.
If someone purges without using the correct procedure they can waste hundreds of
dollars in purging compound, which in turn gives the purging compound a bad
name.
