What to check on with your molder, if you have clear, white, or lightly colored parts

Part of the price you pay your injection-molding provider, includes an assumed or predetermined scrap factor. When your part is clear, white, or light colored, you may be paying extra if the molder has difficulty switching from deeper colored resins to your clear, white, or light colored resin.

Your molder must purge the resin from the prior run to prepare the press for your parts run. The biggest issues are residual resin in some part of the injection system and carbon build-up on the injection components, meaning screw, barrel, check ring, and nozzle.

Evidence that the molder did not switch over resins adequately, will be discolored parts or inclusions of black specs (carbon) in the parts now being run. Most the molder will see during the start-up of the new parts. These will translate into initial scrap you will not see directly, but wrapped into the part cost. Some bad parts appear during the run as both stubborn residual resin or carbon is freed from pockets, gouges or surfaces.

Ask about the purging protocol, injection unit maintenance steps, and between run cleaning procedures. This will give you good feedback  on how controlled the production changeover is conducted. Ask how many different colors and how frequently changeovers are performed from colored to clear. Ask if they have a press dedicated to clear parts. While it is one answer to colorant problems, the carbon spec issue may still exist and the cost may be affected if capacity on that press is not high enough to spread the costs over multiple jobs.

An entire industry exists that helps molders purge from one color to another or clear/light colored parts. Be sure to inquire about it when you are evaluating your molder.