Much like finding a contractor experienced in the type of building you need, select a molder that has experience with the resins you are considering. First off, the mold will need to be designed to accommodate the engineered resin. Even with the mold prepared, molders heavily invested in the polypropylenes and other commodity resins need to be educated in the intricacies of engineered resins and composites. Initial quotations that revolve around cycle times will be blown out of the water once experience is gained during the lost project time. Price increases and renegotiated delivery times are not a conversation purchasing departments want to have once projects are handed off from engineering.
The engineered plastics even without additives mold much differently that the commodity resins. Heat, and lots of it, comes into play. Their melt temperatures are much higher, and as such; the downstream issues are magnified:
- The gates utilized to get resin into the cavities get large, sometimes very large. If not, the materials shears badly being squeezed through small openings.
- Even after opening the gates, the fill needs to be slowed down, again to avoid causing surface discrepancies that will be very visibly noticeable.
- The mold will need to be heated to temperatures well beyond what some molders are used to running. From barely warm, molds will and can be heated to 175o, 200o or even up into the 300o’s using hot oil systems instead of water.
If you select composites that add fillers to the engineered resins like fiberglass, carbon fiber or mineral based fillers, your problems may be “compounded” (sorry for the pun) even more.
It is not all negative, molders experienced with engineered resins/composites recognize that they are able to retain their shapes at much higher temperatures that the commodity resins, as such, while fills times are longer and bigger runners/gates means longer packing, parts can be ejected sooner, if you know what you are doing.
If you are contemplating moving to the engineered resins or already have but sense struggles, talk with your molder about the adaptations they have made due to the resin. Perhaps even talk with a molder that works with engineered resins regularly to see what avenues may be untried yet.
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