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  • Material Recovery Issues at Start-Up

    Discussion in 'Plastic moulding' started by PlasticNoob, Aug 7, 2019.

    1. PlasticNoob

      PlasticNoob New Member

      Aug 2019
      Likes Received:
      Our company has ~40 machines and we mostly mold PBTs and Nylons. On some of the PBTs and Nylons it takes up to a half hour to get the material to feed into the screw and purge properly. Once the material starts purging well we have no other process issues once in cycle. We’ve tried raising the rear zone temperatures, hotter feed throat, high/low manual BP, high/low RPMs, pulling the screw back then trying to extrude, starve feeding material, and forcing the material down into the feed section using a piece of wood (seems to work the best but we cannot do this on modern machines as we cannot get to the feed throat due to the large purge shields on the machine).

      Some info on our machines:

      Barrel sizing: 22mm to 40mm

      All electric Roboshots

      GP screws

      This does not happen for every Nylon or PBT, it seems to be just a few grades. It’s not a terrible problem, just annoying and you end up wasting a good bit of time and material trying to get the machine to purge. When we’re having this issue and pull all the material out to look at the screw it is never wrapped and in good condition. Any ideas?

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