We produce PVC WPC foam boards, 52" before trimming.
When we produce boards of 18mm we encounter two major problems at the moment.
1. Dimples (or Dents about 1mm to 3mm in diameter and around 0.5mm to 1mm depth) on the surface of the board, appearing randomly along 4"-6" from both the edges. We tried to increase and also decrease die temperature, turn on and off vaccuum pump. adjust the lip opening thickness. adjust the flow, using the screw, the haul-off. All efforts have failed.
We have tried to increase the water cooling flow rate, and also reduce the flow. decrease the temperature of the chilled water to 12 dec.C. and also increase the temperature to 18 deg.C increase die temperature, all efforts have failed.
I have reviewed your questions and have some possible causes for you.
1) Many times these dimples are caused by trying to force too much product into the sizer. These types of product usually have a die to sizer draw down ratio of 1:1. If you are using a die that is large than this it may be the cause.
2) your shrinkage may be caused by a few things. First would be the foaming agent percentage. If there is too much, the cell structure will collapse in the sizer and cause an undersize dimension and possibly an overweight board. The other possibility is that you are running at a speed that is not matched to the sizer template size. To test this try slowing the line slightly. If it changes, you will need to either slow the process or increase the sizer lengths. The board is not spending enough time in the sizer to maintain size.
I am looking for the equipment produce heat shrink tubing for electrical wires.
Thank you for the question on the heat shrink tubing line equipment. Much of this is homemade but I do believe that Nokia Mallifer has a system available. Reifenhauser also has a system they sell to the shotgun shell manufacturers for making the tubing for the shell body. It is a difficult system to develop but once you have it, it is not too bad to run.
I hope that helps.