- molds and plastics  injection troubleshooter -



• Weld Lines- plastic injection troubleshooter


• Description:

These lines occur where two plastics flow fronts in the mould meet. The streams of plastic should be hot enough to fuse adequately.

Weld lines are not just surface marks, but can be points of weakness: notches, stress raisers.


• Causes:
part · wrong part design
machine · injection speed too slow
· injection pressure too low
· injection time forward too short
mould · mould too cold
· insufficient venting
· inaccurate functioning of back flow valve
· distance from gate excessive
material · melt too cold


• Actions:

1st. increase injection pressure
2nd. increase injection hold time
3rd. increase injection speed
4th. raise melt temperature by increasing cylinder temperatures
5th raise mould temperature
6th check for proper venting of the part
7th vent the cavity in the weld area
8th provide an overflow well next to the weld area
9th change gate location to alter flow pattern
10th increase gate and/or main runner system
11th reduce gate land length
12th spot heat particular area with thermal pins or cartridge heaters
13th use textured surfaces


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