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plastic weld lines

• 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


contact: jmfalcao@moldplast.com