Weld Lines on Plastic Products

Weld  lines(weld mark)  is the very common  defects in the injection molding products.To the untrained eye,a weld line  may seem to be a crack,only a few very simple parts without weld line,it occurred on the most plastic injection parts(usually a line shape or V-shaped slot) ，especially occured whenever using insets,lattices,or multi-point gates.

Why there is weld line on plastic products?

1.plastic products with holes (lattices,round holes,square hole) and inserts or those  complicated structure with uneven wall thickness  can cause the weld lines.

2.plastic melt will form two or more flow filling in the cavity and the welding structure shall be unavoidably formed at the front confluence.

3.low- temprature during the confluence of melt

4.The number and location of gate

5.Poor gas vents(method and location)

6.Too much release agent

How to avoiding  weld  lines?

1.Improving welding temperature to a degree as high as possible,high plastic temperature

2.using one sprue gate,because the molten material doesn’t come from two directions,or change the gate position which can make weld line appear in and inconspicuous place.

3.increase plastic mould temperature,raise the barrel temperature and increase the holding pressure.

4.improving the gas venting

5.use release agent as less as possible

Weld lines affect the parts appearance,influence the products using life,we should do our best to avoid.