About Knit Lines
The plastic injection molding process is simple standard job , plastic raw material is heated to its melting point ( for example ABS resin), it was forced into your injection molds to produce your plastic parts through injection molding machine. The molten material is often the coolest surface and to solidifying at all of leading edge .
When the molten plastic meets an obstruction, then the flow resin must travel around and meet at the other side. It can easy happen knit lines on plastic parts surface when they meet past an obstruction, If the plastic has too much cooling during the plastic injection molding process.
Cnmoulding technicians try to minimize any knit lines, but we must balance this with other challenges like avoiding sink mark or blush, to achieve the perfect surface. So what we can do to help avoid knit lines happen when designing the new part at beginning.
Here are a few things to consider. First, thicker walls will slow down the cooling rate of the resin and thereby help to improve the appearance and strength of any knit lines. Second, the resin you select may make a difference. For example, unfilled materials will tend to have stronger knit lines than filled materials. In fact, knit line strength will decrease with higher filler content as well as with longer fibers. In addition, materials that that tend to outgas a lot (e.g. Santoprene) or contain additives like flame retardants, lubricants and mold releases can further exacerbate the problem. Third, it may be possible to improve the situation by working with Cnmoulding to optimally place the gate(s) so that the knit lines are minimized or moved to a less critical area.
Knit lines are most common downstream of holes created in parts where the molten material meets. While knit lines can be present it does not always mean the structural integrity of the plastic part is compromised.
If you are concerned about potential knit lines, turn to the mold flow of your part and address any design issues that can be easily modified, second review similar materials that may be less prone to show knit lines.
With good part design and mold design with right gate point , knit lines can often be reduced