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 should be consider.
- Big thickness part design will slow down the cooling rate of the plastic resin ,so help to improve the appearance of knit line.
- Difference plastic resin selection is one of variable quantity. Fiber glass resin have less knit lines than normal materials,Fiber rought surface will cover knit lines. In fact, additives like flame retardants, lubricants and mold releases can further exacerbate the problem.
- Cnmoulding will optimally place the gate so that the knit lines are minimized ,usually it should move to a less critical area through improve our job.
If you are concerned about potential knit lines happen in your new project ,use CAE software to analyze mold flow of your part and address any design issues that can be easily modified, and review similar plastic resin that may be good way to show knit line position there. Remeber ,good industrial design and injection mold design, improve right gate point , knit line can often be reduced easy.