How to prevent sink marks from Plastic Injection Mold
You can take the following actions:
1. Make sure your melting temperature is correct
Melting temperature is one of the first parameters we check during processing to make sure the sink is correct. The melt temperature should be within the resin manufacturer's recommendations. If set too high, the chips will take longer to cool, causing sink marks.
2. Modify the packaging and storage time
You want to make sure your hold and hold time is long enough to solidify the plastic at the part gate, preventing any plastic from entering or leaving the cavity. Once the plastic leaves the cavity, you can no longer adjust the shrinkage that occurs during cooling. Sink marks can be avoided by increasing the hold time and double-checking that the door is closed.
3. Avoid excessive mold temperature
High mold temperatures can also cause sinks. If the mold temperature is set too high, the time required for the gate to seal may be affected. Recommended mold temperatures can be found on the resin manufacturer's website. Make sure the mold is connected correctly and once the proper temperature range is set, there should be no water flow issues.
4. Confirm proper part and mold design
When it comes to sinks, waterline positioning is one of the most important parts of mold design. Thicker regions of the part are often sufficiently cooled on the part surface, while the inner regions of the thicker regions are often overlooked. Injecting water into the inside of a thick section can be difficult, but it improves sink, part quality, and cycle time.
Remember, the goal is to provide consistent cooling to the area where the sink is located.
5. Make sure you have enough packing material and keep the pressure
Enhanced packaging and retention may cause more plastic to settle in the sink. If you can put enough plastic into the space with enough tension to eliminate the sink, the particles will no longer pull on themselves.