Causes

1. High melt temperatures cause sink marks because the prolong the cooling time of the part. This slows down the coolin of the molten core.

2. If the pack pressure or holding pressure is too low, not enou material will be pushed against the cavity wall. This lack ressure will not supply enough resistance to the molten con shrinking away from the cooler part wall.

3. Lower injection forward time can create sink marks sinc both pressure and time are needed to assure that the part is coole and packed sufficiently.

4. Short cooling times will prevent the molten core of the pa from solidifying creating sink marks.

5. Obstructions in the nozzle restrict flow, underpack the par and also cause sink marks.

6. If the gate freezes off too soon, the part will not pack ou completely, allowing sink marks to form.

7. Smaller cross-section runners, such as half rounds. will cod and solidify faster and as a result restrict flow to the cavity.

8. Mold temperatures that are too cold will set up the skin of th geat much faster than the molten core.

Solutions

1. Reducing the melt temperature will reduce the cooling time of the part and reduce the sink marke.

2. Higher packing pressure or hold pressure will provide more pressure on the cavity wall to cool the skin and core to prevent sil nk marks.

3. High injection speeds increase melt temperature due to high shear, and lowering injection speed will reduce melt temperature and sink mark.

4. Workpieces need enough cooling time in the cavity to solidify the skin and core.

5. Enough shot size needs to be provided to assure that enough material enters the cavity and fills it completel

6. Gate seal time needs to be examined to determine if the gate is freezing off before the cavity is ful.l

7. Moving to larger-diameter runners, such as full round, trapezoidal, and modified trapezoidal runners, will keep the runner more molten and hotter, allowing the material to flow more easily into the cavity

8. Increasing mold temperature will slow down the as dead spots areas where the melt can stagnate.

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