This is an interesting question, because the lineal mold shrinkage is characteristic percent shrinkage of a plastic between melt processing and the final cooled article. Specifying materials of low shrinkage will make it easier to avoid problems of warpage and to increase dimensional precision of injection moldings. Mineral or glass filled plastics have lower shrinkage and are often specified to reduce molding problems.
Also it depends on several factors.
1. You can work with the same mold, but you need to consider what happening with the cavity surface, due to a great friction inside if try a 50% of G.F., your mold must be have a surface treatments, or special finishing protection, also some time is better use special oil.
2. If the sink marks is continuously you can try to improve some special test runs into the injection molding machine process, I recommend you try with 3-4 different profiles at the second pressure in order to led the flow front advance and fill the cavities more properly.
3. The data of the material that you are using is around of: Linear mold shrink for PA66+30GF 0.2-0.6%
Melt temperature 428-579 °F
Mold temp. 104-140°F
Linear mold shrink for PA66+50GF 0.09-0.11%
Melt temperature 455-590 °F
Mold temp. 104-140°F
Well at this point maybe is better to invite at your material representative or require the complete process data to run most properly, if you want to run some trial there is no problem, also verify the tonnage of your press in order to compare the weight of you parts, maybe if you try to test the next press it will be better, don’t forget, write a notes and compare pressure, weights, temperature and make measurements in some special diameters or bosses in order to evaluate your sink marks tuning.
The article comes from China injection mold manufacturer - Mold Best Assurance Company Limited, website is www.mbamoldanddesign.com
