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concerns with fll pressures using a 0.007-in.-thick gate. When we ran the new tool with a 0.006-in. ring gate, our fll pressures were touching the limits on the high side. Needless to say, I was surprised because I had not seen this on the prototype, but the production tool was not an apples-to-apples comparison regarding cavitation or part geometry. We increased the gate thickness to 0.012 in., ran the tool, and the pressures did not drop at all. It wasn't the gate causing the high pressures. Now think in reverse, If we had built the tool with a gate that was 0.012-in. thick and the process was pressure limited, you would have thought I was nuts if I suggested we reduce the gate thickness to 0.006 in. You probably would have bet everything you owned that the pressures would have increased. A thickness reduction of 0.006 in. may not seem like much, but it was a 50% reduction in gate volume. ABOUT THE AUTHOR: Randy Kerkstra has been in the plastics industry for over 26 years, occupied frequently with troubleshooting injection molding. He is currently a tooling manager for a large, multi-plant molding and manufacturing company. You can learn more and ask ques- tions on his tech blog, "Randy's Corner" at nanomoldcoating.com. it had 50 % more volume, I knew something was not right. I looked closely and found the sub-gate tapers were slightly diferent, not enough to be noticeable without very close examination. I increased the taper on the cavity that was short to match the taper on the other cavity. Wow, what a change! The cavity that had been short now flled way ahead of the other cavity. With the D-Style sub-gate the taper is taken out of the equation for fow restric- tions because there is not a gradual taper of mass like the standard sub-gate. You can also sub-gate into angled walls, where when using a standard sub-gate you would end up with a gate vestige. Also, you can gate into shorter walls than with a standard sub-gate. I have gated into cavity walls that were 0.125 in. tall. You have endless opportunities with D-gate orifces. You can increase the tip of the cone on the D-gate to create a wider orifce. It is important to understand the volume of the gate orifce. You can use a much thinner gate orifce because you are increasing volume with the extra width. THINNER CAN BE BETTER Pretty much everyone with whom I have discussed gate geometry over the years automatically assumes you will have an increase in fll pressures if you go thinner in gate dimensions. I have found it's more about volume, which can be maintained by increasing the width whenever I go thinner. Some materials prefer the higher shear with thinner gates. Here's another example: We had a trailing ring gate on an ABS part with only a 0.006-in. gate orifce. On a prototype I had no 0.060 Ø 0.125 Area = 0.005 sq.in. 0.033 Ø 0.125 Area = 0.002 sq.in. The D-gate style sub-gate provides a much cleaner break than a standard sub-gate. It can also gate into shorter walls and even angled walls, where a standard sub-gate would leave a vestige. The two examples pictured show how the dimensions can be varied: The 0.060-in. thickness provides a larger volume than the standard 0.060-in. subgate and the 0.033-in. thickness matches the volume of a standard 0.060-in. subgate but reduces the gate-seal time. High strength. High stiffness. High performance. Period. Structural components are pushing the limits of materials. We've got polypropylene compounds that push back. Customized Resin Solutions ASAHI KASEI PLASTICS @plastechmag 37 Plastics Technology T O O L I N G