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would you expect to see? Now if you put a tip with a rectangular orifce that was thin and wide, what would the fow look like? The diference is pretty drastic between a small, straight, jetting stream and a fanned-out stream. With the thin-and-wide concept I have been able to reduce cycle times with a quicker gate seal, maintain or reduce fll pressures, eliminate high gates or vestiges on cashew gates, help minimize gate blush, eliminate jetting, elimi- nate pulls, and eliminate faking. One example is a PC/ABS part where I was addressing high gate marks. It had a cashew gate with a 0.040-in. diam. orifce. We changed the orifce from 0.040 in. round to a rectangular shape of 0.020 x 0.080 in., which increased the gate volume. In this case we not only were able to help reduce the high-gate defect but were able to drop the fll pressures from 16,000 to 11,000 psi. This created a larger process window on a part that had struggled with fash and shorts. In another example we were able to eliminate two defects—jetting and pulls—on a larger glass- flled PP part that was causing a lot of scrap. The 750-ton tool had no process window allowance to address the defects. The part had two cashew gates with 0.110-in. diam. round orifces. In this case I could go thinner but not wider because the geometry of the taper would not allow it. I started by welding up the orifce and going from the 0.110 in. round to a 0.050 x 0.110 in. rectangle. I was concerned about increasing fll pressures because I was reducing the orifce volume. When we ran the tool after the change there was no increase in fll pressures. Jetting was improved but we still had some issues with the pulls. The pulls were the result of the part shrinking away from the gate area before ejection. So, we had another idea: If we made the gate thinner than 0.050 in., would it break while the part was shrinking away, reducing the pull defect? Because the frst change had no impact on fll pressures we thought it was worth a shot. We welded the gate orifce and reduced it from 0.050 x 0.110 to 0.025 x 0.110 in. This time around our fll pressures did increase from around 10,000 psi to 13,000 psi but the pulls were eliminated and the process window drastically improved, with less jetting and thou- sands of dollars in scrap savings. I worked on a program of PP parts that were having high-gate issues. In this case the cashew gates were 0.040 in. diam. We went to 0.020 x 0.080, and the high gates were eliminated, and there was no increase in fll pressures. GATE SIZE, SHAPE & TAPER Accompanying images show geometry alternatives to the industry standards. The D-gate style sub-gate versus the standard simulates the thin/wide concept and will provide much cleaner gate breaks than the standard sub-gate. And with this style in one case I was able to reduce gate-seal time by 5 sec, saving an equal amount in overall cycle time. Another important part of the gate geometry is the mass and taper leading up to the orifce. It should always taper down to the orifce to prevent fow restrictions. If it doesn't it can cause an increase in fll pressures and in some cases fow imbalances. One example of this was on a two-cavity mold with sub-gates. This mold had a righthand and lefthand part that were exactly mirrored so there was no diference between cavity size but the cavities were signifcantly unbalanced. I was asked to open up the sub-gate orifce on the cavity that was short even though the gate orifces were the same size (not always a good idea). After opening the orifce to where Get more insights on tooling from out expert authors: short.ptonline.com/toolingKH Learn more at PTonline.com KNOW HOW TOOLING Making a gate thinner and wider often has positive results on flling and part quality without narrowing the process window. Two real-world examples in which a round cashew-type sub-gate was replaced with a thinner gate to address flling problems. In the example at right, the gate was made thinner and wider, enlarging the total orifce area and reducing pressure to fll—and it eliminated the high-gate issue. In the example on the left, part geometry required making the gate thinner but no longer than the original gate diameter, reducing the total orifce area. Filling pressure did increase, but jetting and pulls were reduced. Ø 0.040 in A= 0.001257 in 2 Ø 0.020 in x 0.080 in A= 0.001514 in 2 Ø 0.025 in x 0.110 in A= 0.002616 in 2 Ø 0.110 in A= 0.009503 in 2 Area = 0.002 sq.in. 0.033 Here is an example of a standard subgate with a 0.060- in. orifce. The standard subgate has an eliptical orifce, which is not best suited for a clean break. It also can affect pressure with the taper, while the D-gate style has more mass before the orifce and not the gradual taper. 0.060 Area = 0.002 sq.in. 36 DECEMBER 2014 Plastics Technology PTonline.com T O O L I N G K now How