Plastics Technology

NOV 2018

Plastics Technology - Dedicated to improving Plastics Processing.

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Contact us for full list and details Scratch/Dent Models available at extreme discounts Tel: 860 496-9603 TEMPRO basic C200 9 kW, ¾ HP DRYMAX E30-70-M (25 lb/h) ATON basic H120-300-M (112 lb/h*) *per an average between Nylon, ABS & PC $1,595 $6,995 $10,795 There is a transition section between the clearance hole and the land area in the core. It is formed by the angle on the tip of the drill bit—typically 118° or 135°. While it's not usually necessary, it is good practice to blend the sharp edges at the beginning and end of the transition. Using a ball mill instead of a drill bit helps, but a tapered reamer is consider- ably better. This prevents the tip of the pin from chipping during assembly—especially if the pin has a texture, engraving, or a contoured shape on the end. Note: When engraving an ejector pin or core pin with a cavity number or other indicia, stay at least 0.020 in. away from the perimeter, especially if the pin is nitrided. If the engraving is too close to the edge of the pin, the pin becomes extremely weak and fragile. If a mold has interchangeable cores and they are "face" or parting-line mounted, the relief holes for the ejector pins should be reamed with a full taper from the back face of the core to the start of the land diameter. Sometimes it's possible to wire-EDM this taper (Fig. 4). This makes it much easier to align the ejector pins to the land diameter without damaging the pins during the changeover assembly. Since ejector pins need to be cut to a precise length, care should be taken to remove any small burrs on the tip of the pin. If you are super meticulous and don't like the aesthetics of the heat-induced blue color on the end of a pin, there are various chemicals avail- able to safely remove it. Several toilet-bowl cleaners work just as well at a fraction of the price. It is not uncommon for the diameter of a boss on a part, or especially on a runner, to be exactly the same as the ejector pin's land diameter. In cases such as this, take a polishing stone and break the edge of the perimeter of the ejector pin—just enough to prevent the sharp edge from digging into the sidewall of the core. A better idea is to make the diameter of the boss at least 0.010 in. larger than the ejector pin. This will also help prevent down- flash as the pin begins to wear or corrode. Clearance holes installed with (l. to r.) a drill bit, ball end mill and tapered reamer or wire EDM. FIG 4 T O O L I N G

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