Plastics Technology

SEP 2018

Plastics Technology - Dedicated to improving Plastics Processing.

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an ejector pin to collapse as a result of the material's plastic pressure on the face of the pin. Let me prove it: Table 3 specifies the maximum unsup- ported length using a Slenderness Ratio of 100 for various size ejector pins— from 1/32 in. up to a full 1.0 in. It then shows how much force it takes for the pin to buckle at that unsupported length. Lastly, it shows how much force is applied to the face of the pins using a ridiculously high plastic pressure value of 40,000 psi. Every pin can withstand two or three times more than this excessive amount of pressure. ABOUT THE AUTHOR: Jim Fattori is a third-generation injection molder with more than 40 years of molding experience. He is the founder of Injection Mold Consulting LLC, and is also a project engineer for a large, multi-plant molder in New Jersey. Contact jim@injectionmoldconsulting.com; injectionmoldconsulting.com. There are several methods you can use to reduce the unsupported length of an ejector pin. FIG 2 walled drill bushing, which I have found to be excellent for this appli- cation. Here's a test: Which ejector pin or pins in Fig. 1 still has/have a good chance of buckling due to excessive unsupported length? Let's revisit the practice of providing lateral float around an ejector pin in the ejector return plate. While it sounds like a prac- tical idea to compensate for any misalignment, one study suggests that this added clearance actually promotes wear of the through hole in the core and reduces the force the pin can withstand before it buckles. If the through hole in the ejector retainer plate has significant clearance, the unsupported length increases by an amount equal to the length of the through hole. For example, ejector retainer plates are usually ½ in.- or 5/8 in. thick. Small- diameter ejector pins have a head thickness of 1/8 in. Therefore, the unsupported length of the pin increases by 3/8 to 1/2 in. That can be a significant amount if the diameter of the ejector pin is 7/64 in. or less, but not much of a concern for pins larger than 1/8-in. diam. As long as you adhere to the maximum unsupported length calculated using a Slenderness Ratio of 100, it is impossible for It is nearly impossible for an ejector pin to collapse due to high injection pressures. @plastechmag 49 Plastics Technology T O O L I N G 525 East Stop 18 Road Greenwood, Indiana 46142 Phone: 317-887-6352 Email: sales@TempTek.com For information online www.Temptek.com Factory Phone 317-887-6352 Outdoor Central Chillers • Complete Outdoor Chilling System with Refrigerant Zones and Pumping System • For Use In Most Outdoor Climates • Central Unit for Plant Wide Cooling for Many Processes • Integral Air-Cooled Condenser Indoor Portable & Central Chillers • Use Inside Plant Facility for Single Process or Plant Wide Cooling • Microprocessor Controller and Display • Small Footprint to save floor space • Environment Friendly Refrigerants • Internal Coolant Reservoir And Cirulation Pump Water Chillers with New Product Warranties, industry recognized components for Maximum Reliability, Economically Affordable capital equipment providing perfect bottom-line returns, and a network of factory trained technicians for Unbeatable Service. • Environment Friendly Refrigerants • Microprocessor Instrument Controls • Non-Ferrous Construction • Small Footprint • Other Products: Temperature Control Units, Pump Tanks, Cooling Towers, Material Dryers, Loaders, Granulators

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