Plastics Technology

JUL 2017

Plastics Technology - Dedicated to improving Plastics Processing.

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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. in. Therefore, a standard 9/32-in. sprue-bushing orifice would work nicely in this example. When selecting the orifice size for parts that are direct sprue gated, I like to think of what size I would use if it was edge gated, because the bushing orifice is effectively the gate. I then calculate the area of that gate and convert it to the equivalent diameter. For the part above: 0.060 x 0.120 in. gate = 0.0072 in 2 . That converts to about a 3/32-in. sprue-bushing orifice. The examples above are intended to help you estimate the best sprue-bushing orifice size, so as to prevent excessive shear and injection pressure. But we are also concerned about reducing the mass of plastic at the parting line. If the material has a low viscosity, such as with many unfilled nylons and polyolefins, you may not have an issue using a smaller sprue orifice. Finite- Element Analysis (FEA) can help predict whether the orifice size will be a problem or not. In lieu of that, it is often a good idea to start off with a slightly smaller orifice. If you end up fighting sink, burns, or high peak pressures during the initial mold sampling, you can always increase the steel-safe orifice size later. Reducing a sprue bushing's overall length, internal taper, and orifice size can drastically reduce the mass of plastic at the mold's parting line. These improvements reduce the weight of the sprue and often the cycle time RETHINK FILTRATION NO MOVING PARTS. NO HYDRAULICS. NO LEAKS. • Consistent process pressure and homogeneous melt temperature are maintained due to constant differential pressure across the screen • Minimal polymer residence time with streamlined flow paths • Low maintenance, economical to operate, minimal operator intervention • The system's 120' roll of filter screen advances automatically, delivering many months of operation with no process interruptions HITECH ™ continuous filtration systems for thermoplastic resins are designed with a small footprint and high level of process integration. The Leader in Continuous Melt Filtration Since 1969 WWW.NORDSONPOLYMERPROCESSING.COM EXTRAORDINARY TECHNOLOGIES FOR TODAY'S PLASTICS 'On-the-fly' layer ratio adjustability increases up-time and precision, allowing for greater end product versatility Integrated profiling actuators with interchangeable bars allow for thickness uniformity of individual layers to be finely tuned Optional larger tha n standard channel widths reduce shear stress and enhance end product quality The EDI ® Ultraflow ™ V-T Feedblock Cutting Edge Technology to Meet Your Coextrusion Needs @plastechmag 31 Plastics Technology T O O L I N G

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