Plastics Technology

AUG 2018

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breakage problems. PLASTICS has a publi- cation entitled Classification of Injection Molds for Thermoplastic Materials. It speci- fies that Type 101 and 401 molds must have guided ejection, and this is recom- mended for Type 102 and 402 molds as well. As a point of interest, Mike Noggle and Chuck Brewer Jr., along with Jack Kelly and Jim Atchison, hammered out the details of these mold classifications and assigned their work to the trade association in 1978. Very large molds should have six or eight ejector-return pins—not the typical four. Additional return pins help ensure the ejector plates are pushed back evenly. And if the ejector plates are not tied into the machine's ejector cross, the added return pins will reduce the amount of coining on the face of the cavity plate. This also happens on small molds made of pre-hard or softer steels. Some quick-change mold inserts are supplied with only two return pins and they are considerably smaller than what is required for a long-running mold. Bottom line: To help avoid ejector-pin failure, the ejector plates should travel parallel to the centerline of the mold, and the plates should receive and apply an evenly distributed load. Always equip a mold with all of the possible machine knock- out patterns, and be generous with the rest buttons. 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. Resins: PET, PLA, PP, PS, HDPE Model: HVTSE ® 105mm-52D Rate: 3,500 lb/hr (1,590 kg/hr) Width: 40 in (1m) Gauge: 15 - 40 mils (0.38 - 1.00 mm) Process: Inline thermoforming Twin Screw by Bandera LEADING SHEET EXTRUSION TECHNOLOGY HVTSE ® DRYERLESS ™ EXTRUSION SYSTEMS Processing Technologies International, LLC | 2655 White Oak Circle Aurora, IL 60502 | Tel: 630.585.5800 | Fax: 630.585.5855 G-Series ® Configurable J-Stack roll stands yield superior sheet performance LIW feeders provide quick formulation set-ups and changeovers 100% flake feeding capability minimizes regrind inventory build-up changeovers Thermoforming Conference Sep 18-20 2018 Sep 24-26 2018 BOOTH 101/103 BOOTH 419/421 Cleveland, Ohio Fort Worth, Texas conditions. The core and the support plate are rarely at ambient temperature. Ejector plates are almost always at ambient tempera- ture. If the core plate expands (or contracts) and the ejector plates don't, some of the ejector pins will be out of alignment—typically the outboard ones. It all comes down to what the temperature delta is, and what is the distance between the outboard ejector pins. This thermal-expansion problem can easily be solved by doing two things: First, add cooling lines (water or oil), in the ejector plate. Second, if the ejector plates are guided, mount the guide pins in the support plate—not the ejection clamp plate. My personal preference is to mount the guide pins in the support plate in every mold. If you ever wonder whether you should add a guided ejector system, ask yourself if the plates are heavy, or is the annual number of cycles 100,000 or more. If you answer yes to either question, the ejector system should definitely be guided. Otherwise, you can expect to eventually get premature ejector-pin wear and its associated down-flash sometime during the mold's lifespan. Even if the answer is no, it's still a good idea to help avoid wear and pin 30 AUGUST 2018 Plastics Technology PTonline.com K now How

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