Plastics Technology - Dedicated to improving Plastics Processing.
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processor strategies plastic tooling co. new Drying technology helps Moldmaker get back to Molding if you want something done right, as the old adage goes, sometimes it's best to do it yourself. Ptc Molds of arizona recently found that to be indeed the case, and in the process expanded its position in injection molding by taking on a project that another processor was having diffculty executing. PTC, based in Scottsdale, has been in business more than 40 years, specializing in producing complex, tight-tolerance molds primarily for medical applications. It used to do a lot of custom medical molding as well, before selling off that part of the business about 15 years ago, recalls Phil Mitchell, the former owner of the company who still serves as its president. Since then, PTC's six injection presses have been used primarily for mold validation. Last year, PTC invested more than $250,000 to get back into the molding business. This included purchasing a new Arburg 60-ton machine that was equipped with a Novatec membranetype dryer with a throughput capacity of 5 lb/hr, and Novatec's MoistureMaster, a novel in-line moisture analyzer that debuted last March at the NPE2012 show in Orlando, Fla. This about-face wasn't what Mitchell had in mind when he built a four-cavity mold for a longstanding customer in the molding business. The PBT part, for an undisclosed medical application, is 3/8-in. long with wall thicknesses ranging from 0.006 to 0.060 in. The trouble was, the parts kept fracturing, and the original molder, despite embarking on a stringent QC inspection program, could not determine whether bad material, a poorly designed mold, a snafu in drying, or something else altogether was causing the failures. Convinced that poor material was not the culprit, the customer sent the mold back to PTC and asked the moldmaker to prove that the tool could actually produce the parts to spec. At frst, PTC found that approximately 75% of parts were too brittle to satisfy the OEM's requirements. At that point, Mitchell recalls, PTC got down to business, building a clean room and ordering the new press with the Novatec drying technology. After some initial testing to fnd the optimum moisture content of the PBT needed to make non-brittle parts consistently, PTC was able to mold parts that were virtually 100% defect-free and passed the fracture test. PTC then took over the molding job. 56 february 2013 Plastics technology Novatec membrane dryer combined with the MoistureMaster (left) ensures PBT is fed to the press in the best condition possible for molding a medical part. Above are PTC's Phil Mitchell (right) and Doug Arndt of Novatec. "We cut no corners on this project," Mitchell states. "We look at the MoistureMaster as an 'insurance policy' that gives us confdence the machine is being fed material in the best condition possible." When PTC is ready to start molding each day, it starts up the NDM-5 membrane dryer. It produces the required 250 F process air, at a consistent -40 F dewpoint, without desiccant. After the material reaches the proper temperature and is exposed to the low-dewpoint air, the machine operator flls approximately 1 lb of resin into the MoistureMaster chamber and gets an immediate reading of the moisture content. When the moisture content gets to the required level, the material is fed to the press and molded. Since NPE, Novatec (novatec.com, moisturemaster.com) has invested about $100,000 in its Drying Technology Center in Baltimore, adding four new offine moisture analyzers, reports Doug Arndt, drying systems engineer and MoistureMaster product manager. It has run more than 1000 validations tests of resins such as ABS, PC, ABS/PC, nylon 6, glass-flled nylon 6, PBT, and PUR. The MoistureMaster measures the actual moisture in the resin, so processors no longer have to infer resin moisture values based solely on drying-air temperature and dewpoint (see Close Up article last March). Novatec is the exclusive supplier for MoistureMaster technology in North America. The unit can be retroftted to virtually any drying hopper, silo, material line, or machine throat. By James J. Callari, Editorial Director