Plastics Technology - Dedicated to improving Plastics Processing.
Issue link: http://pty.epubxp.com/i/827817
Jeremy Williams has more than 16 years' experience in the plastics industry serving the medical, automotive, furniture, and appliance industries. He previously worked as a principal engineer, taking projects from design concept to saleable products. Jeremy earned his Master Molder II certification in 2011, became an RJG Certified Trainer in 2012, and started at RJG Inc., Traverse City, Mich. in 2016. In addition to his extensive manufacturing background, he holds degrees in plastics and business. Contact 231-947-3111; jeremy.williams@rjginc.com; rjginc.com. WHICH ELBOW PROBLEM DO YOU NEED TO SOLVE? PROBLEM CAUSE SOLUTION Formation of streamers, angel hair and snake skins when conveying plastic pellets Plastic pellets skidding against the outside radius of conventional elbows create friction and heat, melting pellet surfaces. Smart Elbow ® replacements from HammerTek eliminate these problems by eliminating impact Unlike conventional "impact" elbows and "plugged-tee" elbows that rely on material impact to change direction, HammerTek's Smart Elbow ® design features a spherical chamber that protrudes partially beyond the desired 90º or 45º pathway, which causes a ball of pellets suspended in air to rotate, gently deflecting incoming pellets around the bend. No impact means no wear and no fines and no streamers, angel hair or snake skins. Wear and failure when conveying glass-filled, mineral-filled or other abrasive pellets Abrasive pellets hit the outside radius of conventional impact elbows at high speed, continually wearing through the elbow wall. EE-0299 Free, No-Risk Trial Offer See how Smart Elbow® deflection elbows eliminate conventional and plugged-tee impact elbow problems—at no cost or obligation. 1-610-814-2273 sales@HammerTek.com www.HammerTek.com 45° and 90° elbows available in diameters ranging from 1.25 to 18 inch Part quality is not the only item affected when excessive clamp tonnage is applied. There are long-term effects from over- clamping that will damage the mold and machine. First let's review several of the side effects on the mold: • Crushed vents; • Rolled parting line; • Broken inserts; • Cracked core or cavity block. Figure 3 is an example of a mold that was clamped at four times the required tonnage. Based on surface area, material, and gating, the mold required roughly 100 tons (at 3 tons/in. 2 ). The molder was inexperienced and set the clamp tonnage to the machine maximum of 400 tons (12 tons/in. 2 ). Despite a robust mold design, quality steel, proper machining, and correct heat treating, the result of excessive tonnage was that the cavity block separated in two locations. Each split ran the entire depth of the cavity block (roughly 10 in.) from parting line to clamp plate. This was a catastrophic failure that caused delays in production and upwards of $100,000 to expedite the manu- facturing of a new cavity block. Here are some potential failures on the molding machine when excessive clamp force is applied: • Cracked hydraulic-cylinder mounting plates; • Deformed platens; • Fractured machine frame. In Fig. 4, there were several contributing factors that caused the frame rails to break on this vertical C-clamp molding machine. First, the mold required about 10 tons to be held shut against the forces of injection, but the clamp tonnage was set to 100 tons. Second the mold-base size covered less than two-thirds of the platen in both direc- tions. Combining these two poor practices over years not only fractured the machine rails, but caused molding defects and mold failure. No one was sure when the failure occurred on the machine, but they did identify when it was first discovered and documented its progression over time. Replacing both machine rails cost thou- sands of dollars for materials alone. If we factored in the labor hours to disassemble and reassemble nearly the entire machine, and the scrap produced over the years before the rails failed, the number could easily exceed $200,000. @plastechmag 39 Plastics Technology I N J E C T I O N M O L D I N G