Four years of development and over $7.5 million have resulted in what is believed to be the largest part ever made by gas-assist injection molding and also the largest ever made by the structural-web process, a variant of gas assist. This 75-lb polypropylene part is a section of a stormwater chamber from 风暴科技 LLC in Weathersfield, Conn. Measuring 50 in. wide, 30 in. high, and 7 ft long, the thin-walled chamber imposed molding challenges that required a new type of 2000-ton structural-web machine from Uniloy米拉克龙, Manchester, Mich., which owns the structural-web patents.
风暴科技 is a new 50/50 joint venture formed last July by Infiltrator Systems Inc. (ISI) of Old Saybrook, Conn., and Advanced Drainage Systems, Inc. (ADS) of Hilliard, Ohio, to 恩gineer and manufacture chambers for underground stormwater detention and retention systems. ISI is reportedly the leading producer of polyolefin septic chambers and subsurface stormwater chambers, while ADS is said to be the leader in corrugated HDPE pipe for stormwater systems.
ISI过去十二年来一直是结构化网络技术的最大用户之一，并且是世界上唯一完全致力于此过程的模塑商。很少数量的模塑商使用该技术本身。但是在最近三年中，人们的兴趣大大增加了。“我们目前销售的低压机器中约有50％用于结构幅材，” says Ed Hunerberg, executive director of structural-foam business at Uniloy米拉克龙.
风暴科技’s new stormwater chamber pushes the 恩velope of this technology to a new level. ISI uses Uniloy米拉克龙 machines from 1500 to 2500 tons for structural web, but 风暴科技’s new 2000-ton machine differs from past models in that it has 110 x 107 in. platens with 2.5 times more clamp tonnage per square inch than previous machines. Before the 风暴科技 chamber, the largest structural-web chamber molded by ISI weighed 35 lb, according to Roy Moore, v.p. of manufacturing at ISI, which molds products for 风暴科技. Molding a larger part with thin walls required a machine with a beefier clamp. It also has an 8-in. extruder with 30:1 L/D and 1000-hp, variable-frequency AC drive instead of the usual 6-in., 600-hp, DC-drive extruder. This gives it larger shot capacity (160 lb) and higher plasticating rate (6000 lb/hr) than any previous structural-web machine.
Uniloy米拉克龙’s structural-web technology is a short-shot process that creates controlled internal hollow channels in parts that increase stiffness and strength while saving material and cycle time. It can be performed on the same multi-nozzle, low-pressure injection machines that Uniloy米拉克龙 builds for structural foam. The difference is that for foam, nitrogen gas is injected into the extruder barrel and mixed into the melt to produce a part with a solid skin and cellular core. For structural web, the nitrogen gas is injected through special polymer/gas nozzles directly into the mold. The result is a solid skin with hollow thick sections such as structural ribs. Mold cavity pressure is only 400 to 600 psi, as compared with 2000 to 4000 psi for gas assist.
Moore says 风暴科技’与竞争的真空成型HDPE隔室相比，PP雨水隔室重量更轻，并且具有更好的耐热性和ESCR性能。他补充说，低压结构腹板成型在控制壁厚以及端盖和接头的精确配合方面击败了热成型。它还赋予较低的内部应力，并且部件仅产生一个热历史。另一个优点是改善了设计灵活性，使薄壁部分具有厚的空心肋。