New Sheet Line Makes a New Kind of Glazing.

The first sheet line designed to make window glazing from polyester resin instead of polycarbonate or acrylic was due to be shipped last month to ACI in Sydney, Australia. ACI will produce the glazing from Spectar PETG resin, made by Eastman Chemical Co., Kingsport, Tenn. The sheet will have three PETG layers, with uv stabilizer in the outer skins. An Eastman source says PETG glazing would be cheaper than polycarbonate and tougher than acrylic.

A special sheet line for this product was built by HPM Corp., Mt. Gilead, Ohio. A new feature of this line (which HPM will use on future optical-quality sheet lines) is the drive system, designed to minimize "chatter marks" on the sheet. 11PM worked with suppliers of motors and gear reducers to solve this problem. The solution involved raising the base speed of the motor and using more precise gearing, so as to make any chatter marks less visible. The line is supplied with two sets of gear reducers, one for 0-30 fpm to make glazing up to 1/2 in. thick, and the other to run at 30-125 fpm making thinner packaging webs.

The line has an adjustable roll stack set at a 450 angle so that the sheet will touch both nip rolls at the same moment. If the web touched the bottom roll first, it could entrap air and cloud the sheet, according to extrusion division president Dennis Paradise.

Three extruders and the 57-in. die are elevated on a platform that is solidly built to minimize die vibrations. The main extruder is a 41/2 incher with a vertically mounted melt pump; the two coextruders are 2 in. diam. All have HPM Triple Wave screws. Total output capacity is up to 2500 lb/hr. Three Koch static mixers are mounted in the feed pipes from the extruders to the die. The latter is an EDI AutoFlex die with Fast Gap closed-loop thickness control based on feedback from a Measurex beta gauge.