Integrated melt filter/gear pump protects extrudate quality.
Known in this country primarily for supplying German-made filtration equipment, Gneuss Inc., Langhorne, Pa., has now publicly introduced integrated packages of its continuous rotary screen-changer with a compatible gear plump and a single control system that can also run the extruder if desired. Gneuss has supplied a few of these systems here without fanfare over the last two years.
Gneuss has also begun to actively market its total downstream engineering capability. According to v.p. of sales Joseph Altimari, the company can engineer, install and start up entire extrusion lines. Gneuss then guarantees all the components. "We assume responsibility for the entire line," he says. So far, Gneuss has not sold any of these complete systems in the U.S., though the company has installed more than a dozen large-scale lines in Europe over the past year.
DUAL QUALITY PROTECTION
Gneuss' approach to closely integrating melt pumps and filters is intended to address manufacturers' quality. The gear pump's role in maintaining product quality is relatively familiar--by providing uniform volumetric output through the die, it helps ensure consistent extrudate dimensions. Gneuss, however, would have processors view the quality role of the melt filter in a new light.
Aside from its ability to remove contaminants without interrupting production, a continuous screenchanger helps maintain the quality and consistence of the melt itself. Because it can index frequently between a number of clean filtering surfaces in response to a pressure signal, the continuous screenchanger minimizes fluctuations in backpressure in the extruder. As a result, the degree of working and shearing of the melt is held more consistent. By contrast, a filter device that is unable to respond sensitively to pressure increases as the filter becomes dirty permits a gradual reduction in flow through the screen and consequent increase in melt residence time. That reduction, in turn, often prompts a compensating increase in screw speed to maintain output against the growing restriction to flow. The net effect could be greater degredation of the melt and a change in plastic properties that would be imperceptible to a line operator.
The Gneuss screenchanger design features a filter wheel that holds between 10-12 screens. The control unit that determines the indexing between screens runs from either the pressure differential across the screenchanger or the pressure at the extruder tip.
Gneuss does not make the pumps itself but purchases them from various suppliers, such as Luwa Corp., Charlotte, N.C., and American Barmag Corp., Charlotte, N.C. "We're not married to any one pump maker," Altimari says.
Gear pump suppliers such as Luwa, Normag Corp., Hickory, N.C., and Zenith Pumps Div. of Parker Hannifin Corp., Sanford N.C., say they too have provided combinations of a melt filter with a compatible pump for several years, but not generally as a pre-engineered, preassembled package. Gneuss supplies a unitized package of filter, pump and adapters on a single cart. The company notes that its approach to integration involves more than just bolting together a collection of components. Gneuss claims that its melt channels are particularly streamlined because the adapters between extruder and filter and the filter and pump are deliberately engineered for rheological efficiency.
Normag has also recognized the benefits of an integrated pump and screenchanger combination. It has teamed with Extek, Marblehead, Mass., to develop such a unit. Normag President Steve Fox said it would likely be on the market by spring.
JUST RIGHT FOR RECYCLING
Altimari notes that the pump/filter duo can be applied to any extrusion or compounding line, but post-consumer recycling is an especially attractive application. Gneuss sells two items specifically suited to the more rigorous filtration needs that arise when processing reclaimed material.
The company's self-purging rotary screenchanger continuously cleans contaminated screens with a burst of melt diverted from the main flow via a small channel in the filter block (see PT, Jan. '90, p. 76). Gneuss claims that this backflushing system normally allows the device to operate for up to a full week without removed of the screen elements.
For filtering material highly contaminated with larger debris, Gneuss makes an automatic screenless filter called "The Separator." It collects contaminants on a breaker plate without stopping the melt flow. A rotary scraper continuously cleans the plates so the dirt build-up doesn't impede the melt. Used, for example, in reclaiming both plastic and melt components of wire scrap, the Separator is combined with a second stage of finer filtration.
PHOTO : Gneuss designs integrated screenchanger/ gear pump combos with melt quality in mind.
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|Date:||Jan 1, 1992|
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