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Plastics and Elastomers

Originally Published MPMN November 2003

PRODUCT UPDATE

Plastics and Elastomers

Norbert Sparrow

Dust Removal System Gives Polymers Clean Bill of Health

Offered by Amicon Plastics, a bearing-grade PEEK material with internal lubrication
is suited for the fabrication of pump parts, shaft bushings, and other medical device components.

Dust particles that cling to plastic pellets as they are injected into molds can burn or melt into a liquid or gas. This produces foggy microbubbles or char marks on the finished part, rendering it unusable in many applications. "Flaws in medical films and related products are often caused by dust," notes Jerry Paulson, inventor of a dust removal technology and founder of Pelletron Corp., which manufactures associated equipment. The use of a dust contaminant removal system in the production process can translate into dramatic reductions in scrap and substantial cost savings, he adds. The company offers a line of equipment that is designed to make this technology accessible to small and medium-size manufacturers. This article also includes updates on recent advances in polymers with medical applications. 

Into the Flux

As plastic pellets move through a processing system, they collide with the piping and bump against each other, causing minute particles to break off. This dust reattaches itself to the pellets under the influence of a static charge and ultimately produces defects in the finished product. "Scrap rates can be huge for the manufacturer," notes Heinz Schneider, who was recently appointed president and CEO of Pelletron Corp. "One company that recently purchased our equipment was processing polycarbonate, which costs about $2.60 per pound. The firm had a parts nonacceptance rate approaching 40% before installing one of our dedusters. The return on investment was three to four weeks," says Schneider.

Pelletron's dedusting technology is built around a flux field generator, which creates a low-power electromagnetic field. This disrupts the electrostatic bond between the pellets and dust particles. The pellets and contaminants fall to the surface of the primary air wash deck, where blasts of pressurized air lift the lighter-weight contaminants above the main product stream. The pellets then pass through a venturi chamber. A stream of bypass air, whose upward velocity can be adjusted, separates the remaining dust and large stringy contaminants from the pellets. The particles are drawn by vacuum to a dust filter separator. The pellets receive a final cleaning in a secondary air wash deck before exiting the unit via another flux field generator.

The company's dedusting technology can ensure the removal of particles smaller than 1 µm, says Paulson. Buyers of resin are becoming more and more demanding, he notes. "Ten years ago, 500 parts per million (ppm) of fines was acceptable. Five years ago, it was 200 ppm. Now, it's down to 100 ppm, and some are looking at 50 ppm," Paulson explains. Pelletron's line of equipment achieves levels of 25 and even 10 ppm, he adds.

Optical-grade parts molders stand to benefit greatly from the technology. Materials such as clear acrylics, polycarbonates, and ABS are unforgiving when it comes to the presence of fines, fluff, and streamers. Scrap rates as high as 90% have been reported, according to the company. On the Pelletron Web site, contract molding firm Nypro describes the problems it had encountered molding clear medical parts in acrylic and crystal styrene materials.

Black specks were appearing in both materials, but the contamination was especially acute with the styrenic polymer. The material was plagued by fines, because it is typically moved four to five times prior to processing. The movement causes friction, and as the pellets bump against each other, they create dust particles. To remedy the situation, the company mounted a deduster on top of a drying hopper. Fines burning in the styrene ceased immediately, according to Nypro, and the black specks were eliminated in almost every shot.

Pelletron offers 12 different models of dust removers, with processing capabilities exceeding 200,000 lb/hr. With a capacity of 150 lb/hr, the P1 Mini-Deduster is the instrument of choice for small to medium-size medical device molders and extruders, according to Schneider. It is designed to fit above the feed throat of an injection molding machine or extruder, or at the inlet of a drying hopper. The fan and dust collector are remotely located to keep the equipment stack as small as possible. A specially designed agitator limits the product flow through the Deduster to prevent exceeding the rated capacity. This allows the P1 to be choke-fed from a vacuum loader. A window on the unit allows the operator to monitor the operation. The P1 can also be installed off-line as a regrind or scrap recovery system. A version with a cast body was introduced in October.

The firm also recently launched a redesigned P5 unit. Designed for small to medium-size plastic product manufacturers, the equipment is reportedly one of the few dust removal systems able to clean regrind and virgin materials that have been mixed together. It has a capacity of 500 lb/hr.

Bearing-Grade PEEK Introduced

A dust removal system from Pelletron Corp. was made for small to medium-size manufacturers
of plastic products and can process up to 150 lb
of raw material per hour. Its use can dramatically reduce scrap.

A bearing-grade PEEK material is suited for applications where high load, chemical and high-temperature resistance, and low wear are desirable properties. In the medical and pharmaceutical sectors, Amiloy 22 can be used to fabricate shaft bushings, bearings, piston rings, pump parts, and slide pads.

Available from Amicon Plastics, the material's internal lubrication eliminates the need for external lubricants and greases, thus allowing its use in dynamic parts in cleanroom environments. Tribological characteristics and wear resistance also benefit from this property. Amiloy 22 withstands temperatures up to 500°F, is corrosion resistant, and has a low moisture absorption rate. Additional features include dimensional stability and mechanical strength.

Medical Technical Polymers

Five new grades of polyphenylene sulfide (PPS) and eight grades of liquid-crystal polymer (LCP) for medical device, drug packaging and delivery, and other healthcare applications were recently introduced by Ticona. The materials provide a wide range of design and processing options.
Filled and unfilled grades are available for injection molding and extrusion, as well as grades with various flow properties and additives that render parts exhibiting low friction and wear, desirable surface appearance, enhanced stiffness, and other special properties. Compliant with USP Class VI biocompatibility standards, Fortron MT grades of PPS offer good dimensional stability, toughness, and rigidity; can tolerate repeated sterilization; and resist hydrolysis and the effects of most chemical media. They include glass-fiber-reinforced grades. Vectra MT grades of LCP provide strength, stiffness, creep resistance, dimensional stability, and high flow in long, thin sections. In addition to an unfilled grade for medical packaging, this family of thermal- and chemical-resistant polymers includes versions with glass-fiber, carbon-fiber, and mineral fillers for enhanced performance attributes. 

Copyright ©2003 Medical Product Manufacturing News

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