An MD&DI April 1997 Feature
MEDICAL PLASTICSExtruding, molding, and sealing systems help manufacturers save time, money, and materials.
To produce plastic medical devices, manufacturers must either purchase and operate the processing equipment themselves or contract with component manufacturers. Because unit prices start in the tens of thousands of dollars and the cost of complete systems often exceeds hundreds of thousands of dollars, many device manufacturers employ third parties to do their molding and extruding. But bringing the component manufacturing process in-house has its advantages, such as being able to closely monitor quality, making modifications in the production process quickly, and increasing product volumes without incurring significant additional costs other than for labor and materials.
Equipment manufacturers are also making such purchases even more attractive by offering standard equipment that reduces production times and material and energy waste, and by customizing equipment to meet specific applications. They are also designing joining technologies that speed the manufacturing process.
A number of companies are marketing equipment designed to expedite medical plastics processing. The equipment either incorporates time-saving features such as quick-change parts or is part of a larger family of machines that are designed to operate together, thereby eliminating the concern for mismatched units.
Genca (Clearwater, FL).The company manufactures the Smart Head series of auxiliary equipment designed to work with extruders in R&D applications. The series includes multiple application heads that attach to a common base without the use of tools. Each head contains the mechanisms and intelligence necessary for programming the base to perform the required application. Capabilities include strand pelletizing, traverse spooling, nip roll pulling, and torque winding. "Typically, operators don't use every piece of auxiliary equipment at the same time," explains Robert Furlan, sales engineer for Genca. "This series enables users to have a complete laboratory by buying only one or two bases and a number of heads."
Auxiliary units for extrusion processes from Genca offer versatility.
Harrel, Inc. (East Norwalk, CT).To produce tubing quickly from two or more different polymers, the firm has invented a machine that can extrude a tube that is made from one polymer at one end and another polymer at the other end--all without having to join two separate tubes together. The automatic system consists of an extruder and several other downstream units that are all tested in the company's laboratory before shipment. An overall system processor coordinates all the system elements, eliminating the need for specially skilled operators. One system recently designed by the company for the medical industry has an output of 15 lb/hr. There are, however, no limitations on the output when larger extruders are used. The Alternate Polymer system may also be used to extrude shapes other than tubing, such as profile, sheet, and blown film.
Killion Extruders (Cedar Grove, NJ).Many companies offer several separate machines designed to work together for particular applications. This company manufactures a full line of extruding equipment, including blown film, cast film, and sheet units; vacuum tanks; water troughs; pullers; winders; and pelletizers. It also manufactures specialized cutting systems such as servo cutters, flywheel cutters with servo pullers, bump/taper tubecutting systems, and corrugated tubecutting systems.
Wayne Machine & Die Co. (Totowa, NJ).To complement its full line of extrusion equipment, Wayne has introduced its Yellow Jacket corotating, intermeshing twin-screw extruder. The machine modifies polymers to produce materials with enhanced physical, electrical, mechanical, optical, chemical, and other properties. These materials include mineral-filled, glass-reinforced, flame-retardant, liquid-modified, devolatilized, and degassed polymer compounds. The Yellow Jacket is designed to operate with the company's downstream equipment such as a push-pull flexible-lip sheet die and a three-roll stack sheet takeoff system.
Twin-screw extrusion system from Wayne Machine & Die Company, Inc.
Hull/Finmac, Inc. (Warminster, PA). Hull/ Finmac custom engineers full turnkey systems for medical device manufacturers. Because the company manufactures transfer, compression, and injection molders, it can design equipment to handle almost any type of material. The firm also manufactures mold tooling and can modify a client's tooling to work with its molders. In addition to providing the equipment, Hull/Finmac provides technical support and on-site training for its customers. "We don't leave them in the lurch," explains Jack MacInnes, sales manager.
Equipment manufacturers are also inventing machines that help plastics processors minimize operating costs. While an extruder that can switch from a horizontal to a vertical operating position is not a unique product, a small extruder that can make such a switch is. Genca has devised a benchtop extruder that has a 12-in. 24:1 steel screw and can switch from horizontal to vertical operation. The small extruder maintains a short residence time, minimizing the possibility of material degradation caused by overheating. Because the alloy steel screw is tapered, it can use standard-size pellets, saving processors the cost of specially ordering or making small-size pellets to fit a small extruder. Ideal for R&D applications, the unit can also accommodate low-volume production runs.
Illinois Precision Corp. (Wheaton, IL). Plastics processors are also becoming more concerned about the environment. There is an increasing demand for production practices that cut material and energy waste and use environmentally friendly materials. For example, Illinois Precision Corp. has designed a rotary insert molding machine that operates at a lower injection pressure than most machines, allowing users to mold with maximum clamping pressure while minimizing energy use. The average amount of kilowatt-hours used for thermoplastics is 4.0 kWh and for thermosets is 5.4 kWh. The company also produces mold tooling designed with gates and runners that minimize material waste.
Harrel has designed a family of turnkey extrusion lines that can handle metallocene-catalyzed polymers, which have been manufactured by companies such as Dow/DuPont as alternatives to PVC. Demonstrating flexibility properties similar to those of PVC, metallocenes are easier to process because they do not degrade as readily as PVC. Harrel has optimized all units of its system, including the hopper, the screws, the die, and the conveyor systems, to accommodate metallocenes.
To produce complex medical devices, manufacturers need to do more than just extrude or mold. They must join plastic components to create the IV components, surgical components, and other plastic devices used in the medical industry. Available technologies include hot plate welding, vibration welding, radio-frequency welding, ultrasonics, and use of adhesives. The use of welding equipment usually eliminates the need for adhesives or solvents, thereby reducing operating costs. And because the welders join plastics more quickly than solvents do, the use of such equipment can speed manufacturing.
Branson Ultrasonics Corp. (Danbury, CT). Branson manufactures a variety of plastics-joining equipment such as linear and orbital vibration welders, hot plate welders, and ultrasonic equipment. Vibration and hot plate welding can be used to join devices that require hermetic seals and are usually joined by adhesives. Ultrasonics can be used to assemble surgical instruments that are typically joined by screws and solvents.
Sebra (Tucson, AZ). Sebra manufactures a line of radio- frequency generators and welding heads designed to weld, thermoform, or seal PVC, EVA, polyurethane, polyethylene, nylon, polyester, and custom thermoplastics. These generators can be used with a variety of optional or custom welding and sealing elements that are either handheld or benchtop. The company also markets PIRF catheter-manufacturing welders and thermoformers consisting of compact, interchangeable, customized platforms and molds.
Herrmann Ultrasonics, Inc. (Schaumburg, IL). Herrmann recently redesigned its Vario-Process ultrasonic machine to offer thermoplastics processors a unit with improved force control. A proportional valve allows constant regulation of the weld force throughout the welding cycle. Another feature of the machine is its quality control system that verifies the actual welded part quality during process by comparing it to ideal weld profile curves and graphs.
Daphne Allen is associate editor for MD&DI.
Daphne Allen is associate editor for MD&DI.