The vacuum controls on the MedLine cutter can be located remotely on hand-held operator-interface panels or at the upstream end of the vacuum tank. This way, the set-up technician can readily see the tubing as it enters the tank, even while adjusting vacuum levels and puller speed.

Recent machines that make tubing for medical applications do more than just extrude and cut material. They expand and heat tubing, make products with multi-channels, and work with varying materials. Take the tubing expander from Engineering by Design, San Jose, Calif., (www.ebdesign.com) for example. It makes heat-shrinkable tubing that meets the exacting requirements of the medical industry. The machine processes small diameter plastic tubing by heating it while pressurizing the inside to expand it. The expanded tubing is wound onto an output spool in a continuous process. A recirculated hot air system provides accurate temperature control and a high-heat-transfer rate for the production of smaller diameters, thinner walls and greater expansion ratios. “These new heating and cooling systems let users run higher speeds with less waste and fewer tubing bursts,” says Dale Henson, the company's president. “The expander's controls help make more consistent products with higher yields and less trouble for the operator.” Recirculating hot air eliminates problems associated with radiant heating systems as the tube temperature cannot exceed the temperature set in the recipe. Line stoppages therefore will not cause melting.

The precise control of all process variables is increasingly important as the materials get smaller and the specs tighter. Programmable pressure, temperature, speed, and pull ratios are stored in recipes for easy editing and retrieval. Opening hot and cold-air chambers for loading eliminates the need for awkward threading through small access passages. A cold-air box helps bring the tube back down to room temperature, so diameter measurements are repeatable and consistent. An automatic pressure system reacts to small diameter variations to maintain overall product uniformity. Adjustable alarm limits ensure that the entire run is acceptable. Statistical data is also reported for each run making it possible to verify product quality and use the information to refine the manufacturing process.

Downstream extrusion equipment targeted at lines producing small-diameter medical tubing has been redesigned and updated to increase precision and to make set up and operation easier. The MedLine puller/cutter from Conair, Cranberry Twp., Pa., (www.conairgroup.com) is a key component for extruders making multi-lumen microbore tubing used for heart and brain catheters. The software can independently control up to eight lumens, the hollow channels inside a catheter tube. MedLine software controls the dimensions of up to eight lumens, without slowing response, or diminishing resolutions, or losing repeatability. This unit also uses advanced servo-drive technology to periodically adjust the outside and inside diameters to expand the tube at a point where the catheter would be attached to other medical equipment. The control then triggers a blade to cut the tubing at exactly the right place to yield a nearly finished catheter tube. Nominal outside diameter for this kind of tubing is between 0.020 and 0.070-in., with wall thickness of 0.006-in. or less.

The programmable cutter from Eraser Co. processes over 7,500 pieces/hr.

“Medical extruders say the key to success lies in controlling process variables,” explains Bob Bessemer, Conair's Downstream Extrusion Product Manager. “With independent position-controlled servo drives on the upper and lower belts, and twin in-line planetary gear reducers, Conair has been able to all but eliminate speed variation in the MedLine puller.”

To transform stock into tubing products, manufacturers can improve their efficiency with a tubing cutter from Eraser Co. Inc., Syracuse, NY (eraser.com) that trims multiple pieces of the same material at one time. The MMC200 cuts round or flat material up to 100-mm wide by 16-mm thick. The microprocessor-controlled unit is easily programmed to cut any length (in inches or millimeters), with a 1% or better tolerance depending on material construction. With a maximum cutting force of 600 lb, the unit cuts most materials, including copper wire and cable, silver solder, power cords, fiberglass sleeving, fabrics, belting, flat and ribbon cable, strapping, hosing, tubing, and more. The MMC200 is programmable for up to 99 batches, 10 fixed feed rates, and up to 7,592, two-in. pieces/hr.