A new multipass cooling tank and related technologies from Conair now make it possible for producers of plastic tubing to reduce wall-thickness tolerances and cut material use dramatically while increasing productivity and reducing floor-space requirements. Systems are available for extrusion of medical tubing and also for non-medical products like aquarium tubing, small-gauge irrigation tubing and pneumatic airway tubing. The extrusion equipment was exhibited for the first time in booth 3643 in the West Hall at NPE 2012 being held April 1-5 in Orlando, FL.
With new and innovative OD, ID, and wall-control algorithms, new tension-control devices, and precision puller technology, this new combination vacuum/multi-pass tank technology is reducing commodity tubing tolerances to levels never seen before.
“Like any multipass tank, this new unit cuts floor space requirements by sending the tubing along a back-and-forth path through the cooling water, but that’s where the similarity ends” explains Bob Bessemer, Medical Downstream Extrusion Sales Manager for Conair. “The first thing you notice is that part of the tank is taken up with a vacuum-sizing chamber. Because vacuum sizing is inherently more controllable than air-pressure sizing, Conair has advocated this technology for over 15 years and we’ve demonstrated success in extrusion of flexible PVC, TPE, TPU and PE tubing. By reducing tolerances from ±0.005 inch (±0.127 mm) down to ±0.003 inch (±0.076 mm), for instance, processors can save tens of thousands of pounds of material while increasing the amount of product produced. As the industry migrates from PVC to more expensive materials, savings of even a few percent in material use becomes very important.”
Besides using vacuum-sizing, the new MedLine™ Multipass tank has several other advanced features, each of which contributes further to improved process stability, tighter control of wall thickness, ovality and cut-to-length tolerances.
An oversized, driven roller at the end of the tank reverses the direction of the tube as it exits the vacuum chamber and begins a second pass through the tank. The large diameter and precision design minimizes the potential for tube distortion or flattening, and because this roller is actually driven by a closed-loop vector drive or digital servo, it acts as the primary puller in the line. Located close to the beginning of line, it minimizes the stretching that can occur when the primary puller is a hundred feet or more down the extrusion line.
Precision glass bearings on non-driven rollers reduce drag and stretching as the tubing makes subsequent passes through the tank at line speeds that now sometimes approach 800 feet/minute.
A load cell measures tension on the tubing. This device sends a signal to the secondary puller outside the tank to automatically adjust speed to maintain a consistent and repeatable tension and prevent shrinkage issues.
Two gauging units – an ultrasonic gauge upstream and a laser gage at the downstream end – are linked to the pullers to automatically control wall thickness, concentricity and ovality of the tubing.
Automatic Cut & Transfer Coiler automatically cuts and transfers tubing from full coil to empty coil, permitting line rates up to 800 ft (244 m) per minute with minimal operator involvement for significant labor savings.
Because the MedLine MultiPass tank uses vacuum sizing instead of air-pressure in free extrusion, Bessemer also reports that is less affected by automated downstream functions like cutting to length and coil winding. “Where processors might have avoided using these techniques because of their impact on overall tube tolerances,” he says “they can now confidently institute these labor saving techniques and cut costs further while increasing productivity.”
The Conair Group (www.conairgroup.com) is the world’s leading supplier of auxiliary equipment for plastics processors, including resin drying systems, blenders, feeders and material-conveying systems, temperature-control equipment and granulators. Extrusion solutions include line-control systems, film and sheet scrap-reclaim systems and downstream equipment for pipe and profile extrusion. Over 450 individual products solve problems, save energy, cut waste and are easy to use. Conair is also an international company, with long-standing operations in Europe, Asia and South America. The industry’s most complete product line, top-flight engineering and unbeatable service, all combine to give processors the confidence they need to succeed in today’s competitive global marketplace.