Medical tubing, like all other extruded products, is experiencing further tightening of tolerances on OD, ID, wall thickness, ovality, and concentricity, while processors are seeking faster line speeds and enhanced material properties. The main difference between medical tubing and other products is that, in many cases, extruders are working with ten-thousandths of an inch tolerances instead of the more typical thousandths of an inch. And while extruder and melt pump manufacturers are enhancing their products to offer extremely consistent throughputs, and compounders are working to make the materials as repeatable as possible, advances in puller technology are also having dramatic effects on the precision and throughput rate.
The puller is really the heart of the tubing extrusion process.While material throughput rate is generated by the extruder and the tubing is initially formed in the die, it is the puller that develops the inside and outside diameter (ID and OD) and wall thickness. The accuracy of those dimensions – as well as the ovality or ‘roundness’ and overall quality of the tubing – will be determined by the accuracy and repeatability of the puller speed control. Consistency of speed, in turn, is the product of several different variables in the puller drive train, all of which have been the subject of recent intensive research and engineering. It is important to understand how each of these design details contribute to improved puller performance and why buying a cheaper puller may be false economy.