PTFE Tubing: Process Parameters and Their Impact

PTFE Tube extrusion is considered to be one of the most difficult processes within the polymer space. All polymers have their typical properties and these properties impact both their processing and machining. PTFE tube comes with such varied process parameters, that every tube manufacturer will find it difficult to find a combination that works consistently.

 Parameters and their effect on the End-product

Whenever you think of PTFE processing one of the first things that are overlooked but needs our attention, is handling resin. Due to the structure of PTFE tubing, the fibrils that form extrusion depend on the strength of the final tubing. One of the reasons for the poor formation of fibrils is excessive shearing of the resin, before extrusion. This then, causes a dent in the achievement of good final properties.

·         Blending- Blending is one of the parameters which impact the final product and this can only be fixed with extensive trial and error. Unless the blending is done in the correct manner, the final extrudate will either be too soft or too dry. Also, if the blend is not uniform, the preform billet will have uneven densities, and the extrusion will then have quite a few issues.

·         Preforming-Preforming is mainly done to create a shape that can be fitted easily into the extruder. Preforming ideally has two functions: first, obviously, it gives shape and second, it also removes any air pockets from within the material. The process has to be done keeping in mind the one fact that too little pressure does not allow for an adequate venting of the air within the material. 

·         Extrusion-Extrusion is certainly one of the most important steps, as when the preform billet gets loaded into the extruder, then the preceding processes have already defined a lot of the tube’s most defining characteristics. However, it is also true that extrusion offers the tube its final shape and this process primarily helps maintain the adequate pressures on the billet at the same time ensuring the concentricity of the final tube. 

·         Sintering- When the tube is heated the temperature has to be heated for both a drying section along with a sintering section. The drying section needs have to be adequately warm to evaporate all traces of vapour from the tube. And, if it is too warm, the vapours may get ignited. Also, although PTFE does not melt, it may do so under its weight, it may even get elongated during sintering, causing changes in dimensional deviations. Therefore the temperature needs to be sent to make sure that the PTFE is able to reach the characteristic ‘gel state’ just before it goes out of the sintering chamber, so it can cool down when it reaches the room temperature. 

Apart from the above-mentioned parameters, PTFE tube also undergoes various other processes such as pigmentation, the addition of anti-static fillers and also the extrusion of specific profiles. Each of these requirements needs to undergo all of the above processes and understand how they need to be modified for a specific end-result.