High performance plastic extrusion process for tubes, films & tapes
The extrusion process allows to produce long parts. Tubes and profiles or tapes and films are the two main product families produced by extrusion. The available extrusion process will depend on the material.
Thermoplastic extrusion is possible for most high performance polymers
Extrusion is a common process in thermoplastics industry. By forcing the molten polymer into a die, this process is the basis for production of tubes, films and tapes. It is also used for more complex profiles, for example rectangular rods or bars.
For thermoplastics, extrusion is precious as it is a continuous process suitable for high length products. To provide a global quality and constant performance of extruded high performance plastics, high stability in the process is required: melting, cooling and crystallinity control, extruder speed and pressure.
Tubes, rods, films and tapes each have specific requirements. For example, high precision extrusion of tubes also require fine control of eccentricity in the die, for low thickness walls or low tolerance tube walls. That’s especially true for high performance plastics extrusion as they require higher temperature, and equipments based on less sensitive materials.
Paste extrusion is a process dedicated to PTFE
Gel viscosity of PTFE (in its melted state) is too high to transform this material through traditional extrusion. That’s why PTFE requires specific equipments and know-how for extrusion.
In fact, in such a process, a lubricant is added to the PTFE powder, making it a slurry, or a paste that can be forced into a die. The PTFE-lubricant mixture becomes a soft paste, lowering the bulk viscosity of PTFE fine powder to gain extrusion capabilities. This is not a continuous process and is limited in lengths compared to usual thermoplastic extrusion. This is why it is referred as paste extrusion.
Depending on the die and on other equipment, PTFE can then be extruded as a tape, a film, as a tube or even with a squared profile.
After gaining this shape, lubricant is removed. Depending on the final product, PTFE can be partially or totally sintered to keep its shape and gain its properties.
Thus, extrusion for PTFE is widely used and is even at the origin of 2 widely used products: PTFE unsintered tapes and PTFE tubes.
PTFE Ram extrusion offers semi-finished parts similar to extruded parts
Along with paste extrusion, other processes are available to transform PTFE in tubes or in films. Such processes allow to produce thicker parts compared to lubricated extrusion.
Ram extrusion combines molding and extrusion in a continuous process, without the need of a lubricant. It is one of the solution for extrusion of tubes up to 3 meters long. And such dimensions are usually hard to reach with the more classical molding process.