Wuhan Handern Extrusion, Push Forming Equipment and Process

1. Extrusion of PTFE

Because the melt viscosity of PTFE is greater than 10-16 Pa·s (360°C), it cannot be molded like other thermoplastic materials. If the PTFE profile is continuously produced, only the sintering extrusion method can be used.

The extrusion molding of PTFE is different from the extrusion molding of general thermoplastic resins. Screw extruder or plunger pusher can be used, but its screw is equidistant and has no compression ratio, so it is different from plunger The same only plays the role of conveying materials, without the ability to shear and plasticize.handern.comBreathable Film Machinery

1. The principle of plunger pushing

Plunger pressing is a method of continuous production of ultra-high molecular weight polymers such as polyethylene, polytetrafluoroethylene and other profiles (sintering extrusion method). It consists of two steps: batch feeding, continuous sintering under pressure in a feeding tube, and compression of powder. It can be extruded into bars and tubes. Plastics with extremely high melt viscosity such as nitrocellulose can also be molded.

The polytetrafluoroethylene powder is added to the extrusion pipe through a metering device, and the plunger is used to compress it into a ring; then the plunger is lifted, new powder is added, and then compressed. The extruder compacts the powder into a compact and transports it to an extruded tube heated to 380°C. In this area, the parison is sintered into a tube rod or profile.handern.comBreathable Film Machinery

The extrusion pipe and the axis are cylindrical. Due to the thermal expansion of PTFE, when the hot extruded product moves forward, the extrusion die wall generates high friction. Therefore, the powder should be compressed properly. Back pressure.

2. Push molding of PTFE

1. Push forming principle

Push molding is also paste extrusion molding, which is the main method for producing PTFE pipes. The raw material used for push molding is dispersion polymerized polytetrafluoroethylene. It takes advantage of the characteristic of dispersing resin that it is easy to become fibrous under the action of shearing force. The resin is mixed with additives and pre-compressed into the preform, and the preform is mechanically forced through the mold with a certain cone angle, so that the Obtain uniform and neatly arranged tubular fibrous materials, and then remove the squeezing aid, and after sintering, make it into a strong pipe.

When pushing, the parison is first compacted, and gradually fills the cone, and finally enters the die, ejects the positioning pin and is continuously pushed out. This reduction in cross-sectional area is called the compression ratio. The content of additives, mold design, equipment capacity and product performance are affected by the compression ratio when pushing.  handern.comBreathable Film Machinery