DE2152463A1 - METHOD FOR PROCESSING PLASTIC POWDERS TO BE SINTERED - Google Patents

Description

Method of processing / ^{00 to} sintered plastic powders.

The invention relates to a method that plastics only by a sintering process can be processed, thereby faster, better and more uniform sintering that the heat required for sintering in the interior of the sintered body itself partially or generated entirely by introduced ultrasonic energy. .;

Various technically important plastics (e.g. polytetrafluoroethylene & flupraethylene) can only be processed in two different ways using sintering processes. One is the powdered one Plastic is compacted cold under pressure in appropriate dies and then with or without a die in an oven after a heated to a specific temperature plan until the entire plastic body is homogeneously sintered and solidified.

On the other hand, cylindrical bodies - rods, pipes, etc. - can be produced by continuous extrusion. Here is the Plastic powder is pressed into the vertical extruder tube by a ram moving up and down, which over a length is surrounded by a few meters with heating jackets. On the way through the extruder pipe, the plastic is heated and sintered. Because of the low thermal conductivity of the above plastics both sintering processes are very tedious. Sintering in the furnace takes several hours, depending on the size of the workpiece. When extruding, you achieve depending on the diameter of the rod or tube 0.25-1 m / h feed. The process according to the invention shortens the processing time of these plastics in that the heating is carried out by ultrasound from the inside out.

The thermal effects of ultrasonic vibrations are It has been used for a long time in ultrasonic plastic welding, but the conversion of acoustic into thermal energy always takes place only at the interface between the two bodies to be welded and these should be fused together. In addition, for plastic welding with Ultrasound only suitable for certain easily melting plastics. In the method according to the invention, on the other hand, there is one

- 2 303819/0370

Volume heating instead of melting the plastics to be sintered furthermore not, otherwise they could be processed quickly like thermoplastics on injection molding machines.

The new process is mainly used to increase throughput when extruding the plastics to be sintered. Here, the plastic powder is replaced by one in relation to the total. Extruder length, a relatively short pipe is pressed, which is excited to radial vibrations by vibrating elements attached to the outside. The tube can be attached at the inlet in the middle or at the end of the extruder tube; it has the same inner diameter as the rest of the extruder tube. The pressurized powder strand, for example, first passes the oscillating tube, where it is heated from the inside in a short time and, starting from the tube axis, sinters up to a certain edge zone. The remaining cross-section is then easily sintered to the end in the usual way from the outside by conventional heating. The increase in throughput due to the rapid ultrasonic heating can be twice to three times the normal production. When sintering in the die, the ultrasonic energy can be introduced into the body to be sintered in a similar manner by suitably shaped ultrasonic vibrators which excite the die jacket essentially perpendicular to its surface.

3Q9819 / Q37Q

Claims (3)

2152483 PATENT CLAIM Method for processing plastic powders to be sintered, characterized in that the heat required for sintering is generated in the interior of the sintered body partially or entirely by introduced ultrasonic energy. 2. The method according to claim 1, characterized in that the ultrasonic energy through a radially vibrating tube in the Sintered body is initiated. 3. The method according to claim 1, characterized in that the sound energy over the jacket of the die, which is substantially perpendicular to its surface to ultrasonic vibrations is excited, is introduced into the sintered body. 309819 / Ö370