Basic principle of plunger punching extruder
The plunger punching extruder adopts a double-station position, and connects two sets of link mechanisms with one crankshaft to drive a plunger to reciprocate respectively. This planning method greatly improves the production power and the production cost of the product is also Dropped significantly. The plan of the extruder firstly utilizes the forging process principle. The reciprocating motion of the plunger presses the material into the barrel, and the material is gradually reached in the barrel under the combined effect of shear heat and external heat source. In the molten state, together with the pressure pushing effect, the material is moved to the die, and finally the material is extruded through the die. The plunger of the extruder generally has a relatively small cross section, and the plunger maintains the material in the barrel in an uninterrupted manner at a higher frequency and speed of movement, which is the most common equipment of the device and the conventional plunger extruder. The obvious difference is that the resistance of the preforms in each working section due to the conflict between the resin and the resin and the wall of the cylinder, combined with the resistance generated by the continuous expansion of the die during the sintering of the die, makes the multi-stage preform The successive extrusion molding is completed at the exit position of the die, and the quality of the product obtained is relatively uniform, and the appearance is basically free from defects, and the most important thing is to improve the production power.
Process flow of plunger punching extruder
1. Solid feed section. In this section, the selection of materials is a very important factor. In order to ensure the quality of extrusion, the materials used should meet the following conditions: high bulk density, good free mobility, and the particles should have satisfactory stability and hardness. Cleanliness, etc. Since the solid feed section is divided into two processes of powder compaction and solid plug flow, it should also be carried out from these two aspects when depicting the production process of the section.
(1) The powder is compacted. In this section, when the plunger is retracted, the effect of gravity on the loose material will fall into the punching chamber by itself, and when the plunger is gradually advanced and the material is kneaded at the beginning, the granular body will It is then compacted into a dense solid plug, which is essentially the process of the mechanical plunger kneading pressure.
(2) Solid plug flow. As the material continues to move forward with the plunger, the solid plug advances the material in the entire barrel forward under the effect of the punch. And in this process, the solid plug is subjected to the pushing force and front end and resistance from the back end, and then stores a lot of energy. When the plunger reaches the farthest stroke, the start is quickly retracted, and the material will release the energy stored in the front, so that the material can continue to move forward. Due to the large creep of PTFE itself, when the plunger is pressed down, it will store a certain amount of energy due to deformation. This part of energy will be gradually released following the retraction of the plunger. This process will cycle back and forth. .
2. Melting section. When the solid plug travels, it will collide with the wall of the barrel to generate heat. Together with the heater outside the barrel, the temperature of the solid plug will rise continuously, and then the material will melt and melt in the process. membrane. The melting of the material is generally started from the part closest to the wall of the cylinder, and gradually melts from the outside to the inside. As the material continues to advance, the thickness of the investment increases, and the radius of the solid plug increases. The smaller it is, the more the section of the barrel stops until the melt fills.
3. The diversion section. At the beginning of a typical pipe mold there is a splitter cone which has the effect of forming a thin ring of melt through the portion which aids in heating and plasticizing and forming a predetermined conduit. When the material flows through this section, under the conflict blocking effect of the device such as the splitter cone, the melt builds up the pressure, which is beneficial to the composition of the compacted product, and the material is subjected to intense shearing effect in this section. To a certain extent, the melting of the residual solid material is accelerated, and the material can be substantially completely melted when it enters the next stage.
4. Melt conveying section. When the material enters the section, it has completely melted and melted, but the pressure has a certain shake, and the PTFE melt still has a certain elasticity. This is because the material has been in the process of energy storage to discharge during the process of traveling. In order to ensure that the movement can be carried out in succession; as the material continues to move, the pressure will become smaller and smaller, and the movement will become more stable. Since the plunger punching extruder uses an extended die layout, it is useful to extend the time during which the material stays in the die, and then further improve the uniformity and compactness of the product. Since PTFE itself has a relatively high melting point, it is required to heat the die during extrusion, and the length of the heating section has a certain influence on the extrusion pressure and speed, and then affects the processing power of the extruder. According to the experimental results, the longer the heating section, the greater the extrusion pressure and the better the physical function of the product. However, if the heating section is too long, it is possible to cause the article to exhibit cracks. In order to deal with this problem, the heating section of the barrel can be divided into three sections, each section independently controls the temperature, and an aluminum sleeve is placed between the barrel and the electric heating coil, so that the temperature balance of the barrel can be ensured. .
5. Cooling section. This section promotes the cooling and setting of the material. In this process, the temperature of the material can be lowered below 250 ° C, and the temperature is required to be > 200 ° C when the material is extruded into the thin-walled tube. Then, the pipe that is extruded into the thin-walled pipe is cooled in the air for the next step, and the cooling moment is controlled. It must be noted that if the cooling section is too short, the product will be introduced into the air cooling stage, which will result in an oversize, a reduced shortening, and an increase in internal stress. In order to improve the quality of the product, the mandrel should be appropriately larger than the length of the barrel to ensure that the mandrel can provide good support during the air cooling stage.