WhenPFA GranulesThe granulation process is an important factor in determining the quality of PFA granules.
(1) Heating temperature The heating temperature depends on the softening point or melting temperature of the carrier PFA. The higher the softening point or melting temperature of the carrier PFA, the higher the heating temperature. Generally, it should be about 5°C higher than the melting temperature of the PFA. If the heating temperature is too low, PFA cannot be fully melted, and the limited carrier PFA cannot completely cover the inorganic powder. The surface of PFA particles has voids in the middle of rough particles, and PFA and inorganic powder cannot form a uniform system. If the heating temperature is too high, the additives are easy to volatilize, and the screw shear force is not suitable for plasticization, which also affects the quality of PFA particles. Under normal circumstances, the temperature of the second zone should be the highest temperature of granulation. The temperature of the first zone is about 10 ℃ lower than that of the second zone. The temperature of the third zone and the fourth zone is basically the same as that of the second zone, starting from the fifth zone until the head is gradually reduced by the gradient of 5~10 ℃.
(2) The speed of the main engine For a certain specification of the twin-screw extruder, the speed of the main engine is determined by the output. The higher the speed of the main engine, the greater the output. Practice has proved that for any twin-screw extruder, the greater the output, the better, the general control in the host maximum speed of 60 ~ 70% is appropriate. If the speed is too large, the residence time of PFA particles in the screw is small, and naturally the plasticization is not good. The rotation speed of the main machine should also match the rotation speed of the feeder and the rotation speed of the pelletizer, otherwise abnormal phenomena such as material spilling or too large or too small particles will occur.
------ This is not a single problem of simple host speed or feeding speed. Macroscopically speaking, the host speed reflects the speed of PFA particles coming out of the host screw, while the feed screw speed reflects the speed at which the feed screw conveys PFA particles to the host screw. So what is important here is whether the feed screw speed and the host screw speed match.
1. When the feeding screw speed is too small relative to the main screw speed, the PFA particles in the main screw do not completely fill the screw gap. In the main screw, the PFA particles are relatively small and the load is small. At this time, the PFA particles present in the screw. A low-pressure shear cannot achieve a good dispersion effect. (It can be seen that the dispersion of fillers is not only related to small molecular dispersants, but also closely related to the production process and mixing process.)
2. When the rotating speed of the feeding screw is too high relative to the rotating speed of the main machine screw, the materials transported by the feeding screw into the gap of the main machine screw are always too late to be transported out by the main machine screw, and then pelletized by water cooling. As a result, the gap of the main machine screw is oversaturated, and the PFA particles that are too late to be transported out collide everywhere under the action of huge extrusion and compaction to find a breakthrough. At this time, causing the glass fiber mouth to take or return material, or even vacuum blockage.
In general, it is advisable to control the rotation speed of the main engine at 60 ~ 70% of the highest rotation speed. This actually considers the situation that the excessively high rotation speed of the main engine is 1, while the excessively low rotation speed of the main engine is 2. This should actually be regarded as production abnormality. Of course, some other problems may be involved, such as the excessively high rotation speed (100 of the maximum rotation speed of the main engine) and the high load operation of the machine, may reduce the service life of the machine and other issues.
(3) The use of water pumps and vacuum pumps The water pump is used to adjust the temperature of the screw. Unless the temperature in a certain area is too high, the water valve should be closed as much as possible to save power consumption. As long as the temperature of each area is adjusted reasonably, the water pump can be used.
A vacuum pump is a device used to remove low volatile components, generally used for grafting reactions or the production of starch PFA granules. For the production of inorganic powder PFA particles, it is preferable to use no or less. The vacuum is easy to remove the additives in the PFA particles, which affects the dispersion or processing of the PFA particles in the matrix PFA.
This article comes from:www.tflpfa.com
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