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With China Plastic Machinery
With China Plastic Machinery
Plastic granulation is a process of plastic mechanical processing. In the process of plastic granulation, the quality and process of plastic products can be continuously improved according to the performance of the machine and practical exploration. Compared with landfill and incineration, recycled granulation is a real resource recycling.
Learn to listen to the sound
The speed of the feed and the change of temperature will make the sound of the machine very different. This requires continuous exploration in practice, and try to keep the machine in the sound state when it is running best.
Learn to look at the material
It is very important to look at the material coming out of the machine head, because it is the first key to find the cause. If there is raw material, the temperature is too low and it must be heated; if there is coke, the temperature is too high and it must be cooled, etc.
Look at the gloss and density of the particle surface
Poor plasticization and loose particles: The surface is dull because the granulation temperature and cooling water temperature are improperly controlled.
In short, in the process of plastic granulation, you must listen more, watch more, and explore more to find problems and correct them in time. Plastic granulation skills must be based on the different performance of the machine and your own actual exploration, and accumulate experience.
1. Requirements for product performance The application range of plastic is very wide. The differences in use occasions, conditions, and environments have different requirements for performance. Before designing, you should have a deep and detailed understanding of the performance requirements of the product.
2. Raw material sources and costs The selection of raw material varieties should be combined with the difficulty of raw material sources. Under the condition of meeting performance requirements, the cost of products should be as low as possible, otherwise it will affect widespread use.
3. Molding process The molding process routes are different, and the equipment and molding conditions (temperature, time) are also different. Therefore, the materials are heated and pressed differently. The formula design should adapt to the characteristics of the molding process.
Whether a designed formula is suitable needs to be tested through molding processing, product performance testing, and use. It often takes repeated practice to improve.
After the formula of the filling masterbatch is determined, the granulation process is an important factor in determining the quality of the masterbatch.
The heating temperature depends on the softening point or melting temperature of the carrier resin. The higher the softening point or melting temperature of the carrier resin, the higher the heating temperature. Generally, it should be about 5¡ãC higher than the melting temperature of the resin. If the heating temperature is too low, the resin cannot be fully melted, and the limited carrier resin cannot completely cover the inorganic powder. The surface of the masterbatch is rough and there are cavities in the middle of the particles. The resin and the inorganic powder cannot form a uniform system. If the heating temperature is too high, the additive is easy to volatilize, the screw shear force is reduced and it is not suitable for plasticization, which also affects the quality of the masterbatch. Under normal circumstances, the temperature of zone 2 should be the highest temperature for granulation. The temperature of zone 1 is about 10¡ãC lower than that of zone 2. The temperature of zones 3 and 4 is basically the same as that of zone 2. From zone 5 to the head, the temperature gradually decreases by 5~10¡ãC.
For a twin-screw extruder of a certain specification, 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 higher the output is not necessarily better. It is generally advisable to control the maximum speed of the main engine at 60~70%. If the speed is too high, the particles will stay in the screw for a short time, and naturally the plasticization will not be good. The speed of the main engine should also match the speed of the feeder and the speed of the pelletizer, otherwise there will be abnormal phenomena such as overflow or particles that are too large or too small.
------This is not a simple single issue of the speed of the main engine or the speed of the feeder. In a macro sense, the speed of the main engine reflects the speed at which the material comes out of the main engine screw, while the speed of the feeder screw reflects the speed at which the feeder screw transmits the material to the main engine screw. So the key point here is whether the speed of the feeding screw matches the speed of the main engine screw.
1. When the speed of the feeding screw is too small relative to the speed of the main engine screw, the material in the main engine screw does not completely fill the screw gap. In the main engine screw, there is relatively little material and the load is small. At this time, the material in the screw presents a low-pressure shear, which cannot achieve a good dispersion effect. (From this, it can be seen that the dispersion of fillers is not only related to small molecule dispersants, but is actually closely related to factors such as production process and mixing process.)
2. When the speed of the feeding screw is too large relative to the speed of the main engine screw, the material sent by the feeding screw to the gap of the main engine screw is always too late to be sent out by the main engine screw, water-cooled and pelletized, so the gap of the main engine screw is oversaturated. The material that has not been sent out in time collides around under the huge extrusion and compaction, looking for a breakthrough. At this time, it will overflow from the glass fiber mouth or vacuum channel, causing the glass fiber mouth to overflow or return, or even vacuum blockage.
Under normal circumstances, it is appropriate to control the main engine speed at 60~70% of the maximum speed. This actually considers that the main engine speed is too high, which is the case of 1, and the main engine speed is too low, which is the case of 2. This should actually be regarded as production abnormality. Of course, there may be some other problems involved, such as too high speed (100% of the main engine's maximum speed), high-load operation of the machine, which may reduce the service life of the machine.
The water pump is a device 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 in general, which can save power consumption. As long as the temperature of each area is reasonably adjusted, the water pump can be omitted.
The vacuum pump is a device used to remove low-volatile components. It is generally used for grafting reactions or the production of starch-filled masterbatches. For the production of inorganic powder-filled masterbatches, it is best not to use or use less. Vacuuming can easily remove the additives in the material, affecting the dispersion or processing of the masterbatch in the matrix resin.
1. When filling, operators must be careful not to let debris enter the material and control the temperature.
2. If the material does not form strips and sticks to the die head when the machine is turned on, it is because the die head temperature is too high. It will be normal after a little cooling. Generally, there is no need to stop the machine.
3. The water temperature should generally be between 50-60¡æ. If it is too low, it is easy to break the strips, and if it exceeds the temperature, it is easy to stick. It is best to add half hot water when starting the machine. If there is no condition, when pelletizing, people can transport it into the pelletizer for a period of time, and let it pelletize automatically after the water temperature rises to avoid breaking the strips. After the water temperature exceeds 60¡æ, cold water needs to be added to the internal circulation to maintain the temperature.
4. When pelletizing, the strips must be pulled evenly before entering the mixing roller, otherwise the pelletizer will be damaged. If the exhaust hole leaks out violently, it means that impurities have blocked the filter screen. At this time, the machine must be stopped and the screen must be replaced. The screen can be 40-60 mesh.
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