Why does the screw not feed?

When the injection molding machine screw creates pressure difficulties at the charging port, or fails to form sufficient adhesion along the length of the barrel to convey the material, then injection molding machine screw slippage occurs. In the pre-molding stage of the injection molding machine screw, the injection molding machine screw rotates in the barrel to convey the material along the direction of the screw and backs up to accumulate the material in preparation for the next injection, the injection molding machine screw will also slip. If the injection molding machine screw begins to slip during the pre-molding phase, the axial movement of the screw will stop as the screw continues to rotate. Usually screw slippage leads to degradation of the material before injection molding, and also to product quality problems such as short shots and extended processing cycle times. \x0d\ \x0d\\ injection molding machine screw slippage occurs due to back pressure is too high, the second half of the barrel is overheated or overcooled, the barrel or screw is worn out, the screw charging section of the screw is too shallow, the hopper is not designed properly, the hopper is out of material or clogged, the resin is wet, the lubricant content of the resin is too high, the material is too fine in particle size, the resin used is poorly cut and shaped or recycled material is used. \x0d\ \x0d\1, the influence of process parameters \x0d\ Low temperature in the rear section of the barrel is usually the main cause of injection molding machine screw slippage. The barrel of the injection molding machine is divided into three sections. In the rear of the charging section, a thin layer of molten polymer is formed during the heating and compression of the material. The molten film layer is affixed to the barrel. Without this thin layer, it would be difficult for the granules to be transported forward. \x0d\ \x0d\ The material in the charging section must be heated to a critical temperature to produce the critical molten film layer. Often, however, the retention time of the material in the barrel is too short to allow the polymer to reach that temperature. This can occur due to the small size of the machine and the corresponding small barrel and screw configuration. Residence times that are too short tend to cause the polymer to melt or mix insufficiently, which can cause the screw to slip or stall. \x0d\ \x0d\ Now two simple treatments for this problem are described. Start adding a small amount of material from the end of the barrel for cleaning and check_ the melt temperature. If the dwell time is short, then the melt temperature will be lower than the barrel temperature setting. The second method is to observe the molded product, if you find such things as marbling, black spots or light streaks, then the material is not well mixed in the barrel. \x0d\ \x0d\ One of the solutions to the occurrence of screw slip attempts is to gradually raise the temperature of the charging section until the screw rotation and back-off are harmonized. Sometimes the barrel temperature has to be raised above the recommended setting to achieve this range. \x0d\ \x0d\ Setting a back pressure that is too high can also cause the screw to stall or slip. Increasing the back pressure setting also increases the amount of energy going into the material. If the back pressure is set too high, then the screw may not be able to generate enough forward melt delivery pressure to overcome the backpressure of the backpressure, and the screw will rotate in a certain position without backing off, which will do more work on the melt and significantly increase the melt temperature, which can adversely affect the product quality and cycle time. The back pressure applied to the melt can be adjusted by means of a control valve on the injection barrel. \x0d\ \x0d\2, Equipment Influence \x0d\ If the cause of injection molding machine screw slippage is due to the processing equipment rather than the process parameters, then screw and barrel wear is likely to be the problem. As with the charging section, the resin adheres to the barrel wall as it melts in the compression section of the screw. As the screw rotates, the material is sheared away from the barrel wall and transported forward. If there are wear areas on the screw and barrel, the screw will not effectively convey material forward. If wear is suspected, the screw and barrel should be inspected and the mating gap between them checked. If the fit clearance between the screw and barrel exceeds standard values, replacement or repair work should be initiated. \x0d\ \x0d\\ injection molding machine screw design parameters, especially the compression ratio (depth of the charging section over the depth of the homogenizing section) plays a crucial role in plasticizing uniformity. A too shallow charging section (to get a smaller compression ratio) reduces output and can cause screw slippage due to underfeeding. Suppliers of various resins generally have recommended optimum compression ratios for injection molded materials. \x0d\ \x0d\ 3. Failure of the non-return ring (check valve) can also cause the screw to slip. When the screw is rotating and plasticizing. material, the non-return ring should be in the front (open) position, contacting the stationary ring seat. If the non-return ring is in the backward (closed) position, or between the forward and backward positions, the molten polymer will resist passing through the gap between the non-return ring and the ring seat. If you suspect a problem with the non-return ring it should be replaced immediately. \x0d\ \x0d\ Resin feed hoppers can also be responsible for a wide range of injection molding screw slippage. Correct hopper design is essential to ensure that a consistent flow of material can be delivered, but this is often overlooked. Generally speaking, new, uniformly sized pellets work well in a square hopper (with a sudden narrowing at the bottom) that contains a sudden change in compression zone. However, this is not the case when recycled material is added. The shape and size of the re-crushed pellets are very inconsistent, which affects the uniformity of the feed. Inconsistent feeding means that the injection molding machine screw rod cannot maintain uniform delivery pressure on the melt, which in turn creates slippage. To solve this problem and address the difference in size of the recycled material and the new pellet size, try using a round hopper that involves a gently compressed zone (a gently gradient shape at the bottom). \x0d\ \x0d\4, Material Uniformity \x0d\ As mentioned above, the shape and size of the material pellets affects the coherence of the feed. Poorly shaped granules can cause degradation of screw processing performance, fluctuations in output, and injection molding machine screw slippage. Uniformly shaped pellets are more tightly packed in the charging section of the screw. The more tightly packed the pellets are in the screw, the more time the material has to melt and move forward in the screw. Poorly shaped pellets will have more free volume (lower bulk density or more vacuum zones between pellets) and will be difficult to feed, causing the screw to slip. Increasing the temperature in the rear section of the barrel allows the material to start melting faster and the melt stream to gain more compressibility. \x0d\ \x0d\ When processing hygroscopic materials such as nylon, moisture can also cause screw slippage. Improper material drying can significantly reduce the viscosity of the material in the barrel and create water vapor, making it difficult for the injection molding machine screw to convey material forward. A hygrometer should be used at the bottom of the drying hopper to measure the humidity value of the granule and compare the reading with the humidity content recommended by the material supplier. Dongguan Huahong suggestions, hope to adopt