Detailed introduction

10

2022

-

10

How to prevent the alloy screw from slipping? Let's take a look


Whenalloy screwWhen it is difficult to press the material at the feed port, or sufficient adhesion force cannot be formed along the length of the barrel to convey the material, the screw slips. In the screw preforming stage, when the screw rotates in the barrel to convey the material in the direction of the screw and retreat for the next injection to accumulate the material, the screw will also slip. If the screw starts to slide during the preforming stage, the axial movement of the screw will stop as the screw continues to rotate. Usually, screw slippage will lead to material degradation before injection molding, and some product quality problems such as short injection and prolonged processing cycle will occur.

  

合金螺杆


The reasons for the slippage of the alloy screw include excessive back pressure, overheating or overcooling of the rear half of the barrel, wear of the barrel or screw, too shallow screw groove of the screw feed section, improper design of the hopper, lack of material or blockage of the hopper, wet resin, The lubricant content in the resin is too high, the particle size of the material is too fine, and the cutting shape of the resin or recycled material is poor.

Influence of process parameters:

The low temperature of the rear barrel is usuallyalloy screwThe main cause of slippage. The barrel of an injection molding machine is divided into three sections. At the rear of the feed section, the material forms a thin layer of molten polymer during heating and compression. The molten film layer adheres to the barrel. Without this thin layer, the particulate matter is difficult to transport forward.

The material in the feed section needs to be heated to a critical temperature to produce a critical molten film. However, the residence time of the material in the barrel is often too short to allow the polymer to reach this temperature. This situation may be caused by the small scale of the apparatus and the corresponding configuration of the smaller barrels and screws. If the residence time is too short, the polymer will melt or be insufficiently mixed, which will cause the screw to slip or stop.

Now, introduce two simple ways to deal with this problem. Add a small amount of material from the end of the barrel for cleaning and check the melting temperature. If the residence time is short, the melting temperature will be lower than the set value of the barrel temperature. The second method is to observe the molded product. If marble markings, black spots or bright stripes are found, the materials in the barrel are not well mixed.

One of the ways to solve the slip of the alloy screw is to gradually increase the temperature of the feed section until the rotation and retreat of the screw are coordinated. Sometimes, in order to achieve this range, the barrel temperature needs to be increased above the recommended set point.

Setting too high a back pressure can also causealloy screwStall or slip. Increasing the set point of the back pressure also increases the energy entering the material. If the back pressure is set too high, the screw may not be able to generate enough positive melt pressure to overcome the back pressure of the back pressure, and the alloy screw will rotate at a certain position without receding, which will do more work on the melt and significantly Increase the melt temperature, which will adversely affect product quality and cycle time. The back pressure exerted on the melt can be adjusted by means of a control valve on the injection cylinder. Impact of equipment

If alloy screw slip is caused by processing equipment rather than process parameters, screw and barrel wear may be a critical issue. As in the feed section, when the resin is melted in the compression section of the screw, it will adhere to the barrel wall. When the screw rotates, the material leaves the cylinder wall and is transported forward after being subjected to shear force. If there are worn areas on the screw and barrel, the screw cannot effectively convey the material forward. If equipment wear is suspected, check the screw and barrel, and check the fit clearance between them. If the fit clearance between the screw and the barrel exceeds the standard value, it should be replaced or repaired.