Prevent the injection molding machine screw slip, from these aspects to consider!

When the screw slippage, the material is likely to gather in the feed mouth, and can not be normally transported to the end of the Injection Machine. When the screw rotates and retreats in the barrel to transport the material and prepare for the next injection, screw slippage occurs in the plasticizing section. At this time, the rotation of the screw is still inherited, but the axial activity of the screw will stop, that is, the slippage will occur. Screw slip often causes the material degradation before injection, the product quality will be reduced (such as lack of material), and the molding cycle will be prolonged.
The reasons for screw slipping are various, Probably because the back pressure is too high, the end of the barrel is too hot or too cold, barrel or screw wear, feeding section thread is too shallow, hopper is blocked, resin wet, resin lubrication, material is too fine resin and recycled material unfair cutting and other factors.
Process setting

The undercooling at the end of the cylinder is one of the main reasons for screw skidding. The cylinder of the injection machine is divided into three sections
At the end, that is, the feeding section, in the process of heating and compression, a layer of melt film will be formed and bonded to the screw. Without this film, the particles are not easily transported to the front end.

The material in the feeding section must be heated to a critical temperature to form a melt film. However, the residence time of the material in the feeding section is usually very short and can not reach the required temperature. This environment is generally produced on small injection machines. Too short residence time will cause the melting of polymer and the incomplete process of inclusion, which will lead to screw slippage or stall.

There are two simple ways to determine whether the screw produces skidding. One way is, to the end of the cylinder.
A small amount of material is added to the end to detect the melt temperature. If the residence time is too short, the melt temperature will be lower than the set point of the cylinder temperature. The second method is to check the finished product: if there are markings or dark stripes on the finished product, it means that the material is not evenly mixed in the cylinder.

Once the screw skidding phenomenon occurs, one of the solutions is to improve the temperature and straightness of the feeding section.
There is no obstacle to the rotation and retraction of the screw. In order to achieve this goal, the cylinder temperature must probably be improved to the setting point across the guarantee.

High back pressure can also cause screw stagnation or skidding. Progress back pressure setting, will improve the energy applied to the material. However, if the back pressure is set too high, the screw will not have sufficient pressure to reduce the back pressure, so that the material can not be transported to the front of the screw. At this time, when the screw rotates in a certain position without normal shrinkage, it will do more work on the material, thus significantly improving the melt temperature, resulting in the reduction of the quality of the finished product and the prolongation of the molding cycle. The back pressure of the melt can be controlled by conditioning the valve of the injection cylinder.
Hardware problems
If the screw slip is caused by equipment and not by process settings, the screw and
The wear and tear of the barrel is probably the main culprit. The resin melts in the transition section and sticks to the barrel wall, just like the feeding section. As the screw rotates, it cuts the melt down and delivers it to the front end. If the screw and barrel wear, it is difficult for the screw to effectively transport the material to the front end. If you can not determine whether it is subject to wear, you can measure the crack width between the screw and the barrel, once it is not suitable for service, it should be replaced or repaired.

The screw project, especially the compression ratio project, plays a nervous role in plasticizing. Feeding section over
Short, that is, the compression ratio is too small, will lead to low delivery and screw slip. Resin suppliers will recommend the best compression ratio for their materials.
Cause screw slip is also probably the boiler check valve (check valve) does not work properly. When the screw rotates
When turning to prepare injection, the retaining ring should be located at the front end (open position) and connected with the convex buckle of the retaining ring frame. If the retainer is at the end (i.e. closed position), roughly midway between the tail and the retainer frame, it will be difficult for the polymer melt to penetrate this crack. If there is a problem with the invention retaining ring, it should be replaced in real time.

In addition, the resin feed hopper is probably one of the factors causing the screw to slip. The precise planning of the hopper is the key to the average feeding, but this is often overlooked. A square hopper with a fast compression section (i.e., a sharp tightening at the bottom) is more suitable for processing average raw materials, but is not suitable for processing recycled materials. Since the particle size distribution of the recycled material is wide, it will affect the average feed, which means that the screw cannot transport the melt at the same pressure, which will eventually lead to slippage. To solve this problem, use a circular hopper equipped with a gradual compression section (i.e. tapering at the bottom) to handle materials with a wide particle size distribution.
Average of materials

As mentioned above, the length, particle size, and shape of the material will affect the average feed - pellets
Poor shape can also cause the screw to slip, resulting in a change in output. The average size of the pellet will be close in the feeding section, easy to melt and transport.

The shape of the individual particles will cause the free volume is too large (excess space between the particles), difficult to transport, resulting in screw slip. In this regard, you can improve the barrel end temperature, so that the melting process began earlier, but also to make the material compressed more closely to start!