Auto Unscrewing Injection Mold: Threaded Plastic

September 22, 2021

Internal plastic thread carries high accuracy due to forced ejection and auto screwing

In comparison to auto unscrewing injection plastic molding, forced molding in injection processes happens in three different conditions. The forced injection is perfect for the material that is soft as glue. For instance, the materials like PVC, PP, and PE work well with this process.

One of the most vivid differences between auto unscrewing injection and forced ejection is the difference in the shape of the tooth profile. The tooth profile of forced ejection carries a circular shape. The height of the tooth profile in forced ejection also appears to be considerably smaller in comparison to the unscrewing.

In auto unscrewing injection, some points are of integral value. It includes:

Analysis Of the Plastic Parts

The analysis of the plastic parts in auto unscrewing injection molding focuses on the plastic part that acts as a connecting pipe. This, connected pipe happens to join and connect the mechanical products. ABS is the material that manufacturers commonly use.

The most striking feature of this plastic is that it has a shrinkage rate of only 0.5%. Furthermore, plastic parts in molding injection processes are cylindrical parts. For all these parts, the most prominent feature is the presence of threads both inside and outside in a continuous pattern. The unit for the internal thread is M20 and that of the outer thread is M44. Hence, for an auto unscrewing injection, the teeth are triangular and thus there is no chance of ejecting the plastic forcibly. Releasing the mold appears to be the most difficult step in mold designs.

Analysis Of the Mold Structure

There are two ways to analyze the mold structure in auto unscrewing injection molding. Let us discuss each here:

First Case

Here the plastic part acts as a rotating body. Also, the customer is looking for 4 cavities for a project. Therefore, according to the rules and mechanism, the scenario would be, according to the assembly position of the plastic parts on the product, the production of external thread happens because of the side pulling and parting mechanism in ejection. However, on the other hand, the internal threads, adopt the formula of “motor ten chains ten sprockets”. This mechanism is the source to have internal threads.

Second Case

There are certain cases and models where we can only set the cavity of the model as per horizontal shape. This happens because of the structure of the mold. Here, we see that a plastic part makes itself the part of a circulating rotating body. Moreover, for a large end face, the gate design appears to be the best choice. In this case, the pouring system of the mold appears to go through the main channel, a gate, and a flow distribution channel.

Analyzing the Design of the Mold Part

In the auto unscrewing injection molding process, the moveable mold carries the shape of a mosaic structure.  This structure helps much in easing the overall manufacturing and also venting the cavity of the mold.

Here the mold consists of ratings 24 and 26. Moreover, for the sake of machining cavities, the combined machining method is also used. However, the mosaic structure is capable and conducive to exhaust.

Auto Screwing Thread Mechanism and Ejection System

If we are to discuss the most difficult and complex core structure in injection molding, the auto unscrewing injection happens to be the one. To work it the right way, the automatic thread removal mechanism works and it carries the structure of motor ten roller chain ten sprocket ten thread core.

By this, it means that motor 23 drives the roller chain 22. Furthermore, the roller chain 22 in turn drives the sprocket 16. Whereas, the sprocket 16 eventually drives the large sprocket shaft number 18 with the help of key 19. After that, the large sprocket shaft helps in driving the core 25 with the help of a square wedge.

We also observe that during the rotation of the threaded core, there is an attachment of reinforcing rib, which helps in playing a critical role by stopping the rotation. To do this, the plastic part in the system moves up and away from the model cavity, which is moving, in the axial direction. In the last step, using the ejector pin, we cab push the bypass in the gating system.

However, to connect the bypass to the plastic part, there is wide use of a gate. Through this, you can get the plastic move out of the box. The ejection system of this auto screwing mold and injection carries the mold using ejector pin 15. It also includes an ejector fixing plate of number 12 and so on.

Design Of the Temperature Control System

If you are looking at the mold quality of the plastic parts in auto unscrewing injection molding, the very first thing that affects the quality is the temperature control system. Furthermore, the temperature control system in the injection molding process also directly affects labor productivity.

Therefore, it is a recommendation that if someone needs to avoid affecting the melt-filling, it is the best practice to reach rapid cooling and balanced cooling. This is to be done as much as possible.

The moving side in the molding process gets colling by cooling water pipes. However, as an alternative, the fixed mold gets cooling through the use of a water well plus water pipe. Thus, if we achieve this status, then we can safely claim that the product appears to be the best in plastic quality. Otherwise, there is no guarantee for this.


Advantages of Transmission Method

We have seen that the power source in all this auto unscrewing injection molding process is the electric motor. Hence, the transmission method for is motor ten single-row roller chain plus three arc-linear tooth sprockets. To use this method, we consequently get the advantage such as:

  • The average transmission ratio of the model appears to be accurate without causing any possible slippage.
  • It carries a compact structure and holds low pressure on the shaft.
  • High transmission efficiency 98%.
  • Lower bearing cost.



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