Injection mold failure, should be eliminated......

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The structure form and processing quality of injection mold directly affect the quality of plastic products and production efficiency. In this paper, the most common failures in mold production are briefly analyzed.

 

1. Difficulty in gate stripping

In the process of injection, the gate is stuck in the gate sleeve and is not easy to come out. Crack damage occurred during mold opening. In addition, the operator must use the tip of the copper rod from the nozzle to knock out, so that the loose rear can be demoulded, seriously affecting the production efficiency.

 

The main reason for this failure is poor finish of the taper hole of the sprue, and there are knife marks in the circumjacent direction of the inner hole. Secondly, the material is too soft, after a period of time, the small end of the taper hole is deformed or damaged, and the spherical radian of the nozzle is too small, resulting in the riveting head of the sprue material here. The taper hole of the gate cover is difficult to process, so standard parts should be used as far as possible. If you need to process by yourself, you should also make yourself or buy special reamer. Taper hole shall be ground to below RA0.4. In addition, a gate pull rod or gate ejection mechanism must be provided.

 

2. Guide pillar damage

The guide pillar in the mold mainly plays a guiding role, in order to ensure that the core and the cavity of the forming surface in any case do not touch each other, cannot be used as a guide pillar force or positioning parts. Under the following conditions, moving and fixed mold during injection will produce huge lateral deflection force:

 

(1) when the wall thickness of plastic parts is not uniform, the rate of material flow through the thick wall is large, and a large pressure is generated here;

 

(2) the side of the plastic parts is not symmetrical, such as the stepped parting surface of the mold, the opposite two sides of the back pressure is not equal.

Injection mold 

3. Moving and fixed mode deviation

For large molds, due to the different charging rates in each direction and the influence of the dead weight of the molds, the moving and fixed mold deviation will occur.


In these cases, the lateral deflection force will be applied to the guide post during injection, and the guide post surface will be drawn during die opening, and the guide post will be bent or cut off in severe cases, or even unable to open the die.

 

In order to solve the above problems, a high strength positioning key is added on the parting surface of the mold. The most simple and effective one is the cylindrical key.


The verticality of guide hole and parting surface is very important.


In the processing is the use of moving, fixed mold alignment position after clamping, the boring machine once finished, so as to ensure the moving, fixed mold hole concentricity, and minimize the verticality error.


In addition, the heat treatment hardness of the guide post and guide sleeve must meet the design requirements.

 

4. Moving template bending

When the mold is injected, the molten plastic in the mold cavity produces huge back pressure, which is generally 600 ~ 1000 kg/cm ². Mold makers sometimes do not pay attention to this problem, often change the original design size, or replace the moving template with low strength steel plate, in the mold with jacking rod jacking, because of the large seat span on both sides, resulting in the injection of the template bending down. Therefore, the moving template must choose high quality steel, to have sufficient thickness, A3 and other low strength steel plate must not be used, when necessary, should be set up under the moving template supporting column osupporting block, in order to reduce the thickness of the template, improve the bearing capacity.

 

5. Bending, breaking or leakage of jacking rod

Self-made top rod quality is better, that is, the processing cost is too high, now usually choose standard parts, the quality is general. If the gap between the jacking rod and the hole is too large, there will be leakage, but if the gap is too small, the jacking rod will expand and become stuck due to the high mold temperature during injection. More dangerous is that sometimes the jacking rod is pushed out of the general distance on the jacking and broken, the results in the next die closing this exposed jacking rod cannot be reset and hit the die.

 

To solve this problem, the jacking rod was reground with a 10-15mm fit section on the front end of the jacking rod and a 0.2mm smaller fit on the middle part.


All the jacking rod in the assembly, must strictly check the match clearance, generally within 0.05~0.08 mm, to ensure that the whole jacking mechanism can advance and retreat freely.

 

6. Poor cooling or water leakage

The cooling effect of the mold directly affects the quality and production efficiency of the products, such as poor cooling, large shrinkage of the products, or uneven shrinkage and surface warping deformation and other defects. On the other hand, the mold as a whole or part of the overheating, so that the mold can not be formed normally and stop production, serious causes the jacking rod and other movable parts of thermal expansion stuck and damaged. The design of the cooling system and the processing are determined by the shape of the product. Do not leave out the system because of the complex structure of the mold or the difficult processing. Especially the large and medium-sized mold must fully consider the cooling problem.


We are aware of the importance of timely elimination of injection mold failures. Siko will provide you with the reasons for the best quality engineering plastic manufactured by our highly skilled and experienced personnel using advanced technology. For more information, please contact us in time: kevin@sikopolymers.com


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