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Skills and methods to troubleshoot injection mold failures (part 2)

update:28-01-2021
abstract:

5. The ejector rod is bent, broken or leaking The self- […]

5. The ejector rod is bent, broken or leaking

The self-made ejector rods are of better quality, but the processing cost is too high. Nowadays, standard parts are usually used and the quality is average. If the gap between the ejector pin and the hole is too large, leakage will occur, but if the gap is too small, the ejector pin will become stuck due to the increase in mold temperature during injection. What's more dangerous is that sometimes the ejector rod will not move and break when it is ejected for a normal distance. As a result, the exposed ejector rod cannot be reset during the next mold clamping and will damage the die.

In order to solve this problem, the ejector rod was re-ground, and the mating section of 10~15 mm was retained at the front end of the ejector rod, and the middle part was ground 0.2 mm smaller. After all ejector rods are assembled, the fitting clearance must be strictly checked, generally within 0.05~0.08 mm, to ensure that the entire ejector mechanism can move forward and backward freely.

6. Poor cooling or water leakage

The cooling effect of the mold directly affects the quality and production efficiency of the product, such as poor cooling, large product shrinkage, or uneven shrinkage, resulting in warping deformation and other defects. On the other hand, the whole or part of the mold is overheated, so that the mold cannot be formed normally and the production is stopped. In severe cases, the movable parts such as the ejector rod will be thermally expanded and become damaged.

The design and processing of the cooling system depends on the shape of the product. Don't omit this system because of the complex structure of the mold or the difficulty in processing. Especially for large and medium-sized molds, the cooling problem must be fully considered.

7. The length of the guide groove is too small

Some molds are limited by the area of ​​the template and the guide groove length is too small. The slider will be exposed outside the guide groove after the core pulling action is completed. This will easily cause the slider to tilt during the core pulling stage and the initial stage of mold closing and resetting, especially during mold clamping. At this time, the slider is not reset smoothly, causing damage to the slider, or even bending damage. According to experience, after the slider completes the core pulling action, the length left in the chute should not be less than 2/3 of the full length of the guide groove.

8. The fixed-distance tensioning mechanism fails

Swing hooks, buckles and other fixed-distance tensioning mechanisms are generally used in fixed mold core pulling or some secondary demolding molds. Because such mechanisms are set in pairs on both sides of the mold, their actions must be synchronized, that is, The mold is closed at the same time, and the mold is opened to a certain position and released at the same time.

Once the synchronization is lost, it will inevitably cause the template of the drawn die to be skewed and damaged. The parts of these mechanisms must have higher rigidity and wear resistance, and adjustment is difficult. The life of the mechanism is short. Avoid using it as much as possible. You can use other mechanisms. When the core pulling force is relatively small, the spring can be used to push out the fixed mold. When the core pulling force is relatively large, the core can be used to slide when the movable mold is retracted. The core pulling action is completed first and then the mold is divided. A hydraulic cylinder can be used to pull the core on the mold. The oblique pin slider core pulling mechanism is damaged. The more common problems of this kind of organization are mostly inadequate processing and too small materials.