The structure and processing quality of Stool Mould directly affect the quality and production efficiency of plastic parts. Some stool mould failures and their main causes are the most common in the production of stool moulds and plastic products.

1. It is difficult to *** the gate. In the process of injection moulding, the sprue is stuck in the sprue bushing, which is not easy to come out. When the mould is opened, the product appears *** damage. In addition, the operator must knock out the nozzle with the tip of copper rod to loosen it before demoulding, which seriously affects the production efficiency.

2. The guide pillar is damaged. The guide pillar mainly plays a guiding role in the mould to ensure that the moulding surfaces of the core and the cavity do not collide with each other under any circumstances, and the guide pillar cannot be used as a force-bearing part or a positioning part. In the following cases, when the injection is moving, the mould fixing will produce huge lateral offset force:

(1) When the wall thickness requirements of plastic parts are uneven, the material flow passes through the thick wall at a high speed, which produces a large pressure here;

(2) The sides of plastic parts are asymmetrical, such as the dies with stepped parting surfaces, and the opposite sides are not equal in back pressure.

3. For large dies, due to different filling rates in different directions, and due to the influence of die dead weight during die loading, moving and fixed die offset occurs. In the above cases, the lateral offset force will be applied to the guide pillar during injection, and the surface of the guide pillar will be galling and damaged during mould opening. In severe cases, the guide pillar will be bent or cut off, and even the mould cannot be opened.

4. Bending of moving formwork. When the mould is injected, the molten plastic in the mould cavity produces huge back pressure, which is generally 600 ~ 1000 kg/cm2. Sometimes die makers don’t pay attention to this problem, and often change the original design size, or replace the moving die plate with low-strength steel plate. In the die with ejector pin, because of the large span of two side seats, the die plate bends down during injection.

5. The ejector rod bends, breaks or leaks. Self-made mandrels have better quality, that is, the processing cost is too high. Now, standard parts are generally used, and the quality is poor. If the gap between the ejector pin and the hole is too large, material leakage will occur, but if the gap is too small, the ejector pin will expand and become stuck during injection due to the increase of mould temperature. What’s more dangerous is that sometimes the ejector pin can’t move and break when it is pushed out by a general distance, and as a result, the exposed ejector pin can’t be reset during the next mould closing, thus damaging the female die.

6. Poor cooling or water leakage. The cooling effect of dies directly affects the quality and production efficiency of products, such as poor cooling, large shrinkage of products, or uneven shrinkage resulting in warpage and other defects. On the other hand, the whole or part of the die is overheated, which makes the die unable to form normally and stops production. In severe cases, the moving parts such as ejector pins are stuck and damaged by thermal expansion.

7. The distance tensioning mechanism fails. Fixed-distance tensioning mechanisms, such as swinging hooks and buckles, are generally used in fixed mould core-pulling or some secondary demoulding moulds. Because these mechanisms are set in pairs on both sides of the mould, their actions must be synchronized, that is, closing the mould while snapping, and opening the mould to a certain position while unhooking.

8. Due to the limitation of template area, the guide slot length of some dies is too small, and the slider is exposed outside the guide slot after core pulling, which easily causes the slider to tilt in the post-core pulling stage and the initial stage of closing and resetting, especially when closing the mould, the slider is not reset smoothly, causing damage to the slider and even bending damage. According to experience, the length of the slider left in the chute after core pulling should not be less than 2/3 of the total length of the guide groove.

9. Finally, when designing and manufacturing the mould, according to the requirements of plastic parts quality, batch size, manufacturing period and other specific conditions, it can not only meet the product requirements, but also be the most simple and reliable in mould structure, easy to process and low in cost, which is the most perfect mould.

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