The structure and processing quality of injection mold directly affect the quality and production efficiency of plastic parts. In the injection mold production and the plastic product production practice most common, most frequently appears some mold breakdown and its main reason analysis elimination are as follows.
1. It is difficult to discharge the gate. In the process of injection molding, the sprue is stuck in the sprue sleeve and is not easy to come out. Crack damage occurred in the product during mold opening. In addition, the operator must use the tip of the copper rod from the nozzle, make it loose before demoulding, seriously affecting the production efficiency. The main reason for this kind of failure is the poor finish of the gate taper hole and the knife marks in the peripheral direction of the inner hole. Secondly, the material is too soft, the small end of the taper hole is deformed or damaged after a period of use, and the spherical arc of the nozzle is too small, resulting in riveting head of the sprue material here. The taper hole of gate sleeve is difficult to process, standard parts should be used as far as possible, if you need to process by yourself, you should also make or buy special reamer. Taper hole should be ground to Ra0.4 or above. In addition, a sprue pull rod or sprue ejection mechanism must be provided.
2. Damage of guide column. Guide column mainly plays a guiding role in the mold, to ensure that the core and cavity molding surface in any case do not touch each other, can not be used as a guide column force parts or positioning parts. In the following cases, when the injection is moving, the fixed mold will produce huge lateral offset force: (2). The side of the plastic part is not symmetrical, for example, the two sides of the stepped parting face of the mold are not equal to the negative pressure.
3. For large molds, due to the different filling rate in each direction, as well as the impact of the dead weight of the mold in the process of filling, dynamic, fixed mold deviation. In the above several cases, the lateral offset force during injection will be added on the guide column. During mold opening, the guide column surface will be pulled and damaged. In severe cases, the guide column will be bent or cut off, or even the mold cannot be opened. In order to solve the above problems in the mold parting surface to add a high strength positioning key four sides each one, the most simple and effective is the use of cylindrical keys. The verticality of the guide column hole and the parting surface is very important. In the processing is the use of moving, fixed die alignment position clamping, boring machine finished at a time, so as to ensure that the moving, fixed die hole concentricity, and make the verticality error is the minimum. In addition, the heat treatment hardness of guide column and guide sleeve must meet the design requirements.
4. Flexible formwork bending. When the mold is injected, the molten plastic in the mold cavity will generate huge negative pressure, generally 600 ~ 1000 kg/cm? . Mold makers sometimes do not pay attention to this problem, often change the original design size, or the moving template with low strength steel plate instead, in the mold with ejector rod jacking, because the two sides of the seat span is large, resulting in the injection of the template bending. Therefore, the moving formwork must be made of high quality steel with sufficient thickness. Low-strength steel plates such as A3 cannot be used. When necessary, support columns or blocks should be set below the moving formwork to reduce the thickness of the formwork and improve the bearing capacity.
5. Bending, fracture or leakage of the ejector rod. The quality of self-made jacking rod is better, which means that the processing cost is too high. Now standard parts are generally used and the quality is poor. If the clearance between the ejector rod and the hole is too large, there will be material leakage. However, if the clearance is too small, the ejector rod will be stuck due to the high mold temperature rise and expansion during injection. What is more dangerous is that sometimes the jacking rod is pushed out of the general distance and the jacking is not moving, the result is that the exposed jacking rod cannot be reset at the next closing and the punch is damaged. In order to solve this problem, the ejector rod is re-polished and grinded. The matching section of 10 ~ 15mm is reserved at the front end of the ejector rod, and the middle part is grinded 0.2mm smaller. All ejector rods must be strictly inspected for fit clearance after assembly, generally within 0.05~0.08 mm, to ensure that the entire ejector mechanism can advance and retreat freely.
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