Plastic mold accessories are tools for producing plastic products; It is also a tool to endow plastic products with complete structure and precise size. The structure and processing quality of plastic mold accessories directly affect the quality and production efficiency of plastic products. The most common failure causes and troubleshooting methods of plastic mold accessories in the production practice of plastic mold accessories and plastic products are detailed as follows:
1. The gate is difficult to unload. In the injection molding process, the gate is stuck in the gate sleeve and is not easy to come out. When the mold is opened, the product is cracked and damaged. In addition, the operator must knock out the nozzle with a copper rod tip to loosen it before demoulding, which seriously affects the production efficiency. The main reason for this kind of failure is the poor finish of the gate taper hole and the knife mark in the circumferential 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 radian of the nozzle is too small, causing the gate material to produce rivet heads here. The taper hole of the sprue sleeve is difficult to process, so the standard parts should be used as far as possible. If you need to process it yourself, you should also make or purchase a special reamer. The taper hole shall be ground to Ra0.4 or above. In addition, the gate pulling rod or gate ejection mechanism must be set.
2. The guide post is damaged. The guide pillar mainly plays a guiding role in the mold to ensure that the molding surface of the core and cavity will not collide with each other under any circumstances. The guide pillar cannot be used as a force bearing part or positioning part. In the following cases, when the injection is moving, the fixed mold will produce huge lateral offset force: (1) When the wall thickness of the plastic part is required to be uneven, the material flow will pass through the thick wall at a high speed, which will generate a large pressure here; (2). The side of the plastic part is not symmetrical, for example, the opposite sides of the mold with stepped parting surface are subjected to unequal back pressure.
3. For large molds, due to the different charging rates in all directions and the influence of the self weight of the mold during mold installation, the dynamic and fixed mold offsets occur. In the above cases, the lateral offset force will be applied to the guide post during injection, and the surface of the guide post will be roughened and damaged during mold opening. In severe cases, the guide post will be bent or cut off, or even unable to open the mold. In order to solve the above problems, one high-strength positioning key is added on the parting surface of the die, and the most simple and effective way is to use a cylindrical key. The perpendicularity between the guide post hole and the parting surface is very important During processing, the moving and fixed die are aligned and clamped, and then the boring is completed on the boring machine at one time, so as to ensure the concentricity of the moving and fixed die holes and minimize the perpendicularity error. In addition, the heat treatment hardness of guide post and guide sleeve must meet the design requirements.
4. The movable formwork is bent. When the mold is injected, the molten plastic in the mold cavity produces a huge back pressure, which is generally 600~1000 kg/cm. Mold makers sometimes do not pay attention to this problem, and often change the original design size, or replace the moving template with low strength steel plate. In the mold with ejector rod for ejecting, due to the large span of both sides of the seat, the template bends down during injection. Therefore, the movable formwork must be made of high-quality steel with sufficient thickness. Low strength steel plates such as A3 shall not be used. If necessary, support columns or blocks shall be set under the movable formwork to reduce the thickness of the formwork and improve the bearing capacity.
5. The ejector rod is bent, broken or leaked. The quality of self-made ejector rod is good, but 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 be stuck due to the expansion of the mold temperature during injection. What is more dangerous is that sometimes the ejector pin can not be moved when it is pushed out for a general distance and breaks off. As a result, the exposed ejector pin cannot be reset during the next mold closing, which damages the mold. In order to solve this problem, the ejector pin shall be reground. A fitting section of 10~15mm shall be reserved at the front end of the ejector pin, and the middle part shall be reground by 0.2mm. After all ejector rods are assembled, the lifting and fitting clearance must be strictly checked, generally within 0.05-0.08mm, to ensure that the whole ejector mechanism can move forward and backward freely.