1.Guiding column damage
The guide post mainly plays a guiding role in the mold to ensure that the molding surfaces of the core and the cavity do not touch each other under any circumstances, and the guide post cannot be used as a force member or a positioning member. In the following two cases, when moving, the fixed mold will produce a huge lateral offset force: When the wall thickness of the plastic part is not uniform, the flow rate through the thick wall is large, and a large pressure is generated here; The sides of plastic parts are asymmetric, such as a stepped parting surface mold, and the opposing pressures on the opposite sides are not equal.
2. Difficult to discharge gate
During the injection molding process, the gate is stuck in the gate sleeve and is not easy to come off. When the mold is opened, crack damage occurs. In addition, the operator must knock out the nozzle with the tip of a copper rod to loosen it before demoulding, which seriously affects production efficiency.
The main reason for this failure is the poor finish of the taper hole of the gate and the presence of knife marks in the circumferential direction of the inner hole. Secondly, the material is too soft, the small end of the tapered hole is deformed or damaged after a period of use, and the spherical curvature of the nozzle is too small, which causes the gate material to produce a rivet head here. The taper hole of the gate sleeve is difficult to process. Standard parts should be used as much as possible. If you need to process it yourself, you should also make or buy a special reamer. Taper holes need to be ground to Ra0.4 or less. In addition, a gate pulling rod or a gate ejection mechanism must be provided.
3.Movement and fixed mold offset
For large molds, due to the different filling rates in each direction, and due to the weight of the mold during mold loading, shifting of the movable and fixed molds occurs. In these cases, the lateral offset force will be added to the guide post during injection. The surface of the guide post will be fuzzed and damaged when the mold is opened. In severe cases, the guide post will be bent or cut off, and even the mold cannot be opened.
In order to solve the above problems, a high-strength positioning key is added on each side of the mold parting surface, and the most convenient and effective is to use a cylindrical key. The verticality of the guide hole and the parting surface is very important. During processing, the moving is used. After the fixed mold alignment position is clamped, the boring is completed once on the boring machine. This can ensure the concentricity of the moving and fixed mold holes 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 generates a huge back pressure, which is generally 600 ~ 1000 kg / cm 2. The mold maker sometimes does not pay attention to this problem, often changes the original design size, or replaces the movable template with a low-strength steel plate. In a mold that uses ejector pins, the template has a large bending span during injection, which causes the template to bend down during injection.
Therefore, the moving formwork must be made of high-quality steel, and it must have sufficient thickness. Low-strength steel plates such as A3 must not be used. When necessary, support columns or blocks should be set under the moving formwork to reduce the thickness of the formwork and improve the carrying capacity.