Industry information

Injection mold malfunction, emergency treatment tips

2021-09-23

Injection mold malfunction, emergency treatment tips!

1, guide column damage

The guide column in the mold mainly plays a guiding role, to ensure that the core and cavity of the 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 two cases, the moving and fixed mold during injection will produce a large lateral displacement force:

• When the wall thickness of plastic parts is not uniform, the material flow is too thick and the wall speed is large, which produces large pressure here;

• The sides of the plastic parts are not symmetrical, such as a step parting die, the opposite sides are not subjected to equal back pressure.

2. It is difficult to strip the gate

In the process of injection molding, the gate is stuck in the gate sleeve and is not easy to come out. Crack damage occurs when the die is opened. In addition, the operator must use the tip of the copper rod to knock out from the nozzle, so that it can be loosened before demoulding, seriously affecting the production efficiency.

This kind of fault is mainly caused by poor finish of the sprue conical hole and knife marks in the circumferential direction of the inner hole. The second is that the material is too soft, after using for a period of time, the small end of the cone hole is deformed or damaged, and the spherical radian of the nozzle is too small, resulting in the riveting head of the gate material here. The cone hole of the gate sleeve is difficult to process, so standard parts should be used as far as possible. If you need to process by yourself, you should also make a special reamer or buy it. The taper hole shall be ground to below Ra0.4. In addition, a sprue puller or sprue ejector must be installed.

3. Dynamic and fixed mode migration

Large mold, because of the different charging rate in each direction, as well as the influence of die weight when loading mold, dynamic and fixed mold deviation. In these cases, the lateral offset force will be added to the guide column during injection, and the surface of the guide column will be pulled and damaged when the mold is opened. In serious cases, the guide column will be bent or cut off, or even unable to open the mold.

In order to solve the above problems, a high strength positioning key is added on the parting surface of the mold, the most simple and effective is to use cylindrical keys. The perpendicularity of the guide hole to the parting surface is very important. In processing is the use of dynamic, fixed die alignment position after clamping, boring in the boring machine, so as to ensure the dynamic, fixed die hole concentricity, and make the verticality error minimum. In addition, the hardness of heat treatment of guide column and guide sleeve must meet the design requirements. 

4, dynamic template bending

When the mold is injected, the molten plastic in the mold cavity produces huge back pressure, generally in 600 ~ 1000 kg/cm 2. Mold makers sometimes do not pay attention to this problem, often change the original design size, or replace the moving template with low strength steel plate, in the mold with a jacking rod, because of the large span on both sides of the seat, resulting in the injection of the template bending.

Therefore, the moving template must choose high-quality steel, to have enough thickness, must not use A3 and other low strength steel plate, when necessary, should be set under the moving template support column or support block, in order to reduce the thickness of the template, improve the bearing capacity.

5, push rod bending, fracture or leakage

Self-made push rod quality is better, that is, the processing cost is too high, now usually choose standard parts, the quality is general. If the gap between the ejector rod and the hole is too large, there will be leakage, but if the gap is too small, the ejector rod will be stuck due to the rise of mold temperature during injection. More dangerous is that sometimes the push rod is pushed out of the general distance and does not move and break, so that the next time the die is closed, the exposed push rod cannot be reset and the concave die is broken.

In order to solve this problem, the push rod is reground, keeping 10~ 15mm fitting section at the front of the push rod, and grinding 0.2mm smaller in the middle part. All ejector rods must be strictly checked after assembly, generally within 0.05~0.08 mm, to ensure that the whole ejector mechanism can advance and retreat freely.

6. Poor cooling or water leakage

The cooling effect of mold directly affects the quality and production efficiency of products, such as poor cooling, product shrinkage, or uneven shrinkage and warping deformation defects. On the other hand, the mold as a whole or part of the overheating, so that the mold can not be normal molding and production, serious make the push rod and other moving parts of the thermal expansion stuck and damaged.

Cooling system design, processing depends on the shape of the product, do not omit this system because of the complex structure of the mold or processing difficulties, especially large and medium-sized molds must fully consider the cooling problem.

7. The length of the guide groove is too small

Some molds are limited by the template area, the length of the guide groove is too small, and the slider is exposed outside the guide groove after the core-pulling action is finished. In this way, the slider is easy to tilt in the stage after the core-pulling and the initial stage of the mold reset, especially when the mold is closed, the slider is not reset, so that the slider damage, even bending damage. According to experience, the length of the slide block left in the chute should not be less than 2/3 of the full length of the guide chute after the core-pulling operation is completed.

8. The distance tension mechanism is out of order

Swing hook, buckle and other distance tension mechanism is generally used for fixed mold core pulling or some secondary demoulding mold, because this kind of mechanism is set in pairs on the two sides of the mold, its action requirements must be synchronized, that is, the mold at the same time buckle, open the mold to a certain position at the same time decoupling.

Once the synchronization is lost, it is bound to cause the template skew and damage of the drawing mold. The parts of these institutions should have higher stiffness and wear resistance, and it is difficult to adjust. The service life of the institutions is short, so avoid using it as far as possible and use other institutions. In the case of relatively small pumping force can be used to push the method of fixed mold spring, in the case of relatively large core pulling force can be used to move back when the core sliding, first complete the core pulling action and then mold parting structure, in large molds can be used hydraulic cylinder core pulling. Inclined pin slide block core-pulling mechanism is damaged.

The most common faults of this mechanism are not in place in processing and the material is too small, there are mainly the following two problems:

• A large dip Angle of the pin;

• The advantage is that large core pulling distance can be produced in short die opening stroke.

However, if the inclination Angle A is too large, when the pulling force F is A certain value, the bending force P=F/COSA received by the inclined pin in the process of pulling the core is also larger, and it is easy to appear the deformation of the inclined pin and the wear of the inclined hole.

At the same time, the upward thrust N=FTGA generated by the inclined pin on the slide block is larger, which increases the positive pressure of the slide block on the guide surface in the guide groove, thus increasing the friction resistance of the slide block when sliding. Easy to cause smooth, guide groove wear. As A rule of thumb, inclination A should not be greater than 25°.