Reasons for frequent problems with injection molds

1. Difficult to take off the sprue

During the injection molding process, the sprue sticks in the sprue sleeve and is not easy to be taken out. When the mold is opened, the finished product shows crack damage. Besides, it is necessary for the operator to knock out from the nozzle with a copper rod top to make it loose before demoulding, which seriously affects the production power.

The primary element of this shortcoming is the poor brightness of the conical hole of the sprue and the knife marks in the circumference of the inner hole. Secondly, the material is too soft, and the small end of the cone hole is deformed or damaged after using for a period of time, and the arc of the nozzle sphere is too small, resulting in the riveting head of the sprue material here. The tapered hole of the sprue is difficult to process, so standard parts should be used as much as possible, and if you need to process it by yourself, you should also buy a special reamer. The tapered hole should be ground to Ra0.4 or more. In addition, it is necessary to set the sprue pulling rod or sprue ejecting.

2. Large moulds moving and fixed mould offset

Large molds have different charging rates in each direction and the mold is affected by the weight of the mold when it is installed. In the above cases, the lateral offset force will be added to the guide column when the needle is punched, and when the mold is opened, the exterior of the guide column will be stretched and damaged, and when it is serious, the guide column will be bent or blocked, and even the mold cannot be opened.

In order to deal with the above problems, in the mold parting surface to add a high-strength positioning key on each of the four sides, the most simple and useful is the use of cylindrical keys. The straightness of the guide pillar hole and the parting surface is crucial, in the processing is the choice of dynamic, fixed die alignment after clamping, boring machine in a boring, so as to ensure the concentricity of the dynamic, fixed die hole, and make the straightness of the minimum error. In addition, the guide pillar and guide sleeve heat treatment hardness is necessary to reach the program requirements.

3. Guide pillar damage

Guide pillar in the mold plays a primary role in guiding, to ensure that the core and cavity molding surface in any case do not touch each other, can not be used as a guide pillar force or positioning parts.

In several cases, endless lateral deflection force will occur in the moving and fixed mold when punching. When the wall thickness of the plastic part is not uniform, the material flow through the thick wall at the rate of large, where a larger pressure; the side of the plastic part is not symmetrical, such as step-shaped parting surface of the mold on the opposite side of the two sides of the counter pressure is not equal.

4. Dynamic template bending

When the mold is shot, the molten plastic in the mold cavity occurs endless counterpressure, usually in 6001000kg/cm. Mold makers sometimes do not pay attention to this problem, usually change the original program standards, or perhaps replace the dynamic template with low-strength steel plate, in the mold with the top bar top material, due to the large span of the two sides of the seat, constituting a needle when the template down bending.

Therefore, it is necessary to use excellent steel for the moving template, to have sufficient thickness, not A3 and other low-strength steel plate, when necessary, should be set up under the moving template support column or support block, in order to reduce the thickness of the template, to advance the bearing capacity.

5. Top bar bending, cracking or leakage of material

The quality of the top bar is better, that is, the processing cost is too high, now usually use standard parts, the quality is worse. Top bar and the hole gap is assumed to be too large, it presents leakage, but the gap is assumed to be too small, due to the increase in mold temperature, top bar expansion and jamming when hitting.

More risky is that sometimes the top bar is jacked out of the usual interval on the top can not be broken, the role of a mold when this section of the exposed top bar can not be reset and hit the concave mold. In order to deal with this problem, the top bar from scratch grinding, in the front of the top bar to save 10 15 mm collaboration section, the base of some grinding small 0.2 mm. All the top bar in the installation, it is necessary to strictly check the collaboration gap, usually in 0.05 0.08 mm, to ensure that all the ejector arrangement can move in and out freely.

6. Poor cooling or water leakage

The cooling effect of the mold directly affects the quality of the finished product and production power, such as poor cooling, the finished product shortened, or shortened unevenly and presented warped surface deformation and other shortcomings. On the other hand, all or some of the mold overheating, so that the mold can not be normal molding and stop production, the severe case so that the top bar and other moving parts of thermal expansion stuck and damaged.

Cooling system program, processing to commodity shape, do not due to the mold structure or processing difficulties and omit this system, especially the medium and large mold must be s adequate consideration of cooling problems.

7. Slider tilt, reset is not smooth

Some molds are bound by the template area, the length of the guide slot is too small, the slider in the core action after the end of the exposed guide slot outside, so in the core after the period and the initial period of the mold reset are briefly constitute the slider tilt, especially in the mold, the slider reset is not smooth, so that the slider damage, and even bending damage. According to experience, the slider end of the core action, the length of the slide should not be less than 2/3 of the full length of the guide slot.

8. Fixed distance tensioning arrangement failure

Pendulum hooks, buckles and other fixed distance tensioning arrangements are usually used in fixed die core or some secondary demoulding molds, because these arrangements are set in pairs on both sides of the mold, the action requires synchronization, that is, the mold together with the buckle, open the mold to a certain position together with the hook.

Once the synchronization is lost, the template of the pulled mold will be tilted and damaged, the parts of these arrangements should have high stiffness and wear resistance, and the adjustment is also very difficult, the life of the arrangement is short, try to prevent the use, and can use other arrangements.

In the case of small extraction force can be used to push out the fixed mold taut spring approach, in the case of large extraction force can be used when the dynamic mold retreat core sliding, the first end of the core extraction action before the mold structure, in large molds can be used in hydraulic cylinder core extraction. Inclined pin slider type core extraction arrangement damage.

This arrangement more often presents the shortcomings are mostly processing is not in place as well as the material is too small, the first two questions are as follows.

Slant pin inclination angle A is large, the benefit is to be able to occur in a shorter mold opening stroke than the large core distance. However, if the angle of inclination A is too large, when the extraction force F is a certain value, the bending force P=F/COSA in the process of core extraction will be bigger, and the bevel pin will be easily deformed and the bevel hole will be worn.

At the same time, the upward thrust force N=FTGA on the slider is also bigger, which increases the positive pressure of the slider on the guide surface in the guide groove, and then increases the resistance of the slider when sliding. Easy to constitute the sliding is not smooth, guide groove wear. According to experience, the angle of inclination A should not be greater than 25.

9. Injection mold in the exhaust is not smooth

There is often gas in the injection mold, which is caused by what?

The air in the cavity of casting system and mold; some materials are rich in water that has not been dried and swept away, they will be vaporized into water vapor at high temperature; because the temperature is too high in injection molding, some unstable nature of the plastic will be differentiated and gas occurs; some of the plastic material additive vaporization or chemical reaction with each other to generate the gas.

The reason for poor exhaust is also to be found out quickly. Poor exhaust of injection mold will bring a series of damage to the quality of plastic parts and many other aspects, the primary embodiment: in the injection process, the melt will replace the gas in the cavity, assuming that the gas is not discharged in a timely manner will constitute a difficult filling of the melt, resulting in a shortage of shots and can not fill the cavity; poor clearance of the gas collar will constitute a high pressure in the cavity, and in a certain degree of tightness into the plastic interior, constituting a void, The quality shortcomings such as air pore, sparse arrangement and silver pattern;

As the gas is highly constricted, the temperature in the cavity rises sharply, resulting in the surrounding melt differentiation, baking, so that the plastic parts show some carbonization and scorching scene. It is mainly found in the merging of two melt flow, the gate flange; gas removal is not smooth, so that the melt into the cavity speed is not the same, and therefore easy to constitute the activity and fusion marks, and the mechanical function of the plastic parts decline; due to the obstruction of the gas in the cavity, will reduce the filling speed, affect the molding cycle, and reduce the tax power.

The distribution of bubbles in the plastic part, the air in the mold cavity, often scattered in the part opposite to the gate; plastic material in the differentiation or chemical reaction bubbles along the thickness of the plastic part; plastic material in the residual water vaporization bubbles, is irregularly scattered in all plastic parts.