When the mold encounters these problems, no longer scratch your ears...
1. Difficulties in gate stripping
During the injection molding process, the gate is stuck in the sprue sleeve and is not easy to come out. When the mold is opened, the finished product shows crack damage. In addition, it is necessary for the operator to knock out the top of the copper rod from the nozzle so that it can be demolded after it is loosened, which severely affects the production power.
The main element of this shortcoming is the poor brightness of the gate taper hole and the knife mark in the circumferential direction of the inner hole. The second is that the material is too soft, the small end of the taper hole is deformed or damaged after a period of use, and the spherical curvature of the nozzle is too small, causing the sprue to be riveted here. The taper hole of the sprue bushing is more difficult to process. Standard parts should be used as much as possible. If you need to process it yourself, you should also suppress yourself or buy a special reamer. The taper hole needs to be ground to Ra0.4 or higher. In addition, it is necessary to set the gate pull rod or gate ejection.
2. Large-scale mold moving and fixed mold offset
Due to the different filling rates of large molds, and the influence of the weight of the mold during mold installation, the movable and fixed molds will deviate. In the above-mentioned situations, the lateral deflection force will be added to the guide post during injection, the guide post will be roughened and damaged when the mold is opened, and the guide post will be bent or blocked in severe cases, and the mold cannot be opened.
In order to deal with the above questions, a high-strength positioning key is added on each of the four sides of the mold parting surface. The most concise and useful one is to use a cylindrical key. The straightness of the guide pin hole and the parting surface is the most important thing. In the processing, the movable and fixed molds are aligned and clamped, and the boring machine is completed at one time. This can ensure the concentricity of the movable and fixed mold holes. Minimize straightness errors. In addition, the heat treatment hardness of the guide post and the guide sleeve must meet the requirements of the plan.
3. Guide post 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 collide with each other under any circumstances. The guide post cannot be used as a force-bearing part or a positioning part.
In several cases, the moving and fixed molds will have infinite lateral deflection force during injection. When the wall thickness of the plastic part is not uniform, the material flow passes through the thick wall at a high speed, and greater pressure occurs here; the side surface of the plastic part is asymmetric, such as the stepped parting surface of the mold on the two opposite sides. The back pressure is not equal.
4. Dynamic template twists and turns
When the mold is injecting, the molten plastic in the mold cavity generates infinite back pressure, usually 600~1000 kg/cm. Mold makers sometimes don't pay attention to this question, and usually change the original plan standard, perhaps replace the movable template with a low-strength steel plate. In the mold with ejector rod ejection, due to the large span between the two side seats, the template will bend when the injection is made.
Therefore, it is necessary to use excellent steel for the movable formwork, which must meet the thickness, and can not use low-strength steel plates such as A3. When necessary, support columns or support blocks should be set under the movable formwork to reduce the thickness of the formwork and adjust the forward load.
5. The ejector rod is twisted, cracked or leaked
The quality of the self-restraining ejector rod is better, because the processing cost is too high. Nowadays, standard parts are usually used, and the quality is worse. If the gap between the ejector pin and the hole is too large, the material will leak, but if the gap is too small, the ejector pin will become stuck due to the increase of mold temperature during injection.
What's more risky is that sometimes the ejector rod is pushed out and usually does not move at intervals and breaks. The exposed ejector rod cannot be reset when the mold is clamped once, and the concave mold is damaged. In order to deal with this question, the ejector rod was re-ground, and a 10~15mm collaboration section was saved at the front end of the ejector rod, and the base was slightly grounded by 0.2 mm. After all the ejector pins are installed, it is necessary to strictly check the cooperation gap, usually within 0.05~0.08 mm, to ensure that all ejection arrangements can move forward and backward freely.
6. Poor cooling or water leakage
The cooling effect of the mold directly affects the quality and output of the finished product, such as poor cooling, large shortening of the finished product, or uneven shortening, resulting in warping deformation. On the other hand, the whole mold may be overheated, so that the mold cannot be formed normally and production is stopped. In severe cases, the movable parts such as ejector rods may be damaged due to thermal expansion.
The cooling system plan depends on the shape of the product. Don't omit this special system due to the messy structure of the mold or the difficult processing. Especially large and medium-sized molds must be adequately considered for cooling.
7. The slider is inclined and the reset is not smooth
Some molds are bound by the area of the template and the guide groove length is too small. The slider is exposed outside the guide groove after the core pulling action is completed. So in the period after core pulling and the initial period of mold closing and resetting, the slider is simply inclined, which is particularly close. During the die, the sliding block is not reset smoothly, causing damage to the sliding block and even bending damage. According to experience, the length of the slider in the chute should not be less than 2/3 of the total length of the guide groove after the core pulling action of the slider is finished.
8. The fixed distance tightening arrangement fails
Fixed-distance tensioning arrangements such as swing hooks and buckles are usually used in fixed mold core pulling or some secondary demolding molds. Because this type of arrangement is set in pairs on both sides of the mold, its actions must be synchronized. , That is, the mold is closed and buckled together, and the mold is opened to a certain position and unhook together.
Once the synchronization is lost, the template that constitutes the drawing die must be tilted and damaged. The parts of these arrangements must have higher rigidity and wear resistance, and adjustments are also difficult. The arrangement life is short. Try to prevent use. You can switch to other parts. arrangement.
In the case of a small core-pulling force comparison, you can use a tension spring to push out the fixed mold. When the core-pulling force is large, you can choose a structure where the core slides when the movable mold retreats. Hydraulic cylinders can be used to pull cores on large molds. The oblique pin slider core pulling arrangement is damaged.
The disadvantages of this arrangement are mostly inadequate processing and too small materials. The first two questions are as follows:
The oblique pin inclination angle A is large, and the advantage is that a larger core pulling distance can occur in a shorter mold opening stroke. However, an excessively large inclination angle A is adopted. When the extraction force F is a certain value, the bending force P=F/COSA encountered by the inclined pin during the core-pulling process, the larger the inclined pin deformation and the inclined hole wear.
At the same time, the upward thrust of the inclined pin on the slider N=FTGA is also greater, this force increases the positive pressure of the slider on the guide surface in the guide groove, and then increases the resistance when the slider slides. It is easy to form that the sliding is not smooth and the guide groove is worn. According to experience, the inclination angle A should not be greater than 25.
9. Poor exhaust in the injection mold
Gases often occur in injection molds. Why does this happen?
The air in the pouring system and the mold cavity; some materials are rich in moisture that has not been swept away by drying, and they will vaporize into water vapor at high temperatures; due to the high temperature during injection molding, certain unstable plastics will occur Differentiation produces gas; certain increase agents in plastic materials may be produced by chemical reaction with each other by transpiration.
At the same time, the cause of poor exhaust is also required to find out quickly. Poor venting of the injection mold will bring a series of damages to the quality of plastic parts and many other aspects. The first manifestation is that the melt will replace the gas in the cavity during the injection molding process. If the gas is not discharged in time, it will form a melt. The filling is difficult, resulting in the shortage of injection volume and the inability to fill the cavity; the poorly swept air will cause high pressure in the cavity, and enter the inside of the plastic under a certain degree of contraction, forming voids, pores, sparse and silver patterns, etc. Quality shortcomings;
Because the gas is highly compressed, the temperature in the cavity rises sharply, which in turn causes the surrounding melt to differentiate and burn, which makes the plastic parts show some carbonization and charring. It is mainly present at the junction of the two melts and the flange of the gate; the gas is not cleaned smoothly, which makes the speed of the melt entering each cavity different, so it is easy to form movable marks and fusion marks, and make the plastic parts The mechanical function is reduced; due to the obstruction of the gas in the cavity, the filling speed will be reduced, the molding cycle will be affected, and the tax power will be reduced.
The dispersion of air bubbles in the plastic part, the air bubbles generated by the air trapped in the mold cavity, are often scattered on the opposite part of the gate; the bubbles in the plastic material that differentiate or chemical reaction are scattered along the thickness of the plastic part; in the plastic material The bubbles caused by the vaporization of the remaining water are scattered irregularly on all the plastic parts.
