What Happened To These Injection Mold Failures (1)

- Mar 27, 2018-

6. Poor cooling or water leakage 

         The cooling effect of the mold directly affects the quality and production efficiency of the product, such as poor cooling, large shrinkage of the product, or uneven shrinkage and defects such as warping surface deformation. On the other hand, the whole or partial overheating of the mold may cause the mold to not be properly formed and be discontinued. In severe cases, the movable parts such as the ejector rods may become stuck due to thermal expansion and be damaged. The design of the cooling system depends on the shape of the product. It is not necessary to dispense with this system because of complicated mold structures or difficult processing. In particular, large and medium-sized molds must fully consider the cooling problem. 

7. The slider tilts and the reset is not smooth 

          Some molds are limited by the area of the template, the length of the guide groove is too small, and the slider exposes the outside of the guide groove after the core pulling operation is completed, so that the slider tilting is easily caused in the post-pulling core stage and the initial stage of mold clamping reset, especially in the mold clamping. When the slider is not smoothly reset, the slider is damaged and even bent. According to experience, after the slider completes the core pulling action, the length left in the chute should not be less than 2/3 of the total length of the guide chute.

8. Fixed distance tension mechanism failure           Fixed-length tensioning mechanisms such as hooks and buckles are generally used for fixed-mold core-pulling or some secondary mold-releasing dies. As these mechanisms are set in pairs on both sides of the mold, their motion requirements must be synchronized, ie Simultaneous mold clamping at the same time, open the mold to a certain position at the same time unhooking. Once the synchronization is lost, it is bound to cause the template of the die to be worn out and be damaged. The parts of these mechanisms must have high rigidity and wear resistance, the adjustment is also very difficult, the life of the mechanism is short, and the use of other mechanisms can be avoided as far as possible.            In the case where the pulling force is relatively small, the spring can be used to push the fixed die, and when the core pulling force is relatively large, the core can be slid when the moving die retreats, and the structure of the split die can be completed after the core pulling operation is performed. Hydraulic cylinders can be used to pull cores on the mold. The oblique pin slider core-pulling mechanism is damaged. The most common problems with this type of organization are that the processing is not in place and the materials are too small. There are mainly two problems.

         The inclination angle A of the oblique pin is large, and the advantage is that a relatively large core pitch can be produced within a short opening stroke. However, when a large inclination angle A is adopted, when the drawing force F is a certain value, the bending force received by the oblique pin in the core pulling process is P=F/COSA, and the oblique pin deformation and oblique hole wear are likely to occur. At the same time, the oblique pin generates an upward thrust force on the slider N=FTGA, which increases the positive pressure of the slider on the guide surface in the guide groove, thereby increasing the frictional resistance when the slider slides. It is easy to slip and the guide groove is worn. According to experience, the dip angle A should not exceed 25.

9 injection mold die exhaust           Gases are often generated in injection molds. What caused this? The air contained in the casting system and the mold cavity; Some raw materials contain moisture that has not been removed by drying. They vaporize into steam at high temperatures; When the temperature is too high, certain unstable plastics will decompose to produce gas; some of the additives in the plastic material volatilize or react with each other to form a gas.

          At the same time, the reason for poor exhaust is also needed to find out as soon as possible. The poor exhaust of the injection mold will bring a series of harms to the quality of the plastic parts.

          The main performance is that the melt will replace the gas in the cavity during the injection process. If the gas is not discharged in time, it will cause melt. Difficult to fill, resulting in insufficient injection volume and can not fill the cavity; the exclusion of poor gas will form a high pressure in the cavity, and infiltrated into the plastic within a certain degree of compression, causing voids, stomata, tissue sparse and silver lines, etc. Defects in quality; As the gas is highly compressed, the temperature in the cavity rises sharply, causing the surrounding melt to decompose and burn, causing partial carbonization and scorching of the plastic parts. It occurs mainly at the junction of the two melts, at the gate flange; the gas is not removed smoothly, and the melt velocity entering the various cavities is different.                  

           Therefore, flow marks and weld marks are easy to form, and the mechanics of the plastic parts are made. Reduced performance; due to the obstruction of gas in the cavity, the filling rate will be reduced, affecting the molding cycle and reducing the taxation efficiency.           The distribution of air bubbles in plastic parts and the bubbles generated by the accumulation of air in the mold cavity are often distributed on the parts opposite to the gate; the bubbles generated by decomposition or chemical reaction in the plastic raw materials are distributed along the thickness of the plastic parts; plastic raw materials Air bubbles produced by gasification of residual water are irregularly distributed throughout the plastic part.