News Descritpion
  • Plastic mold common fault analysis and solution
  • Date:2018-05-10    From:    Click:555
  • First, fixed distance tension mechanism failed.


    Fixed-length tensioning mechanisms such as hooks and buckles are generally used for fixed-mold core-pulling or some secondary mold-releasing dies. As such mechanisms are set in pairs on both sides of the mold, their motion requirements must be synchronized. 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 will inevitably 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, and the adjustment is also very difficult. The life span of the mechanism is short, and the use of other mechanisms can be avoided.


    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 slide when the moving die retreats, and the structure of the die splitting can be completed after the core pulling operation is performed. A hydraulic cylinder can be used to pull the core on the mold, and the oblique-pin sliding core-pulling mechanism can damage the plastic mold.


    Second, 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. The system should not be omitted due to the complexity of the mold structure or processing difficulties. In particular, large and medium-sized molds must fully consider the cooling problem.


    Third, 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. Moldmakers sometimes do not pay attention to this problem, often changing the original design size, or replace the moving plate with a low-strength steel plate. In a die with a tipping material, the two-passenger frame has a large span, causing the template to bend under injection.


    Therefore, the moving plate must be made of high-quality steel, and must have sufficient thickness. It is not possible to cut low-strength steel plates such as A3. When necessary, support columns or support blocks should be set below the moving plate to reduce the thickness of the plates and increase the bearing capacity.


    Fourth, the top bar is bent, broken or leaking material.


    The quality of the self-made ejector rod is better, that is, the processing cost is too high, and now standard parts are generally used and the quality is poor. If the clearance between the crowbar and the hole is too large, leakage occurs, but if the clearance is too small, the ram swells and seizes due to the increase in mold temperature during the injection. What is even more dangerous is that sometimes the top bar is broken at its normal distance from the top and the result is that the exposed top bar cannot be reset and hit the die at the next clamping.


    In order to solve this problem, the top bar is reground, leaving a 10 to 15 mm mating section at the front end of the jack, with the center section being 0.2 mm. After assembly, all ejector rods must be strictly checked for fit clearance, generally within 0.05 to 0.08 mm, to ensure that the entire ejector mechanism can move freely.


    5. It is difficult to discharge material from the gate.


    In the injection molding process, the gate is stuck in the sprue bushing and it is not easy to escape. When the mold is opened, the product is cracked. In addition, the operator must use the tip of the copper rod to knock out from the nozzle, make it loose and release it, which will seriously affect the production efficiency.


    The main cause of this failure is the poor finish of the tapered hole in the gate, and the tool hole in the circumferential direction of the inner hole. The second is that the material is too soft. After a period of use, the small end of the tapered hole is deformed or damaged, and the curvature of the nozzle's spherical surface is too small, causing the gate material to produce a rivet at this point. The taper hole of the sprue bushing is more difficult to process. Standard parts should be used as far as possible. If it is necessary to process it by itself, special reamers should be made or purchased. Taper holes need to be ground to Ra0.4 or more. In addition, a gate puller or gate ejector must be provided. The