Gating difficult to strip
In the injection molding process, the gate stick in the sprue sleeve, easy to prolapse.When the mold, the product cracks occur.In addition, the operator must use the tip of the copper tap out from the nozzle, so that after loosening before stripping, serious Affect the production efficiency.
The main reason for this failure is poor gate cone finish, the hole in the circumferential direction of the knife marks, followed by the material is too soft, after a period of time tapered end of the small deformation or damage, and the nozzle spherical arc is too small, resulting in gate material in this The riveting head produces.It is difficult to process the taper hole of the sprue sleeve and should adopt standard parts as far as possible.If self-processing is required, self-made or purchased special reamers should be made.It must be grinded to Ra0.4 or above.Moreover, Sprue rod or sprue gate.
Large mold fixed mold offset
Large mold due to the different charge rates for each direction, as well as in the mold by the weight of the mold under the influence of movement, fixed mold offset in several cases, injection lateral offset force will be added to the guide column, open When the mold surface guide column surface hair, damage, serious when the guide column bent or cut, or even can not mold.
In order to solve the above problems, it is most convenient and effective to adopt a cylindrical key to add four high-strength positioning keys on the mold parting surface. The verticality of the guide column hole and the parting surface is crucial, , Fixed mold alignment position clamping, the boring machine in the last boring, so as to ensure that dynamic and fixed mold hole concentricity, and to minimize the vertical error.In addition, the guide post and guide sleeve heat treatment hardness must meet the design requirements .
Pillar injury
Lead in the mold guide the main role in order to ensure that the core and the molding surface of the cavity in any case do not touch each other, can not be used as a guide column as a force member or positioning member.
In several cases, the injection, the fixed mold will have a huge lateral deflection force.When the plastic wall thickness requirements are not uniform, the rate of flow through the thick wall at a large, where a greater pressure; plastic Side of the piece is not symmetrical, such as the stepped parting surface of the mold on both sides of the opposite side of the back pressure is not equal.
Dynamic template bending
Mold in the injection, the mold cavity molten plastic has a huge back pressure, usually in the 600 ~ 1000 kg / cm mold makers sometimes do not pay attention to this issue, often change the original design size, or the dynamic template with low-strength steel instead, In the top mandrel mold, due to the large span of the two sides of the seat, resulting in the template when the injection bend, so move the template must use high-quality steel, to have sufficient thickness, must not use A3 and other low-strength steel, if necessary , Should be set in the dynamic template below the support column or support block to reduce the thickness of the template to improve the carrying capacity.
Lever bent, broken or leaky material
Homemade ram better quality, that is, the processing cost is too high, and now generally use standard parts, the quality of some worse. If the ram and hole clearance is too large, there is leakage, but if the gap is too small, at the time of injection As the mold temperature increases, ejector expansion and stuck.
Even more dangerous is that sometimes the mandrel is pushed out of the top of the general distance to the top and break, resulting in the next clamping when the exposure of the mandrel can not reset and hit the die. In order to solve this problem, the mandrel reground , At the front end of the mandrel to retain 10 to 15 mm of the mating section, the middle part of the mill 0.2 mm small.All rams in the assembly, must be strictly checked with the gap, usually within 0.05 ~ 0.08 mm, to ensure that the entire ejection mechanism Can move forward and retreat.
Poor cooling or water leaks
Mold cooling effect directly affects the quality of products and production efficiency, such as poor cooling, shrinking products, or inconsistent shrinkage appear warping deformation and other defects.On the other hand, the whole or part of the mold overheating, the mold can not be normal molding and production, Severe cases, such as mandrels and other moving parts of thermal expansion stuck and damaged. Cooling system design, processing, product shape and not because of the complexity of the mold structure or processing difficulties and save this system, especially large and medium-sized mold must take full account of Cooling problem.
Slider tilt, reset is not smooth
Some molds due to the template area constraints, the guideway length is too small, the slide block in the core after the exposure is exposed outside the guide groove, so that after the core pulling stage and the initial stage of clamping are likely to cause the slider tilt, especially in the clamping When the slider is not smooth reset, the slider damage, or even bending damage.According to experience, after the completion of core pumping action slider, the length of stay in the chute should not be less than 2/3 of the full length of the guideway.
Tensioning mechanism failure
Pendulum hooks, buckles and the like Tensioning mechanism is generally used for fixed-core or some secondary demoulding mold, as these institutions in the mold on both sides of the paired set, its action must be synchronized, that is Mold at the same time buckle, mold to a certain position at the same time decoupling.Once the loss of synchronization, will inevitably cause the mold template is skewed and damaged, the parts of these institutions have high stiffness and wear resistance, the adjustment is also very difficult, institutions Short life, try to avoid using, you can switch to other agencies.
In the case of pumping force is relatively small, the spring can be used to launch a fixed-mode method, in the case of large core-pulling force can be used to retreat when the dynamic mode core sliding, core-pulling action to complete the first sub-mold structure, Die hydraulic core can be used to draw the core.Climatic dowel block core pulling mechanism damage.Is the most common defects of this mechanism are processing is not in place and the material is too small, there are the following two problems.
Oblique inclination angle A large, the advantage is that in a shorter mold opening stroke to produce more than large core. However, to take too much inclination A, when the extraction force F is a certain value, in the core pulling process skew The bending force P = F / COSA is also greater, prone to skew deformation and inclined hole wear.At the same time, skew pin thrust upward thrust on the slider N = FTGA the greater the force of the slider on the guide groove Positive pressure inside the guide surface increases, thereby increasing the sliding friction of the slider resistance. Easy to cause sliding slip, channel wear. According to experience, the angle of inclination A should not be greater than 25.
Exhaust poor injection mold
Gas is often produced in injection molds, what is caused by this? The air trapped in the casting system and the mold cavity; some of the material contains moisture that is not removed by the drying process and will vaporize into water vapor at elevated temperatures; When the temperature is too high, some unstable plastics will decompose and generate gas; some additives in the plastic material volatilize or react with each other to generate gas.
At the same time the poor exhaust poor reasons, but also need to find out as soon as possible.Examination of poor injection mold will give the quality of plastic parts and many other aspects of a series of hazards, the main performance: the injection process will replace the melt Cavity gas, if the gas is not discharged in time will result in the difficulty of filling the melt, resulting in insufficient injection volume can not be filled cavity; excluded poor gas will form a high pressure in the cavity, and to a certain degree of compression into the The interior of the plastic, resulting in holes, porosity, microstructure and silver quality defects;
Due to the high degree of compression of the gas, the temperature in the cavity rises sharply, which in turn causes the surrounding melt to decompose and cauterize, resulting in localized carbonization and charring of the plastic part, which occurs mainly at the confluence of the two melts, Department; poor gas removal, making the melt into the various cavities at different speeds, it is easy to form the flow marks and weld marks, and to reduce the mechanical properties of plastic parts; due to the gas cavity obstruction, will reduce the filling speed , Affect the molding cycle, reduce tax efficiency.
The distribution of the bubbles in the plastic part and the air bubbles in the mold cavity which are accumulated in the air are often distributed on the opposite parts of the gate; the bubbles generated by decomposition or chemical reaction in the plastic material are distributed along the thickness of the plastic part; Bubbles generated by residual water vaporization are irregularly distributed throughout the plastic part.