2, improper control of process conditions If the injection molding machine specifications larger, screw speed is too high, the injection pressure is too large, injection dwell time is too long, it will form an overfill, making the molding shrinkage than expected, demoulding this is difficult. If the barrel and the melt temperature is too high, the injection pressure is too large, the hot melt easily into the gap between the mold inserts to produce flash, leading to poor demoulding. In addition, the nozzle temperature is too low, the cooling time is too short and the injection cut off, will cause demoulding bad. Therefore, in the exclusion sticky mold and mold failure, should appropriately reduce the injection pressure, shorten the injection time, reduce the barrel and melt temperature, extend the cooling time, and to prevent the melt cut off.
3, raw materials do not meet the requirements Mixing of raw materials with impurities during packaging and shipping, or mixing of different grades of raw materials during pre-drying and preheating, as well as foreign matter in the barrel and hopper, can lead to mold sticking. In addition, the particle size of the raw material is too large or too sticky mold to a certain extent. Therefore, the molding material should be well cleaned and screened.
4, release agent improper use The purpose of using the release agent is to reduce the adhesion between the surface of the plastic part and the surface of the mold cavity and prevent the two parts from sticking to each other in order to shorten the molding cycle and improve the surface quality of the plastic part. However, since the mold release effect of the mold release agent is affected not only by the chemical reaction but also by the physical conditions, and the molding raw material and the processing conditions are different, the optimum type and amount of the selected mold release agent must be determined according to the specific situation to make sure. If used improperly, often can not produce a good mold release effect. The molding temperature, the effective operating temperature of the oil-free mold release agent generally not more than 150 degrees, should not be used at high temperature molding; silicone oil and metal soap mold release agent operating temperature is generally 150 degrees to 250 degrees; poly four Fluoroethylene release agent working temperature can reach more than 260 degrees, is the best mold release agent under high temperature conditions. In terms of raw materials, soft plastic parts are more difficult to demold than hard plastic parts. In terms of method of application, the pasty release agent is to be applied with a brush, and the sprayable release agent is sprayed using a spray device. Because the paste release agent in the brushing is difficult to form a regular uniform mold layer after mold release surface will have a wave marks or stripes, it should be possible to use a sprayable mold release agent.
5, over filling Molding at an excessively large injection pressure resulted in a smaller than expected shrinkage of the mold, and demolding became difficult. At this time if you reduce the injection pressure, shorten the injection time, reduce the melt and mold temperature, it becomes easy to mold release. In such situations, it is more effective to use a mold release agent that reduces the friction between the plastic and the mold. For the mold to improve the degree of light, remove the convex side wall, grinding, increase ram and other methods are also effective. When forming deeper parts, blowing compressed air between the part and the part helps to release the part (see Overfilling in Cracks, Cracks, Microfission and Whitening).
6 parts stuck on the static mold There are two reasons for this, that is, the nozzle and the cavity are stuck, or the static mold release resistance is greater than that of the movable mold, so that the workpiece sticks to the static mold. Due to the resistance between the nozzle and the cavity caused by sticking in the static mold on the situation are: the nozzle radius R radius R than the mold corresponding to the larger, when clamping the mold and the mold nozzle is not concentric, or nozzle Between the mold and the leakage of plastic and so on. In either case, the parts are stuck and the parts stuck to the static mold. In order not to happen, the mold should be correctly installed. Static mold release resistance is due to the low finish or sidewall caused by bump. At this time, Z-type pull rod should be set on the side of the movable mold to pull the workpiece. In the mold design, take full account of this phenomenon does not occur. Parts in the move, with static mold on both sides - set the temperature difference is also valid.
(1) plastic mold over-stuffing, reducing injection pressure; reduce injection volume injection cylinder temperature is too high (2) injection pressure to maintain the time is too long, reducing the screw forward time (3) mold surface scratches, porous or abrasion, remove stains and polishing the mold surface (4) the mold of the mold angle is not enough, the use of each side is 0.5 degrees minimum exit angle (the greater the angle, the more easy ejection, the faster the operation) (5) Inverted design, to ensure that there is no Fengjian Feng corner (6) The injection molded parts adhere to the highly polished mold surface and the exhaust valves are used to remove the vacuum generated when the injection molded parts are extruded from the highly polished surfaces. (7) improper ejection device, increasing the number of ejector rods or put on different systems (8) lack of plastic lubrication, if allowed to use plastic mold; add external lubricants, such as zinc stearate