USES the small gate in the home appliance plastic mold injection molding

Home appliance plastic mold runner gating system is in a critical period of material circulation, in addition to the mainstream way type pouring outlets, most of the gate are minimum sectional area of the gating system, the numerical average is only 3% ~ 9% of bypass road cross-sectional area. For plastic melt flow obey Newton's law, due to its viscosity and shear rate, big gate area can reduce the flow resistance, improve the melt flow rate, the plastic injection mold filling in injection molding for electrical appliances mold rubber and molding quality are good. For the vast majority don't obey the plastic melt flow law of Newton, adopt reduce cross-section of gate, he could make the melt shear rate increases, often due to the shear heat effect, will result in the melt apparent viscosity, instead of a big drop in May to fill more than large cross-section gate. As for the small gate forming pressure drop caused by increasing the flow resistance, can be used within a certain range of the increase of injection pressure method to compensate. Home appliance plastic moulds, in general, the small gate in injection molding, has the following advantages: (1) the small gate of both ends there is a big pressure difference before and after, can effectively increase the shear rate of melt and generate larger shear heat, leading to the melt apparent viscosity decreased, liquidity enhancement, is advantageous to the mold filling. The characteristics of the small gate for thin-walled products or products with fine decorative pattern and such as polyethylene ( PE） And polypropylene ( PP) , polystyrene, PS） Such as plastic molding viscosity to shear rate is more sensitive, is of great benefit. (2) electrical appliances mold in injection molding process, the holding feeding stage is generally going to continue to the gate melt frozen, or melt in cavity will go back to the cavity. If the gate size is larger, the pressure will continue feeding time is longer, therefore has the potential to increased flow deformation and the macromolecular orientation degree, within the products, especially near the gate caused great feeding stress, lead to products appear buckling deformation in the end. If the small gate, may through the test mould or repairing the mould adjust the volume of small gate, the gate of the melt in the process of the pressure maintaining frozen in time, so as to properly control the feeding time, avoid the above phenomenon. (3) in the plastic injection mould manufacturing due to the small gate volume, quick freezing, so the production of some products, can do not need to stay after the small gate freeze products all internal curing, as long as the external solidified layer has enough strength and stiffness can will product release, so as to shorten the molding cycle, improve production efficiency. (4) in the multimode cavity die if in non-equilibrium gating system using the small gate, the gate of the plastic melt flow resistance will score flow of melt flow resistance, so that it could in the melt flow channel and establish enough pressure, each cavity to feed fill in approximately the same time. So, the small gate in the multimode cavity can balance the feed speed of each cavity for gating system balance. 5. If you use a larger runner molding products, in the case of high surface quality requirement of products, often need the right tools or machine was carried out on the products after processing to remove the gate scar, especially when the gate is too large, gate setting material must also saw, cut method to remove. However, the small gate can avoid this kind of trouble. For example, the small gate setting material can be quickly removed by hand, or the utilization of special die structure during demoulding automatically removed. In addition, the small gate after excision of scar small, generally do not need or you just need a little nap polishing work. Therefore, using the small gate is not only beneficial to force, extended their lead to feed fill. But should note that despite the small gate has these advantages, but the gate is too small will cause a lot of flow resistance, extended their lead to feed fill. Therefore, the high viscosity and shear rate have little impact on apparent viscosity of plastics melt ( Such as poly (formic acid ester and polysulfone, etc. ) , are unfavorable use small gate shape. In addition, in the large home appliance plastic molding, also should pay attention to the gate area corresponding amplification, sometimes need to amplify gate section height to near products, one of the biggest thickness can improve the liquidity of the melt. In addition to the above situation, for larger wall thickness, shrinkage rate and larger products, generally require enough feeding time, so in this case, the gate area is not designed to be small.