The location of the gate
because the runner and cavity is connected to a certain Angle, formed a blade can cut off the gate, the edge while stripping or parting shear force formed by gate can be automatically cut off, but for a strong plastic should be used. Different gate form filling characteristics of plastic melt, forming quality and the performance of the molded parts will produce different effects. All kinds of plastic for the performance difference on different forms of gate will have different adaptability.
in order to ensure that the plastic melt smoothly mold filling, the transfer of the injection pressure effectively, and at the time of melt liquid contraction can get adequate feeding, generally the location of the gate should be open in the plastic parts wall thickness. The plastic melt in the mold cavity during filling, will appear in the flow direction orientation of polymer molecules and packing. Because perpendicular to the flow and parallel to flow to the point of strength and stress cracking tendency is distinct, often perpendicular to the flow to the low bearing strength, easy to produce stress cracking, so when choosing gate location, should give full attention to this.
gate in the form of many, but no matter adopt what kind of gate, the opening of the location of the quality of plastic parts forming performance and forming are of great influence, therefore, the rational selection of open gate location is an important design to improve the quality of plastic parts. In addition, the gate location of different can also affect the structure of the mould. Choosing gate location, need according to the structure and process characteristics of plastic parts and molding quality requirements, and analysis of the technological characteristic of plastic raw materials and the flow of the plastic melt in the die, molding process conditions, considering the comprehensive.
the gate location should be selected to ensure rapid and uniform filling mold cavity, as far as possible, shortening the distance between the melt flow of the large plastic parts is more important. Small gate if facing a larger width and thickness of cavity, the melt through the gate due to the high shear stress, will produce the melt fracture phenomenon such as injection and peristalsis. Sometimes one end of the plastic melt directly from the cavity injection to the other end of the cavity, causing fold, produced in the plastic corrugated marks or other surface defects. To overcome this kind of phenomenon, can be appropriately increase the cross section of gate size, or the impact type gate, avoid the generation of the melt fracture phenomenon.
latent runner is also known as shear gate, by point gate variation. The gate of the distributary channel in the mold parting surface, and the gate is a cover for oblique opening in the mold. Plastic melt by the side of the cavity or push rod end of injection mold cavity, so injection on external surface of the machined part is not damaged, not due to the gate marks affect the surface quality of plastic parts with a beautiful effect. Latent runner is usually circular cross section, its dimension design can reference point gate.
when parts of wall thickness is large, if the gate opening in thin wall place, then the plastic melt into the cavity, not only the flow resistance is big, but also easy to cooling, affect the melt flow distance, it is difficult to ensure full mold filling. Think in terms of contraction, plastic wall thickness is often melt solidification, the late if gate opening in thin wall place, take the wall thickness of local surface formed by the feeding will not melt contraction depression or craters.
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