What principles should be followed in the design of injection mold nozzles?
1. The gate should be opened at the thickest part of the plastic part as much as possible. In this way, the cooling at the gate will be slower, which is conducive to the filling of the melt into the cavity through the gate, so it is not easy to have defects such as depressions.
2. The location of the gate should make the melt flow the shortest, the flow direction change the smallest, and the energy loss is the smallest. Generally the gate is at the center of the plastic part.
3. The position of the gate should be conducive to the discharge of gas in the cavity. If the molten material entering the cavity closes the exhaust system prematurely, it will be difficult to exhaust the gas in the cavity, and even affect the quality of the product. At this time, an exhaust groove should be opened at the last position of the molten material reaching the cavity. Li exhaust.
4. The gate position should be set in the position facing the cavity wall or the thick and large core, so that the high-speed melt flow directly impacts the cavity or core wall, thereby changing the flow direction, reducing the flow rate, and filling the cavity smoothly. Eliminate obvious weld marks on plastic parts and avoid melt fracture.
5. The number of gates should not be too much. If entering the cavity from several gates, the possibility of welding marks will be greatly increased. If there is no special need, do not install more than two gates.
6. The gate position should make the flow of the melt flow from the main runner to all parts of the cavity the same or similar to reduce the occurrence of weld marks.
7. For plastic parts with cores or inserts, especially cylindrical plastic parts with slender cores, eccentric feeding should be avoided to prevent core bending or insert displacement.
8. The location of the gate should avoid the phenomenon of melt fracture. When the small gate is facing a cavity with a large width and thickness, the high-speed melt flow through the gate will be subject to high shear stress, thus Melt fracture phenomena such as jetting and creeping occur. The sprayed melt is easy to cause folding, causing ripple marks on the product.
9. When the plastic melt is injected into the cavity at high speed through the gate, it will have a directional effect. The position of the gate should try to avoid the adverse effects of the directional effect of the polymer, and this directional effect should be used to have a beneficial effect on the plastic .
10. When determining the gate position and quantity of a mold, the flow ratio must be checked to ensure that the melt can fill the cavity. The flow ratio is determined by the ratio of the total flow channel length to the total flow channel thickness. The allowable value varies with the properties of the melt, temperature, injection pressure, etc.
11. For flat plastic parts, because it is prone to warpage and deformation, this is caused by inconsistent shrinkage in all directions. If multiple gates are used, the effect is much better.
12. For frame-type plastic parts, gates can be set diagonally to improve the deformation of plastic parts caused by shrinkage.
13. For circular plastic parts, the gate should be placed in the tangential direction, which can reduce weld marks, increase the strength of welded parts, and facilitate exhaust.
14. For plastic parts with uneven wall thickness, the gate position should be as consistent as possible. Avoid turbulence.
15. For the shell plastic parts, the gate arrangement with the center full-feeding can be adopted to reduce the welding marks. 16. For cover-shaped, slender cylindrical, thin-walled plastic parts, in order to prevent material shortage, multiple pouring points and craft ribs can be set. The above-mentioned selection principle of the gate position may cause conflicts in application, and it needs to be handled flexibly according to the actual situation.
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