Although the structure of moulds may vary greatly due to the different types and properties of plastics, the shape and structure of plastics products and the types of injection machines, the fundamental structure is different. The die is mainly composed of pouring system, temperature regulating system, forming parts and structural parts. Among them, the casting system and the moulding parts are directly in contact with the plastics, and change with the plastics and products. They are the most complex parts in the moulds, which require the highest processing brightness and accuracy.
1. Gating system
The gating system refers to the part of the runner before the plastic enters the cavity from the nozzle, including the main runner, the cold material hole, the shunt runner and the gate, etc.
Gating system, also known as runner system, is a group of feeding channels that lead plastic melt from injector nozzle to cavity, usually composed of main runner, shunt runner, gate and cold hole. It is directly related to the forming quality and consumption efficiency of plastic products.
2. Main Street
It is a passage connecting the injection moulding machine nozzle to the shunt channel or cavity in the mould. The top of the main channel is concave to connect with the nozzle. The inlet diameter of the main channel should be slightly larger than that of the nozzle (0.8mm) to prevent spills and to avoid blocking due to improper connection between the two. Import diameter depends on the size of the product, usually 4-8 mm. The diameter of the main passage should be extended inward at an angle of 3 to 5 degrees in order to release the excess of the passage.
3. Cold Material Points
It is a hole located at the end of the main channel to trap the cold material produced between the two injections at the end of the nozzle, thus avoiding the obstruction of the diversion channel or gate. If the cold material is mixed into the cavity, the internal stress will easily occur in the product. The diameter of the cold material hole is about 8-10 mm and the depth is 6 mm. In order to facilitate demoulding, the bottom of the demoulding rod is usually supported by the demoulding rod. The top of the demoulding rod should be designed as a circuitous hook or a sinking groove, so as to pull out the main stream of redundancy smoothly when demoulding.
4. Shunt Channel
It is the channel connecting the main channel and each cavity in the multi-groove die. In order to make the melt fill the cavity at the same speed, the shunts should be arranged symmetrically and dispersed at equal intervals on the plastic mould. The shape and size of the shunt section have an effect on the activity of the plastic melt, the demoulding of the products and the manufacturing of the die.
If the flow resistance of the circular section is the smallest according to the activity of the same amount of material. However, because the cylindrical channel is smaller than the external surface, it is not conducive to cooling of the diversion channel, and the diversion channel must be set on the two-half die, which is labor-intensive and difficult to align.
As a result, trapezoidal or semi-circular cross-section dividers are often used, and they are arranged on half of the die with a demoulding rod. The runner surface must be polished to reduce moving resistance and provide faster filling speed. The size of the runner depends on the type of plastic, the size and thickness of the product. For most thermoplastics, the cross-section width of the shunt is not more than 8m, the super-large can reach 10-12m, and the super-small can reach 2-3m. On the premise of meeting the demand, the section area should be reduced as far as possible to increase the shunt redundancy and prolong the cooling time.
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