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Injection molding is the basic requirement of plasticizing, injection and molding. Plasticizing is the precondition for the implementation and ensure the quality of molding products, to meet the requirements of molding, injection must ensure that there is enough pressure and speed. At the same time, because of the high injection pressure, and accordingly a high pressure in the cavity (average pressure within the cavity is in commonly between 20 ~ 45 mpa), so you must have enough clamping force. Thus, mould device of injection device and is the key to the injection molding machine parts.
4. The injection device
4.1 cylinder
The analysis of the operation from the plunger type injection device know, cylinder is the main task of the plasticizing plastic, and under the impetus of the plunger to molten material into the cavity. Therefore required cylinder on the premise of guarantee the plastic plasticizing good, should try to reduce the resistance in the process of plastic movement. According to this principle we discussed the size of the cylinder.
The diameter of the loading chamber and the determination of plunger stroke is based on the injection volume. Fall into the feed chamber plastic, plunger
Forward is pressed into a cylindrical charge column. The size of V is determined by the products weight. The maximum value should be with the machine one of the biggest injection volume V. Rather, as a result of the stock column density is small, melting so the V should be bigger than injection quantity. Based on experience, general V. Is 20-25% larger than the number of injections.
In addition, should keep the proper proportion between d and l. Because l is too long, can make the pressure loss increases; Too short will make d increases, so that the injection pressure drop. Generally take l/d for the range of 1-1.5 is better.
In order to make a loose plastic join smoothly, charging room should have enough space, the feed chamber S segment volume V1 generally take the measure of the injection machine is a heavy volume 2-2.2 times.
Plunger after back to the final location, shall also have the part stay inside the cylinder, the length of S1, S1 is commonly (1.5 -) 2 d. In this way, the feed chamber total length L = L + S + S1. Cylinder material buckle, rectangle and its axial length is 1.5 d, width is about two-thirds of d. In order to make the feeding mouth plastic welding, ensure the smooth feeding, cooling device should be near the loading port Settings.
4.2 the nozzle
The nozzle is connected to the cylinder and mould parts. Its main function is:
Forecast model, establish a back pressure, eliminate gas, to prevent the liquid flow, improve the quality of plasticizing.
Injection, the nozzle and the mold runner good contact, ensure the molten material not spillover under high pressure.
Injection, to establish the melt pressure, improve the shear stress, and the pressure is converted to kinetic energy. Improve the injection rate and temperature, mixing effect and strengthening homogenization effect.
Pressure, easy to want to cavity filling material; After heating, can increase the backflow power, prevent the reverse flow of liquid in the cavity.
Nozzle also undertake air-conditioning, heat preservation and the function of break.
At present, the production on the nozzle form a lot, but according to its structure can be pided into straight-through and self-locking type two kinds big.
We here with straight through:
General type nozzle, the nozzle structure is simple, manufacture easily, less pressure loss. The downside is when the nozzle from mold, low viscosity of molten material easy to flow from the nozzle, which produce the so-called flow phenomenon, in addition, because of the nozzle without heating device, molten material is easy to cooling. Therefore, the forms of main nozzle with high viscosity plastic melting.
Extended nozzle, it is a general formula of nozzle type, simple structure and manufacture easy. This form of nozzle due to increased the length and diameter of nozzle body, and is equipped with heating circle, so the molten material not cooling, feeding effect, use in the production of the thickness of products.