Nozzle

Melt glue usually flows from the nozzle into the nozzle, but in some molds, the nozzle is part of the mold because it extends to the bottom of the mold. There are also two main types of nozzles: open nozzles and closed nozzles.

In injection molding, open nozzles should be used more because they are cheaper and less likely to stay. If the injection molding machine is equipped with a pressure-removing device, this nozzle can be used even for melts with low viscosity. Sometimes a closed nozzle must be used. This nozzle acts as a stop valve to block the plastic in the injection cylinder.

Make sure that the nozzle is correctly connected to the nozzle sleeve. The top hole is slightly smaller than the nozzle sleeve. This makes the nozzle easier to withdraw from the mold. The hole of the nozzle sleeve is 1mm larger than the nozzle, that is, the radius of the nozzle is 0.5mm thinner than the radius of the nozzle sleeve

Filter and combined nozzle

Plastic impurities can be removed by the filter of the extensible nozzle, that is, the melt and the plastic flow through a channel, which is divided into narrow spaces by inserts. These narrows and gaps can remove impurities and improve the mixing of plastics.

Therefore, to extend it, a fixed mixer can be used to achieve a better mixing effect. These devices can be installed between the injection cylinder and the nozzle to separate and remix the melt. Most of them make the melt flow through the stainless steel channel.

exhaust

Some plastics need to be exhausted in the injection cylinder during injection to allow the gas to escape. In most cases, these gases are just air, but it may be molten moisture or single-molecule gases. If the gas cannot be released, the gas will be compressed by the melt and carried into the mold, it will expand and form bubbles in the product.

To get rid of the gas before it reaches the nozzle or mold, reduce or reduce the diameter of the screw root to depressurize the melt in the injection cylinder. Here, the gas can be discharged from the hole or hole in the shooting cylinder. Then the diameter of the screw root is increased, and the melt glue of the devolatile matter is adapted to the nozzle.

Injection molding machines equipped with this facility are called exhaust injection molding machines. This kind of exhaust injection molding machine should have a good fume exhauster with a catalytic burner to remove potentially harmful gases.

Increase the effect of back pressure

In order to obtain a high-quality melt, the plastic must be heated or melted consistently and mixed thoroughly. Use the correct screw to melt and mix properly, and there is enough pressure (or back pressure) in the injection cylinder to achieve the consistency of mixing and heat.

Increasing the resistance of oil return can produce back pressure in the shooting cylinder. But the screw takes longer to reset, so there is more wear and consumption in the drive system of the injection molding machine. Keep back pressure as much as possible, isolate it from air, and also need the same melting temperature and mixing degree

Check valve

No matter what kind of screw is used, its tip is usually equipped with a stop valve. To prevent the plastic from flowing out of the nozzle, a pressure reducing (reverse cable) device or special shooting nozzle is also installed. If you use anti-abortion supply and marketing, you must check regularly, because it is an important part of the shooting tank.

At present, the switch-type nozzle is not commonly used because the plastic inside the nozzle equipment is easy to leak and decompose. At present, each type of plastic has a suitable nozzle type.

Screw back (reverse cable)

Many injection molding machines are equipped with screw retreat or suction devices. When the screw stops, it is withdrawn by hydraulic pressure to suck back the plastic at the tip of the nozzle. This device allows the use of an open nozzle. The amount of sucking back may be reduced because the ingress of air can cause problems for some plastics.

Screw gasket

In most injection cycles, it is necessary to adjust the amount of rotation of the screw, so that after the injection of the screw, there will be a small amount of soft cushion plastic, which can ensure that the screw reaches an effective advancing time and maintains a fixed shooting pressure.

The cushion material for small injection molding machines is about 3mm; for large injection molding machines, it is 9mm. No matter how large the screw gasket value is used, it must remain unchanged. Now the size of the screw gasket can be controlled within 0.11mm.

Screw rotation speed

The rotation speed of the screw significantly affects the stability of the injection molding process and the heat acting on the plastic. The faster the screw rotates, the higher the temperature. When the screw rotates at a high speed, the friction (shear) energy transferred to the plastic improves the plasticization efficiency, but also increases the unevenness of the melt temperature.

Due to the importance of the screw surface speed, the screw rotation speed of a large injection molding machine should be less than that of a smaller injection molding machine. The reason is that the shear heat generated by the large screw is much higher than that of the small screw at the same rotation speed. Due to different plastics, the speed of screw rotation is also different.