Injection molding process personnel must know 18 basic knowledge (1-6)
Writer： Admin Source： MDM Date：2022-03-24
1) Nozzle
The melt glue usually flows from the nozzle into the injection port, 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 nozzle: open nozzle and
closed nozzle. In injection molding, open nozzles should be used more often because they are cheaper and less
likely to linger.
If the injection molding machine is equipped with a pressure removal device, this nozzle can be used even for
melt adhesives with low viscosity. Sometimes it is necessary to use a closed nozzle, which acts as a flow valve
and blocks the plastic in the shooting cylinder. Ensure that the nozzle is properly connected to the nozzle sleeve
and the top hole is slightly smaller than the nozzle sleeve to allow easier withdrawal of the nozzle from the
mold. The hole of the nozzle sleeve should be 1mm larger than that of the shooting nozzle, that is, the nozzle
radius should be 0.5mm smaller than that of the nozzle sleeve.
2) Filter and combined nozzle
Plastic impurities can be removed by a filter with an extended nozzle, whereby the melt and plastic flow through
a channel separated by the insert into narrow Spaces. These Narrows and gaps remove impurities and improve
plastic mixing. Therefore, by extension, a stationary mixer can be used to achieve better mixing results. These
devices can be installed between the injection cylinder and nozzle, separation and remixing of melt glue work,
mostly to make the melt through the channel of stainless steel.
3) exhaust
Some plastics need to exhaust in the injection cylinder when injection molding, so that the gas is
discharged. Most of the time this gas is just air, but it can be water released by melting or a single molecule
gas. If these gases cannot be released, the gas is compressed by the glue and carried to the mold, where it
expands and bubbles form in the product. To drain the gas before it reaches the nozzle or die, lowering or
reducing the screw root diameter can reduce pressure on the melt in the injection cylinder.
At this point, the gas can be discharged through holes or holes in the ejector cylinder. Then the diameter of the
screw root increases, and the melt glue of the volatiles is suitable for the nozzle. The injection molding machine
equipped with this facility is called exhaust injection molding machine. The exhaust injection molding machine
should have a catalytic burner on top of it and a good exhaust device to remove potentially harmful gases.
4) Increase the role of back pressure
To get a high quality melt, the plastics are uniformly heated or melted and well mixed. Using the correct screw
can melt and mix exactly, and there is enough pressure (or back pressure) in the cylinder to achieve consistency
of mixing and heat.
Increasing the resistance of oil return creates back pressure in the firing cylinder. But the screw takes longer
time to reposition, so there is more wear and consumption in the drive system of injection molding machine. As
far as possible to maintain back pressure, isolated from air, also need to melt glue temperature and mixing
degree of consistency
5) check valve
Either type of screw is usually fitted with a stop valve at the tip and a pressure relief (cable back) device or a
special nozzle to prevent plastic from flowing out of the nozzle. If the abortion control is used, it must be
checked regularly, because it is an important part of the shooting cylinder. At present, switch nozzle is not
commonly used, because the nozzle equipment is prone to leakage of plastic and decomposition. Each type of
plastic now has a specified nozzle type.
6) Screw back (back cable)
Many injection molding machines are equipped with a screw back or suction device. When the screw rotation
stops, it is hydraulically withdrawn to suck back the plastic at the tip of the nozzle the device allows the use of an
open nozzle. The amount of resuction may be reduced because of air intake problems for some plastics.
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