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The technicians must understand the 15 methods of making injection moulding machines.

Publisher : Wia   Release time : 2019-4-10 10:06:02

Injection Molding Machine-Learning Materials for Injection Molding Technicians

01 shooting nozzle

Melt usually flows from the nozzle to the injection port, but in some moulds, the nozzle is part of the mould because it extends to the bottom of the mould. There are two main types of nozzles: open nozzles and closed nozzles. Open nozzles should be used more in injection moulding because they are cheaper and less likely to remain. If the injection moulding machine is equipped with a pressure relief device, the nozzle can be used even if the viscosity of the melt is low.

Sometimes it is necessary to use a closed nozzle, which acts as a stop valve to block the plastic shade in the injection cylinder. To ensure that the nozzle is properly connected to the nozzle sleeve, the top hole is slightly smaller than the nozzle sleeve, which makes it easier for the nozzle to withdraw from the die. The hole of the nozzle sleeve is 1 mm larger than that of the nozzle, that is, the radius of the nozzle is 0.5 mm smaller than that of the nozzle sleeve.

02 filter and combined nozzle

Plastic impurities can be removed by filters with extensible nozzles, i.e. melting and plastics flow through a channel separated by inserts into narrow spaces. These narrows and gaps remove impurities and improve the mixing of plastics.

Therefore, when extended, a fixed mixer can be used to achieve a better mixing effect. These devices can be installed between the ejector cylinder and the nozzle to separate and re-mix the melt, mostly through the stainless steel channel.

03 Exhaust

Some plastics need to exhaust in the injection cylinder to let the gas out. In most cases, these gases are only air, but they may be water or single-molecule gases released from melting. If these gases cannot be released, the gas will be compressed by the melt and carried to the die, which will expand and form bubbles in the product. To remove the gas before it reaches the nozzle or die, reducing or reducing the screw root diameter can decompress the melt in the injection cylinder.

Here, gas can be discharged from the holes or holes in the ejector cylinder. Then the diameter of screw root is increased, and the melt adhesives for the removal of volatiles are directed to the nozzle. The injection machine equipped with this facility is called exhaust injection machine. The exhaust injection moulding machine should have a good exhaust fume exhauster with a catalytic burner, which can remove harmful gases.

04 Increasing Back Pressure

In order to obtain a high quality melt, plastics should be heated or melted uniformly and mixed sufficiently. The proper screw is used to melt and mix properly, and sufficient pressure (or back pressure) is provided in the injection cylinder to achieve consistency of mixing and heat. Increasing the resistance of return oil can produce back pressure in the cylinder of shooting material. However, the screw needs to be reset for a longer time, so there is more wear and tear in the drive system of injection moulding machine. Maintain backpressure as much as possible, isolate from air, and also require the same melt temperature and mixing degree.

05 check valve

No matter which type of screw is used, the tip of the screw is usually equipped with a stop valve. In order to prevent plastic from flowing out of the nozzle, a pressure reducing device or a special nozzle will also be installed. If abortion stop is used for supply and marketing, it must be checked regularly because it is an important part of the shooting material cylinder. At present, switching nozzles are not widely used, because the contents of nozzles are easy to leak plastic and decompose. At present, each type of plastic has a list of suitable nozzle types.

06 Screw Back (Back Cable)

Many injection moulding machines are equipped with screw back or suction devices. When the screw rotation stops, it is withdrawn by hydraulic pressure to suck back the plastic device at the tip of the nozzle, which allows the use of an open nozzle. The number of siphons that will be sucked back may be reduced, as air entry can cause problems for some plastics.

07 screw pad

Most injection cycles need to adjust the rotational momentum of the screw village, so that when the screw injection is completed, a small amount of cushion plastic will be left, so as to ensure that the screw can achieve effective propulsion time and maintain a fixed shooting pressure. The cushion material of small injection moulding machine is about 3mm, and that of large injection moulding machine is 9mm. No matter how much screw pad is used, it must be kept unchanged. Now the size of screw gasket can be controlled within 0.11mm.

Rotation Speed of 08 Screw

The rotational 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 is. When the screw rotates at a high speed, the friction (shear) energy transferred to the plastic improves the plasticizing efficiency, but at the same time increases the non-uniformity of the melt temperature.

Because of the importance of screw surface velocity, the screw rotation speed of large injection moulding machine should be less than that of small injection moulding machine. The reason is that the shear heat energy produced by large screw is much higher than that of small screw at the same rotation speed. Because of the different plastics, the speed of screw rotation is also different.

09 injection volume

The evaluation of syringe moulding machines is usually based on the amount of PS that can be injected in each injection, possibly in ounces or grams. Another positioning system is based on the volume of melt injected by the injection moulding machine.

10 plasticizing capacity

The evaluation of an injection moulding machine is usually based on the amount of PS that can be melted uniformly within an hour or heated to a uniform melting temperature (in pounds and kilograms). This is called plasticizing capacity.

11 Plasticizing Capacity Estimation

To determine whether the quality of Lvq can be maintained throughout the production process, a simple formula for yield and plasticizing capacity can be used as follows: t= (total injection impact gX3600)(plasticizing capacity kg/hX1000 of injection moulding machine)

T is the lowest cycle time. If the cycle time of the mould is lower than t, the injection moulding machine will not be able to fully plasticize the plastic to achieve uniform melting.

Please note that some plastics stay in the injection cylinder longer than the calculation time, because they are agglomerated in the injection cylinder.

13 Calculating residence time and importance

In general, the residence time of a plastic on a particular injection moulding machine should be calculated. Especially when the large injection moulding machine uses less injection quantity, the plastic is easy to decompose, which is not detectable from observation. If the residence time is short, the plastics will not be plasticized evenly, and the properties of plastics will decrease with the increase of the residence time. Therefore, we must keep the same detention time.

METHODS: The plastics imported into the injection moulding machine were guaranteed to have stable composition, uniform size and shape. If there are any abnormalities or wear and tear in the parts of the injection moulding machine, they should report to the Maintenance Department.

13 Shot Cylinder Temperature Environment

It should be noted that the melt temperature is very important and that any injection cylinder temperature used is only instructive. If you have no experience in processing a particular plastic, start with the minimum setting. Usually the temperature of the first zone is set to the lowest value, which can prevent the premature melting and adhesion of plastics in the inlet and outlet.

The temperature in other areas gradually rises until it reaches the nozzle. In order to prevent dripping, the temperature at the tip of the nozzle is usually slightly lower. Dies are also heated and cooled. Dies are also distinguished due to the size of many dies, but unless specified, each zone should be set to the same size.

14 melt temperature

The nozzle can be measured or measured by air injection method. When measuring with the latter, care must be taken to ensure that no accidents occur when cleaning hot-melt plastics, because the high temperature of hot-melt plastics can burn or even corrode the skin. Burns were accidental in the injection moulding workshop.

Therefore, gloves and masks should be worn when dealing with hot plastics or in danger of splashing hot melt plastics. To ensure safety, the tip of the heat control needle should be pre-heated to the temperature to be measured. Each plastic has a specific melt temperature. To achieve this temperature, the actual injection cylinder adjustment depends on the rotating speed, back pressure, injection volume and injection cycle of Luocun.

15 Mould Temperature

Always check whether the injection machine is set and operated at the temperature specified on the record sheet. This is very important. Because the temperature will affect the surface finish and production of injection parts. All measured values must be recorded and the injection machine checked at the specified time.

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