Do you know the basic knowledge that injection molding technicians must know?

1. Filter and combined nozzle
Plastic impurities can be removed by the filter of the extensible nozzle, that is, the melt and plastic flow through a channel, which is separated into a narrow space by the insert. These narrowing and gaps can remove impurities and improve the mixing of plastics. Therefore, the fixed mixer can be used to achieve better mixing effect. These devices can be installed between the injection cylinder and the injection nozzle to separate and remix the molten glue. Most of them make the melt flow through the stainless steel channel.

2. Exhaust
Some plastics need to be vented in the injection cylinder during injection molding to allow the gas to escape. In most cases, these gases are only air, but they may be water or single-molecule gases released by melting. If these gases cannot be released, they will be compressed by the melt glue and brought into the mold, which will expand and form bubbles in the product. To discharge the gas before it reaches the nozzle or the 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 holes or holes on the injection cylinder. Then, the diameter of the screw root is increased, and the melt glue with volatiles removed is applied to the nozzle. Injection molding machines equipped with this facility are called exhaust injection molding machines. Above the exhaust injection molding machine, there should be a catalytic burner and a good smoke extractor to remove the potentially harmful gases.

3. Check valve
No matter what kind of screw is used, its tip is usually equipped with a stop valve. In order to prevent plastic from flowing out of the nozzle, a pressure reducing (reverse rope) device or a special nozzle will also be installed. In case of using the anti abortion supply and marketing, it must be checked regularly, because it is an important part of the firing cylinder. At present, the switch type nozzle is not widely used, because it is easy to leak plastic and decompose in the equipment. At present, each type of plastic has a list of suitable types of shooting nozzles.

4. Rotation speed of screw
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 transmitted to the plastic improves the plasticizing efficiency, but also increases the unevenness of the melt temperature. Due to the importance of the screw surface speed, the screw rotation speed of large-scale injection molding machine should be less than that of small-scale injection molding machine, because 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.

5. Estimation of plasticizing capacity
To determine whether the production quality can be maintained in the whole production process, a simple formula related to the output and plasticizing capacity can be used as follows: T = (total injection blow gx3600) ÷ (plasticizing amount of injection molding machine kg / hx1000) t is the minimum cycle time. If the cycle time of the mold is lower than t, the injection molding machine can not fully plasticize the plastic to achieve uniform melt viscosity, so the injection molding parts often have deviation. In particular, when injection molding thin-walled or precision tolerance products, the injection amount and plasticizing amount must match each other.

6. Calculate retention time and importance
As a general practice, the residence time of a certain plastic on a specific injection molding machine should be calculated. Especially when the large injection molding machine uses a small injection quantity, the plastic is easy to decompose, which is not detectable from observation. If the retention time is short, the plastic will not be plasticized uniformly; The plastic property will decay with the increase of retention time.
Therefore, the retention time must be kept consistent. Methods: to ensure that the plastic input into the injection molding machine has stable composition, consistent size and shape. If there is any abnormality or loss in the parts of the injection molding machine, report to the maintenance department.

7. Mold temperature
Always check whether the injection molding 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 yield of injection molded parts. All measured values must be recorded and the injection molding machine checked at the specified time.

Post time: Aug-15-2022