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Injection molding machine multi-stage injection and segmentation injection plastic flow principle

2019-10-06  755

First, the principle of multi-stage injection plastic flow:

1. The first shot glue enters the glue at a low speed, removes the nozzle to the cold head and then increases the two-stage rate of injection to fill the cavity to shorten the time for the plastic flow from the gate to the end, so that the viscosity of the plastic in the filling is kept to a minimum. However, it is difficult to control the correct pressure-holding switching point at high-speed injection, so it is necessary to use multi-stage deceleration to effectively control the holding pressure switching point.

2. The principle of action of segmentation:

The electro-optical control is used to command the flow proportional valve in the oil pressure system to instantaneously obtain the injection speed at a point to achieve the segmental rate of fire.

Second, the relationship between the segmental injection rate and pressure:

1. In the segment injection molding process, the filling process has only one pressure, that is, one pressure, regardless of the number of changes, and the pressure maintaining phase only maintains one speed regardless of several stages of pressure keeping.

2, segmentation example:

(1) The same finished product can be molded with a small clamping force, which can extend the life of the machine and the mold;

(2) Sectional deceleration Mastering the correct pressure holding switching point can effectively ensure the stability of quality;

(3) When the molding plastic flows too well, it is necessary to prevent the raw edges from being shot at a low speed, but the raw materials should not be cooled and solidified. The molten resin should be filled with the speed of the meat to increase the rate of fire and quickly fill the cavity, and the flow marks are gradually melted. The stripe-like pattern that is centered on the gate is caused by the boundary between the resin that initially flows into the cavity and the resin that flows into the cavity too quickly.

(4) When the glue inlet (ie, the gate) is formed thicker, the rate of fire will be too fast, which will cause turbulent flow. The cold material will easily leave the passage and form flow marks. Therefore, the low-speed low-pressure glue should be used to push the cold head to make the back. The plastic entered smoothly.

(5) In the injection molding process, the nozzle part is in contact with the mold. The temperature of the mold is cooled by the mold cooling water. The temperature of the mold is lower than that of the nozzle. Some of the heat is taken away by the mold. The nozzle is easy to produce a cold head. These cold heads are injected into the mold and will be at the gate. Obstruction causes flow marks or silver strips, and the extraction of segmented shots can improve this defect.

(6) Precision small parts, the gate size is fine, and the gate balance of most mold cavities is extremely difficult to make. It is easy to use the multi-section injection technology by opening the gate to the same size.

(7) The change of the switching position between the first low-speed injection and the second high-speed injection can correct the local displacement of the weld line, such as the apparent displacement of the part to the less obvious position (such as the labeling).

(8) The phenomenon of depression and fusion is opposite to each other during molding. It can be improved at the same time by this method; the rate of fire in the product recessed area drops sharply, and the filling speed is quickly increased after filling the surface layer to cold solidification, and the weld line should be taken quickly. The glue is injected to prevent poor fusion (generally, the surface of the molded product is depressed at the thickness of the meat, which is caused by the volume shrinkage of the molten resin when it is cooled and solidified).

(9) The stepwise reduction during the pressure holding process can reduce the residual stress of the molded product.

(10) The forming conditions of the molded product are thin and the flow distance is long, and the high pressure can be successfully completed. However, the high-speed high-pressure injection rubber is likely to cause residual stress in the gate portion, thereby affecting the quality, so high-speed feeding, medium-speed filling, low-speed pressure holding and residual stress are eliminated. Thereby preventing deformation of the finished product.

(11) Improvement in mold cooling: If the moving mold temperature is low, the mold temperature is high, and the molded product does not undergo inward warpage. If the moving mold temperature is high, the molded product may be warped outward.

(12) Charring (because of the phenomenon caused by gas compression combustion in the cavity) is most likely to occur at the parting line or welding joint. The surface of the resin exhibits black carbonization marks, and the air gas needs to be smoothly discharged from the cavity, and the rate of fire must be lowered. .