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Precautions when using injection molds

This article analyzes the precautions when using injection molds. The production of injection molding products is inseparable from the molds. The quality of the molds is of crucial importance to the quality of the molded products. The mold creates value in using but gradually loses its value in using. Therefore, the operator must pay great attention to the use of the mold. Generally, the following points should be noted.

(1)Checking whether any impurities and dirt are present in the mold before using. For the remaining plastics and impurities in
the mold, the copper paste must be scraped off with a cotton yarn, and then bonded with a copper knife.

(2)Reasonable choice of clamping force, which does not produce flash when molding the product and cannot be considered as high as possible, what's more it will increase power consumption and damage the transmission parts.

(3)Each transmission part should be lubricated well, so it is necessary to maintain the lubrication of these parts

(4)It is not allowed to hit any part of the mold with a heavy object such as a hammer or a hammer to avoid deformation or even damage to the mold.

Cooling waterway maintenance
The role of the cooling water channel is to cool and solidify the plastic parts in the cavity through the cooling water, which has a great influence on the molding process of the plastic parts.
  • The hazard of cooling water channel plugging
In the long-term working process, the surface of the cooling waterway is prone to deposition of scale, dirt, corrosion, etc. It will reduce the flow area of the cooling water flow path, and greatly reduce the heat exchange between the cooling water in the mold, so that the cooling effect is greatly reduced and harmed.
  • Check the cooling water blockage
The increase of sediment on the surface of the cooling water channel will cause partial blockage of the water channel. This can be determined by measuring the flow rate of the cooling water to determine the internal condition of the cooling water channel. During the measurement, a pressure control valve can be installed between the mold ant the cooling water channel. Under the same conditions, the pressure drop of the cooling water through the mold is measured. From this, it is possible to determine the clogging of the cooling water channel. If it is blocked to a certain extent, it must be cleared up in time.
  • Cooling water cleaning
It is inconvenient to disassemble because the design of the cooling water channel is related to the shape of the cavity and the shape of the cooling water channel is twisted and twisted. Therefore, it cannot be cleaned mechanically and only the cleaning agent can be used for flushing.

Maintenance of mold release

After the injection mold has completed a given production task, it needs to be removed from the injection molding machine. When disassembling, the residual plastic must be removed carefully, and different cleaning methods should be adopted according to the different properties of different plastics. Soap water is generally used to remove residual plastic and other deposits from the mold, after which the mold is air dried. If there is rust on the surface of the cavity, it should be removed, polished, coated with lubricant, and placed in stock.
During the working process of injection molds, there will always be more or less failures, and they will have adverse effects on product quality, productivity, molds, etc., which will be described below.

Mold deformation and its elimination

Deformation of the mold means that the mold has undergone excessive elastic deformation or plastic deformation during the work process, which makes the mold not work properly or the quality of the product is unqualified. The causes and exclusion methods are as follows.
1.Lack of rigidity
During injection molding, the mold is subjected to a huge holding pressure. If this pressure cause's permanent deformation of the mold, the mold will not be usable, but even within the elastic limit, the deformation produced by the mold can be restored during deformation. The curing molding will make the opening of the mold difficult to meet, and it cannot even open. When this happens, it is impossible to remold the mold from the structural point of view, but the injection pressure can be appropriately reduced, or the reinforcing rigidity can be added to the frame from the outside. Although it does not look good, it is also used.
2.Mold assembly misalignment
If the mold is improperly assembled, for example, if the mold is poorly centered, the mold is not accurately centered at the mold-clamping point and its junction, which makes the melt mold unbalanced and easily causes deformation or misalignment of the mold. In this regard, the molds should be reassembled. For mold imbalances, corrective gates can sometimes be used.

C
avity damage and its exclusion
The cavity is the place where the plastic part is molded. Its damage will directly affect the product quality. The cavity damage is the hard wound on the inner surface of the cavity, causing defects such as scratches, pits, and cracks on the surface, and the causes of these damages. The exclusion method is as follows.
1. Hard object damage cavity
Sometimes it is difficult to take a plastic part after mold opening, and it is difficult to use a hard tool such as a screwdriver to remove it, which can easily injure its cavity. In addition, after opening the mold, accidentally dropping a hard object such as a wrench or a hammer into the cavity causes damage to the cavity.
2. Improper operation
If the plastic part is not taken out, the mold is closed, especially in the automatic molding, the cured plastic part is easy to hurt the cavity and the mold.
3. Damage repair
After the cavity is damaged, it is difficult to continue the work without repair. There are several methods for repairing the cavity.
(1) Welding is a commonly used repair method. The most commonly used welding method is gas welding. If using electric welding, because the temperature is too high, the mold is likely to be deformed or even cracked. With electric welding repair, the mold must be preheated and heat treated after welding.
(2) For a smaller area and deeper damage, it can be repaired with inserts, usually after inserting holes into the inserts. When drilling, care must be taken not to drill through the cooling channels and screw holes. The fit of the insert and the cavity should be tight, and it should be smoothed after being installed.
(3) For defects less than 0.5mm in depth, it is better to use electroplating method to repair copper and chromium plating.
(4) For softer cavities, a blind hole can be drilled in the back of the damaged area, and then the bottom of the blind hole can be tapped to make the bump out of the bulge; or the dent can be raised by knocking 3 mm away from the damage point. Then polish, grind and polish the raised part.

The gas generated by the decomposition of the melt 

Some raw materials will produce volatile gases after heating, and many raw materials will also generate volatile gases when they are overheated. These gases are highly corrosive. They permeate around the machine. When the mold does not work, they will corrode the mold. In this regard, when the machine stops working, use a soft cloth to clean the mold and close the mold. If it is not used for a long time, spray the rust-proofing agent in the cavity, and then apply grease when closing the mold.

Cooling water in the mold

The multi-pass cooling water in the mold wakes to wake up, so the water vapor around the machine is more. If the mold is cooled to the dew point, the moisture in the air will form water droplets on the surface of the mold. If it is not wiped off in time, it will easily rust. Especially after the mold stops working, condensation water will soon be generated. Therefore, do not stop molding easily. Even if you want to stop, turn off the cooling water and dry the mold.

Carbide generated during molding

After the mold has worked for a long time, the forming material is precipitated and decomposed to form carbides, which often causes the mold to wear, corrode, or rust. In this regard, if carbide formation is found, it should be immediately wiped off with a dry cloth.


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