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Die casting Pitting Hole Defect Solution


Exudative stomata

Defect characteristics:
When the alloy solidifies, the dissolved gas in the alloy liquid gradually precipitates as the temperature of the alloy liquid decreases, but as the alloy solidifies, gas that cannot escape from the alloy liquid will remain in the product and form pores. It has a smooth surface, sometimes the surface is bright, scattered and concentrated. It is most likely to occur in most of the castings. The closer you are to the center, the more pores there are. Therefore, the larger the machining allowance of the casting, the easier it is to find such a defect.
Discovery method:
Visual inspection or x-ray inspection after machining.
The figure above shows the solubility curve of [H] in liquid aluminum alloy.
Cause Analysis:
(1) In the raw material alloy ingot, the H content is too high.
(2) The alloy material is contaminated and damped at the same time, causing hydrogen peroxide to enter the charge.
(3) Incomplete baking in the melting furnace, incomplete drying of the smelting tool, etc., causing volatile substances and water (H 2 ) to enter the alloy.
(5) Water (H_2) enters the alloy liquid due to the slag cleaning agent or the moisture of the refinery itself.
_ The retraction load is severe, and the surface is Al(OH)3.
(5) The agitation during the smelting process is incorrect, resulting in more gas entering the alloy liquid.
_ Alloy smelting time is too long, and the holding time is too long, resulting in increased absorption of alloy gas.
Preventive measures: (Based on the above reasons, there are the following preventive measures)
(1) Bake the furnace before smelting and completely remove water or volatile substances that may enter the alloy liquid from the furnace body (refractory or surface) to prevent an increase in H.
(2) All tools in contact with the alloy solution must be uniformly baked and coated and must be dried before use.
(3) Alloy materials should be well protected from rain and moisture to prevent the accumulation of large amounts of aluminum (OH) 3 on their surfaces. Feeding in time allows the ingot or return to be preheated and baked before smelting.
(4) The raw material should be strictly controlled for the gas content of the alloy ingot itself.
(5) The material handle, overflow block, furnace return, etc. should be placed in the melting chamber in time (to be smelted). At the same time, in the production process, defective products, overflow blocks, soup channels and vacuum flow paths that fall on the abdomen of the machine should not be contaminated by the separating agent (spraying water) under the spraying machine, and should be in time.
(5) Strictly control various oil contaminations to the alloy (liquid) to prevent an increase in H.

_ In the degassing process of alloy white alcohol refining, attention should be paid to the smoothness of the agitation and the moisture resistance of the degreaser to prevent the increase of water vapor.


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