Why does metal melt need degassing?

Degassing can reduce gas content of metal melt before casting or die-casting, raise qualified rate and lower cost!

Why does metal melt need degassing?

The purpose of degassing is to get rid of the hydrogen fromALmelt. Other chemical impurity or alkaline substance can be also removed during degassing process.

Hydrogen

Hydrogen exists in the air, and can easily dissolve in theALmelt. The hydrogen mixed in theALmelt will cause white spots or air holes, defecting the ultimate products. The defectedALproducts, for instance, probably cannot meet the mechanical or physical performance standards, and also may fail to meet tensile strength standards. Fatigue cracking on materials may be caused by mixed hydrogen, too.

Pinholes of the cast itself or generated during process can probably cause cast scrappage. Pinholes can also be caused by leak holes during cast pressurization. In round ingot processing, gas pinholes may lead to bumps on cast products, squeezed products, thin plates and thick plates. Bad surface features, such as spalling during casting and bumps during heat resistance process, prove the existence of hydrogen.

Hydrogen solubility inALmelt is 20 times higher than in solid aluminum. Because of the difference of solubility, during solidification, hydrogen tends to overflow from the melt, spread slowly, or form bubbles and generate hydrogen molecules. Bumps appear when the pressure of hydrogen is higher than the tensile force and static force.    

Therefore, hydrogen will exist in solid forms, pinholes or breakpoints, if hydrogen content is too high in theALmelt during solidification.

Impurity and alkaline substance

Impurity refers to the solid, liquid or gas exotic substance surrounded by theALmelt. The metal and non-metal impurity should be removed, because it can damage the mechanical performance of the products. The impurity will also increase tool wearing when in process and polishing.       

The impurity and oxidation film are generated during melting, or taken in as oxidation from the surface of the feeding materials. Comparing with theALmelt, the impurity and oxidation have different density, if heat preservation time extends, they will eventually flow to the melt surface or sink to the bottom. However, the whole natural separation takes too much time for manufacturing process. Degassing can accelerate the speed of impurity floating to the surface and the separation process. Filtering before casting is also one of the impurity removal methods.