The aluminum shell is produced and cast under high temperature conditions. The aluminum shell is produced too fast and 

the cooling intensity is relatively large, resulting in some elements in the alloy cannot be transformed into required elements 

within the specified time. Because this material has needle like structure, high hardness and poor plasticity. Moreover, the 

tensile strength of this manufacturing process is very low. Under high temperature, not only yellow rust will appear, but also 

cracks will appear. The aluminum shell produced in this way will have granular burrs. If this burr is not cleaned, it will have a 

poor hand feel. This particle is often accompanied by a tadpole like tail, which can be observed under the microscope, and 

the color of this impurity is gray, containing a lot of iron.