Six castings commondefects’causes and prevent methods, not collecting will beyour loss! ((Part2)

　　We will continue to introduce you to the otherthree kinds of casting common defectsand solutions.

　　4 Crack (hot crack, cold crack)1)Features:The appearance of the crack is a straight or irregular curve, hot crack surface is strongly oxidized dark gray or blackandno metallic luster, cold crack surface is cleanand metallic luster.The general casting’souter cracks can be seen directlybutinner cracks need to use other methods. Cracks are often associated with defects such as porosity andslag, occurred in casting insidecorner, junction thickness section,pouring riser connected with casting hot section.

　　2)Causes:Metal mold casting prone to crack defects, because the metal mold itself is not concession, cooling fast easily results increased stress in the casting. Opening too early or too late, pouring angle is too small or too large, paint layer is too thin ect all will cause casting cracking. Mold cavity cracks itself can easily lead to crack.

　　3)How to prevent:

　　ITo pay attention to the structural technology so the casting wall thickness uneven parts can transition uniformly by using suitable round size.

　　ITo adjust coating thickness so all casting parts reach required cooling rate as far as possible to avoid too much stress in the casting.

　　ITo control metal mold temperature, adjust the mould rake and timely core cracking, removing castings cold slowly.

　　5 Cold shut (bad fusion)1)Features:Cold shut is a seam or surface cracks with round sides, was separated by the oxide and incomplete integration, serious cold shuts which became "less casting" . The cold shuts often appear at the top wall of casting, thin horizontal or vertical surface,connection of thick and thin walls, or on thin panels.

　　2)Causes:

　　IExhaust design of metal mold is not reasonable

　　I The operating temperature is too low.

　　IPaint coating quality is bad (man-made or materials).

　　IThe designed runner position is not appropriate.

　　IPouring speed is too slow and so on.

　　3)How to prevent

　　IThe correct design of the runner and exhaust system.

　　ILarge-area of thin-wall castings, coatings should not too thin and appropriate thickening coatings to molding easily.

　　ITo appropriately increase mold operating temperature.

　　ITo use inclined pouring method.

　　ITo use mechanical vibration metal casting for pouring.

　　6 Blister (sand hole)1)Features:Relatively regular holes are in the casting surface or inside,shape same with sand, visible in surface from which you can take out sand grains. Multiple sand holes exist at the same time and casting surface is orange peel shape.

　　2) Causes:

　　ISand core surface falling sand was wrapped in metal and casting surface to form a hole.

　　ISand core surface strength is not good, scorched or not fully cured.

　　IThe size of the sand core and the external mold does not match, when mould clamping crushed sand core.

　　IMold is dipped in sand graphite water.

　　ISands from sand core friction in ladle& runner are falling into the cavity with metal liquid.

　　3)How to prevent:

　　ITo make sand core strictly in accordance with the process and check the quality.

　　ITo match sand core and outer mold sizes .

　　ITo clean up graphite water in time.

　　ITo avoid ladle and sand core friction.

　　ITo clean sands in mold cavity when lay the sand core.