casting common defects 2
Six castings common defects’ causes and prevent methods, not collecting will be your loss! ((Part 2)
We will continue to introduce you to the other three kinds of casting common defects and 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 black and no metallic luster, cold crack surface is clean and metallic luster. The general casting’s outer cracks can be seen directly but inner cracks need to use other methods. Cracks are often associated with defects such as porosity and slag, occurred in casting inside corner, 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:
I To pay attention to the structural technology so the casting wall thickness uneven parts can transition uniformly by using suitable round size.
I To adjust coating thickness so all casting parts reach required cooling rate as far as possible to avoid too much stress in the casting.
I To 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.
I Exhaust design of metal mold is not reasonable
I The operating temperature is too low.
I Paint coating quality is bad (man-made or materials).
I The designed runner position is not appropriate.
I Pouring speed is too slow and so on.
3) How to prevent
I The correct design of the runner and exhaust system.
I Large-area of thin-wall castings, coatings should not too thin and appropriate thickening coatings to molding easily.
I To appropriately increase mold operating temperature.
I To use inclined pouring method.
I To 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.
I Sand core surface falling sand was wrapped in metal and casting surface to form a hole.
I Sand core surface strength is not good, scorched or not fully cured.
I The size of the sand core and the external mold does not match, when mould clamping crushed sand core.
I Mold is dipped in sand graphite water.
I Sands from sand core friction in ladle& runner are falling into the cavity with metal liquid.
3) How to prevent:
I To make sand core strictly in accordance with the process and check the quality.
I To match sand core and outer mold sizes .
I To clean up graphite water in time.
I To avoid ladle and sand core friction.
I To clean sands in mold cavity when lay the sand core.
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