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Causes and prevention methods of common defects in castings-Chapter Tree

Update:19 Apr 2019

Fourth, cracks (hot cracks, cold cracks) Characteristic […]

Fourth, cracks (hot cracks, cold cracks)

Characteristics: The appearance of the crack is a straight line or an irregular curve. The surface of the hot crack fracture is strongly oxidized to dark gray or black, no metallic luster, and the surface of the cold crack fracture is clean and has a metallic luster. Generally, the outer crack of the casting can be seen directly, and the internal crack can be seen by other methods. Cracks are often associated with defects such as shrinkage and slag inclusions, which occur mostly in the inner side of the sharp corner of the casting, at the junction of the thick section, and the hot joint where the riser is connected to the casting.

Reason for formation:

Metal mold casting is prone to crack defects, because the mold itself has no retractability, the cooling speed is fast, and it is easy to cause the internal stress of the casting to increase. The opening type is too early or too late, the pouring angle is too small or too large, and the coating layer is too thin. It is easy to cause cracking of the casting, and it is easy to cause crack when the mold cavity itself has cracks.

Control method:

1. Attention should be paid to the structural and structural properties of the castings, so that the parts with uneven wall thickness of the castings are evenly transitioned, and the appropriate rounded corners are used.

2, adjust the thickness of the coating, as far as possible to achieve the required cooling rate of each part of the casting, to avoid the formation of too much internal stress.

3, should pay attention to the working temperature of the metal mold, adjust the mold slope, and timely core cracking, take out the casting slowly.

Five, cold separation (poor fusion)

Characteristics: The cold partition is a kind of slit or surface with a rounded edge. The middle is separated by the scale, which is not completely integrated. When the cold partition is serious, it becomes “under-cast”. Cold insulation often occurs on the top wall of the casting, a thin horizontal or vertical surface, a thick wall joint or a thin support plate.

Reason for formation:

1. The metal mold exhaust design is unreasonable.

2. The working temperature is too low.

3. The quality of the paint is not good (man-made, material).

4. The location of the sprue is improper.

5. The pouring speed is too slow.

Control method:

1. Design the runner and exhaust system correctly.

2, large-area thin-walled castings, coatings should not be too thin, appropriate thickening of the coating layer is conducive to molding.

3. Appropriately increase the working temperature of the mold.

4. Adopt the inclined casting method.

5. Casting with mechanical vibration metal mold.

Six, sand holes (sand holes)

Features: relatively regular holes are formed on the surface or inside of the casting, the shape of which is consistent with the shape of the sand. The sand inlaid on the surface of the casting can be seen when the mold is released. The sand can be extracted from the surface. When multiple sand eyes are present at the same time, the surface of the casting is orange peel. shape.

Reason for formation:

The sand falling from the surface of the core is surrounded by the copper liquid and forms a hole with the surface of the casting.

1. The surface strength of the sand core is not good, burnt or not fully cured.

2. The size of the sand core does not match the outer mold, and the sand core is crushed when the mold is closed.

3. The mold smashed the graphite water contaminated with sand.

4. The sand that is rubbed off by the ladle and the sand core at the sprue is flushed into the cavity with the copper water.

Control method:

1. The sand core is strictly produced according to the process and the quality is checked.

2. The size of the sand core matches the size of the outer mold.

3. The ink should be cleaned up in time.

4. Avoid rubbing the ladle with the sand core.

5. When blowing the sand core, blow the sand in the mold cavity.

Obvious article here.

Chapter One

Chapter Two