Analysis of Common Problems in Sand Mould Casting
Produced. Porosity is due to the insufficient permeability of the casting mould (core) and the large amount of gas produced during pouring, which can not be discharged in time.
1) Identification of Shrinkage
Shrinkage holes in castings are characterized by rough hole walls and irregular shapes, which often occur at the thicker part of the final solidification of the castings or at the junction of the casting walls. The main methods for identifying shrinkage are as follows:
(1) To observe the surface shape of casting defects, such as uneven surface, very rough, and dark gray, irregular shape hole, that is shrinkage.
(2) Holes are shrinkage holes if they are located at the final solidification thickness of the casting or at the hot spot intersecting the two walls, and at the middle or upper part of the section.
(3) Shrinkage or air shrinkage is the most concentrated hole defect in the thick and large section of steel castings.
2) Identification of stomata
There is a big difference between porosity and shrinkage in castings. Its characteristics are as follows.
(1) The pore wall is smooth, and the inner surface is bright white or with slight oxidation color.
(2) The stomata are round, long or irregular.
(3) The size of stomata varies greatly, ranging from several centimeters to a fraction of a millimeter.
(4) Pores often exist in a single, several or honeycomb shape on the surface of castings or near sand cores, chills, core braces or pouring and risers, sometimes covering the entire section.
2. Identification of wrong type, wrong core and partial core
1) Identification of Mistyping
Misalignment is a defect in which one part of the castings and the other part are separated from each other at the parting surface. It is generally caused by improper fitting and positioning.
If there are sand cores in the mould and the sand cores are placed in the lower mould, the defect is the wrong shape rather than the partial core.
2) Identification of wrong core
The staggered core is that the sand cores are staggered at the core-separating surface, which makes the inner cavity of the castings deform. It is wrong core and not wrong shape, so the shape of the outer surface of the casting is correct.
3) Identification of partial core
The core deviation is due to the undesirable change in the position of the sand core, which results in the discrepancy between the shape and size of the castings and the pattern. Core deviation
3. Differentiation between not pouring and not pouring
1) Identification of defects that cannot be poured
Imperfection refers to the defect on the casting, the contour shape is incomplete, or the contour is complete, but its edges and corners are round and glossy. Defects that cannot be poured on castings often occur far away from the gate and in thin-walled areas, while the pouring system is filled with liquid metal. It is not due to insufficient liquid metal during pouring, but due to poor fluidity of liquid metal or too large flow resistance.
2) Identification of Unfilled Defects
Unfilled is the lack of meat at the upper part of the casting position, and the corner of the casting is slightly circular at the lack of meat. Unfilling is different from not filling. Unfilling is caused by insufficient liquid metal entering the cavity, such as insufficient liquid metal in the pouring ladle or interruption of pouring, etc.