Defects in Casting

Methods of Inspection for detecting out as Defects in Casting.

In casting process, first some of the castings will be inspected as per allowances and dimensionally and the pattern is qualified afterwards, only few random inspection will be done. Every casting must be inspected for labelling out the defects in casting process.

Different methods of inspection for searching out defects in casting process are discussed below

1. Visual Inspection

2. Hydrostatic Pressure Test

3. Magnetic Particle Inspection

4. Radiographic Examination

5. Ultrasonic inspection

6. Dye Penetrant Inspection

7. Coin Testing

1. Visual Inspection

Well-known defects such as surface roughness, obvious shifts, omission of cores and surface cracks can be detected by a visual inspection of the casting. Cracks may also be detected by hitting the casting with a mallet and listening to the quality of the tone produced.

2. Hydrostatic Pressure Test

The Hydrostatic pressure test is conducted on a casting to be used as a pressure vessel and shell.

In this test, first all the flanges and ports are blocked.

In addition, the casting is filled with water, oil or compressed air, moreover, the casting is submerged in a soap solution when any leak will be evident by the bubbles that come out.

3. Magnetic Particle Inspection

The Magnetic particle test is conducted to check for very small, tiny or minor dent, scratches and voids and cracks at or just below the surface of a ferromagnetic material. The test involves inducing a magnetic field through the geometry section inspection. Completion of preliminary process, the powdered ferromagnetic material is spread out onto the surface. The presence of dent or scratches or voids or cracks in the section results in an abrupt change in the permeability of the surface; this, in turn, causes a leakage in the magnetic field. The powdered particles accumulate on the disrupted magnetic field, outlining the boundary of a discontinuity.

4. Radiographic Examination

The radiographic method is expensive and is used only for subsurface exploration. In this, both X-rays and γ-rays are used. With help of γ-rays, more than one film can be exposed simultaneously; however, x-ray pictures are more distinct. Various defects, like voids, nonmetallic inclusions, porosity, cracks and tears, can be detected by this method. The defects being less dense, film appears darker in contrast to the surrounding.

5. Ultrasonic Inspection

In the Ultrasonic method, an oscillator is applicable for sending an ultrasonic signal through the casting. such as signal is fluently transmitted through a homogeneous medium. However, on encountering a discontinuity, the signal is reflected back. This reflected signal is properly detected by an ultrasonic detector. The time interval between sending the signal and receiving its reflection determines the spots of the discontinuity. The method is not convenient for a material with a high damping capacity (e.g. cast iron) because in such a case the signal gets considerably weakened and poor over some distance.

6. Dye Penetrant Inspection (DPI)

The dye penetrant inspection method is known for detect invisible surface defects in a nonmagnetic casting. The casting is brushed with, cotton with sprayed with, or dipped into a dye containing a fluorescent material. The surface to be inspected is the wiped, dried and viewed in darkness. The discontinuous stressed in the surface will then be readily discernible.

7. Coin Testing

By hitting with coin on to the component surface and by hearing the sound coming from the casting, the presence of defect can be estimated.