Inspection by comparison methods

Inspection by comparison methods:

In these methods the surface texture is assessed by observation of the surface. The surface to be tested is compared with known value of roughness specimen and finished by similar machining process.

The various methods which are used for comparison are

1. Touch Inspection.

2. Visual Inspection.

3. Microscopic Inspection.

4. Scratch Inspection.

5. Micro Interferometer.

6. Surface photographs.

7. Reflected Light Intensity.

8. Wallace surface Dynamometer.

·        Touch Inspection

It is used when surface roughness is very high and in this method the fingertip is moved along the surface at a speed of 25mm/second and the irregularities as up to 0.0125mm can be detected.

· Visual Inspection

In this method the surface is inspected by naked eye and this measurement is limited to rough surfaces.

· Microscopic Inspection

In this method finished surface is placed under the microscopic and compared with the surface under inspection. The light beam also used to check the finished surface by projecting the light about 60° to the work.

· Scratch Inspection:

The materials like lead, plastics rubbed on surface are inspected by this method. The impression of this scratches on the surface produced is then visualized.

· Micro-Interferometer

Optical flat is placed on the surface to be inspected and illuminated by a monochromatic source of light.

· Surface Photographs

Magnified photographs of the surface are taken with different types of illumination. The defects like irregularities are appear as dark spots and flat portion of the surface appears as bright.

· Reflected light Intensity

A beam of light is projected on the surface to be inspected and the light intensity variation on the surface is measured by a photocell and this measured value is calibrated

· Wallace surface Dynamometer:

It consists of a pendulum in which the testing shoes are clamped to a bearing surface and a pre determined spring pressure can be applied and then, The pendulum is lifted to its initial starting position and allowed to swing over the surface to be tested.