Established in 1952

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Flaw Evaluation with Small Spherical Probes

Ball Scribe

By applying the end of a given spherical tipped probe, also known as a ball scribe, across a flaw in a machined or ground surface, the proportions of individual imperfections can be evaluated.

The evaluation is conducted by mechanically scanning across the flaw with a hand held probe. If the spherical tip penetrates the flaw by any appreciable amount, a very evident click will be felt. If the radius of a given spherical tip does not penetrate the flaw, but instead spans it, there will be no noticeable click and the part is acceptable.

If the spherical tip drops into a flaw, the probe will move up and down, and a distinct click will be felt.	If the spherical tip spans the flaw, no click will be felt.

The conventional spherical probe diameters are 0.020 inch, which is 0.5 mm, or 0.04 inch, which is one mm diameter, and 1/16 inch, which is one and one half millimeter diameter, but somewhat smaller and much larger spheres are also being used.

It is of great significance that it is the spherical radius of the test probe that is used, as the sensor element, so that the initial contact surface is only one half the spherical diameter. Then only a small cord of the spherical radius senses the void that constitutes the flaw, so the overall sensitivity of this system is many times greater than might be expected.

The useful life of these test probes is greatly enhanced by supplying the spheres made with tungsten carbide material. This cermet is very hard with a wear resistance that is 30 times that of hard steel.

Because of their small diameter, it is important that the balls be tenaciously attached to the probe handle so they will not be picked off. This attachment is best accomplished by brazing the ball, in place, on the probe tip. Although this task on such small balls would normally be considered impossible, we have mastered the technology to accomplish it. The probe itself is made of highly corrosive resistant metal that is polished for clean room compatibility.

These items are made to order. Price and delivery will be quoted.