Current Flow (Headshots) – Test Piece 1 (TP1)

When current flow techniques are used on bench units, the following test should be carried out for each wave form available for use:

1. Ensure the test piece is thoroughly demagnetised and pre-cleaned satisfactorily.
2. Position the test piece (see diagram below) between the head and tailstock of the bench equipment.
3. Slowly introduce a current and apply ink until the first hole (closest to the external surface) is visible.
4. Note the applied amperage and continue to apply the current progressively until the second and third holes are noted.

Magnetic flow - Using Test Piece 4 (TP4)

If magnetic flow is being used, a similar procedure to the above would still apply, except that the dial readings/switch settings would be taken instead of amperage values and the following test piece would be used.

Fig. 8.6 - Test piece for magnetic flow and rigid coil techniques

A similar version is often used but with 5 holes (1 to 5mm) depths from the top surface) to assess the equipment over a greater range.

Rigid coil

If a rigid coil is being used the magnetic flow reference block would be employed, being placed within the coil and again noting amperages when the hole(s) become visible.