YOKE GP 4264368 - Caterpillar

Illustration 25 g06003178
Pear Shaped Centrifuge Tube
Wet magnetic particles are fluorescent and are suspended in a vehicle in a given concentration that will allow application to the test surface by spraying.
Concentration:
The concentration of the suspended magnetic particles shall be as specified by the manufacturer and be checked by settling volume measurements.
Concentrations are determined by measuring the settling volume by using an ASTM pear shaped centrifuge tube with a 1 mL (0.034 oz) stem with 0.05 mL (0.0017 oz) 1.0 mL (0.034 oz) divisions, refer to Illustration 25. Before sampling, the suspension shall be thoroughly mixed to assure suspension of all particles, which could have settled. A 100 mL (3.40 oz) sample of the suspension shall be taken and allowed to settle for 30 minutes. The settling volume should be between 0.1 mL (0.0034 oz) and 0.25 mL (0.0085 oz) in a 100 mL (3.40 oz) sample.
Wet magnetic particles may be suspended in a low viscosity oil or conditioned water.
The oil shall have the following characteristics:
Low viscosity not to exceed 50 mSt (5.0 cSt) at any temperature at which the vehicle is to be used.
Low inherent fluorescence and be non-reactive.
The conditioning agents used in the conditioned water shall have the following characteristics:
Impart good wetting characteristics and good dispersion.
Minimize foaming and be non-corrosive.
Low viscosity shall not exceed a maximum viscosity of 50 mSt (5.0 cSt) at 38° C (100° F).
Non-fluorescent, non-reactive, and odorless.
Alkalinity shall not exceed a pH of 10.5.
Equipment should include a "U" shaped electromagnetic yoke made from highly permeable magnetic material, which has a coil wound around the yoke. This coil carries a magnetizing current to impose a localized longitudinal magnetic field into the part. The magnetizing force of the yoke is related to the electromagnetic strength and can be tested by determining the lifting power of a steel plate. The yoke shall have a lifting force of at least 4.5 kg (10 lbs).Procedure
Ensure surface to be inspected is dry and free from oil, grease, sand, loose rust, mil scale, paint, and any other contaminants.
Apply the magnetic field using the yoke against the surface in the area to be inspected.
Illustration 26 g03536210
For case hardened and ground surfaces:
Due to the sensitivity required to locate the grinding cracks, inspection of case hardened and ground surfaces require that the yoke is applied so that the magnetic field is 1.57 rad (90°) to the expected direction of the indications. Also, due to the increased sensitivity resulting when the yoke is energized, the yoke is not moved until the evaluation is completed in the first direction. An AC yoke shall be used. See Illustration 26 for an example of yoke placement.
Visually inspect for indications of discontinuities using the proper illumination.
Record the size and shape of any discontinuities found.Ultrasonic Testing (UT)
Note: Crack depth cannot be accurately determined by UT, only full depth cracking can be consistently determined. For cracks that are not full depth, an indication of a partial depth cracks can be detected by an experienced technician.
All personnel involved in ultrasonic testing shall be qualified to