Characteristics of Rapid Cure Magnetic Rubber Inspection Formulations

摘要

Magnetic rubber inspection (MRI) is a form of magnetic particle inspection. In this particular form the magnetic particles are suspended in a liquid rubber curing at room temperature. The rubber, after the addition of a catalyst and a stablisizer, is poured into, or around, the area to be inspected, where it may be contained, if necessary, by a specially constructed reservoir. A magnetic field, complying with the principles of magnetic particle inspection, is then applied to the part for a period of approximately 2 to 4 minutes, after which the rubber solution continues to cure to the solid state. The flexible solid rubber cast is then removed from the part and the surface of the cast is examined in detail, in the relevant areas, using a low-power binocular microscope. Evidence of surface and near-surface defects in the material with which the rubber was in contact during the curing/magnetization period appears at the surface of the cast as corresponding concentrations of magnetic particles. Over the last 10 years the magnetic rubber inspection method has proved very useful for the detection of very small (0.2mm surface length) fatigue cracks and other surface discontinuities (e.g. non-metallic inclusions) in magnetic materials. In many instances, it has been the only method whereby such defects could be detected non-destructively. The introduction of rapid-cure magnetic rubber inspection formulations has raised questions as to whether there may be some impairment of the sensitivity and reliability of the inspection technique relative to its performance with the well-established, slower curing formulation. This memorandum attempts to answer these questions.