GB833267A - Improvements in or relating to magnetic test particles - Google Patents

Abstract

833,267. Magnetic particles. STEELE, J. D. Dec. 31, 1957 [Feb. 8, 1957], No. 4475/57. Class 38 (2). Magnetic particles for tracing flaws in a magnetic body are made by a process which includes the steps of forming a partially cured resin containing magnetic material and tracer material, pulverizing the mixture and completing the cure of the resin. The magnetic material may be carbonyl iron of 5 micron particle size, red iron oxide of less than six micron particle size or a ferromagnetic alloy powder; the resin may be transparent and may be one of a number of specified epoxy resins or an amidealdehyde resin such as a melamine-formaldehyde or urea-formaldehyde resin modified or unmodified or blended with each other or an epoxy resin; the tracer material may be a fluorescent substance such as 2-hydroxy-1-naphthaldazine, or a fluorescent metallic salt of 8-hydroxyquinoline (e.g. of zinc), or a non-fluorescent pigment such as titanium dioxide, vermilion, molybdate orange, " Hansa " yellow (Registered Trade Mark), Milori green, copper phthalocyanine blue or carbon black. Rhodamine may be used for both fluorescent and non-fluorescent testing. A diffuse-reflecting opacifying agent such as titanium dioxide may be incorporated. In one process carbonyl iron was mixed to a thick paste in a solution of a catalyst, metaphenylene diamine, in an epoxy resin and allowed to stand at 85‹ C. until the resin had set to a friable solid. It was then pulverized at room temperature to spheroidal particles of iron coated with resin, milled with the fluorescent pigment for 24 hours and cured for ¢-hour at 150‹ C. The product, a rather brittle slightly porous mass, was milled to a powder of 6-7 microns particle size, resinous dust and free pigment being separated by washing. A somewhat inferior product resulted when the magnetic and tracer powders were added together, either in the liquid resin, or after the solidified resin had been milled. The use is described of such materials that cooling with dry ice is needed before pulverization, and the final material is milled while cooled by liquid nitrogen.