T.O. 33B-1-13-105c. StraighteningCracks. The process of heat treating often causes some warping of the part due to non-uniform cooling during quenching. A hardened shaft, for example, may come from the heat treatoperation not quite straight. In many cases these can be straightened in a press, but if the amount ofbend required is too great or if the shaft is too brittle, cracks may be formed. Again, these are veryreadily found with magnetic particlesd. GrindingCracks. Surface cracking of hardened parts, as the result of improper grinding is frequently asource of trouble. Grinding cracks are essentially thermal cracks. They are caused by stresses set up bylocal heating under the grinding wheel. They are avoidable by using proper wheels, proper cuts, andproper coolants. They are sharp surface cracks and they are easily detected with magnetic particleinspection. Such surfaces usually crack severely and extensively, as illustrated in Figure 3-64 andFigure 3-65.Figure 3-64. Fluorescent Magnetic Particle Indications of Typical Grinding Cracks.Figure 3-65. Magnetic Particle Indications of Grinding Cracks in a Stress-Sensitive, Hardened Surface.e. EtchingandPicklingCracks. Hardened or cold worked parts, that contain high internal and externalresidual stresses, may crack if they are pickled or etched in acid. Acid attack of the surface layers ofthe metal gives the internal stress a chance to be relieved by the formation of a crack. Before this action
Integrated Publishing, Inc. - A (SDVOSB) Service Disabled Veteran Owned Small Business
