Thomas W. Grossman

Examination and Diagnosis of Musculoskeletal Disorders

Examination and diagnosis of musculoskeletal disorders , Examination and diagnosis of musculoskeletal disorders , کتابخانه مرکزی دانشگاه علوم پزشکی تهران

8.1 Introduction

Wear generates debris. The debris comes in a wide variety of sizes and shapes. Wear debris turns motor oil black. You can see it on your hands if you shake hands with your garage mechanic. The black in used oil is like a pigment — it is nanometer-size colloidal metal particles (and carbon) suspended in the oil. If you take an oil filter apart, you will find other types of wear debris. Some are shiny metal particles visible to the naked eye and in the millimeter size category. If you are in the surface mining business, you will find even larger metal particles in the gravel produced by rock crushers. This is metal that is gouged from the metal jaws in the crusher. In a factory grinding room, dust swept up from the floor and examined in a scanning electron microscope will show perfect micron-size metal spheres from rapidly solidifying drops of molten metal generated by the grinding wheel. Examples of these unique debris particles will be found later in this chapter. Wear debris represents loss of geometric accuracy of moving contacting parts. It can also foul orifices and close spaced parts. Although the total material lost as wear debris in a machine is minute compared to the volume and weight of the moving parts, it can signal failure of gears or bearings, and expensive repairs or warranty payments. Because wear debris can be carried in a circulating oil lubrication system, the condition of an engine or a critical machine can be diagnosed by analyzing a sample of the oil. Debris can be removed from the oil by centrifuging or by a magnetic process. The separated debris can then be examined in a microscope to determine morphology, or it can be chemically analyzed. A standard test, the spectrographic oil analysis program (SOAP), has been used for condition monitoring by railroads, truck fleets, and the military for tanks and aircraft. Until the Industrial Revolution and the development of steam and internal combustion engines, wear was taken for granted. When wear of machinery and tools became a problem, the development of wear-resistant materials and the study of wear itself increased rapidly. Now we have a large body of information developed from experience and scientific investigation that can be used in the design and maintenance of more reliable and economical machinery.