Milling Journal - Q4 2008 - (Page 20) Vibration—Bearings Gloves are recomneed to be stored away mended when handling from excessive vibraindividual elements. tion. Constant exposure Mounting to too much shaking, Proper bearing such as when trains mounting is another rumble past the mill, key to preventing bearcauses scratching on the ing failure. Improper bearing alignment can cup of tapered roller Misalignment and imresult in a broker retainer (center). bearings, which reproper fit—When bearduces life expectancy. ings are not mounted properly, two things Bearings need to be stored flat, not on can happen, but with the same result. Insuftheir sides, in sturdy cartons or pallets, ficient or excessive interference—a meain areas that are clean and dry, or the sure of tightness between the shaft and the bearings could begin to fail even before bearing bore—produces either undesired they are taken out of the box. rotation or undesired preload. Rust—Excessive moisture levels almost Together, they produce excessive heat, always result in rust forming on bearing surlubrication failure, and eventually, prefaces which reduces their life expectancy. mature bearing failure. To eliminate this type of damage, store The purpose of a good fit is to prebearings in a room low in humidty. vent creeping. Once creeping begins, If the problem persists, millers should temperatures rise, and abrasion particles consider switching to ceramic or sealed get into the bearing causing it to become bearings. noisy, and eventually the bearing burns Improper or excessive handling—Damup. age also can occur when bearings are exMounting solutions—Check the shaft posed to rough or excessive handling. and housing for correct conformity (diThey should be handled with care to mension to 3 decimal places), roundness, avoid flaking at intervals along the raceway. casting sand, burrs, concentricty, and shoulder squaredness. Be sure to apply a thin coat of machine oil to the shaft and housing prior to mounting bearings. History of Bearings The earlist bearings, though no direct evidence exists, appeared at Giza, Egypt, where the pyramid builders rolled large stones on wooden dowels made from tree trunks. Later, wooden roller bearings reached a higher level of precision which allowed them to be used in more sophisticated applications, like clocks. In 1740, noted clock maker John Harrison, while working with a principal first described by Galileo a hundred years ealier, invented the first caged roller bearing—made of wood—which he placed in his H3 marine timepiece. The bearing was used to smooth a limited oscillating motion. Later, he developed a similar bearing for a contemporary regulator clock that is thought to be the first ever used for an authentic rotary application. 20 Fourth Quarter 2008 Response No. 201 Response No. 202 MILLING JOURNAL http://www.VAAeng.com http://www.jebbbrush.com http://www.VAAeng.com http://www.jebbbrush.com
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