Document mBgJEkVoQ2VOY28n07bkykEv0

DIESEL-BEARING EVOLUTION FROM CAST-IN TO SUP-IN BABBITTED bearing east In place In housing rvt in tlow-epeed engines INTEGRAL bearing woi forerunner of some preeent designs. Cyllndero held together by bolts wore babbitted and machine-finished on outside diameter, Thla design reduced lining thickness, hand fitting needed for replacement. Rebsbblttlng could be done at factory INTERCHANGEABLE design comprises bronze back with eentrlfugally east lining; finishing stock la provided on 10 for machining or ecraplng to fit esiNKPIM BOX without bearing In- babbitt being chemically bonded d're'ctly to box. Used occasionally PRECISION bearing consists of a backing and thin lining machined for interchangeable At before assembly MONO-ALLOY bearing follows me* ehanleal features of precision-insert design but Is mode of a elnglo metal For Top-notch Diesel Operation Know Your Sleeve-Bearing Fundamentals \ i':-f y. ,11 & fJ To meet today'* heavier demands, improved bearings have been developed. Here's the way they came into use, the reasons why, and an explanation of their mechanical construction features* * Conditions in diesel kncines make life tough for bearings. To meet these over more severe demands, bearing de signs have undergone radical changes since Isaac Babbitt introduced the bear ing alloy now known by his name. The early ides was to apply a gener ous quantity of a high-tin alloy directly to a cast-iron or bronze housing. Be cause chemical bonding was unknown, mechanical means of making the lining stay in the housing had to be used. Meth ods included tapping large holes with coarse threads, and upping and screwing-in flat-head screws, but the common procedure involved casting or machin ing dovetail grooves into the housing (see above), tn large diesels, lining sometimes reached a thickness of 1% in., or more. In spite of casting difficulties, such bearings worked rather well where unit loads were low and speeds slow. Never theless, wear eventually reached a point where the babbitt had to bo recast and brought to a fit, an operation requiring time, equipment and ekill, and success was not otwoys sure. Yesterday's Searing*. Forerunner of some present bearings wos the integral design, consisting of a babbitt-lined split cylinder held together by bolls. The OD was machine-finished to 6t the housing. Thus main bearings could be assembled to the cronkshaft and the whole laid into a bedplate bored to mete OD of bearing backings. In this design, lining thickness was re duced to A to % in., depending on backing material and thickness. Dove tail grooving was less drastic, but still used in most cases. These bearings could be replaced, with some hand fit ting and shimming, and rebabbitling nnd machining could be done by the engine builder or a bearing maker. Nezt step was the interchangeable unit, consisting of a backing, usually bronze, with suitable lining material centrifugally or gravity east by modern methods capable of obtaining a chemi cal bond between lining and backing. Allowance for finishing was made on the ID. Bedplate and corresponding msinbcorlng caps were bored and th bearing OD machined to fit them. Stock was usually left at the parting (aces, as well, for subsequent fitting. Methods of boring the assembled bearings to fit the ahslt were sometimes employed, bat usually laborious hand scraping was considered best. Resulting oil clearance was variable, and high and low spots on the bearing * surface could not be avoided. Also, be cause bearings were finished to height by hand filing, contact of these surfaces with the corresponding half bearing was not too accurate. Unings still had to be relatively thick (Vfc to V4 in.) to offset inaccuracies m initial bedplate haring as well as to allow for bond scraping. When bearings of this type are put in new engines today the linings are machine bored to a truly round hole for a round shoft. Development of methods for chemi- colly bonding lining to backing led to occasional direct babbitting of crankpin boxes. Elimination of lining anchor- -if <u Itlt Iou *mt e*i rwr c*)*- nn W '>* 0(1 lU r*mi DltOUm, HUB, tm MUrtUailn fttttt m Swrta#, wot OnWN H> S outiin iV 0 <T UNk. CliWnl OrisMW Imt* c*.- a v NicmoI iwUf iMw *-. um c*i tr a run. Car,; 0 * WW, ilralam Ct tl Ametif, VU arftal*. Ill Hln t* !*Bm, U (nfctMllM IN fru Wapiti!** tj tti* N*. 64 (22) POWER January ! HOW BEARING OIL FILM FORMS Theory pictures formation of oil Aim aa ehown above! At rest, actual contact exists between theft, bearing. When shaft starts to turn, It tends to roll to left Speed rises, shaft drags oil Into wedge-eheped spaee, pressure builds up, Hfte shaft off bearing. At full epesd, hydraulic pressure tends to push shaft to side METALS IN DRY FRICTION Some metal-to-metal friction usuelly occurs in any bearing. Frictional resistance It proportional to the reel .ares of eontact A end the shear strength 8 of the softer metal. As diagramed above, the desired condition of keeping both A and 8 small la obtained by thin film of left metal on herd metal >OW|R January 1948 (231 es k*i