AUTOMOBILE HUB BALL BEARINGS ByHENRY HESS This isanaccount ofcertain experiments undertaken tode termine thebehavior ofballbearings asused inanautomobile hubunder proper andimproper conditions. TheBearing. The bearing selected fortest isofthewell known Hess-Bright type, having two-point contact, races of uniform cross-section, i.e.,uninterrupted byanyfilling opening, and with elastic, individual separators interposed between the balls. The size isthat known asNo.308; itsdimensions are given inFig. 1.This isasizevery widely used inthehubs ofautomobile touring cars. UseConditions. In ahubtheload willbepurely radial, i.e., atright angles totheaxiswhen thecarisgoing straight ahead. When rounding curves orweaving from side toside anend Editor's Note. Through adraughtsman's error theexplanation reads "spd andhead" instead of"speed and load," Downloaded from SAE International by University of British Columbia, Tuesday, September 25, 20184 AUTOMOBILE HUB BALL-BEARINGS thrust, parallel totheaxis, willbeimposed inaddition. Prop erlymounted andtaken care of,thebearing willbeamply lubri cated andkept freeofrust andgrit. Test Conditions. Test conditions were arranged toconform, asnearly asmight be,totheproper andimproper conditions that would befound inactual use. They, therefore, embraced: (I) Radial loads only. (IIandIII) Combined radial andthrust loads; and (IV) Thrust loads only. The latter condition isnotlikely toobtain inahuboraxle, butisofinterest, asthequestion ofbehavior under thatcondi tion isoften raised. Test runs with (A) copious lubrication, (B) practically no lubrication, (C) with rust, and (D) with grit, were repeated under each load condition. The loads ranged from alowload ascompared with thecapacity ofthebearing toavery decided overload. The radial load started at600pounds andwasraised by200-pound increments to2,000 pounds. The thrust loads ranged from 50pounds to400pounds by50-pound increments. Thespeed wastaken at300r.p.m.,thiscorresponding approxi mately tothirty miles perhour ofacar. Copious lubrication was provided byallowing thebearing todipinto arelatively large reservoir ofoil,sothat thebottom balls were carried through that. For dryrunning thebearing was rinsed outin gasoline andthen dried outinanairblast; thisleftavery slight oilfilm, notperceptible tothetouch, butnevertheless present. After thistestthebearing wasrusted inwater until alight coat was deposited on all surfaces. Owing tothehigh finish ofthe balls andraces therust filmonthese wasnotthick; onthesepa rators, which arenotpolished, therust was much heavier and interfered decidedly with their elastic action. Grit waspro vided bythrowing sharp building sand between theraces. Comparative Results. The measured friction coefficient may safely betaken asanindex oftherunning under each condi tion. Itiscertain that alowcoefficient means favorable running andlong life, while anincrease inthefriction indicates anad verse development. TheApparatus. The machine employed isaspecial friction measuring machine, capable ofdefinitely measuring theforce ofthefrictional resistance duetoradial loads upto15,000 Downloaded from SAE International by University of British Columbia, Tuesday, September 25, 2018SOCIETY OF AUTOMOBILE ENGINEERS 5 pounds, ofthrust loads upto10,500 pounds, andofcombined radial andthrust loads inanyratio within these limits, and atspeeds ranging from 200to2,000 r.p.m. The radial load isapplied tothebearing under test byasystem of weighing beams through atension rodthat isjointed near thetest bearing. The friction ofthebearing swings the joint tooneside byanamount depending upon thefrictional force. This movement issmall, butmeasurable byamicroscope andwithin anegligible error. Thethrust load isapplied bya second system ofweighing levers through asmall wire ofhigh elastic limit attached toayoke resting against theouter race ofthebearing. The friction tends torotate this yoke. This tendency isresisted byadelicate setofscales, anerror ofobser vation ofn