internal bearing geometry when designing ball bearings for optimum performance internal bearing geometry is a critical factor for any given bearing load internal stresses can be either high or low depending on the geometric relationship between the balls and raceways inside the ball bearing structure when a ball bearing is running under a load force is transmitted from one bearing ring to the other through the ball set since the contact area between each ball and the rings is relatively small even moderate loads can produce stresses of tens or even hundreds of thousands of pounds per square inch because internal stress levels have such an important effect on bearing life and performance internal geometry must be carefully chosen for each application so bearing loads can be distributed properly definitions raceway track diameter and track radius internal bearing geometry direction parallel to the bearing axis figure 2 illustrates these concepts since radial play and axial play are both
|
materials/cages/retainer s bearing materials chrome steel materials/cages/retainers bearing steel used for standard ball bearing applications in uses and in environments where corrosion resistance is not a critical factor 52100 or equivalent the retainer also referred to as the cage or separator is the component part of a ball bearing that separates and positions the balls at approximately equal intervals around the bearing s raceway there are two basic types that we supply the crown or open end design and the ribbon or closed ball pocket design the most common retainer is the two-piece closed pocket metal ribbon retainer the most commonly used ball bearing steel in such applications is sae 52100 or its equivalent due to its structure this is the material chosen for extreme noise sensitive applications mkj3 chrome steel developed by nmb s parent company mkj3 is a high carbon chromium bearing steel combined with a heat treating process this steel has a higher hardness and a more stable
|
lubrication lubricant types oil lubrication oils and base fluids petroleum mineral lubricants oil is the basic lubricant for ball bearings previously most lubricating oil was refined from petroleum today however synthetic oils such as diesters silicone polymers and fluorinated compounds have found acceptance because of improvements in properties compared to petroleum base oils diesters in general have better low temperature properties lower volatility and better temperature/viscosity characteristics silicones and fluorinated compounds possess even lower volatility and wider temperature/viscosity properties virtually all petroleum and diester oils contain additives that limit chemical changes protect the metal from corrosion and improve physical properties grease petroleum lubricants have excellent load carrying abilities and are naturally good against corrosion but are useable only at moderate temperature ranges 25° to 250°f greases that use petroleum oils for bases have a high dn o
|
lubrication type dn lubrication continued temperature range f° c° silicone diester petroleum 200,000 400,000 600,000 100 to +400 73 to +204 65 to +350 54 to +177 25 to +250 32 to +121 figure 1 relationship between lubricants dn values and temperature ranges speed factor the maximum usable operating speed of a grease lubricant is dependent on the type of oil the speed factor is a function of the bore d and o.d d of the bearing in millimeters mm and the speed of the bearing n in revolutions per minute rpm where dn d od 2 mm x n rpm 1,000,000 500,000 400,000 300,000 dn factor bore in mm x rpm oil viscosity at 100°f cs 345 200,000 10 20 43 100,000 65 86 13 0 17 3 50,000 40,000 30,000 9 21 6 20,000 10,000 40 60 80 100 120 140 160 180 200 operating temperature °f figure 2 courtesy of exxon corp 4-10 818-341-0820 25 30 2
|
and fatigue life dynamic radial load rating the dynamic radial load rating cr for a radial ball bearing is a calculated constant radial load which a group of identical bearings can theoretically endure for a rating life of one million revolutions the dynamic radial load rating is a reference value only the base value of one million revolutions rating life has been chosen for ease of calculation since applied loading equal to the basic load rating tends to cause permanent deformation of the rolling surfaces such excessive loading is not normally applied typically a radial load that corresponds to 15 percent or more of the dynamic radial load rating is considered heavy loading for a ball bearing in cases where loading of this degree is required please consult an nmb application engineer for information regarding bearing life and lubricant recommendations rating life the rating life l10 of a group of apparently identical ball bearings is the life in millions of revolutions or number of
|
preloading ball bearing systems are preloaded preloading the spindle assembly thus saving the cost of locating shoulders shims or threaded members normally a spring preload would not be used where the assembly is required to withstand reversing thrust loads solid stack preloading where precise location control is required as in a precision motor figure 2 or a flanged tape guide figure 3 a solid preload system is indicated a solid stack hard or rigid preload can be achieved in a variety of ways theoretically it is possible to preload an assembly by tightening a screw as shown figure 3 or inserting shims figure 4 to obtain the desired rigidity it should be noted that care must be taken when using a solid stack preloading system with miniature and instrument bearings overload of the bearings must be avoided so that the bearings are not damaged during this process 1 to eliminate radial and axial looseness 2 to reduce operating noise by stabilizing the rotating mass 3 to control the ax
|
assembly and assem fitting procedurebly preload levels preloading is an effective means of positioning and controlling stiffness because of the nature of the ball/raceway contact under light loads the ball/raceway contact area is very small and so the amount of yield or definition is substantial with respect to the amount of load as the load is increased the ball/raceway contact area increases in size the contact is in the shape of an ellipse and so provides increased stiffness or reduced yield per unit of applied load this is illustrated in the single-bearing deflection curve shown in figure 5 when two bearings are preloaded together and subjected to an external thrust load the axial yield rate for the pair is drastically reduced because of the preload and the interaction of the forces exerted by the external load and the reactions of the two bearings as can be seen by the lower curve in figure 5 the yield rate for the preloaded pair is essentially linear miniature and instrumen
|
table of recommended fits typical applications shaft fit shaft diameter housing fit diameter housing general application-inner ring rotation inner ring press fit outer ring loose fit general application-outer ring rotation inner ring loose fit outer ring press fit tape guide roller drive motor spring preload precision synchro or servo potentiometer encoder spindle gear reducer light duty mechanism clutches brakes inner race floats pulleys rollers cam followers outer race rotates .0000 .0004t .0000 .0004l .0000 .0004l .0001t .0003l .0001t .0003l .0001t .0003l .0001t .0003l .0000 .0004l .0000 .0004l .0000 .0004l .0000 .0004l d 0000 d 0002 d.0002 d.0004 d.0002 d.0004 d.0001 d.0003 d.0001 d.0003 d.0001 d.0003 d.0001 d.0003 d.0002 d.0004 d.0002 d.0004 d.0002 d.0004 d.0002 d.0004 .0000 .0004l .0000 .0004t .0001l 0003t .0000 .0004l .0001t .0003l .0000 .0004l .0001l .0003t .0000 .0004l .0000 .0004l .0001t .0003l .0000 .0004t d 0002 d 0000 d.0002 d.00
|
quality assurance qual ty ass dimensionalicontrolurance nmb quality control systems meet iso 9002 standards in addition to the normal incoming material first article lot and in-process component inspections the qc department maintains process surveillance on all production operations particularly heat treat deburring grinding and race finishing this is to ensure that these operations which generate the characteristics of the finished product remain in control at all times much effort is also expended in correlating gages and gaging methods with user qc departments this is always mutually beneficial and any user or potential user of nmb bearings is urged to contact the quality assurance department to discuss correlation this is particularly important where low runouts low torque or low noise is required the company has equipped the quality assurance department with the latest and finest test and measurement equipment available roundness concentricity and squareness are measured every be
|
temperature tempe conversion table r ature conver sion table °f °c °c/°f °f °c °c/°f °f the numbers in the center column refer to the temperatures either in celsius or fahrenheit which need conversion to the other scale when converting from fahrenheit to celsius the equiva lent temperature will be found to the left of the center column if converting from celsius to fahrenheit the answer will be found to the right °c °c/°f °f °c °c/°f -79 -73 -68 -62 -57 -51 -46 -40 -34 -29 -23 -17.7 -17.2 -16.6 -16.1 -15.5 -15.0 -14.4 -13.9 -13.3 -12.7 -12.2 -6.6 -1.1 4.4 9.9 15.6 21.0 26.8 32.1 -110 -100 -90 -80 -70 -60 -50 -40 -30 -20 -10 0 1 2 3 4 5 6 7 8 9 10 20 30 40 50 60 70 80 90 -166 -148 -130 -112 -94 -76 -58 -40 -22 -4 14 32 33.8 35.6 37.4 39.2 41.0 42.8 44.6 46.4 48.2 50.0 68.0 86.0 104.0 122.0 140.0 158.0 176.0 194.0 37.7 43 49 54 60 65 71 76 83 88 93 99 104 110 115 121 127 132 138 143 149 154 160 165 171 177 182 188 193 199 100 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250 26
|
