PIC Design - RBC Bearings

LINEAR MOTION SYSTEMSSTEPBEARING SELECTIONTwo types of bearings, self-aligning recirculatingball bearings and engineered plastic bearings, areavailable from PIC for use in linear motionsystems. Both types are available in inch ormetric sizes, and closed or open styles.SELF-ALIGNING BEARINGSThe formulas and tables listed below will enablethe designer to select the proper self-aligningbearings to meet the required life.Basic Dynamic Load Ratingand Life ExpectancyThe basic dynamic load rating of a selfaligningbearing is the load which allows arating life of 2,000,000 inches or 50,000meters of travel, without change in magnitudeor direction. The rating life of a bearing for aparticular application can be calculated fromthe following equations:For inch calculations,L=f h ●C 3 ● 2● 106f w PFor metric calculations,L(km) = fh C 3●●50f w PWith:L = rating life in inches for inch calculations,in kilometers for metric calculationsf h = hardness factor (1.0); shafts are60-65 HRCf w = load coefficient (refer to table 1)C = basic design load rating in pounds forinch calculations, in Newtons for metriccalculations (refer to table 2 or 3)P = force in pounds for inch calculations,force in Newtons for metric calculations,determined from load calculationdiagrams 1 through 5, as applicableRating life in hours can be calculated from thetravel distance per unit of time, as follows:L h =L2 L ● ●s n ●1 60With:L h = rating life in hoursL s = stroke length in inches forinch calculations, in meters formetric calculationsn 1 = rating in cycles per minuteTable 2. C Dynamic Load Rating of Inch BearingsTo calculate the basic dynamic load rating, useC=3.3/8 95 PFL-6 —L f● w ●.1/2 230 PFL-8 PFL0-8P2 ● 10 6 .5/8 400 PFL-10 PFL0-10f h .3/4 470 PFL-12 PFL0-12the following formulas:Shaft RatingPIC Part No.Diameter (inch) (lb) Closed OpenFor distances in inches,.1/4 60 PFL-4 —1. 850 PFL-16 PFL0-16For distances in kilometers,1.1/41.1/212301480PFL-20PFL-24PFL0-20PFL0-24C=3L f● w ●Table 3. C Dynamic Load Rating of Metric BearingsP1 ● 50 f hShaft Diameter Rating(mm) (Newtons)PIC Part No.Example of Calculations using standard PICcomponentsExpected Life: 20,000 hoursNumber Of Bearings: 4Weight On Carriage: 175 lbStroke Distance: 24 inchesTraveling Speed: 1000 in. / minCycle:2 x 24 inchesShaft:A10L seriesFrom the life expectancy in hours formula, thelife expectancy in traveling distance is:L h =L2 L s n ●1 60L=L h● 2 L ● s● n ●1 60L = 20,000 ● 2 ● 24 ● 1000●602 ● 24L = 1.20 x 10 9 inchesFrom the dynamic load rating formula:C=C=3C = 553 lbL●f w ●P2 ● 10 6 f h31.2●10 9 1.5●●1752 ● 10 6 1.0 4The assumption is that the 175 pound loadis distributed evenly between bearings;therefore, using diagram 3 with1-inch with 1-inch diameter bearings having a load capacityof 850 pounds is selected.Table 1. Load CoefficientOperating Conditionsf wOperation at low speed (50 ft/ min or15 m/ min or less) without impulsive 1 - 1.5shock from outsideOperation at intermediate speed(200 ft/min or 60 m/min or less) 1.5 - 2.0without impulsive shockOperation at high speed(over 200 ft/min or 60 m/min) 2.0 - 3.5with impulsive shock from outsideCLOSED TYPE12 650 MPFL-1216 800 MPFL-1620 1500 MPFL-2025 2500 MPFL-2530 3200 MPFL-3040 5550 MPFL-40OPEN TYPE12 750 MPFL0-1216 920 MPFL0-1620 1560 MPFLO-2025 2600 MPFLO-2530 3330 MPFL0-3040 5740 MPFL0-40ENGINEERED PLASTICLINEAR BEARINGSPIC self-lubricating plastic bearings aremaintenance free, run quietly, are not subjectto catastrophic failure, do not gall or brinellthe mating shaft, and can run on “soft” noncorrosive303 stainless steel shafting. Thesebearings are also capable of operation inhostile environments and are interchangeablewith PIC self-aligning, recirculating bearings.Bearing PV RatingThe performance capabilities of engineeredplastic linear bearings are defined by thePV rating of the bearings, where P is thepressure in pounds per square inch on theprojected bearing area, and V is thevelocity in feet per minute of the wearsurface. Maximum PV for continuousoperation is 7500 PSI/FPM. To calculatePV for a particular application, divide thetotal load in pounds on the bearing by theeffective area in square inches, andmultiply by the average bearing velocity infeet per minute.Example of Calculation:Number Of Bearings: 4Weight On Carriage: 175 lbLoad Per Bearing: 175/4 = 43.75 lbTraveling Speed: 1000 in./min or83.33 ft/minBearing Selected: PLC-16 (1 in. = ID,2.25 in. long = L)P= Load (lb.) 43.75= = 19.44 PSIID L 1 2.25● ●PV = 19.44 83.33 = 1620 PSI/FPM●www.pic-design.comInteractive catalog ■ CAD ■ e-commerceDESIGN®Phone: 800-243-6125 ■ FAX: 203-758-8271E-Mail: sales@pic-design.com1-3