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MECHANICAL COMPONENTS FEATURE


Although slewing bearings are typically used in applications where their ability to transmit relatively high loads is of primary importance, there are other


potential application requirements that can have a significant impact on their selection. To help you through the process KAYDON bearings supplier, R. A. Rodriguez, has put together a 9-step guide for standard slewing applications


A 9-STEP GUIDE


TO SLEWING RING SELECTION


1


. Determine what is required of your application in terms of load, speed, accuracy, torque, environment, coatings, mounting arrangements


and lubrication. Then determine all maximum bearing loads, being sure to include all dynamic and static loads imposed on the bearing. 2. Consider all the applied forces to the bearing and gear, not only at


Forces acting on a bearing


rated and working loads, but also loads imposed during extreme weather conditions, impact or testing, assembly or disassembly, for example. These loads in turn must be simplified into the forces acting at the bearing’s centre. 3. KAYDON recommends the next step should be to multiply the resultant bearing force by an applicable service factor. These are based on various considerations, the most important of which is the frequency of bearing use at


higher versus normal loads and the potential for extreme or impact loads. So, aerial lift devices, normal duty cranes and occasion-service robots


would have a service factor of 1. Excavators whose load is limited by tipping and frequently used indexing tables with intermittent rotation would carry a value of 1.25. And 1.5 would apply to logging cranes and steering gear with solid tyres subjected to dynamic and shock loads due to transit forces. These factors may be superseded by customer specification, finite


element analysis or regulations by certifying authorities. But, if in doubt, consult the bearing manufacturer. 4. If an integral gear is needed, determine the required gear capacity.


As with bearing loads, consider all conditions that would generate potential gear loads such as dynamic loads while working versus static loads, loads on the incline and overload testing. Consider the duty cycle at each of these conditions. 5. Determine the preferred mounting arrangement, considering the


pinion and gear location. Take into account requirements for installation and continued maintenance of the bearing and retaining bolts. 6. Review the bearing styles and cross sections available. 7. Make a preliminary bearing selection by comparing the resultant


operating bearing forces, including service factor, to the bearing’s rating curve. For a bearing to be appropriate for a given application, all required


resultant force combinations should fall below the curve. All extreme load conditions should also fall below the bearing’s rating curve. If extreme load condition is static and only occurs several times during the bearing’s service life, do not include the service factor.


 Slewing ring bearing cross sections The maximum thrust rating of the bearing should exceed three times


the maximum operating thrust force on the bearing, regardless of the moment force at that condition. This criterion is due to concern for rigidity of the supporting structure and ability to distribute the load properly around the bearing’s diameter. If the bearing does not meet this criterion, contact the bearing manufacturer for assistance. 8. Check the gear size, quality and rating for suitability. 9. Double check the bearing you have selected meets all your


design requirements. KAYDON provides a selector to help you gather preliminary data and it is always advisable to submit such a specification data sheet to the manufacturer for confirmation. Ultimately, the responsibility for choosing the appropriate bearing rests with the equipment designer – so it pays not to take any chances.


R. A. Rodriguez www.rarodriguez.co.uk


600 500 400 300 200 100100 0


L: MT-324


M: MT-324X N: MT -415 O: MT-470 P: MT-540


T-


FA 050100100 0 50


LN O FM


L M 150200 150 Moment (ft-lbs x 1,000)


*Max resultant bearing forces FR≤ 0. 10 x Fa x SF ≤ 5,000 lbs


FA= a F x SF = 50,000 lbs FM= m F x SF = 180,000 lbs


Example of load curves on bearings DESIGN SOLUTIONS | JULY/AUGUST 2019 31 * 200


P 250 250


Thrust (lbs x 1,000)


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