The Design of Rolling Bearing Mountings
The Design of Rolling Bearing Mountings The Design of Rolling Bearing Mountings
77–78 Gantry of a floating craneFloating cranes are used in harbours for transportationof heavy and bulky goods, in shipyards for repair workand for ship outfitting. Due to their mobility they arean ideal complement to stationary cranes.The pillar of the crane described is attached to theship. The slewing gantry with the crane superstructureis supported on the crane pillar. The bearing mountinghas to take up the weight of the superstructure and thepayload. Since the common centre of gravity of payloadand gantry is outside the pillar axis, a tilting momentis produced causing horizontal reaction forces inthe bearings at the upper and lower pillar end.At the upper pillar end the gantry runs on the so-calledpillar bearing mounting. It consists either of one singlespherical roller thrust bearing or one spherical rollerbearing combined with one spherical roller thrustbearing, depending on the amount of radial loading.GantryCrane pillar bearingCrane pillarRoller track assemblyAt the pillar foot the gantry is supported on a rollertrackassembly (see example no. 79).109 FAG
77 Crane pillar mounting with a spherical roller thrust bearingOperating dataThrust load (crane superstructure and payload) F a =6,200 kN; radial load (reaction forces resulting fromtilting moment and wind pressure) F r = 2,800 kN;speed n = 1 min –1 .Bearing selection, dimensioningThe thrust load, consisting of the weight of the slewingsuperstructure and the payload, is much higherthan the radial load resulting from the tilting momentand wind pressure. Therefore, the crane pillar bearingmust have a high thrust load carrying capacity. Moreover,the bearing must be self-aligning to compensatefor misalignment and elastic deformation unavoidableon these crane structures. Due to the low speed of1 min –1 the bearing is chosen with regard to its staticload carrying capacity.A spherical roller thrust bearing FAG 294/630E.MBwith a static load rating of C 0 = 58,500 kN; factor X 0 =2.7 is selected.For spherical roller thrust bearings under combinedload the ratio F r /F a must be small in order to ensurethat most of the rollers transmit loads. Condition:F r /F a ≤ 0.55.In this exampleF r /F a = 2,800/6,200 = 0.45Thus the equivalent static loadP 0 = F a + X 0 · F r = F a + 2.7 · F r= 6,200 + 2.7 · 2,800 = 13,800 kNThe index of static stressingf s = C 0 /P 0 = 58,500/13,800 = 4.24Thus, the requirement f s ≥ 4 for spherical roller thrustbearings (FAG catalogue WL 41 520) whose housingand shaft washers – as in this example – are fully supportedis met.With f s values ≥ 4...≤ 6 the shaft washer and the housingwasher must be fully supported axially, and goodradial support of the housing washer must also be provided.Machining tolerancesShaft washer to j6; housing washer to K7Lubrication, sealingOil bath lubrication, with the rollers fully immersed inoil. The oil level should be maintained to the upperedge of the shaft washer and is controlled by means ofan oil level indicator.Due to adverse ambient conditions existing for floatingcrane applications, high-efficiency seals must beprovided (oil-filled labyrinths). The inner and theouter labyrinth are interconnectd by oil holes. The oillevel in the labyrinths is also checked with an oil levelindicator.77: Crane pillar mounting with a spherical roller thrust bearingFAG 110
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77–78 Gantry <strong>of</strong> a floating craneFloating cranes are used in harbours for transportation<strong>of</strong> heavy and bulky goods, in shipyards for repair workand for ship outfitting. Due to their mobility they arean ideal complement to stationary cranes.<strong>The</strong> pillar <strong>of</strong> the crane described is attached to theship. <strong>The</strong> slewing gantry with the crane superstructureis supported on the crane pillar. <strong>The</strong> bearing mountinghas to take up the weight <strong>of</strong> the superstructure and thepayload. Since the common centre <strong>of</strong> gravity <strong>of</strong> payloadand gantry is outside the pillar axis, a tilting momentis produced causing horizontal reaction forces inthe bearings at the upper and lower pillar end.At the upper pillar end the gantry runs on the so-calledpillar bearing mounting. It consists either <strong>of</strong> one singlespherical roller thrust bearing or one spherical rollerbearing combined with one spherical roller thrustbearing, depending on the amount <strong>of</strong> radial loading.GantryCrane pillar bearingCrane pillarRoller track assemblyAt the pillar foot the gantry is supported on a rollertrackassembly (see example no. 79).109 FAG
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