Slewing drives (slewing bearing with drive)

01

Size output torque, tilting moment and axial and radial loads

Chiaravalli describes a heavy-duty slewing drive as a slewing ring combined with a worm gear system, used on truck cranes, aerial work trucks, port machinery, timber grabs, beam carriers and fog cannons. Its CHWD9 lists nominal torque 6.3 kN·m (safety factor 1 at 1 rpm), maximum torque 9.5 kN·m, holding torque 38.7 kN·m, static axial load Coa 578 kN, static radial load Cor 215 kN, dynamic axial load Ca 136 kN, dynamic radial load Cr 115 kN and tilting moment 35.6 kN·m; the larger CHWD21 lists 23 kN·m nominal, 34.5 kN·m maximum and 105.8 kN·m holding torque, Coa 1,598 kN, Cor 640 kN, Ca 385 kN, Cr 335 kN and 203 kN·m tilting moment. Each model sheet carries a moment load chart of axial static load against tilting moment, and the operating point must remain under that curve. [1]

SKF's slewing bearing catalogue sizes the bearing from the resulting axial load Fa and tilting moment Mt, each multiplied by an application load factor fL — 1.5 for mobile cranes and concrete pumps, 1.33 for mini excavators, service cranes and aerial platforms, 2 for carrousels and compactors — and the resulting point is checked against two curves per bearing: raceway capacity and bolting capacity, the latter valid for grade 10.9 bolts tightened to SKF's values. Radial loads up to 5% of the axial load may be neglected; above Fr/Fa = 0.6 SKF asks to be consulted. In its mini-excavator example, Fa = 65 kN and Mt = 120 kNm become 87 kN and 160 kNm after the 1.33 factor. [3]

Editorial calculation: on the Chiaravalli sheets, holding torque is about 6.1 times nominal torque for the CHWD9 (38.7 ÷ 6.3) and about 4.6 times for the CHWD21 (105.8 ÷ 23), so a quote should state both values rather than one torque figure. [1]

Give the supplier the machine and duty, the axial load, radial load and tilting moment at the worst working radius, the load factor or standard you design to, the required output torque and speed, holding torque at standstill, mounting orientation (horizontal or vertical axis), the support structure and bolts, environment and temperature, and quantity.

02

Choose a worm or pinion drive, gear ratio and how the load is held

Liebherr's worm slew drives come as ball-bearing versions with raceway diameters of 223 to 725 mm, maximum torque up to approx. 140,000 Nm and weight up to approx. 750 kg, and roller-bearing versions of 363.5 to 713.5 mm and up to approx. 190,000 Nm; the worm is single or double thread, the brake is either self-retention or a mounted brake, and lubrication is oil or grease. Liebherr lists steering gear, port mobile cranes, construction machinery and satellite antennas among the applications and also offers spur gear and belt slewing drives. [2] Chiaravalli's worm drives state worm ratios of 62:1 (CHWD9), 79:1 (CHWD12), 86:1 (CHWD14), 104:1 (CHWD17) and 90:1 (CHWD21), efficiency of approx. 40%, backlash of 0.1° to 0.15°, an input either as a Ø25 hole or a 6B spline, and a motor mounting position that can be turned by 90°. [1]

Where a motor and gearbox turn a pinion on the bearing's gear ring, SKF calls for a 20° involute spur pinion, hardened and ground, extending past the bearing gear by approx. 5 mm on each side, with tip relief of 0.01 × module. Backlash is set at the blue marking on the bearing gear — for example 0.45 to 0.675 mm for modules over 10 up to 12.5 mm — because zero backlash can produce structural overloads that cut gear life. The pinion may be fixed relative to the bearing axis or rotate around it. [3]

03

Excavator swing motors and crane slewing gear units

Eaton's JMF swing drive motors are fixed-displacement axial piston motors of 29 to 250 cc/rev with an integrated planetary reduction gearbox, fail-safe parking brake, brake release valve, shockless relief, anti-reverse and anti-cavitation valves, for excavators, concrete pumps, cranes and drilling. The JMF029 gives 1,929 N·m maximum output torque at gear ratio 19.5, 63 rpm reducer speed, 230 bar normal and 276 bar peak pressure, 137 N·m brake torque, a module 7, 13-tooth output pinion and 75 kg mass, for 5–6 ton machines; the JMF250 gives 24,858 N·m at ratio 22.0, 52 rpm, 320 and 385 bar, 1,049 N·m brake torque, a module 14, 15-tooth pinion and 440 kg. The wet multi-plate brake is spring-applied and pilot-released, with a delay valve giving six seconds for the motor to stop before it engages; operating temperature is −20 to +95 °C and minimum oil cleanliness NAS 9 or ISO 4406 20/18/15. [4]

Bonfiglioli's 700T slew gears are flange-mounted with a splined output shaft or integral pinion, cover 1,000 to 80,000 Nm — 1,200 to 80,000 Nm for building cranes and 1,000 to 20,000 Nm for rough-terrain, truck-mounted and crawler cranes and drilling machines — with gear ratios starting at 3.48, hydraulic brakes or hydraulically released parking brakes, DC or AC electric brakes, and piston hydraulic, orbit or IEC electric motors. [5]

Editorial calculation: the JMF250's output torque is about 23.7 times its brake torque (24,858 ÷ 1,049), close to its 22.0 gear ratio, consistent with the brake acting on the motor side of the reducer. [4]

04

Compare what suppliers offer

The companies in the manufacturer list below show this product on their own websites. Confirm the legal seller, factory and scope for your order.

When requesting quotations, ask each supplier for the torque and holding-torque ratings with the speed and safety factor they refer to, the moment load chart, static and dynamic axial and radial load ratings, bearing type, gear ratio, backlash, brake or self-retention details, motor options, and drawings.

05

Trace the slewing drive

This is a functional reference built from the sources cited; it is not one maker's design.

06

Fill the specification fields with values for your project

A slewing drive quotation needs values for your project. The table explains each field, gives published values where a reviewed source states them, and says what to obtain from the supplier.

07

Send the loads, torque and holding duty together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Machine: [ship loader; crane; excavator; tracker]
Loads: [axial kN; radial kN; tilting kN·m; load factor]
Torque: [output; holding; speed rpm]
Drive: [worm; pinion; ratio; backlash]
Motor: [hydraulic cc/rev, bar; electric kW, V]
Holding: [self-retention; brake]
Quantity: [units]

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