{"id":2026,"date":"2026-07-22T07:53:27","date_gmt":"2026-07-22T07:53:27","guid":{"rendered":"https:\/\/gearrack.top\/?p=2026"},"modified":"2026-07-22T07:53:27","modified_gmt":"2026-07-22T07:53:27","slug":"ring-gears-for-slewing-drives","status":"publish","type":"post","link":"https:\/\/gearrack.top\/ja\/ring-gears-for-slewing-drives\/","title":{"rendered":"Ring Gears for Slewing Drives"},"content":{"rendered":"
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GEAR APPLICATION GUIDE \u00b7 RING GEAR \u00b7 R05<\/span><\/p>\n

Ring Gears for Slewing Drives:
\nCrane Slewing Rings, Solar Tracker Drives and Excavator Slew Mechanisms<\/span><\/h1>\n

Slewing drive ring gears are among the most dimensionally imposing gear components in industrial machinery \u2014 the slewing ring gear of a 100-tonne mobile crane has an OD of 2.5\u20133.5 metres and must transmit the full superstructure slewing torque while simultaneously carrying the combined radial, axial, and moment loads from the crane boom through an integrated raceway bearing. The design integration of the ring gear tooth profile, the rolling element bearing raceway, and the structural cross-section of the slewing ring represents a unique engineering challenge that differs fundamentally from all other ring gear applications, and that demands a manufacturing process \u2014 hobbing or profile grinding the gear teeth on the same part as the precision-ground bearing raceway \u2014 that requires specialised machinery found in only a handful of gear manufacturers worldwide.<\/p>\n

42CrMo4 \u00b7 50Mn \u00b7 42CrMo \u00b7 OD 300\u20135000mm<\/span>
\nInternal \/ External \u00b7 DIN 7\u20139 \u00b7 Induction Hardened<\/span>
\nCrane \u00b7 Solar \u00b7 Excavator \u00b7 Wind \u00b7 Medical<\/span><\/div>\n<\/div>\n<\/div>\n
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OD RANGE<\/p>\n

300 \u2013 5,000 mm<\/p>\n

Slewing drive ring gear OD range. Solar tracker single-axis: 300\u2013600 mm. Compact excavator (1\u20135 t): 400\u2013700 mm. Standard excavator (6\u201340 t): 700\u20131,400 mm. Mobile crane (20\u2013100 t): 1,200\u20133,000 mm. Port crane \/ shipyard crane: 2,500\u20135,000 mm. Wind turbine pitch ring: 1,800\u20134,000 mm<\/p>\n<\/div>\n

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TOOTH FORM<\/p>\n

Internal \/ External<\/p>\n

Slewing ring gears are manufactured in both external-tooth (pinion drives the outer ring) and internal-tooth (pinion drives inside the ring, more compact) configurations. External tooth: crane slewing rings, solar tracker drive rings. Internal tooth: excavator slewing rings (the pinion is inside the ring gear, giving a more compact turntable), wind turbine pitch ring. Tooth form: straight or helical spur on the slewing ring<\/p>\n<\/div>\n

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MATERIAL<\/p>\n

42CrMo4 \/ 50Mn<\/p>\n

Standard slewing ring gear materials. 42CrMo4 (EN 1.7225): European standard for crane and excavator slewing rings, QT to HB 280\u2013320 before tooth induction hardening. 50Mn (Chinese standard GB): equivalent in crane slewing ring applications. 42CrMo (Chinese standard, equivalent to 42CrMo4): common for solar tracker and standard industrial slewing rings. Case carburized 20CrMnTi for small precision slewing rings (OD < 600 mm)<\/p>\n<\/div>\n

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HARDENING<\/p>\n

Induction HRC 50\u201358<\/p>\n

Tooth surface hardening for slewing ring gears: induction hardening of the tooth flanks (and the bearing raceway on the same part) to HRC 50\u201358 after the gear blank is QT treated. Through-hardening by induction produces a case depth of 2\u20136 mm at the tooth surface, with a transition to the QT core that maintains ductility for the dynamic loads of crane and excavator slewing operation. Flame hardening is an acceptable alternative for very large rings where induction coil size is impractical<\/p>\n<\/div>\n<\/div>\n

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Slewing Drive Ring Gear Engineering \u2014 Combined Gear and Bearing Design<\/h2>\n

The slewing ring gear is the only standard gear component that simultaneously functions as a gear and a rolling element bearing \u2014 the same ring forging contains both the precision-machined gear tooth profile on its periphery (inner or outer depending on the configuration) and the hardened, ground rolling element raceway on its face. This design integration creates a manufacturing sequence that is unique among gear types: the blank must be rough-machined, QT heat treated, semi-finish machined (both tooth profile and raceway reference surfaces), induction hardened (both the tooth flanks and the raceway in the same or adjacent operations), and then finish-ground (the raceway) and finish-hobbed (the tooth profile) with the bearing reference surfaces used as the datum for both machining operations, ensuring concentricity between the gear pitch cylinder and the bearing raceway to within 0.1\u20130.3 mm TIR depending on the ring diameter.<\/p>\n

Korea Ever-Power’s ring gears for slewing drives<\/a> are manufactured in 42CrMo4 (for crane and excavator applications under European standards), 42CrMo (for solar tracker, standard industrial, and Chinese-market excavator slewing rings under GB standards), and 50Mn (for large crane slewing rings where the higher manganese content provides better through-hardening depth in the thick cross-sections of large-diameter rings). The manufacturing process for Korea Ever-Power slewing ring gears follows the DIN 3992 and ISO 6336 calculation standards for gear capacity, combined with ISO 76 bearing load rating calculation for the integrated bearing function \u2014 the slewing ring is both a gear and a bearing, and both functions must be independently rated for the combined loads at each application. For applications requiring a complete slewing drive assembly including the pinion, motor, and housing, Korea Ever-Power’s planetary gearbox<\/a> product line covers several configurations that integrate with standard slewing ring gears.<\/p>\n

The combined load analysis of a slewing ring gear is fundamentally different from a standard ring gear load analysis because the slewing ring carries three types of simultaneous load: the tangential (torque) load from the drive pinion engaging the ring gear teeth, the axial load from the weight of the superstructure being slewed (which compresses the bearing raceway axially), and the overturning moment from the offset between the superstructure centre of gravity and the slewing ring centreline (which creates a tilting moment that increases the load on one side of the bearing raceway while reducing it on the other). The equivalent bearing load for a slewing ring bearing is calculated from these three simultaneous components using the ISO TR 10715 method, which combines them into a single equivalent radial load for the rolling element fatigue life calculation. Korea Ever-Power performs this combined load analysis for each custom slewing ring gear application and provides the calculated bearing L10 life (the number of slewing revolutions at which 90% of a batch of rings would be expected to survive without bearing fatigue failure) alongside the gear tooth bending and contact fatigue safety factors in the application engineering report.<\/p>\n

\"alloy
Korea Ever-Power 42CrMo4 QT internal-tooth slewing ring gear for 20-tonne excavator application \u2014 M8, 120 internal teeth, OD 980 mm, bore 860 mm, ring cross-section height 70 mm, face width 65 mm. Tooth flanks induction hardened HRC 52\u201356 to effective depth 3.5\u20134.5 mm; core HB 280\u2013320 (QT condition retained below the induction hardened zone). Bolt holes: 24\u00d7 M24 equally spaced on two bolt circles (outer bolt circle for upper structure, inner for undercarriage) per the specific excavator model mounting pattern \u2014 Korea Ever-Power can supply slewing rings with any bolt circle pattern specified by the excavator OEM. Tooth quality: DIN 8 (hobbed, not ground \u2014 the induction hardening distortion on large rings precludes precision grinding of the tooth profile, which is why all large slewing ring gears are DIN 7\u20139 quality versus the DIN 4\u20136 of smaller precision gears). MPI of all tooth surfaces and raceway after induction hardening. Surface treatment: tooth and raceway surfaces packed with Mobilgrease XHP 220 NLGI 2 EP grease before shipment to prevent transit corrosion.<\/figcaption><\/figure>\n<\/section>\n
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Slewing Drive Application Specifications<\/h2>\n
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APPLICATION 01<\/p>\n

MOBILE CRANE
\nSLEWING RING<\/p>\n<\/div>\n

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Ring gear specification:<\/strong> 42CrMo4 QT, M10\u2013M16 external or internal tooth, OD 1,200\u20133,000 mm, DIN 8\u20139, tooth induction hardened HRC 50\u201356, four-point contact ball bearing or crossed roller bearing raceway in the same ring, bolt circles per crane OEM drawing. Mobile cranes (all-terrain, rough terrain, truck-mounted) use the slewing ring as the structural and mechanical interface between the crane undercarriage (which travels on wheels or tracks) and the superstructure (which rotates 360\u00b0 continuously in lifting operation). The slewing ring of a 50-tonne mobile crane sustains a combined vertical load from the superstructure and lifted load of up to 500\u2013800 kN, a moment load from the offset boom tip load of up to 1,500 kN\u00b7m, and a drive torque from the slewing motor and planetary gearbox of up to 80\u2013120 kN\u00b7m \u2014 all simultaneously during lift and slew operations. The gear tooth on this slewing ring is not the structural limiting element (the rolling element bearing raceway fatigue is usually the first failure mode) but it must sustain the slewing torque without tooth fracture for the crane’s rated 30-year service life, which at a typical crane utilisation of 2,000 slewing cycles per year means 60,000 slewing engagements on each ring gear tooth. Korea Ever-Power mobile crane slewing ring gears are manufactured with a tooth root fillet radius at 0.35 \u00d7 module to improve tooth root impact resistance for the variable-speed, reversing-direction slewing loads characteristic of crane operation.<\/p>\n<\/div>\n<\/div>\n

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APPLICATION 02<\/p>\n

SOLAR TRACKER
\nSLEWING DRIVE<\/p>\n<\/div>\n

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Ring gear specification:<\/strong> 42CrMo QT, M6\u2013M10 external tooth, OD 300\u2013800 mm, DIN 7\u20138, tooth induction hardened HRC 50\u201354, slew angle \u00b160\u00b0 (azimuth) or \u00b145\u00b0 (elevation), coated (dacromet or zinc phosphate) for 25-year outdoor corrosion resistance, drive pinion from worm or planetary reducer. Solar tracker slewing drives (the electromechanical actuator that rotates a solar panel array to track the sun’s daily and seasonal position for maximum energy capture) use a compact external-tooth slewing ring that is driven by either a worm gear reducer + electric motor or a small planetary gearbox + motor. The solar tracker slewing ring operates at extremely low speeds (the sun tracks across the sky at approximately 15\u00b0\/hour, so the ring gear rotates at less than 0.04 RPM average) and with very low transmitted torque compared to a crane \u2014 the dominant load on a solar tracker slewing ring is not the drive torque but the wind load on the panel array (which can create a moment of 15\u201330 kN\u00b7m per tracker in a 30 m\/s storm condition). Korea Ever-Power solar tracker slewing ring gears are specified with a 25-year outdoor corrosion resistance requirement \u2014 the tooth surface and non-functional surfaces receive a dacromet coating (360-hour salt spray resistance per ISO 9227) in addition to the standard induction-hardened tooth surface, providing the corrosion protection needed for desert solar farm installations where the slewing rings cannot be reached for re-greasing without significant access effort.<\/p>\n<\/div>\n<\/div>\n

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APPLICATION 03<\/p>\n

EXCAVATOR
\nSLEWING RING<\/p>\n<\/div>\n

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Ring gear specification:<\/strong> 42CrMo4 or 50Mn QT, M6\u2013M14 internal tooth, OD 600\u20132,000 mm (depending on excavator weight class), DIN 8, tooth induction hardened HRC 50\u201358, high-shock service factor from frequent reversal and impact loads, grease nipple pattern per OEM specification. Excavator slewing rings are the highest-shock slewing ring application \u2014 the 360\u00b0 continuous rotation slewing operation is combined with rapid direction reversals during bank excavation, and the bucket crowd and boom swing frequently transmit impact loads through the slewing ring as the bucket enters dense soil or rock. The internal tooth configuration (pinion inside the ring) is standard for excavator slewing rings because it produces a more compact turntable height (the pinion is positioned below the slewing ring level rather than beside it), and the internal mesh has a higher contact ratio than external for the same pitch diameter, distributing the impact loads more smoothly. Korea Ever-Power excavator slewing ring gears are cross-referenced to major excavator OEM specifications \u2014 Caterpillar, Komatsu, Hitachi, Volvo, Doosan, Sany, XCMG \u2014 and can be supplied as aftermarket replacements with dimensional verification against the original ring specifications provided by the customer.<\/p>\n<\/div>\n<\/div>\n<\/div>\n

\"planetary
Korea Ever-Power ring gear product range showing the scale relationship between planetary reducer ring gears (left, OD 180\u2013380 mm for servo and motor drives) and slewing ring gears for crane and excavator drives (right, OD 800\u20132,500 mm). The slewing ring gear OD and structural cross-section must be sized to carry the combined bearing and gear loads from the crane superstructure and lifted load \u2014 this requires the ring cross-section height to be typically 8\u201312% of the ring OD (a 1,200 mm OD crane slewing ring has a cross-section height of 96\u2013144 mm), compared to the thin-ring planetary ring gears where the wall thickness is only 15\u201325% of the tooth height. The large cross-section of the slewing ring provides the structural stiffness that limits ring distortion under the overturning moment \u2014 ring distortion under moment load shifts the rolling element contact into a partial arc of the raceway, increasing the contact stress above the Hertzian design value and reducing the bearing fatigue life. Korea Ever-Power calculates the ring distortion under the rated moment load as part of the slewing ring design \u2014 rings where the calculated distortion exceeds the allowable limit for the bearing design are specified with a thicker cross-section or a higher-grade material.<\/figcaption><\/figure>\n<\/section>\n
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Slewing Ring Gear Installation, Greasing and Maintenance<\/h2>\n

The service life of a slewing ring gear is determined primarily by the lubrication and maintenance quality during operation \u2014 the bearing raceway fatigue life (calculated as 50,000\u2013200,000 slewing revolutions depending on load and ring size) assumes adequate lubricant film in the rolling element contact zone at all times. In practice, slewing rings on cranes and excavators operate in outdoor environments where the greasing interval is difficult to maintain precisely, the grease can be diluted or washed out by rain or high-pressure cleaning, and the bearing raceway and gear teeth are simultaneously exposed to abrasive contamination (sand, grit, concrete dust on construction sites). The combination of inadequate lubrication and abrasive contamination is the most common cause of premature slewing ring failure in field service.<\/p>\n

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SLEWING RING GEAR \u2014 MAINTENANCE PARAMETERS<\/p>\n

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GEAR TOOTH GREASING<\/p>\n