On the slewing platforms of large cranes, slewing bearings carry the full weight of booms and loads ranging from tons to hundreds of tons, maintaining smooth operation during frequent start-stops and rotations. Between the upper and lower structures of excavators, slewing bearings withstand enormous tilting moments and impacts from digging forces, supporting 360° continuous rotation of the upper structure. In wind turbine yaw systems, slewing bearings drive the nacelle to align with wind direction under enormous wind loads. On precision machine tool rotary tables, slewing bearings support workpiece rotation and indexing with extremely high positioning accuracy. In every large slewing device requiring combined loads and tilting moments, slewing bearings are the core precision components achieving smooth rotation and precise positioning.

 

Slewing bearings (also known as slewing rings or turntable bearings) are large special bearings capable of simultaneously withstanding axial loads, radial loads and tilting moments. Their basic structure consists of inner rings, outer rings, rolling elements (balls or rollers), cages, seals and mounting holes. Slewing bearings are typically large in size——inner diameters from 100mm to over 5000mm, outer diameters from 200mm to over 6000mm, capable of supporting loads from tons to thousands of tons. Based on rolling element type, slewing bearings are classified into four-point contact ball slewing bearings and cross-roller slewing bearings——four-point contact ball slewing bearings use steel balls as rolling elements with four-point contact between balls and raceways, capable of simultaneously withstanding axial loads, radial loads and tilting moments, suitable for low-speed and complex-load applications; cross-roller slewing bearings use cylindrical rollers as rolling elements with rollers arranged at 90° crossing angles, capable of simultaneously withstanding axial loads, radial loads and tilting moments with higher rigidity and rotational accuracy, suitable for high-precision and high-rigidity applications.

 

Slewing bearings feature mounting holes on outer or inner rings for connection to equipment upper and lower structures using high-strength bolts. Slewing bearings typically use open configurations with periodic lubrication through external lubrication systems. Slewing bearings usually employ full-complement rolling element configurations (without cages) to maximize rolling element quantity and load capacity. Slewing bearings are widely used in cranes, excavators, wind turbines, solar tracking systems, medical equipment, machine tool rotary tables, industrial robots, port machinery, metallurgical equipment, marine equipment, radar antennas and various large slewing and oscillating mechanisms.

 

NMT Slewing Bearing Technology Solutions

 

Japan NMT slewing bearings are specialized product series developed specifically for the stringent requirements of large slewing equipment——high load capacity, anti-tilting capability, long life and high reliability.

 

Four-Point Contact Ball Slewing Bearing Design——Four-point contact ball slewing bearings are the most commonly used type in the slewing bearing family. NMT four-point contact ball slewing bearings feature double-arc groove designs on both inner and outer ring raceways, with four-point contact between balls and raceways. This unique contact geometry enables the bearing to simultaneously withstand axial loads, radial loads and tilting moments. Under axial loads, loads are transmitted through balls to the upper and lower contact points on raceways; under radial loads, loads are transmitted through balls to the left and right contact points on raceways; under tilting moments, loads are uniformly distributed through four-point contact of balls in raceways. Balls undergo precision screening and grouping with sphericity and diameter deviation controlled to minimal ranges, ensuring uniform load distribution across all balls. Raceways undergo precision hardening and grinding with surface hardness reaching HRC60 or higher, with case depth precisely controlled to ensure load capacity and excellent fatigue resistance. Four-point contact ball slewing bearings suit low-speed, complex-load-direction applications and are the standard choice for cranes, excavators and wind turbine yaw systems.

 

Cross-Roller Slewing Bearing Design——Cross-roller slewing bearings are the highest-precision and highest-rigidity type in the slewing bearing family. NMT cross-roller slewing bearings feature rollers arranged at 90° crossing angles, with adjacent roller axes perpendicular to each other. This unique roller arrangement enables a single bearing to simultaneously withstand axial loads, radial loads and tilting moments, with load capacity and rigidity far exceeding four-point contact ball slewing bearings. Rollers undergo precision crowning to eliminate edge stress concentration, ensuring uniform load distribution along the full roller length. Raceways undergo precision grinding and superfinishing with surface roughness controlled to extremely low levels, providing excellent rotational accuracy and rigidity. Cross-roller slewing bearings suit high-precision, high-rigidity and high-load applications such as machine tool rotary tables, industrial robots, precision turntables, medical equipment and aerospace equipment.

 

Large-Size Structural Design and High-Strength Materials——Slewing bearings are far larger than ordinary industrial bearings, requiring special technical capabilities for design and manufacturing. NMT slewing bearings utilize high-strength bearing steel (50Mn or 42CrMo) with precision forging and heat treatment, ensuring material density and uniformity. Inner and outer ring wall thicknesses are specially calculated to maintain extremely low deformation under enormous loads. Raceways undergo precision hardening with surface hardness HRC60 or higher, with case depth precisely controlled based on bearing size and load (typically ≥3mm). Mounting hole positions are precision-machined with hole spacing deviation controlled to minimal ranges, ensuring reliable connection to equipment upper and lower structures. Inner and outer ring end faces and mounting surfaces are precision-machined with flatness and parallelism controlled to extremely high levels, ensuring uniform load distribution after installation.

 

High Load Capacity and Anti-Tilting Capability——The core value of slewing bearings lies in their high load capacity and anti-tilting capability. NMT slewing bearings maximize axial load capacity, radial load capacity and tilting moment capacity within limited space through optimized ball/roller diameter and quantity, precise raceway curvature radius and contact angle control. Four-point contact ball slewing bearing rated axial loads and tilting moments are precisely calculated and validated, ensuring ample safety margins under typical operating conditions for cranes, excavators and wind turbines. Cross-roller slewing bearing rated loads and rigidity are rigorously tested, meeting strict positioning and repeatability requirements for precision equipment. Bearing static safety factors and dynamic life are precisely calculated to ensure safe and reliable operation throughout the full lifecycle.

 

High-Performance Sealing and Lubrication Systems——Slewing bearings typically operate in dusty, rainy, sandy and corrosive environments, with sealing and lubrication systems directly determining bearing life. NMT slewing bearings employ high-performance multi-lip sealing systems——primary sealing lips block external dust and moisture, secondary sealing lips provide auxiliary sealing under low-pressure differential conditions, and dust lips block direct impact from large particles. Seal materials utilize ozone-resistant, UV-resistant, temperature-resistant specialty rubber formulations (chloroprene rubber or HNBR), maintaining long-term elasticity and sealing performance in harsh outdoor environments. Inner and outer rings feature lubrication holes and grooves for periodic grease replenishment through centralized lubrication systems or manual grease guns. Grease distribution in raceways is optimized to ensure adequate and uniform lubrication for balls/rollers during operation. Grease is formulated with high-viscosity synthetic base oils and extreme-pressure anti-wear, rust-preventive additives, maintaining stable lubrication under heavy-load and harsh conditions.

 

Installation and Maintenance Convenience Design——Slewing bearing installation and maintenance directly affect equipment efficiency and safety. NMT slewing bearings feature precision-machined mounting holes on both inner and outer rings for connection using high-strength bolts. Mounting hole positions are precision-machined with hole spacing deviation controlled to minimal ranges. Inner and outer rings feature locating pin holes for precise positioning during installation. Inner or outer rings feature gears (straight or helical) for power transmission through meshing with drive pinions. Gears are precision-machined (tooth surface hardness, pitch accuracy, tooth profile accuracy) for smooth and precise slewing motion. NMT provides detailed installation and maintenance guides, including bolt preload recommendations, lubrication intervals and grease specifications, and seal inspection and replacement methods, ensuring correct field installation and maintenance.

 

Diverse Product Range——NMT slewing bearings offer diverse product ranges for different application scenarios and load requirements. Four-point contact ball slewing bearings (010/020 series)——Steel balls as rolling elements, suitable for low-to-medium speed, complex-load applications. Cross-roller slewing bearings (070 series)——Cylindrical rollers as rolling elements, suitable for high-precision, high-rigidity, high-load applications. Three-row roller slewing bearings (130 series)——Three rows of rollers separately withstanding axial loads, radial loads and tilting moments with highest load capacity, suitable for ultra-large load applications such as large port cranes and tunnel boring machines. Light-load slewing bearings (110 series)——Compact structures for light-load and low-speed applications such as solar tracking systems and small robots. All series are available with gearless, internal gear and external gear configurations, as well as standard and sealed protection options.

 

Why Choose NMT Slewing Bearings?

 

Compared to conventional bearings and industry-standard slewing bearings, NMT slewing bearings offer distinct advantages:

 

Four-point contact ball and cross-roller dual technology paths for different load and precision requirements

 

High-strength bearing steel precision forging for dense and uniform material with high strength and toughness

 

Precision-hardened raceways with HRC60+ hardness and ≥3mm case depth

 

Precision-screened and grouped balls/rollers for uniform load distribution

 

Four-point contact ball design for simultaneous axial/radial/tilting moment loads

 

Cross-roller crossing arrangement for extremely high rigidity and precision

 

Precision-crowned rollers eliminating edge stress concentration

 

Multi-lip high-performance sealing systems blocking dust, moisture and sand

 

Inner/outer ring lubrication holes and grooves for centralized or manual lubrication

 

High-strength mounting holes and locating pin holes for precise positioning

 

Internal/external gears (straight/helical) for pinion drive engagement

 

010/020/070/110/130 multiple series for different load ratings

 

Gearless/internal/external three gear configurations for different drive methods

 

Passed load, tilting, seal and life testing

 

These performance advantages establish NMT slewing bearings as the core precision components for cranes, excavators, wind turbines, machine tool rotary tables, industrial robots and various large slewing and oscillating mechanisms.

 

Application Scenarios

 

Large crane slewing platform bearings

 

Excavator upper/lower structure slewing bearings

 

Wind turbine yaw system bearings

 

Solar tracking system slewing bearings

 

Machine tool rotary tables and indexing device bearings

 

Industrial robot base and joint bearings

 

Port handling equipment slewing bearings

 

Medical imaging equipment (CT) slewing bearings

 

Precision Manufacturing

 

Produced strictly according to ISO precision standards and slewing bearing manufacturing specifications, with zero-defect quality execution, NMT slewing bearings utilize high-strength bearing steel (50Mn or 42CrMo), processed through precision forging, normalizing and quenching/tempering heat treatment, precision raceway hardening and grinding, precision ball/roller screening and grouping, seal precision assembly, precision mounting hole machining, precision gear machining, specialized grease filling, rotational accuracy inspection, clearance control, load testing and seal performance testing. Every product is processed through fully automatic machining and finishing in temperature-controlled clean workshops, with critical dimensional tolerances strictly controlled—ensuring high load capacity, anti-tilting capability and long-life reliability.

 

Product Range

 

Four-point contact ball slewing bearings (010 series)

 

Four-point contact ball slewing bearings (020 series)

 

Cross-roller slewing bearings (070 series)

 

Light-load slewing bearings (110 series)

 

Three-row roller slewing bearings (130 series)

 

Internal gear slewing bearings

 

External gear slewing bearings

 

Custom non-standard slewing bearings

 

Global Industrial Service

 

Japan NMT supplies high-quality slewing bearings to global crane manufacturers, excavator producers, wind turbine suppliers and heavy industrial users. With high-capacity anti-tilting precision engineering and long-term stable reliable performance, NMT continuously empowers smooth rotation and precise positioning for global large slewing mechanisms.