Slewing Bearing Production Process: A Deep Technical Insight

Slewing Bearing Production Process: A Deep Technical Insight

What are Slewing Bearings?

Slewing bearings, also referred to as slewing rings or turntable bearings, are large-scale anti-friction bearings engineered to simultaneously support axial loads, radial loads, and tilting moments. Unlike conventional bearings that primarily manage one or two load directions, slewing bearings provide rotational support between two structural components in heavy machinery. Typical applications include cranes, excavators, wind turbines, aerial work platforms, medical imaging devices, and radar systems.

A slewing bearing consists of an inner ring, an outer ring, rolling elements (balls or rollers), spacers or cages, integral seals, and mounting holes. The raceways are precision-ground to allow smooth oscillation or continuous rotation under substantial loads. Slewing bearing diameters range from approximately 100 mm to over 10,000 mm, serving everything from light-duty positioning tables to massive offshore cranes. Their ability to integrate gear teeth directly into one ring further distinguishes them from standard bearings, enabling direct power transmission from a pinion.

Key Features of Slewing Bearings

Slewing bearings offer several distinctive characteristics that make them indispensable in heavy rotating machinery:

• Combined Load Capacity: They support vertical (axial) forces, horizontal (radial) forces, and tilting moments simultaneously within a single, compact component. This eliminates the need for multiple bearing arrangements and complex housings.

• High Rigidity with Compact Cross-Section: Despite their often-large diameters, slewing bearings maintain relatively low cross-sectional heights. Crossed roller designs deliver exceptional rigidity for precision applications such as indexing tables or robotic positioners.

• Integrated Gear Options: Many slewing bearings include internal or external gears machined directly into one ring. These gears are induction-hardened to resist wear while maintaining a tough core, allowing direct engagement with a drive pinion.

• Robust Sealing and Lubrication: Heavy-duty lip seals protect raceways from contaminants including water, dust, sand, and debris. Pre-drilled grease fittings allow periodic relubrication without disassembling the surrounding machinery.

• Long Service Life Under Intermittent Motion: Slewing bearings frequently operate in oscillating, indexing, or slow-rotation modes. Their design prioritizes resistance to false brinelling, fretting corrosion, and raceway indentation.

• Mounting Versatility: Through-holes in both rings allow direct bolting to adjacent structures, simplifying installation and reducing overall machine weight.

  
  

How to Produce Slewing Bearings?

Producing a high-precision slewing bearing requires a tightly controlled sequence of cutting, forging, machining, heat treatment, grinding, and assembly. Each step directly influences the final bearing’s load capacity, rotation smoothness, and service life. The following eight steps detail this manufacturing journey.

Step 1: Steel Raw Material Cutting

The raw materials extensively employed in the fabrication of slewing ring bearings primarily consist of overall hardened carbon chromium-bearing steel. Specifically, the slewing rings are crafted from surface-hardened steel, with 50Mn steel being a prevalent choice, exemplified by materials such as S48C, 42CrMo, and 5CrMnMo. The initial stage involves the utilization of cylindrical raw material billets, which are transported from the steel factory. These billets undergo precision cutting using carbide saw blades, tailored to the specific size requirements for the subsequent slewing ring processing. These carbide saw blades exhibit a series of outstanding performances, contributing significantly to the seamless and high-precision preparation of raw materials for the production of slewing ring bearings.

Step 2: Billet Forging

Within the confines of the heating furnace, the steel billet undergoes a transformative process wherein it is meticulously heated and skillfully forged into a distinctive round cake shape. This forging phase assumes paramount significance, serving as a crucial juncture in guaranteeing the overall reliability and extended service life of the resultant bearing. Post-forging, the raw material undergoes a metamorphosis, culminating in the formation of the bearing ring blank. This forging operation not only shapes the bearing ring but also contributes to enhancing the overall structural integrity of the raw material. The organizational structure of the initial raw material undergoes a refinement process, leading to increased density and streamlining. This transformation, in turn, serves to elevate the reliability and longevity of the eventual slewing ring. The quality of the forging process emerges as a critical determinant, directly influencing the utilization efficiency of raw materials. As a consequence, the intricacies of the forging process play a pivotal role in shaping not only the slewing ring bearing’s performance but also impacting the production cost through its influence on raw material utilization rates.

Step 3: Forging Ring

The billet, having undergone preliminary heating, is subjected to the precision of a ring rolling machine, where it is expertly forged into a distinctive ring-shaped steel configuration. This specialized forging process serves as a transformative step, introducing enhancements to the internal structure of the steel. Through this forging technique, the steel’s mechanical properties undergo significant improvement, manifesting in heightened strength, increased plasticity, enhanced impact toughness, and various other mechanical attributes. The ring rolling operation ensures a continuous grain flow along the circumferential direction, which is essential for withstanding the cyclic stresses encountered during bearing operation.

Step 4: Rough Turning

Once the steel ring is positioned within the machine tool, the machining journey commences with the rough turning process. This initial phase involves the precision turning of various grooves and raceways into the steel ring, contributing to the intricate design and functionality of the component. Subsequently, the steel ring is securely affixed onto the gear milling machine, where teeth are meticulously cut out if a geared configuration is required. The primary objective underlying these machining steps is to ensure that the finished ferrule attains an identical shape to the envisaged final product. This precision in shaping and detailing is imperative, laying the groundwork for the subsequent stages of the grinding machine processing. Rough turning removes scale and decarburized layers from the forging surface while establishing the fundamental geometry.

Step 5: Quenching (Heat Treatment)

Following the machining processes, the steel undergoes a critical phase of enhancement through quenching, where its strength is significantly bolstered. This heat treatment method not only elevates the hardness of the steel but also imparts improved wear resistance, heightened fatigue strength, and enhanced toughness to the metal. The quenching process stands as a pivotal link in the manufacturing chain, playing a crucial role in augmenting the overall performance and durability of the bearing. The heat treatment phase involves subjecting the bearing ring, post-forging and turning, to high-temperature treatment. This step directly influences the uniformity of carburization within the bearing ring, thereby enhancing both wear resistance and hardness. Beyond the mechanical attributes, the heat treatment process bears a profound impact on the reliability and lifespan of the bearing, positioning it as an indispensable component in ensuring the optimal functioning and longevity of the final product. Typically, raceway surfaces are induction-hardened to 55–62 HRC, achieving a hardened case depth of 2–4 mm while retaining a tough, ductile core.

Step 6: Hole Processing

To facilitate installation, precision drilling of the installation holes is conducted on the end face of the steel ring. This pivotal step in the manufacturing process requires careful consideration of the center and cutting angle when drilling the slewing ring bearing. The choice of drilling equipment is also of utmost importance, with options ranging from specialized drilling machines to versatile hand-held electric drills and traditional hand drills, each selected based on specific operational requirements. When drilling the slewing ring bearing, meticulous attention is paid to determining the optimal center and cutting angle. This precision ensures the creation of installation holes that align seamlessly with the slewing ring bearing’s specifications. The versatility of using drilling machines, hand-held electric drills, or hand drills allows for adaptability to various manufacturing scenarios, ensuring the drilling operation is executed with the required precision and efficiency. Hole patterns typically follow ISO standards or custom customer drawings, with countersinking for socket head cap screws.

Step 7: Fine Grinding

Fine grinding serves as the meticulous refinement phase, wherein the intricacies of the roughly formed bearing, post-opening of the installation holes, are precisely trimmed to ensure the utmost refinement of its appearance. This critical step in the manufacturing process plays a pivotal role in influencing the rotation flexibility of the bearing and enhancing the machining accuracy of its surface. The impact of fine grinding extends beyond cosmetic considerations, delving into the intricate details of the slewing ring bearing’s mechanical attributes. This process is instrumental in mitigating any deformations that may have arisen from earlier manufacturing stages. By honing the bearing’s finer details through precise grinding, the rotation flexibility is optimized, contributing to the overall performance and functionality of the slewing ring. Raceway surfaces achieve roughness values of Ra ≤ 0.4 μm, and roundness is held within 0.01 mm. After grinding, each ring’s raceway geometry is measured to enable proper matching of inner and outer rings.

Step 8: Assembly Work

Assemble the meticulously processed components, encompassing the outer ring, inner ring, rollers or balls, and cage, which have undergone a series of intricate manufacturing procedures. These processes include the precise insertion of rolling elements, the incorporation of isolating blocks or spacers, and the addition of grease and sealing strips. The objective is to meticulously craft a set of finalized slewing rings tailored to specific technical and precision requirements. For ball-type bearings, balls are loaded through a filling hole and then distributed uniformly using spacers or cages. For crossed roller bearings, rollers are inserted alternately with separators to maintain proper orientation. Lip seals are pressed into their grooves to protect against contamination. After assembly, each bearing is manually rotated to verify smoothness, and final inspections check rotation torque, axial and radial runout, and gear accuracy (if applicable). Passed bearings receive anti-rust coating and are packaged for shipment.

LyraDrive: Customized Slewing Bearing Supplier

Luoyang LyraDrive is a professional one-stop slewing device manufacturer majored in design and development, customized production, sales and service on slewing bearings and slewing drives. Our product portfolio includes three primary types: Single Row Slewing Ring Ball Bearings for general light-to-medium duty applications requiring cost-effective rotation; Double Row Ball Slewing Ring Bearings for increased load capacity and superior moment resistance in demanding environments; and Crossed Roller Slewing Bearings offering exceptional rigidity, precision, and smooth motion for indexing, oscillating, or high-accuracy positioning equipment.

LyraDrive works with customers to customize slewing bearings for different projects. Request a quote to get more information on how our custom services can meet your project requirements. For any customized slewing bearing need, please contact us immediately.