Application of a New Gear Surface Hardening Process by ZZ Bearings

2023-01-25

Gear surface contact fatigue is one of the primary factors limiting the service life of slewing bearings. This is particularly true in the operating environments of heavy machinery—characterized by frequent start-stops and exposure to impact loads—where gear surface spalling often leads to the premature scrapping of the entire component. To overcome this bottleneck, the Process Engineering Department at ZZ Bearings has introduced the latest deep induction hardening technology and has implemented a comprehensive, precision-focused overhaul of its existing carburizing and quenching process workflow.

While the traditional carburizing and quenching process is well-established, it is prone to issues such as uneven hardening layer depth and suboptimal residual stress distribution when applied to large-diameter ring components. The new process adopted by ZZ Bearings utilizes high-frequency induction heating paired with computer-controlled water spray cooling. This allows for precise control over both the heating zone and the cooling rate, resulting in the formation of a hardened layer on the gear surface characterized by an optimal depth and a gradual hardness gradient. Metallographic analysis reveals that gear surfaces treated with this new process exhibit a finer and more uniform martensitic microstructure, alongside significantly elevated levels of residual compressive stress—factors that collectively and substantially enhance resistance to contact fatigue.

During accelerated life bench tests conducted by an independent, authoritative third-party laboratory, ZZ slewing bearings treated with the new process demonstrated exceptional durability. Under simulated heavy-load impact conditions, these bearings exceeded 1.5 times their designed service life—measured in operational cycles—without exhibiting any discernible pitting. In contrast, the products in the control group failed after completing the same number of cycles. The data conclusively demonstrates that this new process extends the product's contact fatigue life by more than 50%. This technological upgrade not only enhances product competitiveness but also translates into tangible benefits for end-users, enabling longer replacement intervals and a significant reduction in Total Cost of Ownership (TCO). Currently, this advanced process has been fully integrated into the production lines for our company's mid-to-high-end slewing bearing product lines.

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