Bearing Race Heat Treatment for Roundness and Residual Stress Control
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Solution Overview
Problem
Rolling bearings face challenges in maintaining high roundness and rotational accuracy due to elliptical deformation from heat treatment and subsequent polishing, leading to increased manufacturing costs and reduced productivity, which affects fuel economy in applications like automobile transmissions.
Innovation Solution
A method is developed to control residual stress in bearing rings by rapid cooling after quenching, synchronizing the martensitic transformation timing between the surface and core, and maintaining a gentle residual stress gradient, thereby reducing deformation and ensuring uniform stock allowance during polishing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If quenching treatment is performed to achieve high hardness, then the bearing ring obtains required hardness, but elliptical deformation occurs and roundness deteriorates
Solution Approach 1:
The quenching process is divided into two distinct stages: first quenching to achieve high hardness, and second quenching after surface hardening to correct deformation. This segmentation allows each quenching step to serve a specific purpose - the first for hardness, the second for shape correction - thereby resolving the contradiction between obtaining hardness and maintaining roundness
Solution Approach 2:
Surface hardening treatment (carburizing or carbonitriding) is performed as a preliminary action before the second quenching. This preliminary hardening creates a hardened surface layer that, when followed by controlled quenching, generates compressive residual stress to counteract the elliptical deformation caused by the first quenching, thus preserving roundness while maintaining hardness
2Length of moving object
If surface hardening treatment by carburizing or carbonitriding is performed to reduce thickness, then the bearing ring can be thinner, but additional quenching and re-quenching are required which promotes elliptical deformation
Solution Approach 1:
Surface hardening treatment is performed as a preliminary action before the second quenching step. This preliminary hardening of the surface layer creates a structure that, when subsequently quenched, generates compressive residual stress to counteract deformation. This sequence allows thickness reduction through surface hardening while using the controlled second quenching to maintain roundness
Solution Approach 2:
The patent controls the quenching parameters (temperature, cooling rate) in the second quenching step to optimize the balance between hardness and deformation. By adjusting these parameters, the compressive residual stress is controlled to counteract elliptical deformation while maintaining the required surface hardness, thus resolving the contradiction between thickness reduction and roundness maintenance
3Manufacturing precision
If polishing is repeatedly performed to achieve required dimensional accuracy, then the bearing ring obtains sufficient roundness, but productivity decreases and manufacturing cost increases
Solution Approach 1:
The patent performs preliminary shape correction through controlled second quenching and tempering before the polishing step. This preliminary action reduces the amount of material that needs to be removed during polishing and minimizes the number of polishing passes required, thereby maintaining high roundness while improving productivity by reducing the polishing burden
Solution Approach 2:
The patent replaces repeated mechanical polishing operations with a thermal-mechanical process (controlled quenching and tempering) that achieves shape correction. This substitution reduces reliance on extensive mechanical polishing, thereby improving productivity while maintaining the required roundness specification
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method effectively suppresses deformation and maintains high roundness, achieving excellent rotational accuracy and reducing manufacturing costs by minimizing residual stress and elliptical deformation, resulting in improved bearing performance.
Implementation Method 1
quenching treatment is required, and elliptical deformation due to the quenching treatment is inevitable
Implementation Method 2
carburizing or carbonitriding is performed to increase the amount of retained austenite on a bearing ring surface
Implementation Method 3
carburizing or carbonitriding is performed to increase the amount of retained austenite on a bearing ring surface
Implementation Method 4
the bearing ring may be distorted during the polishing processing
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
A production method for a race of a rolling bearing comprising a series of steps for cutting an annular member from raw material, creating a surface hardened layer, quenching and tempering, and then polishing an inner diameter surface and an outer diameter surface of the annular member, wherein after quenching, tempering is carried out by suddenly cooling the annular member is such that the surface temperature thereof is no more than 50°c. In said manner, the following can be obtained: an intermediary member of the race of the rolling bearing in which the absolute value of the average residual stress in each location along a radial direction from a surface to a core part thereof is 0-191 MPa; the race in which an inner diameter surface and an outer diameter surface of the intermediary member is polished such that the race is highly circular; and the rolling bearing which comprises the race.