Rolling-Contact Shaft Nitrogen Enrichment and Tempering
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Solution Overview
Problem
Conventional approaches to improve rolling contact fatigue life and torsional strength of rolling-contact shafts with joint claws often compromise one or the other, and fail to effectively manage secular dimensional distortion and surface-origin fractures.
Innovation Solution
A rolling-contact shaft with a nitrogen-enriched surface layer, subjected to induction heating for tempering, which reduces hydrogen content and grain size, enhancing both rolling contact fatigue life and torsional strength while maintaining surface hardness within optimal ranges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the rolling-contact shaft is reduced in size to meet demand for compactness, then space is reduced, but the contact pressure between the needle roller and the outer cylindrical surface increases, reducing rolling contact fatigue life
Solution Approach 1:
The patent applies different heat treatment conditions to different regions of the shaft. The raceway region undergoes induction hardening to achieve high hardness (58-65 HRC) and improved rolling contact fatigue resistance, while the joint claw region undergoes tempering to achieve appropriate toughness. This local differentiation allows the shaft to maintain high reliability at the raceway even when overall size is reduced and contact pressures increase.
2Volume of moving object
If the rolling-contact shaft is reduced in size, then space is reduced, but the torsional stress on the joint claw increases, reducing torsional strength
Solution Approach 1:
The patent applies different heat treatment conditions to different regions of the shaft. The joint claw region undergoes tempering after induction hardening to achieve appropriate toughness and torsional strength (HV 250-450), while the raceway region maintains high hardness. This local differentiation allows the shaft to maintain adequate torsional strength at the joint claw even when overall size is reduced.
3Reliability
If high carbon chromium bearing steel is used and multiple heat treatments are applied to improve rolling contact fatigue life, then rolling contact fatigue life is improved, but the manufacturing process becomes more complex
Solution Approach 1:
The patent combines induction hardening and tempering processes into a sequential manufacturing workflow. The induction hardening is performed first to achieve the required surface hardness and rolling contact fatigue resistance, followed by tempering of the joint claw region to achieve appropriate toughness. This integrated approach, using a single heat treatment device for both operations, reduces overall process complexity compared to using multiple different heat treatment methods.
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 solution significantly improves rolling contact fatigue life, torsional strength, and reduces secular dimensional distortion, effectively addressing the limitations of conventional methods by creating a fine metal structure with controlled austenite content and surface hardness.
Implementation Method 1
A nitrogen-enriched layer is formed at a surface layer of a rolling-contact shaft with a joint claw (1). The grain size number of austenite grains in the nitrogen-enriched layer exceeds number 10.
Implementation Method 2
The joint claw is subjected to tempering by induction heating. The hydrogen content of the rolling-contact shaft with a joint claw is at most 0.5 ppm.
Implementation Method 3
The grain size number of austenite grains in the nitrogen-enriched layer exceeds number 10... The metal structure is rendered fine due to the smaller austenite grains, and embrittlement of the metal structure is obviated since the hydrogen content is reduced.
Data Source
AI summary
A steel-made rolling-contact shaft with a joint claw improved in both the rolling contact fatigue life at the raceway and the static fracture strength (torsional strength) at the claw includes a joint claw at one end, and has a portion of the outer cylindrical surface functioning as a raceway of a needle roller qualified as a rolling element of a needle bearing. The joint claw is subjected to tempering by induction heating. A nitrogen-enriched layer is formed at the surface layer of the rolling-contact shaft with a joint claw. The grain size number of austenite grains in the nitrogen-enriched layer exceeds number 10. The hydrogen content of the rolling-contact shaft with a joint claw is not more than 0.5 ppm.