Surface Hardening of Gears: How Many Do You Know?

The common surface quenching methods for gears include flame quenching, induction quenching, contact resistance heating quenching, and advanced laser quenching.

By performing surface heating and quenching, a hardening layer can be created on the surface while maintaining the original microstructure and properties of the gear core. This enhances the fatigue strength and wear resistance while preserving the core’s excellent toughness. Additionally, this process is energy-efficient and reduces distortion during gear quenching.

1. Classification of surface hardening

See Table 1.

Table 1 Classification of surface hardening

ClassificationTechnology
Rough separationSubdivision
Heating method for heatingInduction quenching, flame quenching, salt bath heating quenching, electrolyte quenching, contact resistance heating quenching, laser quenching, electron beam quenching, ion beam quenching, high-frequency pulse current induction quenching, solar heating quenching, etc.
energy densityLower energy density heatingInduction quenching, flame quenching, salt bath heating quenching, electrolyte quenching, etc.
High energy density heatingLaser quenching, electron beam quenching, ion beam quenching, contact resistance heating quenching, solar heating quenching, etc.
energy sourceInternal heat source heatingInduction fire, pulse current induction quenching, etc.
External heat source heatingFlame quenching, salt bath heating quenching, electrolyte quenching, contact resistance heating quenching, laser quenching, electron beam quenching, ion beam quenching, solar heating quenching, etc.

2. General technical requirements for surface hardened gears

1) See Table 2 for the technical requirements of surface hardened gears.

Table 2 technical requirements for surface hardened gears

ProjectPinionBig gear wheelInstruction
Depth of hardened layer / mm(0.2-0.4)m①Effective hardened layer depth, as per GB / T5617-2005
Tooth surface hardness (HRC)50~5545~50 or 300~400HWIf the transmission ratio is 1:1, the tooth surface hardness of large and small gears can be equal.
Surface organizationFine needle martensiteFerrite is not allowed on the teeth
Heart hardness (HBW)Quenching and tempering:Carbon steel 265 ~ 280Alloy steel 270 ~ 300For some gears with low requirements, normalizing can be used as preliminary heat treatment.

① m is the gear module (mm).

2) Distribution form, strengthening effect and application range of hardened layer on gear surface

a. The tooth root is not hardened

Process method:

Rotary heating quenching method.

Enhancement effect:

The wear resistance of the tooth surface is improved;

The bending fatigue strength has little influence, and the allowable bending stress is lower than the level of the steel after tempering.

High frequency (including ultra audio frequency) quenchingMedium frequency (2.5KHz, 8kHz) quenching Flame quenching 
The diameter of induction processing gear is determined by the equipment power;Gear width 10 ~ 100mm;m≤5mm。The diameter of the processing gear is determined by the equipment power, and the gear width is 35 ~ 150mm;Individually up to 400mm;m≤10mThe gear diameter can reach 450mm;Special quenching machine;m ≤ 6mm, m ≤ 12mm in some cases

Note: m – gear module (mm)

b. Tooth root hardening

Process method:

Rotary heating quenching method.

Enhancement effect:

The surface wear resistance of the teeth and the bending fatigue strength of the tooth roots are improved. The allowed bending stress is 30% to 50% higher compared to a quenched and tempered state. This process can partially substitute for carburized gears.

High frequency (including ultra audio frequency) quenchingMedium frequency (2.5KHz, 8kHz) quenching Flame quenching 
The diameter of induction processing gear is determined by the equipment power;Gear width 10 ~ 100mm;m≤5mm.The diameter of the processing gear is determined by the equipment power, and the gear width is 35 ~ 150mm;Individually up to 400mm;m≤10mThe gear diameter can reach 450mm;Special quenching machine;m ≤ 6mm, m ≤ 10mm in some cases

c. Tooth root hardening

Process method:

Single tooth continuous heating quenching method.

Enhancement effect:

The wear resistance of the tooth surface is improved, but the bending fatigue strength may be impacted to some extent (generally, the hardening layer ends 2 to 3mm from the tooth root). The allowed bending stress is lower than that of the steel after tempering.

High frequency (including ultra audio frequency) quenchingMedium frequency (2.5KHz, 8kHz) quenching Flame quenching 
Gear diameter is not limited, m ≥ 5mmGear diameter is not limited, m ≥ 8mmGear diameter is not limited, m ≥ 6mm

d. Tooth root hardening

Process method:

Continuous heating and quenching along the tooth groove.

Enhancement effect:

The surface wear resistance of the teeth and the bending fatigue strength of the tooth roots are improved. The allowed bending stress is 30% to 50% higher compared to a quenched and tempered state. This process can partially substitute for carburized gears.

High frequency (including ultra audio frequency) quenchingMedium frequency (2.5KHz, 8kHz) quenching Flame quenching 
Gear diameter is not limited, m ≥ 5mmGear diameter is not limited, m ≥ 8mmGear diameter is not limited, m ≥ 10mm

3) Typical machining process of surface hardened gears: blank → normalizing (or annealing) of forging stock → mechanical rough machining → quenching and tempering → mechanical semi finishing (blank making) and gear making → surface quenching → low temperature tempering → mechanical finishing → finished products.

Don't forget, sharing is caring! : )
Shane
Author

Shane

Founder of MachineMFG

As the founder of MachineMFG, I have dedicated over a decade of my career to the metalworking industry. My extensive experience has allowed me to become an expert in the fields of sheet metal fabrication, machining, mechanical engineering, and machine tools for metals. I am constantly thinking, reading, and writing about these subjects, constantly striving to stay at the forefront of my field. Let my knowledge and expertise be an asset to your business.

Up Next

Mastering CAD/CAM: Essential Technologies Explained

Basic Concepts of Computer-Aided Design and Computer-Aided Manufacturing Computer-aided design and computer-aided manufacturing (CAD/CAM) is a comprehensive and technically complex system engineering discipline that incorporates diverse fields such as computer [...]

Virtual Manufacturing Explained: Concepts & Principles

Concept of Virtual Manufacturing Virtual Manufacturing (VM) is the fundamental realization of the actual manufacturing process on a computer. It utilizes computer simulation and virtual reality technologies, supported by high-performance [...]

Understanding Flexible Manufacturing Systems: A Guide

A Flexible Manufacturing System (FMS) typically employs principles of systems engineering and group technology. It connects Computer Numerical Control (CNC) machine tools (processing centers), coordinate measuring machines, material transport systems, [...]

Exploring 4 Cutting-Edge Nanofabrication Techniques

Just as manufacturing technology plays a crucial role in various fields today, nanofabrication technology holds a key position in the realms of nanotechnology. Nanofabrication technology encompasses numerous methods including mechanical [...]

Ultra-Precision Machining: Types and Techniques

Ultra-precision machining refers to precision manufacturing processes that achieve extremely high levels of accuracy and surface quality. Its definition is relative, changing with technological advancements. Currently, this technique can achieve [...]

Exploring High-Speed Cutting: Tech Overview & Application

Cutting machining remains the most prominent method of mechanical processing, holding a significant role in mechanical manufacturing. With the advancement of manufacturing technology, cutting machining technology underwent substantial progress towards [...]

Top 7 New Engineering Materials: What You Need to Know

Advanced materials refer to those recently researched or under development that possess exceptional performance and special functionalities. These materials are of paramount significance to the advancement of science and technology, [...]

Metal Expansion Methods: A Comprehensive Guide

Bulge forming is suitable for various types of blanks, such as deep-drawn cups, cut tubes, and rolled conical weldments. Classification by bulge forming medium Bulge forming methods can be categorized [...]
MachineMFG
Take your business to the next level
Subscribe to our newsletter
The latest news, articles, and resources, sent to your inbox weekly.
© 2024. All rights reserved.

Contact Us

You will get our reply within 24 hours.