1. Mechanisms of Gear Grinding Burn

1.1 Definition of Grinding Burn

1.2 Causes of Grinding Burn Formation

• Heat Source Mechanism: Approximately 60-95% of the energy generated during the grinding process is converted into heat.

• Temperature Distribution: The instantaneous temperature can reach 1000-1500°C, but the duration of this high temperature is extremely short (0.1-1ms).

• Phase Transformation Process: Gear steels (e.g., 20CrMnTi) undergo austenitization at high temperatures. Subsequently, depending on the cooling rate, microstructures such as martensite, bainite, or tempered structures may form.

1.3 Classification of Grinding Burn

2. Detection Methods for Grinding Burn

2.1 Traditional Detection Methods

2.1.1 Visual Inspection

• Principle: Observe changes in surface color (temper color).

• Advantages: Simple, fast, and low-cost.

• Limitations: Can only detect severe burn and is highly subjective.

2.1.2 Etching Method

• Steps: First, clean the gear surface; then, apply a 2-2.5% nitric acid-alcohol solution; finally, observe surface color changes (burned areas darken).

• Standard: Complies with GB/T 3481-2017 Gear Burn Detection Method.

2.1.3 Microhardness Testing

• Method: Measure microhardness at different positions on the tooth surface.

• Criterion: A hardness change exceeding ±10% of the base material hardness indicates burn.

2.2 Advanced Non-Destructive Testing Technologies

2.2.1 Barkhausen Noise Testing (MBN)

• Principle: Utilize noise signals generated by the movement of magnetic domains in ferromagnetic materials.

• Equipment Parameters: Frequency range: 1-1000kHz; Sensitivity: Capable of detecting burned layers as thin as 0.01mm.

• Advantages: Fast, non-contact, and quantifiable.

2.2.2 Eddy Current Testing

• Principle: Measure changes in electrical conductivity using electromagnetic induction.

• Parameter Settings: Frequency: 50-500kHz; Probe type: Differential or absolute.

• Applicability: Suitable for high-volume online testing.

2.2.3 Infrared Thermography

• Technical Parameters: Thermal sensitivity: <20mK; Spatial resolution: 1mrad.

• Operation Process: Conduct real-time monitoring during the grinding process and identify abnormal temperature rises through temperature field distribution.

2.2.4 X-Ray Diffraction Residual Stress Analysis

• Principle: Calculate residual stress by measuring lattice strain.

• Criterion: Surface tensile stress exceeding 300MPa may indicate burn.

2.3 Laboratory Analysis Methods

2.3.1 Metallographic Analysis

• Sample Preparation Requirements: Sampling direction: Perpendicular to the grinding direction; Etchant: 4% nitric acid-alcohol.

• Typical Structures: White layer (untempered martensite with hardness >800HV); Transition zone (tempered martensite); Base material (original structure).

2.3.2 Scanning Electron Microscopy (SEM) Analysis

• Observation Content: Surface morphology (e.g., remelting, cracks) and element distribution (oxidation degree analysis).

2.4 Burn Severity Grading and Disposal Recommendations

3. Prevention Measures for Grinding Burn

3.1 Optimization of Process Parameters

3.1.1 Grinding Wheel Selection

• Abrasive: CBN (suitable for hardened steel).

• Grain Size: 80-120#.

• Hardness: K-M grade.

3.1.2 Cutting Parameters

• Linear Speed: 20-35m/s.

• Feed Rate: 0.005-0.02mm/stroke.

3.1.3 Cooling Fluid

• Requirements: High pressure (>1MPa) and large flow rate (>50L/min).

3.2 Process Monitoring Technologies