I. Mechanical properties test
1. Hardness test
Test purpose: Hardness is a key indicator to measure the wear resistance and fatigue strength of the large ring gear.
Method:
Use Rockwell hardness tester (HRC) or Vickers hardness tester (HV) to measure multiple points at key parts such as tooth top, tooth root, tooth surface, etc.
Standard: It must meet the design requirements (such as the hardness of the tooth surface after carburizing and quenching usually requires HRC58-62, and the core HRC30-45), and the hardness uniformity deviation does not exceed ±2HRC.
2. Strength and toughness test
Tensile test: Determine the tensile strength and yield strength to ensure that the large ring gear can withstand the transmitted torque.
Impact test: Test the toughness of the material through the Charpy impact test to avoid fracture under impact load.
3. Wear resistance and fatigue life
Bench test: Simulate the actual working conditions for fatigue testing, observe the wear of the tooth surface (such as wear ≤0.01mm after 1000 hours of cumulative operation) or whether pitting and peeling occur.
2. Microstructure Analysis
1. Metallographic Observation
Method: Cut the cross section of the large ring gear, grind, polish and corrode, and observe it with a metallographic microscope (500-1000 times).
Qualified Standard:
Carburized and quenched large ring gear: The surface should be fine needle-shaped martensite + evenly distributed carbides, and the core should be low-carbon martensite + ferrite (ferrite content ≤5%).
Quenched and tempered large ring gear: The structure should be tempered troostite, without overheating (coarse grains), overburning (grain boundary oxidation) or network carbides.
2. Carburized layer depth detection
Method: Metallographic method (measure the depth of the transformation from the surface to the core) or hardness gradient method (measure the hardness every 0.1mm, and HRC50 is the effective depth of the carburized layer).
Standard: It must meet the design requirements (such as the effective carburized layer depth of 0.8-1.2mm), and the depth deviation must be ≤±0.1mm.
3. Dimensional accuracy and deformation control
1. Geometric dimension measurement
Testing items:
Tooth tip circle diameter, tooth root circle diameter, tooth thickness, normal length, etc., using a three-coordinate measuring instrument or gear measuring center.
Geometric tolerance: roundness, cylindricity, end face runout (≤0.03mm), detected with a dial indicator or roundness meter.
Standard: Dimensional tolerance must meet the requirements of the drawing (such as gear accuracy grade ISO 6-7), and the deformation after heat treatment is ≤ the design allowable value (such as tooth tip circle deformation ≤0.05mm).
2. Tooth shape and tooth direction accuracy
Use a gear detector to measure tooth shape error (≤0.015mm) and tooth direction error (≤0.02mm) to ensure meshing stability.
4. Surface quality and defect troubleshooting
1. Surface defect detection
Non-destructive testing:
Magnetic particle testing (MT): detect surface and near-surface cracks (such as quenching cracks).
Penetrant testing (PT): Applicable to non-ferromagnetic materials to check for fine cracks or folds.
Visual inspection: The surface should be free of oxide scale and decarburization layer (decarburization layer depth ≤ 0.05mm), and the color should be uniform (such as dark gray after carburizing and quenching).
2. Surface roughness
Use a roughness meter to measure the tooth surface roughness (Ra ≤ 1.6μm) to ensure that the friction coefficient meets the requirements during meshing.
Chemical composition and residual stress
1. Chemical composition review
Use a direct reading spectrometer to detect the material composition (such as the content of elements such as C, Cr, Ni, Mo, etc.), which must be consistent with the design grade (such as 20CrMnTi), with a deviation of ≤ ± 0.05% (mass fraction).
2. Residual stress detection
Use X-ray diffraction to measure surface residual stress. The ideal state is compressive stress (such as residual compressive stress on the tooth surface ≥ -400MPa), which can improve fatigue resistance and avoid cracking caused by tensile stress.
Functional simulation and batch consistency
1. Installation test
Install the large ring gear into the equipment, conduct no-load and load test runs, and observe:
Whether the noise (≤85dB) and vibration (amplitude ≤0.05mm) are normal.
Temperature rise (large ring gear temperature ≤80℃ after 2 hours of continuous operation) and oil leakage.
2. Batch sampling test
Sampling according to GB/T 2828.1 standard, test the performance discreteness of the same batch of products (such as hardness fluctuation ≤±3HRC, carburized layer depth deviation ≤±0.1mm), and the qualified rate must be ≥98%.
Reference standards and process documents
Industry standards: such as GB/T 8539 (technical conditions for gear heat treatment), ISO 6336 (gear load capacity calculation), etc.
Enterprise process documents: It is necessary to compare the consistency of the heat treatment process card (such as heating temperature, holding time, cooling medium and other parameters) with the actual implementation.
Summary
The success of the hot large ring gear treatment process must be determined by combining performance indicators, microstructure, dimensional accuracy and actual application effects, and multi-dimensional testing must be performed to ensure that it meets the design and use requirements. If a certain indicator does not meet the standard, the process links (such as insufficient heating temperature, improper cooling speed, etc.) need to be analyzed and optimized until all items are qualified.
