How Can the Core Dimensions of a Gear Be Verified Through Inspection？

Gear precision directly determines a machine’s transmission efficiency, operational stability and service life — from automotive gearboxes and industrial robot joints to aero-engine transmission systems. Defects such as tooth profile errors, tooth surface wear or cracks can cause vibration, noise and energy loss at best, or lead to complete machine failure at worst. Therefore, gear inspection acts not only as a quality control measure during production, but also as a critical safeguard for the reliability and safety of mechanical equipment. It integrates into the entire lifecycle: from design and machining, through assembly, to operation and maintenance.

Dimensional Accuracy Inspection: Verification of Fundamental Parameters

1. Module and Pressure Angle:The module determines the size of the gear tooth profile, while the pressure angle affects transmission smoothness. Operators commonly measure these parameters with gear calipers or universal gear profilometers. For high‑precision applications, they may use laser interferometers to achieve micrometre‑level calibration.
2. Pitch Diameter and Root Diameter:These diameters directly influence gear meshing clearance. Inspectors typically measure them with outside micrometers or optical projectors. During mass production, dedicated gauges allow rapid screening.
3. Centre Distance and Tooth Width:Errors in centre distance can lead to poor meshing, and tooth width impacts load‑bearing capacity. Using coordinate measuring machines (CMMs), technicians perform three‑dimensional scans to ensure assembly compatibility.

Geometric Precision Inspection: The Core Assurance of Transmission Smoothness

1. Profile Error:This refers to the deviation between the actual tooth profile and the theoretical involute curve. Inspectors use an involute measuring instrument to identify common errors such as tooth profile bulging and convexity. Precision typically must fall within 5–10 μm.
2. Tooth Direction Error:Tooth direction error represents deviation in the tooth trace straightness along the tooth width, often leading to uneven tooth contact. Technicians typically measure it using a tooth direction gauge or a CMM equipped with a specialized probe, making it especially suitable for inspecting helical and herringbone gears.
3. Pitch Error:Pitch error includes both cumulative and individual deviations between adjacent tooth pitches, which impair meshing uniformity. Inspection personnel achieve efficient batch measurement using pitch gauges or laser pitch measurement systems.
4. Radial Runout:Radial runout indicates coaxiality deviation between the gear reference bore and the gear ring, which can cause transmission eccentricity. Using runout inspection instruments or CMMs with the reference bore as the datum, operators ensure radial precision.

Surface Quality Inspection: Key to Extended Service Life

1. Surface Roughness:Tooth surface roughness directly affects the meshing friction coefficient. Inspectors use roughness testers to measure the Ra/Rz values, with industrial gears generally requiring Ra ≤ 0.8μm.
2. Surface Defects:Magnetic particle testing (MT) detects surface cracks in ferromagnetic gears, while penetrant testing (PT) suits non-magnetic materials. Ultrasonic testing (UT) can reveal internal hidden defects. High-end sectors such as aerospace and high-speed rail often use eddy current testing (ET) for rapid, non-destructive inspection.
3. Hardened Layer Depth:For carburized or quenched gears, technicians perform microhardness tests to determine the hardened layer depth, ensuring an optimal balance between surface strength and toughness.

Mechanical Properties and Meshing Performance Testing: Simulation Validation under Actual Operating Conditions

1. Mechanical Properties Testing:This testing covers tooth surface hardness (using Brinell or Rockwell testers), tensile strength, and impact toughness. Sample tests verify that the material meets all mechanical specifications.
2. Meshing Transmission Testing:On a gear transmission test bench, this process simulates actual loads to measure transmission efficiency, noise levels, and vibration acceleration, evaluating gear stability under high-speed, heavy-load conditions.
3. Fatigue Life Testing:Fatigue testing machines apply millions of cyclic loads to validate gear fatigue resistance, providing data to support equipment lifespan prediction.

Gear inspection tangibly embodies the principle that precision reigns supreme in mechanical manufacturing, and each inspection metric directly impacts equipment reliability and safety. Advances in inspection technology will make gear quality control more precise and efficient, thus fortifying safeguards for high-end equipment manufacturing. Whether in traditional mechanical domains or emerging sectors such as new energy and robotics, gear inspection remains a pivotal process—it propels transmission technology toward higher precision, longer service life, and lower noise levels.