Gear inspection service

Gear Inspection Service – Dimensional Accuracy and Performance Verification for Power Transmission Components

At zhongxi testing, we provide specialized gear inspection services for automotive manufacturers, industrial machinery producers, power transmission equipment suppliers, and maintenance workshops in Bahrain. Gears are critical components in engines, gearboxes, pumps, compressors, and wind turbines; their performance depends on precise tooth geometry, surface finish, material quality, and heat treatment. Defects such as profile deviation, pitch error, runout, surface roughness, microcracks, or improper case hardening can lead to noise, vibration, premature wear, and catastrophic failure. Our ISO/IEC 17025 accredited laboratory performs comprehensive inspection – including gear profile measurement (involute, helix, pitch), surface roughness, hardness testing (core and case), microstructure analysis, runout measurement, and non‑destructive testing – to ensure compliance with international standards (ISO 1328, AGMA 2000, DIN 3961, ASTM E18) and Bahraini industrial requirements.

Types of Gear Samples We Test

Our laboratory handles a wide range of gear types and sizes used across Bahraini industries:

Spur gears, helical gears, bevel gears, and worm gears
Internal gears and ring gears
Planetary gears and sun gears
Gear shafts and pinions
Gears made from carbon steel, alloy steel, stainless steel, cast iron, bronze, and plastics
Hardened and ground gears (carburized, nitrided, induction‑hardened, or through‑hardened)
New production batches (incoming quality assurance for gearbox manufacturers)
In‑service gears removed during maintenance (wear and fatigue assessment)
Prototype gears for design validation
Competitor gear benchmarking (profile, noise, and load capacity)

Key Inspection Parameters and Test Methods for Gears

1. Gear Profile Measurement (Involute, Helix, and Pitch) – ISO 1328 / AGMA 2000

The most critical parameter in gear inspection is tooth geometry accuracy. Using a CNC gear measuring machine with a diamond stylus or a coordinate measuring machine (CMM) with a gear‑specific software package, we measure the involute profile deviation (total, form, and slope deviations), helix deviation (total, form, and slope), and pitch deviations (single pitch, cumulative pitch, and runout). For gears with module 1‑10 mm, typical tolerances follow ISO 1328 grades 5‑8. For high‑speed gears (e.g., turbine gears), grades 4‑5 are required. Profile deviation exceeding the specified tolerance by > 20% results in increased noise and reduced load capacity.

2. Radial Runout and Concentricity – AGMA 2000 / ISO 1328

We measure radial runout (Fr) by placing the gear on a precision mandrel and rotating it against a dial gauge mounted on the tooth flank or pitch circle. The total indicator reading (TIR) across one full revolution is recorded. For general industrial gears, Fr ≤ 0.05 mm is acceptable; for precision gears, ≤ 0.02 mm. Excessive runout leads to uneven load distribution and vibration.

3. Surface Roughness (Tooth Flank and Root) – ISO 4287 / AGMA 2000

We measure the surface roughness (Ra, Rz, and Rq) on the tooth flank and root using a contact profilometer with a stylus tip radius of 2 µm. For ground gears, typical Ra is 0.2‑0.5 µm; for hobbed or shaped gears, Ra is 1‑3 µm. For high‑load gears, Ra < 0.4 µm is recommended. Excessive roughness (> 2 µm) increases friction, promotes scuffing, and reduces gear life.

4. Core Hardness and Case Hardness – ASTM E18 / ISO 6508

We measure Rockwell hardness (HRC) on the tooth surface (case) and on a cross‑section of the tooth (core). For carburized gears, case hardness is typically 58‑62 HRC; core hardness is 30‑40 HRC. For induction‑hardened gears, case hardness is 50‑55 HRC. A hardness difference between the tooth tip and root > 5 HRC indicates uneven heat treatment. We also perform a microhardness traverse from the surface to the core (using Vickers HV 0.5 or HV 1) to determine the effective case depth; typical case depth for a module 4 gear is 0.8‑1.2 mm.

5. Microstructure Analysis – ASTM E3 / ISO 4496

We cut, mount, grind, polish, and etch a tooth cross‑section using nital (2‑4%) to reveal the microstructure. Under an optical microscope (100×, 500×), we evaluate the grain size, carbide distribution (for carburized gears), retained austenite content, and the presence of any non‑martensitic phases. For aerospace‑grade gears, retained austenite should be < 10%; for general industrial gears, < 20%. Excessive retained austenite reduces hardness and wear resistance.

6. Non‑Destructive Testing (Magnetic Particle or Dye Penetrant) – ASTM E1444 / ASTM E165

We inspect gear teeth and roots for surface cracks using magnetic particle inspection (for ferromagnetic steels) or dye penetrant inspection (for non‑magnetic and stainless steels). We apply a magnetic field (for MPI) or penetrant, dwell, develop, and examine under UV or white light. Any linear indication longer than 0.5 mm is considered a defect. For critical gears, we also perform ultrasonic testing of the gear blank for internal porosity or inclusions.

7. Tooth Contact Pattern Check (for assembled gears) – AGMA 2000

For gear sets, we apply a thin layer of marking compound (red lead or Prussian blue) to the teeth of one gear and rotate the pair under light load. The contact pattern (location and shape) is inspected visually. A centred, elliptical contact pattern with length 40‑60% of the tooth width is ideal. One‑sided contact or edge contact indicates misalignment or improper tooth bearing.

8. Dynamic Noise and Vibration Testing – ISO 10816 / AGMA 6000

For gears to be installed in noise‑sensitive applications (e.g., gearboxes for hospitals, marine, or aerospace), we perform a spin test on a gear test rig at operating speeds (up to 10,000 rpm). We measure sound pressure level (dB(A)) and vibration velocity (mm/s) using an accelerometer and a sound level meter. For a gearbox, noise levels > 85 dB(A) at full load indicate manufacturing or assembly defects.

9. Tooth Bending Fatigue Test – ISO 6336 / ASTM E466

We perform pulsator fatigue testing on a gear tooth (simulating cyclic bending) using a servo‑hydraulic tester. The test applies a sinusoidal load (10‑30 Hz) until the tooth fractures. The endurance limit (stress amplitude at 10⁷ cycles) is determined. The measured endurance limit must be ≥ 80% of the design value; otherwise, material or heat treatment is inadequate.

10. Dimensional Inspection of Bores and Keyways – ASME B89

We measure the bore diameter, keyway width, and keyway depth using a bore gauge, micrometer, and depth micrometer. Tolerances are typically ±0.01 mm for the bore (H7 fit) and ±0.02 mm for the keyway. Oversized bores or keyways can cause shaft‑gear slippage under load.

Quality Grading and Acceptance Criteria

Based on our gear inspection services, we classify gears into three grades (clients provide specific acceptance criteria for their application):

Grade A (Premium – Aerospace, High‑Speed) – ISO 1328 grade 4 or better, runout ≤ 0.02 mm, surface roughness Ra ≤ 0.3 µm, case hardness 58‑62 HRC, core hardness 35‑40 HRC, retained austenite < 5%, no cracks, dynamic noise < 75 dB(A).
Grade B (Standard – Automotive, Industrial) – ISO 1328 grade 6‑7, runout ≤ 0.05 mm, surface roughness Ra ≤ 0.6 µm, case hardness 55‑60 HRC, core hardness 30‑35 HRC, retained austenite < 15%, minor surface indications allowed, noise < 85 dB(A).
Grade C (Reject – Not Suitable) – ISO 1328 grade > 8, runout > 0.08 mm, surface roughness Ra > 2 µm, case hardness < 50 HRC, visible cracks, retained austenite > 25%, excessive noise – immediate rejection.

Reporting and Deliverables

Our gear inspection report includes: gear identification (type, module, number of teeth, material, heat treatment, batch number, manufacturer), profile measurement results (involute, helix, pitch errors), radial runout (mm), surface roughness (Ra, Rz), hardness values (case and core), microstructure images, NDT findings, contact pattern photos, noise and vibration levels, fatigue test results, bore/keyway dimensions, and a clear pass/fail conclusion based on client‑supplied criteria. Raw data (gear measurement files, hardness graphs, micrographs) are archived for 10 years.

In summary, a comprehensive gear inspection service from zhongxi testing ensures that your gear components meet the required dimensional accuracy, material properties, and operational reliability for Bahrain’s automotive, industrial, and energy sectors. Contact our laboratory to schedule batch testing for your next gear production or maintenance program.