STAGE 1

Planetary (Low Speed)

Ratio: 4:1–6:1. Planet gears: helical (or spur for older designs). Input: rotor shaft 5–20 RPM. Ring gear: 18CrNiMo7-6 nitrided. Planet and sun: 18CrNiMo7-6 carburized HRC 60–62. Highest torque stage — largest gears in the gearbox.

STAGE 2

Parallel Helical (Intermediate)

Ratio: 4:1–6:1. PLV: 15–35 m/s. 18CrNiMo7-6 carburized, HRC 60–62, ground DIN 4. Helix angle 15°–18°. Double helix (herringbone) used in some designs to eliminate thrust bearing requirement.

STAGE 3

Parallel Helical (High Speed)

Ratio: 4:1–6:1. PLV: 50–100 m/s. 18CrNiMo7-6 carburized, HRC 60–62, DIN 3–4 ground + superfinished (Ra <0.2 μm). Highest gear quality requirement in the gearbox — dominant noise source if quality insufficient.

MATERIAL 01

18CrNiMo7-6
CARBURIZED

Application: Primary specification for all wind turbine gearbox helical gear stages above 500 kW turbine capacity. Per AGMA 6006 and Germanischer Lloyd wind turbine gearbox standard. Case carburized to effective case depth 1.0–1.5 mm (intermediate stage) or 1.2–1.8 mm (low-speed stage), HRC 60–62 tooth surface, core hardness HB 300–360 for maximum shock absorption under rotor wind gust loads. The high nickel-chromium-molybdenum alloy content of 18CrNiMo7-6 provides excellent core impact resistance after carburizing — critical for surviving the 1.5× rated load extreme wind gust events that occur throughout the 20-year design life. Tooth root shot peened to introduce compressive residual stress, improving bending fatigue limit by 15–25% vs non-peened condition.

MATERIAL 02

20MnCr5
CARBURIZED

Application: Used for intermediate and high-speed stage helical gears in turbines below 1 MW, and for replacement gear supply for older turbine gearboxes where 18CrNiMo7-6 is specified by cost rather than by performance requirement. 20MnCr5 has lower alloy content than 18CrNiMo7-6, resulting in lower hardenability (maximum effective case depth achievable without distortion is approximately 1.2 mm), and lower core toughness. At turbine outputs below 1 MW, where gears are smaller and the absolute shock energy at extreme wind events is lower, 20MnCr5 carburized gear performance is fully adequate to meet the 20-year design life requirement when designed to ISO 6336 safety factors S_H ≥1.20 and S_F ≥1.40 for the full load spectrum.

SURFACE TX

SUPERFINISHING
HSS PINION

Application: High-speed stage (HSS) output pinion superfinishing — mass-finishing or Isotropic Superfinishing (ISF) to reduce tooth flank Ra from the ground value of 0.4–0.8 μm to below 0.1–0.2 μm. At PLV 50–100 m/s, the EHL oil film thickness at the tooth contact is 0.5–1.5 μm — only slightly thicker than the sum of the two tooth surface roughnesses in the ground condition. Superfinishing reduces the surface asperity contribution to film thickness ratio below 1.0, preventing micro-pitting and surface fatigue that is the dominant HSS pinion failure mode in early-generation wind turbine gearboxes. Korea Ever-Power applies superfinishing as a standard option for all wind turbine HSS pinion orders above 500 kW turbine capacity.

What is the most common helical gear failure mode in wind turbine gearboxes, and how does modern design prevent it?

The dominant helical gear failure mode in wind turbine gearboxes — particularly in first-generation 1.5–2 MW turbines installed in the 2000s — is micro-pitting (also called grey staining or frosting) on the high-speed stage pinion tooth flanks. Micro-pitting is a surface fatigue phenomenon occurring when the EHL oil film at the tooth contact is insufficient to separate the tooth surface asperities during meshing, causing micro-scale plasticity and fatigue crack initiation at the highest surface asperities. Unlike classical pitting, micro-pitting initiates at loads well below the gear’s rated contact stress capacity and progresses gradually over thousands of operating hours. Prevention in modern wind turbine gearbox helical gear design: (1) Superfinished tooth flanks on the HSS pinion to Ra <0.1 μm — eliminates the highest surface asperities that initiate micro-pitting. (2) ISO VG 320 or VG 460 synthetic PAO or polyglycol gear oil with anti-micropitting additive package (AT minimum AGMA EP-MPI classification). (3) Profile crowning 10–20 μm to prevent edge loading from housing deflection. (4) Minimum DIN 4 quality class for HSS gears — transmission error peaks at low quality class increase dynamic contact stress fluctuation that accelerates micro-pitting. Korea Ever-Power applies all four measures as standard for wind turbine HSS helical gear supply.

Can Korea Ever-Power supply wind turbine gearbox helical gear replacement sets for major OEM gearboxes such as Winergy, Bosch Rexroth, or ZF Wind Power?

Korea Ever-Power supplies replacement helical gear sets for wind turbine gearboxes from all major OEM gearbox manufacturers including Winergy (FLENDER), Bosch Rexroth, ZF Wind Power, Moventas, NGC (formerly Nanjing High Accurate Drive), and CSIC (China Shipbuilding Industry Corporation). Two supply modes: (1) Cross-reference supply: for gearbox models with known specification, Korea Ever-Power can supply replacement helical gears to the original module, tooth count, helix angle, material, and quality class from the reference database — customer provides gearbox model and stage designation (IMS pinion, IMS wheel, HSS pinion, etc.). (2) Reverse engineering from failed gear: for gearboxes with no accessible specification, Korea Ever-Power performs dimensional measurement of the failed or worn gear (or of the mating gear if the failed gear is no longer intact), verifies the material specification by spark test and hardness measurement, and manufactures the replacement to the original specification with one step of material or quality upgrade where failure analysis indicates the original specification was insufficient. Contact Korea Ever-Power with the turbine OEM, gearbox serial number or model, and the stage requiring replacement gear supply.

How long does it take to replace the high-speed stage helical gears in a wind turbine gearbox, and what is the typical cost saving vs a full gearbox exchange?

High-speed stage (HSS) helical gear replacement in a wind turbine gearbox — the most commonly repaired stage because it is the most accessible and the most likely to develop micro-pitting — is typically a 2–4 day procedure per turbine when conducted by an experienced wind turbine gearbox repair team with the correct tooling. The HSS pinion and wheel are accessible through the gearbox high-speed end housing after removing the coupling or brake disc, without the need for a full nacelle crane lift. Typical cost comparison for a 2 MW wind turbine HSS gear replacement: full gearbox exchange (OEM remanufactured unit) — EUR 80,000–150,000 plus crane and installation; HSS helical gear set supply from Korea Ever-Power plus repair labour — EUR 12,000–25,000 for the gear set (depending on module and face width) plus EUR 15,000–30,000 for the installation team and crane day rate, total EUR 27,000–55,000 against EUR 80,000–150,000 for full gearbox exchange. The gear set replacement restores the gearbox to full design life on the repaired stage. Korea Ever-Power can advise on the full scope of replacement including the required inspection of bearings and housing before repair — contact Korea Ever-Power with the turbine model, gearbox serial number, and failure description for an assessment.

Spur Gears

M1–M20 · C45, 20CrMnTi, 316L

Helical Gears

18CrNiMo7-6 · wind turbine · DIN 3–4

Ingranaggi conici

Right-angle drives · straight & spiral

Worm Gears

High ratio · self-locking · yaw drive

Ring Gears

Wind turbine · yaw & pitch ring gear

Planetary Gears

Low-speed stage · wind turbine · compact

Plastic Gears

POM · Nylon · sensor · auxiliary drive