High Speed Train Hard Tooth Flank Helical Gear – 56-62 HRC

High speed train and locomotive hard tooth flank helical gears are the most performance-critical gear application in land transportation. The traction gearbox of a high-speed train or electric locomotive must transmit the full traction motor output continuously at high speed, absorb the vibration and shock of rail joints and wheel flats, and do so without maintenance access between scheduled wheelset overhauls that may be separated by hundreds of thousands of kilometres. No other gear application combines high continuous power, high pitch-line speed, and such extended maintenance intervals.

Korea Ever-Power produces these gears in 17CrNiMo6 — a nickel-chromium-molybdenum alloy specifically selected for railway traction gear applications where the nickel content enhances toughness at the tooth root core without sacrificing the case hardenability needed to achieve 58–62 HRC at the tooth flank. The production process: forging → turning → hobbing → carburising → external grinding → tooth grinding. The standard example (Mn=4, Z=132, β=18°) is a large, high-tooth-count helical gear wheel typical of a traction gearbox output stage driving the axle gear through the bull gear.

High Speed Train EMU Sets

Traction gearboxes on electric multiple unit (EMU) sets operating at 200–350 km/h. The combination of high pitch-line speed, continuous maximum power, and million-kilometre overhaul intervals demands the highest gear accuracy and the best available material quality. 17CrNiMo6 carburised to DIN 6 is the standard specification for these applications.

Electric Locomotives

AC and DC electric locomotive traction gearboxes where the gear set must transmit the full continuous traction motor power while absorbing wheel-rail vibration and occasional wheel flat impacts. The large Mn=4, Z=132 wheel example is typical of electric locomotive gear proportions at standard gauge.

Diesel-Electric Locomotives

Diesel-electric locomotive traction gearboxes and final drive stages. The power pulses of the diesel prime mover, transmitted through the alternator and traction motors, create additional dynamic loading on the traction gear set — further emphasising the importance of core toughness in 17CrNiMo6.

Metro and Light Rail

Urban metro and light rail traction gearboxes operating at higher cycle counts than intercity trains due to shorter station spacing. The accelerate-decelerate duty cycle imposes more frequent peak torque events on the gear set — the core toughness of 17CrNiMo6 is well matched to this cyclic torque profile.

Aviation Ground Support

Airport people-mover and baggage-handling system drives using high-accuracy carburised helical gears in 17CrNiMo6. The reliability requirements for airport ground systems are comparable to railway traction — unplanned downtime is unacceptable in a high-throughput terminal environment.

Industrial High-Speed Drives

Industrial gearboxes for compressors, centrifuges, and high-speed test stands where the pitch-line speed exceeds 25 m/s and the gear accuracy requirement is DIN 5–6. The same material, process sequence, and quality assurance applied to traction gears is transferred to these high-performance industrial drives.

What is the difference between 17CrNiMo6 and 18CrNiMo6 used in mining gears?

17CrNiMo6 and 18CrNiMo6 are closely related nickel-chromium-molybdenum case-hardening steels with essentially identical nickel (1.4–1.7%), chromium (1.5–1.8%), and molybdenum (0.25–0.35%) contents. The minor difference is in the nominal carbon content: 17CrNiMo6 has 0.14–0.19% carbon versus 0.15–0.21% for 18CrNiMo6. This difference is within the normal chemistry variation band and does not produce a significant difference in mechanical properties in the finished gear. Both grades are used interchangeably in high-performance traction and mining gear applications; the choice is typically dictated by the OEM's material specification or by what is available in the required bar or forging blank size from the steel mill at the time of order.

Why does the traction gear example have 132 teeth at module 4?

The high tooth count (Z=132) at moderate module (Mn=4) reflects the design trade-off in traction gearboxes. A higher tooth count at the same module gives a larger pitch diameter and therefore a higher pitch-line speed at the gear mesh for a given wheel speed — which improves load sharing across more simultaneously meshing tooth pairs. The pitch diameter of this example is approximately Mn × Z = 4 × 132 = 528 mm, consistent with the bull gear in a typical standard-gauge locomotive traction gearbox. The moderate module of 4 keeps the tooth depth and fillet radius at values that balance bending fatigue strength with the grinding allowance needed to achieve DIN 6 accuracy after carburising.

What documentation is required for railway authority approval?

Railway traction gear sets supplied to rolling stock OEMs typically require: material certificate (chemical composition to the specified grade), mechanical test certificate (tensile, yield, elongation, impact energy from the same heat), heat treatment records (carburising cycle, quench and temper times and temperatures), case depth measurement (microhardness traverse across the tooth section), 100% FMPI certificate, and dimensional inspection report to DIN 3962 Class 6. Traceability code on each gear linking to all of the above. Korea Ever-Power provides all of these as the standard documentation package for traction gear orders. Classification society certification (for marine traction applications) is available as an additional service.

What should I do if I cannot identify a failed traction gear?

Send us the damaged gear. Korea Ever-Power specialises in reverse engineering of railway traction gears. Provide any available information — the vehicle type, wheelset diameter, gearbox manufacturer, and approximate gear ratio — alongside the physical sample. Our team will measure the module, tooth count, helix angle, bore, and hub dimensions, identify the closest standard geometry, and prepare a production drawing for approval before cutting begins. For traction gears where only the mating gear (pinion or wheel) is damaged and the other member is undamaged, we can measure the undamaged member to derive the damaged gear's geometry more precisely.

How is the lowest price achieved for traction gear orders?

The primary cost drivers are gear size (which determines forging blank cost and machine time), material specification, case depth requirement, and accuracy grade. For traction gear programmes with a defined annual quantity, the per-unit cost decreases as the order quantity increases — larger batch sizes allow the carburising furnace run and grinding setup to be amortised across more parts. Providing the complete drawing with all specifications at the enquiry stage gives the most accurate quotation and avoids scope growth during negotiation. Contact our team with your drawing and programme quantity for a detailed price structure.

"We overhaul electric locomotive traction gearboxes and needed Mn=4, Z=132 carburised helical wheels in 17CrNiMo6 at DIN 6. The OEM had a 32-week minimum lead time. Korea Ever-Power produced from our worn wheel sample — measured the geometry, prepared a drawing, submitted for our review within 7 working days, produced, and delivered within our planned overhaul window. Dimensional report confirmed DIN 6 on all tooth parameters."

Kim Jae-il  |  Traction Gearbox Overhaul Manager, Busan Rail Maintenance Depot  ·  Q1 2026

"We supply replacement traction gear sets to metro operators and qualify our suppliers against EN 13260 documentation requirements. Korea Ever-Power's hard tooth flank helical gears passed our incoming inspection and documentation review at first delivery. The traceability code links correctly to the heat treatment and material records in the package. Two years of supply; no gear-related failures in field service."

Lee Sang-chul  |  Quality Assurance Lead, Seoul Metro Traction Equipment Co.  ·  Q3 2025

"We design traction gearboxes for diesel-electric locomotives and engaged Korea Ever-Power for design cooperation on a new gear pair optimised for a revised traction motor. Their R&D team produced the gear geometry proposal including tooth profile modification recommendations for the dynamic loading profile. PPAP Level 3 package was completed and approved at first submission."

Park Sung-jin  |  Traction Gearbox Design Manager, Daejeon Rail Vehicle Systems  ·  Q4 2025

"We operate a fleet of airport people-movers and needed 17CrNiMo6 carburised helical gears at DIN 6 with full traceability for our asset management system. Korea Ever-Power supplied with the traceability code format we specified — linked to our CMMS asset record. After 3 years of operation, the gear sets at planned inspection show wear within the expected range with no pitting initiation."

Choi Byeong-il  |  Asset Engineering Manager, Incheon Airport Ground Transport  ·  Q2 2025

"We manufacture high-speed centrifugal compressors for industrial gas service and qualified 17CrNiMo6 carburised helical gears from Korea Ever-Power for our bull gear stage. HÖFLER-ground to DIN 5 accuracy confirmed by our incoming CMM check. Pitch-line speed at operating point exceeds 80 m/s — no vibration anomaly at the gear mesh frequency detected in the compressor's vibration monitoring system after 18 months of operation."

Ryu Hyeon-woo  |  Rotating Equipment Engineer, Ulsan Industrial Gas Co.  ·  Q1 2026