Heavy Machinery Double Helical Gear – 42CrMo, 50-55 HRC

Heavy machinery double helical gears are the gear form of choice when two requirements must be satisfied simultaneously: the smooth, quiet, high-contact-ratio engagement of a helical gear, and the elimination of the axial thrust force that a single helical gear imposes on shaft bearings and housings. By placing two helical tooth sets of opposite hand side by side on the same gear body, the axial forces from each half cancel — the shaft sees only radial loads. In heavy machinery drives where the shaft and bearing arrangement is already loaded by the equipment's working forces, eliminating gear axial thrust simplifies bearing selection, extends bearing life, and allows more compact housing designs.

Korea Ever-Power produces heavy machinery double helical gears in cast steel and alloy steel to customer drawings or samples. Material is fully customisable across the standard alloy steel grades — from 45# carbon steel for cost-effective medium-load applications through 40CrNiMoA for the highest-load heavy industrial drives. Heat treatment by quenching and tempering produces a soft tooth surface (≤350 HB) with the core toughness needed to absorb the shock and reversing loads typical of crane drives, conveyor head drives, and rolling mill pinion stands.

Zero Net Axial Thrust

The two helical halves in opposite hands produce equal and opposite axial thrust forces that cancel internally. Shaft bearings and housings in heavy machinery drives see only radial loads from the gear — no axial force that would require thrust bearings or additional housing rigidity.

High Contact Ratio

Double helical gears provide a higher effective contact ratio than single helical gears of the same face width, because both tooth sets contribute to load sharing simultaneously. At any instant, multiple tooth pairs on both the left and right helical halves are in contact, reducing the peak load on any individual tooth pair.

Smooth, Stable Operation

The progressive tooth engagement of helical teeth — combined with the load distribution across both tooth sets — produces stable, low-vibration operation even at the low speeds and high torques characteristic of heavy machinery main drives. The quenched-and-tempered soft tooth surface is well matched to the moderate-speed, high-torque duty of heavy industrial gearboxes.

Shock and Reversing Load Tolerance

Quenching and tempering produces a through-hardened core with high impact energy — the tooth root can absorb shock loads from crane hook engagement, press working strokes, and mill bite events without fracture. This is the engineering reason that soft tooth surface gears remain the preference in heavy machinery drives despite their lower surface hardness compared with carburised gears.

Industrial Cranes

Hoisting gearboxes, bridge travel drives, and slewing ring drives in overhead cranes and shipyard gantry cranes. The zero-thrust property is particularly valuable in crane hoisting drives, where inertial thrust loads at start and stop would otherwise stress the housing mounting flanges.

Mining Equipment

Conveyor head drive gearboxes, bucket wheel slewing drives, and hoist drum drives in underground and surface mining equipment. Cast steel double helical gears are appropriate for the large module sizes used in mining drives where forged blank availability may be a constraint.

Rolling Mill Pinion Stands

Pinion stand gears in plate mills, bar mills, and section mills where the thrust-free property of double helical gears prevents the pinion housing from being pushed axially during reversing rolling passes — particularly important in reversing mills that change rotation direction at each pass.

Marine Main Reduction

Main reduction gearboxes on cargo vessels and workboats where double helical gears are specified to eliminate propeller-shaft thrust from the gear stage and reduce noise transmission to the vessel structure. OEM configuration with customer-specified alloy grade and surface finish.

Heavy Compressors

Speed increaser and speed reducer gearboxes in large industrial gas compressors and refrigeration compressors. The vibration-damping effect of the soft tooth flank and the thrust-free double helical configuration together reduce the gear-generated vibration transmitted to compressor pipework and foundations.

Automotive & Motor Drives

Electric motor reduction stages, electric car transmission gears, and motorcycle gearbox stages in production programmes where OEM marking, alloy customisation, and short lead times — 15–20 working days for mass production — are required alongside competitive unit pricing at volume.

What is the lead time for mass production?

Mass production lead time is 15–20 working days, depending on the quantity ordered and the specific configuration. For large or complex gear sets requiring non-standard alloy grades or particularly large cast blanks, the lead time may be extended — confirm with our team at enquiry stage. Prototypes and pre-production samples are also available; lead time for these is shorter and confirmed after the drawing is reviewed.

Is gear grinding available for higher accuracy requirements?

The standard configuration uses gear hobbing without grinding, producing ISO 1328 grade 8–9. Tooth grinding for higher accuracy (grade 6–7) is available on request — specify the required accuracy grade on the drawing and our team will confirm feasibility and the additional cost and lead time. For double helical gears, grinding is more complex than for single helical gears due to the requirement to access the groove between the two tooth sets, and not all configurations are grindable without design modification.

Can the helix angle be freely specified?

Yes — helix angle is custom made to the customer's drawing. Common helix angles for heavy machinery double helical gears are 15°–30°; angles outside this range are possible and are confirmed at the enquiry stage. The helix angle on both halves is equal in magnitude and opposite in direction — this is the defining geometry of a double helical gear and ensures the axial thrust cancellation.

What design and prototyping services are available?

Korea Ever-Power offers parts design, prototyping, mould design, mass production, and internal assembly services. For customers who have a gearbox application but no finished gear drawing, our team can calculate the gear geometry from the application data (required ratio, input speed, output torque, centre distance) and produce a drawing for approval. Prototyping service is available before production tooling is committed.

Is OEM logo marking available?

Yes — Korea Ever-Power provides OEM trademark services. Customer logo and part number marking can be applied to the gear web, bore, or hub face by stamping, engraving, or laser marking. Specify the required marking format and location on the drawing. Contact our team with the drawing and marking requirements to begin the quotation process.

"We manufacture overhead crane hoisting gearboxes and switched the main reduction stage from single to double helical gears sourced from Korea Ever-Power in 42CrMo, quenched and tempered. The bearing temperature in the hoisting drum shaft bearing dropped after eliminating axial thrust from the gear stage. Mass production delivery was within 18 working days for our first batch of 40 gear sets."

Kim Tae-young  |  Gearbox Design Engineer, Incheon Crane Systems Manufacturing  ·  Q2 2026

"We supply reversing hot rolling mill pinion stands and require double helical gears at ISO 1328 grade 8 in 40CrNiMoA. Korea Ever-Power produced to our drawing with OEM marking. No axial displacement of the pinion housing has been observed since conversion from single helical — the issue that caused the original conversion specification."

Lee Dong-woo  |  Rolling Mill Equipment Manager, Pohang Steel Machinery  ·  Q4 2025

"We build marine main reduction gearboxes for fishing vessels and needed double helical gears in cast steel at a competitive price with a short lead time. Korea Ever-Power quoted within 24 hours and delivered 15 working days after drawing confirmation. The OEM marking was applied to the gear web as specified. We have since placed three production orders."

Park Hyun-sik  |  Procurement Manager, Busan Marine Gearbox Manufacturing  ·  Q1 2026

"We used Korea Ever-Power's design service for a double helical gear set in a new electric motor test stand — no previous design existed. They calculated the gear geometry from our input/output parameters, produced the drawing, and had it approved within our engineering review cycle. The prototype gears matched the drawing dimensions at incoming inspection."

Choi Ji-woo  |  Test Equipment Engineer, Gyeonggi Motor Testing Systems  ·  Q3 2025

"We source double helical gears in 20CrNiMo for electric vehicle reduction units. The 15–18 working day mass production lead time fits our monthly production programme. Korea Ever-Power confirmed the helix angle on our drawing was within their hobbing capability before accepting the order — no surprises at delivery."

Yoon Sang-min  |  Component Sourcing Engineer, Seoul EV Drivetrain Co.  ·  Q2 2025