Engrenage à double hélice pour machines lourdes — Flanc de dent en acier moulé à denture douce, QT, classe ISO 8–9

Heavy Machinery Double Helical Gear — Overview

When a gear is large enough that the blank weight approaches or exceeds five tonnes, the forging route that is standard for small and medium industrial gears becomes impractical or prohibitively expensive. The largest gears in the world — ball mill ring gears three metres in diameter, cement mill main pinions with face widths of 700mm, ship propulsion gears transmitting 20,000+ kW — are manufactured from cast steel blanks, where the complexity of the part's final shape can be incorporated into the mold rather than laboriously machined from a forged cylinder. Korea Ever-Power Worm Gear Co.,Ltd supplies heavy machinery double helical gears in custom cast steel grades, quenched and tempered to a soft tooth flank condition, hobbed to ISO grade 8–9 accuracy, for the most demanding large-scale industrial drive applications.

The double helical (herringbone) tooth form is particularly well-suited to heavy machinery applications because it eliminates the axial thrust force that a single helical gear of equivalent size and helix angle would transmit to the shaft and bearings. For a large mill drive gear transmitting several megawatts, this axial force would be substantial — requiring large, expensive thrust bearings or roller-type spherical bearings at both ends of the gear shaft. The double helical configuration removes this requirement entirely, allowing simpler bearing arrangements in very large gearbox housings where bearing accessibility and replacement cost are significant lifecycle concerns. Korea Ever-Power's heavy machinery double helical gears are custom-manufactured to each client's drawing — module, tooth count, helical angle, pressure angle, face width, bore, and keyway dimensions are all specified by the customer. International steel grade cross-reference is supported for customers specifying materials in ASTM, DIN, JIS, or ISO standards.

Spécifications techniques

Product Specifications — Heavy Machinery Double Helical Gear

Common Cast Steel Alloy Grade Equivalents

Why Cast Steel for Very Large Double Helical Gears

The threshold above which cast steel becomes more practical than forged steel for gear blanks is approximately 2–5 tonnes finished weight, depending on the gear body geometry. Below this threshold, forging produces superior grain alignment and fatigue resistance and is preferred for all high-cycle, safety-critical applications (railway, aerospace, offshore). Above this threshold, forging press capacity, handling, and economics favor casting — particularly for double helical gears, where the herringbone tooth geometry adds complexity to an already large blank.

Cast Steel Advantages for Large-Scale Gear Production

• ◈ Complex geometry in one pour: Hub bores, web lightening pockets, spoke patterns, and mounting flanges can be incorporated into the casting mold — eliminating multiple roughing operations that would be required on a forged blank. For large ring gears with integral flanges, casting reduces rough machining time by 30–50%.
• ◈ No forging press tonnage limitation: The largest hydraulic forging presses produce blanks up to approximately 150 tonnes. Cast steel gear blanks can be produced in sizes far exceeding this limit — ball mill ring gears above 1,000 tonnes finished weight exist in large grinding mill installations.
• ◈ Cost-effective for slow-speed high-torque drives: Large slow-speed gears in mills and ships operate at pitch-line velocities of 1–10 m/s, where dynamic load amplification is low. Cast steel at ISO grade 8–9 accuracy is adequate for these operating conditions at significantly lower unit cost than forged and ground alternatives.

Soft Tooth Flank QT — The Right Hardness for Large Mill Drives

Large ball mill and cement mill gears operate in a particularly forgiving load condition compared with railway or aerospace gears: slow rotational speed (5–20 RPM at the mill), high torque, and a moderate number of total load cycles over the mill's 20-year operational life. A soft tooth flank at HB 220–280 (quenched-and-tempered cast steel) is adequate for this duty cycle when the contact stress is checked against the ISO 6336 allowable limits for the HB range. The soft tooth flank also offers the run-in conforming characteristic that helps large gears — where manufacturing geometric accuracy is harder to achieve than for small precision gears — distribute load across the full face width during the initial operating period.

Forged vs Cast Blank Selection for Large Double Helical Gears

Core Engineering Advantages of Heavy-Duty Double Helical Gears

Heavy Industry Application Scenarios

Ball Mill and SAG Mill Main Drives

Large grinding mills in the mining and cement industries use a ring gear (bolted to the mill shell) driven by a pinion gear on the motor-gearbox output shaft. These ring gears reach diameters of 8–14 metres and face widths of 600–1,200mm. The double helical form is standard for the largest mills because the zero-thrust characteristic eliminates the heavy-duty thrust roller bearing assemblies that single helical equivalents would require. Korea Ever-Power supplies replacement pinion gears and ring gear segments for these drives — dimensioned to match the mating gear's existing geometry for drop-in installation during planned mill maintenance stops.

Ship Propulsion Reduction Gearboxes

Large marine vessels use double helical reduction gears to reduce turbine or high-speed diesel engine output to propeller shaft speed. The double helical form is preferred in marine gearboxes because it eliminates axial forces that would otherwise transmit through the hull structure from the propeller shaft line through the gear mesh. Cast steel double helical gears in marine service must meet classification society requirements (Lloyd's, DNV, ABS, BV) for material specification, non-destructive testing, and inspection — Korea Ever-Power provides the supporting documentation package. For an overview of all gear types supplied, visit the fabricant d'engrenages hélicoïdaux Page d'accueil de Korea Ever-Power.

Offshore Winch and Crane Drives

Offshore platform anchor winches, crane main hoists, and mooring capstan drives use large gear reducers where the double helical configuration provides smooth torque delivery under variable loading from wave-induced catenary tension variations. The soft tooth flank in QT cast steel tolerates the occasional shock loads from sudden tension changes without brittle fracture, while the high contact ratio of the double helical form reduces the per-cycle fatigue damage from each load application during the tens of millions of cycles accumulated over a platform's operational life.

Types d'équipements de Corée Ever-Power

Beyond heavy machinery engrenages à double hélice, Korea Ever-Power's manufacturing capability covers the full range of gear types needed in large industrial and marine drive systems:

• ⬡ Engrenage hélicoïdal simple : For large industrial parallel shaft drives at moderate pitch-line velocities where axial thrust is manageable. Full range at our engrenages à denture hélicoïdale catalogue.
• ⬡ Engrenage droit : Large-module spur gears for slow-speed, low-noise-requirement industrial drives — kiln drives, conveyor drives, and mixer drives in heavy process industries.
• ⬡ Engrenage conique : Right-angle shaft drives for large industrial machinery where helical bevel (spiral bevel) gears combine smooth engagement with the compact right-angle configuration.
• ⬡ Engrenage à vis sans fin : High-ratio compact drives for industrial positioning and locking mechanisms. The engrenage à vis sans fin range covers large center distances for heavy industrial use.
• ⬡ Couronne dentée interne : Large internal ring gears for planetary mill drives and epicyclic reducers used in compact high-ratio industrial gearboxes.

For heavy industrial clients requiring a fully assembled boîte de vitesses hélicoïdale rather than individual gears, Korea Ever-Power also provides complete gearbox units. Contact our engineering team with your torque, ratio, shaft configuration, and duty cycle data for a tailored supply recommendation.

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