Rolling Mill Double Helical Gear – 42CrMo, 50-55 HRC, OEM

Rolling mill double helical gears are among the most demanding applications in industrial gear manufacturing. A rolling mill pinion stand — the gearbox that distributes the main drive motor torque equally to two or more work rolls — must transmit very high torque continuously, absorb the shock load when the workpiece enters the roll gap, and do so in both the forward and reverse rolling directions. The double helical (herringbone) tooth form is the standard choice for rolling mill drives precisely because it eliminates the axial thrust that single helical gears would impose on the mill housing and roll chocks.

Korea Ever-Power produces rolling mill double helical gears in 42CrMo (internationally known as AISI 4140 / JIS SCM440 / DIN 42CrMo4) with hardening and tempering heat treatment to achieve 50–55 HRC tooth surface hardness. Module and tooth count are custom to the customer's drawing; gear milling or hobbing manufacturing method; tooth grinding optional. OEM marking and wooden case transport packaging. Can be produced as assembly parts (two-piece herringbone) or as a single integral gear.

Hot Strip Rolling Mills

Pinion stands in hot strip roughing and finishing mills. The double helical form eliminates axial thrust from the work roll drives; 42CrMo at 50–55 HRC provides pitting resistance at the sustained high contact stresses of hot strip rolling.

Cold Rolling Mills

Pinion stands in cold rolling mills for strip, sheet, and coil. Cold rolling generates higher roll separating forces per unit of strip width than hot rolling — the tooth load in cold mill pinion stands is severe, and the 50–55 HRC tooth surface is required to achieve adequate pitting life at these contact stresses.

Plate Mills and Section Mills

Pinion stands in heavy plate mills and structural section mills. The reversing nature of plate and section rolling — where the workpiece is passed back and forth through the rolls — makes the zero-thrust property of the double helical gear particularly important, as axial thrust direction reverses with roll direction.

Marine Machinery

Main reduction gearboxes and deck machinery drives in marine vessels. 42CrMo at 50–55 HRC with wooden case transport packing for protection during sea freight transit. OEM marking for marine equipment builders who brand their drivetrain components.

Agricultural Machinery

Heavy-duty agricultural drive gearboxes in combine harvesters and large tractors where the 42CrMo at 50–55 HRC specification provides higher surface hardness than the induction-hardened 40–45 HRC agricultural series — appropriate for the highest-load agricultural drive stages.

General Heavy Machinery

Any heavy industrial gearbox application where 42CrMo at 50–55 HRC, double helical form, and wooden case transport packing are specified. Custom module and tooth count to drawing; OEM marking available.

What is the difference between high-frequency quenching and furnace carburising for rolling mill gears?

High-frequency (induction) quenching heats only the surface of the tooth by electromagnetic induction to above the austenitising temperature, then quenches rapidly — producing a hard surface (50–55 HRC in 42CrMo) over a tough, less fully hardened core. Furnace carburising introduces carbon into the tooth surface by diffusion at elevated temperature, producing a hardened case (58–62 HRC) over a tough low-carbon alloy steel core. The key practical difference is the hardening depth: induction quenching achieves 1–4 mm effective case depth; carburising achieves 0.8–3 mm. For large-module rolling mill gears, the larger tooth section means more heat input is required to achieve adequate depth by induction quenching than carburising. Korea Ever-Power confirms the appropriate hardening process for each specific gear size and tooth geometry at the drawing review stage.

Should rolling mill pinion stand gears be two-piece assembly or integral single piece?

Both are valid configurations for different situations. Two-piece assembly gears allow each helical half to be hobbed separately (which is simpler and potentially achieves higher accuracy than milling a narrow-groove integral herringbone), and allow independent replacement of each helical half — useful in a reversing mill where one side may wear faster than the other. Integral single-piece gears are more compact, eliminate the assembly interface, and have no risk of fretting between the two halves under reversing load. The choice is typically driven by the original mill design's housing arrangement — provide the existing drawing or worn sample and Korea Ever-Power will produce in the same configuration.

Is tooth grinding available for rolling mill double helical gears?

Tooth grinding is available on request and is noted as an option on the specification table. For two-piece assembly configurations, tooth grinding of each helical half before assembly is straightforward and confirms the highest accuracy achievable. For integral herringbone configurations, tooth grinding is limited by the central groove width — the grinding wheel must pass through the groove without fouling the opposite tooth set. Specify the required accuracy grade on the drawing and Korea Ever-Power will confirm whether grinding is feasible for the specific configuration and what accuracy grade is achievable.

Can other alloy steels besides 42CrMo be used for rolling mill gears?

Yes — all grades in the cross-reference table above are available. For rolling mill gears that require higher core toughness than 42CrMo provides (for example, in mills with severe biting shock loads), 40CrNiMoA (ASTM 4340) provides higher impact energy after hardening and tempering at comparable surface hardness. For carburised rolling mill gears at 58–62 HRC, 20CrNiMo or 20CrMnTi are the standard case-hardening grades. Specify the required material grade or the required hardness and toughness combination and Korea Ever-Power will confirm the material recommendation.

What transport packing is used for rolling mill gears?

Rolling mill double helical gears are packed in wooden cases for transport. The wooden case is designed to support the gear without contact between tooth flanks and the case walls, preventing fretting damage during sea freight transit. For precision-ground tooth flanks (where the surface finish must be maintained), additional protective wrapping of the tooth surfaces is applied inside the wooden case. Contact our team with your drawing and we will confirm the packing design for the specific gear size and transit route.

"We maintain hot strip finishing mill pinion stands and needed 42CrMo double helical gears at 50–55 HRC as two-piece assembly configuration. Korea Ever-Power produced each helical half with hobbing and confirmed the hardness at every tooth by portable Rockwell tester before assembly. Wooden case packing arrived undamaged after sea freight from China to South Korea — tooth flanks showed no transport fretting at incoming inspection."

Kim Byeong-su  |  Rolling Mill Maintenance Manager, Pohang Hot Strip Plant  ·  Q1 2026

"We supply cold rolling mill pinion stands to flat product producers and qualify 42CrMo double helical gear sets from Korea Ever-Power. The two-piece assembly configuration allows us to replace only the worn helical half at service intervals, reducing replacement cost by approximately 40% compared with replacing the full integral herringbone. OEM marking confirmed to our part number on all deliveries."

Lee Sang-cheol  |  Drivetrain Engineer, Incheon Cold Rolling Equipment Co.  ·  Q4 2025

"We manufacture plate mill reversal gearboxes. The reversing load direction in plate milling makes axial thrust management critical — any axial float in the single helical alternative causes housing wear. Korea Ever-Power's 42CrMo double helical gears at 50–55 HRC eliminated the axial float issue that we experienced with a previous supplier's single helical configuration. Three years of operation without a pinion stand housing wear incident."

Park Tae-kyun  |  Heavy Rolling Equipment Design Lead, Gwangyang Plate Mill Systems  ·  Q2 2026

"We needed tooth grinding on a two-piece 42CrMo rolling mill herringbone gear set for higher accuracy in a new finishing mill. Korea Ever-Power confirmed grinding was feasible on each half separately before assembly, produced to the required accuracy grade, and provided the dimensional inspection report. The gear noise at operating speed was the lowest we had measured in this mill generation."

Choi Hyeon-min  |  Precision Rolling Systems Engineer, Ulsan Steel Equipment Manufacturing  ·  Q3 2025

"We source 42CrMo double helical gears for marine reduction gearboxes. The wooden case packing is required by our freight insurer for large steel gears during sea freight. Korea Ever-Power provided the packing specification confirming the tooth flank protection arrangement, which satisfied the insurer's requirement without additional survey. OEM marking applied to hub face as specified."

Yoon Sang-wook  |  Marine Gearbox Procurement, Busan Shipbuilding Equipment Co.  ·  Q1 2025