Conception

33 TONS: manufacturing of an exceptional SPEED reducer for a circular rolling mill

Intended for a steel industry player based in Italy, MERGER manufactured the power transmission components of a circular rolling mill including a main reducer of 33 tonnes and two cone reducers of 10 tonnes each.

100% MERGER design for an Italian steel industry player

CONTEXT

characteristics

STRESS

management

manufacturing-reducer-heavy-industry-steel-rolling-mill

MERGER designed, assembled and tested in its Corbas workshop a mechanical transmission system with a total mass of 53 tonsThis equipment includes 2 cone reducers of 10 tonnes and a main reducer of 33 tonnes is intended for the modernization of a radial-axial circular rolling mill operated by an actor in the steel industry based in Italy.

Restructuring the drive train of a rolling mill: the client's industrial challenges

The steelmaker has begun restructuring its drivetrain to meet three main objectives:

Evolving the infrastructure for allow hot rolling of steel crowns diameters higher, an operation requiring a significant increase in the applied torque.
Limit the diversity of rooms spare parts stored on site by imposing a single type of motorization for the entire process (exclusive use of ABB M3BP 400 type electric motors, each developing 630 kW).
Eliminate the risk of unplanned downtimeIn steelmaking, a transmission failure in a hot flow leads to the cooling of metal blanks, raw material losses, and increased costs. Compliance had to be 100% factory validated before shipment as part of immediate commissioning.

I would like to discuss my specifications

A technical challenge: the specific features of MERGER gearboxes

The rolling mill initially receives a thick, small-diameter, circular blank of raw steel. This solid piece is heated to a high temperature to make it malleable. The main roller then exerts continuous pressure on the wall of this rotating ring. Under the effect of this mechanical force, the steel is crushed, stretched, and thinned. The material expands outwards. This mechanical rolling thus increases the final diameter of the ring while reducing its thickness, in the same way that a ring of dough is enlarged by rolling it. To withstand the mechanical stresses induced by the application, our teams had to install axial load-bearing stops. Particular attention was paid to their sizing.

Location and function of the 33-tonne main reducer

Le reducer principal ensures the training of the central lamination. Its function is to transmit the power required to deform and stretch a hot steel ring.

This power is obtained by coupling two ABB M3BP 400 motors, each developing 630 kW. Operating simultaneously, the power total at the entrance of reducer is 1230 kW.

Kinematics and dimensioning of the main gearbox

Cinematics:

Architecture: Parallel input dual-shaft system (Dual-Input / Single-Output).
Reduction stages: 4-gear train configuration.
Power flow: Both pinions "high speed" entrance receive power from both engines. They mesh on a common intermediate gear to combine the torques. They then transfer this total power to thearbre "low speed".
Direction of rotation: Counterclockwise.

sizing

Exact reduction ratio: 80,248.
Rated power accepted: $2 \times 630\text{ kW}$ (i.e. a total installed capacity of 1,260 kW).
Suitability calculations: The MERGER design office performed the calculations of the geometry and tooth profiles using the software KISSsoft according to ISO 6336. A further study with the CETIM validated the resistance of the tree lines to constraints thermomechanical.

Mechanical characteristics and weight

Mechanical characteristics:

Gear material: 18CrNiMo7-6 steel is used. In metallurgical classification, this grade is by definition a special steel for case hardening. Its low carbon content (~0,18%) necessitates a surface carbon application (case hardening) followed by heat treatment (quenching) and a stabilizing tempering process to achieve the desired hardness/hardening ratio. These operations are commonly referred to as CTR (case hardening/quenching/tempering). These heat treatments are carried out after gear cutting but before the final grinding stage.

Connection and output interface: Hollow fluted shaft according to the standard DIN 5480 (N340 x 6 x 55 – 8H)This tree uses steel. 42CrMo4 treaty ( $R_e \ge 750\text{ MPa}$ ) with induction-hardened grooves at a minimum of 500 HV.
Guidance (Bearings): The shaft lines are supported by bearings. SKF of high capacity. They incorporate a C3 radial clearance to absorb the thermal expansions of the steel industry.
Lubrication and sealing: The system combines splash lubrication with forced lubrication from an external motor-pump unit with a duplex filter. O-rings on the covers and labyrinth seals at the shaft outlet ensure a watertight seal.

Weight:

Empty mass: Approximately 27,000 kg (27 tonnes).
Mass in running order: 33,000 kg (33 tonnes). This weight includes a full tank of lubricant, couplings, and accessories. This is the legacy most heavy built by MERGER in his workshop in Corbas (69).

heavy industry power transmission design

Gear transmission company in France, manufacturer, repairer, and maintenance specialist in the steel industry

The 10-tonne cone reducers

These two units (upper cone and lower cone) manage the legacy de power on the secondary and complementary geometric axes of the radial-axial process. They drive the cones which pinch and calibrate the steel on its end faces. They thus control the height of the crown while the reducer The main one increases its diameter.

These reducers are placed in the immediate periphery of the area of formingThey have an inclined position at $17,50^\circ$ relative to the ground level of the rolling millOne controls the upper training and the other controls the lower training. The two devices rotate in opposite directions.

Kinematics and dimensioning of cone reducers

Cinematics:

Architecture: Orthogonal combined reducer.
Reduction stages: 3-gear train configuration.
Power flow: The first entrance floor uses a couple spiroconic to change the direction of the motor input shaft by 90°. Then, two trains parallel bygears with teeth helical perform the main speed reduction.
Direction of rotation: Clockwise and counter-clockwise.

Dimensioning:

Exact reduction ratio: 19,104.
Rated power accepted: 630 kW per unit.
Nominal speeds: The device reduces the speed from 1,491 rpm at the input (ABB M3BP 400 motor) to 78 rpm at the output.
Suitability calculations: Modeling under KISSsoft guarantees the behavior of the teeth in the face of cycle reversals and penetration shocks on the steel blank.

Mechanical characteristics and weight of the 2 reducers

Mechanical characteristics:

Gear material: As for the reducer principalthe material for the teeth helical and spiroconic is of type alloy steel (CTR) case hardened, quenched, tempered and ground.
Connection and output interface: Rigid hollow shaft associated with a clamping collar (Shrink disc with bore $\emptyset378\text{ H7}$ This system ensures a friction bond without any keys. It eliminates mechanical play and is not subject to vibrations and load reversals.
Guidance (Bearings): The hollow shaft uses tapered roller thrust bearings SKF , taking up the axial thrust of the cone, and large spherical roller bearings (500 x 830 x 325) take over the radial forces.
Lubrication and sealing: A network of internal rigid pipes and injection manifolds spray pressurized oil directly to the points of engagement. Labyrinth seals protect the bearing housings from descaling water, scale, and other surrounding contaminants.

Weight:

Empty mass: Approximately 27,000 kg (8 tonnes).
Mass in running order: 10,000 kg (10 tonnes) per unit. This weight includes the lubrication unit, fluids, engine interface bracket and accessories (sensors, valve, etc.).

I request a quote

Photo gallery

cad-design-main-rolling-retrofit-main-reducer

sizing-kinematics-manufacturing-speed-reducer-variator-heavy-industry

company-merger-manufacturer-reducer-motoreducteur-francais

Interior speed reducer for heavy industry rolling mill

repair-manufacturing-retrofit-calculation-speed reducer-merger

circular rolling mill speed reducer foundry

custom-made speed reducer delivery - merger

Hot rolling: the principle of mechanical deformation

The machine initially receives a rough piece of steel (called a blank or rough ring), which is thick, tall, and has a small diameter. This massive piece is preheated to a very high temperature to make it malleable.

The rolling mill then uses the combined force of several cylinders to crush and stretch the metal:

Radial action (controlled by the main reducer): The main cylinder exerts continuous pressure on the outer wall of the rotating ring. Under this extreme mechanical force, the steel is crushed, thinned, and stretched. This action increases the final diameter of the crown.It's the same physical principle as when you widen a ring of dough by rolling it between your fingers: the thinner the wall becomes, the larger the diameter of the ring gets.
The axial action (managed by the cone reducers): As the diameter increases, two conical cylinders clamp the steel on its upper and lower faces. This action allows to precisely calibrate the height and flatness of the crownpreventing the metal from deforming uncontrollably under the pressure of the main cylinder.

For which finished product?

Thanks to this simultaneous double operation (radial and axial), the rolling mill transforms a compact block of metal into a crown or a large diameter steel ring, perfectly circular, with strictly controlled thickness and height.

These parts (seamless rolled crowns) are then used in high-tech industries to manufacture:

Very large bearings (for wind turbines or tunnels).
Connection flanges for tanks or pipelines.
Components for the aeronautics, rail or space sectors.

The technical constraints of this manufacturing process

Constraints related to the final application:

The hot rolling process for crowns creates a demanding working environment, particularly for transmission components:

Combined multidirectional forces: The process simultaneously applies loads on two distinct geometric axes. The gearboxes must absorb continuous radial forces during the ring thickness reduction, as well as permanent axial forces during the calibration of the end faces.
A regime of repeated mechanical shocks: The engagement of the thermal steel blank between the rolling cylinders causes instantaneous load peaks (penetration shocks) which are directly transmitted to the shaft lines and gears.
Difficult thermal conditions and pollution: The housings operate in the immediate vicinity of the metal in MERGER. They are subjected to strong thermal radiation, water spray related to the descaling process and an atmosphere saturated with scale, a highly abrasive iron oxide particle.

The architectural requirements of the specifications

The steelworks operator has formulated specific criteria with a view to standardizing its plant:

A unique engine constraint: The customer is restricted to the exclusive use of standardized ABB 630 kW electric motors.
A twin-engine architecture is mandatory: To achieve the required power of 1 260 kW on the main drive with these imposed motors, MERGER had to design a specific reducer with a double parallel input shaft incorporating a mechanical power summation system.
Precise reduction ratios: The devices had to adhere to strict kinematics, i.e., an exact ratio of 80,248 for the main reducer (4 reduction gears) and 19,104 for cone reducers (3 stages with 90° angle drive).
Zero defects before shipment: Because of the critical financial costs that a failure on a hot metal flow would entail, MERGER had to 100% validate the performance and durability of the gears on its factory test bench (vibrational, thermographic analyses and blue contact tests) before the delivery agreement.

I need a remanufactured

SKF quality bearings, gears, and Merger speed reducer

mechanical-sealing-lubricating-reducer-multiplier

The specific solutions proposed by our design office

To precisely meet the constraints of the Italian rolling mill, MERGER's design office studied all the constraints related to the specifications and proposed specific solutions validated by the client.

The implementation of a forced lubrication system: To dissipate the heat generated by the process and internal operation, each reducer is associated with an independent motorized lubrication unit, equipped with flow sensors, filters and oil cooling blocks.

A reinforced sealing system: To protect the internal mechanics from process water and scale, MERGER has implemented specific dynamic sealing systems (labyrinth seals and baffles) at the shaft outputs. The shaft outputs are thus protected by non-contact systems, preventing any contaminant from entering the bearings.

The choice of reinforced SKF bearings: The guidance is provided by high-capacity roller bearings from the catalog SKF (specifically the 22344, 22356, and 23264 series for the main gearbox). They were specifically selected with a C3 radial set in order to absorb significant temperature increases without risk of blockage or seizing of the balls/rollers.

Our service: from the initial study to the delivery of rolling mill gearboxes

The engineering phase, calculation notes and modeling

The project begins with an essential study phase to size equipment subjected to extreme torques and repeated shocks.

Gear strength calculations: MERGER's in-house design office used simulation software KISSsoft to model tooth profiles and calculate their resistance to fatigue and breakage according to the international standard ISO 6336. MERGER provided a calculation note for the entire project.

Co-validation of shock resistance: MERGER collaborated with expert engineers from CETIM (Technical Center for Mechanical Industries) to validate the mechanical resistance of the shaft lines and the absence of deformation of the housings with respect to load peaks during the penetration of the steel into the rolling mill.

Design of specific architectures: Our engineers have drawn up the overall plans for the parallel-axis twin-motor housing (main reducer) and the orthogonal housings (cone reducers).

Manufacturing, cutting and thermochemical treatments

Machining and gear cutting : All the gears were machined from a solid block of steel specifically used in metallurgy/steelmaking.
Heat hardening treatments : The sprockets underwent a case hardening-quenching cycle.
Final profile correction : After processing, the teeth are ground on high-precision machines to obtain perfect geometry and very low maximum roughness ( $R_a = 1,6$ This operation is particularly important to obtain smooth gear engagement, limit heat buildup and reduce vibrations.

manufacturing-assembly-mounting--gear reducer-rhone

professional deburring-company-industry-rhone-lyon-69-merger

Mechanical assembly and adjustment in the workshop

The assembly took place in our workshop in Corbas. One month was required from preparation to delivery for the main gearbox.

Bearing assembly: Installation of brand bearings SKF by thermal fitting. Tapered roller bearings for the input shaft of the cones and spherical roller bearings for the main gearbox. The bearings of the main gearbox benefit from a specific adjustment adapted to the thermal constraints of the steel industry.
Checking the reach of the teeth with blue: Before closing the casings, a mechanical contact test using Prussian blue is performed. This allows visual verification that the contact surface between the teeth is perfectly distributed across the entire width of the pinion.
Adjusting and closing the crankcases: The welded steel casings are assembled. The structural screws are of high quality. 12.9They are tightened to the nominal torque using controlled torque tools. All internal keys used undergo a treatment giving them a minimum hardness of 110 daN/mm².

Analysis and control

Before delivery authorization, each unit underwent a control protocol under no-load and load conditions to validate dynamic behavior.

Spectral analysis of vibrations: Accelerometers were used to measure the vibrational behavior of the gears and bearings to detect any meshing anomalies.
Thermographic monitoring: Thermal cameras monitor temperature changes at SKF bearings to validate the proper functioning of the lubrication circuit.
Hydraulic circuit control: MERGER tested the sealing of the covers (equipped with O-rings) and the shaft outlets (protected by labyrinth seals and baffles). The electrical indicators for filter clogging and the temperature probes of the forced lubrication system were tested and calibrated.

Protection and preparation before shipment

Manufacturer's technical file: MERGER has recorded all the control reports, the material certificates of the steels (18CrNiMo7-6 and 42CrMo4) and the test curves in the final technical file.
Protection and heavy transport: The reducers were drained, received a protective internal anti-corrosion treatment, and then painted (RAL 7041 color).

I want a contact at merger