A four-high rolling mill consists of two work rolls and two backup rolls. The work rolls make direct contact with the metal and perform the rolling operation, while the backup rolls support the work rolls from the outside. This support reduces work roll deflection under rolling loads and improves roll gap stability and product dimensional accuracy.
Four-high rolling mills are widely used for producing steel plates, steel strips, and non-ferrous metal sheets and strips, including aluminum and copper products.
Depending on the roll drive arrangement, roll configuration, and production line layout, four-high rolling mills can be designed in different ways. It is important to distinguish between these categories. A driven four-high mill and a four-high tandem mill are not necessarily separate structural types. They describe different aspects of the drive configuration and production arrangement.
Conventional four-high rolling mills
A conventional four-high rolling mill consists of two work rolls and two backup rolls arranged vertically. The upper and lower work rolls form the roll gap through which the metal passes and undergoes plastic deformation under rolling pressure.
The two backup rolls are positioned outside the work rolls. They support the work rolls and reduce elastic deflection under rolling loads. This additional support helps maintain a stable roll gap under relatively high rolling forces, making it easier to control strip thickness and flatness.
Main components
The main components of a conventional four-high rolling mill include:
Work rolls: Directly contact the metal, apply rolling pressure, and control product thickness and surface condition.
Backup rolls: Support the work rolls, reduce deflection caused by rolling forces, and improve the stiffness of the roll system.
Roll bearings and chocks: Support roll rotation and maintain the correct roll positions within the mill housing.
Mill housing and screwdown mechanism: Withstand rolling loads and adjust the distance between the upper and lower work rolls to control the roll gap.
Main drive system: Transmits power to the rolls through motors, reducers, pinion stands, and drive spindles.
Typical applications
Four-high rolling mills are widely used in the production of steel plates, cold-rolled strip, hot-rolled strip, and non-ferrous metal products such as aluminum and copper sheets and strips.
In cold rolling, the relatively small work roll diameter allows significant thickness reduction, while the backup rolls provide the necessary support and stiffness.
In heavy plate hot rolling, the backup rolls help reduce work roll deflection and improve transverse thickness distribution across the plate.
Four-high rolling mills can be designed for reversing or non-reversing operation, depending on the rolling process and production line configuration.
Actively driven four-high rolling mills
Actively driven four-high rolling mills are classified according to their roll drive arrangements. Depending on the design, power can be transmitted to different rolls rather than following only one standard drive configuration.
It is worth noting that conventional four-high rolling mills also normally have powered work rolls. The term actively driven four-high mill should therefore be understood in the context of its specific drive arrangement rather than simply as a mill equipped with an electric motor.
Roll drive arrangements
Depending on the transmission design, four-high rolling mills can use the following drive configurations:
Work roll drive: The motor transmits power through a reducer, pinion stand, and drive spindles to rotate the upper and lower work rolls. The backup rolls rotate through frictional contact with the work rolls. This is a common drive arrangement for four-high rolling mills.
Backup roll drive: Power is transmitted to the backup rolls, which then drive the work rolls through frictional contact. Whether this arrangement is suitable depends on roll diameters, friction conditions, and rolling loads.
Combined drive: Both work rolls and backup rolls have dedicated power transmission paths according to the mill design. Different drive combinations can be used to meet specific rolling requirements.
Each arrangement requires consideration of gear transmission design, roll diameters, contact conditions, and torque requirements. Mill performance cannot be judged solely by the number of driven rolls.
Specialized actively driven four-roll mills
In addition to the drive arrangements used in conventional sheet and strip rolling mills, specialized actively driven four-roll precision mills are available for producing shaped metal wire.
These machines differ from conventional four-high mills with two work rolls and two backup rolls. Their four rolls are arranged around the material, with the roll surfaces working together to form the required rolling pass profile.
For example, some designs use two actively driven upper and lower rolls, while the two lateral rolls operate as driven or idler rolls depending on the machine configuration.
The upper, lower, and lateral rolls work together to control material deformation and the final cross-sectional shape. By adjusting roll positions and pass geometry, the machine can produce shaped wire with specific cross-sectional profiles.
The lateral rolls provide side forming and dimensional control. Their function is not limited to preventing axial movement of the upper and lower rolls.
Four-high tandem rolling mills
A four-high tandem mill consists of multiple four-high rolling stands arranged in sequence. The stands work together to reduce material thickness or form the required cross-section through successive rolling passes.
Compared with a single-stand four-high mill, a tandem arrangement distributes the total reduction across multiple stands. This reduces the reduction required at each individual stand and supports higher production capacity through continuous rolling.
Equipment structure and drive configuration
A four-high tandem mill consists of several rolling stands, each containing two work rolls and two backup rolls.
Each stand is generally equipped with a corresponding drive motor, reducer, gear transmission mechanism, and drive spindles. The electrical control system coordinates the speed, torque, and tension of the stands so that the strip can pass continuously through the entire mill.
The main equipment includes:
Multiple four-high rolling stands.
Independent or combined main drive systems configured according to the mill design.
Entry and exit coilers or other material handling equipment.
Interstand tension measurement and control systems.
Hydraulic screwdown and Automatic Gauge Control systems.
Lubrication, cooling, and auxiliary conveying equipment.
Main process characteristics
Each stand performs a specific part of the rolling process. The entry stand carries out the initial thickness reduction, while subsequent stands continue reducing the strip thickness. The finishing stand controls the final dimensions and surface quality according to product requirements.
Since the stands operate continuously, their speeds and strip tension must remain properly coordinated. A speed mismatch between adjacent stands can cause tension fluctuations, strip wandering, or even strip breakage.
Typical applications
Four-high tandem mills are mainly used in metal sheet and strip production lines requiring high output and continuous rolling. Typical materials include carbon steel, stainless steel, and certain non-ferrous metal strips.
Compared with a single-stand reversing mill, a tandem mill is more suitable for high-volume continuous production. However, it also requires greater equipment investment, more complex automation, and a more comprehensive production line configuration.
Four-roll linked rolling mills
The term four-roll linked rolling mill needs to be understood in the context of the specific equipment design. It is not a universally recognized structural classification that stands independently alongside conventional four-high and actively driven four-high rolling mills.
When several four-high rolling stands are connected in sequence to reduce material thickness through successive stands, the more precise term is a four-high tandem mill or four-high tandem cold rolling mill.
When the equipment contains only one four-high stand, it should generally be described as a four-high rolling mill, with further details provided about its drive arrangement, reversing capability, and intended products.
When preparing equipment specifications, purchasing documents, or production line proposals, the stand quantity, roll configuration, main drive arrangement, and rolling process should be clearly stated. The term four-roll linked rolling mill alone is insufficient to define the actual equipment.
Selection criteria for four-high rolling mills
Selecting a four-high rolling mill requires consideration of the material, product specifications, production capacity, and equipment layout. Different roll configurations and drive arrangements have different load capacities, operating characteristics, and investment requirements.
The main selection factors include:
Rolling material: Identify whether the mill will process carbon steel, stainless steel, aluminum, copper, or other metals, taking their strength and deformation characteristics into account.
Product specifications: Determine the work roll and backup roll dimensions according to finished product thickness, width, cross-sectional shape, and surface quality requirements.
Rolling capacity: Calculate the maximum rolling force, main motor power, transmission torque, and rolling speed.
Production method: Select between single-stand reversing rolling and multi-stand continuous rolling according to production volume and capacity requirements.
Drive arrangement: Determine whether work roll drive, backup roll drive, or a combined drive configuration is required.
Automation configuration: Select hydraulic AGC, roll bending, and online inspection systems according to thickness and flatness accuracy requirements.
Four-high rolling mills contain various precision mechanical components in their work rolls, backup rolls, and drive systems. We provide drawing-based custom machining for shafts, connecting components, sleeves, locating parts, and equipment mounting structures used in different rolling mill configurations.
Hansheng Automation manufactures non-standard precision components according to customer drawings. Our machining services also cover components for tobacco and packaging machinery, filling equipment, yacht systems, and remote-controlled racing cars. Parts are manufactured according to the specified dimensional and assembly requirements.
