What Is an Upper Roll Balance Device in Rolling Mills?

In most rolling mills—except certain stacked thin-sheet mills—an upper roll balance device is installed to stabilize the position of the upper roll assembly.

When no material is being rolled, the upper roll and its chock are affected by gravity, which can create clearances between mechanical components such as:

the roll chock and the screwdown screw
the screwdown screw and its threaded nut

These gaps may cause impact loads when the workpiece enters the roll gap, affecting rolling stability and potentially damaging equipment.

The upper roll balance device prevents this situation by applying an upward balancing force. This force keeps the upper roll chock in contact with the screwdown mechanism, eliminating thread clearance and reducing impact during biting.

In many rolling mills, the balance system also serves an additional function: assisting in lifting the upper roll during roll changes or adjustments.

Why Different Rolling Mills Use Different Balance Systems

The required type of upper roll balancing mechanism depends on the design and operating characteristics of the rolling mill.

For example:

Primary rolling mills or roughing millsoften have large roll travel and frequent, rapid adjustments. These mills commonly use counterweight or hydraulic balance systems.
Three-high section mills, where the upper roll movement is relatively small and rarely adjusted during rolling, typically use spring balancing devices.
Four-high plate or strip millsrequire a different approach due to their specific structural features, including:
- separate work rolls and backup rolls
- frictional transmission between rolls
- relatively small vertical travel of the upper roll

In such mills, hydraulic balancing systems are generally adopted. Additionally, work rolls and backup rolls must be balanced separately to ensure sufficient contact pressure between them during idle acceleration and deceleration, preventing roll slippage.

What Is a Spring-Type Roll Balance Device?

A spring balance device uses the elastic restoring force of mechanical springs to counteract the weight of the upper roll assembly.

This design is commonly used in:

vertical roll section mills
simple rolling mill configurations

Characteristics

Advantages

Simple mechanical structure
Reliable operation

Limitations

Suitable only for mills where the upper roll adjustment range is relatively small (typically 50–100 mm or less)
Springs must be manually removed during roll changes, making maintenance labor-intensive and time-consuming

What Is a Counterweight (Weight-Type) Balance Device?

A counterweight balance system uses heavy weights connected through levers and linkages to balance the upper roll.

This type is typically applied in primary rolling mills where the upper roll must move over a large vertical range.

Characteristics

Advantages

Reliable operation
Convenient maintenance

Limitations

Large overall equipment weight
The balancing force must be transmitted through mechanical lever systems

What Is a Hydraulic Roll Balance Device?

A hydraulic balance device uses the thrust generated by hydraulic cylinders to counteract the weight of the upper roll assembly.

The hydraulic system normally includes an accumulator, while the pump is used primarily to compensate for leakage and maintain system pressure.

Characteristics

Advantages

Compact structure
Convenient operation and control
Adjustable balancing force through cylinder pressure
Allows the upper roll to move vertically without being constrained by the screwdown mechanism
Facilitates roll changing operations

Limitations