In steel rolling production, the roller, as a key tool that directly contacts the rolled piece and causes plastic deformation of the metal, has its selection and parameter design directly affecting the stability of equipment operation, product quality, and the cost per ton of steel. This article starts from the basic structure of the roller and, in combination with the actual application requirements in the production site, analyzes the main parameters of the roller, with the aim of providing reference for equipment management personnel and procurement technicians.
I. Basic Structure and Classification of Rollers
Three parts constitute a roller: the roller body, the roller neck, and the roller head. The roller body contacts the rolled piece and induces plastic deformation in the metal. The roller neck supports the roller within the bearing and transfers the rolling force to the frame via the bearing housing and the screw-down device. Meanwhile, the roller head connects to a coupling to transmit the rolling torque.
According to their uses, rollers can be classified into plate and strip rolling mill rollers, section steel rolling mill rollers, and special rolling mill rollers. For plate and strip mills, engineers design the cylindrical roller body with specific profiles based on the rolling conditions. For instance, they make it slightly concave for hot rolling to compensate for thermal expansion, slightly convex for cold rolling to counteract bending deflection, or shape it with special curves like CVC for advanced control. The roller body of section steel rolling mills incorporates machined grooves (hole shapes) to enable the production of different sectional profiles. For specialized applications, piercing mills, wheel rolling mills, and cross wedge rolling mills utilize custom-engineered rollers tailored to their unique forming processes.
II. Main Parameters of Rollers and Their Determination Principles
2.1 Parameters Related to Roller Diameter
Roller diameter involves four concepts: nominal diameter, working diameter, maximum diameter, and minimum diameter:
Nominal diameter (nominal size): It refers to the marked size of the roller, which matches the center distance of the gear seat in the roughing mill.
Working diameter: It is the diameter of the part that actually contacts the rolled piece during rolling. For section steel rolling mills, the working diameter is the bottom diameter of the groove; for plate and strip rolling mills, it is the equivalent diameter of the rolling area.
Maximum diameter: It is the initial diameter when a new roller is put into use.
Minimum diameter: It is the lowest diameter allowed for use after multiple regrinding and repair of the roller.
When determining the roller diameter, engineers should follow these principles: First, they must limit the ratio of the nominal diameter to the working diameter to generally no more than 1.4 to prevent excessive groove penetration. Second, the diameter must satisfy the maximum bite-in angle requirement, expressed as D₁ ≥ Δh/(1-cosα), where Δh represents the reduction and α the bite-in angle. Additionally, they should perform a strength check on the roller.
2.2 Roller Body Length and Its Ratio to Diameter
The determination of the roller body length (L) mainly depends on the number of groove arrangements, strength conditions, and empirical data. The L/D ratio range for different types of rolling mills is as follows:
Roughing mill: 2.2~2.7.
Section steel rolling mill: 1.5~2.5.
Billet and roughing mill stands: 2.2~3.0.
Finishing mill stands: 1.5~2.0.
The design sequence for plate and strip rolling mills is to determine the roller body length first and then the diameter. The roller body length is determined by L = b_max + a, where b_max is the maximum width of the rolled plate, and a is the allowance, which varies from 50mm to 400mm depending on the width range.
2.3 Determination of Roller Neck Size
The ratio of the roller neck diameter (d) to the roller body diameter (D) (d/D) varies according to the type of bearing and the category of the rolling mill. Taking sliding bearings as an example:
Roughing mill: d/D = 0.55~0.7, l/d ≈ 1.0
Two-high section steel rolling mill: d/D = 0.6~0.7, l/d ≈ 1.2
Medium and heavy plate rolling mill: d/D = 0.67~0.75, l/d = 0.83~1.0
Two-high thin plate rolling mill: d/D = 0.75~0.8, l/d = 0.8~1.0
The selection of roller neck size should take into account the bearing load capacity and the strength of the roller to avoid the risk of fracture due to an overly thin roller neck.
2.4 Form of Roller Head
The form of the roller head is determined based on the connection method and the requirements of the transmission torque. Common forms include cylindrical, conical, and stepped. The selection should ensure a smooth connection and sufficient transmission torque. Roller heads are used to transmit torque, and common forms include star-shaped shaft heads, universal shaft heads, shaft heads with keyways, cylindrical shaft heads, and shaft heads with platforms. The choice of form depends on the transmission method and space constraints.
III. The Impact of Roller Parameters on the Production Process
3.1 The Influence of Diameter Parameters on the Biting Conditions
The diameter of the roller directly affects the size of the biting angle. Under the condition of a certain reduction, increasing the diameter of the roller can reduce the biting angle and improve the biting conditions. This is particularly important for the initial rolling and roughing passes, as it can reduce the slipping phenomenon and improve the stability of the rolling process.
3.2 The Influence of Roller Body Length on Plate Shape Control
For plate and strip rolling mills, the ratio of the roller body length to the diameter (L/D) reflects the rigidity of the roller. When the L/D ratio is too large, the roller is prone to bending deformation under the action of the rolling force, affecting the uniformity of the plate thickness in the transverse direction. In this case, the rigidity conditions can be improved by increasing the diameter of the work roller or using support rollers.
3.3 The Influence of Roller Profile Curve on Plate Shape
A slightly concave profile of the hot-rolled roller body can compensate for the thermal expansion of the roller, while a slightly convex profile of the cold-rolled roller body can compensate for the bending deformation during rolling. Special curve-shaped rollers such as CVC can continuously adjust the shape of the roll gap through axial movement. Reasonable roller profile design is an important means to control plate shape and reduce the transverse thickness difference.
3.4 The Influence of Roller Neck Size on Bearing Capacity
The roller neck, as the supporting part of the roller, its diameter directly determines the bearing capacity of the bearing and the fatigue life of the roller. Insufficient roller neck size will lead to an increase in contact stress, accelerate fatigue failure, and in severe cases, cause fracture accidents.
IV. Technical Suggestions for Roller Selection
Based on the above analysis, in the process of roller procurement and use, the following aspects should be given priority:
Clarify working conditions: Provide detailed rolling parameters to the supplier, including rolling force, rolling temperature, rolling speed, reduction, and product specifications, so that they can carry out targeted roller profile design.
Check key ratios: According to the type of rolling mill, verify whether the L/D ratio and d/D ratio are within a reasonable range to avoid quality problems caused by insufficient rigidity.
Pay attention to roller neck strength: For repaired rollers, confirm whether the diameter of the repaired roller neck meets the bearing requirements, and perform strength calculations if necessary.
Record usage data: Establish a roller usage file. Record the steel passing volume. Document the wear volume. Note the roll change cycle. Identify the failure mode. These records provide data support for subsequent selection.
Conclusion
Roll parameters directly affect rolling stability. They also impact production costs. Therefore, equipment managers must master their meanings. Understanding parameter interrelationships is equally important. Selection should reflect actual working conditions. This ensures both efficiency and economic returns.