Three-Roll Hot Rolling Mill Overview
A three-roll hot rolling mill is a type of rolling mill used in metallurgy to reduce the thickness and change the shape of metal workpieces at high temperatures.
How it Works:
Roll Arrangement: The three rolls are typically arranged in a vertical stack: top, middle, and bottom.
Passage of Material: The hot metal workpiece (e.g., a billet or slab) is fed into the gap between the rolls.
In a "three-high" configuration, the material can pass through one gap (e.g., between the bottom and middle roll) and then, after the direction of the rolls is reversed, pass back through the other gap (between the middle and top roll). This allows for multiple passes without having to transport the material back to the entry side.
Hot Rolling: The process occurs at temperatures above the recrystallization temperature of the metal. This makes the metal more ductile and easier to deform, requiring less force and allowing for greater reductions in thickness per pass.
Key Components:
Rolls: Made of special alloys to withstand high temperatures and immense pressure. They are precisely machined to achieve the desired shape and surface finish on the workpiece.
Roll Stands: Robust structures that house the rolls and bearing assemblies, ensuring their precise alignment.
Screw-Down Mechanism: Used to adjust the gap between the rolls, thereby controlling the final thickness of the rolled product. This can be hydraulic or electromechanical.
Drive System: Powerful motors and gearboxes that rotate the rolls at controlled speeds.
Entry/Exit Guides: Direct the workpiece accurately into and out of the roll gap.
Cooling Systems: To manage the temperature of the rolls and the surrounding equipment.
Run-out Table: A long conveyor system where the hot, rolled product cools down.
Advantages of a Three-Roll Mill:
Reversing Capability: As mentioned, the ability to reverse the material's direction and use both upper and lower roll gaps for successive passes. This reduces material handling and increases efficiency compared to single-direction two-high mills for certain applications.
Increased Reduction: Can achieve significant thickness reductions in fewer passes.
Versatility: Can be used for rolling a variety of products, including plates, sheets, and structural shapes.
Applications:
Three-roll hot rolling mills are commonly used in the production of:
Steel plates and sheets
Beams and structural sections
Rails
Large bars and rods
