Factors Affecting Roll Wear
Roll wear, which is a major factor in the performance of rolling mills and cold rolling processes, affects the grain structure and dimensional constraints of the rolled product. A roll’s lifespan is determined by the severity and type of roll wear and the number of rolling passes. As such, it is important to understand the factors that affect roll wear in order to ensure optimal mill performance and reduce waste.
Roll wear is typically caused by a combination of wear mechanisms, such as fretting and corrosion, abrasion, ploughing and deformation. The type and extent of wear depends largely on operating variables, such as roll material, roll profile and speed of the roll, as well as product properties, including hardness, thickness and lubrication.
Roll Material
Rolls can be manufactured from various materials, such as carbon steel, alloy steel, cast iron, tungsten carbide and ceramic. The choice of material depends heavily on the type of work, type of product and the mill’s requirements in terms of cost and performance.
Carbon steel rolls are the most common and cost-effective option for hot rolling processes. They are less likely to experience galling—a form of wear caused by adhesion between two surfaces—and are suitable for both the first and finishing stands of the rolling process.
Alloy steel rolls are a popular choice for cold rolling processes due to their superior wear resistance. Compared to carbon steel, alloy steel rolls can better withstand abrasion and damage caused by heavy and large workpieces.
Roll Profile
The shape and design of the roll is often referred to as its profile. Rolls can be designed with straight, tapered or curved grooves, and the profile chosen will depend on the type of rolling process and product requirements.
Rolls with straight grooves are usually used for cross-roll rolling processes and produce large and wide flat products. Tapered grooves are ideal for roll throughs and for product tensioning, as it encourages the product to move in the required direction. Curved grooves are suited to rolbox rolling processes and are often employed when working on thin-section materials.
Roll Speed
The speed of the roll is another important factor when it comes to roll wear. The faster the roll, the greater the tendency for wear to occur due to abrasion and elevated temperatures.
On the other hand, slower roller speeds can result in reduced wear due to reduced impact force when rolling. It is important to find a balance between speed and wear, as too slow of a speed can result in an inefficient process.
Product Properties
The hardness, shape and thickness of the workpiece also affect roll wear. Harder products are more prone to abrasion, while softer products can lead to material buildup, which can cause ploughing or gouging of the roll.
Thinner products are usually more abrasive, as the pressure per unit area is higher than with thicker products. For soft or thin products, the roll profile should be designed to reduce the contact area between the roll and the workpiece.
Lubrication is another important factor when it comes to roll wear. Inadequate lubrication can lead to increased wear due to abrasion, and can also increase the risk of galling.
Conclusion
Roll wear is an important aspect of the rolling process and can significantly affect the performance of the mill. Understanding the factors that affect roll wear is essential for ensuring optimal performance and extending the life of the roll. Operating variables, such as roll material, roll profile and speed of the roll, as well as product properties, such as hardness, thickness and lubrication, play a key role in determining the extent and type of roll wear.
