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The Rolling Process is a widely used manufacturing technique in the metal industry that involves passing the metal through a pair of rotating rolls to reduce its thickness and change its cross-sectional shape. This process is highly versatile and capable of producing a wide range of metal products, such as sheets, plates, bars, and structural shapes, with precise dimensions and surface finishes. Rolling offers significant advantages, including improved material properties, enhanced grain structure, and the ability to produce large quantities of metal products with consistent quality.

In the current blog, we shall be discussing Rolling Process. This topic is important for your upcoming examinations like SSC JE ME and RRB JE Mechanical Engineering.

What is Rolling Process?

The rolling process is a deformation method wherein metal, either in its semi-finished or finished form, is passed between two opposing rollers. This compression process reduces the metal’s thickness as the rollers roll around it and squeeze it between them.

Fig 1: Rolling process diagram

Working Principle of Rolling Process

Rolling Process involves two opposing rollers with a metal passing between them. The key principle is ensuring that the gap between the rollers is smaller than the metal’s initial thickness (ingot), facilitating forward motion through the rollers. This process decreases the metal’s thickness while increasing its length and breadth, keeping the overall volume constant.

The Rolling Process consists of three stages of completion, which are explained as follows:

Primary Rolling:

The primary stage involves reducing the thickness of the ingot and transforming it into simpler stock shapes such as blooms and slabs. This step refines the material’s structure, enhances its mechanical properties, and eliminates internal defects.

Hot Rolling:

Following the primary rolling, the blooms and slabs obtained are further processed through hot rolling to produce plates, sheets, rods, and other secondary members. Hot rolling allows for shaping the materials at elevated temperatures, facilitating the creation of various forms.

Cold Rolling:

The last stage of the rolling process is cold rolling, wherein the final products obtained from hot rolling undergo a finishing treatment. This process imparts a superior surface finish, precise tolerances, and further enhances the mechanical properties of the products.

Terminology Used In Rolling Process

Common Terminologies in Rolling:

• Ingot: The initial metal input provided to the rolling process, extracted from casting with various defects.
• Bloom: The first rolled product of an ingot, having a cross-sectional area greater than 230 cm2𝑐𝑚2.
• Billet: A product obtained by further rolling of a bloom with a cross-sectional area greater than 1600 mm2𝑚𝑚2.

• Slab: A hot-rolled ingot with a cross-sectional area greater than 100 cm2 and a width equal to or greater than twice its thickness.
• Plate: A Mill product with a thickness exceeding 6 mm.
• Sheet: A Mill product with a thickness less than 6 mm and a width greater than 600 mm.
• Strip: A Mill product with a thickness less than 6 mm and a width less than 600 mm.

Types of Rolling Mills

Rolling mills play a crucial role in the rolling process by rotating the rollers and facilitating their initiation and completion. A typical rolling mill setup includes one or more roller stands, reducing gears, the main drive motor, stand pinion, flywheel, and coupling gear between the units, all working together to complete the rolling process. Rolling mills are categorised based on the number and arrangement of rolls in a stand, and there are six common types:

Two-High Rolling Mill

It consists of two high stands and rolls placed one over the other, where the rollers rotate in opposite directions after each metal pass, requiring approximately 25-30 passes to convert an ingot to a bloom.

Three-High Rolling Mill

It comprises three high stands with rollers in the same vertical plane, where the top and bottom rollers rotate in the same direction, and the middle roller rotates in the opposite direction. It offers increased productivity and ease compared to the two-high rolling mill.

Four-High Rolling Mill

It incorporates two backup rollers and two working rollers arranged one over the other in the same vertical plane, with the backup rollers having a greater diameter than the working rollers. It is commonly used in sheet rolling to reduce bending and ensure uniform compression.

Cluster Mill

It features two working rollers and two or more backup rollers. The number of backup rollers depends on the required support for working. It is primarily used in cold rolling operations.

Multi-High Roll Mill

It utilises two small-diameter working rollers and an intermediate row of driving rolls and backup rollers. This arrangement achieves exceptional rigidity. It is typically used for producing sheets of minimal thickness.

Universal Rolling Mill

It comprises of two vertical rollers and two horizontal rollers. The vertical rollers are positioned between the bearings of the horizontal rollers in the vertical plane. It is widely used for producing blooms from ingots and rolling wide flange H-section beams.

Types of Rolling Process

Rolling of metal can be carried out through various processes, each suited for specific applications and manufacturing conditions. The selection of a particular rolling process depends on factors such as the desired quantity of the product and the final shape required. Here are the different types of rolling processes:

Thread and Gear Rolling

Involves the use of thread dies on rollers to form threads and gears on metal workpieces. The process ensures consistent thread and gear quality, high production rates, and improved mechanical properties due to the material displacement method employed. It is commonly employed in various industries, such as automotive, aerospace, and machinery, to produce high-quality threaded components and reliable gear systems.

Shape Rolling

Used to cut shapes on metal workpieces, such as I-sections and H-sections, with various rollers employed to achieve the desired shape. The process utilises sets of carefully designed rollers that exert controlled pressure on the workpiece, gradually transforming it into the desired shape with exceptional precision. This method is highly efficient, producing consistent and accurate shapes with minimal material waste.

Ring Rolling

Utilises three rollers, including a drive roller, idler roller, and axial roller, to create rings and tubes by compressing metal. The workpiece is placed between the rollers, and as they rotate, the metal is gradually compressed to achieve the desired shape.

This unique manufacturing technique offers several advantages over other methods. It allows for the production of seamless rings, resulting in stronger and more reliable components compared to rings formed by traditional methods.

Tube Piercing

Two rollers and a stationary mandrel are used to create seamless hollow tubes with thick walls. It involves the use of two rollers and a stationary mandrel. The process begins with a solid cylindrical billet, which is positioned between the rollers. As the rollers exert pressure on the billet, it starts to deform and take the shape of the mandrel, forming a hollow tube. This technique is particularly advantageous for producing tubes with complex geometries and precise dimensions.

Skew Rolling

Specifically used to produce ball bearings, where metal is passed through specially designed rollers, resulting in bearing balls as the finished product. The consistent and uniform shape of the bearing balls ensures optimal load distribution and reduced friction, enhancing the performance and lifespan of the bearings. This technique offers several advantages, including improved material utilisation and increased production efficiency. Skew rolling allows for the rapid production of large quantities of bearing balls with excellent dimensional accuracy and surface finish.

Transverse Rolling

Provides a tapered surface to the material by passing it between two rollers with a certain tapered portion. The rollers are positioned at an angle to the material’s direction of travel, causing gradual deformation and reducing the thickness along the length of the workpiece.

This technique is commonly used to create components with varying thickness profiles, such as tapered shafts, conical shapes, and frustums.One of the key advantages of transverse rolling is its ability to enhance the material’s mechanical properties along the tapered section.

Controlled Rolling

A process performed in a controlled manner to achieve specific grain sizes. It is commonly used in industries like steel production.The primary objective of controlled rolling is to optimize the mechanical properties of the material, such as strength, toughness, and ductility, by manipulating its microstructure. By controlling the grain size and shape, the material’s anisotropic properties can be tailored to meet specific engineering requirements.

Advantages of Rolling Process

The rolling process offers several advantages, including:

• Speed and Time Efficiency: It is a fast and time-saving manufacturing process, allowing for higher production rates.
• Mass Production: Well-suited for mass production, making it ideal for large-scale manufacturing.
• High Efficiency: Provides high efficiency in material utilisation and energy consumption.
• Complex Profile Production: Capable of easily producing workpieces with intricate cross-section profiles.
• Precise Tolerances: Rolling processes can be designed to achieve workpieces with very close tolerances, ensuring accuracy and consistency.

Disadvantages of Rolling Process

The rolling process has certain drawbacks, including:

• High Initial Cost: The initial cost and investment required for setting up rolling operations can be significant.
• Surface Finish: The rolled workpiece may have a less refined surface finish, necessitating additional finishing processes.
• Mass Production Suitability: It is most suitable for mass-production scenarios, making it less efficient for smaller-scale productions.

Applications of Rolling Process

The rolling process is extensively used in various industrial applications, such as:

• Manufacturing of Shafts, Rods, Tubes, Axles, and Spindles.
• Producing Workpieces with Desired Cross-Sections.
• Gear Manufacturing from Gear Blanks.
• Thread Rolling for Threaded Parts, Bolts, and Screws.
• Production of Bearings and Turbine Rings through Ring Rolling.
• Wide Applications in the Automotive Industry.
• Manufacturing of Metal Sheets, Plates, and Panels.