ROLLING INTERVIEW QUESTIONS AND ANSWERS

What is rolling, and what are its main objectives?

Answer: Rolling is a metal forming process in which a metal workpiece is passed through a pair of rotating rolls to reduce its thickness, increase its length, and/or improve its mechanical properties. The main objectives of rolling are to improve the mechanical properties of the metal, reduce its thickness, and produce a uniform cross-sectional area.

What are the different types of rolling processes?

Answer: There are several types of rolling processes, including flat rolling, profile rolling, contour rolling, and spiral rolling. Flat rolling is used to produce flat sheets, while profile rolling is used to produce shapes with curved or angled surfaces. Contour rolling is used to produce shapes with complex cross-sectional profiles, and spiral rolling is used to produce spirally formed parts.

How does the temperature of the metal affect the rolling process?

Answer: The temperature of the metal during the rolling process has a significant effect on the final product. If the temperature is too high, the metal will become too soft and may deform excessively. If the temperature is too low, the metal will be too hard and may crack during rolling. Therefore, it is important to control the temperature of the metal to ensure a successful rolling process.

What are the main factors that determine the quality of a rolled product?

Answer: The main factors that determine the quality of a rolled product include the composition and microstructure of the metal, the temperature of the metal during rolling, the rolling speed, the roll diameter, the roll surface condition, and the lubrication used during rolling.

What are the most common defects that can occur during the rolling process?

Answer: Some common defects that can occur during the rolling process include cracking, tearing, improper grain structure, uneven thickness, and surface defects. These defects can be caused by improper temperature control, incorrect roll setup, or poor roll surface condition.

How do you ensure the safety of the rolling process?

Answer: Safety is a top priority in the rolling process, and there are several steps that can be taken to ensure a safe working environment. This includes providing proper training for all personnel, ensuring that all equipment is in good working order and properly maintained, using appropriate protective equipment, and following established safety procedures and protocols. Additionally, conducting regular safety inspections and risk assessments can help identify and address potential hazards before they result in an accident.

What is the role of lubricants in the rolling process?

Answer: Lubricants play a crucial role in the rolling process, as they help to reduce friction and minimize the amount of heat generated during the process. This not only helps to extend the life of the rolls, but it also helps to improve the quality of the final product by preventing defects such as cracking and tearing. There are various types of lubricants that can be used in the rolling process, including oil-based lubricants, water-based lubricants, and synthetic lubricants, each with its own unique properties and advantages.

What are the advantages and disadvantages of hot rolling compared to cold rolling?

Answer: Hot rolling is a process in which the metal is heated to a temperature above its recrystallization temperature before being rolled, while cold rolling is a process in which the metal is rolled at room temperature. The main advantage of hot rolling is that it allows for the formation of a more uniform grain structure and results in improved mechanical properties. On the other hand, hot rolling is more expensive and requires more energy compared to cold rolling. Cold rolling, on the other hand, is more precise and results in a better surface finish, but it may also result in increased material hardness and reduced ductility.

How do you control the dimensional accuracy of the final product in the rolling process?

Answer: Dimensional accuracy is critical in the rolling process, as even small variations in size can result in significant problems downstream. To ensure dimensional accuracy, it is important to carefully control the temperature of the metal during the rolling process, as well as the speed and pressure of the rolls. Additionally, using high-precision gauges and measuring equipment can help to ensure that the final product meets the required specifications.

Can you explain the concept of work hardening and how it affects the rolling process?

Answer: Work hardening is a phenomenon in which a metal becomes harder and stronger as a result of plastic deformation. In the rolling process, work hardening occurs as the metal is subjected to repeated cycles of deformation and recovery. This results in an increase in the strength and hardness of the metal, but also a decrease in its ductility. Understanding and controlling the effects of work hardening is critical to producing high-quality rolled products that meet the desired mechanical properties.

How do you choose the appropriate rolling mill for a specific application?

Answer: The choice of a rolling mill for a specific application depends on several factors, including the type of metal being rolled, the desired product dimensions, the required output rate, and the available budget. Some of the key considerations when choosing a rolling mill include the size and configuration of the rolls, the type of drive system, the type of cooling system, and the level of automation and control.

Can you explain the difference between rolling and forging?

Answer: Rolling and forging are both metal forming processes, but they differ in the manner in which the metal is deformed. Rolling involves the continuous deformation of a metal workpiece as it is passed through a set of rotating rolls, while forging involves the localized deformation of the metal using hammers or presses. Rolling is typically used for producing long, thin products such as sheets or strips, while forging is used for producing more complex shapes or for improving the mechanical properties of the metal.

What is the role of surface finish in the rolling process?

Answer: The surface finish of a rolled product is an important factor that affects its final quality and performance. A smooth surface finish can improve the product's appearance and reduce the risk of corrosion or other surface defects, while a rough surface finish can affect the product's strength and service life. In the rolling process, the surface finish is influenced by factors such as the roll surface condition, the roll diameter, and the lubrication used during rolling.

Can you explain the difference between tandem and single-stand rolling mills?

Answer: Tandem rolling mills consist of multiple rolling stands arranged in series, while single-stand rolling mills consist of a single set of rolls. Tandem rolling mills are typically used for high-volume production and for producing products with large reductions in thickness, while single-stand rolling mills are typically used for smaller-scale production or for producing products with smaller reductions in thickness.

Can you explain the difference between hot rolling and cold rolling?

Answer: Hot rolling is a process in which the metal is heated to a temperature above its recrystallization temperature before being rolled, while cold rolling is a process in which the metal is rolled at room temperature. Hot rolling typically results in improved mechanical properties and a more uniform grain structure, but is more expensive and requires more energy compared to cold rolling. Cold rolling is more precise and results in a better surface finish, but may also result in increased material hardness and reduced ductility. The choice of hot or cold rolling depends on the specific requirements of the application and the desired properties of the final product.

What is the importance of roll pass design in the rolling process?

Answer: Roll pass design is a critical aspect of the rolling process as it determines the shape, size, and surface finish of the final product. A well-designed roll pass ensures that the metal is deformed in an efficient and controlled manner, and that the final product meets the desired specifications. Roll pass design involves selecting the appropriate number of passes, the reduction per pass, and the rolling parameters such as speed, temperature, and lubrication.

How do you control the microstructure of the metal during the rolling process?

Answer: The microstructure of the metal can have a significant impact on its mechanical properties and performance, and it is therefore important to control it during the rolling process. The microstructure of the metal is influenced by factors such as the starting microstructure, the heating and cooling rate, and the deformation rate during rolling. By controlling these factors, it is possible to produce a final product with the desired microstructure, which in turn leads to improved mechanical properties.

Can you explain the concept of recrystallization and how it affects the rolling process?

Answer: Recrystallization is a process in which a metal changes its microstructure from a deformed state to a more refined, homogeneous state. During the rolling process, recrystallization occurs as the metal is subjected to high temperatures and deformation, leading to the formation of a new, more homogeneous grain structure. The rate and extent of recrystallization can have a significant impact on the mechanical properties of the final product, and it is therefore important to carefully control the temperature and deformation during the rolling process.

Can you explain the role of back-up rolls in the rolling process?

Answer: Back-up rolls are rolls that are positioned behind the work rolls in a rolling mill and are used to support the work rolls and provide additional force during the rolling process. Back-up rolls are critical to the stability of the rolling process and help to prevent the work rolls from bending or deforming under the high loads generated during rolling. The size, shape, and material of the back-up rolls are carefully selected to match the specific requirements of the rolling process and the type of metal being rolled.

How do you control the surface quality of the final product in the rolling process?

Answer: The surface quality of the final product is an important factor that affects its appearance, performance, and service life. In the rolling process, surface quality is influenced by factors such as the roll surface condition, the roll diameter, the lubrication used during rolling, and the speed and pressure of the rolls. To control the surface quality, it is important to regularly inspect and maintain the rolls, use appropriate lubricants, and carefully control the rolling parameters. Additionally, using high-precision measuring equipment can help to ensure that the final product meets the desired surface quality specifications.