Optimizing Performance and Improving Efficiency in Roll Grinding

By Kyle Thompson, Sector Manager – Industrial Production Americas, and Inja Skrinjar, Product Manager, Weiler Abrasives

The roll grinding process is critical in many industries, helping to maintain the accuracy of roll dimensions, surface quality, and the integrity of the roll — which are all essential to achieving high-quality, consistent results in production.

Because of the often demanding conditions of this process, achieving success in roll grinding requires careful attention to several factors. Proper alignment, reducing vibration and selecting the right grinding wheel for the specific roll material are key to producing an even surface without introducing new imperfections. Additionally, regular maintenance and inspection of both the grinding equipment and the rolls themselves can extend the life of the machinery and prevent costly downtime.

Learn more about some best practices that can help end users optimize roll grinding operations, improve productivity and ensure high product quality.

What is roll grinding and when is it used?

Roll grinding is a surface finishing process that reconditions or repairs surface defects such as cracks or cuts on large work or backup rolls that are used in rolling mills where sheet goods are formed and shaped using materials like steel, aluminum, paper, and more. The process is common in many industries, including steel, brass, copper, aluminum and paper mills; textile plants; and for the production of hydraulic cylinders. Roll grinding wheels are typically used when rolls show signs of wear, such as surface defects or inconsistencies in their roundness, and it is essential for keeping machinery running efficiently. It can be used on all roll types whether they are cast or forged, including work rolls, backup rolls, new rolls or old rolls that need renewal.

This process uses a roll mill grinding wheel to remove cracks or surface damage and restore a used roll to its original state or to apply the proper surface finish to a new roll. The time between grinding or reconditioning of the rolls depends on the material that is being processed. For example, mills rolling hot steel require the most maintenance on their working rolls due to the high pressures and thermal exposure associated with that rolling process.

Hot rolling vs. cold rolling

When metal is processed in a mill with roll grinding, the operation uses either hot rolling or cold rolling. The primary difference between the two types lies in the temperature at which the metal is processed and the properties it imparts to the material.

• Hot mill work rolls are exposed to extreme heat and pressure conditions, requiring frequent grinding. The material is more malleable at higher temperatures, making it easier to shape and form. Hot rolling allows for the production of large, complex shapes and reduces the need for additional processing. Hot rolled steel is typically less expensive to produce. However, the surface finish of hot rolled metal is usually rough, and the tolerances are less precise due to the cooling process.
• Cold mill work rolls need consistent refinishing to hold a specific roll profile or surface finish to ensure tight tolerances on the end product. In cold rolling, the metal is processed at or near room temperature. After hot rolling, the material is further processed by passing it through rollers to improve surface finish and dimensional accuracy when thinner dimensions are required. Cold rolling results in a smoother surface finish, tighter tolerances and increased strength due to strain hardening. This makes it ideal for more visually and functionally demanding products.

When choosing grinding wheels for each process type, the main difference is grain size. Wheels with much finer granulations are used for cold rolling since a smoother surface finish is required. Wheels for hot rolling typically have granulations of 36 to 46, while wheels for cold rolling often use 60 to 80 grit.

Challenges associated with roll grinding

While it is essential for maintaining high-quality production in various industries, roll grinding involves several challenges that can impact the precision, efficiency and longevity of both the rolls and the grinding machinery. Common challenges include:

• Material composition and differences: The variety of roll material being ground significantly impacts wheel performance and abrasive consumable costs for users. Different materials require specific grinding wheels and techniques. The hardness and composition of the roll material can cause excessive wear on the grinding wheel, leading to inconsistent surface finishes or the need for frequent wheel dressing and replacement. Designing a single grinding wheel to cover all roll types being ground within a given facility can be challenging. Look for a wheel manufacturer that can offer vast capabilities — from technical resources to manufacturing — so solutions can be developed that achieve the quality needed while helping to reduce consumable spend.
• Vibration and chatter: Vibration during grinding can cause surface imperfections known as chatter, leading to an uneven roll surface. This issue can occur due to running hard specifications and pushing grinders to max loads in order to grind rolls faster. Chatter not only affects product quality but also reduces the life of both the rolls and the grinding equipment.
• Cycle times and operating costs: The performance of abrasive consumables ties directly to the bottom line in most rolling applications, and many end users want to reduce cycle times. As a mill’s output increases, grinders can become backlogged. If the next set of rolls aren’t ready for a roll change, costly production downtime can occur. In addition, the rolls themselves can be quite expensive, and every layer removed for reconditioning means the roll is getting smaller each time. This makes it important for end users to remove as little material as possible when renewing the surface.
• Precision and tolerances: Roll grinding can achieve extreme accuracy and tolerances, down to thousandths of an inch. But achieving and maintaining tight tolerances can be a challenge, especially for rolls used in industries requiring high precision. Even small variations in roll geometry or surface finish can lead to defects in the final product, making it crucial to maintain accuracy throughout the grinding process.
• Machine wear and maintenance: Regular maintenance of roll grinding equipment is vital to preventing issues like misalignment, uneven wear or poor surface finishes. Maintaining the precision of large, complex machines over time can be difficult and requires skilled operators and consistent monitoring.

To address many of these challenges, it’s important to choose a high-performing grinding wheel designed for optimal performance for each specific application. A wheel that cuts properly with a long wheel life will reduce the number of wheel changes and help improve uptime for the end user.

Abrasive products for roll grinding

When choosing the proper grinding wheel for roll grinding, consider the material and specifics of the application. Primarily, organic/resin bonded grinding wheels are used in both hot and cold rolling mills. Some vitrified products are used in specific applications where special roll profiles and surface finishes are required. In hot rolling applications, abrasives with ceramic grains are commonly used to recondition rolls due to roll material hardness and the amount of stock removal required. In cold rolling, abrasives with premium aluminum oxide grains are used to hold a tight roll profile tolerance and apply a specific surface finish to the roll.

Wheel size is usually predetermined by the maximum wheel size the grinder can accommodate. Grinding wheel thickness is also sometimes limited by the grinder specifications, but it can be altered to accommodate custom widths needed for a specific roll profile. Some wheel manufacturers offer features that provide flexibility. Weiler Abrasives, for example, can use an economic center wheel section adjusted to the size when the user removes the wheel from the grinder at “stub out”. This prevents unused high-cost abrasive grains in that section from being discarded, helping reduce abrasive consumable costs.

Wheel shapes and dimensions are also dependent on the application. Wheels ranging from 30 inches (762 mm) up to 48 inches (1220 mm) in diameter and in widths from 2 inches (50.8 mm) to 6 inches (152.4 mm) are found in hot and cold rolling mills.

Another important consideration when choosing a grinding wheel is the product’s G-ratio, which measures the amount of material that one wheel can remove during its life. A higher G-ratio equals a wheel with a better return on investment.

High-performing roll grinding solutions

Selecting high-performance abrasives can offer faster material removal rates, longer wheel life and fewer wheel changeovers. Using the right combination of abrasives, bond, wheel hardness and wheel structure provides the ultimate solution for specific application needs. High-performance abrasives allow greater flexibility in fine-tuning a grinding wheel for maximum end user performance.

Grinding wheel solutions from Weiler Abrasives can address many of the challenges associated with roll grinding, including vibration and chatter. New, innovative bond and wheel formulation technologies allow Weiler to design end user-specific grinding wheel formulations, providing wheels that hold form while carrying sufficient coolant to prevent burning the roll or loading on the wheel face. Technical experts aid end users in determining the best specification based upon material type, grinder and grinding parameters.

Wheel manufacturers must be able to adapt to variances and requirements of the end user and their operation. Dialing the wheel in for the specific grinding application is key. Look for a wheel manufacturer that can develop an appropriate wheel matrix that is suitable for the specific grinder or specific material type being ground.

Also, every mill is set up with unique wheel handling equipment or specific wheel mounting operations. It’s important to work with a wheel manufacturer that can design specific user packaging methods that will eliminate extra steps the end user may be struggling with. This can help ensure safety and speed in mounting new grinding wheels for end users. For example, Weiler Abrasives has machined recesses on both sides of a wheel to accommodate an end user’s specific flange or mounting conditions.

In addition, companies can partner with Weiler Abrasives for technical expertise and on-site support to help optimize grinding wheel performance and machine throughput. By utilizing the Weiler Process Solutions (WPS) program, product experts work alongside end users to collect valuable data and help address pain points. They analyze that information to provide feedback and offer process improvements that can help users reduce abrasive consumable costs and improve efficiency. For example, cycle time reduction is a key factor that is analyzed as part of the program. Cost savings go beyond the initial cost of the wheel. The longer a wheel lasts, the fewer wheel changes users must make. This can save 30 to 40 minutes with each wheel change, adding up to significant savings over time. By utilizing the WPS program, one end user was able to grind longer using high-performing wheels. They used 15 fewer grinding wheels per year, resulting in savings of €21000.

The capability to measure and track vibrations during the grinding process is also important. Vibration during grinding can be caused by many factors, and it’s an issue that can damage the rolls themselves or the finished product and reduce the life of the grinding wheel. Utilizing technical expertise in addition to choosing high-performing products can help end users correct vibration issues.

Lastly, it’s key to make adjustments to improve the grinding process. Each wheel from different manufacturers performs differently, so be sure to monitor and analyze performance and work with technical experts to continually improve the process, rather than just sticking with the initial parameters set on the machine. Of course, it’s also critical to follow all safety requirements, choosing products that meet or exceed EN 12413 & ANSI B7.1.

Optimizing roll grinding

Because roll grinding is a critical process in many industries, it’s important to choose the right solutions that can help provide faster material removal rates, longer wheel life and fewer wheel changeovers. Look for grinding wheels that are engineered for the precision requirements and roll surface integrity demands of roll grinding. This can help end users improve finishes, reduce production costs and enhance productivity.