Roller Mill Sharpening: How to Tell If Your Rolls Are Dull

A common question RMS Roller-Grinder gets when working in the field is how to tell if the rolls on a roller mill are dull.

Roller mills use precision and sharp rolls to grind a raw material to a specific particle size. However, as with all machine components, they will eventually wear out. When the quality or sharpness of the rolls is compromised, it can affect your productivity and the final product.

So what exactly is a dull roll? What are the maintenance requirements for a roller mill? RMS Territory Sales Managers Luke Zebroski and Zach Peterson discuss the characteristics of a dull roll and share how roller mill sharpening keeps your equipment performing optimally.

When to Change Rollers on a Roller Mill

When your rolls are sharp, the peak of the groove comes to a knife point, but dull rolls are usually flat or rounded. A flat or rounded corrugation on a roll is going to impact your roller mill’s operation.

But if you can’t see your rolls, what are the external signs that they’re going dull?

The most common symptom of a dull roll is reduced throughput (aka capacity) through your machine. That’s usually the first sign of your rolls dulling out. Operators may have been able to grind everything in eight hours, but now they’re having to go ten hours just to get the same amount of feed out.

Not only will it take longer, but the quality of the grind will also decrease. The second most common symptom is the inability to hit target particle size. In some cases, we even see an increased number of fines in the final product. Luke and Zach also note that dull rolls may smash or pulverize instead of actually milling the material.

Although regular maintenance is an investment, your equipment is too, so it’s worth keeping up with roller mill sharpening to maintain product quality and efficient operations.

How to Tell When Rolls Are Going Dull

• Loss in capacity: You’re unable to achieve the machine’s rated capacity. “If you bought your roller mill for 24 tons per hour at 500 microns, now that machine’s running at 20 tons per hour at 500 microns,” says Luke. When the corrugations on rolls start to get dull, they “round over,” meaning they can no longer grab the material and pull it into the nip point of the rolls. This is similar to tires on a vehicle–when the treads are worn, you start to lose traction and slip or slide on the road.
• Diminished quality: You’re not able to achieve the same grind quality, average micron size, and standard deviation. When the corrugation on the rolls starts to dull, they no longer shear the material but start to smash it, resulting in varying particle sizes. This is similar to having a dull knife and needing to apply brute force to cut a tomato, resulting in smashing it versus easily slicing it.
• Increased energy consumption: Because the rolls can’t pull the same amount of material into the nip point at the same amount of time, you typically have to run your facility longer than required with dull rolls. Again, this is similar to a vehicle’s reduced fuel efficiency with worn tires.

Measuring Dull Rolls

There are a few ways to measure your rolls to tell if they are dull.

1. Time/bushel-based inspection: This is when you change rolls based on a time interval or the number of bushels that have gone through a machine. This is the least accurate way to measure if rolls are getting dull and to determine if there are other operational opportunities to improve roll life.
2. Visual inspection: This is when you visually inspect the rolls and compare them to a “sharp corrugation” example.  With a well-trained eye and years of experience, early signs of wear can be detected, but this is the second least accurate way to measure rolls.
3. Mold inspection: This is when you take a “negative impression” of the rolls and then analyze it under a microscope to tell how much the rolls have worn and the remaining roll life expectancy. This is a great way to estimate the remaining life on a roll and notice operational improvement. This is included in the RMS Endurance Roll Program to ensure you are getting maximum performance out of your roller mill.
4. Digital inspection: This is when you use an “optical comparator,” which takes a live image of the roll’s surface and compares it to sharp roll corrugation. This is also a great way to measure roll wear and estimate the remaining roll life, but it’s a significantly more expensive option due to the upfront cost of the optional comparator device.

The Impact of Dull Rolls

Dull rolls have negative effects on your operations. Loss of capacity and having to run your facility for longer means more overtime for employees. You might lose customers due to not being able to meet demand and having no excess capacity to sell, meaning you can’t get new customers because you can’t meet current customer demand.

You may also have diminished quality due to a higher standard deviation that upsets customers and negatively impacts your brand reputation, which can result in lost business and revenue. “Reputation is everything in this business,” says Luke. “What comes out of your mill is a perfect representation of who you are as a company.”

With increased energy consumption, you have higher energy bills, which can affect your overall bottom line. “You may not see it when they first start getting dull, but all the sudden, you’re going to start looking at your overtime and see employees’ time start to go up by several hours,” says Luke.

How to Prevent and Correct Dull Rolls

It’s important to regularly schedule roller mill sharpening to keep your machine running as intended and maintain throughput and product quality.

By the time you notice dull rolls and contact someone to come and replace or sharpen them, it can take extra time and compromise product quality. Don’t wait to see symptoms; be proactive about your mill with predictive maintenance. This can help address problems before they occur, empowering your team to resolve issues and keep your rolls sharp and performing optimally.

How often do you need to corrugate rolls? It depends on the material you’re grinding and the number of bushels that run through them. For example, some companies may be able to get by with corrugating once a year, while others may need three or four times a year to ensure optimal performance and uniform particle size. This is especially true of mills that are in constant operation.

Benefits of RMS’s Endurance Roll Program for Keeping Rolls Sharp

RMS Roller-Grinder offers an Endurance Roll Program to help our customers keep their rolls sharp and performing optimally. With our Endurance Roll Program, customers in a variety of industries can increase their machine’s uptime and reduce costs over the life of their machine.

A significant benefit of RMS’s Endurance Roll program is roll reporting. In a roll report, we take data from the machine to tell us about the current life of the roll. Roll reporting takes the guesswork out of determining when rolls are dull and instead provides concrete data about how much life the roll has left.

This empowers companies to be more informed about their roll performance and make better decisions about maintenance and roll sharpening or replacement, which can eliminate premature roll replacement or the hassle of experiencing downtime and suddenly needing to replace rolls.

This way, you don’t prematurely replace or sharpen rolls when they still have some life left in them, but you also don’t wait too long when problems start happening. The result is consistent particle size distributions for a high-quality milled or ground product.

Contact Us to Learn More

RMS is proud to be an industry leader in roller mill production and maintenance, including roller mill sharpening. Learn more about RMS’s Endurance Roll Program by contacting RMS Roller-Grinder today. Our team is happy to help you explore your options for predictive maintenance to keep your roller mill working perfectly for many years.