The heart of a flour mill is the mill stand rolls. These corrugated rolls, also known as fluted rolls in Europe, are essential in the break system to separate the endosperm from the bran and germ.
But many millers do not know enough about roll recorrugation, according to mill roll manufacturers and corrugation experts.
"Only a few millers have a knowledge of when rolls should no longer be used or understand corrugations," said Tom Fischer of Breitenbach GmbH, which manufactures and recorrugates mill rolls at its factory in Seigen, Germany.
Sid Sadowskie, founder of Sid's Corrugating, Wichita, Kansas, U.S., has been perfecting the craft of recorrugation since the late 1960s. He encourages millers to learn more about the recorrugation process, and noted that it might even save them money.
"Many millers haven't toured corrugations shops, so they don't understand the recorrugating process," Sadowskie said. "Millers understand the importance of corrugating, but don't know why a corrugation is working or why it isn't."
Recorrugating involves grinding the roll perfectly round; abiding millers' specifications, such as tapered roll ends to offset swelling when the rolls get hot in the mill; preparing the bearing and gear surfaces; and corrugating.
Sadowskie encourages maintenance personnel and millers to visit a recorrugation shop. "They can gain an idea of what's involved in corrugating rolls, how to take care of the rolls and how to prolong the life of the shafts or the rolls," he said. "There's just little tricks that we've learned over the years, and if it helps the rolls last longer, then it will save the millers some money."
TOOLS OF THE TRADE. Mill rolls are corrugated by either the single-point or multi-point tool method, said Art Henry, president of Creason Corrugating & Machinery Company, Inc., Wichita, Kansas, U.S.
Henry spoke about the differences in corrugation tools at the Association of Operative Millers' technical conference last year in Kansas City, Missouri, U.S.
As the name suggests, single-point corrugating is done with a tool that consists of a single carbide tip. "The carbide- tipped tool is first ground to the specific angle combination," Henry said. Once a single-point tool has been ground to a specific angle, it can be used for any pitch — the number of corrugations in an inch.
Multi-point corrugating is done with a form tool that has the corrugation profile as well as the number of corrugations per inch already formed on the tool. "The carbide form tool enabled corrugators to not only give the corrugations of a single roll uniformity, but also assure uniformity of corrugations from one roll to the next," Henry said.
He explained how the multi-point tool works. "When corrugating with form tools, the operator must first select the tool with the desired profile and number of corrugations per inch preformed on the tool," he said. "The first tooth on the form tool lightly scratches the surface of the roll, then each subsequent tooth imbeds the form a little deeper into the roll until the finishing teeth imbed the completed form into the roll."
In general, European mills and recorrugators favor the single-point method and corrugation profiles with two angles, while North America favors the multi-point tool and corrugation profiles with a combination of angles and radii — the degree of curve on the peak and valley of a corrugation.
WHICH IS BEST? Henry said that he has often heard North American millers with European mill systems say that the original corrugations lasted longer than the recorrugations. Such statements prompted him to explore whether the corrugation tool made a difference in corrugation life.
Part of the problem, Henry noted, was how recorrugations were ordered. He stressed that instead of asking for a familiar corrugation, such as the Getchell or Modified Dawson, millers need to specify the exact requirements for a recorrugation, including the pitch, land, angles, depth and radii.
"This is not to mean that different [corrugation] forms are responsible for the longer life of the corrugation, however it should be considered," he said. "European flows are set up to perform best with the specified angle corrugation, just as the North American flows are set up to perform better with the radial form corrugations."
Land, the true ground surface of the roll left between each corrugation, may be the most important factor in corrugation life, Henry said. "Land helps keep the sharp edge, where the corrugation intersects the roll surface, for a longer period of time," he said. "When the roll begins to wear, you are left with slightly more land. However, it is not until the edges start to round significantly that the angle corrugation loses effectiveness."
On European angle corrugations, land has always been left, he said. This gives the top of the corrugation strength.
"If there were no land or radius at the top of the corrugation, it would be very susceptible to chipping or breaking off," Henry said. "While land has generally not been left on traditional North American break corrugations, it has typically been left on middling corrugations."
Henry warned millers against making hasty corrugation changes. "When land is left on a radial corrugation, the profile is altered," he said. "The performance of the break corrugation should be weighed against the amount of extra life, if any, that is gained from leaving land."
The price difference in the two tools is significant. It takes about 90 minutes to corrugate one 10-inch by 50-inch (250 by 1,250 mm) roll with the multi-point tool method, Henry said. It will take between four to six hours to recorrugate the same roll using the single-point method, depending on the number of corrugations per inch.
Even though the form tool method requires a large inventory of the many profiles available, the time element causes North American corrugators to generally charge double for the single-point method as opposed to the multi-point method.
In North America, price isn't the only deterrent to the single-point method, Henry said. "To my knowledge, it is practically impossible to replicate a radius form on a single-point tool accurately," he said. "If you plan on using the single-point method, you will not have several very common North American profiles available to you, such as Twin City Chunk, Stevens, Getchell and Modified Dawson.
Although the multi-point method is faster, Europeans still prefer single point fluting. "The single point method allows more exact cutting of the single fluting tooth," said Tom Fischer of Breitenbach. "It is the only method to achieve exactly the same geometry for every tooth."
TESTING THE DIFFERENCE. Creason is conducting several tests to determine the difference in single and multi-point tools. One test with a General Mills flour mill in Avon, Iowa, U.S., concluded that the lifetime of single-point and multi-point corrugated rolls were equivalent. General Mills is performing additional tests to verify the results.
Creason also is working on a four-part test with ADM Milling Co. and Kansas State University, Manhattan, to test life of corrugations, particle size distribution and quality.
The first test compares a similar corrugation profile on single-point and multi-point corrugated rolls. The second test compares a single-point corrugation against a radial form tool corrugation.
In the third test, a single-point European corrugation was compared against a typical multi-point radial form tool corrugation on middling stock. The final experiment tested a multi-point European angle corrugation against a multi-point radial form tool corrugation on middling stock.
Henry said the majority of the tests have been completed, and results indicate the lifetime of the single-point and multi-point corrugated rolls was about the same. Quality results from the two different rolls also appears to be similar, he said, but K-State is still analyzing the results.
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