History of Milling, Part II
May 16, 2006
by Meyer Sosland
What began as a laborious hand operation in ancient times evolved into a highly-mechanized process
by Bryan McGee
Editor’s note: This is the second in a three-part series on the history of milling technology. The first installment was published in the April issue of World Grain. The final article will appear in our June issue.
The history of milling technology has been one of continuous innovation in pursuit of technical and commercial improvement. Significant changes have occurred from time to time, but even between technological advances, seldom has there been stagnation. Cereal milling and cereal science remain full of promise.
This article focuses primarily on the evolution of wheat milling technology during the first half of the 20th century.
ROLLERMILL REVOLUTION The first 15 years of the 20th century in Europe were marked by the development of the "vertical" roller mill, which was popular because it allowed mills to save floor space.
Before that, Baumeister in Hamburg, Germany designed a diagonally disposed machine that won a gold medal at the World Exhibition in Antwerp in 1894.
By contrast, U.S. manufacturers, almost without exception, settled on a horizontal roll disposition and concentrated their efforts on maximizing throughput and simplifying operation and maintenance. Some of these machines, made by engineers such as Nordyke & Marmon and Allis-Chalmers, are still in operation today.
These models are also distinguished by their use of "tunnel" shafts and flat belt drives to achieve the roll differential speeds without the need for lubricated chains or gears. Thomas Robinson offered these machines in Europe for a time but they failed to gain widespread acceptance.
Such designs have now been largely phased out due to difficulty in meeting current safety regulations. Despite the considerable merit of these very effective designs, Peter Kozmin wrote in 1917 that European millers and engineers seemed surprisingly indifferent to them.
In 1927, MIAG of Braunsweig, Germany took the first step toward automation by introducing a hydraulic servo regulator to engage and disengage the rolls in accordance with variations in the feed to the machine. This invention marked a significant step in the quest for plant automation.
In the 1950s, Allis-Chalmers, Milwaukee, Wisconsin, U.S., introduced pneumatic conveying to U.S. milling and unveiled its "Air Set" roller mill. This groundbreaking machine had a fabricated frame and used compressed air for the first time via diaphragms to activate the roll grinding and air motors to drive the feed rolls.
After building one mill with the new system, the parent company withdrew from cereal milling and opened the way for the European milling engineers to build complete plants in the U.S. for the first time. Simon built a mill in 1956 for the California Milling Corporation, but it was not until 1978, when Simon introduced its model "K," that air was again used for all main roller mill functions.
One of Thomas Robinson’s greatest contributions to technology was its 1951 invention of the first practical system for the pneumatic direct lifting of mill stocks. Direct lifting, combined with individual driving of roll pairs, enabled multiple roller mills to be located for the first time at ground level, thus dispensing with dangerous line-shaft drives. This resulted in savings in building height and structural support, which consequently reduced the cost of constructing a new plant.
In 1979, Buhler took advantage of new cost- and weight-saving tooling and manufacturing methods when they introduced the MDDK roller mill. This piece of equipment had a comparatively light-weight and unstressed fabricated frame supporting the roll pairs as independent modules. It superseded Buhler’s previous traditional design, with its diagonally disposed rolls and a heavy cast frame. The grinding forces were contained within the modules.
In 1983, Simon, which was still constructing its machines with heavy cast side frames, took advantage of new flexible-toothed belt transmission materials and patented the "Twin Power" differential drive, which eliminated the need for any oil lubrication in a roller mill. In this and other respects, the design responded to the need to improve food processing hygiene standards.
PURIFIERS Purification is the third of the principal activities — grinding and sifting being the other two — in a typical flour mill.
Advances in grinding and sifting techniques for the production of white flours highlighted the need for improved separation of stocks that have been graded on a sifter to be of similar particle size but are still of differing quality.
Although George Smith of the U.S. is often credited with the invention of the modern purifier, it was Perrigault in France who in 1860 patented a design that can claim to be the forerunner of the modern purifier.
The La Croix brothers, Edmund and Nicholas, took the idea with them when they moved to Canada and later the U.S. and developed it further. But they still failed to perfect a method to keep the sieve meshes clear. It was Smith who made the machine practical when he conceived and patented a powered traveling brush for this machine, thus solving the chronic operational problems. This led to a rapid adoption of purifiers in the late 1800s in the U.S. and later in Europe.
Few machines have undergone so many changes in overall design as the purifier, but all sought to separate stocks by floating the feed material over an oscillating fluid bed screen through which air is drawn to carry the lower density particles away with the exhaust air or to discharge product over the end of the deck. The higher-density material, which is generally purer endosperm, drops through the screen as a cleaner product for further processing.
The modern purifier has two or even three decks of sieves with ball or brush cleaners. Complex drive systems have given way to simple contra-rotating vibro-motors that oscillate the sieve assembly in a longitudinal direction.
SIFTING Sifting is a fundamental activity in the milling of refined products. The weaving of textiles of uniform character enabled sieving devices to separate the coarse, impure particles from the finer, purer particles. This led to the development of a more gradual and better controlled milling process to replace earlier "sudden death"-type systems.
Sifting machines fall into two basic categories:
• Revolving cylindrical drums with or without internal beaters; • Flat or inclined sieves, usually arranged in several decks.
Cylindrical sifters take many forms, including reels, which Kick describes as originating in the U.S. in the 19th century. However, the inventor was probably Milne, a Scot, and his brother-in-law, who in Rochdale, U.K. patented such a design in 1765.
As described by Kick, the U.S. bolting machines were generally polygonal and clothed with brass wire mesh for coarse sieving and silk for flour dressing. They were very long, ranging from 4 to 8 meters in length, inclined at about five degrees and run at 25 to 30 rpm. Due to their low cost, easy maintenance and low power, they were used almost to the present day for scalping break stocks.
Another type of cylindrical sifter is the centrifugal, in which the effective sieving area is increased by its rapidly revolving internal beaters that pick up the material and throw it against the mesh screen to help propel the material along the machine. This more intensive action is particularly effective for dressing of flour. Gustav Lucas of Dresden, Germany later arranged for the outer screen to revolve slowly at 30 to 35 rpm in the same direction as the beaters (200 rpm) to even out the wear and prolong screen life.
Reels and centrifugals were favored by British millers much more than in the U.S. or continental Europe, despite the cumbersome need for perhaps 60 units in a sophisticated 200-tonne mill.
As recently as 1950, Joseph Rank contracted with Henry Simon to build a large new mill with all sifting carried out by centrifugals and reels. This mill finally closed in November 2005, virtually bringing to an end to the use of this technology.
PLANSIFTERS Although forshadowed by another of Milne’s inventions in 1770, it was more than a century before the multiple sieve plansifter became widely adopted.
The advent of the roller mill along with the sophistication of the "Hungarian" milling system revolutionized milling practices across Europe and the U.S. The pursuit of higher capacities stimulated the development of many plansifter variants. The first notable plansifter in Europe was built by Carl Haggenmacher of Budapest, Hungary in 1878. But its mechanical deficiencies were not overcome for another 20 years, when Julius Konegen, of the firm which later became MIAG, produced a commercially successful sifter. This configuration was adopted by others and became the European standard for the next 50 or 60 years.
In the U.S., Great Western, Nordyke & Marmon and Allis Chalmers pio- neered very efficient plansifters that owed little to contemporary European designs. Europeans, in turn, paid little attention to these concepts and their capacity benefits until after World War II.
In the 20th century, many sifter configurations were developed, but only two — and eventually one — prevailed. The "drawer" type, which featured withdrawable sieves, enjoyed some popularity due to the excellent accessibility for maintenance of individual sieves.
The "Speight" sifter of 1932 was a trend-leading design, which Simon followed with its "Flowmaster" in 1950, and Buhler with its MPAD.
Improvements in sieve clothing quality reduced the benefits of such easy access so that European designers eventually recognized the merits of capacity and flexibility inherent in the American-type square sieve free swinging plansifter, as pioneered by Nordyke & Marmon and Great Western.
It was upon these principles that the "Senior Sifter" from Simon and "HM" from MIAG were based in the 1950s. Apart from Robinson, who also manufactured wood-working machinery, the Europeans shunned the timber construction and opted for all metal bodies and structures. All leading manufacturers continue to base their larger sifter designs on variations of this theme. WG
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