Doing more with less

by Stormy Wylie
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Advances in roller mill technology has made it possible for some companies to reduce the number of roll stands by a third and still achieve the same capacity and flour quality.

New roller mills offer more efficiency with existing capacity or can increase capacity within a given space. Combined with automation capabilities in new roller mill controls, the new technology has the potential to also reduce manpower requirements in the mill.

The General Mills plant in Carlisle, Iowa, U.S., has two mills, one equipped with all new roll stands (although not the latest technology available) and the other equipped with older roll stands manufactured in the 1950s. Brent Johnson, mill and elevator manager, said the mill with the newer roll stands produces two and a half times the capacity as the older equipment it replaced within less square feet.

"Newer roll stands can do a lot more with fewer machines and in less space," Johnson said. "More inches of roll surfaces can be put into the same square footage vacated by an older roller mill."

Not only are the newer roll stands more efficient and produce more capacity, but they grind better, tighter, and stay in adjustment better than older stands, he added. In some cases, mill rolls are changed less often in newer stands. By getting the work done with fewer machines, fewer rolls require changing.

However, new roll stands do require more training for personnel, Johnson added, as they are equipped with pneumatics and electrical components not found on the older models.

Because new roller mill designs are not all the same, millers should ensure that a new roll stand fulfills the primary considerations of roller mill selection: increased capacity and precise roll gap adjustment.

Millers may have many reasons to change to new roller mills, but they should first determine which new roll stand fulfills their milling requirements while providing an optimum return on the investment, according to Darryl Tateishi, sales and marketing manager for Jaymark, a milling equipment supplier based in St. Catharines, Ontario, Canada.

Tateishi said the size and design of older roller mills often restrict capacity. "Roller mills with 9-inch diameter rolls in lengths of 30 and 36 inches have a maximum design capacity of 3 to 4 tonnes per hour, per pair of rolls, on first break," he said. "Some new roller mills, 250mm diameter (10 inches) and in lengths of 1,000 and 1,250 mm (40 to 50 inches), are capable of 8 tonnes per hour, per pair of rolls, on first break."

Increased diameter and length of the roll accounts for much of this increase in capacity, but other design differences allow new roller mills to increase tonnes per hour, with less horsepower per tonne than older roller mills, Tateishi said.

Older roller mill designs have bearings that are as much as 15 centimeters from the end of the rolls. In new roller mills, "press fit" roller bearings are as close as possible (2 to 3 centimeters) to the face of the roll chill to minimize bending. The ends of the rolls often are tapered to allow the rolls to bend.

Tateishi said most new roller mills have a redesigned feed mechanism to ensure a consistently even stream of stock to the "nip" of the rolls. Many new roller mills also have micrometer dial indicators to allow precise adjustment of the roll gap.

Most, but not all, new roller mills are designed to have roll adjustment and roll engage/disengage of the "slow" roll, he added. The "fast" roll is held rigid in most new roller mill designs to minimize bending. This allows milling on head reduction passage without "hot spots" or irregular corrugation wear.

Many roll stands designed at the turn of the last century are driven by flat belts and counter shafts. The "fast" roll (the outside roll) also became the roll that was mechanically adjusted for roll gap and engaged/disengaged, Tateishi said.

"The older Nordyke roller mills had the outside roll held more rigidly than the Allis type, which explains why many millers preferred the Nordyke," he said.

Of course, there must be economic justification to change from older roller mills to new roller mills. "Determining the best value to maximize return on investment is an everyday challenge, made more difficult by the variety of choices in new roller mill design," Tateishi said.

NEW ON THE MARKET.

A wave of new roller mill designs have recently been introduced to the industry.

Buhler AG, Uzwil, Switzerland, introduced the Newtronic in 1999 after years of research and after comprehensive field tests on various continents and in different applications. "The roll stand was designed to provide reliable feeding, consistent grinding, total sanitation, full isolation to prevent condensation, substantial noise reduction and easy operation to complement a fully integrated control system and low maintenance requirements," said Walter Eugster, Buhler’s chief milling technologist.

Stock is gravimetrically measured across the roll stand’s wide inlet to ensure consistent feeding, even with a variety of grain. Feed rolls are automatically controlled and monitored by an electronic system, with infinite variation of the feed rate.

"In roll stands that process the same product on both sides, the control system ensures equal feed and grinding action," Eugster said. For break rolls, larger feed rolls ensure the uniform discharge of difficult products.

The compact roll pack offers precision adjustment and uniform grinding action. The roll gap can be adjusted manually or by remote computer control. "The most unique aspect of our newest roll stand is the ability to make extremely fast roll changes," Eugster said.

To reduce maintenance requirements, a swing-out feed module allows the feed section to be easily cleaned. All roll bearings are supported by a central lubrication system, which allows safe greasing during plant operation.

"State-of-the-art construction materials were selected to substantially reduce the noise level and prevent condensation," Eugster said. The inlet aspiration system ensures a controlled airflow, also preventing condensation and dust accumulation.

Each roll stand also has its own independent local control system, which maximizes operational reliability and ensures a consistent production process.

Eugster said the success of the new Buhler roller mill lies in the strength and durability of each individual component and in its perfectly harmonized performance in the overall plant. To date, Buhler has installed over 1,000 of the new roll stands in 48 countries.

The GBS Group, Padova, Italy, unveiled its new Synthesis roller mill just last year. "The main idea for the new roll stand came about two years ago," said Lodovico Bernardi, whose family operates the company. "The design, development and testing process went on for a year, but before starting the real design process we spent at least six months evaluating different materials and different manufacturing options."

The new roll stand was designed to be a reliable, flexible machine with high sanitation standards and easy and quick maintenance, at an affordable price.

Bernardi said the goal in developing a new roller mill was to meet new needs and expectations of the milling industry, rather than to correct any flaws in past generation machines.

The name of the new roller mill, Synthesis, comes from the collaboration of engineering experience from the company’s two brand names: Golfetto and Sangati Berga.

"We exploited a concept tested through tens of years of operation, based on a robust, vibration-absorbing cast-iron frame," Bernardi said. "We tried to standardize many parts to make the machine less expensive and easier for the miller to operate."

The company installed Siemens and Allen Bradley "off the shelf" software and components instead of tailor-made electronic systems. This option was considered especially for the U.S. market, Bernardi said.

The Synthesis roll stand was engineered to accept 10- or 12-inch rolls, with the same overall external dimensions. The machine is made up of two identical halves that can be installed as a stand-alone unit. Features such as the sliding feed rolls cartridge and easily removable panels make any part of the machine quickly accessible for cleaning and inspection.

Bernardi said the construction materials used in the new roll stand — T6060 anodized aluminum alloy and stainless steel — are a key advantage in the areas of both sanitation and cost. "The surfaces of this machine are untouchable by oxidization or rust," he said.

Mass production of the Synthesis began in October 2001. Bernardi said orders for 150 of the new machines have been received from mills in Italy, Africa and China.

The new RMX roll stand from Ocrim S.p.A., Cremona, Italy, was in development for nearly two years before its commercial release in 2001. "Our main objectives were to develop a machine that could guarantee a constant performance throughout the milling process while satisfying market demands and international regulations," said Guido Santi, marketing and advertising director.

During the design phase, emphasis was placed on hygiene, maintenance, safety and automation.

Ocrim’s new roll stand was designed to minimize the risk of product contamination. Stainless steel construction materials resist corrosion, and a micro-sphere polishing technique eliminates the need for a protective coating and aids in the removal of mold and bacteria.

A lamellar cast-iron base is made from a single casting. Using modern CAD 3-D design techniques, the RMX roll stand was designed so that all structural forces are on the base, diminishing and neutralizing vibration. All protective covers are made of a composite, non-deformable material to aid in sanitation and noise reduction.

The milling process was optimized by a constant feed of product onto the grinding rolls. The grinding rolls are driven by belts and pulleys instead of gears, which eliminates vibration.

The grinding rolls can be easily removed in about 10 minutes, without the use of a winch. A set of bearings fixed on rolling guides allows the rolls assembly to be lifted and removed onto a trolley.

The feed rolls also are located within a self-supported module, and can be easily assembled and disassembled. The feed tube can be opened for easy cleaning.

Many safety features were designed to reduce the risk of injuries or accidents. An isolation switch, which can be activated in case of emergency, blocks access to the electrical chamber and interrupts all on-board equipment. "This feature diminishes and eliminates the risk of dangerous contact with power circuits and injuries due to unexpected mechanical movements," Santi said.

The automatic RMX is "destined to change production management," Santi said. The electronic control uses the Profibus communication for integration with the central control system.

"By fully availing planning functions, handling of recipe production, automatic lot change and remote control, the RMX becomes essential to ‘lights out’ plant management," he said.

The onboard touch screen enables millers to check, set or adjust the product level in the tube, feeding speed, main motor load, roll gap, rotation speed of the grinding roll and alarms.

Ocrim has installed several RMX roller mills in new and existing facilities in a range of climates, from Greece to the Philippines, Italy to Honduras.

Ugur Machine Industry, Corum, Turkey, began the design of its new Rollermatic roll stand in May 2000. Testing began in December of that year. "The main difference is the PLC control system of the feed rolls," said Okcul Barlik, sales manager. "The machine can be calibrated with one button."

Benefits of the new roll stand include homogenous grinding, high extraction and standard finished product. The machine was designed for easy and rapid roll changes, and a timing belt transmission provides quieter operation.

Barlik said high-quality, standard materials were used in the new roll stand, and a special painting system allows a high degree of sanitation. "Our goal is to produce quality machines and improve our volume of business," he said.

Spomasz, based in Ostrow Wielkopolski, Poland, will introduce new models of FM05 and FM06 roller mills in 2002. Additional features addressing sanitation and safety are included in the new models.

The main design features that make Spomasz roller mills reliable and user-friendly have been retained, according to Darryl Tateishi, whose company Jaymark represents Spomasz in North America. The new roller mills will be built with internationally available components, including Festo pneumatics, Gates transmission belt drives, Endress Hauser sensors and Siemens electronics.

Roll gap adjustment and bearing arrangement remain a proven design to stabilize the rolls, and allow precise roll gap adjustment for high pressure on reduction passages. The energy efficient design is capable of consistent loads on first break of 8 tonnes per hour, per pair of rolls, with less than 50 horsepower.

Equipped with centrifugal cast rolls manufactured at the Spomasz casting center in Poland, Spomasz roller mills include both corrugated and "self matting" smooth rolls. Self matting rolls have proven to increase flour release on reduction passages by up to 40%, with less pressure than smooth rolls with a sandblast finish, Tateishi said.

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