On the catwalk

by Emily Wilson
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Grain handling facilities in recent years have been calling for bigger and stronger catwalks, manwalks and support systems. This trend has resulted in expanded product lines for manufacturers. The three dynamic factors forcing these new designs are increasing weight, capacity and size dimensions.

Catwalks, which include a walkway next to a conveyor support, manwalks and towers to support the catwalks are intricate parts of any grain handling facility. "Any time they put up a grain bin, they're going to need a conveyor between the bins, and 99% of time, they install a catwalk for conveyor maintenance and service requirements," said Nathan Grube, sales manager, Brownie Systems, Waverly, Nebraska, U.S.

"The equipment we have to support is getting larger," Grube explained. "More and more facilities are using belt conveyors, which are wider than drag conveyors. For instance, last year Brownie's widest catwalk was 84 inches. Now, it is 96 inches wide."

Jim Gable, a registered professional engineer working with Sweet Manufacturing, Springfield, Ohio, U.S., also has witnessed the trend. "Customers want bigger equipment with fewer support towers because anytime you bring something down to the ground, it is potentially in the way," Gable said. "We are trying to reduce the number of support towers by 25%."

The towers often get in the way when piling grain on the ground, he explained, so minimal ground obstructions is key.

"The industry has been asking for this since the mid-1990s," Gable said. "We've had to invest a lot of money and time into new equipment to meet these demands."

CHANGING TIMES. The designs of catwalks and support towers are following suit with the rest of grain handling equipment — all subject to the never-ending push for increased efficiency. More efficient transfer of grain means higher profits.

"This trend started about three years ago," Grube said. "Back then, you often saw conveying capacities of 10,000 to 15,000 bushels per hour. Now, it's pretty common to see 30,000, 40,000 or 60,000 bph," he added.

More of Brownie's customers are now using conveyors weighing around 350 pounds per foot and up to 700 lbs/ft loaded. To support the heavier conveyors, Brownie designed a heavier catwalk, weighing 171 lbs/ft.

"We had to make our equipment larger to accommodate the customer's larger conveying equipment," he said. "Three years ago, Brownie's lightest catwalk weighed 30 lbs/ft. Now, our lightest catwalk weighs 69 lbs/ft."

Customers also want longer freespans to cut down on the number of support towers needed. The increasing size of grain bins also requires catwalks with longer freespans. "Twenty years ago, a 60-ft diameter bin was typical," Gable said. "Now, 90-ft diameter bins are common and 105 ft diameters are not uncommon."

Before, Gable said, the goal was to leave 60 to 75 ft between supports. Now, Sweet is trying for 75 to 100 ft between towers.

To accomodate heavier loads, longer freespans and fewer support towers, the equipment needed heavier construction, upgraded design to carry heavier loads and longer catwalk sections, Gable said.

"It has been a challenge to redesign this equipment," he said. Sweet has been working on the financial and equipment investments for several years, and more intricately with the design alterations for about a year, he said.

One of the new designs is Sweet's new 20-ft sections of the Silver Span® catwalk; manufacturing is to begin in early 2001. Gable said the new 20-ft sections will enable longer spans without supports, reduce installation costs because there are fewer pieces to connect and improve the overall catwalk strength.

Stronger leg and support towers are also needed, Grube added. "With the weight of conveyors, conveyor loads and catwalks themselves all increasing, stronger support towers are necessary to stabilize free-spanning catwalks between grain bins," he said.

Brownie offers two column, four column and sidewall brackets support options. Access braces in patterns varying from the standard "X" are also available for easier access to equipment within the tower, such as a distributor or cleaner.

Sweet developed a fabricated design for support towers, as opposed to its former structural design. The fabricated design, also known as formed steel, keeps the same size and shape as structurally formed angles and pieces, but the weight is decreased while strength is maintained or often increased. "This decreases the cost by about 20% to 25%," Gable explained, "because fabricated material is thinner and weighs less."

CARE-FREE MAINTENANCE. Fortunately, after installation of a catwalk or support tower, there is little maintenance required. "After installation, you can pretty much walk away from it for years," Grube said. Besides using touch-up paint after any welding to prevent rusting, he said, the catwalks and support towers are maintenance-free.

Parts rarely need to be replaced due to extensive wear. Most replacements of catwalks or towers are actually upgrades necessary for bigger equipment.

Grube also suggested that companies planning to add extra equipment to an existing support tower should first call a manufacturer to make sure the original structure was designed to hold the additional weight and wind loads.

Most catwalks have an enamel finish, which is durable but might require touch up painting to prevent rust. Brownie Systems uses a powdercoat finish, which is a baked-on powder coating that is less likely to chip, especially during shipping. The polyester powder formulation offers resistance to weather, salt and scratches, thus reducing fading and chalking. And because the finish contains no solvents, thinners, lead or other heavy metals, welding will not release any hazardous fumes or chemicals.

Galvanized steel, which has a zinc coating to withstand weathering, is another durable metal option to prevent rust and equipment failure. "With galvanized steel, there is next to no maintenance," Gable said. "It is much more maintenance-free than painted coatings."

He estimates that painted catwalks need repainting every five to seven years to prevent any rust damage.

"Rust is a sign that the metal is deteriorating," Gable said. "And if the metal is deteriorating, it is losing strength."

SHOPPING TIPS. For facilities in the market for a new catwalk, a manufacturer needs to know how much the loaded conveyor will weigh per foot and how far the catwalk will freespan, Grube said. "The answers to these two questions will determine the specific grade of catwalk needed," he said.

To price a leg tower, he added, know equipment dimensions and the weights of distributors and cleaners. If concerned about engineering specifications, Grube suggested asking for engineering documentation of construction plans to ensure the structure's stability. Also, make sure the overall design meets all necessary safety standards.

Look for rigid materials and a slip-free walkway plank, Grube recommended. Recently, Brownie began offering a safety-strut walkway with built-in, four-inch toe board on both sides of the walkway. "It's an aggressive tread, non-slip surface that meets all safety specifications," Grube said.

Sweet Mfg. produces its own proprietary decking, Silver Grip Grating®, with slip resistance and integral toe boards.

Buying equipment from a manufacturer in a different country should not be a problem. Sweet works in several different markets, but the main difference in the products supplied is the capacity, Gable said. "North America wants two to three times as much capacity in the conveyors, but everybody wants catwalks to go further with fewer support towers," he said.

Safety standards are similar across international boundaries. "Typically, the U.S. Occupational Safety and Health Association (OSHA) standards — and sometimes more — are requested in international countries, especially throughout Europe and Latin America," Gable said.

Also, look at the various shipping and installation options when ordering from another country, he said. Sweet uses bolt-together construction to ship the pieces in smaller containers. Sweet ships one assembled section and compactly ships the pieces of other sections, Gable said. "Then they assemble the rest following the example of the one pre-assembled piece," he added.

Brownie uses a special knockdown design for economical shipping of its catwalks and compactly ships the nuts and bolts in buckets.

Often, customers don't realize the importance of catwalks and support towers, as Teta Engineering has found. Based in Ankara, Turkey, Teta began manufacturing catwalks and support towers as part of its turnkey grain storage projects in 1995. "We give the priority to the strength of the catwalks and towers, but most clients in our region consider this equipment as simple steel structures and they are not technically aware of what they are buying," said Talat Isik, general manager. "We generally have a hard time explaining the differences and advantages of our designs."

Teta offers three different catwalk designs, available painted or galvanized, with spans up to 10, 20 and 28 meters and encourages customers to realize the options and technical implications of catwalks and support towers.