Category Archives: Channel Bending

Curving Unistrut or P1000 Channel

Straight and Curved Unistrut channel (also called ”Flexstrut”, “Kindorf”, “Strut channel”, “SuperStrut”, “Strut”, and “Metstrut”), along with a wide variety of connectors, can supply light structural support for electrical, mechanical, heating, ventilating and air conditioning systems. Although typically P1000 is made of galvanized steel, strut also can be made of aluminum or stainless steel.

Because of the unique shape of P1000 it takes special care and unique techniques to make sure there is no concavity when bending the channel member.   Continue reading Curving Unistrut or P1000 Channel

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Non-Commodity Steel Channels Through Forming/Bending

The term “non-commodity” is used to describe steel shapes when the size and alloy in demand is not produced for distribution to the masses. The demand for these specialty steel members does not occur with enough frequency for rolling mills and reduction mills to consider this type of work. So, specialty steel fabricators with bender/roller capabilities are contacted when non-commodity steel shapes are required. These fabricators have the ability to produce custom sizes and shapes in short runs/batch production. This demand is often seen in pipe/tube sizes that are required for the energy markets, i.e. nuclear. These non-commodity steel products can often be made in custom lengths, shape, dimensions, and alloys. A recent request for a structural application required 48ft of 16” grade 50, steel channel to be used in the fascia of a newly constructed commercial building.

Through the use of large press brakes, which can be made up to and exceeding 3000 tons x 40ft long, non-commodity steel channels can be formed with accuracy to specified dimensions. When proper machine setup techniques are used, forming heavy plate into 90degree bends is somewhat straight forward. Custom size, steel angles, channels and even tubing can be formed by bender/rollers on a brake with a large enough capacity and the proper tooling. In the application described above, ½” A572-50 needed to be formed into a channel that was 16” deep with 5” legs. 4pcs were required at 12ft long each, totaling 48ft.

Bending with a Bottom V-Die and a Male Punch Die

Determining proper die selection is key to bending. Without the correct dies in place, a few things can go wrong:  the material being formed may get damaged leaving cracking or severe tooling marks; the bend may not be accurate; or in extreme cases, the tooling may be damaged. When set up correctly, however, press brakes are capable of forming 90deg bends accurately in plate thicknesses and lengths according to the machine’s respective capacity chart. For the non-commodity channel required in the above scenario, a 4” V-die was used with a 5/8” radius punch die on a 1000ton brake. The plate was marked with bend locations, and then hit 1 time at each location forming 2 separate 90deg bends. The formed channels final dimensions are checked for accuracy of forming/bending.

Checking for Plate Bending Accuracy
Finished Formed Fascia
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Curved Steel Channel for the Vets

Representative of the Elks USA located in Chicago via e-mail:  “Can you supply two 40in diameter rings of 3in channel in stainless steel rolled with the flanges out for the reconstruction of our flagpole base?”

Rusted Base of the Flagpole

Estimator of the Bender Roller Company:  “Here is the quotation for the work.”

Elks:  “I have a few questions.”

Estimator:  “We could provide 180 degree segments for no extra cost, and when you’re ready to order, we could look at the price again and try to bring it down.”

Marketer at Bender Roller Company to Elks:  Can you tell me if all is right with our quotation to you?

Elks:  “I have talked to the contractor to see if you could drill some holes, and I could fabricate the base myself instead of going to another fabricator who would charge an additional $4,500. Let me send you some conceptual drawings of where the holes needed to be drilled.”

Conceptual Drawing of Curved 3in Channel in 180 Degree Segments

Estimator:  “Here is the revised quotation to roll the channels and also provide straight lengths with holes and/or slots per the prints for $2,750.

Elks:  “Can you please, please bring this price down.  The Elks need this flagpole base by the end of July.  This is for a war memorial, and I’m hoping the vets can get a good price.”

Estimator:  OK. For the vets.  Here’s your price of $2,200.

Elks:  “Looks good.  Let’s order!”

The Elks National Headquarters in Chicago

The flagpole is outside the Elks National Veterans Memorial that was originally dedicated to the Elks veterans who died in World War I, and rededicated to veterans from WW2, the Korean War, the Vietnam War, and all future wars.  The memorial is a national landmark.

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Curving Formed Steel Channels

Of all the structural steel sections that are curved in a variety of ways, one of the most difficult to curve is the steel channel rolled against the strong axis.

Sketch of Structural Channel Rolled the “Hard Way”

When bending a channel the “hard way” in a three-roll bender, the section tends to distort in a number of ways.  The web tends to become compressed and, in the worst case, cripples.  The flanges tend to bend in toward the center of the web and lose their 90degree angle with the web.  The section also tends to twist.  There sometimes is a bump in the web where it meets the flange.  And the tighter the radii, the more difficult bending becomes.  Similarly, the thinner the channel and the wider the web and flanges, the more difficult bending becomes.  However, with the proper tooling, with the right machinery, and, most importantly, with an experienced machine operator, channels can be successfully curved even to tight radii.

Structural Channels Curved the “Hard Way” as a Guide-Rail for Installation of a Sea-Wall

What I have been talking about so far is curving structural channels, channels that have an outside sharp corner 90degree edge where the flanges meet the web.  But channels can also be made by forming plate on a press brake.  The resulting section typically has a radiused outside corner that takes the shape given by the press brake punch and die.  A benefit of a formed channel is that it can be made to dimensions not available with structural channels, i.e. different plate thickness, different web width, and different flange height.  A drawback of a formed channel is that it is more difficult to curve than a structural channel.

A current application involves curving 12.75″ x 2″ x 1/4″ formed channels to a 320′ inside radius.  Although the radius is large, the web is wide and the plate is thin, the formed sections are rolling well.  Since these channels are being formed to become a waler cap for a seawall near a resort in St. Joseph, Michigan, appearance was a big concern.  This is the first time these engineers have used formed steel channels for the cap.  I think they will be happy with the product.

Formed Steel Channels Curved the “Hard Way”
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The Challenges of Rolling Formed, Metal Channels

Of all the structural shapes – angles, bars, beams, channels, tees, pipe and tube – everything else being equal, the most difficult shape to bend is channel the “hard way,” i.e. against the strong axis.  As you can imagine, pressing against the flanges to curve the metal shape is likely to push them inward, especially at the “toes.”  And trying to curve the web like a hard way bar (like a washer) is likely to cause the web to buckle.

Roll formed channels, i.e. channels made by bending sheet or plate, is even more difficult.  Structural channels typically have flanges that get thicker closer to the web.  And structural channels are reinforced where the flanges meet the web both with a square corner on the “outside” and a fillet on the “inside.”  Formed channels may have a large or small radius at the corners, both of which can be challenging to roll.  A precise set-up is required to insure that the corners do not move or become deformed.  Formed channels have only one thickness and therefore are not reinforced as structural channels are.

A recent requirement was for channels formed from rather thin, 11-gauge material with outside corner radii of 1/4in.  Four segments 7ft long with a 3-1/8 web and 1 1/2 flanges were rolled the hard way to a 61-1/2in inside radius; six segments 79in long with a 3-1/4 web and 3in flanges were rolled flanges-in to a 60in inside radius.  Complicating matters, the channels had round holes and slots cut into the webs and flanges.  Such cut-outs sometimes cause the channel to deform and/or are deformed themselves in the rolling process.  In this particular case, everything curved correctly.

Had they not been near perfect, these channels would not function as intended:  they are used in custom observatories and in enclosures for telescopes.

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Rotary Channel Splitter

A rotary channel splitter is a device that cuts with revolving steel wheels.  A blade that is stationary rotates to push the channel against another blade that causes the material to experience highly localized shear stresses between the two blades.  In a rotary shear process, materials are cut in the pinch between two overlapping hardened metal disks.  The disks create stress in the shear mode necessary to separate the channel.

Rotary shearing is a very accurate cutting process that produces pieces that have a very high cut tolerance.  The cutting results are affected by the cutting machine and if the machine is calibrated correctly you can expect very smooth cuts without any burr or rough edges.

Cutting problems can occur resulting in twist, camber and bow.  The major factors that cause cutting problems are too big of a cutting angle, blunt blades, incorrect clearance, and unnecessary bending of the frame and axles in the cutting machine.  A rotary splitter produces very clean cuts and saves the end user money by making the cut in a fraction of the time it would take to make the same cut with a saw or torch.

A rotary channel splitter was used by Chicago Metal to split MC10 x 22 steel channels into two angles dimensioned at 3.315″ x 2″ with the two legs having different thicknesses.  Then the custom angles were curved with the 2″ leg in to an inside radius of 1ft 11in.

These angles are being used to hold up a canopy for a bus station located in Texas.  When the commuters are waiting for their bus they will be protected from the sun and the rain by an engineered canopy incorporating curved angles with unusual dimensions.

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Aluminum Channel Bent to Represent a Double Helix DNA Model

Bending aluminum channel can be difficult.  Under extreme conditions, it tends to crack.  Bending aluminum channel into a helix is even more of a challenge.  With the right tooling, machine, machine operator and process, however, some impressive bends can be achieved.

The new Manning Family Science Building, designed by architects Bartzen & Ball, recently went up at Woodberry Forest School in Madison County, Virginia (a private boarding school for boys, grades 9-12).  Centered in the front vestibule of the building will hang a sculptural light fixture, the “Double Helix Chandelier”, meant to represent human DNA.  4″ aluminum channel was rolled in a right-hand helix at an extreme pitch of 48 degrees to represent the sugar-phosphate backbone of the human DNA.  These helical rails will be assembled, with their respective cross braces, and installed by Gropen Company.  The cross braces, that will represent the adenine/thymine & guanine/cytosine bases, will be made of LED media tubes, manufactured by Traxon Technologies.  DOT XL LED lighting will also be affixed to the outside of the helical rails.  Once combined, the LED media tubes and the DOT XL LED lighting will be programmed to emit a pattern of colors that represent the components of the DNA strand.

Aluminum Channel Curved into a Helix

Other projects involving curved steel sections have been inspired by the DNA helix.  The monumental, circular staircase at the Drexel University Integrated Sciences Building mimics this design by using curved plate.

Steel Plate Curved into a Helix

And a sculpture at the Laboratory Corporation of America in Burlington, Vermont, one of the nation’s largest in stainless steel, is comprised of pipe bent into a helix.

Steel Pipe Curved into a Helix

Artists, engineers, steel fabricators, and owners are attracted to these helical designs and turn to specialty steel fabricators, primarily benders and rollers, to see if they can turn their ideas into reality.

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Curved Steel Beams and Channels Used as Walers

Steel beams and channels rolled into a circle and installed horizontally are often used to reinforce soil in trenches.  These rings are called walers.  Typically, steel sheet piling is driven into the ground behind the walers.  This creates a ring template used to protect workers and to allow construction equipment access to an excavated area.

Excavating and pile-driving companies, as well as the Army Corp of Engineers, use walers in their shoring, seawall or cofferdam projects.  Since these systems are designed to prevent collapsing, engineers must specify the size of the steel member based on its section modulus.  This measure of strength determines how much the waler will yield against the pressure of the earth or water.

Walers Reinforcing Steel Piling
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Alternatives to a Mandrel Bend of a Large Channel to a Minimum Bending Radius.

When one considers ways to bend a large channel flanges-out to a minimum bending radius, doing a mandrel bend is one alternative.  A recent requirement was for more than 200 rolled channel, bump protectors to cover cement columns in an airport.  The design called for MC12 x 10.6 curved to a very tight 12-1/2 inch inside radius in 180 degree segments.

Using a rotary draw machine to do a mandrel bend would provide good productivity and quality but would require the development and manufacturing of a special set of tooling.  (Most bending companies would not have tooling for this unusual size.)   The customer’s very tight delivery schedule, however, did not allow time to make the tooling.

Another way to make these parts was considered:  rolling the channels on a three-roll section bender. Like a mandrel on a rotary draw bender, the tooling on the three-roll bender would support the web of the channel.  But when the company referred to its records of previous work like this, it looked like this method would not yield the quality and productivity needed even though the tooling was already made.

Curving these channels on a specially designed plate roll was also considered and that method turned out to provide the best quality, productivity and short turn-around time.  A template was made to ensure the needed quality.

If a bending company has a wide range of similar machines and a wide range of machine types, it is often the case that alternate methods to produce a curved steel section can be explored.  It is beneficial, for example, to match the right size section bender to the steel section to be bent.  Having  separate machines to bend 1×1 angle, 2×2, 3×3, 4×4 all the way up to 10×10 angle, to give one range of sizes and sections, allows such a company to put the material on the machine that will best minimize the trim or waste at the end of the rolled section while providing the highest quality, productivity and fastest turn-around time.

Furthermore, if a company has a wide range of machine types, it can explore alternate methods to create a curved steel section.  Bending companies might have rotary draw machines, three-roll section benders, plate rolls, ram benders, press brakes, and other machines to curve steel.  To the degree that a company has some or all of these machines and knows how to use them, to that degree it can be the most versatile in providing solutions to its customers’ steel bending requirements.

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Dialogues About Beam Bending, Channel Bending and Tube Bending

Specialty subcontractors who curve steel often enter into a dialogue with their customers about beam bending, channel bending and tube bending.  The results of these discussions can determine which steel sections to use in a project and what the costs might be. And the earlier that these conversations take place between the specialty subcontractor, the structural steel fabricator, the engineers and architects—indeed everyone who is involved—the better.  Sometimes the dialogue leads to unusual solutions.

For example, at the San Jose International Airport, one solution for roof supports called for two beams to be welded together.  This fabrication required a profile tolerance of +/- 1/16 of an inch to ensure that the beams curved by the rolling house could be welded together by the steel fabricator.

Another requirement called for bending aluminum channels.  When no channel was found large enough, the solution was to cut one flange off on each of two 12in channels and then to weld the resultant angles together to make a 24in channel. This channel was then curved for a canopy.

A recent inquiry came to a bender/roller for bending 12 x 8 tubing against the strong axis to a 7ft radius—a tight bend—for the entry to a stadium.  The project engineer at the rolling house discussed bending the tube on a large section bender, bending two 6 x 8 tubes against the weak axis that would be stacked one on the other, or using heat induction bending.  The structural steel fabricator is going back to discuss the options with his customers.

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