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OEM Report: Heavy Equipment/Construction

Up in the air

By Meghan Boyer

November/December 2010- A system malfunction on an aerial tram or lift--especially one that carries more than 100 passengers a distance of 3,100 ft. up to 250 ft. in the air--potentially can place passengers at risk. Ensuring their safety begins with proper engineering and quality fabrication and continues through rigorous parts testing--all before a single passenger boards the system.

It is important to have the proper designs for components, says Tom Clink, sales manager for Leitner-Poma of America, Grand Junction, Colo. "The fabrication of components is critical as well as the amount of [testing] that’s done afterward."

L-POA engineers, manufactures and installs ropeway transit systems for the ski industry, tourism, amusement parks and urban transport. The company has completed roughly 430 projects since 1981 out of its Grand Junction facility. Sometimes, however, the company tackles a different type of project, like the large-scale modification of the Roosevelt Island Aerial Tramway in New York.

The tram transports commuters 3,100 ft. between stations at Roosevelt Island and Manhattan across the East River. Annually, more than 2 million people ride the system, which opened in 1976. A system malfunction in 2006 stranded 69 people in the tramway for roughly 12 hours, and a power failure in 2005 trapped roughly 100 riders for two hours. The difficulties in part led the Roosevelt Island Operating Corp., New York, which oversees the tram system, to update it.

"They wanted to make sure that regardless of anything that might happen, it was going to be able to operate," says Clink. The existing system, known as a jig-back tram, had the two tram cars connected on opposite ends so they both had to move together. L-POA created a new design that enables the cars to operate independent of each other. "If one tram has an electrical/mechanical problem, the other one can still operate," he says. The company also established a number of redundant operating systems to avoid the potential for stranded commuters.

One of the benefits of the tram renovation is each car can operate independently in the event of malfunction, maintenance, rush hours and other scheduling requirements, according to the Roosevelt Island Operating Corp. Transit on the tramway stopped March 1 for modifications, and it is expected to reopen this year. The only parts remaining from the original system will be the bases of the three towers, which will hold new tracks to accommodate a wider-gauge cable and more advanced transit system, notes the company.

Each tram car can hold 115 passengers, which puts immense tension on the cables--more than 100,000 lbs., says Clink. "We did all the tower modification," he says. "The actual towers that were existing were reused, and then the top part of the tower and the crossarms that support the cables were replaced." Working on the tram meant fabricating components in larger sizes than the company typically creates for ski lifts, which makes the project unique for the company, he says.

Larger components
For the Roosevelt Island project, L-POA created four track saddles for each tower that each measure 120 ft. long. "Normally we do not do pieces that large," says Clink. The tram cars run on track ropes supported by the track saddles, which are long and curved "so that the ride is ultra-smooth. You don’t get a big bump as you go over the tower as you change from climbing to horizontal between the towers and then back down to the stations," he says.

The track saddles are pieces of plate that workers cut in a radius and welded together, says Clink. Workers flame cut the plate because it was greater than 1/2 in. thick, says Clink, noting the company uses plasma cutting on metal less than 1/2 in. thick. "Being 120 ft. long, we can only cut 16 ft. at a time. It was a bunch of plates that were welded together that has this particular radius to them," he says. Workers then placed bar stock that measures roughly 3/8 in. by 6 in. at a 90-degree angle to the vertical curvature and welded it on.

L-POA purchased a machine for the project that chamfers the steel that runs along the vertical pieces of plate and cuts the corner off to allow for a fillet weld, says Clink. The purchase ultimately saved workers time. "We bought this machine that actually cuts the corner off of that radius and gives us a clean place to weld rather than spending days grinding," he says.

The company also fabricated all the crossarms for the towers that support the track saddles. "All of those parts had to be modified to attach to the reused towers, so there are tons of angle iron and other parts that were fabricated to support those," says Clink.

L-POA has a full fabrication shop at its facility that contains band saws, plasma cutters, lathes and machining centers. Workers typically cut everything from I-beams to rectangular, square and round tubing to length and then perform machining on it for shafting, pulleys and various other components, says Clink. The company typically uses mild steel because of its fatigue resistance and also uses a lot of cast aluminum, he says.

The Grand Junction facility is on 19 acres with 92,000 sq. ft. under roof. Typically, the company completes between 10 and 18 projects annually, but the recession has slowed business somewhat. L-POA employs roughly 100 people in Grand Junction and field crews of 30 to 40 that install projects.

Unique needs
To meet specification needs for its various components, the fabricating team at L-POA has created not only some of its own manufacturing techniques but also some original equipment, says Clink. Ultimately, the company performs the programming and builds special tools. "Most of the machines we use are not necessarily standard," he says. "They are ones that we’ve modified."

To create bullwheels, "we use a submersible arc welding machine that is fairly standard, however the components used to support and rotate the bullwheels while running sub arc were designed and fabricated by L-POA," says Clink. "We buy standard products, but they all need little tweaks to make them work for our particular fabrication applications."

Each of the two bullwheel drive assemblies for Roosevelt Island is an impressive piece of technical design and fabrication, says Clink. They propel each haul rope, causing the tram car to move. Two electric motors and gear boxes attach to the center shaft, one on each side. Additionally, there is a ring gear with a hydrostatic drive, plus there is a second parallel bullwheel on each. This allows a separate hydrostatic drive to move the car by moving the haul rope to the second wheel. The redundancy of the totally independent drives and bullwheels helps to ensure passengers will not be stranded should a malfunction occur on any drive component.

The bullwheels measure 4 meters in diameter, and they are within 2 thousandths of being perfectly true, says Clink. "There is a lot of welding on a bullwheel, and every time you weld, it pulls it some direction. You weld on the other side, and it pulls in the other direction," he says. "Getting it to remain absolutely flat takes a very specific welding process and technique."

L-POA engineers developed a way to bend a piece of 60 ft. channel to the correct radius to fit around large bullwheels that measure 4 meters to 4.5 meters in diameter, says Clink. The process requires only one weld to the channel instead of multiple welds, which is the case if the engineers were to use three pieces of channel. "We developed this machine to be able to bend a 60 ft. piece of channel in the correct radius so that there is only one weld," he says.

The machine consists of multiple rollers. Workers place a straight piece of 4-in. channel into the machine and adjust the dimensions of the rollers so the spacing produces the correct radius for the corresponding bullwheels, says Clink.

The engineers also developed a method to machine the bullwheels. The bullwheels come out nearly perfectly flat, but then workers machine them to within 2 thousandths of being flat. They use a horizontal bullwheel lathe, says Clink. "We fit this big wheel onto this machine that we built and, just like you trim the brake discs on your car, we machine the surface," he says.

Testing for accuracy
L-POA uses conservative engineering to "overbuild" components for its lift systems, notes Clink. The company also uses a series of checks throughout the manufacturing process to ensure everything it produces meets regulatory requirements. The workers conduct non-destructive testing on the components that go into L-POA projects, including the Roosevelt Island tram. Testing typically includes wet and dry mag particle and some ultrasonic testing, says Clink.

"With mag-particle testing, workers induce a magnetic field to the component being tested. They then spray dust-like ferrous particles on the piece. As long as it creates a visually smooth surface, it’s OK," says Clink. "If there’s some variation in the weld where it is not totally connected, then it will leave a hump or a bump because the magnetic field doesn’t transfer evenly through the piece," he says. The magnetic field breaks when there is a problem with the welding, and the ferrous dust gives a visual indication. A break in the weld may occur with stick welding if a worker stops and starts again without connecting the new bead to the one he or she left behind, says Clink, noting L-POA mostly uses wire feed welders. "With welding, you have got to penetrate the steel. If you are not penetrating enough, you’ll see the variations because of how the magnetic field transfers," he says.

The company performs 100 percent non-destructive testing on all critical components after workers have welded or fabricated them, says Clink. "On less-critical components, we do anywhere from 100 percent down to 10 percent, depending on how critical the components are and what the results of potential problems are," he says. The company adheres to the ANSI B77 code for aerial ropeways in the United States.

Only two major ropeway manufacturers exist worldwide, says Clink. L-POA and its parent companies Leitner in Italy and Poma in France compete with an Austrian manufacturer. Attention to detail and quality engineering and fabrication is required in the ropeway industry, but a competitive advantage for L-POA is that the company performs all of the major fabrication and engineering work together onsite at its Grand Junction facility for projects in North America, New Zealand and Australia.

"If one of our fabricators has a problem, they can walk upstairs and talk directly to the designer," says Clink. The engineers receive a lot of feedback from the fabricators regarding component design, which increases efficiency for fabricators and reliability for customers. "That’s one thing that I?think is really important--to have the engineering staff and the fabricators here in the same building," he says. FFJ

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Sources

  • Leitner-Poma of America
    Grand Junction, Colo.
    phone: 970/241-4442
    fax: 970/241-3023
    www.leitner-poma.com

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