Aluminum versus Steel Aerial Ladders
Jim Salmi, the director of aerial product development for E-ONE, is considered one of the aerial gurus in the nation. He has more than 30 years of experience designing and building aerials, has been actively involved with industry organizations, serves as chairman of the aerial subcommittee of the Fire Apparatus Manufacturers Association (FAMA) and as a group chair for the National Fire Protection Association (NFPA).
“Ladder material has largely become a matter of department preference,” Salmi said. “It’s like the Ford or Chevy debate. When properly designed and validated, both are very viable materials to use for the fire service.”
He said a lot of people have strong opinions. “They’ll say ‘I hate Ford, but does Ford make a good pickup truck, yeah.’”
While it might be a matter of personal opinion about which material is better, there are differences, Salmi said. For example, steel has a higher resistance to heat and it is minimally affected by higher temperatures. Aluminum requires tempering to strengthen it, Salmi said. Virgin aluminum has a strength rating of 15,000 to 18,000 psi, which can be increased to 35,000 to 38,000 psi through heat treating.
Conversely, it takes less heat to take the tempering out of the aluminum than steel. The integrity of aluminum should be checked when it’s exposed to temperatures of 300 degrees Fahrenheit and above. Steel, on the other hand, can withstand temperatures of up to 800 to 1,000 degrees Fahrenheit, Salmi said.
To make up the difference, aluminum ladder manufacturers use thicker materials, and can manage the weight because aluminum is one-third the weight of steel. Aluminum can also be extruded into shapes that are designed to handle stress and be stronger than the virgin material left alone.
“Lighter aerial devices can reduce the amount of outrigger stance needed for stability and reduce the set-up space,” Salmi said. “It comes down to which you are more familiar with. Chicago has steel and aluminum and they are happy with both materials.”
Salmi explained that steel has a greater surface hardness and it’s a tougher material whereas aluminum is not quite as resilient. The trade off is that steel is much more susceptible to rust and corrosion and it must be painted and sealed to keep out water, one of the key ingredients to rust.
“Steel ladder manufacturers go to great lengths to seal materials to prevent corrosion,” he said.
Aluminum, on the other hand needs very little to control corrosion, according to Salmi, who noted that aluminum doesn’t need any surface treatment. Some people like the look of the brushed swirling on the rails and other aluminum ladder components.
But, there’s a caveat to the corrosion issue, Salmi said. Aluminum and steel- and zinc-coated steel don’t like each other very much and if the materials touch each other, there can be corrosion on aluminum aerials as well, called galvanic corrosion. Salmi said aluminum is the sacrificial metal so it can possibly corrode when in contact with steel, stainless steel, or zinc-coated steels. So where the ladder interfaces with the turntable, or waterways, lights and other steel materials that get affixed to the aluminum aerial, there’s a chance for corrosion to occur. The designs most consider the means of isolation of the metals in areas of contact.
“So it goes both ways,” Salmi said of the corrosion issue.
Salmi also said aluminum extrusions mean the rungs can be shaped with tread grips already in place. On a steel aerial, the treads have to be affixed to the rungs by glue, epoxy or some other means.
Steel is an easier metal to weld than aluminum, according to Salmi, who noted that if a repair has to be made, there are generally more facilities with certified steel welders than aluminum. Steel welds can be visually and magnetic particle tested for defects and aluminum welds are normally visually inspected as well with an occasional use of dye penetrant to check for defects.
E-ONE, which is widely known for its aluminum aerial products, introduced a steel aerial last year. Salmi said it has nothing to do with one material being better than the other. Rather it has to do with competing in both the domestic and the world market.
Salmi said the international aerial market is dominated by steel and that has to do with the Germans who developed the first aerials, which were made of steel. So, that’s the material most of the world is familiar with.
“If you don’t have a steel product, you’re limited in the world market,” he said. “Steel is the standard in many countries around the world and if you don’t have it, you can’t compete.”
So from Salmi’s perspective, the debate is really one similar to the “Ford vs. Chevy” argument.
“The higher strength steels that are now available at 100,000 psi yield allow the weights of steel and aluminum devices to be very similar,” Salmi said. “There really is very little performance difference between well-designed aluminum and steel aerials.”
Firehouse.com, BY ED BALLAMRead The Full Article