August 10, 2015 / best practices, blade failure, blade life, blade selection, cost per cut, industry news, LIT, preventative maintenance, productivity
As reported in our recent Metal-Cutting Industry Report on Non-Residential Construction, the use of industrial and structural steel tube and pipe is growing. According to a market tracker from Metal Bulletin Research (MBR), the category is growing at the fastest rate since the recession, mostly due to economic growth and falling oil prices.
“Construction demand for structural tubing is now growing at a steady pace in most regions of the USA,” the MBR report states. “There has been some concern among market participants that the drop in oil prices and the associated hit to the local energy-centered economies would be detrimental to their construction outlook, especially since these were some of the initial drivers of growth in the recovery. So far, construction continues unabated, as contracts, financing and permitting have already been settled.”
Industry players are also optimistic. HGG, a supplier of tube-processing machinery, told MetalForming magazine it expects the category to grow by about 15 percent in North America alone. (You can read the full MetalForming article here.)
This is good news for fabricators that serve the industrial and commercial construction industries or that cut structural tube for other applications. In either case, most shops are working with hollow structural steel (HSS) tube specified to ASTM A500 (the standard specification for cold-formed welded and seamless carbon steel structural tubing in round, square and rectangular shapes). Although most shops wouldn’t categorize HSS as difficult to cut, it does have some unique characteristics operators need to understand to ensure proper cutting.
Unlike solid tubing, which only requires one cut, HSS tube requires the blade to cut through two thin solids with a space in between. These types of cuts—known as interrupted cuts—are best suited for bi-metal band saw blades because they are designed to withstand the vibration. Carbide band saw blades, on the other hand, have strong, durable teeth, but they are not shock resistant. Therefore, bi-metal blades that reduce harmonics are the best choice.
HSS tubes also aren’t ideal for bundle cutting. While cutting tubing in bundles can allow shops to increase the number of parts per shift, it can substantially reduce blade life. In fact, some experts say that any increased part volume efficiency is offset by a 20 to 25 percent reduction in band life.
A recent article from thefabricator.com highlights several other best practices for sawing structural tube. The following are a few of the industry publication’s tips:
- Look for variable clamping pressure. This allows for the vise-clamping pressure to be reduced to prevent deformation of thin-wall tube. The pressure should be enough to hold the tube firmly to ensure it doesn’t move, but not enough to bend it.
- Watch for the weld orientation. Although quality saws will cut a tube regardless of the weld orientation, a fabricator should position the weld at the top or side of the saw entrance, rather than at the bottom, to maximize tool life. (Note: In a bottom-up cutting configuration, the weld should be at the bottom or on the side.)
- Be aware of blade bias. When cutting non-round tubing in a band saw, it is preferable to have a bias on the blade (ie, a canted head). This is valuable for both good cut quality and longer blade life. Having the blade penetrate the material at an angle allows the fabricator to use the most efficient tooth configuration and prevents overloading of the blade gullet. Even a 1- to 3-degree bias will do the trick; a very large bias, however, will add to the overall cut time.
- Pay attention to tooth geometry. Using the correct tooth geometry for a particular application helps to ensure a quality cut, while also prolonging the blade life. Although it is possible to use one type of blade for most structural tube applications, fine-tuning it for longer production runs is worth the additional effort. As a general rule, a fabricator using a band saw wants six to 12 teeth to be exposed to the widest part of the cut.
For more guidelines on cutting HSS tube, including a discussion on circular saw blade options, you can read the full thefabricator.com article here.