I am watching once again as our shop splits "W"s into "WT"s to be used as diagonal bracing (WT 4 x 5 this time). Once again they are warped and require much labor to straighten. We are using plasma and a straight edge to cut the "W"s in half. They have tried cutting from one end to the other, leaving an inch or two left at the end to separate the two halves. We have tried to cut from the center out with the same basic results. There must be a better way to do this and save the labor of straightening them afterwards. Does anyone have a procedure or a suggestion to split "W"s and reduce or eliminate the labor intensive straightening routine?
Some of that distortion is inherent to the material as it was processed (rolling/heating/cooling). I have seen cold saw and water jet-cut parts that have distortion and you can actually see it during the cutting process as the shape or plate is cut. The parts oil-can or flop around as the internal stresses are relieved.
I don't think you will eliminate it completely.
Excuse my lack of knowldge here but I am not sure I am familiar with the terms "W" and "WT". Could someone enlighten me?
Thanks,
Brian Maas
Brian:
If you have an AISC Manual of Steel Construction - ASD manual, look in Part 1, these refer to structural shapes.
W = Wide flange beam
WT = Tees (T)
Thank you,
I knew that but for some reason it just didn't register.
W indicates a wide flange beam and WT indicates a Tee produced by cutting a beam (W), lenghtwise
Give some thought to intermittent thermal cutting. Start your cut several inches in from one end. Make that cut 12" to 18", depending on the L.O.A. of your material. Start your next cut 6" to 8" from where the previous cut was terminated. Use the same procedure the entire length of the material. Allow the metal to cool to 125 - 150 degrees. After cooling, cut the material remaining between the existing kerfs. I have seen this procedure used when I worked at a shipyard. The results were favorable and distortion was at a minimum.
I've never used, but have always been curious about the vibratory stress relief systems that claim to aid in the elimination of distortion and residual stresses.
I bet your particular situation would be a good test for this type of system’s abilities. Perhaps you could get a sales rep to set up a demonstration on your materials. If it works, then you'll have proof to warrant the expense for buying the system.
Has anyone out there had success with vibratory stress relief?
Tim
I have seen them stitch cut and then straightened in a press as needed.
Plazma cutting on a water table may help also.
G Austin
Most of the time when we order "T's" they come already cut most of the way down the web and only a few inches here and there hold it. After we cut the remaining few inches it shows its true colors and you will spend a few minutes heating and straightening. Adding to the distortion is the fact that we run the "T's" through our beamline punch before we finish splitting them. Depending on how many holes are punched in the flanges determines the amount of additional straightening required. I'm not sure you can eliminate distortion all together.
Good Luck and let us know if you run across something that works for you.
John Wright
John Wright's post is the easiest way to get straight WTs. If you order your materials to comply with ASTM A6, the supplier must make sure straightness is within the listed tolerances. Most of them use powered rolls to split and straighten the WTs.
{Addenda: I misread John's post. I Thought he meant he buys WTs already split and straightened which is what I meant.}
As far as splitting your own beams, we use a plasma torch and submerge most of the beam in water. We interrupt the cuts every 5 feet or so in order to leave "tabs" along the length. Travel just as fast as you can go while still getting good cut quality. That reduces distortion but will not eliminate it.
Be careful in cutting the tabs to finish the split. The 2 halves are preloaded and can spring apart with a lot of force!!! A safety chain wrapped loosely around beam is a good idea if they do tend to spring apart. (I've seen some beams "un-zip" the tabs for the full length when the 1st tab was cut.) Sometimes the ends curve outward and sometimes the middle curves out, depending on the amount of heat dumped into the beam and internal stresses of the beam.
If straightening is needed, we like to make linear heats with a Bug-o Unibug and small rosebud. It is easy to duplicate the heat input from piece to piece, by keeping flame size the same and noting the speed setting on the Bug-O. Once you find the speed and flame size that works, you can go through a stack fairly quickly.
The key to productivity is to move on to the next piece without waiting for the previous WT to cool. I mention this because there is a tendency for workers to hold back because they see the WT curving the "wrong way" and think they have messed up. They don't immediately realize that the steel will move the opposite way on cooling and actually straighten the piece.
Have fun,
Chet Guilford
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