Hi bankswelding,
Since the joint edges of the thin plates have the tendency to move up or down as welding progresses, you might want to consider the backstep technique as a means to help minimize disortion. In the backstep technique, the general progression of the welding may be, say, from right to left, but each bead segment is deposited from left to right. The technique consists of dividing the continuous weld into short increments, and depends on depositing the beads in a direction opposite to the direction of general weld progression. Tack welds should be evenly spaced every few inches apart, starting with a tack weld on the edge of the plate. The welds may be made in a sequence such as in the order of 1,2,3,4,5,6, and so on. Weld 1 would start at the second tack from the edge of the plate, and is welded back towards the edge. Weld two would start at the third tack, and is welded back towards the end of where weld 1 started, and so on. With the lengths of welds for your application, you can spread out your welding sequence more. The short beads produce triangular heat patterns. Since most beads end up on the start of the previously deposited beads, the heat input is evened out. Because back stepping prevents an accumulation of stress along the joint, there is also less of a tendency for the joint edges to buckle. A variation of backstep is the skip technique, where the welds would be made in the order of 1,3,5,2,4,6, and so on. The key is to distribute the welding heat as evenly as possible through a planned welding sequence and weldment positioning. Using high deposition rates and high speed welding methods will help. Welding vertical down would be a big help too, if this is somehow possible in your application. If you're mig welding, the short circuit transfer mode would help minimize distortion as well. Also, is it possible to use intermittent welds as opposed to continuous?
While back stepping and sequence welding are good techniques for minimizing warpage, I've always found that good design is the best eliminator.
For instance, how about eliminating the 43' weld down the center by turning your sheets the other way. That way you would only have tranverse welds to worry about.
Also, do these sheets have to be seal welded? Perhaps they could just be stitch welded?
Do they have to be welded at all? Why not just screw them down to the existing floor? If water tightness is a concern, gaskets and or caulking are good for that as well.
If you are welding these sheet together outside the trailer and then installing, a removable angle iron strongback on the opposite side of the plate works great.
It sounds like you're tring to work yourself to death on this one. Just remember that there's more than one way to skin a cat!
Good Luck!
Tim
If the existing floor is sound, do you have to replace it? Could you apply a non skid coating to it (epoxy paint with aquarium gravel, or a commercial product)?
If steel tread plates are required, could you screw or rivet the plates? If you have to weld the plates, maybe screws or rivets could be used to flatten the "puckers"?
You are already doing what is recommended to reduce distortion.
The only other thing I can think of is to heat spots in the middle of the plates to a dull red. You are having a problem with flatness because the welding is shrinking the edges but the center of the plates are not shrinking. A series of round hot spots should help that out. Trial and error will show you where to heat, just start out conservatively. Of course be careful not to set anything on fire.
Chet Guilford
Hi
While there is a lot that you can try to reduce the amount of distortion, with conventional techniques, you will always get buckling when welding long welds on thin plate. If you need to do a lot of these trailers, then you can try to get hold of some very specialized equipment that uses certain paterns of heating and quenching around the weld, as the weld proceeds. The nett effect being that there is in essence no distortion and buckling. This is a specialized technique, using specialized equipment, but it is the only way that I know of.
If you are interested, I can give you a reference to a paper that I have on this technique. (By the way, I do not sell this equipment:)
Regards
Niekie Jooste
Fabristruct Solutions
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