Join Date: Dec 2001
Location: Belleville, Illinois
Thanked 18 Times in 13 Posts
Re: metal thickness and mig welding
[ QUOTE ]
Sure, you can "weld" something 10 feet thick with a tiny welder - with enough passes. But would it be Strong?
[/ QUOTE ]
Yes. A friend who is a union ironworker worked on Lock and Dam 26 at Alton. One of the projects he worked on was one of the lock gates that is a huge curved plate mounted on arms that swing the gate down to the bottom of the lock chamber so that tows can pass above it. I think that it is called a Tanner Gate.
It was assembled in place and he and several other ironworkers spent many days, in shifts around the clock, welding the arms to the gate. It was summer, but they used heating blankets constantly to keep the steel warm, and tents to keep the wind off.
They would spend an entire shift laying in pass after pass. Then at the start of the next shift an engineer crew would come in and X-ray the weld. If there were any flaws they were gouged out with an air-arc. Then the next crew would start laying in weld.
It's been ten years or more and I don't remember a lot of the details, but I think the welding went on for several weeks. And I believe that when they were finished with the welding they spent several more days, if not weeks, with the heating blankets slowly cooling the assembly.
The Corps of Engineers is happy, and the welds haven't broken. So yes, multiple pass welds can be strong. I believe the consideration in multi-pass welds is 'wetting', which says that if the new weld bead wets, or melts into the surface, it is bonded. The surface is as strong as what's under it, so there's no need to penetrate a great distance into the base metal.
Of course, they didn't use a 110 volt inverter to weld it, they used BIG welders so that they could burn lots of BIG wire into the puddle, and do it hour after hour without stopping. Their progress was discussed in terms of pounds per shift. But the principals should hold for a smaller weld with a smaller machine and smaller wire; it's all in the joint design, preparation and technique. If they're right you will have a good weld.
Where penetration really becomes critical is in a joint where the pieces aren't V'd out. If you butt the square edges of two quarter-inch plates together, your machine better be capable of melting a puddle a quarter inch deep.