hoping maybe somebody can help me get a handle on a little problem i got. The company i'm currentley working for is making military surplus parts. lifting slings for humvees and what ever else the can bolt em to to lift with the helicopters. anyways welding parameters are very strict and have to be perfect everytime. basically the are 12" 2.5 1/4 wall square tubes with ears welded on the sides of them and a 1x1 1/4 fb on the ends where holes get drilled through for reinfocment. so heres my problem. im using a miller shopmaster 300 and running 98 2 gas at 28.5 volts and alot of wfs (sorry no number i just got a dial on this dinasour) but i can run one pass great and then the pass on the other side of the plate i almost always end up with a nipple or a small hole, sometimes a huge hole! ive tried so many ways to stop this problem with no luck. I'm guessing its trapping air somehow and pushing out at the end of the weld. i hope i explained this good enough cause it's starting to really tick em off im tired of grinding pinhloes out!!!!
Hello jesusno2, I believe you could be experiencing expansion of trapped gases between the parts, or relative to enclosing the tube as one possible reason. Just the other day one of the other fellas on the forum was commenting on something similar, he said that he would allow the part to cool a bit before putting the finish pass on. I'm not completely following your description, but possibly set-up quite a number of these and as you're welding them out, do so in such a manner that you are able to allow a bit of cooling time before welding the pass in that has been giving you the pinhole issue. You might also need to look at the condition of these parts before fitting and welding them. You mentioned that one of the components for this weldment is tube steel, the preservatives that they use on these when you receive them from your supplier are somewhat oily/greasy and could be contributing to the problems that you are seeing. You could possibly be experiencing additional issues if the sawing fluids aren't being cleaned from the parts before you are fitting and welding. If you have any "metal core" wire available you could use this product to provide a possible improvement in your condition. When this stuff first came out I was told by a Lincoln rep. that it was designed for use on tube steels for dealing with some of the issues associated with these materials and reduced or eliminated the amount of cleaning necessary. A few thoughts to consider. Best regard, aevald
Allen has a great point in that saw cutting fluid is most likely causing the problem. On long sections of tube this is usually not a problem since the heated gasses inside has plenty of area to expand before they cause pressure to build and escape during the last few millimeters of the closing weld. However on sections less than..let's say 8-10 inches, the boiling gasses from the cutting fluid trapped inside can create a problem when sealing the last weld. Also, the heat input has a great effect also and as your parameters indicate, you're running spray which will produce a lot of heat into the base metal. If your tubes are short enough to push a rag through with a flat bar or screwdriver, try wiping the inside a few times and see if that helps. I also agree with Allen in welding up one side of them in a batch, then welding the second side.
running 035 hardwire on these parts today i fought like hell with these holes "again" i did try the cooling idea and it did seem to work sorta sometimes it seemed to make it even worse. the tubes come to me cleaned and pretty free of oil. and being a production part their is no time to clean them really if needed when we have to pretty much meet a quota at the end of the day. i'm pretty sure its a gas expansion problem cause it does it the same time almost everytime. i'm wondering if maybe a preflow and a postflow would help this problem although my machine is not setup for it their is one that is.
Hello jesusno2, I don't believe that a pre or post-flow would be the answer to the problems you are experiencing. Your external gas shielding isn't what is causing these holes. You have some form of contaminating oil/or otherwise that is causing a volatization of gas from an internal source. You need to remove the cause for this by doing some form of cleaning or prevent it from reaching a level that will build up enough pressure to blow out the molten pool before it has solidified. One other possibility would be to convince the powers-that-be to provide a vent-hole in the design of these parts and thus provide an outlet for this internal pressure and remove the problem with the welding. A bit more food for thought. Best regards, aevald
Well I had the same problem, But with 20" pipe 12` long with the closing weld. We cooled about 2` of the pipe with liquid nitrogen, then imediately closed the weld.
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