Re: Heavy 10 Single Tumbler Gearbox - Want to Buy
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I know it is not common excepted practice, but I used to turn up the argon/mix on my Mig and welded cast all the time without failure of the welds. I did weld some broken castings from a 24 inch X 12 foot South Bend of about 1920 vintage. They welded easily with the mig and were still in service when the lathe sold 30 yrs later. My guess is the mig allowed less heat and a more flexible filler metal. It has worked for me on a multitude of items, but try at your own risk.
On Saturday, September 11, 2021, 03:07:11 PM CDT, eddie.draper@... via groups.io <eddie.draper@...> wrote:
I have a good number of successful C/I weld repairs to my name. I use only pure Nickel MMA (stick) rods and a DC welder, with the job bombarding the electrode with electrons so it gets 2/3rds of the heat and the job only 1/3rd. (I.e. electrode +, job -, the usual arrangement with DC welding.)
There are 2 ways to proceed, either you need lots of tea and get very thirsty, or you can drink lots of tea.
The first way is to make the whole job red hot and keep it that way throughout the process, allowing it to cool uniformly afterwards. One way to achieve uniform cooling is to insulate and therefore cool slowly, but there are other ways. This is very good where the size of the workpiece brings it within your heating capabilities. There are professional outfits that weld large objects like this, by building a firebrick oven around the job, sticking a gas torch through a hole, and then welding via another hole. Not a pleasant way to earn a living on a hot day. British Rail used to have locomotive cylinder heads of V16 3300 HP Diesel engines (10" bore x 12" stroke, which is approximately 15 litres per cylinder) welded like this, and they lasted no worse than a new one.
The other way is to heat only to take the chill off, say 50C, and weld for no more than 3 seconds at a time, immediately then hammering with a pointed chipping hammer, then allowing heat soak for a while to spread the temperature throughout the object. For large objects, and especially handy where there is more than one job to work on. I once repaired 5 cast iron window frames like this, keeping moving from one to the next almost without dead time.
Both methods need a weld prep that is virtually like one for steel, BUT the materials have a quirk, and that is that the arc tries to stick to one side of the groove or the other so you need to have a groove that is wide enough for you to be able to keep pulling it back & forth.
I always try to make the job stronger than the original, especially if I don't know why the crack occurred. One of the attached photos shows a radius rod lifter from my steam loco which contained a longitudinal crack. I can't imagine how that occurred, so after welding, I shrank on some steel reinforcing rings. The original profile is still on the RH end.
The other photo is me grooving out an oil tray from the underside of an axle bearing. I could see why this was cracked, a weak design in conjunction with heavy handed spannering, so the only post weld "reinforcement" here has been painting the oil side with fibre glass resin to keep the oil from penetrating any porosity, and being careful with the spanners.
Both the above jobs were in the "small" i.e. hot category. I welded a longitudinal crack in one of the cylinders the cold way, as heating the whole cylinder was entirely unfeasible (just over 8" bore and probably weighs 1/4 ton). Additionally, it had just been rebored and the valve face skimmed, so I didn't want any distortion. The crack started at a weak point where a cylinder drain cock hole was in line with a hole for a cover fastening stud (it would have been so simple to avoid this alignment and weakness at the design stage, but that was pre 1914). In addition to welding up as much of the crack as I could, I drilled & tapped across the line of the crack through the drain cock boss for a grade 12.9 Allen screw, bolted a block either side of the crack and pulled these together with 2 more Allen screws, and added some extra cylinder cover fasteners either side of the existing and made sure those were properly tight. The weld needed to be ground back a little below the rubbing surface for the piston rings, as Nickel is a poor bearing material, known to cause crankshaft bearing seizures in Diesel engines if the interlayer that prevents diffusion between layers of a shell becomes exposed to any great extent.
I suggest you practice on a piece of scrap first, in order to prevent the job from becoming just that! Take care to preserve critical alignments during all processes. In the case of you gearbox, it would be the holes for your shafts. Maybe clamping across the crack to hold it shut during the hot work would be the right thing to do.
Good luck and best wishes,