How to weld 1/2"armour plate?

Darrin Wright · #1 28-11-12, 13:07

After info and advice on how to weld 1/2" mild steel plate into the existing front armour of the BGC (Australian).

Over the years I have heard of reverse polarity when using welding rods, also to pre-heat the armour with oxy and then to mig weld it or just weld away like normal.

What are peoples experiances when conducting welding repairs on this type of steel? In the next couple of weeks I want to get this repair work done to my hull.

Thanks

Richard Farrant · #2 28-11-12, 20:33

Quote:

Originally Posted by Darrin Wright

After info and advice on how to weld 1/2" mild steel plate into the existing front armour of the BGC (Australian).

Over the years I have heard of reverse polarity when using welding rods, also to pre-heat the armour with oxy and then to mig weld it or just weld away like normal.

What are peoples experiances when conducting welding repairs on this type of steel? In the next couple of weeks I want to get this repair work done to my hull.

Thanks

Hi Darrin,
I don't know about Australian armour plate, but British armour was welded with Nickel Chrome electric rods, hence the shiny welds. I do have a copy of a War Office booklet on armour plate welding. One thing for sure the edges of all plates to be butt welded have to be vee-ed out in order to get penetration. If armour plate is welded with normal rods, it can crack down the side of the weld, so best to use the correct procedures. I would think Colin Jones from Adelaide will be your local man on the subject.

regards,
Richard

Lynn Eades · #3 28-11-12, 21:18

My British built (welded hull) carrier, was welded with stainless steel rods. (I couldn't tell the difference between stainless and nickel chromium)
I was given some free old stainless rods which I found very forgiving (of my very average welding ability). Under normal circumstances, stainless would be a more expensive option.
Back in the day, arc welding rods were cumbersome and fragile, with the flux contained around the rod with a paper wrapping. They needed a high amperage to get them started. Hence the seemingly large amounts of spatter around some of the original welds.
I think back then, rods were "non contact", Now days, they are "contact"
(easier to use)

BTW, stainless welds wont gas cut, but arc-air gouging works well on it.

I too am waiting for Colin to chime in. I expect him to make it sound very easy.

Richard Farrant · #4 28-11-12, 22:05

Just found the booklet, Welding Technique - the Repair of Armour Plate in the Field, dated 1943.

The rods they describe are Austenitic, but it does state;
"if armour plate electrodes are not available welding may be attempted with ordinary 'stainless steel' electrodes of 18% Cr and 8% Ni type"

"All austeniitc armour plate electrodes should be operated on reverse polarity (ie. electrode positive = work negative) at approx the following values;
6 SWG rod size ; 120-180 amps
8 SWG ; 100-140 amps
10 SWG ; 80-100 amps "

Hope this is of help.

cletrac (RIP) · #5 28-11-12, 23:56

I would think a low hydrogen 7018 would be a good modern choice. They don't cause hydrogen embrittlement like most rods do.

Mike K · #6 29-11-12, 04:51

Hi Darrin

I'm not one to give welding advice , but

For steel that thick , you would be best to use a 3 phase welder , or a big DC welder driven by a petrol/deisel generator , you need big amps , single phase welding is not powerful enough .

If you have a TAFE near you, you may be able to enroll in a course and use their welding gear, they usually have big WIA 3 phase welders .

Try to study the original welds on the hull .

Also, they developed a substitute hardener for the local armour plate as they could not use Tungsten or Nickel as it wasn't available in Australia at the time ?

At a guess, the Aust. armour plate would have been made by BHP ?

Mike

The Bedford Boys · #7 29-11-12, 05:21

If you can, get the use of a decent MIG welder. Vee the edges of the material and then weld away.

I have welded up cracks in a carrier hull with a small Arc welder, using rods that weren't anything special and it came up pretty good. No cracking around the weld at all. Wouldn't want to do a whole carrier hull with it though, MIG is the way to go. Easier to tack things in place with a MIG too.

The welding on LP hulls can be pretty damn shocking from factory if you look at it closely. The factory welds on the bottom of the floor of my hull are spectaculary crappy, highly peaked and bugger all penetration. So don't run your welder too cold.

Keen to hear what Mr Jones thinks.

Joe Lorenzino · #8 29-11-12, 06:22

I have been working in a welding repair shop for a few years, so this is what I would suggest.

Although I haven't welded armour plate, we do have to repair cutting edges on loader buckets and such. The normal procedure is to "V" it out properly, then fill it in with narrow "stringer" beads using 1/8" dia. low hydrogen ( _ _18 series, i.e.: 7018, 8018, 11018 ) electrodes at around 125 amps.. If you have a DC machine, they are always run DC Reverse. If you have an AC machine, and it has sufficient open circuit voltage to start and run an _ _18 series rod (many of the lighter ones do NOT) then use a 7018AC rod which has ionisers in the flux to allow it to run properly on an AC machine. On plate that thin, preheat is not essential, but would help prevent possible cracking. A preheat of 200°-250°F is ample, and mostly used to dry out any moisture that my contribute to hydrogen embrittlement.

A better choice is a more "forgiving" low hydrogen rod (higher percentage-of-elongation) such as an ArcTec 223 from ArcTec Alloys. This allows the weld to stretch more than an _ _18 series rod, and so puts less stress in the base metal. We use this rod for the long welds when attaching cutting edges to buckets as it causes less warpage and has higher impact resistance.

Stainless rods ARE nickel/chromium, and the 18-8 they speak of would be a standard 304 grade. All of the "300" grades of stainless are "austenitic" meaning nonmagnetic and nonhardenable. Higher nickel (first number) makes it tougher, higher chromium makes it harder. If using this type of rod, a 304L, or 309L would be good choices as the "L" signifies "Low Carbon", and it will not pick up as much hardness from the base material. The drawback is the price, and that they do not weld very well out of position. A better choice in this category would be ArcTec 265 Unichrome, which has a much higher strength rating, and welds some what better out of position.

If wanting to use a MIG, I would lean towards a Flux core, Dual Shield, or Metal core type of wire, for added weld ductility. If using solid wire, a type ending with S2 or S3 would be preferable to an S6 wire because of a higher elongation value. If Mig welding, I would definitely use a preheat to prevent the weld from cooling to fast and causing hardness/brittleness problems.

A high nickel rod designed for use on cast iron, like an ArcTec Supercast 90, would likely give very good results as well.

cletrac (RIP) · #9 29-11-12, 09:04

Well, there we have it from an expert on the subject! Joe, I was by your shop the other day but you weren't around.

colin jones · #10 29-11-12, 09:09

Hey guy's! Darrin, quite simply, prepare, as in grind clean, V out about least half the thickness you're welding to both pieces and leave a little gap for penetration, High amps on your welder, set gas to 18-20. Solid wire welding with mig is already low hydrogen. If you're going to war then preheat if you're not "don't bother" inert mig gas prevents hydrogen from affecting your welds. watch your welding while you're doing it, you can see if it's flowing or sitting on top. if it's not a flowing a flatish weld then you need more heat or you're dragging instead of pushing. If you welder is on high amps it will put plenty of heat into the material anyway. Don't try and weld an oxy cut that still has slagg on it as it won't work.
"My 2 bobs worth""
Colin.

eddy8men · #11 29-11-12, 13:22

great thread fella's and thanks to all those that have given advice, i'll be needing it soon

cheers

rick

cletrac (RIP) · #12 29-11-12, 14:19

It looks like you have your work "cut out" for you!

eddy8men · #13 29-11-12, 19:18

very true

Lynn Eades · #14 29-11-12, 20:43

Thanks for your very useful posts. For those of us not so skilled, it is great to be able to pull up this thread in the future, as a reference.

Darrin Wright · #15 29-11-12, 21:38

thanks guys for all your input.
I am picking up a heavy duty mig today from a friend and will look at preparing the steel this weekend and commence welding next week.

I think (and this thread has confirmed) preparation is a very important factor, so will grind a vee on both sections of the hull & panel, and ensure any slag is removed.
Weld in some braces to support the new panel, some minor tacks to get it in the right spot, adjust with a hammer, then weld away alternating from side to side so that heat expansion does not affect the new panel.
When finished grind and tidy up the welds, then run over it with a flapper sanding disc to get the surfaces right. When the hull is blasted get them to concentrate on the welded area to get the surface texture the same.

Thanks again

Ian Mastin · #16 30-11-12, 12:02

G'day Darrin,

One more tip for you mate make sure you have tin of nozzle dip!!! this dip will help keep the head of the mig welder clean when welding.

cheers for now and good luck

warren brown · #17 06-12-12, 05:13

I don't know if it is the same but I had some cracks welded on the scout car. It was a mongrel of a job. A mobile weder bloke did it and after much mucking around successfully welded using rods with a high nickel content - from memory. As Richard mentioned we had to cut a vee in preparation for the weld. I seem to remember heating the rods up in my mum's oven - I don't know if that helped in any way and certainly not for her cooking - but the welds were good.

Mike K · #18 06-12-12, 09:16

Quote:

Originally Posted by warren brown

I seem to remember heating the rods up in my mum's oven - I don't know if that helped in any way and certainly not for her cooking - but the welds were good.

The TAFE I did welding at, kept the welding rods in a warm oven, it keeps the rods dry . The rods are much better to weld with when they are dry . Any moisture in the rods, it somehow detracts from their performance .

Mike

Lynn Eades · #19 06-12-12, 10:57

I thought in a country, where your slice of bread curls up and dries out, in the 3 seconds before you try to butter it, that keeping your welding rods dry and warm, wouldn't count........ or is that only in the bad lands out west?

colin jones · #20 07-12-12, 01:04

Don't forget, darrin is using a mig and not ark. Heating your welding rods is for preheated cast iron and tempered steel of high stress levels and would not be a issue in this case.

Colin.