Hardfacing Technique Question

In the course of our operation, we have a crusher and disintegrator station to break up our material- dried clay, which includes "clay dogs"

Presently we have a roller setup, J.C. Steele, that utilizes 12 insert disintegrator bars that are hardfaced. During the normal course of operation, we notice that the hardfacing breaks off the mild steel backer bar, which requires us to reweld these several times a month.

A call to Steele gave us info that the bars are tool steel, or not. They are indeed mild steel, and we have been filling the larger divots with 7018 prior to hardfacing the surface with Stulz
5/32 or 3/16 hardfacing rod. This rod tends to "pull", and develops heat cracks if aggressively welded.

Got a box of Cronatron 7770 and 750 to build up and face the bars, at the recommendation of a local supply outfit.

Any suggestions about specific techniques in welding this- there is less than 1/2" of the bar hanging out of the roller, and they are not easily removable. I was told preheating the bars to 250 to 300 degrees would make the welds take better, but this may be difficult to accomplish with so small an exposed surface.

I plan on using AC reverse welding, electrode positive, 180 amps on the 5/32 7770, and 180 amps on the 3/16" 750 to finish.

Any experience out there I can tap into?

Billy

hey there, preheating is prbably the best bet. if you have access to a weed burner ( large torch that hooks to a propane cylinder ) and preheat to 'at least' 300 degrees. you can check the temperature with temp sticks. you should be able to get these at welding supply stores. if you want to go to the extra work, if you can even do this with the parts you are working on, after it is heated and welded, slowwly dump sand on the parts while heating it( or if you caould heat some sand in a metal bucket to the same temp). make sure it is completely covered with a little extra. the hot sand will keep the metal from cooling down quickly and might help it hold a little better. best of luck edx42

I did similar jobs many years ago on sheeps-foot rollers. However, I didn't experience this kind of problem and I don't understand why you are seeing this much cracking if the stubs are mild steel.

I suspect that the hardfacing rod is causing the problem - most do get somewhat brittle on occasion. If it were me, I'd build up the holes with 7018 and then cover pass with a high manganese rod only - not a hardfacing rod. If this holds up to the work, don't worry about trying to recreate the factory job with hard facing. You didn't say how big the work surfaces are but it's also common practice to lay beads in a basket weave, which leaves "levees" where the beads are and "bayous" where the faces are. Dirt builds up between the beads, which actually cushions and protects the steel.

If you want to try the Cronatron rods, then Ed's weed burner suggestion is a good one. You can get tempil sticks if you want, but I use the "sizzle" method. When a drop of water dances and pops, it's hot enough (usually about 300-400).

Guys-

Thanks for the info so far-

These disintegrator bars are 1 inch thick, 2-1/4 inches tall, and 18 inches long. They are held captive in slots milled 2 inches deep in a solid steel roller, 24 inch diameter, so only the top 1/4 inch or so is exposed.

The question here is- is there a good way to heat the bar without heating the entire roll?

The right way to reface these would be to pull them out, but after a couple months' use there's so much clay packed between the bars and the roller slots, the bars come out looking like bananas and aren't reusable. It may just be the mechanic's technique, but I haven't fared any better in removing them either.

Billy

Have you tried simply building up with mild steel (7018) but without the hardfacing? If it's easier, faster, cheaper not to do the extra steps - and the pieces get damaged anyway, it might be most cost efficient to do the least amount of work.

An O/A rosebud tip would suffice to preheat the bar as you work. Heat a bit, weld, heat a bit, weld, etc.

Thanks, guys, for the input-

Now to convey the message to the troops- I've got a couple of ?welders/ who attempt this repair, but I am certain they need a little more education and practice. Tough getting good all-around help nowadays.

The plant engineer and I can do this repair, but I just don't understand why "experienced" maintenance men can't.

Billy

truly experienced personnel know how to get out of work.

In a past life I've done enough hard facing to last me for ever, including digging out hard packed clay to get at the job. Here's my 2 cents for what it's worth.

I'd preheat to well over 300F, as far up the bar as possible because cold will rob preheat like there's no tommorrow, ........ build up the big patches with mild steel (over here in the UK we use ''low hydrogen'' to prevent cracking) then while still hot lay on the hard face, then do what ever you can to slow the cooling as much as possible, if nothing else I've put an old leather apron over the job just to shield it from a cold wind. Best of luck.

Thanks-

I have given my "experienced" welders a couple of "show and tell" sessions, and it would appear that the advice I have recieved will make this job a lot more durable, since the preheat portion had been "forgotten"

Billy

Replacement parts and advice can be obtained from Femco Machine, Punxsutawney PA.

http://www.femcomachine.com/

Their field service welders will come to your site and show you how it's done.