We have a cast steel valve bonnet (alloy seems to be similar to 4140) which has a hole pattern with several 3/4 inch threaded holes (not thru holes) x 3 inches deep that are oversized. In service, the threaded holes carry an extremely high tensile load. The hole pattern cannot be rotated. The wall thickness does not permit sufficient margin to install a heli-coil or a keensert. The customer cannot allow oversizing to a 7/8 inch thread. So we must fill, drill and tap.
We can't seem to find a way to cleanly fill the hole without trapping slag or guaranteeing proper penetration. We V-contoured a hole as much as we could, and tried stick and tig but nobody seem confident enough to get it done and pass inspection, oh did I mention it must pass x-ray. To add to the complication, customer does not want PWHT for fear of upsetting other critical machined dimensions, and that is how the temper bead idea came about.
So, tips on deep narrow hole repair are cordially invited. If this can't be done in temper bead fashion, what is your best way to fill a deep narrow hole? The TIG or MIG route seems to be a nonstarter unless we carve out the side of the bonnet and rebuild.
Thanks to all who can help.
this might be completely out there but that thermite welding they do/did on railroad tracks might work but i don't know enough to say for sure.
also what is the distance from the bottom of the hole to the other side perhaps you could bore through and split the weld difference between the top/bottom of hole supposing that there is not three inches of material past the bottom of the hole. any way you could post pictures.
darren
You sure have been given a challenging project! I hope I have the right picture in my mind's eye.
I do not have any experience with narrow gap welding. I do have experience welding and testing 4140 weldments and I do not see how you are going to avoid hardenning this weld area, no matter how you weld it. I doubt if the temper bead welding concept can work in the joint configuration you are describing. If you are going to re-drill into that weld zone, you are going to hit hard material. If you go anywhere near the original BM HAZ or the WM / BM interface, you are going to find harder material. I was told that it is possible to EDM threads in a 5/8 IN. Dia. hole, but i've never seen it done. This EDM Process would seem to help with the hardness issues for a drilling and tapping operation. I do not know how the resultant hardness effects the servicability of the valve bonnet.
The only thing I can think of is possibly using a capillary tube inserted approximately half way down the hole to run your purge gas with (Argon). Run the purge gas extremely slow so as not to aspire any atmosphere and then GTAW without a nozzle so you can see the bottom. I use to do a similar thing with O-let ID's.
As far as temper beading is concerned, without precise placement of the beads it won't really be effective, though you may experience some improvement.
A little more on temper beading. You would have to run a test piece and determine exactly how much fill per pass to use and determine exactly what your weld parameters should be in order to maximize the tempering effect. It doesn't really promise to work too well becasue of the space restriciton. but it certainly is possible.
js55-
I'll deal with the stress relief and hardened B/M later but I'm interested in your ideas first, could you maybe explain a little more? sounds like you're just sticking the tungsten tip down the hole along with the rod and a seperate tube connected to an argon bottle. And what kind of a capillary tube are you talking about? what kind of flow- like about 5 cfh? or less.
Thanks.
Tom,
By capillary tube I'm talking about a real small diameter steel tube similar to what is used in air conditioning units. It would also handle the heat well. This way you aren't taking up much space in your hole.
As far as gas flow, I'm not even sure you would consider it in terms of cfh. All you need is just enough for a positive pressure, since Argon is heavier than air. We're talkning about a really small volume to fill.
If you have ramp starts, or a foot pedal, on the GTAW torch that would be helpful too so you can start with low amps keeping the arc from disturbing the gas envelope.
As you get higher up in the hole you can then replace the ceramic nozzle on the torch.
If you use a full length tungsten you can easily reach all the way down inside the hole. Although your welder needs to make sure that he doesn't make physical contact with the side of the hole with the tungsten, for obvious reasons.
Keep an eye on our tungsten, it will oxidize when hot in air.
It is not going ot be easy. This is the only way I can see to tdo it.
I saw on a website someplace an inflatable plastic purge chamber- You fill the chamber with argon and work through gloves. I have seen pictures of a cabnet system that looked like a bead blast cabnet for this purpose, would iether of these work in this aplication?
If you could braze it, and apply heat from the bottom or opposite side of the base metal, then capillary attraction would help fill the hole all the way to the bottom?
I guess the hardest part would be to keep from getting it too hot and crystalizing the flux, causing inclusions...
Just thinking out loud here.
Tim
Tim- we do alot of brazing, but I'm not sure I follow what you're driving at. Are you thinking about brazing in a plug then drill & tap? The bolt loads may be TOO high for that idea. But clarify if you can.
Hello tom cooper, with the material you're working with and all of the restrictions and complications that it sounds like you're up against you may want to consider one more "out there" type of suggestion. You said that the holes are oversized. Is it possible that you could have a special tap ground that would tap the holes out to a consistent oversized geometry and then have studs or bolts machined to match them? Know this sounds kind of wild but it may be your most economical way to deal with the problem. Some food for thought. Regards, aevald
Working from aevald's angle consider having the thereads milled with a CNC mill rather than having a tap made, then getting the bolts made to match.
Yes, i guess you could braze in a plug, or you could just fill the entire hole with filler metal.
I was invisioning the filler metal free flowing all around the inside of the hole, collecting at the bottom first, and then filling the hole.
I'm sure the ultimate tensile strength of the filler metal could be checked first, and of course test runs could be made.
If it works, it would be easy and cheap...
Tim
A Bortech machine may do the job to build up the bore enough for threading without welding it solid (
http://www.bortech.com/products/306p.asp). The Model 306 will weld down to 0.5" bore at 3" deep and can be rented. To get the tempering of the HAZ, you'll need at least 2 weld layers on the bore. A temper bead procedure qualification using the new ASME Section IX qualification requirements should be performed on a mockup of the same material and bore dimensions to confirm the properties are acceptable (
http://www.sperkoengineering.com/html/articles/Exploring%20Temper%20Bead.pdf). For a 4140-type material, a low carbon welding material should be used to keep the weld metal hardness down such as ER70S-B2L or ER80S-B3L.
More just brainstorming but if you ream the holes till just beyond the threads and then make studs that are smooth on one end and have the right interference and then heat the bonnet as much as possible and chill the stud as much as possible (thinking at least liquid nitrogen here) and then assemble (quickly) when the temperatures equalize it will grab pretty tight. I leave the engineering and testing to you.
If that's not sufficient you could then drill in from the side into the stud and install pins.
Really fine threads wouldn't increase the size of the hole much and might be acceptable, again you have to custom make the stud and probably the tap.
Some sort of friction welding process might be able to weld in a stud but I know little about these processes.
Bill
Hope things are going your way by now. This is a tough one. I've done narrow groove mechanized welding several inches thick but never narrow hole welding. Visibility will be one problem. Space to feed wire another. Was wondering if preforming tig wire i.e. K-rings to fit hole size and weld them one at a time. Would need to tack them so tungsten wouldn't draw it. After each pass drop another ring in and fuse it.
If I understand the situation correctly you only half to "butter" the walls enough to rethread to obtain the 3/4" hole and do not have to plug completely.
We had a 5 degree groove angle and the tungsten had to be dead center so that it would not arc off of the wall. You mentioned that you V contoured it, that will help. Normally a gas lens would be best but for visibility maybe not this time. As mentioned before you shouldn't need too much argon.
Hope the owner had a good reason for not going with 7/8" holes.
I haven't seen a GTAW coldwire feeder in 20 years don't know if they are small enough.
Just a suggestion; weldreality.com Don't know if he can help but he does telephone, email and in person consultation.
Good luck
Thanks all for the ideas and advice, we've been fashioning up some contraptions mainly following js55's ideas and trying not to kill or maim anybody, but when I saw MBSimms post about the Boretech System, I stopped everything and decided to give those guys a call. I think we need one of these machines! I'll post an update when I have something to report.
Again I thankyou all for your interest.
Regards,
Tom
There is a boretech overlay head where I work at. We have had alot of trouble getting this head to run consistently. The wire will "flip" once the torch neck starts getting hot, leaving voids in the overlay. There are also voltage fluctuations to contend with. Compared to other automated MIG equipment on the market this is a crude piece of equipment (but we haven't seen any other MIG BORE overlay equipment to compare it to). You might also want to check into a AMI model 94 TIG head if this is a critical repair. The AMI head is a real workhorse and we've used it on alot of critical threaded hole and ID overlay repairs. It is pretty expensive even as a rental and requires a higher skill level to operate. There are several companies that have experienced operators and machinists available that have developed repair processes for this problem.
Forum
