After reading your replies and your secondary posts it would appear there are "issues" you need to consider. If you are making a high pressure tank you need to MINIMIZE welding through design. The only bumper tank I would suggest is heavy wall pipe with ends welded on. It sounds like you have ALOT more welding in your design. A weld length ways would be a red flag to me. Keep in mind you are building a potential bomb here with 110 psi surrounded by metal !!! This is NOT just project welding you must KNOW you have 100% penetration and with the GMAW in short curcuit mode its not happening friend. Go to
http://www.weldreality.com/ to find your GMAW (mig) answers. Order his book and you will become a GMAW pro !! Its that good and user friendly. Personally I would change my design to eliminate as much weld as possible then root and cover pass those welds. Remember, when designing, "the best weld is no weld at all".
Don.
I am not concerned with the strength of the weld. It has already proved it's strength during numerous 4 wheeling sessions. I have an ESAB Mig Welding Handbook that explains WHAT spray arc welding is but doesn't say HOW to do it. Thus I couldn't tell you if I am doing it or not. I am just welding this air tank as I have been welding bumpers, suspensions, skidplates and other 4x4 goodies for years. Could you explain the spray arc welding? That is HOW to do it.
There was not any wind blowing the shielding gas away, work was done in a closed shop. The weld areas were ground shiny to remove any oil and mill scale prior to weld. I did however use a soap and water solution to locate the holes and only blew off the solution well with compressed air before welding the holes. Is it possible that the very little amount of soap in the solution could be causing the fact that the welds don't hold air?
Thanks
Darrell T
I posed a number of questions on the technical board, that you may want to answer, as these might give us a better idea of what is going on. Here I just want to answer your question regarding spray transfer welding.
In MIG welding, there are in essence three different modes of metal transfer:
1)Short circuit (Dip)
2)Globular
3)Spray
Exactly in which transfer mode you are in, depends on the welding voltage, wire diameter and gas. The most important variable being the voltage.
With the gas and materials you are working with, spray transfer should be experienced at around 27 V and above. The best bet is to obtain a datasheet for the gas you are using from your gas supplier. This will show you exactly when you are operating at the different metal transfer modes. This does obviously mean that you need a suitable volt and amp meter.
Just before I explain how you can do this approximately without the volt and amp meter, let me just explain one or two basics regarding MIG power sources.
Most dedicated mig power sources are Constant Voltage (CV) power sources. What this means is that if your arc gap changes (This determines your voltage) the current changes rapidly to again bring the system into equilibrium. It is this characteristic that allows you to weld in short circuit mode. I am telling you this, so that you can understand the settings you are making on your machine. The setting that you appear to think is a "power" setting would in fact be the voltage setting. (You mentioned it was on 4. - Without having calibrated this, this number means nothing in itself.) The power is increased and decreased by increasing and decreasing the wire feed speed.
Assuming that you do not have the voltage and amp meters, you can try the following:
Adjust your machine voltage setting to a relatively low setting. Also set a relatively low to medium wire feed speed. When you strike the arc, you should hear a very uneven sputtering. Adjust your voltage setting untill the sputtering becomes a very even sound. You should now be in dip transfer. Keep increasing the voltage. You will then again go through a stage where the even sound becomes a rough sputter. Increasing it further will result in the sputtering dissapearing, and a "blowing" sound being heard. At this stage you should be in spray transfer. (Approx 30V) Make some adjustments to the wire feed speed to just optimize the settings.
Other evidence would be that the puddle becomes large and very fluid. It would not be possible to weld vertically with the machine at these settings.
I want to stress that the method above is only a very rough guide and would not be the best way of doing it.
Regards
Niekie Jooste
REPOSTED FROM TECH
Niekie
The repairs are leaking around my repair welds. The welds are just the size of a spot weld. A round puddle if you will and leak at the edge of the pool. Since the finished product needs to look like it isn't a weld for asthetic reasons it has to be ground smooth. The finished welds look nice, maybe not proffessional grade but pretty darn close. I do have years of practice and work on making the welds look good as well as have good penetration but I have never tried welding a tank before....at least nothing with 16 feet or more of welds.
As best as I can tell from the owners manual for my welder is that setting 4 is 90 Amps at 18 volts Supposedly good enough for welding 3/16 steel in a single pass with 1/8 or so gap between pieces.
Darrell T
By -
Date 11-04-2001 16:48
If the 4 setting on your machine is equivalent to 18V, then you are welding dip transfer. With dip transfer, you are quite likely to get poor penetration unless you are quite an expert.
You also said in your reply on the TECH board that you machine can go to 28V. At those voltages, you should be in spray transfer. The low current ability 130A, suggests to me that the machine is actually designed for sheet metal use. For this use, you almost always use dip transfer. For 3/16", you should start looking at spray transfer.
I believe that possibly all your welds, irrespective if they look good, has a lack of fusion. Any repairs will only tend to open up any areas of poor fusion. In addition, if you are using simmilar voltages for the repairs, you will again probably get lack of fusion.
Try to inspect your ground welds with magnetic particle inspection. They may reveal some of your problems.
If you want to try welding with spray transfer, set your machine on its maximum voltage setting and try again.
Regards
Niekie Jooste
Don,
I wonder if the pre-weld cleaning was sufficient. You say the you ground the metal shiny before welding to remove oil and mill scace. I doubt if you removed the oil with a grinder. The oil could be the source of the porosity. Are the welds leaking from actual holes, or from along side the welds? Leaks from along side the welds indicates a lack of fusion. You say you used the soapy water to find the leaks. As you did this after you first tried to unsuccessfully weld the tank, I doubt the source of your problems is the soap.
A soap test shouldn't be necessary to locate leaks from porosity or worm holes(piping porosity). Piping porosity(usually seen as a bottomless hole in the middle of the weld) is usually induced from outgassing from a contaminate(oil, paint, rust, etc...) while the weld is solidifing. Did you clean the inside of the tank, close to where your trying to weld as well?
Welding the air tank and welding 4X4 "goodies" have very different requirements. Any flammable residues present an explosion hazard. Any residual moisture can flash to steam, and will always attempt to increase it's volume to 1700 times it's original volume! This creates enormous pressure if the steam doesn't have any place to expand to.
Just the addition of the heat from welding will build pressure inside the tank as the air inside is heated.
The tank must have some kind of fittings on it that you can remove, to avoid a pressure build up.
Better safe than sorry, or dead!
One last thing. You might try to remove the leaky sections with a grinder instead of the drill. The drill doesn't remove enough material to allow access for repair welding. In other words, you won't get the penetration you need. The weld would likely just sit on top of the hole, and any air escaping would likely result in the hole remaining.
Keep us updated
Dale Simonds
Dale
To answer a few of your questions. The areas that were to be welded were either plasma cut or cut with a chop saw. I was thinking this would create enough heat to burn off any of the oil that is put on the raw steel after manufacter to prevent rust. Also before the final piece was installed on an end I had already installed the bung for the air fitting thus allowing expanding air to leave this route instead of blowing out my weld. I welded the piece in sections 4" long at a time alternating on end to the other and the middle since there are two welds 6 feet long and then the multi pieced end caps. The origional holes came from the places where the welds ran into each other I believe, I say this becouse the welds had to be ground down so it didn't look like a weld in the finished product. The "repair" welds have leaked both in the center of the weld pool and on the ends of the pool.
I will try using the grinder instead of a drill bit. I thought of the weld not going all the way into the hole so I used a 1/4" bit and started the arc in the center of the hole thinking this would allow better penetration. I doesn't seem to be the case tho.
Thanks
Darrell T
Darrell,
I'd bet the reason for the remaining holes in the drilled areas resulted from shrinkage while the weld cooled. The ends of the weld leaking indicate lack of fusion.
Niekie2 is correct about the state of the welds. The heat from the repairs is opening up the areas that still contain a lack of fusion. I think at this point, I'd start over.
Have you ever tried gas shielded Flux core wire? You never stated what diameter wire your using. Flux core doesn't have the lack of fusion issues that solid wire has. It's very operator friendly. With your solid wire experience, the transition should be a piece of cake. E71T-1 is an excellent choice for mild steel.
The trick to welding in dip transfer is to stay on the leading edge of the puddle. If you can't see the base metal melting as you progress forward, then your probably not completely fusing the weld to the base metal. It is just piling up on the surface. The process definitely keeps one on his toes!
I think you'll find that the increase in voltage with the E70S-6 will commit you to the flat only domain. But you should have much better luck. Grinding the starts and stops would be helpful, no matter how you weld it.
Dale Simonds
Darrell, I'm in agreeance with Don on this subject. You are potentially making a bomb then your going to hang it on the end of your vehicle correct?
With the volumes of compressed air your obviously talking about, has it even occurred to you of the dangers that you face and possibly others that may be involved in any accident you may have?
Your ideas are foolhardy in the extreme and this whole exercise is fraught with danger.
As a four wheel driver myself here in Australia I know there are other methods available to you with regards to compressed air supply that are far safer even if a bit slower.
Regards Andrew.
if it were my job i would cut out all previous bad weld areas ,bevel all pieces ,set a 3/32"or so gap, tack pieces together 4 or 6 spots, grind tacks down ,turn machine to high and down-handweld enough passes to fill joint,grind to suit
By JimA
Date 11-08-2001 01:59
Lit may say 28volts for this machine, but I doubt you get 24volts. Any time you are doing spray arc, Co2 mixture must be less than 25%. You'll know when you are spraying by the arc. The arc will form a V shape and is actually spraying the wire into the base metal. Short arc (dip) occurs when the wire is shorting out, melting, then shorting out again very rapidly. Some say that you can't get into a true spray arc with wire less than 035. My opinion is that you are not getting enough heat for full penetration. Beveling and multi pass is your best bet with this machine.
Here's my 2-cents worth, to begin with, use spray transfer (28+-volts) with a tri-mix gas, if you're using about 18 volts with mig your'e short-arcing, good for thin materials, but probably not good for what you're doing. If everything else goes bad, E7018 3/32", or Tig. (ps with a 75\25 mix you will probably get an erratic arc.)
Oh my,
My name is Don and I am not sure why everyone is replying to me, I did not post the question, just replied to it. Darrell T. , are you confused yet? Once again go to www.weldreality.com and get the REAL GMAW answers. Don't believe everything you read about GMAW. You need to take a SERIOUS look at your design !! A good designer minimizes welding !!!!! The best weld is no weld at all !!! Short Circuit will not give you a full penetration weld on 3/16" steel with enough throat regardless of root opening !!! Start over, rethink your design to minimize welding, root pass then grind and cover pass, leave PLENTY of ventilation for internal pressure. Good Luck.
Don,
You are right. He must use spray arc to have CJP on 3/16" plate.
Regards Geza
