Newbie asks OAW question

By mksqc

Date 08-29-2005 20:13

A FEW AFTERNOONS DOSNT SOUND RIGHT.ARE YOU SURE THAT YOU CLOSE TANKS AFTER USEING THEM?

By MDG Custom Weld (***)

Date 08-29-2005 20:18

That tank should last for many (like 8-10 ) hours of welding time. Maybe your valve has a leak, or you regulator has issues. We see valve problems a few times per year at our plant where a full 300 cf tank will have 500 lbs pressure when it gets opened up for the first time. Make sure the valves are off after every use.

By AaronHG Date 08-29-2005 22:10

I am very carefull with the valve opening and closing procedures as I am very aware of pressures at the torch. What I am seeing is my A is zilch and O is down at 200.
I have been trying to work with equal pressures (5 to 7) each. I have an extra (but older) set of regulators that I'll try.

By jerrykroll (**)

Date 08-30-2005 00:00

gas consumption for a typical tip used to weld, say, 1/8 inch thick material (tip numbers vary widely among brands and series) should be about 5-8 cubic feet per hour each gas - thereby 75/5 = 15 hours continuous use .

See if you can find a good tip chart for your specific tips, with flow stats in cubic feet per hour(cfh).

Acetylene cylinders are invoiced by WEIGHT - each 15 cubic feet equals approx. 1 pound. Your 75 cubic foot cylinder should weigh about 5 pounds less when empty than when full. This is one reason that you will see that they are stamped with a "tare weight". I don't believe that the Tare Weight includes the acetone that is added to stabilize the acetylene under cylinder pressure. Acetylene in acetone is kind of like the fizz (CO2) dissolved in pop/beer. That's why withdrawal rates, and avoiding laying acet. cylinders on their sides is important.

Also - acetylene tends not to behave like oxygen in a straight line (pressure vs. quantity). e.g. 2200 psi full - 1100 psi 1/2 full. Acetylene, as it is dissolved in a liquid, pressure tends to stay around 200-250 for a long time, diminish to 50 or so, and then there may still remain a significant quantity remaining. If you are withdrawing too fast, or little or none remaining - your flame will burn with a purple color and lose heat (acetone burning). If you use a low flow rate, or weld for brief periods, you can probably get much more from your cylinder. When watched CAREFULLY, when a cylinder gets "low", I will set the Acetylene outlet (torch) pressure at 10-12 psi and use it 'til it drops just below that.

Hope this helps.

PS - always work with equal pressures when welding, and never starve a torch by throttleing it down - go to the next smaller tip instead - to keep the velocity of the burning gases outside of the tip and thus avoiding backfires and flashbacks. ALSO - Consider investing in reverse flow check valves and( /or in combination) flashback arrestors.

By AaronHG Date 08-30-2005 05:06

Thanks for the great information.
I am begining to think that my old torch has some metering issues as I recall it erratically switching from a slight hiss to a quiet flame a few times. I also have a Victor torch (100?) in nicer condition but it is not as easy to hold, and it needs bigger tips for what I am working on.
I do use the flashback arresters.
The responses are appreciated.

By chillin Date 08-30-2005 05:37

use flashback arrestors

By billvanderhoof (****)

Date 08-31-2005 06:31

This is probably only of historical interest but there used to be torches that used the energy of the oxygen flowing through a venturi to suck in the acetylene. I assume they date to the use of acetylene generators which made acetylene by reacting calcium carbide with water. In general I believe those generators produced only low pressures (until they exploded which I hear was not unusual). Those torches expected oxygen pressures several times the acetylene pressure.

See injector type torches table here-
http://www.fortunecity.com/village/lind/247/weld_book/Ch11.htm
as well as lots of info about oxy/fuel in general.
Bill

By Northweldor (***)

Date 08-30-2005 11:21

Your flow-rate seems excessive, even with 3/16 " material. Try balancing and setting according to the instructions here, and you should decrease some gas expenditure.

http://www.aws.org/cgi-bin/mwf/topic_show.pl?id=6789#31337

Northweldor

By AaronHG Date 08-30-2005 16:04

I have been using this approach since finding the posting on this site a few days ago.
Very helpful.
Thanks Northweldor!
I wonder if I do have mixture problem though because I have been spending my time grinding out my welds and rewelding due to cracks in the fillets.
I think I have been working with a slightly carburized flame - leading to brittle welds.
Do have this right?
It would explain the acetelyne usage.

By Northweldor (***)

Date 08-31-2005 11:44

This is correct, although a carburizing flame would be obvious due to the extension of the "feather" beyond the bright inner cone. When you are welding, if the puddle appears cloudy or, as if it had a film over it, your flame is carburizing. If the puddle appears to be boiling or, bubbling bright yellow, your flame is oxidizing. If the puddle appears to be clear and transparent, your flame is neutral (as it should be for most OA welding).

By AaronHG Date 09-01-2005 05:55

This has been troubling me. No matter how much I clean my parts, and am carefull
with my flame type I have been ending up with cracked welds. At first I thought there was not enough penetration so I went up in puddle size, which helped. Then my parts started shrinking alot as they cooled, which would cause the weld to rip apart.
I've tried peening the weld with no result.
Makes me want to use the MIG welder, but I want to learn OAW!
It would seem that what apears to be a neutral flame is giving me the results of both carburizing and oxidizing flames.
I am tired of the sound of the angle grinder (with hearing protection of course).
Some of the really ugly welds (which blow through, and have to be built up) don't crack, but they end up looking pocked and gnarly.
The pretty welds are great for about 10 minutes.

By bobby1

Date 09-01-2005 09:02

you say that the tip size is a #3 and you are welding metal that is 3/16''. ok, try this out the tip you are using is designed to weld 1/8'' you should be using a #4 and your mixture should be oxygen pressure= 4, acetylene pressure=4. burn through is caused by lingering to long in one area, keep a consistant travel speed and pay close attention to the flame, just because you set it once does not mean that you wont have to continue adjusting throughout the welding process.your torch sounds like and your welds sounds like that your not getting enough gas pressure at times. this will cause your torch to make a poping sound and will lead to welds that you are describing. try increasing flow to correct and proper tip will also help in your troubles.when setting up plates make sure you maintain 1/16'' gap at the start position and an 1/8'' gap at the end to compensate for expansion and shrinking. this should help you acheive the desired welds.

By Northweldor (***)

Date 09-01-2005 11:20

Are you using ordinary (mild steel) structural material? Also, are you using a proper filler rod? Are your welds concave (not enough filler rod)? What about joint preparation and gap (tacking)? Are you seeing a key hole just before you add rod? Are you adding rod to the puddle and not melting it off with your flame?

Hang in there. This is definitely not normal!

By AaronHG Date 09-01-2005 15:35

I started the project with some scrap from a space frame being built for a movie. It may not be mild, the rest is is. I started with R45 rod and switched to R60. The scrap is 3/16" and some of the other parts are 1/8" wall. The scrap material is alot harder to puddle. The joints were sanded/beveled, but as the project has come together and I grind out the problems it has become more difficult to re-prep as cleanly. Some of the earlier welds are concave but have not cracked. I have made some welds with a #7 that I have, but it's bit much, I'll get a #4 today.
I know to add rod to the puddle, but my patience is pushed as the 1/8 blows away before the 3/16. I general start the puddle away from the joint and move it closer once started

By AaronHG Date 09-02-2005 00:53

I started out today by trying to get a #4, well I couldn't find one anywhere so I tried a #5. Off the top it was a little better. Less cracking. I think that I was over zealous with the O when using the #3 tip because I could not get the 3/16 to puddle with a neutral flame. Thus the cracks. One joint had been re-cobbled so many times that I cut out a section because by now it was mostly filler rod. The fresh joint seems to be good. However there is much stress because the seam for the patch is mis-aligned. I think I will need to use heat to bring them together.
What is the metallurgical (is it a word?) explanation for the cracking. I know that with a carburizing flame carbon is being added to the metal but with an oxidizing flame what happens?, and why does it crack in the fillet center instead of where the fillet meets the welded componants?

By Northweldor (***)

Date 09-03-2005 11:54

I forgot to ask about the type of joint you were using, but it appears that at least some are lap joints (fillet welds). Where are you getting the cracking? Causes will be different for cracking in different types of joints.

An oxidizing flame will add oxygen to the metal, and an oxidized weld will have a dull porous surface, and will crack because of the structural weakness of iron oxide (a rusted area on a car-body is an example). Cracking in the fillet center will likely be because most of the additional oxygen is being added there. However, if you followed my earlier instructions about puddle appearance, you should know as soon as you start if your flame is not neutral, so I think the cause of the cracking may be due to your parent metal being incompatible with the rod you are using. Do you still get cracking when you have a clear transparent puddle and you are working on material you KNOW is mild steel? If not, then your problem may be due to your scrap steel being an unknown alloy. (Try grinding a piece of your scrap and a piece of mild steel and comparing the spark streams. If they are not identical, your scrap is an alloy). Also, none of your welds should be concave.

By bobby1

Date 09-06-2005 09:03

to help with what seems to be the problem at the end of your welds try this... as the torch is being withdrwan at the end of the pass, fill the crater by adding filler rod. You are asking about metalurgy yes this is a real word it defines what makes up the steel and how different welding applications change the structures. When you heat up steel to a molten puddle the atoms float around without any relationship to one another, as the metal starts to cool the crystals of pure iron stars to to solidify. this is followed by a crystallization of austentic grains, and eventually the entire mass becomes solid.If you do not take the proper care to prepare your project or understand how the atmospher will affect the welding proceedures then the job becomes very difficult. make sure that your base metal is compatable with your filler rod. let your welds cool slowly try letting your torch stay over the weld for a few seconds as the puddle becomes solid in order to keep the atmospheric conditions from manipulating your weld. metallurgy can not be explained in one sentence if you are going to be a welder i would suggest taking a class by understaning one part (welding) but not the other causes an information gap and a large margin for error.

By AaronHG Date 09-08-2005 04:41

Very informative. I've found that this sctructure being made of square tube seemingly requires that I am tactful as to the sequence of the welds. Because the the parts are as short as a foot and as long as four feet I have seen signs of tension.
So, I've been welding the joints in short lines, corner of joint to corner, not going for the whole joint. The cracks are showing where one weld finishes/overlaps another welds start point. I have been pausing at the end of welds as to not shock them.
The joints are but jounts on side veiw, t-joint on insides.
Maybe this is a big point....the weld beads are not convex, they are concave, reverse fillet...
I'll do the grinder test tomorrow.
Thanks.