Annoying welding problem

Hi folks

I have this problem with my torch. I use an Uniweld type 17 (Victor type J) #4 tip for some 1/8 scrap. Bought the tip only some months (but it seems manufactured way back in 1997) and has not seen much use yet. I'm setting the recommeded pressures (8 and 8 psi). And here it comes: even with a small gentle flame, the molten puddle forms and then very so often bang! the metal explodes putting out the flame and causing the torch to flashback (good thing that I have arrestors mounted in the torch). A small crater forms in the metal. This is so frecuent that I'm unable to make any decent welding and have to turn up all the flame (blowy, roaring!) getting huge awful tack welds. I'm at a loss at this folks. I never experienced this before with the smaller #2 tip. I remove the rust with a steel wire wheel. Some rust remains in the metal . Often I see a shower of small sparks as if there was excess oxygen but the flame is neutral. I'm positive I'm not sticking the inner flame cone into the puddle. Any advice? I'm becomming leery of picking the torch to weld (loud bang, torch shrieking, molten metal flying, etc)

Any advice thanked in advance,

Regards,

Mongke

Reply to
mongke
Loading thread data ...

in general, i've heard/seen/experienced that is caused be insufficient (proportionally?) fuel flow (generally percieved as pressure)

Reply to
dogalone

Are you sure this is steel? Have you tried another torch tip? If this is some cast metal, it may have pores where water or oil have collected over time, or just corrosion and air pockets. Rolled steel won't have these sorts of inclusions in it, but many cast metals, over time, can accumulate all sorts of oddities in the pores.

Jon

Reply to
Jon Elson

Classic example of too low of a pressure on your gasses. Bump the acetylene to 10, and up your oxygen to about 12-15.

I teach gas welding every quarter at school, and have been for 6.5 years.

Reply to
Ernie Leimkuhler

Your pressures aren't right. O2 at 17-20 psi and 7-10 psi fuel (I can't spell acetylene) Open the valve on the O2 at the hose all the way and regulate your pre-heat flame on the torch head. Mix to a nutral flame or slightly reducing. Remember it's a chemical reaction not heat that cuts.

Reply to
Tom Gardner

Sounds like too large of a tip for the steel you're welding. If you switch back to a #2 the problem will probably lessen or disappear.

Some good info here

Pete

Reply to
Peter Snell

Ernie sez: "> Classic example of too low of a pressure on your gasses.

Are you saying to run pressures higher than manuf. recommended as a matter of course? I've always wondered about that - it seems like a good idea in that extra pressure would tend to override minor problems with the tips, etc. Can you comment further on this matter?

Bob Swinney

Reply to
Robert Swinney

Ok I'll try the #2 tip. However I have this uncertainty: If I'm making a T joint with 1/8 stock, doesn't it make the root joint close to 1/4?. That was my reasoning when choosing the tip size.

Mongke

Some good info here

Reply to
mongke

Yessir, just common 1/8 HR angle. One other piece is an old tank that I've been welding on the outside surface.

Mongke

Reply to
mongke

It doesn't really matter who made it, or wht they put in their little booklet. If you get consistent popping like that it means you either have your pressures too low for that tip, or you are running too small of a flame with that tip.

You are alowing the flame to backfire up inside the tip which is what causes the pop.

Reply to
Ernie Leimkuhler

I had the same problem with a #4 tip and 1/8" mild steel. Make sure you aren't boiling the base metal and/or the rod. The puddle should be smooth not sparking or boiling. The final bead should also be clear. I eventually dropped back to a #3 tip and 3/32" R45 rod and the problem disappeared. If that isn't an option, try a larger diameter rod for better heat control of the puddle. Good luck.

Reply to
JohnP

I can't believe I am trying to improve on one of Ernie's responses, but here goes. I think Mongke has plenty of pressure on the torch, but has too large a tip for the material being welded. As a result, he has closed down the torch valves to reduce the heat, resulting in too little gas velocity in the flame--which is the problem Ernie has identified. However, raising the pressure will not solve the problem. A smaller tip probably will.

I suggest a #2 tip. With the torch valves open about 3/4 turn, raise the pressures with the regulators to get a balanced flame that does not detatch from the tip, and then fine tune the flame using the torch valves.

Ernie, can I have a job as a teaching assistant?

Reply to
Leo Lichtman

My own addition (experience - UK City & Guilds training, plenty of use oxy-acet at work)

Nozzle size. You want a certain amount of heat, so you will try to put a certain mass per unit time of oxygen and acetylene through the nozzle, regardless of its size, so

- too small and the gas velocity is too high and it blows the molten metal away - as soon as the metal melts it sprays away on the far side, so you end up reducing the size of the object you are heating but never welding it, at the extreme

- too large and the gas velocity is lower than the flame velocity and you get light-backs into the inside of the nozzle, with noted bangs and the weld pool being thrown around, usually over you, especially in your hair.

The nozzle size if fairly critical. By that I mean, if the job rightly calls for a #3, you would be happy neither with a #2 nor a #4.

Another reason for "banging" is that the nozzle simply gets so hot that there is lighting of the mixed oxygen and acetylene in the inside of the nozzle. If you really do have to work for a long time in an awkward corner, it is OK to dip the nozzle of the torch in a bucket of water every now and again. Told flame will stay lit while you do this, but never tried it...!

Pressure at the regulator. I don't think it will have any effect on the lighting-back. The reason is the given-massflow argument regarding the amount of heat you need at the weld. If you raise the pressure out of the regulator, you would restrict back the flow in proportion with the valve on the torch. So the pressure in the nozzle will be exactly the same! (surely?). I tend to set pressure so that the torch valve is quite well open and a lot of movement makes a small adjustment. That gives you easy fine adjustment. For goodness sake, you can set the acetylene pressure at the regulator by setting the torch adjustment valve wide open and having the regulator set way low, light the acetylene and turn up the acetylene regulator pressure until the flame is a bit bigger then the flame you know you will need to weld. Then you restrict back on the torch valve to the correct flame. Same with oxygen. You will likely end up with pressures less that 8 and 8 (psi, that is). That will give you fine control in the range you want. This works because, burning acetylene only, you identify the range the nozzle will be correctly drive at because it is when, increasing the acetylene supply, the acetylene-only flame stops being smokey and becomes a clean roaring incandescent yellow/white. I have to admit the main reason I do this is to be a flash bastard and show off by operating the torch very rapidly wiht one hand, using only the fingers of the hand it is held in. You can "drive the nozzle hard" by increasing the acetylene supply beyond the point where the acetylene-only flame burns clean. With the oxygen on and a proper "neutral" flame, the gas velocity will be higher and you can actually use this. I found it helpful in some fillet joints, where you might drive a #2 hard rather than go to a #3 driven at normal rate, for the same heat.

Haven't used oxy-acet much for a while. Would have thought try #3. #2 would be too small for 1/8th inch, for sure (?).

BTW - filling technique - you know that "melting off the filler rod like sealing wax for a letter", with metal dripping into the melt pool, is definitely a defect in oxy-acet? You get an oversized uncontrolled overheated looking weld if you do this, compared to the controlled fine-looking weld with desired profile if you dip ("harpoon") the rod into the weld pool as needed far slightly afar.

I will gladly be stood corrected if any of the above is not correct.

Richard Smith

Leo Lichtman wrote:

Reply to
Richard Smith

What's the pressure drop in the flashback arrestors?

Just a thought.

Mark Rand RTFM

Reply to
Mark Rand

The James F Lincoln Welding Foundation publishes books on welding. The book " Design of Welded Structures " usually has everything that is in " Design of Weldments " but in this case the thinner book has a rule of thumb that is not in the thicker book. It is that the leg size of fillet welds is 3/4 of the plate thickness when welded on both sides and for the full length of the plate. This is for a full strength weld.

This is modified by saying one needs to use 3/16th for 1/4 inch plate to comply with AWS recommended minimums for 50 % and 33% of full strength welds.

Unfartunately it does not cover anything smaller than 1/4 inch plate. But it does sound as if you are putting in a lot more filler than necessary. Even less is needed if you bevel the one sheet.

Dan

Reply to
Dan Caster

Sure but it pays nothing. You do get to clean out behind the shear though.

Reply to
Ernie Leimkuhler

Oops, the arrestors of course. Hadn't counted them in the equation. Went to Victor page and downloaded the pressure drop chart for flashback arrestors. Now the problem is the charted flow rates are HUGE. The flow rates for my tips are 25 SCFH and less, so I'm far below the lowest pressure drop curve fo 5 psi. So I'll go with Uniweld's advice of "increase working pressure 2-3 psi for check valves"

Regards,

Mongke

Reply to
mongke

I have not tried this method before. I'll have to see how does it work for me.

Supposeddly an #2 is good up to 1/8. I dont own a #3 so I'm stuck with #2 or #4 anyway.

well I was trying to do "harpoon" as it is the righteous thing to do but with the huge heat it turned out to be partly "sealing wax"

Reply to
mongke

I will, since the flashback arrestors have to be counted in and I had neglected them. BTW, and out of curiosity, what is suppossed to happen if one screws in the AC regulator past 15 psi? Does the gas light itself in a stream of flame out of the regulator, or does it detonate still inside the regulator body?

And something else, now how to clean the soot inside the nozzle and mixer assembly?

Inquiring minds want to know

Regards,

Mongke

Reply to
mongke

eh, pressure not same as flow; tips are engineered for volumetric efficiency

have had ultimately righteous results keeping (trying to) the rod feeding smoothley into the the puddle

Reply to
dogalone

PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.