Team Go Dog, Go! Modified Partial Streamliners

[wobblywalrus]

The lower heating value in BTU per pound fuel divided by the recommended stoichiometric ratio by weight gives an idea about the heat available in a pound of fuel air mix.  The Standard 110 octane leaded gas has this:  18,700 / 15.0 = 1,247 BTU per pound air fuel mix.

The SS100 104 octane unleaded has 18,000 / 14.2 = 1,268

The 260 GT Plus 104 octane unleaded has 17,400 / 13.7 = 1,270

The leaded gas is more efficient.  It has a leaner stoichio ratio.  It also costs a lot less.  The unleaded gases have the potential to make as much or a bit more power.

Octane needs are a big unknown factor.  The piston crowns, exhaust ports, valve heads, and combustion chamber will be ceramic coated.  I am not sure if this will retain heat and require more octane than an uncoated engine.     

[wobblywalrus]

A 90 degree bend in 304 stainless tubing needs to be made into a 64 degree bend.  A pie shaped slice is cut out of the middle of the bend.  The wall thickness is very thin at the outside compared to the inside of the bend.  The weld area is cleaned up and it is tacked.  Tri mix is used from the gun and there is no back purge.  308 stainless wire 0.030 diameter is used with 7 volts and 60 feet per minute wire speed.  This works OK on the thicker wall.  The voltage is dropped to 6.5 with 60 feet per minute wire speed for the sides and this does the job.  The voltage is 6.5 with a 50 fpm wire speed for the outside of the bend.  The tacking blows a hole through the pipe.

[wobblywalrus]

Finer .025 308L stainless wire is installed after this catastrophe.  An argon tank and regulator is set up for back purging.  A dissipator is made to bleed the argon purge gas into the pipe.  An attempt will be made to weld this thing after Rose and me get back from dinner, a movie, and a couple of pints at the local.

[Peter Jack]

Bo, you don't need the dissipator. Plug both ends of the pipe with a cap of some sort, tape works but it's messy. Insert the hose or a piece of tubing to which the hose is attached through the cap. Make a small hole in the cap at the other end. Let the back gas flow for a couple of minutes, then weld away. This will make for a solid atmosphere of argon instead of random flow. I think if you taped your dissipator into the pipe that might be a good fix.

Pete

[Koncretekid]

 An attempt will be made to weld this thing after Rose and me get back from dinner, a movie, and a couple of pints at the local.

You might want to wait till morning!

[Peter Jack]

A long time ago I posted pictures and a short narrative of how I reworked my regulator so I could use it effectively for both welding and back purge at the same time. This is a fairly common practice in industry. Hopefully this link works.

http://www.landracing.com/forum/index.php/topic,10731.0.html

Pete

[wobblywalrus]

The logic was that I need to buy a regulator and argon tank for welding aluminum so the separate tank system looks good from a cost viewpoint.  Also, argon costs a lot less than tri-mix.  Is there a problem with using argon for a purge gas in this application?  If so, I will switch to the setup you show.  I have all of those fittings in the plumbing spare parts box.

[Peter Jack]

I see no reason why Argon should not work as a purge gas. Then again I always tig stainless so I have no experience with this setup. If you have a couple of thin stainless coupons you could try it before you get serious. If I were doing it I'd turn the heat way down, try the weld on a coupon before I tackled the real thing and pulse the trigger using a push with the gun at about 30 degrees.

Good luck.

Pete

[wobblywalrus]

My big night out with Rose is tomorrow.  I have been thinking it is Wednesday all day.  So, a 90 degree bend has been cluttering up the shop and wrecking my life.  It is gone.  A spiff 64 degree bend has taken its place.

Pete, how do you do the pulsing?

[Peter Jack]

Just pull the trigger for short bursts at a time. It allows the weld to cool between bursts so you don't continue to build heat in the weld. It's generally the heat buildup that causes burn through. The resulting weld will look somewhat like a tig weld because it will result in ripples similar to those caused by feeding the rod with tig.

Pete

[Peter Jack]

Bo, PM sent.

[wobblywalrus]

The back purge gas is from the argon tank.  It is heavier than air and a flame will not burn in it.  The purge hose is stuck in one end of the pipe and that end is taped shut.  The other end is raised above the table a little bit and taped shut.  An air escape hole is made in the highest point of the taped end.  The pipe is purged with argon until a flame goes out when a match is held near the escape hole.  This indicates the pipe is purged.  Then it is welded.  This purging seems to be needed to make the weld metal melt in and penetrate on the back side of the weld.  The weld on the inside of the pipe is much smoother if the purge is effective.  I have no clue about why this happens.

[Peter Jack]

Glad to hear it's working for you Bo. Don't bother to question it, just be happy that you're getting the desired results. 

Pete

[wobblywalrus]

The professor looked at the welded pipe before class this morning.  He asked me if the pipe ends were in contact with each other when welded.  I said yes.  Both of us butt welded together some metal strips that were contacting each other.  Then we welded some more that had a little gap between them.  The penetration was much better and more consistent with the gapped strips.  He said to set the pipes up with this small gap before e welding.  Also, he recommended an ER308L-SI wire for this 304 stainless tubing.  I was using ER308L.

An expert PM'ed me and said I should not grind the welds flush until I get good enough to always have good penetration.  This makes sense.  Tonight another joint will be welded up with a gap between the two halves.

[Peter Jack]

Make it a very small gap and it will work great. If you try to stretch it out a bit that thin section at the outside of the bend will become a real challenge. It sounds like you have a really competent instructor who cares. Good deal. You'll find the wire he recommended will flow a little nicer.

Pete