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Other use for my SGTC? (URGENT!)

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oucivileng

Fri Feb 20 2009, 04:53AM

Registered Member #1772 Joined: Tue Oct 21 2008, 05:23AM
Location: Athens, OH
Posts: 71

This might be kind of a stupid question but it's kind of a spur of the moment thing...
For a bridge design competition I'm working on I need to press fit some steel tube. Basically I have a piece of tube steel that's 1.25"OD and 0.750" ID and a round solid bar that's just over 0.75" OD. I want to heat the end of the larger tube so I can slide (or pound) the smaller bar into it about 2-3 inches. When it cools it creates a very strong connection. We were going to have a local shop do it but they bailed on us. I would like to know if I could just take my SGTC primary circuit, remove the primary coil and replace it with a small coil I'll make out of leftover copper tube to create an inductance heater. If it's possible, does anyone think it would be able to heat that thick of a bar of steel significantly so that I could make this work? I understand that inductance heaters typically run on AC but I figured that the pulse caused by the spark gap could have a similar effect.

I'd be using my 15kv/25ma transformer with a .015uF tank and static spark gap.

Normally I would spend more time figuring this out by myself but I need to get started press fitting that steel in the next day or two and I've got school work to finish too. If anyone has any advice, it would be VERY much appreciated.

Thanks

Chris Russell

Fri Feb 20 2009, 05:15AM

... not Russel!
Registered Member #1 Joined: Thu Jan 26 2006, 12:18AM
Location: Tempe, Arizona
Posts: 1052

It's a question of power. Your NST is putting out 375 watts. Even if the setup were tuned properly to transfer 100% of its power to the steel, it's unlikely that you're going to be able to heat that much steel to a workable temperature. You'll just end up with some hot steel, and even less time to finish your project.

...

Fri Feb 20 2009, 06:00AM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

I vote use a propane torch, cheeper faster and notable less deadly

Shaun

Fri Feb 20 2009, 06:21AM

Registered Member #690 Joined: Tue May 08 2007, 03:47AM
Location: New Jersey, USA
Posts: 616

Yeah, what's wrong with a torch? While the steel's temperature may go up slightly using the tesla primary, it will be very inefficient and will almost definitely do nothing to help you. A powerful, properly designed amateur induction heater could do this easily, but not an SGTC tank alone.

oucivileng

Fri Feb 20 2009, 06:22AM

Registered Member #1772 Joined: Tue Oct 21 2008, 05:23AM
Location: Athens, OH
Posts: 71

Yeah, we might just do that. I was hoping that we could use inductance because it would heat much more uniformly than a propane torch. We don't have much tolerance to work with.

Electroholic

Fri Feb 20 2009, 11:25AM

Registered Member #191 Joined: Fri Feb 17 2006, 02:01AM
Location: Esbjerg Denmark
Posts: 720

or you can get some LN2 to cool the 3/4 od piece.
And about heating the piece uniformly, I think the heat transfer coefficient is going to take care of it.
in any case, good luck

oucivileng

Fri Feb 20 2009, 02:30PM

Registered Member #1772 Joined: Tue Oct 21 2008, 05:23AM
Location: Athens, OH
Posts: 71

yeah, I'm just worried that it's going to be difficult with the torch because we need to slide the bar in about 2.5-3 inches in some cases to get the required strength (about 5-6 kips!). To keep about 3 inches of the tube hot enough with a propane torch might be a challenge. Maybe we'll just have to hold several of them to it at once or something.

ConKbot of Doom

Fri Feb 20 2009, 04:02PM

Registered Member #509 Joined: Sat Feb 10 2007, 07:02AM
Location:
Posts: 329

Get 2 of the standard plumbing torches that will sit up on their base on their own, crank em up high, and set them so their flames cross. Hold the tube stock in the flames, once the temp comes up the flame should wrap arond the pipe.
Also, if this is a college thing and LN2 is availible definitely try to chill the barstock in LN2 if feasible.

Terrorhertz

Fri Feb 20 2009, 04:32PM

Registered Member #1965 Joined: Sun Feb 08 2009, 02:14PM
Location: Herefordshire UK
Posts: 3

You could try heating the tube and freezing the rod but you would have to work very quickly!

StevenCaton

Fri Feb 20 2009, 07:25PM

Registered Member #1845 Joined: Fri Dec 05 2008, 05:38AM
Location: California
Posts: 211

I tried to heat a piece of metal with a SGTC primary circuit *just for the hell of it* and it doesn't work (well, not much at least). I replaced the primary coil with a solenoid type coil, put a bolt inside, and after a full minute, the bolt was a little bit too hot to touch, but absolutely no where near red hot. This was done with a 12KV 30ma NST.

It's a waste of time to do this with a NST.

Use some arrangement of torches.

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