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**fun4now** · 04-12-2006, 07:33 AM

the dyn.300DX will do fine

the 300DX should be fine for the 1/2" i don't have my calc. with me its in the shop so I'll double check and get back to ya if I'm wrong, but as a general starting point it's 1 amp. per .001 thickness when TIG'ing, as you are working with .250 you will be in the area of 250amps so the dyn300DX (a sweet choice by the way

) should handle it just fin.

..as for the alloy to weld it best leave that up to one of the TIG pro's.

**jolane** · 04-12-2006, 08:47 AM

Uh Fun, he said his pieces are 1/2" thick, or .50", which equates to 500 Amps.

Tony,
I am certainly not the person to answer your question, but I do have a comment or two.
1. I have seen similar sized SS parts welded with Stick, and the parts warped pretty good. It was a flange to a round tube, and the flange warped bad (to be expected I guess).

2. Can you use multipass? Do you even need something cose to full penetration?

3. I know the general rule is 1A per .001" thickness. Stainless though is a rather poor thermal conductor, which means that it will retain more heat around the weld area than say aluminum. This should make it easier to weld thicker section with less power as well.

I am not sure whether any of this helps, but I hpe so.
Joshua

**Coalsmoke** · 04-12-2006, 08:57 AM

This is maybe more of a technicality than anything, but I always thoguht stainless was a poor conductor of eletricity, with greater resistance per unit of metal, hence why it heated up more. Thermally speaking, I think stainless is a good conductor.

**jolane** · 04-12-2006, 09:47 AM

Coalsmoke,

SS is a poor conductor of heat actually. It also does have more electrical resistivity than other materials, but the important thing when welding is more the thermal conductivity. This is why the melt poor does not spread out as much as say aluminum. Steel is between the two...

I looked up some numbers on this for you. Invar is considered a very low thermal conductor. Aluminum and Copper are obviously very good.

Invar 10 W/m*K
316SS 16.3 W/m*K, 7.4E-5 ohm-cm
Titanium 17 W/m*K
Steel, CR 52 W/m*K, 1.6E-5 ohm-cm
Aluminum 210 W/m*K
Copper 385 W/m*K, 1.7E-6 ohm-cm

I found these values on www.matweb.com. As you can see, SS is very low, which means it retains more heat around the heat source, and longer. This is why aluminum heats and cools so quickly, the heat spreads out quickly, thus requiring more input power. Finally, this is one reason why copper is so hard to weld, and people use Helium (more heat) when welding this material.

Joshua

**calweld** · 04-12-2006, 10:09 AM

Stainless does warp and distort more than mild steel when welding, I would design this to minimize welding -- put all the load-bearing bars on top of the endpieces, I assume they are standing on end, I would also weld little cross-members in between the bars on the ends, or run another bar over the top to be tacked to each bar, thereby keeping them from folding over from any weight. If you design it correctly, all the load is being supported by steel, little or none by welds, all the welds are doing is holding everything together. I would weld in this case with stick, it is faster and uses less total heat than tig would on heavy sections, basically just a little more than a tack in each case.

**Coalsmoke** · 04-12-2006, 10:11 AM

ohm-cm is electrical resistivity, watts per metre-kelvin is thermal conductivity. You're right about the welding charactericts of higher thermally conductive metals, no doubt about that, your standard 304 stainless has a value of 21.4 W/m-K, compared to Al. of 237W/m-k, or copper at 401W/m-k

Edit, sorry Josh, I missed the thermal units and only saw the ohm-cm values. Bah! need to get to sleep before I start making more of a mess than I can clean up. Thanks for the lesson in thermal conductivity

**wb5jhy** · 04-12-2006, 10:43 AM

Tony

The 300DX should handle that job easily.

**POWERSTROKE** · 04-12-2006, 10:53 AM

When I bought machining and parts for stainless steel food & chemical processing equip. You learn VERY fast that SS has very poor heat transfer. For critical heating & cooling We had to use pure Nickel 200, then a Duplex SS machined to a thinner wall, then the 316 alloy.
I don't know what this coal grate totally has to support but using 1/2"x2" 316L flat sure sounds like a VERY expensive part and over-kill unless the material is scrap at scrap prices or FREE?. You could probably have a cheap wooden pattern made to cast a replacement at an iron foundry cheaper than the material for that stainless material. I'd strongly suggest talking over the actual requirements with your Customer. The grates in My fireplace at home are just 1/2" rebar tacked together and it's been in place for almost 25 years.

**jolane** · 04-12-2006, 11:01 AM

Colasmoke,
No problem. I didn't mean to make it seem like a lecture. Rather, I hoped that it might help someone in the future understand part of the how and why...

I worked at a company where this stuff meant a lot to the overall technology. We were melting (not cutting, rather building up) metals with lasers, and cared a lot about this. It ends up being a very complex problem when trying to couple laser power into shiny metal, but it not only the reflectivity that matters.

On a side note it is amazing at how much a pure Argon environment affects the convective heat transfer of things compared to Nitrogen. Argon is a poor at cooling also, and made things overheat. It doesn't take a large change in thermal conduction coefficient to affect things sometimes.

Joshua

**Tailshaft56** · 04-12-2006, 01:17 PM

If you can't get full penetration you could always weld a bead from both sides. Just a suggestion.

**joebass** · 04-12-2006, 01:58 PM

The 1 amp. per .001 thickness is a guideline, and for SS I usually use about 30% less. The 300 should do it fine. I would use pulse to minimize heat input and cool with a wet rag or air. It will warp pretty good also. I see no need for full pen. welds. I made some grates like that last year for a customer. I used 1/4x1/2 304L flat bar though.

**fun4now** · 04-12-2006, 04:09 PM

ooops.

sorry about that , had a brain fart.

still i agree the 300 will still do the job and really don't see any need for full penetration. also as said above designed will allow for lil to no wait being put on the actual welds, but rather the welds just holding it all in place.

if SS is about 30% less needed then steel then .0007 would be the weld calculation meaning you need 350 amps so you would still be close for full pen. if ya wanted it.again full penetration will also open up more warpage isues.

**imported_RoydRage** · 04-12-2006, 04:12 PM

Great

Thanks Guys...

You are all really great, and knowledgable.... My Tig Calculator suggests 325-425 Amps... I was hoping with an Inverter such as the Dynasty 300DX that you can get away with welding a little thicker than the amps suggest due to the Arc keeping the heat local, and not spreading out as much, as they indicate with Aluminum for this unit...

I'm worriing about everyone saying that the SS will warp greatly... Not because of the welding... But because of what it's being made for... The coals in this oven will melt a glass bottle if you put it in there... And the Cast iron original only lasts about 6-8 Months...

Now someone suggested to them making out of SS, but I'm starting to doubt their credibility/

Thanks, Tony

**joebass** · 04-12-2006, 04:57 PM

If it gets that hot I would use 310 or 321 SS. Not sure why they would recomend 316 anyways. I always thought that that was used mostly in the marine industry.

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