Inert bonding/welding with stainless

I would like to make some items using stainless mesh that would require welding to a stainless shell. These would be used for a distillation process, and thus the bond material would need to be inert.

Is it as simple as TIG welding the connections using thin stainless rods?

https://www.amazon.com/Blue-Demon-ER316L-stainless-welding/dp/B00GJU7HTW/

I have a friend that owns a metal shop with all the welding gear, but I wanted to make sure and order the right rods.

Also, is there an inert way to bond stainless to aluminum? Thanks!

After a bit more reading, it seems that ER308L might be the better choice since I will be using 304 mesh and supports. They make the 308L for both MIG in a spool and TIG with sticks. Does one create a more inert result over the other, or if the line/stick are same diameter, just a matter of welder preference?

it does not really matter the process as long as the filler is the right alloy. and ofcourse the parameters of the machine are set for the work. a welder will know all these things though. also make sure to clean the welds good with a passivation agent and you will have beautiful welds that will last forever.

Hey Sticky! Appreciate the info! My buddy does not typically work with stainless. These will be light welds binding the stainless mesh to a stainless frame. Any ideas on a specific passivation process (citric acid?)

https://en.wikipedia.org/wiki/Passivation_(chemistry)

Stainless steels are corrosion-resistant by nature, which might suggest that passivating them would be unnecessary. However, stainless steels are not completely impervious to rusting. One common mode of corrosion in corrosion-resistant steels is when small spots on the surface begin to rust because grain boundaries or embedded bits of foreign matter (such as grinding swarf) allow water molecules to oxidize some of the iron in those spots despite the alloying chromium. This is called rouging. Some grades of stainless steel are especially resistant to rouging; parts made from them may therefore forgo any passivation step, depending on engineering decisions.[9]

Passivation processes are generally controlled by industry standards, the most prevalent among them today being ASTM A 967 and AMS 2700. These industry standards generally list several passivation processes that can be used, with the choice of specific method left to the customer and vendor. The "method" is either a nitric acid-based passivating bath, or a citric acid-based bath. The various 'types' listed under each method refer to differences in acid bath temperature and concentration. Sodium dichromate is often required as an additive to promote oxidation in certain 'types' of nitric-based acid baths.

Common among all of the different specifications and types are the following steps: Prior to passivation, the object must be cleaned of any contaminants and generally must undergo a validating test to prove that the surface is 'clean.' The object is then placed in an acidic passivating bath that meets the temperature and chemical requirements of the method and type specified between customer and vendor. (Temperatures can range from ambient to 60 degrees C {140 degrees F}), while minimum passivation times are usually 20 to 30 minutes). The parts are neutralized using a bath of aqueous sodium hydroxide, then rinsed with clean water and dried. The passive surface is validated using humidity, elevated temperature, a rusting agent (salt spray), or some combination of the three. However, proprietary passivation processes exist[10] for martensitic stainless steel, which is difficult to passivate, as microscopic discontinuities can form in the surface of a machined part during passivation in a typical nitric acid bath.[11] The passivation process removes exogenous iron,[12] creates/restores a passive oxide layer that prevents further oxidation (rust), and cleans the parts of dirt, scale, or other welding-generated compounds (e.g. oxides).[13][14]

It is not uncommon for some aerospace manufacturers to have additional guidelines and regulations when passivating their products that exceed the national standard. Often, these requirements will be cascaded down using Nadcap or some other accreditation system. Various testing methods are available to determine the passivation (or passive state) of stainless steel. The most common methods for validating the passivity of a part is some combination of high humidity and heat for a period of time, intended to induce rusting. Electro-chemical testers can also be utilized to commercially verify passivation.

WaterFarmFan said:

I would like to make some items using stainless mesh that would require welding to a stainless shell. These would be used for a distillation process, and thus the bond material would need to be inert.

Is it as simple as TIG welding the connections using thin stainless rods?

https://www.amazon.com/Blue-Demon-ER316L-stainless-welding/dp/B00GJU7HTW/

I have a friend that owns a metal shop with all the welding gear, but I wanted to make sure and order the right rods.

Also, is there an inert way to bond stainless to aluminum? Thanks!

Click to expand...

It is as simple as TIG welding with a compatible alloy. For 304Ss, I usually use 316SS filler for the higher chromium content.

You can braze aluminum to stainless, but not weld it.

Where in your system are you using aluminum?

Thanks GW. This is to make custom shelves for my vacuum oven to dry fresh flower material. I thought about starting with stock aluminum shelves and then cutting out the middle, but I think it would be easy and cheaper to use simple stainless pieces for support and weld it in place using an inverse mold to create the 1/2" deep screen section.

What sixe mesh are you planning to use? Fine mesh or anything with a wire size undet 0.030 is going to need a specialized joint to keep the mesh from melting prematurely.

Hey Ricky. I ordered a #20 mesh with 850 micron openings to get max breathability, with the plan to just place a fine mesh screen on top if dealing with hash consistency material. These have 0.0162 304L wires. Are you saying the mesh wires will melt when welded? By specialized joint, do you mean like sandwiching the mesh between two thin strips of stainless and then welding the strips of stainless together instead of welding the mesh?

Edit - I found a local supplier with cut to order stainless pieces. I decided to go with a simple approach and use .5" strips (11.5" & 8.5" lengths). 4 of these can be welded to create a separate top and bottom, and then with a mold in middle, the screen can be sandwiched between the plates and then the outer edges can be welded. I will trim any excess mesh, so it does not matter if the mesh melts during outer weld.

My question now pertains to grinding. Should the welds simply be left alone after, or is some grinding ok after? I am pretty anal about things being clean when it deals with evaporation. Is there an industrial cleaning technique recommended to make sure any welding shop residue is removed before use?

Thanks everyone!

use a stainless steel wire brush to polish the welds. then you can use a passivation substance to clean them and remove the junk and carbon. you don't necessarily need to use a grinder. you could use a hand brush with wire bristles if you want. just make sure its clean (new, not covered in grime and foreign materials). a carbon steel brush will contaminate the weld and ruin all your hard work so make sure its stainless! as for a passivation substance you can use any mild acid. just make sure its not too corrosive that it would etch into the material and degrade the weld. I worked in a shop that used a passivation medi called avesta and it was very powerful. it was so powerful that it would smoke if left too long and you needed to wear full body protection to handle it. they changed to a gel based one that had hydrochloric acid. it was called "go green" and it was safe to rinse down the drain when diluted with water.you could probably track it down in a hardware store im sure (the go green) but people have even used pure vinegar in a pinch. it just takes a lot longer and more applicatons!

WaterFarmFan said:

Edit - I found a local supplier with cut to order stainless pieces. I decided to go with a simple approach and use .5" strips (11.5" & 8.5" lengths). 4 of these can be welded to create a separate top and bottom, and then with a mold in middle, the screen can be sandwiched between the plates and then the outer edges can be welded. I will trim any excess mesh, so it does not matter if the mesh melts during outer weld.

My question now pertains to grinding. Should the welds simply be left alone after, or is some grinding ok after? I am pretty anal about things being clean when it deals with evaporation. Is there an industrial cleaning technique recommended to make sure any welding shop residue is removed before use?

Thanks everyone!

Click to expand...

A professional weld will not have any deep laps and can be cleaned with a stainless wire brush and wiped clean with a solvent like acetone.

You also need to passivate 300 series stainless to remove the iron splatters, or it will speckle with iron rust.

Unless you also solution anneal afterwards, some of the chromium ends up tied up with the carbon, in the form of chromium carbides, taking the chromium out of solution and reducing the anti corrosive properties.

To minimize that, you can use welding wire with higher chromium content, like 316 or 347SS and cool the welds rapidly to below 750F.

Stickybred420 said:

use a stainless steel wire brush to polish the welds. then you can use a passivation substance to clean them and remove the junk and carbon. you don't necessarily need to use a grinder. you could use a hand brush with wire bristles if you want. just make sure its clean (new, not covered in grime and foreign materials). a carbon steel brush will contaminate the weld and ruin all your hard work so make sure its stainless! as for a passivation substance you can use any mild acid. just make sure its not too corrosive that it would etch into the material and degrade the weld. I worked in a shop that used a passivation medi called avesta and it was very powerful. it was so powerful that it would smoke if left too long and you needed to wear full body protection to handle it. they changed to a gel based one that had hydrochloric acid. it was called "go green" and it was safe to rinse down the drain when diluted with water.you could probably track it down in a hardware store im sure (the go green) but people have even used pure vinegar in a pinch. it just takes a lot longer and more applications!

Click to expand...

Most helpful! Will pass along details to my friend. Ordered a stainless brush.

Gray Wolf said:

A professional weld will not have any deep laps and can be cleaned with a stainless wire brush and wiped clean with a solvent like acetone.

You also need to passivate 300 series stainless to remove the iron splatters, or it will speckle with iron rust.

Unless you also solution anneal afterwards, some of the chromium ends up tied up with the carbon, in the form of chromium carbides, taking the chromium out of solution and reducing the anti corrosive properties.

To minimize that, you can use welding wire with higher chromium content, like 316 or 347SS and cool the welds rapidly to below 750F.

Click to expand...

I went with 316 based on your recommendation with 304. Plan is use a bit of acetone followed by a citric acid (I already have a bunch) bath. What is a common practice to rapidly cool SS welds below 750F? Spray bottle? Thanks!

Also, is 100% Argon better than 75/25% mix for this application?

WaterFarmFan said:

Also, is 100% Argon better than 75/25% mix for this application?

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+

Yes. The mixes are typically used for Mig (GMAW) rather that Tig (GTAW).

Thanks. My buddy has both MIG and TIG, and he suggested just going with MIG. Spool of 316L arrives tomorrow. Will post some photos of finished products in a few days,

WaterFarmFan said:

Most helpful! Will pass along details to my friend. Ordered a stainless brush.



I went with 316 based on your recommendation with 304. Plan is use a bit of acetone followed by a citric acid (I already have a bunch) bath. What is a common practice to rapidly cool SS welds below 750F? Spray bottle? Thanks!

Click to expand...

Usually shielding gas until it loses its glow and then compressed air.

After solution anneal, 300 series is typically water quenched.

Most excellent info. I printed this entire thread to take to my friend. You guys F'n rock!!!

WaterFarmFan said:

Thanks. My buddy has both MIG and TIG, and he suggested just going with MIG. Spool of 316L arrives tomorrow. Will post some photos of finished products in a few days,

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With a wall thickness of .065 to .083, it will take a shorting arc to Mig weld it, which are pretty messy with minute dingleberries.

They also typically use a 95% Argon-5% CO2 gas mix.

I suggest using the Mig wire and Tig welding it for the prettiest job and highest integrity.

waterfarm, I see this is a bit late response, im sorry im new here, just got in the door


I am a welder for over 30 years, this IS my forte
oil making, not so much...but im learning


ER308 stainless is good for a lot of stainless to stainless applications
even at x-ray quality...for high pressure welding, found in nuclear reactors


ER309 stainless is excellent as well, but with a twist...
it is specifically designed for stainless to carbon steel applications
as well as it also can be used for stainless to stainless applications
being much more versatile then say ER308


based on what you want to weld, (you aint building no nuclear reactor)
the ER309, is just fine, and way more versatile rod to have laying around your shop
for other future uses and/or projects that "pop up"


as for "bonding" aluminum to stainless, never heard of it....
good choice of words tho, I credit you for that...
because as you know there is a difference between bonding , and fusion


and I can tell you this about it, off the top of my head
never in a million years could you get fusion between
the 2 metals aluminum and stainless, they are 2 totally different animals
not even remotely close in properties, metallurgy, tensile strength,
molecular structures, can not be possible...


that being said, perhaps a bonding yes, but not as simple as that...
you can "bond" alot of stuff together, using brazing rod, this requires a lot of controlled heat...a hot MAPP gas flame or acetylene flame...brazing rod


because aluminum dissipates heat almost as fast as you heat it...
it is problematic from the very start, thereby bonding by brazing rod, wouldn't even be considered by the most experienced welder, because he knows better...
it simply wouldn't stick....incompatible...


not to be discouraged tho....
there are always work arounds to the more experienced


I would delve deeper into it, "cladding"....there are many unlike and like materials
nowadays simply bonded together by cladding process, highly developed by the auto industry of course....
my mind says it is possible to clad aluminum together with stainless


depending on the joint design of the 2 unlike materials, work around options could be had,


for example if I wanted to go from aluminum to stainless in a piping application
Id look for utilizing a threaded scenario , using threads and a reducer coupling...
a stainless pipe turns into aluminum pipe via threads utilizing a reducer


if it was a flat and linear application 2 small plates together...
you know what...id go with riveting...nice clean, easy peasy


riveting is nothing to snear at....
all steel ships prior to WWII were in fact ALL riveted...
as where ALL bridges you drive across on, and even the Eiffel tower....riveted


so there you have it, 2 suggested work around solutions
for 2 un like materials...


hope that helps...


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