# Best Bonding Agent for Stainless?



## stumpy1972 (Jun 27, 2007)

I have a situation where I need to fix a stainless steel pin in a mating hole drilled in stainless steel. What would be the recommended bonding agent? I need something that will be sweat proof (high chemical resistance). :thanks


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## dbl_ (Mar 22, 2009)

stumpy1972 said:


> I have a situation where I need to fix a stainless steel pin in a mating hole drilled in stainless steel. What would be the recommended bonding agent? I need something that will be sweat proof (high chemical resistance). :thanks


Epoxy resin (2 component epoxy glue) will fix it.


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## Rikku (Feb 18, 2008)

stumpy1972 said:


> I have a situation where I need to fix a stainless steel pin in a mating hole drilled in stainless steel. What would be the recommended bonding agent? I need something that will be sweat proof (high chemical resistance). :thanks


yeah epoxy or CA might work.

try to scuff up the mating surfaces to increase grip, I suppose.


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## Somewhere else (Feb 17, 2006)

Hard soldering is the best way to go. there are types of hard solder made for gunsmiths with a color to specifically match most stainless steel.


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## stumpy1972 (Jun 27, 2007)

Thanks for the replies fellas. :-!

Hard solder would surely do it, but I'm not sure I wanna heat up the metal to soldering temp especially for the small parts I would be fixing.

If I were to go the epoxy route, is there a particular kind of epoxy. Does JB Weld fall into this category? 

:thanks:thanks:thanks


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## dbl_ (Mar 22, 2009)

stumpy1972 said:


> Thanks for the replies fellas. :-!
> .
> .
> If I were to go the epoxy route, is there a particular kind of epoxy. Does JB Weld fall into this category?
> ...


JB Weld would be excellent. Just remember to degrease elements (eg. with isopropanol or acetone) before applying mixed adhesive. You may also roughen surfaces to strenghten joint (eg. with sand paper - this will form anchor poins to the adhesive).


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## stumpy1972 (Jun 27, 2007)

Very good. Thanks for all the info! :-!


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## neutron (Aug 2, 2009)

In my experience as a professional machinist an epoxy would not be adequate. Soft solder would be better, and the melting point is low enough that the stainless steel won't be affected. But do NOT use an open flame; this will decarburize the steel causing it to change colors and lose its "stainless" part. Use a hot plate instead.


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## dbl_ (Mar 22, 2009)

neutron said:


> In my experience as a professional machinist an epoxy would not be adequate. Soft solder would be better, and the melting point is low enough that the stainless steel won't be affected. But do NOT use an open flame; this will decarburize the steel causing it to change colors and lose its "stainless" part. Use a hot plate instead.


Definitely can't agree. Please consider what parts have to be joint, and how tight the pin fits into the hole. There should be enough place between pin and the inner surface of the hole to take solder metal (I hope you did not propose to solder the pin in the upper part - not in the hole).

Besides, unless proper flux is used soldering stainless steel is problematic or even impossible with soft solder based on tin.

Epoxy adhesive has very good mechanical properties, v. good chemical resistance to water, sweat etc. and it really last very long as a joint.
The main rule with adhesives is cleaness and degreasing. The same to certain extent applies to soldering 

Last not least, it may be applied when almost zero clearance between elements exist - simply after roughening surfaces.

BTW - all that is based on my experiences as professional chemist and electronic hobbist.


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## thales (Jul 17, 2008)

Don't be a fool.

Use Loctite 609. Available in better hardware and auto parts stores everywhere.


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## lysanderxiii (Oct 4, 2006)

> Last not least, [epoxy] may be applied when almost zero clearance between elements exist - simply after roughening surfaces.


Just about every adhesive I know of require a bondline anywhere from 0.002 to 0.008 inch, usually around 0.005.

A sweated (brazed, or hard solder) would be the strongest solution, however, Loctite 609 would be the simplest.


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## skoochy (Jan 6, 2009)

neutron said:


> In my experience as a professional machinist an epoxy would not be adequate. Soft solder would be better, and the melting point is low enough that the stainless steel won't be affected. But do NOT use an open flame; this will decarburize the steel causing it to change colors and lose its "stainless" part. Use a hot plate instead.


Since you're a machinist, I thought I would ask what you think about crimping (well, knurling) the pin to reduce the clearance and then press fitting it in. We don't have a lot of info about his application but I think that this would be superior to an adhesive in most cases?

(And depending on the type of stainless, won't soft solder have a hard time sticking?)

-s-


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## stumpy1972 (Jun 27, 2007)

I'm gonna give the Loctite 609 a try. It's a bit runny and will be easier to work with on a very tiny pin and hole vs the JB weld (epoxy). :thanks for all your input.


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## lysanderxiii (Oct 4, 2006)

skoochy said:


> Since you're a machinist, I thought I would ask what you think about crimping (well, knurling) the pin to reduce the clearance and then press fitting it in. We don't have a lot of info about his application but I think that this would be superior to an adhesive in most cases?
> 
> (And depending on the type of stainless, won't soft solder have a hard time sticking?)
> 
> -s-


 Knurling will improve the grip of adhesive as it will provide an additional mechanical hold on the parts.


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## neutron (Aug 2, 2009)

skoochy said:


> Since you're a machinist, I thought I would ask what you think about crimping (well, knurling) the pin to reduce the clearance and then press fitting it in. We don't have a lot of info about his application but I think that this would be superior to an adhesive in most cases?
> 
> (And depending on the type of stainless, won't soft solder have a hard time sticking?)
> 
> -s-


 Sorry, I didn't see your post earlier otherwise I would have replied sooner.

Knurling or otherwise fretting the pin would certainly help with fit and adhesion. Or, get a new pin with a larger O.D.

Stainless steel can be joined with any of the processes normally used on carbon steels, and a stainless piece can be joined to a non-stainless piece by welding or soldering. Soft solders are no problem and very easy to use even by a novice. The key to remember is to not expose the stainless to a naked flame. For a household job it would be fine to warm up the watch case and pin in a toaster oven and get the joint to final temp with a high-power soldering iron. But, if the job can be done solely on a hot plate this would be the best route; just be sure to let the entire workpiece cool down by convection (do not quench).

A tin-lead solder melts at the lowest temp and has the best gap-bridging capability. These are 37-40% lead and 60-63% tin. The tin-silver solders (Harris Stay-Brite is awesome) are stronger and more "watery" in their molten state... I cannot recommend using a tin-silver for this job because of the high working temps involved, around 550°F, which would probably change the color of the steel to blue or straw.

BTW, for this job I would highly recommend using a flux made for stainless steel. In school we were told not to use acid flux on stainless, but as far as I can tell ALL stainless fluxes are acidic.


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## P. Loatman (Mar 22, 2009)

neutron said:


> But do NOT use an open flame; this will decarburize the steel causing it to change colors and lose its "stainless" part. Use a hot plate instead.


I don't mean to pick apart your post but aren't stainless steels "stainless" because they contain nickel in their alloy? I don't see how oxidation would cause that to change, in fact adding a layer of oxide to steel is a very common method of preventing oxidation from occurring any further on normal steels, but that's different from a stainless alloy. The only way it would lose it's stainless characteristic would be to extract the nickel molecules from the alloy.


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## neutron (Aug 2, 2009)

P. Loatman said:


> I don't mean to pick apart your post but aren't stainless steels "stainless" because they contain nickel in their alloy? I don't see how oxidation would cause that to change, in fact adding a layer of oxide to steel is a very common method of preventing oxidation from occurring any further on normal steels, but that's different from a stainless alloy. The only way it would lose it's stainless characteristic would be to extract the nickel molecules from the alloy.


 From your signature, I gather you've seen stainless steel exhaust manifolds. They don't stay bright and stainless after being exposed to high exhaust port temperatures do they? The portion of the manifold closest to the engine always has the most rust and/or discoloration.

Let's talk about WHAT IS STEEL? Your basic textbook steel consists of two ingredients: Iron and carbon. A medium carbon steel is approximately 95.5% iron and 0.5% carbon by weight.

Now... you are probably partially correct that stainless steel gets its properties from the nickel content. In addition to iron and carbon, 316L contains cromium, nickel, molybdenum, manganese, silicon, phosphorus and silicon (I had to look it up). I can't say for certain which one or combination thereof is mostly responsible for the corrosion resistance, but for argument's sake let's say it's nickel.

If we have a watch case we're heating to soldering temp (say 350 °F) with a hot plate, oven or soldering iron we can control its temperature and heat the workpiece to a precise degree. 350° is well within the working temperature envelope of 316L, meaning it will not get soft, change strength, change color, etc.

Exposing the workpiece to an open flame, say a household natural gas flame (3,500 °F) runs a high chance of overheating the "skin" of the workpiece. At 3,500 degrees, the CARBON, not the nickel, is well beyond its oxidization temperature and will leach from the steel. Removing the carbon from steel is "decarburizing," which I first mentioned in post #8. If you do not have carbon then you do not have stainless steel.

Nickel is one of many ingredients that can be extracted from steel to chemically alter it. It just so happens that the carbon is far more likely to be extracted, and doing so would turn steel from stainless to iron slag with cromium, nickel, molybdenum, manganese, silicon, phosphorus and silicon contamination.

You've probably seen a burned-out steel car body. Invariably, it will be rusted due to the loss of carbon, essentially converting the steel to iron.

This is all different than "black oxide" hardware. I see what you're saying, about adding a corrosion layer to prevent continued corrosion, but this is not how it works on steel. "Black oxide" is really a conversion coating, meaning what turns it black is not corrosion, but a conversion of the outer layers of iron to magnetite by introducing nitrate and/or nitrite in a controlled temperature caustic bath.


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## P. Loatman (Mar 22, 2009)

neutron said:


> From your signature, I gather you've seen stainless steel exhaust manifolds. They don't stay bright and stainless after being exposed to high exhaust port temperatures do they? The portion of the manifold closest to the engine always has the most rust and/or discoloration.
> 
> Let's talk about WHAT IS STEEL? Your basic textbook steel consists of two ingredients: Iron and carbon. A medium carbon steel is approximately 95.5% iron and 0.5% carbon by weight.
> 
> ...


My mistake, i was mistaking nickel for chromium, the nickel allows it to be non-magnetic not corrosion resistant. I haven't studied chemistry in a while.

However, if you ignore that and switch what i said about nickel with chromium then it's the same. Stainless steel can't lose its stainless properties without extracting the chromium molecules. The reason for it can be explained with simple chemistry. The chromium combines with oxygen in the surrounding atmosphere and creates a rust resistant layer because the chromium atoms are similar in size to the oxides and that layer essentially protects the steel from corroding. However burning it off will only cause the chromium to combine with more oxygen and create another protective layer almost immediately.

I've heard many times from people who should know better that the carbon content of steel is what prevents or causes rust, but it has nothing to do with it, and you can't burn away the carbon in steel with a small flame, you'd need to bring the steel up to smelting temperatures and not allow any exposure to any carbon rich minerals.

Iron rusts because the iron atoms are much smaller than the oxides in the atmosphere so when they combine they don't pack together as tightly as the chromium will, which makes the atomic structure unstable and that allows it to corrode. Iron and steel both rust, the carbon is only good for giving iron the potential for so many different physical characteristics.

Another thing is that "stainless" steel doesn't mean it'll be shiny and new-looking forever even if you keep it away from a flame, it'll form a thick visible layer of oxides with a good deal of exposure, other particles could cling to the surface and make it look rusty, but it won't corrode and that's the difference.

What i'm trying to say is that you can heat stainless steel up even to the austenite phase and it won't lose it's corrosion resistance, it just won't look so pretty, if you're heating stainless up and it starts to change colors, the only thing you have to do is polish it up again and it'll be fine. Infact even if you left it in one of the temper colors it would still be fine as far as corrosion resistance goes.

Also, i never said that adding a "corrosion layer" would protect steel, that doesn't even make sense, if it's corroding then it's not being protected, i said adding a layer of oxide will protect it, what it does it basically makes a barrier from the atmosphere and the steel so the oxides can no longer come into contact with the steel under the protective layer, similar to what stainless steel does naturally, normally iron can't do it because in nature iron won't be subjected to such a dramatic change so suddenly, so left to it's own it will just slowly form a loose layer of oxide combined with iron on the surface which will flake away and "rust".

In essence stainless steel will not lose it's stainless characteristics from a flame. It's physical properties can be changed though.


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