How do Penetrating Oils Work??

[RWebb]

... at the film chemistry level, that is

I'm curious about what happens in between the threads of a stuck or corroded fastener that requires a much larger torque to "break it loose" than the spec. torque for installation.

e.g.
1. does steel on the cap screw (bolt) weld or alloy to the steel on the nut?
2. does rusting produce dendritic growth of the rust itself between the two surfaces?
3. or??

and, what does the penetrating oil do to reduce the above?

[BK911]

Kinetic versus static friction?
Pen fluids reduce surface tension.
Did I win?

[Zeke]

You have to ask? Get some Kroil and just do it.

[ossiblue]

When iron, or an alloy, rusts, the oxidation process displaces more space than the original iron, thus you get breaking of concrete from rebar rust and the space between an bolt and nut is not only "filled", but pressure is exerted between the two parts by the expansion of the rusted metal.

Can't explain penetrating oil.

[Jeff Higgins]

To expand on ossiblue's explanation yes, the rust, galvanic corrosion, or whatever does in fact "grow" on the parent surface. When two mating surfaces have each "grown their own", they kind of interlock their respective corroded surfaces. Penetrating oil obviously cannot make two interlocking surfaces "glide" over one another - there is a hard mechanical lock between the two. What it can do, however, is make it much easier to break the bond formed between the corrosion and its parent surface. So, if you can break the nut's corrosion off of the nut, and the bolt's corrosion off of the bolt, you no longer have a hard mechanical lock. Now you have a rust and oil slurry between the nut and the bolt. That's the whole idea.

On a related note, the very best penetrating "oil" I have ever used is simply 50/50 ATF and acetone. The acetone acts as the carrier to get it in there and soon evaporates, leaving the ATF to loosen the corrosion. Only mix as much as you need - the acetone will evaporate from the mix, leaving you with ATF again. Doesn't hurt it - just add more acetone - but it does needlessly waste acetone if you're not using it right away.

[javadog]

The best penetrating fluid I have ever used is paraffin wax, melted into a very hot joint from a simple candle. I have used that to loosen critical fasteners in irreplaceable magnesium castings, after every other penetrating oil you can name failed to do the trick.

FWIW

[Jeff Higgins]

Heat alone is actually very good on rust. Heat the fastener cherry red with an oxy/acetylene torch and the oxides break down, reducing the rust to powder.

[javadog]

That’s true, but there are some parts that you can’t heat to those kind of temperatures.

[Jeff Higgins]

Absolutely. It has to be steel on steel or cast iron. Even steel in aluminum is pretty much a no-go.

[sammyg2]

it just does

[john70t]

(only a guess)
The friction resistance is limited to the two separate sides of the threads making contact.
It's not 100% contact overlap.

As time and chemistry wears on, those chrome--on--chrome/iron/steel/aluminum/magnesium friction surfaces change to a rust oxidation bond from the deformed surfaces. Different metals oxidize/catalyze faster next to each other.

Wicking of oils/wax occurs via surface attraction and draws it into the crevices further reducing the contact surface area.
High heat also helps to melt the oxidized material and reduce overall contact.

[cabmandone]

Kroil says it's the oil that creeps so I have to think creeping is involved.

[rfuerst911sc]

Originally Posted by Zeke

You have to ask? Get some Kroil and just do it.

Milt I laughed out loud when I read your reply ........ good one !

[pwd72s]

Originally Posted by cabmando

Kroil says it's the oil that creeps so I have to think creeping is involved.

Kroil was invented by Joe Biden? Kinda like Al Gore invented the internet?

(sorry..couldn't resist)

[wdfifteen]

Originally Posted by cabmando

Kroil says it's the oil that creeps so I have to think creeping is involved.

Ugh! That makes my skin crawl.
Jeff’s explanation is how I understand how it works. Cycling heat - oil, heat - oil can work.
I have a friend who restores 100 year engines. He has several methods for freeing stuck 6 to 10 inch pistons rusted into their bores. For the most resistant he puts the assembly into a press (with pressure on the piston of course) and gets 3 or 4 guys with acetylene torches with rosebud tips to heat it up for hours. When it’s good and hot he drops a couple of pounds of dry ice on the piston. It usually works.

[john70t]

I wonder why there isn't a phosphoric zinc acid oil penetrating out there.
#10 to aggressively eat rust mostly but leave a little oil lube behind.
#1 to cut through old grease and lubricate mostly but leave behind much protective zinc.

[RWebb]

Thanks, Jeff, ossiblue

Milt, I have Kroil - just curious.

Ultimately, you'd like to have some nanobots go in there and chip away at the mechanical 'locks' - I predict you will not see that for a long time after you see nanobots used in surgery.

[GH85Carrera]

The real answer, about 1/10 as well as you hoped for when you bought the oil. Usually poorly.

[flatbutt]

Originally Posted by Jeff Higgins

To expand on ossiblue's explanation yes, the rust, galvanic corrosion, or whatever does in fact "grow" on the parent surface. When two mating surfaces have each "grown their own", they kind of interlock their respective corroded surfaces. Penetrating oil obviously cannot make two interlocking surfaces "glide" over one another - there is a hard mechanical lock between the two. What it can do, however, is make it much easier to break the bond formed between the corrosion and its parent surface. So, if you can break the nut's corrosion off of the nut, and the bolt's corrosion off of the bolt, you no longer have a hard mechanical lock. Now you have a rust and oil slurry between the nut and the bolt. That's the whole idea.

On a related note, the very best penetrating "oil" I have ever used is simply 50/50 ATF and acetone. The acetone acts as the carrier to get it in there and soon evaporates, leaving the ATF to loosen the corrosion. Only mix as much as you need - the acetone will evaporate from the mix, leaving you with ATF again. Doesn't hurt it - just add more acetone - but it does needlessly waste acetone if you're not using it right away.

https://www.bangshift.com/forum/forum/bangshift/tech-section/9336-make-your-own-penetrating-oil-that-s-better-than-kroil

[drkshdw]

Heat is the one to beat but none of them really help at all. At least not in this test. Funny that Kroil, the most expensive, is the worst yet the people who use it swear by it.