Use heat to free up bolt. Can heat draw in penetrating oil?

[CobyRupert]

Other day, someone mentioned trying to get something apart.
I think they used penetrating oil on a bolt/nut then applied some heat to “draw the oil in”.
I’d heard of that before but how does that work? By what principle?

I got curious in what actually forces one is trying to overcome when something is frozen.

My understanding of heat is you’re trying to get metal to expand.
But aren’t you really trying to get the nut to expand at a faster rate than the bolt?

If possible, wouldn’t freezing (bolt) work was well? (Depending on shape of expansion-to-temperature curve of that metal)

Should one only heat the nut and keep bolt as cool as possible?
Would heating nut (and bolt too, because it’s going to get hot), but then shocking it, or cooling it rapidly with squirts of water be more effective?

 

[Big Barn]

You want to heat the NUT red hot quickly.

Should only take 4-5 seconds depending on size. Oxy-fuel torch works best. Using a propane torch will take too long and end up transferring heat to the bolt.

Use wrench or socket and remove.

Edit: sorry Coby. I just realize I gave the procedure using heat but didn’t really answer your question.

 

[goeduck]

Drawing the oil in concept may come from most oils flowing better at hotter temperatures? You are correct in that with heat you want the nut expanding faster than the stud if you are removing a nut. You want the nut to expand away from the stud. But what do members do if it is a stuck bolt where all you have access to is the bolt head and the body of the metal part it is in?

 

[jaxs]

Your assumptions are correct except oil is drawn in as bolt cools. Not red hot by any means if using penetrating oil. The jury is still out on cold water cooling but if metal as red hot,cold water will alter temper. Everyone has their methods,I heat and let it air cool a time or two before putting oil on it. My thinking is swell shrink cycles might open passage for oil. A recent poster cursed it and allowed his dog to watch.:laughing: and he was successful.

 

[/pine]

Heating metal makes the molecules move faster...
What heating does to a bonded/stuck nut on a bolt, stud etc. is breaking that bond (rust etc)...not necessarily making the nut larger by (heat) expansion...As long as the two parts expand at (even slightly) different rates the bond is usually broken...this also allows penetrating fluid past the previous bond

 

[jaxs]

Drawing the oil in concept may come from most oils flowing better at hotter temperatures? You are correct in that with heat you want the nut expanding faster than the stud if you are removing a nut. You want the nut to expand away from the stud. But what do members do if it is a stuck bolt where all you have access to is the bolt head and the body of the metal part it is in?

The consensus seem's to be tap-tap-tap on head combined with heat and/or oil. I often use 6 point socket on air impact wrench for the tap tap.

 

[ray66v]

When freeing up external door hinges on the sides of cargo vans, it is a common practice to lightly heat them before applying penetrating oil.

I have seen them go from so tight you can barely move the door, to free in seconds.

Yes, of course if you are trying to remove a nut, you want to try and heat the nut only. This requires the right equipment, and control of it.

It is sometimes possible to burn a nut off a bolt, and leave the threads on the bolt intact, if done right.

 

[k0ua]

Hmmm.. wonder what would happen on a drain plug???

 

[RNeumann]

The theory is two fold. Heating the nut should cause it to expand. If the heat is applied correctly the nut and bolt will change temps and expand at different rates which can potentially “un- seize” the two.

Most oils become thinner with heat. So heating a part with oil on it will thin the oil and improve its ability to flow.

The oil also has some cohesive properties which can cause it to “draw” into a part. This draw can occur while working with or against gravity. So in this case the heating is hopefully creating some new microscopic pathways between the nut and bolt for the oil to draw/flow.

 

[oosik]

My procedure - first try penetrating oil. If that doesn't work - apply heat to the nut. I've never had a stuck bolt, with only the head showing, that wouldn't come loose with repeated attacks with my impact wrench.