Saturday, June 2, 2012

Winning against rust.

Over the years I have reworked, restored, and used 3 tractors, all built prior to 1950, a 1946 Ford 3 ton stake bed truck, a barn full of farm implements, and more old tools than I can count. Steel being steel most everything was rusted to the point of immobility so making the components perform involved removing what stuck em.

As a 7 year old I used what my Dad had. That consisted of 3 in one oil, motor oil, and lots of elbow grease to loosen rusted parts and then mineral spirits, gasoline, and kerosene to clean the handmedown bicycles, wagons, and other rolling stock that passed through the family on the way to perdition.

When I began mowing lawns at the age of 10, another handmedown job from my older brother, I cleaned mower decks with scrapers and carbs with gasoline.
Some of the money from the mowing jobs ended up supporting an interest in powered vehicles. The best source of power was the various small engines on mowers, pumps, buzzsaws, and rototillers that followed the path of the earlier rolling stock.

Each of these mechanical marvels became available because they were no longer functional in their original capacity. They came from dumps, fence rows, and sheds, where they were exposed to dirt, and water, and they rusted.

With the persistence of youth I oiled, heated, tapped, and beat on various items until they disassembled or broke. I learned new ways to remove broken bolts, pins, shafts, etc. 1st lesson: If you break a bolt while tightening it you have a chance. Break it on the way out and you’re pretty much screwed.

As time passed I became better at the tapping and broke fewer things. Through study I learned that in the case of iron:

Rust is a combination of iron and oxygen.
Rust is harder than iron alone. Crocus cloth is iron oxide bonded to cloth and is used to polish steel.
Rust expands through the binding of the oxygen to the iron making a larger molecule.
The expanded rust fills gaps thus wedging components apart and thereby tightening the fastener to component joint.

I also learned that lubrication was the common link to all the methods of loosening corroded parts, but the lubrication had to be between the parts in order to work. How to get the lubrication in there is the 64 thousand dollar question. I learned that:

Heat expands materials.
Expanded materials cause the joint to move.
When differential heating is applied properly the outer component expands and the inner component remains the same size or only slightly bigger.
Oil is drawn to heat.
The oil is drawn into the gap through heat and capillary action and lubricates the interface between the components.
Lower viscosity light oil flows better.
Higher viscosity or heavy oil has more film strength, withstands higher compressive forces and resists wiping action better.
Mix light oil and heavy oil together and the longer chain molecules that make up heavy oil remain the same size but are dispersed in the lighter smaller chain molecules and the capillary action causes them to flow into smaller spaces.

Heat nearly always works. But if you heat too much the part is destroyed and since the purpose is to not destroy the part the process breaks down.

I found that the key to all of the methods of removal was that tapping, not beating, banging or smashing, but tapping, causes the joint to move. The joint moves and opens paths for the mix of light and heavy oil to be drawn into the gap. The oil fills the gap and lubricates the materials allowing them to move.

So what do I do?
1.      Mechanically remove dirt and loose corrosion from the surface.
2.      Apply a mix of light and heavy oil to be drawn into the gap.
3.      Tap the components with a small hammer.
4.      Wait.
5.      Repeat.

There are still problems that can occur:

Cracks propagated from rust pits can cause flakes to break free from the surface and wedge between the components. End result no movement.
Over time two steel components will weld together from just being in contact. End result no movement. Heat will greatly accelerate the process.
Bends, wrinkles, riveting, swaging, and misalignment can force items into shapes that interlock. Again no movement.
Galling caused by friction between two components will spot weld flakes and chips from one component onto the other. See welding above.

These are my methods. YMMV.

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