can a soft material wear away a hard material

[engineheat]

Let's say a soft material (like sponge) rubs against a hard surface like steel for a long long time, will the steel surface show any wear? Assume the sponge gets replaced periodically.

Thanks

[BravoV]

Forget about sponge, even water drips can do surface damage on a hard surface, provided long enough.

[ataradov]

Sponge is soft as an overall structure, but even softest sponges are very abrasive. So yes, they will easily wear out metal.

[BravoV]

Try melamine sponge, will scratch even hard steel surface easily without too much effort & time, as its so abrasive at microscopic level, but yet so spongy and soft to touch & squeeze with hand.

[T3sl4co1l]

All depends what's stuck in said sponge.

If some abrasive is added, the answer is absolutely yes.  Lapping plates for example are made of gray cast iron, a somewhat spongelike metal where the voids are a few percent of graphite flake (which is so soft as to be practically irrelevant to abrasive particles).  In addition, the iron (ferrite*) phase is soft, tending to be dented by, and thus trapping, abrasive particles.  In both cases, they can wear against a harder surface.

*Metallurgical name, not the ceramic compound (XFe2O4).

This often happens accidentally, in practice, when some grit or shavings get stuck under an oiler pad, or soft metal bearing, or etc., and the substrate gets gouged out (or worse).

Tim

[Bud]

Just yesterday i polished some copper using kitchen paper towels. They are heck of abrasive when dry.   

[Psi]

The wear is always spread across both objects.
All that changes is the distribution of the wear.
The soft side wears at a faster rate than the hard side.

You can't have an object that's so hard it does not wear at all. That would be a fictional extreme, like an unstoppable force or an immovable object.

[Circlotron]

On my car the soft brake pads wear quickly and the hard metal brake disc wears slowly. Gradually gets thinner, most definitely.

[Brumby]

Answer in a nutshell:

The wear is always spread across both objects.
All that changes is the distribution of the wear.
The soft side wears at a faster rate than the hard side.

[Spuddevans]

A soft material can appear to wear away a harder material, very often you can find plain bearings made of (relatively softer) bronze that have worn away motor shafts of hardened steel.

This appears to be contrary to what seems natural, but there's something else that happens. When there is any clearance between 2 moving parts, unless they are kept in a "clean-room", some foreign matter (dust and grit) can and will get into the clearance gap. Some of this material can and does get embedded into the softer material and becomes an effective abrasive and then wears away the harder material.

2 pieces of moving materials in contact with each other will both wear, even when they are dissimilar hardness, but when you get some other potentially abrasive material introduced, this will tend to embed into the softer material and then wear the harder material much more than the softer.

Tim