What Makes an Anvil Rebound?

[bajajoaquin]

Does anyone know what qualities make for good rebound? From reading the threads here, it seems like:

1) wrought iron body and tool steel face rebounds well
2) cast steel, hardened face rebounds well
3) Cast iron body, tool steel face (Fisher): I don't that I've heard a relative comparison here.
4) Cast iron body, cast iron face: poor rebound (and other issues)
5) Mild steel body, hardened face: medium rebound
6) Mild steel body, hard-surfaced face: ?

It seems to me that the rebound qualities come from the hard face supported by a large mass.

If this is so, then case 6 should have pretty good rebound, assuming that the hard face is thick enough and hard enough.

Thoughts?

[MattBower]

case 6 should have pretty good rebound, assuming that the hard face is thick enough and hard enough.

Thoughts?

Right.

[kcrucible]

As far as I know, it's basically just hardness... the ability of the material to keep its molecules in a given position. Thickness and/or backing helps keep the plate from simply bending, so that it's just compression of the material that matters.

You hit it. Because the metal has nowhere to go, the top molecules compress. Because of the hardness they spring back to where they were before, causing the hammer to rebound.

[pkrankow]

Resilience is more important than hardness (they are related though) as hardness is a resistance to deformation, resilience is a a measure of the ability for a material to return energy elastically.

This is why a ball bearing drop test is more valuable for our purposes than straight hardness.

Phil

[ciladog]

Newton's Third law of motion:

The mutual forces of action and reaction between two bodies are equal, opposite and collinear. This means that whenever a first body exerts a force F on a second body, the second body exerts a force −F on the first body. F and −F are equal in magnitude and opposite in direction.

For each action, there is an opposite and equal reaction. Hard to believe but the hammer hits the anvil and the anvil hits the hammer, rebound!!

Depending on the mass and densities of both the hammer and the anvil some force may absorbed by each.

[bajajoaquin]

Newton's Third law of motion:

The mutual forces of action and reaction between two bodies are equal, opposite and collinear. This means that whenever a first body exerts a force F on a second body, the second body exerts a force −F on the first body. F and −F are equal in magnitude and opposite in direction.

For each action, there is an opposite and equal reaction. Hard to believe but the hammer hits the anvil and the anvil hits the hammer, rebound!!

Depending on the mass and densities of both the hammer and the anvil some force may absorbed by each.

But that doesn't explain the poor rebound of cast iron. Or stone, for that matter.

[MattBower]

Absorption of energy is the culprit. But it's not just mass and density that matter; hardness is a big deal. Otherwise a big lump of lead (or gold!) would make a superb anvil.

[ciladog]

But that doesn't explain the poor rebound of cast iron. Or stone, for that matter.

I am of the opinion that it does explain rebound when a hammer hits an anvil. I also think there is a lot more to the equation of why some anvils have good rebound and some do not or appear to not have good rebound. And, if you have ever hit a solid rock with a sledge hammer and had it bounce back at your face you might rethink your statement.

There are over 160 classifications of “cast iron”. There are over 300 classifications of hardenable steel or as we blacksmith call it “tool steel”. Many cast irons can be hardened just like tool steels. Check out this link if you want to boggle the mind Metals database.

Ok, back to rebound. I could very well be wrong in my thinking about this but the densities of most metals, including most quality cast iron that anvils are made from, are very similar in the range from 0.258 lbs/ cubic inch to 0.283 lbs/cubic inch. So I don’t think that the material the anvil is made from is a significant factor.

I have a Hay-Budden anvil that has a 3/8 inch hard face. If I place it on the concrete floor of my shop (10 inches thick) and hit it with a hammer it rebounds pretty well. If I put it on my anvil stand that is made of ½ inch plate in a pyramid shape with a piece of wood between the stand and anvil and is bolted tightly down, then there is almost no rebound and it no longer rings either.

So I assume that something is absorbing the return force and it is not going back into the hammer. I think it has everything to do with physics namely Newton’s first law of motion that says a body at rest will remain at rest (inertia) and his third law that I explained in the earlier post.

[ciladog]

Absorption of energy is the culprit. But it's not just mass and density that matter; hardness is a big deal. Otherwise a big lump of lead (or gold!) would make a superb anvil.

I agree.

[Mainely,Bob]

You also need to look at the interaction of all the elements involved in the process.
Take an anvil with excellent rebound under a good smithing hammer and then hit that same anvil with a cast iron hammer(like stone masons use),a soft brass hammer and a dead blow mallet of the same weight to see what I mean.
The anvil hasn`t changed,the things hitting the anvil make all the difference.Yet another reason to collect hammers,as if we needed one.

[kpotter]

I have three anvils the first one is one that I made it looks like an anvil and is real pretty it is 300lbs and is mild steel with 1/2inch of hard face put on by a welding machine, when I drop a bearing on it it goes thunk and rings like crazy but the bearing doesnt bounce more than an inch off the face the second is a 200lbs buddin the bearing will bounce right back to your hand and ring the anvil, the third is a 275 lbs peddinghause and it will bounce the bearing right back to your hand and ring but not as loud. The buddin is like forging on a spring the hammer flies back at you and the peddinghause is similar but not as crisp and the anvil I built is like hitting a sand bag. The peddinghause is all forged solid tool steel the buddin is wrought iron with a tool steel face and the homemade is a36 plate with a hard face. The buddin is really hard the peddinghause is softer and my a36 is as hard as the buddin but it was welded on hardface wire not a plate like the buddin. I dont know why the buddin works so well.

[ThomasPowers]

What's the RC of the "hard face wire" face? "Hard Face can be quite soft but *very* wear resistant! HB's tend to have quite hard faces compared to many other "good" anvils.

Y'all are dancing around the concepts of elastic and in-elastic collisions. A good college physics course should cover that and then a good materials course explain why some materials tend more toward the one than the other.

[evfreek]

...
Y'all are dancing around the concepts of elastic and in-elastic collisions. A good college physics course should cover that and then a good materials course explain why some materials tend more toward the one than the other.

Thomas is correct, as usual. Some of these points are beyond college treatment of the subject, even for mechanical engineers.

Let's put some numbers on these ideas. When a hammer hits an anvil the energy only has a few places to go: move anvil, rebound hammer, make noise, damage anvil. We can neglect the noise, since it is usually not large. Moving the anvil is also pretty small for mass ratios above 1:10 or 1:20. A hand hammer is capable of exerting an impact force of about 12000 pounds. Take this on faith unless you know some theory of elasticity and PDE's. So, you will reach the elastic deformation limit of hard steel in about a 3/8" circle, if all the force is concentrated in this spot. Any more, and the anvil is getting damaged. This is 3-4X greater than the elastic limit for mild steel, so if you have a mild steel anvil, you are well into the danger zone. You are making a ding, and that's where a lot of your energy is going. How thick does the hard layer have to be? Dimensional analysis of the elastic equations shows that the stress decreases inversely proportional to the square of the spot size, so it should be 1/4 after 3/8", meaning that any thickness over 3/8" is not necessary, since the stress will have decayed to the safe elastic range for mild steel. This is just an approximation, of course, but it does tell you that top plates do not have to be 2" thick.

Note, also, that this simple analysis ignores the deformation of a softer hotter target. But then again, so does the ball bearing test Backyard blacksmiths also make approximations, just like physicists.

[kcrucible]

Thanks for the numbers, evfreak.