Rockwell test mark?

It seems to me that if one wanted to know if it was an accurate Rockwell test coin. You would have to send it in. Not sure if it would be worth it.
I just did some quick research and you can buy this machine.
https://westportcorp.com/products/analog-rockwell-hardness-tester-br-phase-ii-model-900-331

 

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I know what it stated.
I'm not a metallurgist, but I think their statements are incorrect.
So does Fred.

Once again, the strike area would have had to harden so much to prevent metal flow. Even though the top of it was supposedly flowed UP and partially fill that die section. So it would FLOW UP into the die, but not flow IN filling some of the depth??

And if you look half way in the height of that mark, you would see that it is wider than the top and bottom section.

 

Yes, I mentioned that earlier. They are common in metal testing, and you can buy one yourself if you wanted too. Or you can emulate it quite easily at home too.

 

I’m a mechanic. So unless there is a defect in the ball or it was a miss aligned strike then it would create that oval.
A perfect strike .perfect circle.
Imho.

 

The Rockwell test is performed on a planchet. The planchet itself is removed outside of the entire minting process in order to perform the test. it is to test the hardness before striking to make sure it meets the quality control for striking.

So I think you are confusing the two separate process as one.

If they threw it back in the process then it would get struck by the dies.

 

I understand the process completely. Yes they take it from the mint to do a test for hardness.
Perhaps you should reread what I wrote.

Or if you have a piece of metal a punch and hammer. Hit the metal straight on you will have a perfect punch. Hit on an angle you will have a groove going in a certain direction.

 

Sorry,@Clawcoins hope I didn’t say anything out of context. You make great valid points!

 

From a process and metallurgy standpoint, I don't think a test mark is going to survive, even in the unlikely event the planchets were to make it to the minting process.

I would expect the Rockwell test to be performed as part of an incoming inspection. In many production processes, incoming raw materials are sampled and taken to the lab. Once they have met all the testing criteria, the bulk shipment is released for production. Based on my experience in manufacturing, the test samples are discarded as written in the testing procedures.

It makes no sense to use Rockwell as an in line process check. If you find a bad one, you'll have to shut down a high speed production line to remove them. It's a lot easier and cost effective to sample and test a lot prior to putting them in the production stream.

I mentioned my thoughts on the metallurgy previously. @Clawcoins posted the mint used a 15T test, which is the 1/16" ball. That's 62.5 thousandth s. Might the indent induce some localized work hardening? Maybe. I'm not a metallurgist, but I would think it would be very small based on the size /depth of the indent.

Based on manufacturing process control methods and testing it seems that for a Rockwell test piece to make it back into the process would be unlikely, and if one were to make it, there's a good chance, it wouldn't be recognizable. I think Fred's skepticism is warranted

 

Yeah, that is not a Rockwell hardness indent, either before or after striking. I can do a 15T Rockwell hardness test on a zinc cent to show you what one looks like.

What is the approximate diameter and depth of the indent? Also, is there any evidence of exposed zinc (especially around the peripheral), or does it look like the indent occurred before the zinc was copper plated?

 

Here is what a Rockwell 15T hardness indent looks like on a zinc and copper cent (after striking).

 

The Rockwell Tests, in the US Mint,
are done on planchets, NOT on Dies.

 

Who are you responding to? I am sure the mint also checks the hardness of the dies to verify they are properly annealed prior to hubbing and properly re-hardened prior to striking, but they would never check the hardness on the striking face of the die.

 

The Rockwell Test is not used on Dies,
before or after anything.

 

Why wouldn't they verify the hardness of the die? It is a basic quality check that is quick, easy, and non-destructive and is correlated with the total die life. If the hardness is out of spec, either too hard/brittle or too soft, then you can have pre-mature die failure. I previously performed a failure analysis on a Mexican 20 centavos die that pre-maturely failed. I remember seeing the mint had already checked the hardness on the cancelled die face before submitting the die back for analysis. So I know at least the Mexican government has hardness specifications for their dies.

But I'm not sure who originally mentioned anything about the die or if you were responding to me or someone else. I was showing what the hardness indent looks like. The hardness is well within specification for the copper plating zinc planchet (62-72), so the indent would have been the same size on the planchet before it was struck. You can use your imagination as far as how the indent would have deformed under the striking pressure.

 

I'd guess that a R.T. mark INto a Die would
make the die unusable.

 

Having worked in a mint, the Rockwell testing is done on the side, not the face of the die.

 

Yes, thank you. As I previously said, they would never check the hardness on the actual striking face of the die. They would check the hardness on the side using the Rockwell “C” scale which uses a diamond shaped indenter (instead of the 1/16” diameter ball indenter used for the planchet) and then perform a roundness correction per ASTM E18 based on the diameter of the die and the hardness. The hardness indent on the side of the die will not effect the die or make it unusable.

 

I have just recently heard of the Rockwell test and found a Kennedy last night that made me think of it I thought it may have been one until reading this thread. It makes sense that if the test was done on the planchet that if somehow the planchet was to make it to the minting process the mark would be obliterated but do you think that the test could be randomly done to a struck coin at the mint to ensure the hardness after the strike? Like I said I just recently heard of the RW test so I don't know, even if that is possible it wouldn't really matter because if you can purchase these machines anyone can do it and there would be no way to tell if it was done at mint. Here is a pic of my Kennedy.

 

The Rockwell test is an inspection test done to check if a purchased lot of planchets meets the mints spec. (I would expect The sample size and testing frequency to be low, but have no data to prove that). There is no reason to test the hardness after the lot is released to production. This would be the equivalent of Ford measuring the dimensions of a purchased piston or valve after it was assembled into an engine

 

Makes sense, thank you. This indentation is smaller than a BB so instead of target practice someone must have been playing around with it lol. Pretty cool looking in hand though.