I had a debate with our auditor on the number of indentations that can be done on a standard "wilson" B test block. He says according to ASTM E-18-05 there is not enough space between the indentations on our blocks. My question is, " has anyone ever figured out how many (in theory) indentations can be made on a "Wilson" B test block according to ASTM E-18? Assuming the block is 2 1/4 diameter.

As I am not an expert on Rockwell Hardness, but I HAVE calibrated one unit (and no experts have replied).... I will give it a shot.

My intuitive metrologist answer is that for a valid use of the standard, I THINK (opinion only) you need a flat, unused, undamaged area large enough for the indentation and surrounding metal that protrudes upward after the tip presses in.

If the tip presses into used, damaged/disturbed metal, I intuitively believe its mechanical properties would be altered (lattice structure disturbance, etc.).

As to how many indentations can fit in a given metal test block, I don't numerically know; only that you must be able to test in (as above) an undisturbed area.

If it were me in the circumstance, I would review details of both operation of the hardness tester and/or details of use of the test block to see how it's use is described. I might also suggest poking around some in GIDEP (if you are able and run into a dead end).

Hope that is of some help.

I had a debate with our auditor on the number of indentations that can be done on a standard "wilson" B test block. He says according to ASTM E-18-05 there is not enough space between the indentations on our blocks. My question is, " has anyone ever figured out how many (in theory) indentations can be made on a "Wilson" B test block according to ASTM E-18? Assuming the block is 2 1/4 diameter.

Was this an Internal Auditor or an External Auditor (3rd Party)? If it was an External Auditor, then ask, show me where it is required.

But common sense tells me that if the Hardness Block has been used numerous times and a true indentation can not be attained, then I would get a new one, in my opinion.

I had a debate with our auditor on the number of indentations that can be done on a standard "wilson" B test block. He says according to ASTM E-18-05 there is not enough space between the indentations on our blocks. My question is, " has anyone ever figured out how many (in theory) indentations can be made on a "Wilson" B test block according to ASTM E-18? Assuming the block is 2 1/4 diameter.

Hi dbulak,

You need to obtain a copy of ASTM E 18. The question is not how many indentations can be made. The requirement is that the edge of an indentation must be at least three indentation diameters from the block edge. Edges of indentations cannot be closer than 2-1/2 diameters from each other. Make indentations on only one side of the block. The first indentation reading on a part is discarded, then take three additional readings and average them. You many not resurface a block.

On harder blocks, you will be able to get more indentations. On softer blocks, fewer. You should have blocks near the hardness of the parts you are checking. You should also have blocks to cover the range of hardness that you may encounter. This is just a summary, but again, sounds like you need to buy the standard, read it, and then train your people. My opinion is the auditor does understand the requirements of the standard and is trying to help you improve your testing methods.

Wes R.

First of all, I do have a copy of the standard. But my question still stands. Based on the assumption that the "B" block is 2 1/4 inches in diameter how many indentations can be made? Remember, this is a "B" block which uses a 1/16 diameter ball penetrator.

It's not necessarily the size of the indentor, it's the size of the indentation. I've always been told: 'An indention cannot be closer then 2 indentions size away from the nearest indention.' Also, maintain a two indention gap away from the edges of the block.

My experience is usually with rockwell C, but I've seen a superficial C standard with what looked like hundreds upon hundreds of pin size indentions, and a Rc24 which has these huge conical indentions. I doubt you'd get much over a hundred out of that one.

I'd imagine it's much the same with Rb.

Number doesn't matter, spacing does. If you really want a number, take the total area of your block, measure the size of the typical indention, determine the area that that doesn't allow you to measure within, and divide the total area by that.

If you really want a number, take the total area of your block, measure the size of the typical indention, determine the area that that doesn't allow you to measure within, and divide the total area by that.

Assuming that the indentations are perfectly spaced. :rolleyes:

It's not necessarily the size of the indentor, it's the size of the indentation.
Number doesn't matter, spacing does. If you really want a number, take the total area of your block, measure the size of the typical indention, determine the area that that doesn't allow you to measure within, and divide the total area by that.

I stated that the diameter of the indentation is a function of the hardness of the block. As Hawat has correctly stated, the spacing matters.

To get the theoretical maximum number of indentations:

1. Measure the diameter of the top surface, call it D. Note that this is less than the diameter of the block because of the bevel.
2. Measure several indentation diameters and then average them, call the average d.
3. Calculate the available area for the block using A_b = (Pi*(D-6d)^2)/4.
4. Calculate the effective diameter of the circle consumed by one indentation as d_1 = d + 2.5d/2 = 2.25d
5. Assume hexagonal packing of the indentations, all perfectly spaced.
See http://mathworld.wolfram.com/CirclePacking.html
6. Let the area of one indentation = A_i = 2.25d * 6/(Pi*sqrt(3))
7. Max indentations < (A_b)/(A_i)

The Max indentations is less than the division of the two areas because of edge effects due to placing an hexagonal array in a circular area.

Wes R.

Correct me if I am wrong, but using a "B" block would mean that the tester was using a 100 kg load. Therefore, all indentations would be the same depth and width.

Correct me if I am wrong, but using a "B" block would mean that the tester was using a 100 kg load. Therefore, all indentations would be the same depth and width.

You are correct. The dia's on a given block should be very nearly to the same, but certainly won't be "identical". Nothing ever is:cool:

James

We were in the same boat at our last customer audit. And the one before that!!!

My solution: I purchased test blocks with engraved circle grids. There are 100 circles already on the blocks, evenly spaced. So you would know your inspectors can not mess up any more.

The way it looks you should be able to get more than 100 tests on a block, but I would rather pay a little more each month, and have one less issue to worry about.

Correct me if I am wrong, but using a "B" block would mean that the tester was using a 100 kg load. Therefore, all indentations would be the same depth and width.

That is not true. Rockwell hardness blocks come in different ranges. No two blocks have the same values. They come with a certificate that gives 5 readings taken to verify the block. The side of the block will have a number and a tolerance. Depending on the nominal value, typical ranges for tolerance are +/- 1 of the nominal. Softer blocks have a larger tolerance, harder blocks have a smaller tolerance, with the smallest tolerance being +/-0.5 for HRB and HRC blocks. Within a block, you will always get different readings, depending on where you indent, plus the uncertainty of your machine, operator positioning, etc., even with the automatic reading machines.

That is why the standard requires one discard reading and three to average.

Wes R.

Here is a link to the NIST reference for calibration of Rockwell B blocks. Note that currently NIST only sells Rockwell C blocks, but they are working on Rockwell B blocks. The traceability requirement for the blocks is met through calibration of the indentation force and penetration depths.

OIML R 11 International Recommendation. Verification and calibration of "Rockwell B" hardness standardized Blocks (1974).
http://www.oiml.org/publications/R/R011-e74.pdf

Refer to page 9 which shows for various hardness values the repeatability requirement.

Wes R.

I know this is late to the party, but here is a way to terminate
an auditor on this question:

The indents that are too close to the others are the "seating"
tests, which are ignored.

I always tell customers to make these initial indents close to the others as the hardness value obtained does not matter, and you do not waste valuable "valid" space areas.

No offense is intended, but the impression I receive is that the explanation as described exsists only to derail the auditor from his path. If that interpretation is incorrect, I apologize.

As an auditor, after hearing your explanation on why some indentations are too close, I'd be interested in seeing what your work instructions say, how an operator responds to a question regarding the work instuction - is he/she aware of required distance between legitimate tests?, etc. If I was feeling really anal, I might even count the number of too close versus OK tests on a block and compare them to how they should be as per the ASTM requirements.

Needless to say, if I uncovered you were trying to BS me, the audit finding would probably be more detailed than if I hadn't been BS'ed.

The answer is not meant to derail the auditor, but it should have that effect.

My answer assumes that the operator knows what he is doing. As a service engineer, it is part of my job to make sure that he does before I leave the site. If they want to
cut their own throat with their work instructions, then that is their business of course.

There's no BS there, but if the auditor has knowledge of the test, which in my view they should, then the question should not even come up unless the entire block is punched out. Even then, if they have multiple blocks, one could be punched out and still be ligitimate, if it was only used for seating purposes. (but then they'd better have a properly punched one also!) :)

As an auditor, after hearing your explanation on why some indentations are too close, I'd be interested in seeing what your work instructions say, how an operator responds to a question regarding the work instuction - is he/she aware of required distance between legitimate tests?, etc. If I was feeling really anal, I might even count the number of too close versus OK tests on a block and compare them to how they should be as per the ASTM requirements. .

I completely agree. There is a valid reason there is the requirements for the distance between two tests, and also the distance to the edge of the block.
You will not get an accurate reading if you are too close on either of these.

And again what is the point of hardness testing if you know your readings are going to be off?

I had a debate with our auditor on the number of indentations that can be done on a standard "wilson" B test block. He says according to ASTM E-18-05 there is not enough space between the indentations on our blocks. My question is, " has anyone ever figured out how many (in theory) indentations can be made on a "Wilson" B test block according to ASTM E-18? Assuming the block is 2 1/4 diameter.

Was this for accreditation? I suspect so.....but as to whether the calculation has been made I don't know.....and truthfully it is not relevant.....

E 18 specifies the minimum distance between indentations, and from the edge.....of course most of the time the measurement of that is by eyeballing.....in this case, take the calipers or simlar and prove it one way or the other.

Just my thoughts.

Hershal

We use pre-grid blocks. Costs a little more, and has grids for 100 indentations.

I figured I will cut all the guess work, and ensure all our readings are correct and compliant with a cost of about $2 a day.

My time is worth more than that.

I stated that the diameter of the indentation is a function of the hardness of the block. As Hawat has correctly stated, the spacing matters.

To get the theoretical maximum number of indentations:

1. Measure the diameter of the top surface, call it D. Note that this is less than the diameter of the block because of the bevel.
2. Measure several indentation diameters and then average them, call the average d.
3. Calculate the available area for the block using A_b = (Pi*(D-6d)^2)/4.
4. Calculate the effective diameter of the circle consumed by one indentation as d_1 = d + 2.5d/2 = 2.25d
5. Assume hexagonal packing of the indentations, all perfectly spaced.
See http://mathworld.wolfram.com/CirclePacking.html
6. Let the area of one indentation = A_i = 2.25d * 6/(Pi*sqrt(3))
7. Max indentations < (A_b)/(A_i)

The Max indentations is less than the division of the two areas because of edge effects due to placing an hexagonal array in a circular area.

Wes R.

Wesley,
I admire your wisdom:applause: ... but please tell me you had to look this up somewhere and you didn't have this memorized :)