Rc Tester for lead???

[KenH]

Hello all, I've got a HR-150A (Chinese clone) of a Rockwell hardness tester. Works good with both C and B scales. My question, what would be required for testing lead BHN hardness? OR - is it even possible? It does have a 60 Kg setting for the weight as well as the normal 100 and 150 Kg setting.

I suspect a person could use the 60 Kg weight and a larger ball for the penetrator (1/8"? larger?) and do some testing to determine settings on dial for BHN ranges. I'm just wondering if anyone has already done this.

Ken H>

[reddog81]

Do you have access to pure lead, Linotype, other lead alloys with known hardness? I don't know anything about he hardness tester you speak of but if you can get reliable and repeatable readings with known lead alloys you should be able to get a decent idea where a unknown alloy falls on the scale?

[KenH]

I don't have any linotype, but do have some pretty pure lead. I use the marking pencils for testing hardness and have been surprised how repeatable the results are.

[Rcmaveric]

Trying to remember. Some where there is an article about how to do this. You take an ingot of your test sample and an ingot of pure lead. Then you clamp the two ingots together with a ball baring between them. Then you compare the two indents. cross multiply and deivide and you have your hardness. I think the hardness testers use pressure and their own ball bearings is because the charts that come with them are calibrated to a ball bearing pressed into pure lead at N amount of pressure for N amount of time equals this size of reference indent. Since the size of the indent is proportional to the BHN then you just compare the replicated indent.

If you clamp them together like in a vise then you don't need a calibrated chart for pressures. You know have your reference and created indent. The ball bearing was pressed into both ingots at the same pressure and same ball bearing. So you just need to cross muntiply and dived 5BHN/(indent size)= N/(other indent size). N will be the BHN of your questionable lead.

[KenH]

That makes sense to test lead that way. I might play around with that test. Thanks

[KenH]

For an update on the lead hardness testing using the Rockwell tester. I found this page: https://www.gordonengland.co.uk/hardness/brinell.htm

That has the formula to calculate the test, and even better a calculator on the webpage. I made a new penetrator holder for the Rockwell tester with a 1/2" steel ball. The Rockwell tester places 150 kg pressure on the steel ball, measure the diameter of the impression, do the calculations and you've got the BHN for the lead. The numbers I got match up nicely with what I would expect. I've got some "fairly" pure lead that tested at 6 bhn, some range lead that tests at 13 to 14 BHN. Wheel weights measure in the 9 to 10 range depending on the ingot. This is ingots that have been laying around for a good long while (months? years?) so it's nowhere near exact.

I think just as important as the actual number is the repeatable results I get when measuring the same ingot.

All in all, I think it's a tad better than the pencil test I've been using.... I "think" anyway {g}

Ken H>

[W.R.Buchanan]

I've got a better and easier way.

Buy A Lee Hardness Tester.

it will cost you alot less than it will cost to Calibrate your machine.

Randy

[KenH]

Randy, not sure what you mean by calibrate my machine. No calibration involved - well, other than the calibration I do for Rc testing and that's already done for Rc testing. All it has to do is put the 150kg pressure for 60 seconds, then use calipers to measure the diameter of the impression. Made the new penetrator from a scrap bolt in the bin. No cost involved other than a bit of my time learning. That's what I enjoy about retirement - time to learn the things that interest me rather than the things involved with work.

From what I understand, the Lee tester works the same way as my Rc tester does, puts a known pressure on a round ball to indent the lead. You then measure the diameter of the imprint, then look on a chart to determine the BHN of the lead. Same thing I'm doing, so why spend the $60 for the Lee tester to measure the same thing I'm doing?

Ken H>

[W.R.Buchanan]

Ken: Do you have a "Chart" for your machine? That's where the calibration part comes in. You need a reference chart that reflects what your machine is doing.

The Lee Tool has the "Chart."

You have to convert Rc to Bhn using the penetrator you made. Which hopefully is the same as one from the manufacturer of the machine,,, if the machine was designed to do Bhn in the first place.

The only other way to develop a chart would be to test various types of lead of known hardness and record the size of the impressions and then interpolate for all of the in betweens that would exist. The more accurate your measurements the more accurate your chart will be.

In the end you would have a chart that would be "calibrated to your machine."

Lee did the same thing when they developed their tool..

Randy

[KenH]

Randy, sorry I've not checked this thread in a few days and missed your post. As far as calibration, there is none involved. Just measure the diameter of the indentation made by the 1/2" ball, which I know is pressed with 150 KG because that's how the Rc is tested and calibrated. Then using the formula on the linked page in post #6 (or the calculator on the page) the BHN is calculated nicely. Oh, I see your question, I don't read anything off the Rc scale on the Rc tester, just do the preload, pull the handle to put 150 KG pressure on the ball, time for 60 seconds so the ball comes to rest, then measure the diameter of the indentation.

Yes, I have made the calculations for a chart and have printed it out rather than have to run the calculations. I made a spreadsheet to put the BHN values per diameter in, and put the formula in also so all I have to do is plug the measured diameter of indentation in and the calculation is made for me. Spreadsheets are NICE.

In the end you would have a chart that would be "calibrated to your machine."

Nope, my chart is for any tester that puts 150 KG pressure on a 1/2" steel ball for 60 seconds.

Ken H>