bakerjw
09-29-2020, 09:15 AM
Many thanks to @wimms for their thread -> http://castboolits.gunloads.com/showthread.php?315385-What-I-learned-about-Brinell-hardness-test
Since I have lead of questionable metallurgy and am new at casting, I am gathering tools for the task at hand. I am also a test engineer with a heavy electro mechanical background so the math and techniques behind Brinell hardness testing is not a challenge. So, I put together this Brinell tester last night. It is rough at the moment and will need to be mounted properly but I wanted to get it functional and the math straight before making it pretty.
268528
Here is where the sample is placed. It is important that when the sample is being tested that the bar be kept as horizontal as possible, hence the need to shim the sample to an appropriate height.
268530
I started with a 37 1/2" iron bar.
3/4" from one end is a 5/16" pivot hole.
3/4" from the other end is a 3/16" hole for weights.
3" from the pivot hole is a mount for a ball bearing.
This creates a class 3 lever as shown in the next diagram.
268529
Class 3 lever math is rather simple. Fe = Fl x (dl / de)
NOTE DL/DE is IMA (Ideal Mechanical Advantage)
The bar though has weight to it, so I measured the weight at the very end of the bar and came up with 1186 grams and solved for Fe = 1186 grams (36.75"/3") = 14528.5 grams or 32.03 pounds which is what is applied to the sample with no weight at the end of the lever.
I used some widow weights that weigh 6728 grams (14.83 pounds) for my load weight.
Fe = 6728 grams (36"/3") = 80736 grams or 178 pounds which is applied to the sample along with the 32.03 pounds from the bar.
This gives a total force on the sample of 210 pounds which is in the ballpark of most Brinell testers.
Last night, I came across some old very soft lead drain pipe. After melting it down and fluxing it a bit, I poured it into some cupcake tins and set about testing it with my new tester. rather than using an indention diameter measurement, I opted to measure the depth of the indention with a micrometer and a 3/8" ball bearing that was used in the tester.
As an option, I can use a fine pointer on my mill with a magnifier and measure the sample diameter visually.
So... With freshly melted soft lead
.439 sample thickness before test
After the test and using the .376" ball bearing the measurement came out to .791"
.791" - .376" = .415"
.439" - .415" gave a .024" depression.
Using a spherical cap calculator, this gives an indention diameter of .183"
Plugging it into a Brinell calculator
Load = 210 pounds
Steel ball diameter = .376"
Indention diameter = .183"
BHN = 5.26 <--- This seems accurate based on how soft this lead felt when working it to fit into the smelting pot.
Here is the soft sample next to a sample of linotype lead that I was toying around with as I got everything running. I did not get a BHN on the linotype lead as of yet as it was late when I got everything worked out.
268531
For sanity checks, I ran all of my numbers against these calculators.
I converted it all into an excel spreadsheet so I don't have to run the math every time
https://www.ajdesigner.com/phphardness/brinell_hardness_number.php#ajscroll
http://ambrsoft.com/TrigoCalc/Sphere/Cap/SphereCap.htm#cap
Since I have lead of questionable metallurgy and am new at casting, I am gathering tools for the task at hand. I am also a test engineer with a heavy electro mechanical background so the math and techniques behind Brinell hardness testing is not a challenge. So, I put together this Brinell tester last night. It is rough at the moment and will need to be mounted properly but I wanted to get it functional and the math straight before making it pretty.
268528
Here is where the sample is placed. It is important that when the sample is being tested that the bar be kept as horizontal as possible, hence the need to shim the sample to an appropriate height.
268530
I started with a 37 1/2" iron bar.
3/4" from one end is a 5/16" pivot hole.
3/4" from the other end is a 3/16" hole for weights.
3" from the pivot hole is a mount for a ball bearing.
This creates a class 3 lever as shown in the next diagram.
268529
Class 3 lever math is rather simple. Fe = Fl x (dl / de)
NOTE DL/DE is IMA (Ideal Mechanical Advantage)
The bar though has weight to it, so I measured the weight at the very end of the bar and came up with 1186 grams and solved for Fe = 1186 grams (36.75"/3") = 14528.5 grams or 32.03 pounds which is what is applied to the sample with no weight at the end of the lever.
I used some widow weights that weigh 6728 grams (14.83 pounds) for my load weight.
Fe = 6728 grams (36"/3") = 80736 grams or 178 pounds which is applied to the sample along with the 32.03 pounds from the bar.
This gives a total force on the sample of 210 pounds which is in the ballpark of most Brinell testers.
Last night, I came across some old very soft lead drain pipe. After melting it down and fluxing it a bit, I poured it into some cupcake tins and set about testing it with my new tester. rather than using an indention diameter measurement, I opted to measure the depth of the indention with a micrometer and a 3/8" ball bearing that was used in the tester.
As an option, I can use a fine pointer on my mill with a magnifier and measure the sample diameter visually.
So... With freshly melted soft lead
.439 sample thickness before test
After the test and using the .376" ball bearing the measurement came out to .791"
.791" - .376" = .415"
.439" - .415" gave a .024" depression.
Using a spherical cap calculator, this gives an indention diameter of .183"
Plugging it into a Brinell calculator
Load = 210 pounds
Steel ball diameter = .376"
Indention diameter = .183"
BHN = 5.26 <--- This seems accurate based on how soft this lead felt when working it to fit into the smelting pot.
Here is the soft sample next to a sample of linotype lead that I was toying around with as I got everything running. I did not get a BHN on the linotype lead as of yet as it was late when I got everything worked out.
268531
For sanity checks, I ran all of my numbers against these calculators.
I converted it all into an excel spreadsheet so I don't have to run the math every time
https://www.ajdesigner.com/phphardness/brinell_hardness_number.php#ajscroll
http://ambrsoft.com/TrigoCalc/Sphere/Cap/SphereCap.htm#cap