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I stumbled across this on the Corbin site and thought that the information could be of value to those of us that would like to have an inexpensive way to compare results of lead hardness readings across the various devices available to the general public.
I understand that any reading is only for an individual to ascertain the brinell of their particular lead sample however at times it may be of value for two or more individuals to be able to compare known values on their respective gauges even if they are far apart.
I apologize for the length of the post.
Lead Hardness Test
Here is a simple way to test the Bhn number of unknown lead samples: all you need is a caliper, two bottle caps, a vise, a 5mm diameter (aprox. size) ball bearing, and a known pure sample of lead (Corbin can furnish pure lead of 99.995% Pb with trace silver).
Here is the formula:
H = 5 * (D1^2)/(D2^2)
...where H is the hardness of the unknown sample in Bhn number, D1 is the diameter of the indentation formed in the known pure lead sample, and D2 is the diameter of the indentation in the unknown hardness sample.
Why This Works:
The reason that you will always get a number of 1 or greater is that the ball will always go further into soft material (pure lead) than it will into hard material (any alloy of lead with tin, bismuth, antimony, etc.). Therefore, the diameter of the dent will always be smaller in the unknown sample, if it is harder than pure lead, or the same as the known pure sample, if it is also pure lead. When you divide a smaller number into a larger one, you always get something greater than one for an answer. Brinnell numbers are all greater than one. You must multiply the answer by 5 because this is the adjusting constant for pure lead, which is Bhn 5 hardness.
This method is as accurate as your sample purity and your ability to read the diameter of the dent. A smooth surface is necessary so you can get a clean diameter to measure. A rough surface will throw off the answer because you may not get a true diameter to measure, if one side of the lead surface is higher or wavy. But in general, this is as accurate a method as any that uses tools which cost less than $500. A reading with an accuracy of only Bhn plus or minus 0.5 will be more than sufficient for purposes of swaging. When the Bhn number actually increases from 5 to 10, or doubles, the pressure goes up by a factor of four, or the square of the increase in hardness. A number of 5-6 Bhn is close enough to be called pure for swaging purposes. A number of 10-12 is close enough to be considered about "medium" hardness or suitable for -S dies. A number of 18-20 is hard enough to be considered strictly for the -H type hydraulic dies even if used in the CSP-2 hand press.
I understand that any reading is only for an individual to ascertain the brinell of their particular lead sample however at times it may be of value for two or more individuals to be able to compare known values on their respective gauges even if they are far apart.
I apologize for the length of the post.
Lead Hardness Test
Here is a simple way to test the Bhn number of unknown lead samples: all you need is a caliper, two bottle caps, a vise, a 5mm diameter (aprox. size) ball bearing, and a known pure sample of lead (Corbin can furnish pure lead of 99.995% Pb with trace silver).
- Melt enough lead to fill one bottle cap with unknown sample, and the other with known pure lead. Make sure the surface is smooth and flat when the lead hardens and cools.
- When the lead is cold, put the ball bearing between the two lead surfaces and squeeze this "sandwich" in the vise until the ball is driven partly into both surfaces (just enough to make a fair sized dent, but not past the middle of the ball).
- Remove the ball and measure the two dent diameters. First measure the known pure lead dent and write down this number. Then measure the dent diameter in the unknown lead sample and write it down. Square both numbers (multiply times themselves). Then divide the resulting square of the unknown lead dent diameter into the square of the known pure lead dent diameter.
- The answer should be 1 or greater. If it is a fraction, or less than 1 in value, you have inverted the two dents and divided the wrong way. In that case, try again. When you get an answer that is 1 or greater, multiply it by 5. This is the actual Brinnell Hardness Number of the unknown sample.
Here is the formula:
H = 5 * (D1^2)/(D2^2)
...where H is the hardness of the unknown sample in Bhn number, D1 is the diameter of the indentation formed in the known pure lead sample, and D2 is the diameter of the indentation in the unknown hardness sample.
Why This Works:
The reason that you will always get a number of 1 or greater is that the ball will always go further into soft material (pure lead) than it will into hard material (any alloy of lead with tin, bismuth, antimony, etc.). Therefore, the diameter of the dent will always be smaller in the unknown sample, if it is harder than pure lead, or the same as the known pure sample, if it is also pure lead. When you divide a smaller number into a larger one, you always get something greater than one for an answer. Brinnell numbers are all greater than one. You must multiply the answer by 5 because this is the adjusting constant for pure lead, which is Bhn 5 hardness.
This method is as accurate as your sample purity and your ability to read the diameter of the dent. A smooth surface is necessary so you can get a clean diameter to measure. A rough surface will throw off the answer because you may not get a true diameter to measure, if one side of the lead surface is higher or wavy. But in general, this is as accurate a method as any that uses tools which cost less than $500. A reading with an accuracy of only Bhn plus or minus 0.5 will be more than sufficient for purposes of swaging. When the Bhn number actually increases from 5 to 10, or doubles, the pressure goes up by a factor of four, or the square of the increase in hardness. A number of 5-6 Bhn is close enough to be called pure for swaging purposes. A number of 10-12 is close enough to be considered about "medium" hardness or suitable for -S dies. A number of 18-20 is hard enough to be considered strictly for the -H type hydraulic dies even if used in the CSP-2 hand press.
