Home-made hardness testing

[Forgetful]

I read in an earlier post (I tried searching, can't find it) that you can hang a weight on your press arm and use a ball bearing and stopwatch, and then measure the indent with a caliper and use a formula for determining hardness. The press method, lacking a better name for it, determines how "squishy" the lead is. If you think about it, it's testing a combination of hardness AND malleability (compressive stress deformation). Less malleable doesn't necessarily mean stronger.

Seems like we'd be more interested in impact resistance. Or, the inverse proportion of resistance. In electrics, electrical conductivity is the reciprocal of electrical resistance. There should be an analog but I'm not a metallurgist by any means.

I want to take a known length of pvc 1" tube, put a plumb on the side of it from a screw so it hangs away from the body of the tube, rest the mouth of the tube flush against an ingot, and drop a 1" steel ball bearing from the opening. It will have a known velocity at impact and a known mass, therefore a known consistent kinetic energy. Square root of the impact diameter should have proportionality to hardness. And you don't have to waste a bunch of time.

Thoughts? Formulas? Standardization! Seems like an easy solution to home-made testing. I won't take credit if this has already been invented. I just thought of it now, like a lightbulb moment.

[motorcycle_dan]

Lee makes a similar idea hardness tester. Comes with a little scope thingy that is graduated to measure detent size. It works to go get a rough idea of hardness.

My follow-on question is how to test alloy? I have some lead weights given to me. They look like used as part of a big commercial scale. Each is labled 40lb (and they feel about that heavy.) I have no clue what alloy it might be. pure, 90/10, 95/5/5 or ???
is there a method to determine alloy by measuring cast diameter, hardness and weight?

[Forgetful]

The only ways I know how to determine alloy is with xrays or with spectroscopy. You could probably do it with acids and precipitate the metals out one at a time, not sure which would be easier or less expensive.

You can use the volume and mass to determine density, but densities overlap depending on %'s.

[sdcitizen]

Dan, in about 2 weeks I will be bringing a stack of my own samples into work to XRF them, if you haven't found out what it is by then, I could probably get a sample of yours tested at the same time.

[Forgetful]

Oops, forgot to address your question, Dan, about using cast diameter and density. If you know for a fact that an alloy only has Pb, Sb, or Sn.. and you know nothing else is in there.. Then yes, I believe you could determine the alloy. If someone used pewter as a source of tin for making the alloy, and the pewter contained any bismuth.. Then all bets are off because Bi will affect shrinkage negatively.

You would need to measure to 0.0001" to get a diameter precise enough for using in an alloy calculator.. Price comparison check, .1 mil precision caliper/micrometer vs sending away for testing...

[bangerjim]

There are many techniques for measuring hardness but all are based upon math. And the Brinnell scale is one of them specific to softer metals we use.

Still, the width of a "dent" made by a known ball pressed into a sample by a known force is the key. I have both the Cabine and the Lee testers. I have found that timing scheme they recommend really is not needed. If you use a "bump-n-go" technique with the plunger is brought level with the top, the reading is almost the same as the Cabine. No need to waste 30 seconds holding the lever! It is all in the diameter of the point and the spring constant inside the tester.

If you really want to do hardness on the cheap, try the standard Mars artist pencils to do a SWAG hardness test. It is pretty close! I tried it. For $15, you can be in the ballpark on hardness. Do a search on here for the technique and chart. Use this to check your ball drop tube!!!!!!

But as said above, knowing the alloy content is done with an x-ray gun analysis. Not reliably by just hardness. I have an alloy that is 22Bhn and is 52% Bi/15%Sn/12%Sb and another one that also reads 22 that is lino, and another one that is a hardball-sort of alloy that is high Sb that is also 22! So go figure! You just cannot rely on hardness for % content.

Good luck!

bangerjim

[Forgetful]

What would be a suitably minimum thickness of my test ingots? 1/4"? Should they all be the same thickness? I've already cast all my pure lead into 12ga slugs but I have a few small pools of it left I could use for calibration. I expect the bearing will maximally get to a depth around 30% of the radius of the bearing, so a 1" bearing should be used on no less than 5/32" thick lead before it nearly flattens at the center. Approaching that 30% would require geometrically greater force! Just curious if surface tension would come into play, though? (EDIT: in terms of minimum thickness)

I figure I'll datamap the scores from the expected hardness values of %'s vs treatments at various temperatures, and then determine the trendline and use that to give me an equation. Energy would be built into the formula since it would be a constant.

I'll probably get the pencils since aging isn't linear between formulations.

[CountryBoy19]

I read in an earlier post (I tried searching, can't find it) that you can hang a weight on your press arm and use a ball bearing and stopwatch, and then measure the indent with a caliper and use a formula for determining hardness. The press method, lacking a better name for it, determines how "squishy" the lead is. If you think about it, it's testing a combination of hardness AND malleability (compressive stress deformation). Less malleable doesn't necessarily mean stronger.

I think you're confusing metallurgy terms. Let me preface with I am not a expert, but I am a mech. engineer and I tried to focus my course-work on metallurgy in my under-grad classes.

You're right, less malleable doesn't not tell much at all about strength, but neither does hardness. They are all different terms, and they are measured differently.

Hardness is the measure of a metal's resistance to permanent shape change when a compressive force is applied.

Malleability (aka Ductility) is a metal's ability to deform under stress without breaking.

Strength is the maximum stress a material can handle while be stretched or pulled without fracturing.

Toughness is a measure of the energy absorbed in the process of fracturing metals.

With definitions out of the way, lets get right down to it. You are attempting to measure hardness using a method that is typically used to measure toughness (impact testing: look up charpy impact test for more info). While you could measure hardness with an impact test, it's not proper because it is a lot more difficult to calculate and account for "other" things in the test. #1 When your "hammer" device impacts the lead the impact forces is contantly changing. You would need a way to know EXACTLY what the force was at the same specific time that you know what the dent size is. You must also account for the energy that the lead absorbs in the deformation process when calculating your force figures. If you can develop a way to calculate and account for all of that stuff then go ahead and work up a way to test hardness by impacting a ball etc on the metal.

That being said, it's much, much easier to measure hardness by applying a fixed, known force onto a metal and recording the deformation. This is the way practically everybody in the metals industry does it. Rockwell hardness testers, brinell testers, they all measure by applying a fixed force for a short period of time and measuring the deformation of the metal. The reason that the force should be held constant for a short bit of time is because it removes the energy absorption of the deforming metal from the equation. Do you have to hold it for 30 seconds? That depends on what you're measuring, but it's better to be safe. The more consistent you can make your measuring process the more confident you can be in your numbers (at least the relative values of your numbers).

[6bg6ga]

What about a used Rockwell hardness tester? Can these be purchased cheap enough?

[bangerjim]

Rc testers do not go low enough! Follow this: http://en.wikipedia.org/wiki/Hardness_comparison

Rb and Rc (just 2 of the 7 standard Rockwell scales) are calculated for testing anything from aluminum and brass to hard steel and SST alloys. I have a real Bhn tester (not a boolit lead tester). Our little world of 5-30Bhn is way down in the bottom basement of any hardness testing scale. My Bhn tester starts at ~100. It uses the industry standard ball bearing and spring method as pretty much all testers do. Some are hydraulic.

And they are NOT cheap! Follow this as a sample: http://www.amazon.com/s?ie=UTF8&page...dness%20tester


If you want cheap, but a Lee (<$100). Or a Cabine tester (<$200). Or Mars artist pencils (<$20). I have both the Cabine and Lee testers for lead and it's alloys and they are very useful in our hobby. I have also extensively tested and compared the Mars pencils to the Cabine and Lee tests and they are a very good SWAG for hardness. And, after all, that is really all we care about! Just don't get lost in the weeds on the lead hardness thing. We're not NASA!

Best of luck on your quest to measure hardness.

banger