PDA

View Full Version : DIY Hardness Tester



Sloffie
06-13-2012, 06:38 AM
I have had a quick look around and hardness testers are expensive. But what makes them expensive I believe is their precision and that they have some kind of recording system. BUT the basics of how a Brinell Hardness tester works is VERY simple.

http://www.hardnesstesters.com/image.asbx?AttributeFileId=6f7f900a-6810-48d7-a118-2fd7871d0ce6
http://www.hardnesstesters.com/Applications/Brinell-Hardness-Testing.aspx

Basically you take a hard sphere with a known diameter. Then you place it on the specimen and you apply a load. Then you measure the diameter of the indentation and you plug it into the above formula and calculate the Brinell Hardness.

Now I was thinking, why can one not build one? It should be rather easy. Especially for lead as it is softer than steel. Get a 8mm or whatever ball bearing, get a piece of steel tube with an internal diameter just over 8mm. Secure that in a vertical position. Then, make a ram with a platform where you can place a mass piece.
Put the ball bearing into the tube and hold it with your finger so it does not drop out. Place an ingot under the tube so the ball bearing rests on the ingot. Do not drop the BB into the tube as it will dent the lead, giving you a false reading.
Then slide the ram into the tube (the weight of the ram should be known) and place the weights on the platform. Then leave it for some time (this can be experimentally determined when the indentation stops increasing) and then remove everything and measure the diameter of the indentation on the lead.
Take the weight of the mass pieces in Kilogram and plug that and the diameters into the equation.
In theory you should then have the Brinnel Hardness value for your lead.

Here is another thought. The DIY device will not be as accurate or precise as proper lab equipment, BUT it does not have to be. Firstly you only need a rough figure for harness. It does not matter if it is 10 BHN or 11 BHN.
If I want to cast for my .303 and I want a hard bullet and the formula pops out an answer of 30 BHN, I will be happy. Even if in a lab it will be 31.2334455 BHN.
For our purposes measuring the indentation with a vernier caliper will be accurate enough.
I would also believe the smaller your indenter is, the quicker you will have a result but the more inaccurate your calculated value will be.

Also, since you will only be testing lead, you do not need a carbide ball, just a normal ball bearing should do.

After building, one should take a few test pieces with known hardness and see what you get for a hardness value. In theory this should work perfectly fine for our purposes.

Please see my basic sketch attached

Sloffie
06-13-2012, 06:54 AM
Just played around with a few values. When using a 10mm ball bearing and you want a 3mm indentation in a 5 BHN material, you need a load of 577.6kg.

for a 5mm ball bearing and a 2mm indentation you need a load of 128kg

Once you start testing harder lead of about 30 BHN, you need a big weight.

zomby woof
06-13-2012, 10:52 AM
See how I made mine on page two. Same principle.

http://castboolits.gunloads.com/showthread.php?t=147975&highlight=zomby&page=2

Sloffie
06-13-2012, 02:07 PM
The only issue with the system is the impractical mass you need to apply. You can use a lever, but the system Zomby Woof has is much more practical.

HamGunner
06-14-2012, 10:13 AM
Bearing Drop Test

Easy to use some J. B. Weld to place a ball bearing on a short length of solid metal rod or short length of pipe poured full of lead for extra weight and then wrap some black tape for extra diameter if needed, around the rod till it will just barely fit inside a long piece of pipe.

I drop mine through a 5 ft. length of copper pipe onto a known ingot of dead soft lead to get the base diameter for the formula and just use my micrometer to get a close measurement of the diameter of the dent. Using the formula base for soft lead and the diameter reading from the unknown alloy and calculating the formula, gives me a very close measurement of BHN. Same principle as most other measurement methods. Maybe not as accurate and there is no timed pressure included in making the dent, but close enough for my needs and it only takes about 5 minutes.

(Soft PB indentation)2 % (? alloy indentation)2 X 5 = BHN
Soft PB squared, divided by, unknown alloy squared, multiplied times 5 = BHN.

I know that many will say this is not an accurate method for all sorts of various reasons, but I am not using the resulting figures to fly to the moon. :) It does give a very close approximation of BHN and it is repeatable.

Edit: I normally take at least two measurements of my unknown ingot however, just to increase the accuracy of the drop test as well as a double check for my eyeballing of the diameter with the micrometer. I have to use my strongest reading glasses under good lighting to get a good measurement reading.

Gus McCrae
07-19-2012, 01:23 PM
This is a cool idea. I'm surprised it hasn't gotten more attention.

This should be kinda easy to do: http://en.wikipedia.org/wiki/Brinell_scale

Gelandangan
07-21-2012, 12:39 AM
Been using a method from one of the member here (sorry mate can't remember who you are), use an Automatic center punch.
Simply press into the lead, it punches and measure the diameter against a base line number that you previously do.

I ground my center punch to have a 2mm high pyramid diamond sided at about 3mm width, I get something like 0.5mm end to end indentation for 24bhn down to 1.65mm for 5 bhn from lead flashing.

Very handy to carry around.