Confused about alloys

[montana_charlie]

I got a different result before because I wrote a new formula in a blank excel sheet and I'm not sure what I did wrong.
I just double-checked it in the calculator and it works like you said. It's a bit off on the lino and mono calculations, but that's no big deal since it works on most of the common lower % boolit alloys. It is definitely better than the current one.

I'll have to update the calculator with your corrected formula next time I revise it.

Thanks a lot Charlie!

I did a tiny bit more fiddling, and this is the formula that works best for me.
=5+(0.55*B47*100)+(1.45*C47*100)

I input the numbers for 30-1 alloy using 3% tin and 97% lead.
The result returned is 6.65 BHN ... and I already know that the right value for 30-1 is 6.66 BHN.
So this formula is close enough for me.

[PBaholic]

The problem with this is the BHN of different alloys varies depending on more than just the mix. The time since cast and cooling time when cast all effect the harness. This is why you will never find absolute values for different mixes.

Here is a chart of a few simple alloys, and how their hardness changed over hours, days and weeks:



Here is a chart of the some common mixes, and their BHN's:



The initial BHN is typically 1 hour BHN's, and aged is 24 hour BHN's. The Est BHN is the Rotometals formula (Starting with 8.6) is fairly accurate for BHN > 10, and for Sn up to 10%. I use a slightly modified version of that formula starting with 5 for BHN's < 10.

I can only measure BHN to around +/- 0.5 BHN and the chart contains some data from other sources.

[montana_charlie]

Here is a chart of a few simple alloys, and how their hardness changed over hours, days and weeks:

That graph was created to show that alloys with equal amounts of tin and antimony are very stable, but unstable when the amounts differ.


Antimonal alloys age harden, but lead/tin alloys age soften.
The 30-1 alloy in the lower chart is shown to have a hardness of 8 BHN.

The number is wrong, and 'changing hardness' will never produce 8 BHN because immediately after casting it is 6.66 BHN ... and it softens with age.

[PBaholic]

Antimonal alloys age harden, but lead/tin alloys age soften.
The 30-1 alloy in the lower chart is shown to have a hardness of 8 BHN.
The number is wrong, and 'changing hardness' will never produce 8 BHN because immediately after casting it is 6.66 BHN ... and it softens with age.

I didn't create the chart, it came from a study on aging alloys.

I can't confirm or deny it's accuracy, as I don't have pure Pb and Sn to work with. Again, this is not that precise of a science. Much depends on the purity of your metals, and how you cool them after casting.