Calculating Bhn to Odd Ball Alloy Ratios

[John Boy]

Is there a formula to calculate the alloy ratio (Tin:Lead) where the Bhn is known and the alloy ratio is not? This does not apply to standard alloys with standard Bhn values ... the odd ball ratios
Example: What is the formula to determine the alloy ratio for a tin -lead mix where the Brinell hardness number is 6.4?

[bumpo628]

No formula as far as I know. There is a formula from Rotometals that calculates hardness of lead/tin/antimony alloys, but it is not valid for brinell values under 9. It really isn't accurate unless the tin and antimony are both 1 or over, from what I have seen.

Here are the values for brinell hardness of lead-tin alloys that I have gathered from various online sources (such as MidwayUSA and Rotometals).
Pure lead = Brinell 5
40 to 1 = Brinell 8
30 to 1 = Brinell 9
25 to 1 = Brinell 9
20 to 1 = Brinell 10
16 to 1 = Brinell 11
10 to 1 = Brinell 12



Basic Rules for Hardening Lead
For every 1% additional tin, Brinell hardness increases 0.3.
For every 1% additional antimony, Brinell hardness increases 0.9.
For a simple equation,
Brinell = 8.60 + ( 0.29 * Tin% ) + ( 0.92 * Antimony% )
http://www.rotometals.com/Bullet-Casting-Alloys-s/5.htm

[letsmeltlead2693]

A 6.4 hardness would be close to pure lead.