cbrick
03-02-2013, 08:39 PM
It's not unusual for me to get questions from the web site, today I recieved this from Germany. If I am reading this correctly his results are backwards giving a higher (quenched I think) ingot hardness than his boolits. Age hardening is a direct result of how rapidly the alloy cools and the larger mass of the ingot should cool somewhat slower than the less mass of the boolit. Before I send him an answer I thought I would see what the brain power here thinks of his letter.
Rick
Rick:
congratulation for your web pages, always a tremendous source of information! As an avid bullet caster the pages regarding casting, alloys, mould design, lubes, sizing etc. have been read over and over again. Especially Glen Fryxell's book has been my favorite literature.
That said I would like to ask you guys whether you could help me answering a question regarding lead alloy and BH. The question is related to the mechanism behind age hardening.
Let me explain: Using different alloys (for different applications) it is my habit to test BH over a period of time to see how much age hardening will lend to a 'final' BH value. Testing is done with a home made fixture using a cantilever system acting on a 6 mm steel ball via a weight. For multiple tests (over time) I cast a small ingot using short angle sections of aluminum fixed together with a c-clamp. Dimensions are 17mm x 18.5mm x 40 mm (roughly 5/8" x 3/4" x 11/2"). The aluminum is preheated to get smooth surfaces by dipping it into the molten alloy. For every testing 3 indentations are made and from the average the BHN is calculated. Duration of load is 10 seconds.
More or less by chance I made some measurements on a bullet cast from the same alloy from which one ingot was tested. I got a different reading. Somewhat irritated I ran a series of parallel measurements on small ingots and on bullets cast from the same pot at the same time. The results from one alloy are summarized in the enclosed diagram. As can be seen, the BHN of the bullets are lower than those derived from the ingot. My question is: Why that?
The alloy used is range scrap, mixed from a handgun range and a rifle range at a ratio of approx. 1 : 1. I assume that the alloy contains tin and antimony with a higher percentage of the latter. Maybe some arsenic is also present. The small ingot starts at BH 8.5 and increases to 16.7. With the bullets, the increase is much less, from 9.1 to 12.4.
It is not unusual to get age hardening. What puzzles me is the difference between the ingot and the bullets: It's the same alloy, cast at the same temperature (from the same pot) and tested at the same time. The only difference I can imagine is the rate of cooling after casting. I suspect that the ingot cools faster than the bullet. The bullet is contained in the hot mould at least as long as the sprue takes to solidify. The small ingot (although much heavier than the bullet) has only a thin sheathing of aluminum which will dissipate the heat rapidly.
To prove that theory (or refuse it) I would like to know how the rate of cooling affects age hardening. The general effect is quite clear: Solubility of Sb (or SbSn) is temperature dependant. During cooling antimony will precipitate from the (then over-saturated) solution. But what's the time dependancy: Rapid cooling equals coarse cristals (dendrites), slow cooling fine ones? Coarse dendrites yield high BH? Is it that way, that quenching works? Or is it the other way around that rapid cooling results in fine dendrites (but lots of) which support the lead matrix much better, giving high BH?
From the literature I have (including Lyman's Cast Bullet Handbook #3) I was not able to get some conclusion. I hope that you or someone from LASC will take the time to give me an answer (I understand that you do not offer a forum). It will be highly appreciated.
Looking forward to hearing from you.
With Best Regards
Karsten
Rick
Rick:
congratulation for your web pages, always a tremendous source of information! As an avid bullet caster the pages regarding casting, alloys, mould design, lubes, sizing etc. have been read over and over again. Especially Glen Fryxell's book has been my favorite literature.
That said I would like to ask you guys whether you could help me answering a question regarding lead alloy and BH. The question is related to the mechanism behind age hardening.
Let me explain: Using different alloys (for different applications) it is my habit to test BH over a period of time to see how much age hardening will lend to a 'final' BH value. Testing is done with a home made fixture using a cantilever system acting on a 6 mm steel ball via a weight. For multiple tests (over time) I cast a small ingot using short angle sections of aluminum fixed together with a c-clamp. Dimensions are 17mm x 18.5mm x 40 mm (roughly 5/8" x 3/4" x 11/2"). The aluminum is preheated to get smooth surfaces by dipping it into the molten alloy. For every testing 3 indentations are made and from the average the BHN is calculated. Duration of load is 10 seconds.
More or less by chance I made some measurements on a bullet cast from the same alloy from which one ingot was tested. I got a different reading. Somewhat irritated I ran a series of parallel measurements on small ingots and on bullets cast from the same pot at the same time. The results from one alloy are summarized in the enclosed diagram. As can be seen, the BHN of the bullets are lower than those derived from the ingot. My question is: Why that?
The alloy used is range scrap, mixed from a handgun range and a rifle range at a ratio of approx. 1 : 1. I assume that the alloy contains tin and antimony with a higher percentage of the latter. Maybe some arsenic is also present. The small ingot starts at BH 8.5 and increases to 16.7. With the bullets, the increase is much less, from 9.1 to 12.4.
It is not unusual to get age hardening. What puzzles me is the difference between the ingot and the bullets: It's the same alloy, cast at the same temperature (from the same pot) and tested at the same time. The only difference I can imagine is the rate of cooling after casting. I suspect that the ingot cools faster than the bullet. The bullet is contained in the hot mould at least as long as the sprue takes to solidify. The small ingot (although much heavier than the bullet) has only a thin sheathing of aluminum which will dissipate the heat rapidly.
To prove that theory (or refuse it) I would like to know how the rate of cooling affects age hardening. The general effect is quite clear: Solubility of Sb (or SbSn) is temperature dependant. During cooling antimony will precipitate from the (then over-saturated) solution. But what's the time dependancy: Rapid cooling equals coarse cristals (dendrites), slow cooling fine ones? Coarse dendrites yield high BH? Is it that way, that quenching works? Or is it the other way around that rapid cooling results in fine dendrites (but lots of) which support the lead matrix much better, giving high BH?
From the literature I have (including Lyman's Cast Bullet Handbook #3) I was not able to get some conclusion. I hope that you or someone from LASC will take the time to give me an answer (I understand that you do not offer a forum). It will be highly appreciated.
Looking forward to hearing from you.
With Best Regards
Karsten