Leaded Bronze Porosity,Unequal Lead Dispersion Help!
Leaded Bronze Porosity,Unequal Lead Dispersion Help!
(OP)
Hello,
We heat a leaded bronze to 1800 F it cools we then temper it at 725 F. Every once in a while we have a batch that has very bad lead distribution as well as voids. The guys in the shop say it always happens in the spring. Could barometric pressure or humidity play a role in the dispersion of the lead. The other thing is the lead solidifies last and the thermal expansion coefficient is 1.5 times the amount of bronze. So would it be safe to say once the lead cools it shrinks and creates gas pockets? Is there way to increase the lead distribution and or reduce the gas pockets?
Thank you for your time,
Nathan Hatley
We heat a leaded bronze to 1800 F it cools we then temper it at 725 F. Every once in a while we have a batch that has very bad lead distribution as well as voids. The guys in the shop say it always happens in the spring. Could barometric pressure or humidity play a role in the dispersion of the lead. The other thing is the lead solidifies last and the thermal expansion coefficient is 1.5 times the amount of bronze. So would it be safe to say once the lead cools it shrinks and creates gas pockets? Is there way to increase the lead distribution and or reduce the gas pockets?
Thank you for your time,
Nathan Hatley





RE: Leaded Bronze Porosity,Unequal Lead Dispersion Help!
RE: Leaded Bronze Porosity,Unequal Lead Dispersion Help!
How do you deoxidize?
Do you change deox practice based on the weather?
Do you pre-dry charge metals?
= = = = = = = = = = = = = = = = = = = =
Plymouth Tube
RE: Leaded Bronze Porosity,Unequal Lead Dispersion Help!
How "evenly distributed" or just in local spots?
Porosity highest in the thickest sections? The thinnest sections? The first-to-cool? Or the last-to-cool?
RE: Leaded Bronze Porosity,Unequal Lead Dispersion Help!
If it began as a casting, it will probably just alter lead precipitate shape, but if it started as powder met, then changes could be dramatic.
Spring=humidity=hydrogen. I doubt heat treating puts enough hydrogen in to cause porosity. In the steel-backed leaded bronze bearing business we didn't ever anneal. I'm wondering why you do.
Michael McGuire
http://stainlesssteelforengineers.blogspot.com/
RE: Leaded Bronze Porosity,Unequal Lead Dispersion Help!
If you are using a controlled casting process, I don't think you should have a lead segregation problem unless lead content is quite high.
Here are a couple links that might be of interest:
Copper-lead equilibrium phase diagram
Microstructure of continuous cast leaded tin bronze alloy C94100 (20%Pb)
Regarding the tempering step used, does this leaded bronze alloy actually respond to heat treatment?
RE: Leaded Bronze Porosity,Unequal Lead Dispersion Help!
RE: Leaded Bronze Porosity,Unequal Lead Dispersion Help!
Maui
www.EngineeringMetallurgy.com
RE: Leaded Bronze Porosity,Unequal Lead Dispersion Help!
RE: Leaded Bronze Porosity,Unequal Lead Dispersion Help!
http://www.struers.com/resources/elements/12/10116...
RE: Leaded Bronze Porosity,Unequal Lead Dispersion Help!
RE: Leaded Bronze Porosity,Unequal Lead Dispersion Help!
RE: Leaded Bronze Porosity,Unequal Lead Dispersion Help!
As arunmrao suggests, you might consider modifying your tooling/process to provide a more uniform cooling rate throughout the bronze material. There are commercially available analytical tools for evaluating the solidification of cast metal materials. If this problem is costing your company significant time and money, it might be worth looking into using one of these analytical tools to improve your process.
RE: Leaded Bronze Porosity,Unequal Lead Dispersion Help!
Have you considered offering the foundry to overlay the lead bronze on stainless steel. This will avoid reprocessing and the foundry will be better equipped to resolve issues regarding segregation and porosity.