Coefficient of thermal expansion for Pb ?

[robroy]

Who can tell me this tidbit and how much alloying metals change it. If possible please no unitless constants.:roll:

[HORNET]

The material properties tables say 15.1 micro-inch/inch-degree F. I ought to learn how to do scientific notation on here someday.

[Calamity Jake]

Who can tell me this tidbit and how much alloying metals change it. If possible please no unitless constants.:roll:


The material properties tables say 15.1 micro-inch/inch-degree F. I ought to learn how to do scientific notation on here someday.

15.1 Micro-inch = .0000151 inches. At 700° that's .0106 inches expansion. Changeing the alloy and maintaining the same volume won't make a measureable difference.

I'm by no means a scientist, but why is it even important?

[HORNET]

You've got to remember that that is per inch of length. So, if we look at 600 degrees (probably melted before 700 degrees) and something 100" long, you get a length change of .797". That could make a difference in some applications, not necessarily for Lead, but definitely for other materials and higher temperature ranges.

[lwknight]

Lead is basically considered "dead" compared to things like copper,steel and especially aluminum. There is noteable shrinkage upon solidification. As far as hot day VS cool day and boolit size, That would be really hard to measure.

[robroy]

Thanks much I am looking at how much bigger a mould needs to be to drop a specific size boolit. I've been told a .359 boolit needs a .360 mould. I'm just checking this out with an eye to making one for paper patch.

[HORNET]

The appropriate factor for sizing the mold cavity would be the solidification shrinkage, which varies not only with the alloy, but also depending on the processing conditions (mold and alloy temp). The easiest way to find how much to allow for is to cast some boolits from another mold in that approximate caliber, using the intended alloy at about the intended conditions, and measure both the old cavity and the resultant boolit. One thousandth oversize on a .35 cal is probably a good starting point, you can lap it bigger if needed or size it down if that's required. Check with the guys in the paper-patch forum, I'm sure they'd know what you should need.

[robroy]

It is amazing to me that no matter how often you do the math you still end up cutting and trying till it fits.

[HORNET]

If you go to the Vendor/Sponsors forum and pull up the listing for BRP ( BABore's molds), they list a .35PP/.348 Plinker that's available in different lengths and weights for paper-patching for various .35 rifles. That might give you some idea where to start.

[KYCaster]

Ummmm........I think a couple of posters need to check the position of their decimal points.........[smilie=1:

Jerry

[theperfessor]

Without using symbols let me give the equation that is used to calculate expansion due to temperature changes:

change in length = expansion coefficient x change in temperature x original length

Remember that the bullet mould cavities will expand as the mold is heated, just as the bullet will shrink in size as it cools, so to determine the size cavity you need to know what temperature the mold will be at the proper casting temperature and the material the mold will be made from.

Ferrous materials have about half the expansion coefficient that aluminum does. The room temperature cavity size of an iron mold will be different than the room temperature size of an aluminum mold in order to make the same size bullet.

[StarMetal]

.......and let me say that BaBore has it down perfect on his molds for his chosen alloy.

Joe

[tommygirlMT]

For future refrence the easiest way to post math stuff on a forum is to use "Equation Editor" in a blank "Microsoft Word" document and then right click on it and choose copy and then open up "Paint" and choose paste and then save as a picture and post as a picture.

Example:

http://forums.handloads.com/uploads/tommygirlMT/2009-11-23_222540_BC_Formula_for_RB.GIF

[theperfessor]

Good suggestion.