Linstrum
05-15-2009, 10:53 PM
Extrusion of lead and other materials is a very interesting process that is a bit more complicated than one would think. When I was making jewelry findings for a living some years ago, I looked into using extrusion and post-sintered powdered metal extrusion as possible methods for making my own tubing from precious metals. I could not afford to pay the rip-off prices being charged for commercially manufacted silver and gold tubing required for making some of my products because it totally wiped out my profit margin when I sold my stuff at competetive prices.
I found and read a book published in Great Britain in the 1910s (I don't remember the name of the book, I read it 20 years ago) that was the most detailed work available on lead extrusion (which would translate quite well to extruding copper jackets, as well as silver and gold). The author had taken different colors of damp clay and cut them into cubes or long square cross-sectional strips like lengths of fettuccine and then arranged them in his extrusion apparatus so they formed a checker-board in cross section before extrusion. The extrusion barrel and nozzle were split length-wise in half-sections so they could be taken apart to see what was going on inside them and the different colors of clays traced the flow patterns inside the barrel and nozzle. The photos in the book showed in pretty good detail how the material flowed inside the barrel and nozzle and the author pin-pointed problem areas in the shape and angle of the extrusion nozzle and he was able to refine the internal shape of extrusion nozzles to maximize performance.
The big thing he discovered was to avoid sharp internal angles that the lead or clay had to flow around and places where the lead or clay had to change direction radically to enter the extrusion nozzle, since these trouble areas caused non-linear "eddy current" type of flows. The eddy currents did not harm the final product but dramatically increased the force required to get the material to enter and go through the nozzle.
The main difference between what the book covered and what we are doing is the book was oriented toward extruding seemless lead tubing and we are making solid wire. In making hollow lead extrusions, the extrusion die has a torpedo-shaped mandrel inside it that forms the internal bore of the tubing, and the lead has to flow around the arms that hold the torpedo in place inside the nozzle. The arms in the example given in the book were shaped pretty much like knife blades so they would cause the lead to flow around them with minimal disturbance, but it created cuts down the sides of the tubing so it was not seemless. It was expected that the lead would "cold weld" itself back together as it flowed through the nozzle, but plain old-fashioned common sense would say that this would not happen, and it didn't. Back then lead tubing was still used somewhat for plumbing (inexpensive galvanized steel pipe was available in the 1890s) but by 1910 most extruded lead sheathing was used for things like toothpaste and ointment tubes as well as to cover phone and telegraph cables in wet, rainy places, or under water like for the very first Trans-Atlantic Telegraph cables layed back in the 1850s and 1860s, and there was a problem with the lead covering leaking at the seems where the cold weld did not form perfectly. The problem was solved by simply heating the nozzle hot enough so that the lead would solder itself back together as it went through the nozzle since quite a bit of heat was also generated as the lead flowed through the reduction area. Between being externally heated along with the heat from working the lead in the reduction area, the temperature was high enough so the lead would make a truly seemless extrusion.
I saw some photos of the lead extrusion machines used back 140 years ago and they were darn near as tall as a two-story house. The lead blank was as tall as a man, two feet in diameter, and weighed 6-2/3 tons (or 13,333 pounds)! The press that was used to power the extrusion apparatus used steam pressure to drive the piston since hydraulics were not very well developed at the time.
If some of you lead extruders would care to experiment with tubular extrusions, say for making deep hollow points, there are two ways that it can be done. One would be to make lead tubing by attaching the torpedo mandrel to the end of the piston so it moves along with the piston. The mandrel would have to be a bit longer than the piston stroke because part of the mandrel would need to to be inside the extrusion nozzle during the entire piston stroke. This would make retracting the piston back out of the extrusion cylinder a bit difficult, but would not be impossible. The other way, which I would do (and Buckshot is already doing for hollow-base Minie balls), is to make lead cups shaped pretty much like a pistol cartridge with real thick walls by having a die machined to the required body diameter, and then have a mating mandrel that would fit down inside the die with a slightly tapered hollow-pointing tip that would form the hollow cavity inside the lead slug. The finished lead cup would have to be pressed out the bottom of the die, but that isn't too hard if there is a removable plug in the bottom of the die that can be quickly pulled out before pressing the finished piece on through the die and out its bottom.
There are all sorts of things possible that can be done with lead extrusion. Have fun!
rl542
I found and read a book published in Great Britain in the 1910s (I don't remember the name of the book, I read it 20 years ago) that was the most detailed work available on lead extrusion (which would translate quite well to extruding copper jackets, as well as silver and gold). The author had taken different colors of damp clay and cut them into cubes or long square cross-sectional strips like lengths of fettuccine and then arranged them in his extrusion apparatus so they formed a checker-board in cross section before extrusion. The extrusion barrel and nozzle were split length-wise in half-sections so they could be taken apart to see what was going on inside them and the different colors of clays traced the flow patterns inside the barrel and nozzle. The photos in the book showed in pretty good detail how the material flowed inside the barrel and nozzle and the author pin-pointed problem areas in the shape and angle of the extrusion nozzle and he was able to refine the internal shape of extrusion nozzles to maximize performance.
The big thing he discovered was to avoid sharp internal angles that the lead or clay had to flow around and places where the lead or clay had to change direction radically to enter the extrusion nozzle, since these trouble areas caused non-linear "eddy current" type of flows. The eddy currents did not harm the final product but dramatically increased the force required to get the material to enter and go through the nozzle.
The main difference between what the book covered and what we are doing is the book was oriented toward extruding seemless lead tubing and we are making solid wire. In making hollow lead extrusions, the extrusion die has a torpedo-shaped mandrel inside it that forms the internal bore of the tubing, and the lead has to flow around the arms that hold the torpedo in place inside the nozzle. The arms in the example given in the book were shaped pretty much like knife blades so they would cause the lead to flow around them with minimal disturbance, but it created cuts down the sides of the tubing so it was not seemless. It was expected that the lead would "cold weld" itself back together as it flowed through the nozzle, but plain old-fashioned common sense would say that this would not happen, and it didn't. Back then lead tubing was still used somewhat for plumbing (inexpensive galvanized steel pipe was available in the 1890s) but by 1910 most extruded lead sheathing was used for things like toothpaste and ointment tubes as well as to cover phone and telegraph cables in wet, rainy places, or under water like for the very first Trans-Atlantic Telegraph cables layed back in the 1850s and 1860s, and there was a problem with the lead covering leaking at the seems where the cold weld did not form perfectly. The problem was solved by simply heating the nozzle hot enough so that the lead would solder itself back together as it went through the nozzle since quite a bit of heat was also generated as the lead flowed through the reduction area. Between being externally heated along with the heat from working the lead in the reduction area, the temperature was high enough so the lead would make a truly seemless extrusion.
I saw some photos of the lead extrusion machines used back 140 years ago and they were darn near as tall as a two-story house. The lead blank was as tall as a man, two feet in diameter, and weighed 6-2/3 tons (or 13,333 pounds)! The press that was used to power the extrusion apparatus used steam pressure to drive the piston since hydraulics were not very well developed at the time.
If some of you lead extruders would care to experiment with tubular extrusions, say for making deep hollow points, there are two ways that it can be done. One would be to make lead tubing by attaching the torpedo mandrel to the end of the piston so it moves along with the piston. The mandrel would have to be a bit longer than the piston stroke because part of the mandrel would need to to be inside the extrusion nozzle during the entire piston stroke. This would make retracting the piston back out of the extrusion cylinder a bit difficult, but would not be impossible. The other way, which I would do (and Buckshot is already doing for hollow-base Minie balls), is to make lead cups shaped pretty much like a pistol cartridge with real thick walls by having a die machined to the required body diameter, and then have a mating mandrel that would fit down inside the die with a slightly tapered hollow-pointing tip that would form the hollow cavity inside the lead slug. The finished lead cup would have to be pressed out the bottom of the die, but that isn't too hard if there is a removable plug in the bottom of the die that can be quickly pulled out before pressing the finished piece on through the die and out its bottom.
There are all sorts of things possible that can be done with lead extrusion. Have fun!
rl542