Instructions on the use of Rexalloy® Extrusion Die Inserts
Rexalloy® die inserts are usually furnished ground on O.D. and two faces. The die holder can be made from Halcomb 118 bar stock or forgings and should be about 50% thicker than the insert. The holder should be drilled with the hole slightly larger than the extruded bar size, and then counterbored to a depth slightly greater than the thickness of the insert, and to a diameter .008”/.010” less than the diameter of the insert. Larger inserts, greater than 2.000″ O.D. may require .010″/.015″ shrinkage. The die holder should be hardened to about 40 HRC.
After the insert is finished and polished, the I.D. shrunk into the holder which is accomplished by heating the holder to about 400/500 degrees Fahrenheit, and then the insert is cooled in dry ice. A pin gauge a few thousandths longer than the diameter of the insert, when cold, can be used to check the counterbore of the heated die for size before dropping the insert into the die holder. It is important that the Rexalloy® insert be under compression so that there will be a tendency to close up any heat checks which usually form on the inside surfaces in the first or second extrusion pass.
The dies should be preheated slowly to a temperature of at least 700-800 degrees Fahrenheit before the first extrusion. It is important that wide temperature fluctuations be avoided, otherwise heat checking will be extensive, and flake-out may occur. Thus, cooling between pushes is unnecessary, and after the last push, the dies should be slowly cooled with air at room temperature. Do not cool with water.
Rexalloy® dies should be swabbed with a graphite-base lubricant before each extrusion.
Rexalloy® dies are overhauled, when necessary, by belt-polishing with a fine grit abrasive belt or die grinder with a fine stone. Rexalloy® dies hold their size exceptionally well because of their high hardness at elevated temperatures and the fact that Rexalloy® is unaffected by any heat treatment and cannot be tempered or annealed.
We recommend the following abrasive wheels for grinding Rexalloy®
- For Cylindrical Grinding – W-46-JB
- For Surface Grinding – W-46-HB1