Curiously, although this was the last of the three basic Elrod "mold patents" to be issued, it was the first to be filed (1920-04-17).
Apparently the Elrod molds were originally plain cast iron. It was discovered that they improved with age as a coating of mold oil baked onto them. The process described here simply pre-bakes them.
The mold material given as preferably cast iron. Mold oil is described as "heavy mineral oil."
Curiously, the mold is here called an "extrusion die, where in the original Elrod patent great care was taken to insist that the process was not extrusion. (He mentions both extrusion (pushing) and "eduction" (pulling), but says only "extrusion die" in the claims.)
This is a single-file PDF version of this patent created from full-resolution but lossy JPEG conversions of the original USPTO page scans. (7 Megabytes)
These are full resolution lossless PNG conversions of the original USPTO TIFF page scans.
US patent documents are in the public domain. The PDF and PNG versions of them here are similarly in the public domain; I assert no additional rights on these versions.
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