Vertical grinding mill

Claim 1

A dry vertical grinding mill comprising: a shell for containing material to be pulverized and grinding medium; a vertical helically bladed hollow shaft rotatably mounted in said shell and extending through the top wall of said shell and having the bottom end open to the bottom portion of the interior of said shell and the upper part in communication with a source of gas; means connected to said shaft for driving said shaft in a direction for moving the material and the grinding medium upwardly in the shell to agitate the material and pulverize the material to fine particles whereby a portion of the mixture of grinding medium and material to be pulverized is left under a reduced pressure of the mixture at the bottom of said shell; collector means at the top of said shell for collecting the fine particles, said shell being otherwise substantially gas tight; and means for forming a gas current having a suction side connected through said collector means to the top of said shell for drawing gas from the source of gas downwardly through said shaft and laterally from the open bottom end of said shaft into said reduced pressure portion of the mixture at the bottom of said shell and then upwardly in said shell to said collector means for taking the fine particles out of the shell and passing them through said collector means.