Two-stage hammer mill

Claim 1

A two-stage rotary hammer mill, for continuous grinding of a product in two steps, the first grinding stage reducing said product to a predetermined semiground condition, and the second stage reducing said semiground product to a more finely ground end product, said apparatus comprising: housing means enclosing first and second grinding stages and having an inlet opening in said first stage and an outlet opening in said second stage; partition means within said housing means separating said first and second stages; a first rotary hammer mill means and mill screen means therearound, located in said housing means and spaced therefrom, and adapted to reduce said product to said semiground condition, and deliver same between said mill screen means and said housing means; a second rotary hammer mill means in said second stage coaxial with said first hammer mill means and adapted to receive said semiground product, and further reduce the same to said finely ground end product; drive means for said first and second stage hammer mill means; an annular product outlet space around said first hammer mill means; axial opening means in said partition means for conducting semiground product from said first stage to said second stage along the central axis of the second rotary hammer mill means; product passageway means communicating only between said annular space and said opening in said partition; and, fan blade means mounted on said second rotary hammer mill means for rotation therewith to draw air through said first stage and through said axial opening into said second stage and impel air out of said outlet thereby ensuring free flow of product through both said stages.