PURPOSE: To form fine powder by mechanical pulverization under high impingement efficiency by coaxially disposing the outlets of a pair of acceleration wheels consisting of impellers with side plates for accelerating the feed to the pulverizing machine together with air currents opposite to each other under clearances. CONSTITUTION: The outlets 19 and 19a of a pair of the acceleration wheels 12 and 12a consisting of the impellers 14 and 14a with the side plates for accelerating the feed to the pulverizing machine together with the air currents are coaxially disposed by opposing their outlets 19 and 19a respectively under the clearances 21. The acceleration wheels 12 and 12a are relatively moved and the clearances of the outlets 19 and 19a of the acceleration wheels are formed as crushing sections of the feed by impact among the same materials. Namely, the feed may be accelerated along flow passages while the influence of the flow of the air currents outside the flow passages is averted. Even more, the impingement is effected under high kinetic energy by the relative impact velocity in the each other's crushing sections of the acceleration wheels and the fine powder may be formed by the mechanical pulverization under high pulverization efficiency.
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