An agitator-type ball mill has a circumferential wall which bounds a working chamber having an axis and includes two radially spaced jackets which form therebetween a gap for receiving a heat-exchange medium. The jackets are releasably connected with one another so that they can be separated from each other by displacement in an axial direction. A flexible member is arranged in the gap between the jackets, connected with one of the jackets, and forms a substantially helical passage in the gap. The heat exchange medium flows through the thus-formed helical gap. The flexible member may be formed by a band which is inserted in a helical groove provided in one jacket and extends radially into the gap so as to abut against the other jacket with prestress.
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