Patent ID: 8382471

Claim:
A multiple hearth furnace comprising: a vertical rotary hollow shaft including at least one rabble arm fixing node; at least one rabble arm including a tubular structure for circulating therethrough a cooling fluid and a coupling end that is received like a plug in a socket arranged in said arm fixing node, said coupling end including cooling fluid supply and return means therein; and securing means for securing said rabble arm with its coupling end in said socket, said securing means including: a clamping bolt for pressing said coupling end into said socket, said clamping bolt protruding out of the coupling end of said rabble arm where it has a bolt head that can be brought by rotation of said clamping bolt about its central axis into and out of hooking engagement with an abutment surface on said arm fixing node; and a threaded sleeve screwed onto a threaded end of said clamping bolt for exerting a clamping force onto said clamping bolt; wherein: said coupling end has a through boring in which said clamping bolt is rotatably fitted so that its threaded end sticks out of said through boring; and said threaded sleeve, which is screwed onto said threaded end, bears on an abutment surface of said coupling end for exerting said clamping force onto said clamping bolt; wherein said coupling end is formed by a solid plug body which has a front end and a rear end; wherein said tubular structure of said rabble arm comprises an arm support tube, which is connected to the rear end of said plug body, and a gas guiding tube, which is arranged inside said arm support tube and cooperates with the latter to define between them a small annular cooling gap for channeling the cooling gas from the shaft to the free end of the rabble arm, and the interior section of said gas guiding tube forms a return channel for the cooling gas; wherein said cooling fluid supply and return means include at least one cooling fluid supply channel and at least one cooling fluid return channel arranged in said solid plug body around said through boring, wherein at said rear end of said solid plug body, said at least one cooling fluid supply channel is in communication with said small annular cooling gap and said at least one cooling fluid return channel is in communication with said return channel; and said through boring, in which said clamping bolt is rotatably fitted, axially extends through said solid plug body, and said abutment surface, onto which said threaded sleeve bears, is formed on the rear end of said solid plug body.