Pneumatic, expandible shaft with keys

Claim 1

A pneumatic expandable shaft (1) having lateral slits, said shaft having lugs (2) in the interior thereof, said lugs being suitable for blocking bobbins mounted on the exterior of said shaft, which comprises in the interior thereof a tube (7) made of resilient material, valves (6-15) for communicating said tube with the exterior thereof, said valves permitting the inflation of the tube by means of compressed air, said lugs being pushed outwardly under the pneumatic force of said tube (7) through said lateral slits, the shaft comprising a shaped metallic plate (13) interposed between each lug and said tube, and a return spring (14) which causes each lug (2) to return to the interior of said shaft (1) when said tube is deflated, said spring acting in opposition to said tube (7), and a plurality of pairs of cylindrical elements (18 and 19) made of plastic material located inside said shaft and outside said tube, each pair placed end to end and each pair having a rectangular opening which bridges the two elements and permits passage therethrough of one of said lugs.