Tunnel machine having reversible boring head

Claim 1

A TUNNEL BORING MACHINE COMPRISING (A) A NON-ROTATABLE CYLINDRICAL SHIELD WITH ITS AXIS HORIZONTAL, (B) A CUTTING HEAD, (C) MEANS TO MOUNT THE CUTTING HEAD ON THE SHIELD FOR ROTATION IN EITHER DIRECTION ABOUT THE AXIS OF THE SHIELD, (D) DRIVING MEANS TO ROTATE THE CUTTING HEAD IN EITHER DIRECTION OF ROTATION, (E) SAID CUTTING HEAD HAVING AT ITS PERIPHERY AN OUTER ANULUS OF FRUSTO-CONICAL FORMS, AN INNER ANNULUS ALSO OF FRUSTO-CONICAL FORM OF SHORTER AXIAL LENGTH THAN THE OUTER ANNULUS AND SPACED RADIALLY INWARDLY FROM THE OUTER ANNULUS, THE TWO ANNULIHAVING THEIR FRONT EDGES IN THE SAME PLANE, A RING EXTENDING RADIALLY INWARDLY FROM THE REAR EDGE OF THE OUTER ANNULUS AND A PLURALITY OF RADIAL VANES EXTENDING IN PLANES CONTAINING THE AXIS OF ROTATION OF THE HEAD, EACH ATTACHED TO THE TWO ANNULI AND THE RING AND SPACED APART AROUND THE ANNULI TO DIVIDE THE ANNULI INTO A PLURALITY OF BUCKETS WITH MOUTHS OPEN TOWARDS THE TUNNEL FACE AND DISCHARGE OPENINGS OPEN RADIALLY INWARDLY OF THE HEAD BEHIND THE INNER ANNULUS, (F) A PLURALITY OF CUTTING BLADES MOUNTED ON THE CUTTING HEAD, EACH BLADE BEING SYMMETRICAL ABOUT A PLANE THROUGH THE BLADE CONTAINING THE AXIS OF ROTATION OF THE HEAD WHEREBY EACH BLADE IS OPERABLE TO CUT IN EITHER DIRECTION OF ROTATION OF THE CUTTING HEAD, (G) A DISCHARGE CHUTE MOUNTED ON THE SHIELD BELOW THE UPPERMOST DISCHARGE OPENINGS ON THE HEAD, (H) SHEDDER PLATES ATTACHED TO THE SHIELD AND EXTENDING AROUND THE INNER ANNULUS OF THE HEAD ON EITHER SIDE OF THE DISCHARGE STATION TO PREVENT CUTTINGS BEING DISCHARGED BEFORE REACHING THE CHUTE, AND (I) MEANS TO CONVEY CUTTINGS REARWARDLY FROM THE CHUTE.