Blocking apparatus for fixing a metal block to the finished face of a semi-finished spectacle lens blank

A blocking apparatus for fixing a metal block to the finished face of a semi-finished spectacle lens blank by casting low-melting metal into a mold contacting the finished face of the blank, which comprises:

• (a) a housing,
• (b) an open mold supported by said housing and having a fixed section and a movable section arranged for rotary contact with said fixed section, said fixed mold section having an annular seat for supporting a finished blank face and said movable section having relief elements adapted to form positioning reference means in said metal block and to define a system of three orthogonal axes, said system having a first axis coincident with a central axis of said annular seat in an initial position of said movable mold section, and a second axis adapted to be brought into exact alignment with a prescribed cylinder axis for a semi-finished lens blank, the fixed and movable mold sections contact having cooperating partially spherical surfaces defining a ball-joint connection having its center of rotation lying on said central axis of the annular seat, the movable mold section being rigidly attached to a shaft with the shaft having a longitudinal axis coincident with the central axis of said annular seat in the initial position of said movable mold section, said shaft extending along a direction remote from said annular seat,
• (c) means associated with said housing for holding said lens blank on said annular seat,
• (d) casting means associated with said housing for delivering molten low-melting metal into a cavity defined by said open mold through a casting duct formed in said mold,
• (e) control means operatively connected to said shaft for orienting and tipping the movable mold section about said center of rotation of said ball-joint connection in order to define a mold cavity for forming a metal block having a prescribed prism value and a prescribed orientation of the prism axis and to align said relief elements with the prescribed cylinder axis.