Flat seal for a roller cone rock bit

A roller cone rock bit, comprising:

• a bit body having at least one downwardly extending arm terminating in a spindle having an inwardly downwardly directed axis, the spindle also having a sealing surface;
• a cutter cone rotatably mounted on the spindle, the cone having a cavity for receipt of the spindle and having a sealing surface, wherein the sealing surface of the cone and the sealing surface of the spindle define a seal gland;
• a bearing assembly disposed within the cavity, the beating assembly in rotary load bearing engagement between the spindle and the cone and the cavity filled with a lubricant;
• a first seal to maintain the lubricant in the cavity and a barrier to exclude borehole debris and to protect the first seal;
• the first seal blocking the lubricant from the barrier;
• an elastomer seal located adjacent to the bearing assembly to provide the first seal between the spindle and the cavity;
• the barrier formed by a flat seal disposed in the seal gland, comprising:
• a ring-shaped metallic spring, the metallic spring having an inner face with an annular inner edge for contacting the sealing surface of the cone and having an outer face with an annular outer edge for contacting the sealing surface of the spindle, wherein the metallic spring has a relaxed axial pitch greater than a clearance of the seal gland;
• an annular inner elastomer shroud disposed on the inner face of the metallic spring such that the annular inner edge is exposed;
• and
• an annular outer elastomer shroud disposed on the outer face of the metallic spring such that the annular outer edge is exposed;
• and
• the contact between the annular inner edge of the metallic spring and the sealing surface of the cone in cooperation with the contact between the annular outer edge of the metallic spring and the sealing surface of the spindle, providing the barrier to exclude borehole debris and protect the first seal:
• and
• the metallic spring is sized to substantially fill the seal gland defined by the sealing surface of the spindle and the sealing surface of the cone to provide the barrier to exclude borehole debris even after the annular inner elastomer shroud and the annular outer elastomer shroud have been abraded.