Radial force anti-extrusion device for sealed drill string unit

摘要

A drill string reamer-stabilizer includes a main body adapted to be connected as an element of a rotary drill string. Individual bearing shafts are mounted axially along the exterior of the main body to support roller cutters that engage the wall of the borehole. Seal units are positioned around each bearing shaft between each roller cutter and bearing shaft to define a lubricant space. The seal units retain lubricant in the lubricant space and prevent contaminating fluid and materials in the borehole from entering the lubricant space. At least one seal unit comprises an annular cup-shaped elastomer seal member mounted in an annular seal gland in the roller cutter. The seal gland has an inner side adjacent the lubricant space and an outer side exposed to the fluid and materials in the borehole. A split-ring annular spring member fits in the cup-shaped elastomer seal member and maintains the seal member spaced from the outer side of the seal gland so that internal pressure in the lubricant space is vented outward past the seal member but external pressure of fluid and materials in the borehole forces the seal member against the inner side of the seal gland creating a fluid tight seal.