Rock bit lubrication system utilizing expellable plug for obtaining expansion space

摘要

A rotary rock bit is constructed with a lubrication system having an expansion space provided within the lubrication system to accommodate increases in internal volume during drilling. A flexible diaphragm is located in the lubricant reservoir cavity in the bit dividing the cavity into a lubricant portion and an expansion portion. A low melting point wax plug is positioned in the expansion portion of the lubricant reservoir. The lubricant portion of the lubricant reservoir is filled with lubricant. The wax plug prevents lubricant from entering the expansion portion. The bit is heated above the melting temperature of the wax plug allowing the wax to melt and run out of the bit. This provides an expansion space in the bit to accommodate an increase in volume in the lubrication system during drilling.