Expansion assembly for mine roof bolts utilized in small diameter bore holes

An expansion assembly for a mine roof bolt having a nominal diameter of five-eighths of an inch to be utilized in a bore hole having a nominal one inch diameter, said mine roof bolt having a threaded portion at one end and a bolt head at the other end, said expansion assembly comprising:

• a tapered plug having a body portion with a threaded internal bore adapted to be threaded onto said bolt threaded end portion, said tapered plug having four tapered surfaces on the exterior of said body portion that taper inwardly as said four tapered surfaces extend toward said bolt head when said plug is threaded onto said bolt threaded portion, said four tapered surfaces each forming an angle of at least 6.5.degree. to the axis of said bolt when said plug is threaded onto said bolt, said tapered plug body portion having the surface positioned closer to said bolt threaded end formed with a rounded edge to facilitate penetration of resin by said expansion assembly, said tapered plug having longitudinal channels formed therein between said plug tapered surfaces to facilitate the flow of resin down, past and around said expansion assembly;
• an expansion shell having four expansion leaves integrally formed with a support ring and positioned on said bolt so that said support ring is closer to said bolt head and said leaves extend in an axial direction toward said bolt threaded portion, said leaves each having a serrated outer surface and a smooth inner surface, said expansion leaves surrounding said bolt at equal circumferentially spaced distances from each other when said expansion shell is positioned on said roof bolt, each of said leaf smooth inner surfaces being in abutting contact with one of said tapered plug tapered surfaces whereby said leaves are forced radially outwardly when said tapered plug is threaded axially onto said roof bolt and said leaves are restrained from axial movement relative to said roof bolt, each of said leaf serrated outer surfaces having seven separate serrations formed thereon, each of said serrations being formed by the intersection of a planar surface and a conical surface whereby each planar surface is perpendicular to the axis of said mine roof bolt in the position assumed by said expansion leaf relative to said bolt in the unexpanded condition of said expansion assembly and each said conical surface has its conical elements at an angle of 72.3.degree. to said planar surfaces, said serrations being equally spaced from each other and being no less than 0.186" apart and no more than 0.190" apart;
• and
• a stop washer threaded onto said bolt threaded portion closer to said bolt head than said expansion shell whereby said stop washer restricts said expansion shell from axial movement as said plug is threaded onto said bolt threaded portion to force said leaves radially outwardly.