Expansion assembly for mine roof bolts

An expansion assembly for a mine roof bolt having a threaded portion at one end and a bolt head at the other end 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 two legs depending from said body portion that straddle said bolt and extend toward said bolt head when said plug is threaded onto said bolt threaded portion, said body portion and said depending legs forming continuous tapered surfaces that each form an angle of at least 8.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 relieved edge to facilitate penetration of resin by said expansion assembly, said tapered plug depending legs having longitudinal channels formed therein to facilitate the flow of resin down, past and around said expansion assembly;
• a pair of expansion leaves each having a serrated outer surface, a smooth inner surface and tapering edge surfaces joining said inner and outer surfaces, said expansion leaves each surrounding said bolt at a radially spaced distance from said bolt when said expansion assembly is positioned on said roof bolt, each of said leaf tapering edge surfaces being in abutting contact with said tapered plug tapered surfaces whereby said leaves are forced apart 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 nine 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 69.degree. to said planar surfaces, said serrations being equally spaced from each other and being no less than 0.22" apart and no more than 0.27" apart, each of said expansion leaves having a series of vertical channels formed on the ends of said leaves closer to said bolt head to facilitate the flow of resin down, past and around said expansion assembly;
• a metal bail connected to each of said expansion leaves and extending over the end of said roof bolt to prevent axial movement of said leaves relative to said bolt when said tapered plug is threaded onto said bolt threaded portion to force said leaves apart;
• and
• a breakable holding ring formed from flexible plastic material positioned around said expansion leaves to hold said expansion assembly in an assembled position on said roof bolt until expansion of said assembly by forcing said leaves apart causes said holding ring to break.