EXPANSION ASSEMBLY FOR MINE ROOF BOLTS

摘要

An improved expansion assembly for a mine roof bolt has a tapered plug, two expansion leaves that bear against the tapered plug, a bail that connects the expansion leaves and extends over the end of the mine roof bolt, and a breakable holding ring to keep the expansion assembly assembled until after it is placed into the bore hole. The tapered plug has a threaded bore therethrough for threading onto the mine roof bolt. The tapered plug also has tapered surfaces that have an angle of taper of 8.degree. to the axis of the mine roof bolt. The expansion leaves each have nine serrations formed on the surface such that the serrations are formed by the intersection of a planar surface perpendicular to the axis of the mine roof bolt and a frusto-conical surface. The frusto-conical surface is at an angle of 69.degree. to the planar surface. The serrations are equally spaced from each other and have a peak to peak distance of .25". The expansion leaves each have a maximum length of 3". The tapered plug has a relieved upper edge and channels running longitudinally along the outer surfaces of the legs of the plug and the expansion leaves have channels formed near the end of the leaves, all for facilitating use of the expansion assembly with resin. The improved expansion assembly may be utilized with or without resin bonding.