Yieldable cone bolt and method of manufacturing same

A yieldable roof support assembly for use in a predrilled bore hole, the assembly comprising:

• an anchor member comprising a longitudinally extending steel tendon, a slip sheath, and a coating,
• said tendon extending along a tendon axis from a threaded proximal end portion to a distal portion, and further including a mid-portion intermediate the proximal and distal portions;
• the distal portion including at least one wedge member having a proximal-most reduced diameter portion and a distal-most enlarged diameter portion;
• the slip sheath disposed radially about said mid-portion, the coating being interposed between said slip sheath and said tendon, the coating selected to provide a debonding property and an anti-corrosive property,
• the slip sheath comprising a heat shrunk plastic tube mechanically coupled to the mid-portion to selectively allow axial sliding of said tendon relative thereto on the application of a predetermined minimum force to effect yielding movement of said tendon in said bore hole;
• and
• wherein the predetermined minimum force is pre-selected having regard to at least one of the type and extent of said coating along the mid-portion.

A mine roof support system for use in a predrilled bore hole, the system including in combination:

• an elongated cone bolt;
• a threaded fastener for tensioning said cone bolt;
• and
• a resin composition for securing said cone bolt at least partially in said bore hole;
• the cone bolt comprising;
• a tendon elongated along a longitudinal axis and extending from a threaded proximal end portion to a distal portion, and further including a mid-portion intermediate the proximal and distal portions;
• the threaded proximal end portion configured for threaded engagement by said threaded fastener;
• the distal portion including at least one frustoconical wedge member extending radially about the axis from a proximal-most reduced diameter portion to a distal-most enlarged diameter portion;
• a plastic slip sheath disposed radially about at least part of said mid-portion and being mechanically coupled thereto, the slip sheath comprising a heat shrunk plastic tube comprising a plastic selected from the group consisting of polyvinyl chloride, polyvinyl acetate, polyethylene terephthalate, neoprene, a tetrafluoroethylene and poly-alpha-olefin, said slip sheath having an average radial thickness selected at between about 0.4 and 20 mil;
• and
• a coating interposed between said slip sheath and said tendon, the coating selected to provide a debonding property, the coating being maintained substantially in isolation from said resin composition by said slip sheath,
• whereby with said slip sheath engaged by said resin composition, the sheath allowing axial sliding of said tendon relative thereto on yielding movement of said tendon in said bore hole on the application of a predetermined minimum force.