Mine prop jack and method of prestressing a mine prop

Abstract

A telescoping mine prop is prestressed by engaging the prop with a jack and thereby telescopically expanding the prop against opposing surfaces of the mine with the jack. Thereafter the prop is locked in position and the jack is disengaged from the prop for use with the expansion of another prop, thereby leaving the mine prop in a prestressed condition.

1 . A mine prop prestressing device comprising;
 a jack having means for temporarily attaching it to a telescoping mine prop for expanding said prop into prestressed engagement with opposing surfaces.   
     
     
         2 . The mine prop of  claim 1 , wherein said jack consists of a jack post which is expandable against opposing head and foot plates secured to opposite ends of said mine prop for expanding said mine prop with said jack post. 
     
     
         3 . The mine prop of  claim 2 , wherein said jack post is a telescopically expandable post having a hand operated hydraulic jack disposed therein. 
     
     
         4 . The mine prop of  claim 2 , said means for temporarily attaching including upper and lower clamps for temporarily clamping said jack post to said mine prop. 
     
     
         5 . A combination mine prop and jack for prestressing the mine prop, comprising:
 a telescopically expandable mine prop having a head plate and a foot plate secured to opposite ends;   a lock for adjustably locking said prop in an expanded condition;   an expandable jack post disposed between said head and foot plates for expanding said prop against opposing surfaces to a condition of prestress after engaging said lock and releasing said jack post; and   tie means temporarily tying said jack post to said mine prop.   
     
     
         6 . The combination of  claim 5 , wherein said jack post includes a hand operated hydraulic jack. 
     
     
         7 . The combination of  claim 5 , said lock consisting of a longitudinal series of apertures in one portion of said telescopically expandable mine prop which is telescopically movable relative to a second part thereof, and a pin receivable in one of said apertures and engageable with said second part to lock said prop in an expanded prestressed condition. 
     
     
         8 . The combination of  claim 5 , said tie means including upper and lower clamps for temporarily clamping said jack post to said mine prop. 
     
     
         9 . The method of prestressing a telescoping mine prop comprising;
 engaging said prop with a jack;   telescopically expanding said prop against opposing surfaces with said jack;   locking said prop at its expanded position; and   disengaging said jack from said prop for use with the expansion of another prop and thereby leaving said mine prop in a prestressed condition.