Apparatus for controlling yield performance of props for roofs, and methods
The technology provides increased capability and control over the yield performance of the timber prop, a mine roof support. The new Wedge Prop design includes a cut pattern idealized for the specific wood species used in manufacturing and a set of confinement rings varying in strength due to different failure mechanisms. The cut pattern is based on the diameter of the yellow poplar pole, while the confinement rings consist of multiple types of welds to allow for either wire tensile failure or for weld detachment. The cut pattern can be combined in conjunction with various combinations of confinement rings to allow for precise control over the performance of the Wedge Prop in the Propsetter System.
1. A prop for supporting a roof comprising: a pole that is positioned vertically relative to ground; a tensioner positioned at a top of the pole in between the pole and the roof to pretension the pole with respect to the roof to hold the pole in place; and a ring wrapped about the pole and welded together with a weld so failure of the pole under load from the roof is a function of the weld failing before any other portion of the prop fails.
2. The prop of claim 1 wherein there are cuts in the pole in proximity to one end of the pole forming a part of a reduced cross-sectional area in relation to an uncut portion of the pole.
3. The prop of claim 2 wherein the ring is placed around the cuts.
4. The prop of claim 3 wherein the cuts form a pattern which provide a brushing failure mechanism.
5. The prop of claim 4 which has a buckling stress to compressive strength ratio of about 0.45.
6. The prop of claim 5 wherein the pole has a thin wedge dimension of about 1.25 inches, and the pole has a thick wedge to cut length ratio of about 0.3.
7. The prop of claim 6 wherein the ring is made of steel wire which is wrapped about the pole, the ring has a weld of about 0.5 to 1.5 inches in length adjacent a first end and a second end of the wire to hold the first end and the second end together.
8. The prop of claim 7 including a second ring and a third ring, each wrapped around the pole, with the ring and the second ring and the third ring spaced from one another in an axial direction of a length of the pole.
9. The prop of claim 8 wherein the ring is spot welded together about the pole.
10. The prop of claim 9 wherein the second and third rings are positioned on the pole above the ring and have solid welds.
11. The prop of claim 10 wherein the ring is located between 1 and 2 inches above the bottom of the pole, the second ring located 4 times a distance from the bottom of the pole as a distance from the bottom of the pole to the ring, and the third ring is located twice the distance from the bottom of the pole as the distance from the bottom of the pole to the second ring; the end of the cuts measured from the bottom of the pole parallel to the pole axis, falls between the second and third rings.
12. The prop of claim 11 wherein the pole is made of wood.
13. The prop of claim 12 wherein the pole is cylindrical.
14. The prop of claim 13 wherein the tensioner is a head board positioned perpendicular to the pole.
15. The prop of claim 14 including a baseboard position on the ground and on which the pole extends vertically upwards.