1. Field of the Invention
The present invention relates to compressible supports for mine roofs and the like. More specifically, the present invention relates to vertical support columns having compressible supports.
2. Brief Description of the Prior Art
Support columns are used to counteract the force that gravity exerts on the mass of an object. For example, vertical support columns are positioned between two horizontal objects to keep the objects spaced away from one another.
In underground mining, vertical support columns are used as primary or secondary supports for mine roofs. Due to the tremendous forces exerted on the vertical support columns by the earth and rock above the mine roof, including forces resulting from shifting and settling of the overhead earth and rock, rigid vertical support columns can bend or break. Complete failure of a vertical support column can cause an isolated collapse of the mine roof. Therefore, compressible support columns, which yield during settling or shifting of the mine roof, are often used.
In mining operations, compressible vertical support columns are generally positioned perpendicularly between a mine roof and a mine floor. One type of compressible support column is disclosed in U.S. Pat. No. 4,052,029 to Townsend. The Townsend patent uses telescoping members and compressible materials to reduce the overall length of the support column as the earth and rock above the mine roof settles or shifts. Specifically, the Townsend patent discloses a support column having a hollow lower steel member and a hollow upper steel member, where the upper steel member fits over and slideably telescopes toward the lower steel member. The hollow cavity within the lower steel member is completely filled with wood positioned with the grain of the wood oriented parallel to a vertical axis of the assembled column. The hollow cavity in the upper steel member is only partially filled with wood, with the grain of the wood also aligned with the vertical axis of the assembled column. The space left between the wood in the upper and lower steel members is filled with discs, as needed, to adjust the length of the assembled compressible support column between a mine roof and a mine floor.
When earth and rock above the compressible support column disclosed in the Townsend patent shift, settle, or are otherwise subjected to additional force, the wood inside of the upper and lower steel members compresses. The compression reduces the overall length of the assembled compressible support column, easing the force being exerted on the column. Additional settling or shifting of the mine roof further compresses the load resisting material, until the lower steel member is telescoped to its full extent inside of the upper steel member. At this point, the upper and lower steel columns begin to compress, causing the upper and lower steel members to bulge outwardly, away from the vertical axis of the assembled upper and lower steel columns.
One disadvantage of the prior art compressible support columns is that they are expensive to make. Another disadvantage is that adjusting the length of the columns during installation is time consuming. Therefore, one object of the present invention is to provide a column having a compressible support that is inexpensive to manufacture. Another object of the present invention is to make a column having a compressible support that can be installed quickly.
The present invention generally includes a compressible support which includes a male member defining a plurality of ridges and grooves and a collar which has an internal surface defining a plurality of corrugations. The corrugations adjustably engaging grooves defined by the male member, the ridges defined by the male member, and the corrugations defined by the collar yield when the male member and collar are compressed together
One embodiment of the present invention generally includes a post and a collar. A cap and a base may also be provided. The post has a first end, a second end, and a longitudinal axis. The post also includes ridges and grooves, generally in the form of threads, positioned adjacent the first end of the post.
The collar has a first end, a second end, an internal surface, and an external surface. The second end of the collar is positioned adjacent the first end of the post during installation. Corrugations made from a material harder than the ridges and grooves of the post are positioned adjacent the internal surface of the collar. The corrugations adjustably engaging the ridges and grooves of the post, which are generally in the form of threads, are adjacent the first end of the post. The corrugations and threads allow the collar to be adjustable along a longitudinal axis of the post, essentially by threading the collar onto or off of the first end of the post. An optional cap and an optional base may be positioned adjacent the ends of the post and collar to distribute the force applied to the post and collar over a greater surface area.
When an initial or preloading force is exerted on the male member or post and the collar, referred to hereafter as the compressible support, the compressible support provides an equal and opposite force. As the force on the compressible support increases, the ridges positioned adjacent to the first end of the male member crush, yield, fracture, or strip, allowing the collar to move toward the second end of the male member, decreasing the overall length of the compressible support. Additional force causes additional crushing of the grooves adjacent the first end of the male member, until the movement of the collar toward the second end of the male member is arrested. At this point, further force causes the first end of the male member and the collar to compress, further decreasing the overall length of the compressible support.
Another embodiment of a compressible support according to the present invention generally includes a male member, a collar, and a post. In this embodiment, the male member is separate from the post.
These and other advantages of the present invention will be clarified in the description of the preferred embodiments taken together with the attached drawings in which like reference numerals represent like elements throughout.