GB2099040A

GB2099040A - Pit prop

Info

Publication number: GB2099040A
Application number: GB8200673A
Authority: GB
Original assignee: SUBROC SUPPORTS LT Pty
Current assignee: SUBROC SUPPORTS LT Pty
Priority date: 1981-05-27
Filing date: 1982-01-11
Publication date: 1982-12-01
Also published as: DE3200338A1; FR2506833A1; AU7967882A; ZW582A1

Abstract

This invention relates to a yieldable type mine support prop and consists of a sleeve (12) which includes an inward indentation (14) in its wall intermediate its ends to define a constricted throat in the sleeve and a timber pole (10) which is located in the sleeve (12) and which is extruded through the sleeve throat when the support is subjected to a predetermined load in its axial direction. <IMAGE>

Description

SPECIFICATION Pit prop Field of the Invention This invention relates to a load support prop and more particularly to a mine support.

Summary of the Invention A load support prop according to the invention includes a sleeve of rigid material which has its wall inwardly deformed intermediate its ends to provide a throat in the sleeve of lesser internal cross-sectional area than the remaining portion of the sleeve and an elongated load resisting element which is compressible in a direction transverse to its long axis located in and projecting from the sleeve with the degree of inward deformation of the wall of the sleeve in its throat being such that the end of the load resisting element in the sleeve will pass through the throat only when a predetermined compressive load is applied across the support in its axial direction. Preferably, the load resisting element is a timber element the grain of the timber parallel to the long axis of the element.

Conveniently the end of the timber element in the sleeve carries an axially located bore to facilitate compression of that end of the element in a radial direction through the throat of the sleeve. In a preferred form of the invention the sleeve is made from metal and the throat in the sleeve is provided by a peripheral indentation in the outer wall of the sleeve.

In another form of the invention the sleeve has two throats which are spaced from each other in an axial direction and a load resisting element in each end of the sleeve.

A component of a load support prop according to the invention consists of a sleeve of rigid material the wall of which is deformed inwardly to provide an internal throat intermediate its ends of lesser cross-sectional area than that of the remainder of the sleeve. Preferably, the component is made from metal and the throat is provided in the sleeve by a peripheral indentation in the outer wall of the sleeve.

In another form of the invention the throat in the sleeve is provided by discreet indentations in the outer wall of the sleeve.

Still further according to the invention the sleeve includes two throats which are spaced in an axial direction from each other in the sleeve.

Brief Description of the Drawings.

The invention is now described by way of example only with reference to the drawings in which: Figure 1 is a partially sectioned side elevation of one embodiment of the prop of the invention, Figure 2 is a similar view to that of Figure 1 illustrating the mode of operation of the prop, Figure 3 is a sectional side elevation of one end of a timber load resisting element for use with the prop of the invention, Figures 4-6 are three further embodiments of the extrusion sleeve of the prop of the invention, and Figure 7 is a partially sectioned side elevation illustrating a further use of the extrusion sleeve of the invention.

Detailed Description of the Drawings The support prop of the invention is shown in Figure 1 of the drawings to consist of a timber pole 10 and a cylindrical extrusion sleeve 12.

The sleeve 12 is made from mild steel and has a groove 14 rolled into its outer wall to provide an indentation 1 6 on the inside of the sleeve. The indentation 1 6 provides an extrusion throat in the sleeve bore. The degree of penetration of the indentation 1 6 into the sleeve is determined by the hardness of the wood of the pole 10 and the load at which the prop is to yield by extrusion of the end of the pole through the throat. The length of the sleeve above and below the throat is determined respectively by the amount of sleeve necessary to hold the pole stably in the sleeve and the degree of compression required from the prop.

The wall thickness of the sleeve must be sufficient to avoid buckling of the sleeve while the prop is being reduced in length under load. To strengthen the foot of the sleeve, a washer 1 8, as shown in the drawing, or base plate may be welded to the underside of the sleeve.

In use, the pole and sleeve 12 are transported separately to the site for use of the prop. The height of the total prop is estimated and, if need be, the pole is cut to the required length. The pole is inserted into the sleeve and the prop is wedged into position between the hanging and foot wall in the conventional manner. Closure of the hanging on the prop will force the end of the pole 10 in the sleeve through the throat in the sleeve defined by the indentation 1 6 as illustrated in Figure 2. The extrusion force on the prop has proved in tests to be substantially constant and unlike similar conventional props the prop of the invention accepts its load rapidly with little or no initial load loss as the pole 10 is extruded through the sleeve throat.

As mentioned above the degree to which the prop may be shortened under load is determined primarily by the length of the sleeve below the sleeve throat. However, with the space in the sleeve filled with the timber a degree of compression is still available to the prop by compression of the timber fibres in the sleeve. To further extend the yield distance of the prop a second sleeve 1 2 may be located on the opposite end of the pole 10.

To initiate extrusion of the pole 10 through the throat in the sleeve 12 the end of the pole in the sleeve could be slightly chamfered and/or carry an axially positioned bore 20, as illustrated in Figure 3, to facilitate compression of that end of the pole in a radial direction. One or both of these features may, however, increase the axial distance moved by the pole 10 under load before the prop becomes fully load resisting.

A series of support props of the invention were tested with the following results: Two types of timber were used in the test, saligna grandus and a relatively harder saligna piniculata. The poles 10 were turned to a diameter very slightly smaller than the internal diameter of the sleeve 12. The sleeve 12 was made from a mild steel and had a wall thickness of 5 mm, an internal diameter of 1 55 mm with the indentation being rolled approximately to the shape shown in Figures 1 and 2 with a throat dimension of 125 mm diameter. The total length of the sleeve was 360 mm and the throat was located midway between its ends.

In a press with no wedges between the prop ends and press platens the props accepted full load in under 20 mm of compression and yielded under a very nearly constant load to a closure of 1 80.mm. An additional 25 mm reduction in length of the prop was obtained under increasing load by compression of the timber in the sleeve before the props failed. The props employing saligna grandus yielded at a very nearly constant load of 30 tons and the harder saligna piniculata props at 40 tons.

Very little or no initial load loss was exhibited by any of the props under test.

The yield load of the prop of the invention may be made variable for specific conditions by varying parameters such as the wood hardness, sleeve throat diameter and profile and so on.

With mine supports of the above type expense is a critical factor and obviously the thinner the wall thickness of the sleeve the cheaper the prop will be. With throat indentations shaped as shown in Figures 1 and 2 and a sleeve wall thickness of below 5 mm a tendency exists for the end of the pole to roll the peak of the throat formation downwardly to reduce the throat diameter and so the yield load of the prop. The tendency is minimised by the more gradually sloping indentations 1 6 illustrated in Figures 4 and 5.

Another means of obtaining the sleeve throat is illustrated in Figure 6. In this embodiment of the sleeve the indentations are discrete hemispherical indentations 22 which between them define the sleeve throat. Obviously, the throat could be constituted by more or less identations 22 than the four illustrated in Figure 6. Also, the indentations could be of a shape other than that illustrated in Figure 6.

Figure 7 illustrates yet another variation of the prop of the invention which is shown in the drawings to include two timber load resisting elements 10 and a single sleeve 12 which carries two throat defining indentations 1 6 which are spaced apart in the axial direction of the composite prop. The merit of this prop is that a far longer prop may be constructed from the three separate easily transportable components than is possible with the components of the Figures 1 and 2 embodiment.

Claims

1. A load support prop including a sleeve of rigid material which has its wall inwardly deformed intermediate its ends to provide a throat in the sleeve of lesser internal cross sectional area than the remaining portion of the sleeve and an elongated load resisting element which is compressible in a direction transverse to its long axis located in and projecting from the sleeve with the degree of inward deformation of the wall of the sleeve in its throat being such that the end of the load resisting element in the sleeve will pass through the throat only when a predetermined compressive load is applied across the support in its axial direction.

2. A prop as claimed in claim 1 in which the load resisting element is a timber element with the grain of the timber parallel to the long axis of the element.

3. A prop as claimed in claim 2 in which the end of the timber element in the sleeve carries an axially located bore to facilitate radial compression of that end of the element in the throat of the sleeve.

4. A prop as claimed in any one of claims 1 to 3 in which the sleeve is made from metal.

5. A prop as claimed in any one of the above claims in which the throat in the sleeve is provided by a peripheral indentation in the outer wall of the sleeve.

6. A prop as claimed in any one of claims 1 to 3 in which the throat in the sleeve is provided by discrete indentations in the outer wall of the sleeve.

7. A prop as claimed in any one of the above claims in which the sleeve has two throats which are spaced from each other in an axial direction and a load resisting element in each end of the sleeve.

8. A prop as claimed in any one of claims 1 to 6 including a sleeve on each end of the load resisting element.

9. A component of a load support prop which consists of a sleeve of rigid material the wall of which is deformed inwardly to provide an internal throat intermediate its ends of lesser crosssectional area than that of the remainder of the sleeve.

10. A prop component as claimed in claim 9 in which the component is made from metal.

1 A prop component as claimed in either one of claims 9 to 10 in which the throat in the sleeve is provided by a peripheral indentation in the outer wall of the sleeve.

12. A prop component as claimed in either one of claims 9 to 10 in which the throat in the sleeve is provided by discrete indentations in the outer wall of the sleeve.

13. A prop component as claimed in either one of claims 9 or 10 including two throats which are spaced in an axial direction in the sleeve.

14. A load support prop substantially as herein described with reference to and as illustrated in any of the drawings.

1 5. A component of a load support prop substantially as herein described with reference to and illustrated in any one of Figures 1, 2, 4, 5, 6 and 7 of the drawings.