GB2030202A - Mine roof supports - Google Patents

Abstract

A self-advancing, hydraulically powered mine roof support of the kind comprising a base (4), at least one roof beam (2), a plurality of hydraulically extensible chock legs (3) extending between the base (4) and the roof beam(s) (2), a shield (7) provided at a rear of the support, a permanently loaded, force applying means (8) operable in one direction only acting between the shield (7) and the roof beam(s) (2) to apply forward biassing forces thereto, is characterised in that the chock legs (3) are displaceable towards, but not beyond, a vertical position by movement in direction A of a mine roof relative to a mine floor. <IMAGE>

Description

SPECIFICATION Mine roof supports This invention relates to self-advancing, hydraulically powered, mine roof supports, such as are used extensively in longwall coal mining operations.

In longwall mining there usually occurs relative movement between the mine floor and the mine roof and roof supports have been designed to articulate, e.g. from a 50 forwardly inclined position, in order to accommodate such relative movement, firstly to avoid damage to the hydraulically extensible chock legs which extend between the base means of the support and one or more roof beams and secondly to offer some resistance to roof movement, the resistance being provided by the increase in fluid pressure in the chock legs as the latter move towards a vertical condition, and usually a slight retraction of the chock legs if the usual safety relief valve opens upon relief pressure being attained.After a roof support has been so articulated by relative roof and/or floor movement it is necessary to restore the chock legs to a predetermined inclined condition, and in the past this has normally been effected by transmitting a restoring force from the base means and through at least one chock leg to the roof beam(s).However, with shield support which incorporate a shield at their rearward ends, principally to preclude ingress of debris from the goaf to the travelling way along the mineral face, the shield is attached to the roof beam(s) by a lemniscate linkage which allows elements of the shield to move in a vertical plane, but no articulation is allowed, the elements of the shield being of such massive dimensions that if the roof is being extruded rearwards, as is usually the case, the roof slides over the static, non-yielding roof beam, all the forces on the roof beam being transmitted via the shield elements to the base means of the support and hence to the mine floor.It will be appreciated that the dimensions and hence weight and cost of shield elements to perform this function are substantial, while their transportation and assembly underground makes further demands on the limited confines available.

However, in our U. S. Patent No. 4139326 there is described a construction of roof support combining the advantages of both the yielding non-shield supports and non-yielding shield supports, whereby the transmission of restoring forces through the chock legs is avoided, these forces being transmitted from the base means to the roof beam(s) via an interconnecting shield, and it is to a support of this kind that the present invention is directed.

According to the present invention, a selfadvancing, hydraulically powered mine roof support of the kind comprising a base means, at least one roof beam, a plurality of hydraulically extensible chock legs extending between the base means and the roof beam(s), a shield provided at a rear of the support, a permanently loaded, force applying means operable in one direction only on the shield and on the roof beam(s) to apply restoring forces thereto, wherein both the chock legs and the shield are inclined and displaceable towards, but not beyond, a vertical position by relative movement between a mine roof and a mine floor.

Normally, the inclination would be in the forward direction as the normal condition is rearward roof movement. However, on occasion rearward floor movement may be encountered and hence rearward inclination would initially be required.

Preferably, the force applying means is secured to the roof beam and is at least one single acting hydraulic ram, the arrangement being that the maximum permissible leg displacement due to relative movement between the mine roof and the mine floor corresponds to one maximum position of the ram, whether this be extended or retracted. With such an arrangement the shield preferably operates on the lemniscate principle with a pair of links located at each side of the support and serving to connect together the elements of a two-part shield.

Conveniently, the forward inclination is in the range 2" to 80 and preferably is 5 . If two restoring rams are employed, each may conveniently be located at opposite sides of a centre line of the support, and each may be inclined with respect to the centre line so that forward, rearward and lateral displacement forces may all be resisted initially, and if displacement occurs as a result of such forces, restoration effected.

The invention will now be described, in greater detail, by way of example with reference to the accompanying drawings, in which: Figure 1 is a side elevation of a hydraulically powered self-advancing mine roof support according to the invention shown in a first position; and Figure 2 corresponds to Figure 1 but shows the support in a second position.

In the drawings, a mine roof support 1 comprises a roof beam 2 articulated to upper ends of a plurality of hydraulically extensible chock legs 3, in turn articulated at their lower ends to base means 4. The forward end of the roof beam 2 pivotally carries a cantilever 5 urged by a ram 6 into a roof engaging position, as illustrated. The rearward end of the roof support 1 is provided with a shield 7 with a pair of single acting hydraulic rams 8 connected one at each side of the roof support 1 between the roof beam 2 and the shield 7 and serving to urge the roof beam 1 in a forward direction, comprising a lower part 9 fixedly attached to the base means 4 and an upper prt 10 suspended from the roof beam 2, the two parts 9 and 10 being inter-connected by a lemniscate linkage 11.The pivot points of the linkage are so arranged that, as shown in Figure 1, it is possible to give 5" forward inclination not only to the chock legs 3, but also to the shield 7, so that the latter, as the support 1 is displaced from the position shown in Figure 1 to the position shown in Figure 2 by relative movement between the mine roof and floor, i.e. by considering the roof as moving in the direction of arrow A, both the chock legs and the shield are rotated tothe vertical and terminal position shown in Figure 2. It is anticipated, of course, that before the Figure 2 position is attained the chock legs 3 are de-pressurised and the support 1 advanced, in accordance with standard longwall mining practice, the urge of the rams 8 on the roof beam 2 restoring the latter to its Figure 1 position. It will be appreciated that it may be desirable to increase or decrease the 5 inclination in accordance with particular strata conditions.

Claims (8)

1. A self-advancing, hydraulically powered mine roof support comprising a base means, at least one roof beam, a plurality of hydraulically extensible chock legs extending between the base means and the roof beam(s), a shielf provided at a rear of the support, a permanently loaded; force applying means operable in one direction only on the shield and on the roof beam(s) to apply restoring forces thereto, both the chock legs and the shield being inclined and being displaceable towards, but not beyond, a vertical position by relative movement between a mine roof and a mine floor.

2. A roof support as claimed in Claim 1,wherein the force applying means is secured to the roof beam and is at least one single acting hydraulic ram.

3. A roof support as claimed in Claim 1 or Claim 2, wherein the shield operates on the lemniscate principle with a pair of links located at each side of the support and serving to connect together the elements of a two-part shield.

4. A roof support as claimed in any one of Claims 1 to 3, wherein the chock legs and the shield are inclined forwardly in the range 2" to 8".

5. A roof support as claimed in any one of Claims 1 to 3, wherein the chock legs and the shield are inclined forwardly 5 .

6. A roof support as claimed in any preceding Claim, comprising two restoring rams each located at opposite sides of a centre line of the support.

7. A roof support as claimed in Claim 6, wherein each restoring ram is inclined with respect to the centre line.

8. Aself-advancing, hydraulically powered mine roof support substantially as hereinbefore described with reference to the accompanying drawings.