US3218812A

US3218812A - Mobile mine roof support

Info

Publication number: US3218812A
Application number: US194386A
Authority: US
Inventors: Wilkenloh Wilhelm
Original assignee: Rheinstahl Wanheim GmbH
Current assignee: Rheinstahl Wanheim GmbH
Priority date: 1961-05-13
Filing date: 1962-05-14
Publication date: 1965-11-23
Anticipated expiration: 1982-11-23
Also published as: GB985401A

Description

Nov. 23, 1965 w. WILKENLOH 3,218,812

MOBILE MINE ROOF SUPPORT Filed May 14, 1962 2 Sheets-Sheet 1 .9 n a MMI Y .Q5 .A n a fk# 3 um .lw Nw R P. U J r x T n a. A @HU J .w a RL S nh .a M u, .1 n n ,WH

Nov. 23, 1965 w. wlLKENLol-l MOBILE MINE ROOF SUPPORT 2 Sheets-Sheet 2 Filed May 14., 1962 United States Patent Ofi 3,218,812 Patented Nov. 23, 1965 .Lice

3,218,812 MOBILE IVHNE ROOF SUPPORT Wilhelm Wilkenloh, Duisburg-Weilheim, Germany, assignor to Rheinstahl Wanheim G.m.b.H., Duisburg- Wanheim, Germany Filed May 14, 1962, Ser. No. 194,386 Claims priority, application Germany, May 13, 1961, R 39,332 Claims. (Cl. 61-45) The present invention relates to mine roof supports, and more particularly to an improved mobile mine roof support which is especially suited for use in underground excavations whose floors consist of comparatively soft, comminuted or other yieldable material. It is well known that the floor contacting elements of a mine roof support often penetrate into the material of the mine floor so that it is rather ditiicult, if not impossible, to rapidly advance the mine roof support to a new position. Furthermore, it happens rather frequently that the material which is separated from the mine face or which drops from the mine roof accumulates on the Hoor contacting elements of the mine roof support so that it becomes necessary to remove such accumulations of material before the mine roof support can be moved along the mine door. Finally, the mine oor is frequently uneven, i.e., it has depressions and protuberances which might reach such dimensions that they prevent the floor contacting elements from passing thereover when the mine roof support is to be shifted toward the mine face. However, the forward movement of the mine roof support is normally hindered to a lesser degree by the unevenness of mine oor than by sinking of the floor contacting elements at the time the roof engaging cap or caps are in supporting engagement with the mine roof and carry a heavy load of rock, ore or the like.

Accordingly, it is an important object of the present invention to provide a mobile multi-prop mine roof support which is constructed and assembled in such a way that it can rapidly and conveniently extricate and lift its floor engaging elements prior to advancing along the mine floor.

Another object of the invention is to provide a mine roof support of the just outlined characteristics whose props, in addition to enabling the cap or caps to become separated from or to move into supporting engagement with the mine roof, may also serve as a means for extricating and lifting the door engaging elements of the mine roof support before the latter is caused to move toward the mine face.

A further object of the present invention is to provide a multi-prop mine roof support of the above described type whose cap or caps are constructed and assembled in such a way that they can support one or more extensible and contractible props in suspended position as long as at least one prop remains extended to maintain the cap or caps in supporting engagement with the mine roof.

An additional object of my invention is to provide a composite cap for a mine roof support Whose component parts are capable of performing movements with respect to each other so `as to assume optimum supporting positions when they engage the mine roof but which is still strong enough to support one or more props in suspended position and to withstand the weight of material which might have accumulated on the oor engaging elements of the props, such material normally tending to prevent extraction of the lioor engaging elements when the props are caused to contract.

Still another object of the invention is to provide a mobile mine roof support wherein the control system which regulates the extension and contraction of the props and/or the forward movement of the mine roof support may also serve as a means for regulating the extraction of floor contacting elements before the mine roof support is caused to advance along the mine oor.

A concomitant object of the invention is to provide a method of extracting and lifting the licor engaging lower portions of props in a multi-prop mine roof support.

With the above objects in view, the invention resides in the provision of a mobile mine roof support which comprises at least two extensible and contractible pit props each of which has at least two relatively movable portions including an upper portion and a oor engaging lower portion; and a one-piece or composite roof engaging cap which is connected with the upper portions of the props and which is adapted to support one of the props in suspended position and to thereby lift the respective floor engaging lower portion above the mine floor when the other prop is extended and causes the cap to supportingly engage the mine roof, whereby any depressions formed by the floor engaging portions may be iilled in by the operators or are filled automatically by avalanching of the material of which the mine floor consists while the lower portions are alternately lifted above the mine lioor so that, after descending into renewed contact with the mine door, the lower portions will be located at the general level of the mine floor and will not hinder forward movements of the mine roof support. The props are alternately suspended on the cap means so that the respective oor engaging lower portions are lifted above the oor and permit filling of the depressions if the depressions made by the momentarily lifted lower portions are of such depth that they could hinder forward movements of the mine roof support. If the apparatus comprises two or more pairs of props, one or more pairs of props may be suspended simultaneously as long as the cap remains in supporting engagement with the roof and as long as the cap is strong enough to maintain two or more props in suspended position.

The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be 'best understood from the following detailed description of certain specific embodiments with reference to the accompanying drawings, in which:

FIG. l is a side elevational View of a mobile four-prop mine roof support which comprises a composite cap and which embodies one form of my invention;

FIG. 2 is a top plan view of the mine roof support;

FIG. 3 is a transverse section as seen in the direction of arrows from the line III- III of FIG. 2;

FIG. 4 is an enlarged axial section through a pit prop which forms part of the mine roof support shown in FIGS. 1 to 3; and

FIG. 5 is a fragmentary side elevational view of a modified mine roof support which comprises a single pair of props and a one-piece roof engaging cap.

Referring now in greater detail to the illustrated embodiments, and first to FIGS. l to 3, there is shown a mobile mine roof support which comprises four extensible and contractible pit props including two transversely aligned leading props 1, 2 and two transversely aligned trailing props 3, 4. Each of these props comprises a tubular lower portion 5 and a tubular upper portion 6, the former constituting a cylinder and the latter constituting a piston rod which extends into and which is reciprocable in the respective cylinder. The upper portions 6 of the props 1 to 4 are articulately connected with a composite roof engaging cap 7 whose exact construction, excepting for the feature that it is strong enough to support at least two props in suspended position, forms Vno part of the present invention. This cap is disclosed in the copending application Serial No. 189,114 of Karl Barall 3 and Wilhelm Wilkenloh to which reference may be had if necessary. The construction of the cap 7 will be described only to the extent necessary for full understanding of my present invention.

As best shown in FIG. 2, the cap 7 comprises four roof engaging members or

roof bars

8, 9, 10, 11 which assume the form of comparatively large metallic plates and which are respectively secured to the upper portions 6 of the props 1, 2, 3 and 4. The connections 12 between the roof bars 8 to 11 and the respective upper prop portions 6 may assume the form of conventional universal joints so that the roof bars are tiltable to a certain extent in all directions with respect to but remain connected with the portions 6. This is of advantage because the roof bars automatically nd such positions of inclination in which they engage large surface areas of the mine roof 69 (see FIG. l) so that the loads transmitted by the roof to the mine roof support cannot be concentrated in a few areas to cause deformation and eventual destruction of the apparatus.

The roof bars 8 to 11 are connected to each other by four special couplings including a rst pair of couplings 13, 14 which respectively connect the roof bars S, 9 with the

roof bars

10, 11 and a second pair of

couplings

15, 16 which respectively connect the roof bars 8, with the

roof bars

9, 11. The coupling 13 is shown in greater detail in FIG. l, and it will be noted that the component parts of this coupling are carried by a pair of downwardly extending apertured connecting portions or anges 17, 18 the former of which is integral with or secured to and is located at the rear end of the roof bar 8 and the latter of which is integral with or secured to and is located at the forward end of the roof bar 10 so as to normally abut against the connecting portion 17 when the composite cap 7 is caused to descend and does not engage the mine roof 69. One of or both connecting portions 17, 18 are provided with elongated preferably vertically extending slots 19 (see FIG. 3), for a bolt 20 which meshes with a nut 21 and which carries a pair of

washers

22, 23 at the outer sides of the connecting portions 17, 18. A biasing means in the form of a helical spring 24 is interposed between a third washer 74 (which engages the head of the bolt and the Washer 22 so as to normally bias the connecting portions 17, 18 into faceto-face abutment with each other. Since the bolt 20 is slidable in the longitudinal direction of the slots 19 and since the spring 24 yields to a certain pressure, the leading roof bar 8 may be moved to the phantom-line inclined position 8 of FIG. l or to the phantom =line lposition 8" of FIG. 3. the coupling 13 permits similar displacements of the roof bar 10 with respect to the roof bar 8. The strength of the spring 24 is selected in such a way that it can maintain the roof bar 8 in the full-line position of FIG. 1 even if the drop 1 is caused to contract so as to be suspended from the roof bar 8 and to lift a oor engaging element in the form of a sole plate 25 which is secured to its lower portion 5 above the mine iloor 26 as long as the prop 3 remains extended in order to maintain the roof bar 10 and hence the

roof bars

8, 9 and 11 in supporting engagement with the mine roof 69.

The coupling 14 between the downwardly extending apertured connecting portion 27 at the rear end of the roof bar 9 and the downwardly extending apertured connecting portion 28 at the forward end of the roof bar 11 is identical with the coupling 13 and, therefore, is indicated only schematically in FIG. 2 of the drawings.

The coupling 16 is shown in FIGS. 2 and 3, and it will be noted that this coupling is carried by a downwardly extending apertured connecting portion 29 which is provided along the inner longitudinal edge portion of the roof bar 10 and by a similar apertured connecting portion 30 which is provided along the inner longitudinal edge portion of the roof bar 11. These connecting portions are formed with vertically extending slots 19 to Of course, it will be readily understood that receive the bolt 20 of the coupling 16. All component parts of the coupling 16 are identical with those described in connection with the coupling 13 and are identified by similar reference characters. The coupling 15 between the apertured connecting

portions

31, 32 of the respective leading roof bars S, 9 is identical with the coupling 16.

The

roof bars

8, 9 are respectively provided with forwardly extending

lugs

33, 34 which are articulately connected with

front shields

35, 36 by means of

horizontal pivot pins

37, 38. The tips of the

lugs

33, 34 are formed with downwardly and forwardly inclined cam faces which engage with wedges 39 extending through arcuate apertures provided in the rearwardly extending arms 41, 42 of the respective front shields. In such manner, the

shields

35, 36 are maintained in supported engagement with the mine roof 69 to prevent descent of rock or ore onto the customary conveyer 43 which is normally located in front of the leading props 1, 2 and which serves as a means for conveying the material which is being removed from the mine face 44.

The rear `ends of the

trailing roof bars

10, 11 are respectively connected with

rear shields

45, 46 whose purpose is to prevent the lling from descending into the area occupied by the mine roof support.

The manner in which the floor engaging sole plate 25 is secured to the lower portion 5 of the prop 1 is shown in FIG. l. The bottom part of the portion 5 is received in and is rigidly secured to a sleeve 50. This sleeve is vertically reciprocably guided in a pair of spaced rings 51 which are secured to an upwardly and forwardly inclined intermediate portion 52 of a slightly elastic Hoor contacting connecting plate or main support 49 by means of cotter pins 53 or the like. The lower end of the sleeve forms a cup 54 which receives a ball 55 secured to the sole plate 25 so that the sleeve and the ball 55 together constitute a ball and cup joint for the sole plate. The front portion 56 of the sole plate is bent upwardly whereby the latter resembles a runner and is capable of passing over protuberances in the mine floor 26. This front portion 56 carries a pair of apertured brackets 57 (only one shown in FIG. l) for a horizontal pin 58 secured to the lower end of a vertical bolt 59 which is slidably guided in a pair of vertically spaced rings 60, the latter secured to the rear side of a reinforcing plate or traverse 61. This traverse extends substantially to the level of the mine floor 26 and is secured to a box-like receptacle 62 which constitutes the foremost part of the connecting plate 49 and which extends forwardly of the portion 52 and between the leading props 1 and 2. In addition to supporting the rings 60, the traverse 61 also performs the function of a bulldozer blade or grader in that it evens out the mine floor 26 when the mine roof support is caused to advance toward the mine face 44. The extent to which the bolt 59 may reciprocate in the rings 60 is determined by a second horizontal pin 63 which is secured thereto at a point above the upper ring 60. The

rings

51 and 60 enable the sole plate 25 to reciprocate with the prop 1 relative to the connecting plate 49 to the extent determined by the pins 75 on the sleeve 50 and the

pins

58, 63 on the bolt 59. In addition, the joints 54, enables the sole plate 25 to become tilted with respect to the prop 1 in order to move into large-area contact with an uneven mine floor.

The connection betwen the sole plate 64 (see FIG. 3) of the other leading prop 2 and the connecting plate 49 is analogous and, therefore, is not shown in the drawings.

A third sole plate 65 is secured to a sleeve 50' on the lower portion 5 forming part of the trailing prop 3 by means of a ball and cup joint 55', 54 which is shown in FIG. l. The sleeve 50 is vertically reciprocably guided in a pair of rings 51 which are secured to an upwardly and rearwardly inclined portion 66 of the connecting plate 49 by means of cotter pins 53. The upwardly bent front portion 67 of the sole plate 65 carries a pair of brackets 57 for a horizontal pin 58 which is secured to the lower end of a vertical bolt 59. This bolt is slidable in a pair of spaced rings 60 secured to the portion 66 of the connecting plate 49. A horizontal pin 63' cooperates with the pin 58 to limit axial movements of the bolt 59. The connection between a fourth sole plate and the lower portion of the second trailing prop 4 is analogous and is not shown in the drawings.

The mine roof support may be advanced by means of a double-acting hydraulic cylinder 70 which extends between the props 1, 3 and 2, 4 in the longitudinal direction of the apparatus and whose piston rod 71 is coupled to the conveyor 43. The cylinder 70 extends through the aforementioned leading receptacle 62 and through a similar receptacle 68 formed by the rear portion of the connecting plate 49 between the trailing props 3 and 4. The connection between the cylinder 70 and the walls of the leading receptacle 62 preferably assumes the form or" a Cardan joint.

The exact construction of the sole plates, of the connecting plate 49, of the traverse 61 and of other parts shown in the lower part of FIG. l is disclosed in the copending patent application Serial No. 155,109 of Wilhelm Wilkenloh and Karl Barall to which reference may be had if necessary.

FIG. l further shows the manner in which the

sole plates

25, 65 are likely to penetrate into the material of the mine oor 26 when the composite cap 7 is in supporting engagement with the mine roof 69. The sole plates form comparatively deep depressions 72, 73 and respectively assume the positions 65 which are shown in dotted lines.

FIG. 4 illustrates the leading pit prop 1, in axial section. The upper tubular portion 6 of this prop carries at its lower end an annular piston 80 which is slidable in the lower portion 5. The lower end of the tubular portion 5 is Welded to a base plate 81 and, at its upper end, the portion 5 carries a sealing ring structure 82 which slidably receives the upper portion 6. The upper end of the portion 6 is secured to a header 83 which is provided with a pair of

nipples

84, 85 connected to conduits 79 leading to the pressure side of a pump 78 which draws pressure fluid from a source 77. The base plate 81 supports an internal cylinder 86 which extends with play through the piston 80 and whose upper end is sealed by an annular end plate 87 which slidably receives a hollow piston rod 88, the latter secured at its upper end to the header 83 and at its lower end to a second piston 89 which is slidably received in the internal cylinder 86. Adjacent to the piston S9, the piston rod 88 is provided with ports 90 which permit communication of pressure fluid between the internal space 91 of the piston rod 88 and the upper chamber 92 in the cylinder 86, i.e. that chamber of this cylinder which extends between the piston 89 and end plate 87. The lower chamber 93 of the tubular portion 5 communicates with the internal space 94 of the upper portion 6 through the annular clearance 95 between the periphery of the cylinder 86 and the piston 80. The compartment 96 in the cylinder 86 beneath the piston 89 communicates with the atmosphere through a bore 97 provided in the base plate 81. It will be noted that the

nipples

84, 85 respectively communicate with the internal space 94 and with the internal space 91. The part 98 of the tubular portion 6 above the header 83 constitutes an element of the joint 12 between the prop 1 and roof bar 8.

In order to expand the prop 1 and to thereby move the roof bar 8 into rm supporting engagement with the mine roof 69, the pressure side of the pump 78 is connected with the nipple 84 through a distributor valve 76 whereby the pressure uid entering the space 94 and passing through the clearance 95 into the lower cylinder chamber 93 acts against the underside of the piston 84) and expels the tubular portion 6 in upward direction. At the same time, uid contained in the upper cylinder chamber 92 is permitted to flow through the ports 90, through the internal space 91 and is discharged through the nipple 85, through the valve 76, and through a return line 79a. A pressure relief valve 76a in the conduit connecting the nipple 84 with the pump 78 permits return llow of pressure fluid through the line 79a and to the source 77 when the lluid pressure in the chamber 93 reaches a predetermined maximum value, i.e. when the tubular portion 6 has moved the roof bar 8 into satisfactory supporting engagement with the mine roof.

The prop 1 contracts or collapses automatically if the operator connects the pump 7S with the nipple 85 and if the uid lling the chamber 93 is permitted to escape through the nipple 84 and through the line 79a. When the nipple admits pressure iluid, the fluid acts against the upper side of the piston 89 and against the underside of the end plate 87 to move the cylinder 86 and the tubular portion 5 upwardly, it being assumed that the roof bar 8 remains in abutment with the mine roof 69 because the trailing props 3, 4 remain in expanded position. The tubular portion 5 then lifts its sole plate from the phantom-line position 25 to the full-line position 25 of FIG. 1 whereby the operator may till up the depression 72 so that the sole plate 25 now rests on the material which was introduced into this depression. As stated before, it is often unnecessary to actually fill the depression 72 because it is filled by avalanching of material surrounding the sole plate 25.

The construction of the hydraulic expanding and contracting means in the props 2, 3 and 4 is analogous to the construction of PIG. 4. As a rule, the operator will simultaneously contract the leading props 1, 2 while the trailing props 3, 4 remain in expanded position. The springs 24 of the couplings 13, 14 are strong enough to maintain the leading

roof bars

8, 9 in actual abutment with or close to the mine roof 69, i.e. the springs 24 of the couplings 13, 14 are strong enough to maintain the leading props 1, 2 and their respective sole plates 25, 64 in suspended position as long as the trailing roof bars 10, 11 remain in rm supporting engagement with the mine roof. Once the leading sole plates 25, 64 come to rest on the material while now lls the respective depressions, the operator again admits pressure uid to the nipples 84 of the leading props 1, 2 so that these props expand and maintain the leading

roof bars

8, 9 in engagement with the mine roof 69 while the trailing props 3, 4 are caused to contract so that the operator or operators may fill in the depressions which were formed by the trailing sole plates.

The mine roof support is advanced as follows:

Once the depressions formed by the foul sole plates are filled in, the operator causes the leading and/or t-he trailing props to expand so that the respective roof bars engage the mine roof 69 and prevent displacements of the cylinder 70. In the next step, fluid is admitted to the rear chamber of the cylinder 70 in order to expel the piston rod 71 and to move the conveyer 43 toward the mine face 44. The four props are then caused to contract in order to move the composite cap 7 out of actual engagement with the mine roof 69 and, as soon as pressure fluid is permitted to enter into the front chamber of the cylinder 70, the entire mine roof support is dragged toward the conveyer 43 until the piston rod 71 is again withdrawn into the cylinder 70. The mine roof support is then ready to engage a new section of the mine roof.

The pump 78 which operates the hydraulic systems of the props 1 to 4 may also serve as a means for supplying pressure fluid to the cylinder 70. This pump is a stationary structure which is normally mounted in the mine shaft to the rear of t-he mine roof support.

The purpose of the bore 97 is to prevent the compartment 96 from developing partial vacuum when the prop 1 expands and the piston 89 moves in upward direction.

It will be readily understood that the hydraulic system for the props 2-4 and for the cylinder 70 comprises a series of suitable pressure relief and distributor valves and other auxiliaries which are usually accommodated in a single valve block, not shown. This valve block may be mounted directly on the mine roof support or at a safe distance therefrom.

It was found that it is often suicient to lift the leading sole plates 25, 64 and thereupon the trailing sole plates for very short periods of time, particularly if the depressions formed by the sole plates are comparatively shallow. The self-filling action of comminuted material surrounding the depressions is almost instantaneous so that the temporarily lifted props may be immediately reextended to move the respective sole plates into renewed contact with the mine floor.

Referring again to FIG. 4, it will be noted that, in normal operation (i.e. when the prop 1 is expanded), the

chambers

92, 93 may remain under constant pressure. In other words, the

nipples

84, 85 may remain connected simultaneously to the pressure side of the pump 78. Since the effective surface of the piston 80 and base plate S1 is greater than the effective surface of the parts 87, 89, the fluid filling the chamber 93 will automatically retain the prop 1 in extended position. When the operator wishes the prop to collapse, he merely disconnects the nipple 84 from the pump 78 by operating the valve 76 or opens a suitable bypass valve so that the fluid may escape from the chamber 93 whereby the fluid filling the chamber 92 immediately lifts the tubular portion 5 in upward direction to reduce the overall length ofthe prop and to lift the sole plate 25 above the mine floor.

FIG. illustrates a portion of a greatly simplified mine roof support which comprises only two pit props including a leading prop 100 and a trailing prop 101. These props are articulately connected with a one-piece cap 102 which assumes the form of a comparatively rigid plate. The manner in which the

props

100, 101 are extensible and contractible is the same as described in connection with FIG. 4. It is assumed that this mine roof support does not comprise an advancing cylinder such as the cylinder 70 of the mine roof support shown in FIGS. 1 to 3. Therefore, the modified mine roof support must be advanced by an independent advancing device of any known design which is not shown in the drawings.

When the sole plate of the trailing prop 101 is in firm engagement with the mine iloor and when the prop 101 is expanded, the cap 102 is automatically retained in supporting engagement with the mine roof so that the leading prop 100 may be caused to collapse and remains suspended on the cap 102. In other words, here again,

the cap 102 must be strong enough to maintain the leading prop 100 in suspended position when the trailing prop is expanded, and vice versa. Once the depression formed by the sole plate of the prop 100 is filled up, the prop 100 is reextended and the operator then collapses the trailing prop 101 in order to fill the depression formed by the trailing sole plate. It is necessary that the sole plates of the leading and trailing props should have freedom of relative movement with respect to each other to make sure that the leading sole plate or plates may be lifted when the trailing sole plate or plates remain in engagement with the mine floor, and vice versa. Of course, it will be readily understood that, owing to the provision of a four-piece cap 7, the mine roof support of FIGS. 1 to 3 may be brought to a position in which it is ready to advance toward the mine face 44 by first lifting the longitudinally aligned props 1, 3 and by thereupon lifting the similarly aligned props 2, 4 or vice versa. In other words, it is not necessary to first suspend the leading props and thereupon the trailing props because the movability of roof bars 8, with respect to the roof bars 9, 11 is substantially the same as the movability of

roof bars

8, 9 with respect to the roof bars 10, 11.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by

applying knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic and specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. A mine roof support comprising, in combination, two extensible and contractible pit props each having two relatively movable portions including an upper portion and a floor engaging lower portion; fluid operated means operatively connected to said props for moving the portions of `said props with respect to each other; roof engaging cap means comprising two articulately connected sections each secured to the upper portion of one of said props; and biasing means arranged to bias one of said sections in a direction toward the mine roof when the other section engages the mine roof in response to extension of the respective prop, said biasing means being of such rigidity and strength that said one section can support, without substantial turning relative to said other section, the corresponding prop in suspended position when said corresponding prop is contracted to lift its lower portion above the mine floor whereby any depressions formed by said lower portions in the mine floor may be filled in -before the mine roof support is moved along and while the lower portions of the props are alternately lifted above the mine floor.

2. A mine roof support as set forth in claim 1, wherein the fluid operated means -comprises a single source of pressure fluid, said single source being arranged to supply pressure fluid for extending as well as for contracting said props.

3. A mine roof support, as set forth in claim 1, wherein said props comprise a plurality of relatively movable fluid containing cylinders wherein fluid is maintained at an elevated pressure.

4. A mine roof support as set forth in claim 1, wherein each of said articulately connected sections which form said roof engaging cap means is articulately connected with the upper portion of one of said props.

5. A mine roof support as set forth in claim 4, wherein the biasing means are springs.

6. A mine roof support as set forth in claim 4, Wherein the articulate connection between said sections comprises slotted connecting portions provided on said sections and adjacent to each other, bolt means loosely extending through said connecting porticns, and resilient means on said bolt means for biasing said connecting portions into abutment with each other.

7. A mobile mine roof support, comprising, in combination two extensible and contractible pit props each having two relatively movable portions including an upper portion and a lower portion; fluid operated means operatively connected to said props for moving the portions of said props with respect to each other; a floor contacting element provided on the lower portion of each prop; roofengaging cap means comprising two articulately connected sections, each section secured to the upper portion of one of said props; resilient means arranged to bias one `of said sections in a direction toward the mine roof when the other section engages the mine roof in response to extension of the respective prop, said biasing means being of such rigidity and strength that said one section can support, without substantial turning relative to said other section, the corresponding prop in suspended position when said corresponding prop is contracted to lift its lower portion above the mine oor so that any depression formed in the mine floor by said floor contacting elements may be filled in while the floor contacting elements are lifted above the mine floor; a floor contacting main support disposed intermediate said floor contacting elements; and means articulately connecting said main support with said elements so that said elements may be lifted while said main support remains in contact with the mine oor.

8. A mobile mine roof support comprising, in combination, two extensible and contractible pit props each having two relatively movable portions including an 4upper portion and a lower portion; fluid operated means operatively connected to said props for moving the portions of said props with respect to each other; a floor contacting element provided on the lower portion of each prop; roofengaging cap means comprising two articulately connectcd sections, each section secured to the upper portion of one of said props; resilient means arranged to bias one of said sections in a direction toward the mine roof when the other section engages the mine roof in response to extension of the respective prop, said biasing means being of such rigidity and strength that said one section can support, without substantial turning relative to said other section, the corresponding prop in suspended position when said corresponding prop is contracted to lift its lower portion above the mine floor so that any depressions formed in the mine oor by said floor contacting elements may be lled up While the floor contacting elements are lifted above the mine oor; a oor contacting main support disposed intermediate said floor contacting elements; means articulately connecting said main support with said elements so that said elements may be lifted while the main support remains in contact with the mine floor; and ring means for vertically reciprocably receiving the lower portions of said props, said ring means secured to said main support.

9. A mobile mine roo-f support comprising, in combination, two extensible and contractible pit props each having two relatively movable portions including an upper portion and a lower portion; iluid operated means operatively connected to said props for moving the portions of said props with respect to each other; a iloor contacting element provided on the lower portion of each prop; roof-engaging cap means comprising two articullately connected sections, each section secured to the upper portion of one of said props; resilient means arranged to bias one of said sections in a direction toward the mine roof when the other section engages the mine roof in response to extension of the respective prop, said biasing means being of such rigidity and strength that said one section can support, without substantial turning relative to said other section, the corresponding prop in suspended position when said corresponding prop is contracted to lift its lower portion above the mine iloor so that any depressions formed in the mine iioor by said oor contacting elements may be filled in While the oor contacting elements are lifted above the mine oor, each `of said lloor contacting elements having an upwardly bent front portion to facilitate its movements along the mine floor.

it?. A mobile mine roof support comprising, in combination, two extensible and contractible pit props each having two relatively movable portions including an upper portion and a lower portion; fluid operated means operatively connected to said props for moving the portions of said props with respect to each other; a floor contacting element provided at the lower portion of each prop; universal joints articulately connecting said door contacting elements with the respective lower portions; roof-engaging cap means comprising two articulately connected sections, each section secured to the upper portion of one of said props, resilient means arranged to bias one of said sections in a direction toward the mine roof when the other section engages the mine roof in response to extension of the respective prop, said biasing means being of such rigidity and strength that said one section can support, without substantial turning relative to said other section, the corresponding prop in suspended position when said corresponding prop is contracted to lift its lower portion above the mine floor so that any depression formed in the mine floor by said Hoor contacting elements may be lled in while the floor contacting elements are lifted above the mine tloor.

References Cited by the Examiner UNITED STATES PATENTS 2,795,935 6/ 1957 Fitzgerald 61-45.2 3,115,754 12/1963 Joseph 61-45 EARL I. WITMER, Primary Examiner. JACOB NACKENOFF, Examiner.

Claims

1. A MINE ROOF SUPPORT COMPRISING, IN COMBINATION, TWO EXTENSIBLE AND CONTRACTIBLE PIT PROPS EACH HAVING TWO RELATIVELY MOVABLE PORTIONS INCLUDING AN UPPER PORTION AND A FLOOR ENGAGING LOWER PORTION; FLUID OPERATED MEANS OPERATIVELY CONNECTED TO SAID PROPS FOR MOVING THE PORTIONS OF SAID PROPS WITH RESPECT TO EACH OTHER; ROOF ENGAGING CAP MEANS COMPRISING TWO ARTICULATELY CONNECTED SECTIONS EACH SECURED TO THE UPPER PORTION OF ONE OF SAID PROPS; AND BIASING MEANS ARRANGED TO BIAS ONE OF SAID SECTIONS IN A DIRECTION TOWARD THE MINE ROOF WHEN THE OTHER SECTION ENGAGES THE MINE ROOF IN RESPONSE TO EXTENSION OF THE RESPECTIVE PROP, SAID BIASING MEANS BEING OF SUCH RIGIDITY AND STRENGTH THAT SAID ONE SECTION CAN SUPPORT, WITHOUT SUBSTANTIAL TURNING RELATIVE TO SAID OTHER SECTION, THE CORRESPONDING PROP IN SUSPENDED POSITION WHEN SAID CORRESPONDING PROP IS CONTRACTED TO LIFT ITS LOWER PORTION ABOVE THE MINE FLOOR WHEREBY ANY DEPRESSIONS FORMED BY SAID LOWER PORTIONS IN THE MINE FLOOR MAY BE FILLED IN BEFORE THE MINE ROOF SUPPORT IS MOVED ALONG AND WHILE THE LOWER PORTIONS OF THE PROPS ARE ALTERNATELY LIFTED ABOVE THE MINE FLOOR.