GB2077808A

GB2077808A - Improvements in props

Info

Publication number: GB2077808A
Application number: GB8015382A
Authority: GB
Original assignee: LONGWALL MINING EQUIPMENT PROP
Current assignee: LONGWALL MINING EQUIPMENT PROP
Priority date: 1980-05-09
Filing date: 1980-05-09
Publication date: 1981-12-23

Abstract

A mining prop is made by encasing a rigid cylindrical core 30 within a sheath 32 of a composite plastics material. The sheath may be made by wrapping a filament around the core, the filament being passed through a bath of the plastics material to coat it. Longitudinal reinforcements may be applied to the core before wrapping. A preferred longitudinal reinforcement is carbon fibre, and the filament may comprise or include such fibre. The core may be of wood or lightweight concrete, and the filament may be glass or metal. Alternatively the sheath may comprise glass reinforced plastics made from chopped strand matting, woven roving, or cloth, and unidirectional rovings. The core may also comprise two or more juxtaposed cylindrical members. <IMAGE>

Description

SPECIFICATION Improvements in Props Field of the Invention The invention relates to props of the kind used in underground mining to support the hanging wall of an excavation, tunnel or stope.

Background of the Invention Props which yield progressively as the load on them increases, without sudden collapse, are an essential accessory in mining. This means that the prop must maintain substantial symmetry about its axis as it yields, and not bend. This requirement becomes more difficult to attain the longer the prop, and current mining practice in which stope and tunnel heights tend to be increased over past practice calls for longer props.

It is an object of the invention to provide a prop which is effective for hanging-wall heights in excess of what has hitherto been regarded as the norm. Another object is to provide a prop which, despite a longer than normal length, is light enough to be handled without undue effort, and which is, moreover, competitive in price.

Statement of the Invention A prop, according to the invention, is made by encasing a rigid core within a sheath composed of or comprising a plastic material. By "plastic material" is meant a plastic material suitable for the purpose of the invention and may include one or more of the family of synthetic resins.

The prop may be made by wrapping a filament of or comprising the plastic material around the core.

The invention includes also props made in accordance with the method of the invention.

The Drawings Several embodiment of the invention are shown in the accompanying drawings in which: Figure 1 is a schematic representation of one manner in which the prop can be made; Figures 2, 3 and 4 are side elevations of different props; and Figure 5 is an end view of a prop with a multiple-element core.

Description of the Illustrated Embodiments In Figure 1 the apparatus for making the prop which is the preferred form of the invention, consists of any suitable frame (not shown) on which is mounted a collet 12 driven by a motor 14, a tailstock 16 and a workpiece mounted between the collet and the tailstock which consists of a length of timber. While the timber is shown as a right cylinder 26, it is to be understood that in practice it will be a length of timber sawn from the stem or a branch of a tree, and either in its natural state or roughly trimmed to approximate right cylindricality, thus economising on the time and cost of machining.

A spool 18 of filamentary material 20 is mounted on the frame, the filament engaging a guide 22 associated with a bath 24 of fluent settable, curable plastic through which the material passes. The guide is mounted to traverse the mounted timber 26 to and fro, to form a multilayer wrapping as the filament is wound on to the timber which will form the core for the prop. The tension of the wrapping may be adjustable, for instance by means of a friction brake on the spool 18.

The speed of rotation of the guide 22 in relation to the rotational speed of the mounted core 26 determines the pitch of the winding, and this, too, is an adjustable variable.

As the filament 20 passes through the bath 24, it picks up a coating of plastic, and the adjoining and superimposed coils of the winding meld to form a strong sheath 32. Preferably, the sheath is iimited to the central section 28 of the core, leaving the ends 30 unsheathed.

Two props manufactured in accordance with the invention are shown in Figures 2 and 3. The former figure illustrates a helically wound prop in which the windings 32 criss-cross each other and form a lattice-type network. In the latter drawing the windings 34 are applied to the core as hoop windings in the way a thread of cotton is wound on to a cotton-reel The prop of the invention is used in the normal manner underground by bracing the prop substantially vertically between the footwall and hanging of an excavation.

If the prop is too short to extend from the hanging to the footwall use is made of one or more wedges in the usual way. On the other hand, if the prop is too long, at least one of the unwrapped ends 30 of the prop can be sawn off.

In either case the prop once installed exhibits at least the following characteristics. When subjected to loads in excess of a certain magnitude the exposed wooden ends of the prop crumple allowing the prop to yield but the central section of the prop is reinforced by the wrapping and does not deform. However, as the load on the prop is further increased the wooden core deforms and eventually a stage is reached at which the wrappings fray progressiveiy. In practical terms this means that the prop yields with a characteristic which is determined initially by the characteristics of the wood only and thereafter by the characteristics of ths wood and of the winding.

The second characteristic can obviously be adjusted by varying the number of windings on the intermediate section, the thickness of the rovings, and the nature of the windings.

An advantage of the invention lies in the fact that the filament 20 can be applied to unshaped lengths of natural timber and machining costs are therefore avoided. Moreover, the wrapping can be applied in a manner which is chosen to suit the particular requirements.

The preferred filamentary materials ars plasticcoated glass fibre but the invention is not limited to this. Any suitable basic material such as steel wire or rope, or the like could be used. It is moreover not essential to spiral-wind the filament around the timber although for ease of application it is preferable to do so. The sheath could, for example, be applied to the timber as separate hoops or closed rings.

The props shown in Figures 2 and 3 are well reinforced against bursting when subjected to a longitudinally applied force. However,they can bend because the circumferential windings do not add greatly to the stiffness of the timber. To counter a tendency of the timber to bend under load, additional longitudinal windings 36 may be applied as shown in Figure 4. These windings are applied substantially at right angles to the circumferential windings 38 and under them, and consequently, when the element is stressed longitudinally and starts bending, the longitudinal windings on the outer radius of curvature of the element are placed in tension, while the longitudinal windings on the inner radius of the curvature of the element are placed in compression. The windings in tension greatly assist in resisting further bending of the prop and effectively increase the stiffness of the prop.The tensions of the several layers may differ.

In another form of the invention, the reinforcing longitudinals are of carbon fibre. Carbon fibre is a filamentary material that is commercially available. It has, per se, considerable tensile strength, but the applicant has found that when impregnated with a resinous material, the tensile strength is substantially increased.

In the preferred form, the carbon fibres are laid lengthwise against the support member. The fibres can be doubled back to form a continuous pattern of parallel threads (depending, of course, upon the length of fibre available), but preferably the fibre is cut into lengths, laid against the support member, and secured in position, for instance, by stapling top and bottom.

This operation having been accomplished, filamentary material carrying the resinous material is wound around the support member. The filamentary winding material may be, and preferably is, carbon fibre, but it may be, for instance, glass fibre.

The applicant has found that props made with carbon fibre longitudinal reinforcing are more efficient than props made with glass fibre, good as the latter are. The carbon fibre reinforced props have very satisfactory resistance to bending under load. This characteristic is of sufficient moment to offset the greater cost of the carbon fibres relatively to the fibre glass. The props are also very satisfactory as regards resistance to fire.

In a different form of the invention the timber element may be reinforced circumferentially, not by means of windings, but simply by means of a circumferential layer of filamentary material. The method of reinforcing used will depend on the required strength of the prop. Again, use may be made of longitudinal windings to increase the bending strength of the prop.

A further advantage of the invention lies in the fact that use may be made of timber elements which individually are too weak to form the support member of a prop. In this case, two or more of the elements are bunched and the wrapping material is applied around the bundle of elements. Figure 5 illustrates in cross section one possible arrangement of this aspect of the invention. Three reiatively thin elongate timber elements 40, 42 and 44 are arranged side by side and the filament 46 is wrapped circumferentially around the bundle. The resultant prop has a cross sectional area which is larger than that of the props of Figures 2 and 3. In addition interstices 48 are formed between the elements 40, 42 and 44 of the sheath. These interstices provide recesses into which the timber elements can expand when under load. This feature influences the yield characteristics of the prop.

The principle embodied in the form of the invention shown in Figure 5 can be utilised in a prop which is made in a different way. In this the sheath may be preformed and the timber elements may be inserted into it. The invention is, therefore, intended to extend to a prop which comprises a sheath which may be preformed of any suitable material, and at least two elongate support elements located in the sheath with their longitudinal axes substantially parallel to each other or to one another.

The core, while preferably of timber, is not necessarily so. It could be of lightweight or foamed concrete, plastic material or even a plastic material including a filler material.

Claims

1. A method of making a prop which includes the step of encasing a rigid core within a sheath composed of or comprising a plastic material.

2. A method according to Claim 1 in which the material is applied as a filament wound circumferentially around the core.

3. A method of Claim 2 in which the material is wound in multi-layers on to the core.

4. A method according to Claim 2 or Claim 3 in which the material is also applied longitudinally to the core.

5. Method according to Claim 4 in which the material applied longitudinally is carbon fibre.

6. A method according to Claim 3 or 4 in which the longitudinals are laid lengthwise of the core and are secured to it top and bottom.

7. The method of Claim 6 in which the longitudinals are secured by stapling.

8. A method according to any one of Claims 2 to 7 in which the plastic is applied as a fluent settable coating on to a thread.

9. A method according to Claim 8 in which the coating is caused or allowed to cure, to provide the sheath.

10. A method according to Claim 9 in which the thread is of glass fibre or metal.

11. A method according to Claim 9 in which the thread is of carbon fibre.

12. A method according to Claim 3 or any of Claims 4 to 11 as dependent on Claim 3 in which the tensions of the sets of windings are different.

13. A method according to any one of the above claims in which the sheath is applied to an intermediate section only of the core, leaving at least one end of the core unsheathed.

14. A method according to any one of the above claims in which the material is applied to at least two intermediate sections of the core which are spaced from one another.

15. A method according to any one of the above claims in which the core is made of wood or concrete.

1 6. A method according to any one of the above claims in which the core is right cylindroidal.

1 7. A method according to any one of the above claims in which the core includes at least two juxtaposed substantially parallel elongate members.

18. A method of making a prop substantially as herein described with reference to the accompanying drawings.

19. A prop made by the method of any one of claims 1 to 17.

20. A prop which consists of a core encased in a sheath composed of or comprising a plastic material.

21. A prop according to Claim 20 in which the material is applied circumferentially to the core.

22. A prop according to Claim 21 in which the material is also applied longitudinally to the core.

23. A prop according to any one of Claims 20 to 22 in which the material is a glass-fibrereinforced synthetic resin.

24. A prop accoring to Claim 23 in which the glass fibre is a chopped strand matting.

25. A prop according to Claim 23 in which the glass fibre consists of chopped strands.

26. A prop according to Claim 23 in which the glass fibre is a woven roving, a woven cloth, a fabric, or a unidirectional roving.

27. A prop according to Claim 22 in which the longitudinals are made of carbon fibre.

28. A prop according to any one of Claims 20 to 27 in which the core is of wood.

29. A prop according to any one of Claims 20 to 27 in which the core is made of concrete.

30. A prop according to Claim 29 in which the concrete is a lightweight or foamed concrete.

31. A prop according to any one of Claims 20 to 30 in which the core consists of at least two juxtaposed substantially parallel elongate elements.

32. A prop according to any of Claims 20 to 31 in which the sheath is applied to an intermediate section only of the core, leaving at least one end of the core unsheathed.

33. A prop substantially as herein described with reference to any one of Figures 2, 3, 4 or 5.