GB1569165A - Frame for supporting an underground drivage - Google Patents

Description

(54) FRAME FOR SUPPORTING AN UNDERGROUND DRIVAGE (71) We, BOCEXUMER ElsENHurrE HEUfE > ANN G.m.b.H. & Co., of No. 80, Bessemerstrasse, 463 Bochum, Federal Republic of Germany, a company organised under the Laws of the Federal Republic of Germany, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:: - This invention relates to a frame for sup porting an underground drivage, comprising at least two channel sections of which the neighbouring ends are interposed to form a lapped joint which is frictionally tightened by at least one clamp consisting of a top strap member and a bottom strap member connected together by bolts and nuts.

The clamps which are used in this type of support usually have arching substantially U-shaped strap members formed with a flange at each end projecting laterally in the longitudinal direction of the drivage or road. The so-called top strap member spans the back of the channel section nearest the rock, whereas the bottom strap member spans the section facing the inside of the drivage or road. When the two strap members engage the trough sections the flanges of the top and bottom strap members are some distance apart. In order to connect the two strap members and to clamp the channel sections together, bolts are passed through holes in the flanges and secured by nuts.The torque applied to the nuts for tightening the bolts of the clamp must be sufficient to ensure that the lapped trough sections before they begin to slide will offer the required frictional resistance to the roof and sides of the drivage.

Although this type of clamp joint between lapped substantially U-type channel sections is successfully used for support frames, such as arches, which are intended within limits to yield by allowing the joints to slide, considerable damage due to wear.

generally by the metal seizing, is found in practice to occur between the contacting surfaces and particularly between the nuts and the surfaces of the flanges of the bottom strap member which cooperate -with the nuts.

One reason for this type of surface damage on the bottom flanges and on the-nuts is the difference in the nature of the cooperating surfaces. Whereas the surfaces of the bottom strap members which are made from rolled sheet or rolled sections, or forged, are relatively rough, the sides of the nuts facing the bottom strap members are fairly smooth having been plastically formed or machined. An other reason for the surface damage is the high specific surface pressure generated by the considerable torque which is applied to clamp the trough sections sufficiently tightly together to withstand the roof or side pressure before- slidably yielding. The surface damage is aggravated by the fact that only part of the face of the nut near its periphery makes contact with the surface of the bottom strap member.This leads to the generation of high line or point loads. The reason for this partial contact between the nut and the bottom strap member is the scalled skew drawing effect". The parts that are to-be pulled tight-in the present instance the projecting flanges of the upper and bottom strap membersare relatively spaced and when the nuts are tightened they do-not.re- tain their parallelism but assume a position of relative inclination, including an acute Vee-angle between them.

Besides this type of surface damage another major drawback is that the required tightening torque for clamping the -interposed trough sections is in fact applied to the nuts but not fully utilised for tightening the joint because there is a considerable frictional loss between the nuts and/or bolts and the strap members of the clamp. An uncontrolled fraction of the applied torque is taken up by friction, particularly between the nuts and the bottom strap member and this is lost as an effectively transmitted clamping torque although it would be needed for achieving an exactly determined clamping pressure as would -be desirable to control the roof in a predictable way. The yielding load which is substantially determined by the tightening -torque is therefore reduced by an amount which is not amenable to calculation or measurement.

It is therefore the object of the present invention to provide a clamped joint for lapped trough sections used for roof sup ports in underground drivages, in which the yielding resistance of at least two interposed trough sections can be determined with a high degree of accuracy by reference to the torque that is applied for pulling the clamp tight.

To attain this object the present invention provides a frame for supporting an underground drivage, comprising at least two channel sections of which the neighbouring ends are interposed to form a lapped joint which is frictionally tightened by at least one clamp consisting of a top strap member and a bottom strap member connected together by bolts and nuts, and wherein there is provided on at least parts of the contacting surfaces of the nuts and/or the heads of the bolts, on the one hand, and of the clamp which the nuts and/or bolt heads engage, on the other hand, a medium which has friction-reducing properties.

The incorporation of media having friction-reducing properties between the contacting parts, for instance between the nut and the bottom strap member, considerably lowers the frictional resistance between the engaging parts. Tests have confirmed the technological advantage which this inventive thought is capable of providing. The yielding resistance could be raised by as much as 25 percent above the figures hitherto achieved because the energy of the tightening torque which had in the past been partly consumed by the friction between the engaging parts could not be much more efficiently transmitted through the screw connection and utilised for clamping the trough sections more tightly together. Consequently the yielding resistance can be more predictably and more accurately controlled and a safe support system can be thus assured.

The friction-reducing medium can be disposed between the contacting parts in diverse ways. In a preferred embodiment of the invention the medium may be embedded in recesses in the cooperating surfaces of the nuts and/or bolts and/or the clamp. The recesses may be annular grooves. However, reniform recesses of limited length or saucer-shaped recesses are also useful and may be disposed consecutively around the hole through which the shaft of the connecting bolt passes.

These recesses form convenient retaining devices or pockets for substances having the friction-reducing properties and by reason of their configurations and combinations and the substances introduced and--retained-therein they operate in their totality considerably to reduce the friction between the engaging parts, e.g. between the nut and the bottom strap member.

In another desirable- embodiment of the invention the said medium may be constituted by washers having friction reducing properties. Such washers may beinter- posed between flat surfaces of the cooperating parts or alternatively they can be received into conformably contriced recesses in the contacting surfaces of the cooperating parts.

In a preferred development of the invention said medium may be a synthetic plastics material which flows under pressure, and which is at least impregnated with substances having lubricating properties. The pressure due to the tighteining torque squeezes the plastics material sideways out of the gap between the contacting surfaces.

This also applies when a washer made of such a plastics material is interposed, or when the plastics material is directly embedded in recesses in the engaging surfaces of the contacting parts. In any event the pressure expresses the substances having the lubricating properties from the plastics material which serves as a kind of storage means and exudes these substances between the contacting surfaces, thereby reducing the resistance due to friction. Even if the synthetic plastics material is directly contained in recesses in the contacting parts the substances having the lubricating properties can continue to be expressed because the wear of the contacting surfaces, though slight, will continuously cause the plastics material to be re-engaged and the lubricating substance to be released.

Synthetic plastics material which can be advantageously used for the purposes of the invention are epoxy resins enriched and possibly thoroughly impregnated with molybdenus disulphide, or with substances based on graphite. Epoxy resins are particularly suitable for taking up and retaining the above-mentioned lubricating and sliding substances. Furthermore, duromers in the form of hard fabrics or moulding masses filled with textile shreds are also suitable matrix materials.

In certain applications, and according to another aspect of the invention, it may be advantageous for the contemplated medium to consist of a high strength textile material which is at least impregnated with a substance having lubricating properties.

Such a material may also be interPosed in the form of a washer or directly filled into recesses in the cooperating surfaces. The textile material containing the substances having lubricating properties will deform and release these substances when exposed to the pressure generated by the tightening torque, and it - will thus operate to-reduce the friction between the parts, e.g. between the nut and the bottom strap member of the clamp.

Again, in other applications it may be best for the medium constituted by the washer to be a porous metal filled with a substance having lubricating properties.

For such metal washers it is best to use materials that-have pores, such as sintered metals, which are impregnated under pressure with the lubricating substances.

When the nut on the clamp is pulled tight the washers will in such a case retain their shape, but the heat of friction generated during the tightening of the nut will cause the lubricating substance to expand and to exude from the washer surface.

Finally, it would be possible for the medium constituted by a -washer to consist of a plastics material which has been ap plied to a metal base and which has been at least impregnated with a substance having lubricating properties and which flows under pressure.

In other words, an ordinary metal washer could thus be used as a backing for a synthetic plastics material prepared to possess the characteristics that have been described.

An embodiment of the invention will now be described by way of example and with reference to the accompanying drawing, in which: Fig. 1 is a diagrammatic elevational crosssection of an underground road provided with a support system consisting of fourpart arches, and Fig. 2 is a fragmentary cross-section, on an enlarged scale, taken on the line II-II of Fig. 1 of the joint between two lapped channel sections of an arch.

Referring to Fig. 1 the cross-section of an underground road is marked 1 and the road is supported at close intervals in the longitudinal direction of the road by fourpart steel arches 2. Each arch 2 consists of four portions 3 to 6 of a channel section substantially in the shape of a U. The lagging and other parts of the support system have been omitted in the interests of greater clarity.

The ends of neighbouring channel sections of each arch 2 are interposed to form lapped joints 3 4, 45, 5-ó in the manner shown in Fig. 1 and the joints are pulled frictionally tight by clamps 7, at least one clamp 7 being provided in respect of each joint.

Fig. 2 in greater detail shows that each clamp 7 comprises an arching top strap member 8 formed from a steel strip and bridging the back of the clamp section, e.g. 5, nearest the rock strata 9 on the side of the road. The inside surface of the web 10 of the top strap member 8 bears on the flanges 11 of the inner channel section 5. Intermediate portions 12 of the strap member 8 are bent over perpendicularly from the web 10 so as to be close to the sides 13 of the channel section flanges 11.

The ends of the portions 12, remote from the web 10 are each formed with a flange 14 which projects substantially parallel to the web 10 of the strap member 8 in the longitudinal direction of the road. The portions 12 and the flanges 14 of the top strap member 8 are formed with holes 15 for the reception of bolts 16 which will be later described.

Furthermore, each clamp 7 comprises a bottom strap member 17 which is likewise substantially U-shaped and substantially conforms with the outer contour of the channel sections. The bottom strap member 17 of each clamp 7 surrounds the outer channel section, e.g. 6, and the ends 18 of intermediate portions 19 of the bottom strap member 17 bear on the flanges 20 of this outer channel section. The bottom strap member 17 is also formed with flanges 21 which project from the portions 19 in the longitudinal direction of the road substantially parallel to the flanges 14 of the top strap member 8. These flanges 21 are likewise provided with holes 22 for the recep tion of the bolts 16.The bolts used for the clamp 7 in the illustrated embodiment have specially shaped heads 23 which comply with the contour of the transitional region between the portions 12 and the flanges 14 of the upper strap member 8. For connecting the strap members 8 and 17 and thus frictionally clamping together the lapped interposed ends of the channel sections, e.g.

5 and 6, suitably dimensioned nuts 25 are screwed on the threaded portions 24 of the shafts of the bolts 16. Washers 26 are interposed between the nuts 25 and the flanges 21 of the bottom strap member 17.

These washers 26 consist of a base material, such as a plastics material, textile, metal or composite material. This base material is at least impregnated and possibly saturated with a substance having lubricating properties. When the nuts 25 are tightened the substance having the lubricating properties is squeezed out of the washers 26 by the applied torque and/or by the generated heat. According to the nature of the base material the washers 26 may be deformed and the substance expelled between the nut 25 and the bottom strap member 17 to reduce the friction between these two contacting surfaces.

It will also be understood from Fig. 2 that the cooperating surfaces 27 of the nuts 25 and/or 28 of the flanges 21 may be pro- vided with annular grooves 29. These grooves will then serve for the reception of a medium enriched with a substance having lubricating properties, either in the form of a washer which substantially fits into these grooves or the medium may be itself filled into the annular grooves.

WHAT WE CLAIM IS: - 1. A frame for supporting an underground drivage, comprising at least two channel sections of which the neighbouring ends are interposed to form a lapped joint which is frictionally tightened by at least one clamp consisting of a top strap member and a bottom strap member connected together by bolts and nuts, 'and wherein there is provided on at least parts of the contacting surfaces of the nuts and/ or the heads of the bolts, on the one hand, and of the clamp which the nuts and/or bolt heads engage, on the other hand, a medium which has friction-reducing properties.

2. A roof support frame according to Claim 1, wherein said medium is embedded in recesses provided in the contacting surfaces of the nuts and/or bolts and/or the clamp.

3. A roof support frame according to Claim 1 or 2, wherein the medium is constituted by washers having friction reducing properties.

4. A roof support frame according to any one of the preceding Claims, wherein said medium consists of a plastics material which has been at least impregnated with a substance having lubricating properties, and which flows under pressure.

5. A roof support frame according to any one of Claims 1 to 4, wherein the medium consists of a high strength textile material which is at least impregnated with a substance having lubricating properties.

6. A roof support frame according to Claim 3, wherein the washers constituting the medium are made of a porous metal which is at least impregnated with a substance having lubricating properties.

7. A roof support frame according to Claim 3, wherein the washers constituting said medium-consist of a plastics material which has been applied to a metal base and which has been at least impregnated with a substance having lubricating properties and which flows under pressure.

8. A frame for supporting an underground drivage, particularly a multipart arch with sliding joints tightened by clamps, substantially as herein described with reference to and as illustrated by the accompanying drawing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (8)

**WARNING** start of CLMS field may overlap end of DESC **. lubricating properties, either in the form of a washer which substantially fits into these grooves or the medium may be itself filled into the annular grooves. WHAT WE CLAIM IS: -

1. A frame for supporting an underground drivage, comprising at least two channel sections of which the neighbouring ends are interposed to form a lapped joint which is frictionally tightened by at least one clamp consisting of a top strap member and a bottom strap member connected together by bolts and nuts, 'and wherein there is provided on at least parts of the contacting surfaces of the nuts and/ or the heads of the bolts, on the one hand, and of the clamp which the nuts and/or bolt heads engage, on the other hand, a medium which has friction-reducing properties.

2. A roof support frame according to Claim 1, wherein said medium is embedded in recesses provided in the contacting surfaces of the nuts and/or bolts and/or the clamp.

3. A roof support frame according to Claim 1 or 2, wherein the medium is constituted by washers having friction reducing properties.

4. A roof support frame according to any one of the preceding Claims, wherein said medium consists of a plastics material which has been at least impregnated with a substance having lubricating properties, and which flows under pressure.

5. A roof support frame according to any one of Claims 1 to 4, wherein the medium consists of a high strength textile material which is at least impregnated with a substance having lubricating properties.

6. A roof support frame according to Claim 3, wherein the washers constituting the medium are made of a porous metal which is at least impregnated with a substance having lubricating properties.

7. A roof support frame according to Claim 3, wherein the washers constituting said medium-consist of a plastics material which has been applied to a metal base and which has been at least impregnated with a substance having lubricating properties and which flows under pressure.

8. A frame for supporting an underground drivage, particularly a multipart arch with sliding joints tightened by clamps, substantially as herein described with reference to and as illustrated by the accompanying drawing.