GB2274894A

GB2274894A - Rock bolt capsule

Info

Publication number: GB2274894A
Application number: GB9302416A
Authority: GB
Inventors: Robert Hardy Spensley; Paul Francis Reginald Ewings
Original assignee: Exchem PLC
Current assignee: Exchem PLC
Priority date: 1993-02-08
Filing date: 1993-02-08
Publication date: 1994-08-10
Anticipated expiration: 2013-02-08
Also published as: GB2274894B; GB9302416D0

Abstract

A rock bolt resin capsule is provided with differential rates of curing along its length by variation in the inclusion and/or omission of setting-time control agent. Faster setting is obtained at the inner end of the capsule, so that a nut may be used to tension the rock bolt. A setting retarder 10 may be provided in the resin R or in the catalyst C over a larger portion of the capsule length and omitted over a shorter portion; a setting acceleration 10 may be present in the resin in the shorter position but omitted from the remainder; the catalyst in the shorter portion may be increased in amount, or replaced by a setting-accelerator catalyst. <IMAGE>

Description

Rock Bolt CaPsule This invention relates to rock bolt capsules of the kind used for anchoring rock bolts in mine roofs and the like in effecting strata reinforcement.

In the installation of such rock bolts, a bonding agent, generally a settable resinous composition contained in one or more frangible capsules, is placed at the closed end of a bore hole drilled into the rock strata and a rock bolt having a threaded end portion is inserted into the bore hole with its threaded end portion protruding from the bore hole. A washer to act as a bearing plate and a nut are positioned on the threaded end portion and the bolt is then rotated so as to be driven into the bore hole and thereby puncture the resinous capsule and cause the settable resinous composition to be distributed around at least the end of the rock bolt. The rock bolt is then held in a fixed position for a short time to allow the resinous composition to harden and thereby fix the bolt in the bore hole.Thereafter, a tension can be applied on the bolt by tightening the nut onto the bearing plate.

Typically, the resin composition is emplaced in the bore hole in the form of a capsule. A simple such arrangement comprises a frangible longitudinally extending casing having disposed lengthwise therein a synthetic resin based component, with there also being disposed lengthwise in the casing a mixture comprising a hardener component for the resin. Such capsules are described for example in British patent specification No. 1 127 913. Subsequently, twin pack forms of casing have been devised which enable the hardener to be kept separate from the resin until the stage at which the casing is ruptured by the introduction of the bolt.

Such twin pack forms of cartridge are usually produced on a form fill and seal machine off site where there is continuous production of the capsules with each of the two components being filled into their respective separate chambers using continuous pumps or other filling devices. The casings can be produced from a single web of material, for example polyethylene terephthalate/polyethylene laminate with there being both an external seal to define the overall casing and an internal seal where a flap of casing web material is bonded to the interior of the "main" casing to produce a subsidiary compartment. Procedures for the production of such cartridges are known for example from United States patents Nos. 3,861,566 and 4,007,831 and Australian patent specification AU-581195/80.

The "main" compartment of such capsules contains a resin mastic comprising an unsaturated polyester or other settable resin together with extender, inert particulate filler, inhibitors to curtail the selfsetting tendency of the resin, accelerators (to counter the retarding effect of the inhibitors during the setting process) and pigments. The "subsidiary" compartment contains a setting agent, usually a mixture of benzoyl peroxide or other initiator, inert particulate fillers, liquid extenders and pigments.

When a fast setting variety of such a capsule is employed in order to achieve a short time for installing a rock bolt, there is the likelihood of premature setting adjacent to the proximal end of the bore hole, that is the first part of the capsule to have its contents mixed. This may well interfere with the efficiency of emplacement of the rock bolt since it may be fixed in set resin before it has been fully inserted into the bore hole. The fixing of the rock bolt is then ineffective for practical purposes. A practice has thus developed of having zones of differentially setting material at different positions within the bore hole. Normally, it is required to have a slow setting resin composition near the proximal end of the bore hole and a faster setting resin composition at the distal end of the bore hole.This is to allow the rock bolt to reach the distal end of the bore hole before the setting of the slow setting resin near the proximal end has commenced. Setting of the fast resin then holds the rock bolt in a fixed position, whilst the slow setting composition remains in a liquid unset state. This then enables the use of a device such as a "shear nut", as described in GB-B-2,211,260 and GB-B2,211,259 to provide a tensioned rock bolt. It is conventional for the slow setting resin composition to occupy a zone which extends for 50 % to more than 80 % of the length of the bore hole from the proximal end and for the fast setting resin to occupy less than 50 % say, 25 to 40 % of the bore hole length from the distal end. This is normally achieved by use of two or more capsules of the aforementioned type. The introduction of more than one capsule is in itself a source of difficulty.In British coal mines in the United Kingdom, a standard bore hole length is 2.4 metres and the bore hole is filled to a depth of about 1.2 metres with encapsulated resin. The diameter of the bore hole is typically 27 mm and the capsule typically has a diameter of 25 mm. When two cartridges are to be employed, as described, the correct fill is achieved by the fast setting capsule typically having a length of 0.4 metre and the slow setting capsule a length of 0.8 metre. Introduction of the capsules requires accuracy of positioning. There may be used for this purpose a loading tube which is typically formed of plastics material and which should be removed from the bore hole, since otherwise it will interfere with the introduction of the rock bolt.Alternatively, there may be employed a coupling tube between the capsules which will enter the bore hole and also interfere with the introduction of the bolt owing to its taking up some of the available volume. It would therefore be desirable to utilize a single capsule when seeking to achieve differential setting rates along the length of a bore hole.

It is an object of this invention to provide a means of achieving differential setting of resin at different positions along the length of a bore hole using a single elongated rock anchor capsule.

According to the present invention, there is provided an elongated rock anchor capsule suitable for use in securing a roof bolt in a bore hole, comprising a frangible longitudinally extending casing having disposed lengthwise therein a settable synthetic resin component, a setting catalyst component comprising a catalyst for polymerisation of the synthetic resin in the synthetic resin component being disposed lengthwise in the casing and the capsule cross-section composition being varied along the length of the capsule by variation in the incorporation of setting-time controlling agent and/or withdrawal of setting time controlling agent within the length of the capsule.

In the practice of this invention, one means of realising a differentiation in setting time along the length of a single capsule is to incorporate a third and possibly a fourth component in a single capsule over a portion of the length thereof. This is to be distinguished from a three component system, known for example from GB-B-2 097 401 which is however, of tape form and has co-extruded in side by side relationship an epoxy resin band and a curing agent envelope, with curing agent being co-extruded through the interior of the envelope. When subjected to appropriate mechanical action, the curing agent envelope is broken and the curing agent brought into contact with the epoxy resin.

This system is, however, physically unsuitable for use in a bore hole and is of unvarying composition throughout its length. An anchorage bolt bedding composition is, according to GB-B-2 001 619 of multicomponent form, but comprises a plastics sheath with active components separated by a frangible barrier and extending the length of the plastics sheath.

Again, there is no disclosure of a feasible technique for achieving differential rates of curing at different positions along the capsule.

An alternative scheme embodying this invention is to vary the ratio of components in a two component capsule at different positions along the length thereof.

The capsule preferably comprises at least two essential components, namely (I) a component (R) containing unsaturated polyester resin and/or vinyl ester resin and a cross-linking monomer and (Il) a component (C) containing a primary catalyst for the polymerisation of the resin/monomer blend. Such catalyst is typically a peroxide, preferably di-benzoyl peroxide. Both component (R) and component (C) are necessary for achieving a cross-linked resin as in the prior art.

In preferred practice, the setting-time controlling agent will be provided by a setting retarder (i.e. polymerisation inhibitor) which will be present over part of the length of the capsule, being that part which is first contacted by the rock bolt.

A setting retarder component can be added to the capsule together with either component (R) or component (C) over a major section of the capsule to achieve the required "slow" setting portion of the capsule, with the setting retarder being omitted from the remainder of the capsule, representing a minor section of the capsule so that when the bolt acts on this portion of the capsule, relatively fast setting will take place.

This will thus represent the portion of the capsule at the distal end of the bore hole.

Alternatively, a setting accelerator may be added to component (R) in a minor section of the capsule so as to form the "fast" setting portion while the section of the capsule from which the accelerator is omitted will undergo relatively slow setting.

It is even possible for there to be used both a setting retarder and a setting accelerator component to achieve the desired balance between slow setting and fast setting portions of the capsule, with the setting retarder being employed in a major part of the length of the capsule and a setting accelerator component being employed in å minor portion of the capsule.

Over a minor section of the capsule, the primary catalyst component (C) may be replaced by a set accelerating secondary catalyst composition, with catalysis over the remainder of the length of the capsule being achieved by the less active primary catalyst composition (C). The "fast" portion of the capsule may then be formed by both the addition of a set-accelerator component and either a set accelerating secondary catalyst composition as already stated or by increasing the proportion of the catalyst component (C) over that in the remaining part of the capsule.

Thus, with a simple procedure embodying the invention, the use of a setting retarder or setting accelerator may be avoided. The proportion of polymerisation catalyst in component (C), or more usually the amount of catalyst component (C), can simply be increased in order to form the "fast" portion and/or be reduced in order to form the "slow" portion.

By use of a pump to supply the catalyst component and operating intermittently or even continuously but at variable rates, it is possible to define the start points for respective sections of the capsule and also by knowing the flow rate and quantity required, to determine the finishing point for supply of catalyst component. Like principle can be employed for the introduction of any other components.

In each of the various aforesaid embodiments, the catalyst component (C) normally constitutes from 1 to 50 % by volume of the capsule contents. The amounts of setting retarder component and/or setting accelerator component employed, then may total from 0.01 to 50 % by weight of the resin component. The basic inhibitors and accelerators are themselves dispersed in resin/monomer blend or in an inert carrier, or in any mixture of these, optionally together with particulate filler to produce the setting retarder and setting accelerator components.

A capsule embodying this invention is advantageously produced by a modification of conventional procedure for producing rock anchor capsules having settable resin and setting agent or catalyst in side by side relationship and separated from one another until the capsule is subject to the action of a rock bolt. The addition of retarder and accelerator components as third and/or fourth components or differential addition of conventional catalyst composition with or without secondary catalyst composition can be achieved using simple mechanical and/or electrical devices linked to control valves.

Preferably positive displacement pumps are employed.

In this manner, it is possible to position accurately lengths of the additional component (S) within the capsule, controlling both the start and finishing point of the addition.

The portions of fast and slow setting sections within the capsule can be varied to suit local requirements, but it is preferred in current practice that the capsule consists of 60 to 95 % slow and 15 to 40 % fast setting portions, more preferably 60 to 70 % slow and 30 to 40 % fast setting portions. On installation, the fast end of the capsule would, as already stated herein, be inserted into the bore hole first such that when a steel bolt equipped with a shear nut is installed, it will reach the distal end of the bore hole before setting of the slow part of the resin composition has been completed, whereupon fast setting commences and rapidly terminates, so tension can be applied to the bolt almost immediately the bolt has reached the distal end of the bore hole.

Resin component (R) is preferably based on an ethylenically unsaturated polyester resin or vinyl ester resin dissolved in an ethylenically unsaturated monomer, and may be the product Crystic 3601A of Scott Bader Company. The resin component typically also contains a setting accelerator, for example a tertiary amine such as di-methylaniline or di-methyl-ptoluidine, and a thixotrope, for example pyrogenic silica such as the product "Aerosil" of Degussa AG or a surface coated mineral powder such as "Bentone" which is available from NL Industries. The bulk of the resin component is made up of powdered filler, e.g. limestone or silica.

The catalyst component (C) preferably contains dibenzoyl peroxide as active agent, e.g. the product Lucidol KL50 of Akzo Chemie. It additionally contains a liquid plasticizer such as di-butyl phthalate or a chlorinated hydrocarbon and a particulate inert filler such as pulverised limestone or silica.

Any of the inhibitors well known in the art, for example quinones such as benzoquinone, or hydroquinones such as hydroquinone and methyl and ethyl ethers of hydroquinone, or phenols such as p-tertiary butyl catechol, may be employed as set retarder. This is preferably introduced into the polyester resin component and for this purpose it may be introduced in admixture with styrene monomer or polyester resin/styrene blend, pyrogenic silica and powdered mineral. To enable the presence of the retarder component to be identified in the finished capsule, a pigment paste may also be present. However, the use of a pigment can be avoided provided there is some alternative means of identifying which end of the capsule shall be introduced first into a bore hole.

As an accelerator for the curing there may be used a tertiary amine such as p-methyl toluidine or di-methylaniline. This component is preferably introduced into the polyester resin component, preferably together with a thixotropic agent such as pyrogenic silica and pulverised mineral such as limestone or silica and styrene monomer or polyester resin/styrene blend or a liquid plasticizer such as dibutyl phthalate or a low molecular weight saturated polyester.

An accelerating secondary catalyst component typically comprises a catalyst such as 2,4dichlorobenzoyl peroxide blended with di-benzoyl peroxide, liquid plasticizer such as di-butyl phthalate or silicone oil and pulverised mineral such as limestone or silica.

For a better understanding of the invention and to show how the same can be carried into effect, reference will now be made to the drawings wherein: Figure 1 is a transverse cross-section through a casing which is undergoing form-filling to produce a capsule embodying the invention at the position at which contents of the capsule are emerging from supply nozzles therefor into the capsule; and Figure 2 is a cross-section through the capsule after completion of its manufacture.

Referring to Figure 1, a web of casing material 1 formed of polyethylene terephthalate/polyethylene is folded within itself to form a major internal chamber 2 and to leave a defining double walled flap 3, and an internal chamber 4. A resin component R is injected into the main chamber 2 from a wide nozzle 5 while catalyst component (C) is introduced into chamber 4 from a nozzle 6. Additionally, over portions of the length of the capsule being formed, into the resin component (R), but also possibly into catalyst component (C), is/are introduced elongate bodies of retarder component and/or accelerator component. A nozzle through which such component is introduced into resin component (R) is shown at 7. Seals are formed at 8 and 9 so as to prevent any lateral escape of resin component R or catalyst component C.The body thus produced assumes a cylindrical form as shown in Figure 2 with the various components of the contents assuming approximately the dispositions as shown, i.e. the components of chamber 4 extend over the length of the capsule while the setting retarder or accelerator component shown at 10 forms a strip along part of the length of the capsule. The contents of the respective components of the capsule are sufficiently thixotropic to prevent undesired further migration of material, particularly in the longitudinal direction.

Typical formulations for the aforementioned components are as follows: Resin component R Weiaht % Crystic 3601A (polyester resin) 11 Styrene monomer 9 Tertiary amine 0.2 Pyrogenic silica 0.3 Powdered mineral 80 Catalyst Component, C Di-benzoyl peroxide 10 Liquid plasticizer 25 Powdered mineral 65 Retarder ComPonent Inhibitor 0.3 Unsaturated polyester resin 18 Styrene monomer 12 Pyrogenic silica 2 Powdered mineral 67.5 Pigment paste 0.2 Accelerator Component Accelerator 6 Unsaturated polyester resin 9 Styrene monomer 6 Inert liquid 7 Pyrogenic silica 2 Powdered mineral 70 Acceleratina Secondarv Catalyst Comnonent Di-benzoyl peroxide 3 2, 4-Dichlorobenzoyl peroxide 7 Liquid plasticizer 25 Powdered mineral 65

Claims

1. An elongated rock anchor capsule suitable for use in securing a roof bolt in a bore hole, comprising a frangible longitudinally extending casing having disposed lengthwise therein a settable synthetic resin component, a setting catalyst component comprising a catalyst for polymerisation of synthetic resin in the synthetic resin component being disposed lengthwise in the casing and the capsule cross-section composition being varied along the length of the capsule by variation in the incorporation of setting-time controlling agent and/or withdrawal of setting time controlling agent within the length of the capsule.

2. A capsule as claimed in Claim 1, wherein the synthetic resin component is an ethylenically unsaturated polyester resin and/or vinyl ester resin having incorporated therein an ethylenically unsaturated cross-linking monomer and the setting catalyst component comprises a peroxide catalyst for the polymerisation of the resin/monomer blend.

3. A capsule as claimed in Claim 2, wherein the peroxide is di-benzoyl peroxide.

4. A capsule as claimed in any one of Claims 1 to 3, wherein a setting retarder component is present in the synthetic resin component or in the curing catalyst component over a major section of the length of the capsule and is omitted from a minor section of the length of the capsule.

5. A capsule as claimed in any one of Claims 1 to 3, wherein a setting accelerator component is present in the synthetic resin component in a minor section of the length of the capsule and is omitted from the remainder of the capsule.

6. A capsule as claimed in any one of Claims 1 to 3, wherein a setting retarder component is employed in a major section of the length of the capsule and a setting accelerator component is employed in a minor section of the length of the capsule.

7. A capsule as claimed in any one of Claims 1 to 3, wherein the setting catalyst component is replaced over a minor section of the length of the capsule by a set accelerating secondary catalyst composition.

8. A capsule as claimed in any one of Claims 1 to 3, wherein the amount of said polymerisation catalyst is increased in a minor section of the length of the capsule to achieve increased rate of setting.

9. A capsule as claimed in any one of Claims 1 to 3, wherein a setting accelerator component is present in a minor section of the length of the capsule together with either a set accelerating secondary catalyst composition or an increased amount of said polymerisation catalyst over that present in the remainder of the length of the capsule.

10. A capsule as claimed in any one of claims 3 to 9, wherein said minor section of the capsule occupies from 5 to 40 %, preferably 30 to 40 % of the length thereof and said major section of the length of the capsule occupies from 60 to 95 *, preferably 60 to 70 % of the length thereof.

11. A capsule as claimed in any one of Claims 3 to 6, 9 and 10, wherein the setting retarder component and/or setting accelerator component constitute(s) from 0.01 to 50 % by weight of the resin component.

12. A capsule as claimed in any one of Claims 4, 6 and 10, wherein a said setting retarder component is a quinone, a hydroquinone or a phenol.

13. A capsule as claimed in any one of Claims 5, 6, 9 and 10, wherein a said setting accelerator is dimethyl-p-toluidine or di-methylaniline.

14. An elongated rock anchor capsule as claimed in Claim 1, substantially as described herein.

14. A capsule as claimed in any one of Claims 7, 9 and 10, wherein a said secondary catalyst component contains 2,4-dichlorobenzoyl peroxide and di-benzoyl peroxide.

15. An elongated rock anchor capsule as claimed in Claim 1, substantially as described herein.

Amendments to the claims have been filed as follows

1. An elongated rock anchor capsule suitable for use in securing a roof bolt in a bore hole, comprising a frangible longitudinally extending casing having disposed lengthwise therein a settable synthetic resin component and a setting catalyst component comprising a catalyst for polymerisation of the synthetic resin in the synthetic resin component being disposed lengthwise in the casing; characterised in that a setting time controlling agent is added to the resin component so as to be out of contact with the setting catalyst component, the cross-sectional configuration of the casing contents being varied along the length of the capsule owing to the setting-time controlling agent being present in and/or withdrawn from the casing contents over a discrete portion of the length of the capsule, which setting-time controlling agent influences the rate of cross-linking of the resin component when the latter is mixed with the catalyst component as these are brought into contact with each other when a roof bolt is introduced into and rotated through the capsule when the latter is emplaced in a bore hole.

2. A capsule as claimed in Claim 1, wherein the synthetic resin component is an ethylenically unsaturated polyester resin and/or a vinyl ester resin having incorporated therein an ethylenically unsaturated cross-linking monomer and wherein the setting catalyst component comprises a peroxide catalyst for the polymerisation of the resin/monomer blend.

3. A capsule as claimed in Claim 2, wherein the peroxide catalyst is di-benzoyl peroxide.

4. A capsule as claimed in any one of Claims 1 to 3, wherein a setting retarder component is present in the synthetic resin component as setting-time controlling agent over a major section of the length of the capsule and is omitted from a minor section of the length of the capsule.

5. A capsule as claimed in any one of Claims 1 to 3, wherein a setting accelerator component is present in the synthetic resin component as settingtime controlling agent in a minor section of the length of the capsule and is omitted from the remainder of the capsule.

6. A capsule as claimed in any one of Claims 1 to 3, wherein setting-time controlling agent is constituted by a setting retarder component employed in a major section of the length of the capsule and a setting accelerator component employed in a minor section of the length of the capsule.

7. A capsule as claimed in any one of Claims 1 to 3, wherein a setting accelerator component as said setting-time controlling agent is present in a minor section of the length of the capsule and, over said minor section, the catalyst component is either a set accelerating secondary catalyst composition or there is present an increased amount of said polymerisation catalyst over that present in the remainder of the length of the capsule.

8. A capsule as claimed in any one of claims 3 to 7, wherein said minor section of the capsule occupies from 5 to 40 % of the length thereof and said major section of the length of the capsule occupies from 60 to 95 * of the length thereof.

9. A capsule as claimed in any one of Claims 4 to 7, wherein the setting retarder component and/or' setting accelerator component constitute(s) from 0.01 to 50 % by weight of the resin component.

10. A capsule as claimed in either Claim 4 or Claim 6, wherein a said setting retarder component is a quinone, a hydroquinone or a phenol.

11. A capsule as claimed in any one of Claims 5 to 8, wherein a said setting accelerator component is N,N-dimethyl-p-toluidine or N, N-dimethylaniline.

12. A capsule as claimed in any one of Claims 7 to 9, wherein a said set accelerating secondary catalyst component contains 2,4-dichlorobenzoyl peroxide and di-benzoyl peroxide.

13. A capsule as claimed in any preceding claim, wherein a said setting time controlling agent is present in the resin component as a strip extending lengthwise thereof.