DESCRIPTION OF PRIOR ART Tube-formed expandable rock bolts are used in mines and tunnels in order to stabilize the rock roof and wall or as anchoring devices for use as supports for various equipment to be suspended at the rock face. Anchoring of such a rock bolt inside the borehole is accomplished by pressurizing and deformation of an expandable tubular part in order to obtain permanent fixation.

US-A-4 459 067 describes various embodiments of such expandable rock bolts. In the embodiment shown in Fig. 16 the rock bolt is expanded by supplying expansion fluid over an outward hole 45 provided in a cylindrical sleeve 19, which, at a distance inside the hole, has a support shoulder for co- operation with a rock support plate. When the rock bolt is to be expanded, a clamping head is applied to the outside of the sleeve, whereupon, after ensuring a sealed fit, expansion fluid is delivered to the bolt.

When a tunnel which is secured with such bolts is to be finished by spray concrete or the like, a relatively great amount of lining concrete has to be used in order to cover the protruding sleeves of all the rock bolts in the tunnel. This is costly and may also address a technical problem since the free dimensions of the tunnel is reduced.

AIM AND MOST IMPORTANT FEATURES OF THE INVENTION It is an aim of this invention to remedy the above problems and to provide a more economic and effective and yet easily manageable solution.

This aim is obtained through the respective features of claims 1 and 8.

This way a rock bolt is provided having a minimal protrusion from the rock face. This means that the amount of sprayed lining concrete used in order to cover protruding rock bolt parts can be radically reduced. This is economically advantageous and also results in minimizing reduction of free tunnel space in tunneling or mining.

The invention makes it possible to construct technically effective, simple and economic means for connecting an expansion fluid delivering nozzle to a rock bolt. Embodiments of such means can include bayonet couplings or co-operating recesses and protrusions, which come into mutual locking co- operation through a limited rotary movement.

Different advantageous constructions of the connecting portion allows effective joining thereof with the expansion portion of the rock bolt. And in case of a radially extending contact surface, a permanent joint against the expansion portion could be obtained through for example friction welding and resistant welding.

In case the connecting portion includes a fastening sleeve which is a surrounded by an end part of the expansion portion that end part can be deformed in such a way that an inward loop or inward loops, as seen in a radial section through the expansion portion, are displaced outwards into contact with outside loop or loops. The joint can thereafter be obtained by welding.

In case the expansion fluid delivering nozzle comprises an expansion fluid activated clamping device, the nozzle can be mechanically locked at the rock bolt without a rotational movement and besides, the nozzle will be fastened inside the cavity until the entire installation is completed.

In a preferred embodiment of such a clamping device, an expandable sealing and clamping ring is activated by expansion fluid acting on a piston. It is advantageous if the nozzle includes a valve which does not transmits expansion fluid to an expansion portion before the nozzle has been locked inside the cavity.

The dimensions of the nozzle, and thereby the outside dimensions of the connecting portion, is preferably chosen such that the latter dimensions essentially corresponds to that of an unexpanded expansion portion of the rock bolt. This way insertion of the rock bolt into a bore hole at occasions is not obstructed by the connecting portion.

Further advantages are achieved through other features of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described in greater detail at the background of embodiments and with reference to the drawings, wherein: Fig. 1 shows a nozzle and part of a rock bolt according to the invention disassembled in a perspective view, Fig. 2 shows a nozzle, a rock bolt and a rock support plate disassembled, in a longitudinal section, Fig. 3 shows the elements of Fig. 2 in an assembled state, Fig. 4 shows another embodiment of a nozzle and a rock bolt according to the invention, Fig. 5 shows another embodiment of a rock bolt according to the invention in a partial section, and Fig. 6 shows still another embodiment of a rock bolt according to the invention in a partial section.

DESCRIPTION OF EMBODIMENTS In Fig. 1, an expansion fluid delivering nozzle 1 is shown having an expansion fluid channel 2 and a coupling portion 3.

The nozzle 1 is connected over means such as an expansion fluid house to a pressure fluid source (not shown). The coupling portion 3 is intended to fit into a cavity 7 in a connecting portion 6 of an expandable rock bolt 5. For that purpose the coupling portion 3 comprises locking means in the form of bayonet coupling elements one of which being shown as a pin 4 extending radially from a circular cylindrical outward surface of the nozzle 1.

The front end of the nozzle 1 has a reduced diameter and carries sealing means for co-operation with a corresponding part of the cavity 7.

Inside the cavity 7 there are formed bayonets coupling grooves 8 matching the pins 4 on the nozzle 1 such that upon insertion and limited rotation of the nozzle with respect to the connecting portion 6 of the rock bolt 5 locking of the nozzle in an axial direction will be obtained.

In Fig. 1 10 indicates an expansion portion of the rock bolt 5. A support shoulder 9 is position at the outermost or proximal end of the connecting portion 6 for supporting a rock support plate (see Figs. 2 and 3).

Fig. 2 shows the nozzle 1 with both pins 4 of the coupling portion 3 prior to insertion into the cavity 7 of the coupling portion 6 of the rock bolt 5. At the front end of the nozzle 1 there is provided a sealing ring 11 which upon insertion comes into sealing contact with a co-operating surface 13 in a portion of the cavity 7 having somewhat reduced diameter.

Inside the cavity 7 an axial channel 12 is provided for expansion fluid to enter into the inside of the expansion portion 10.

The front end of the rock bolt 5 is provided with a pointed bolt tip 16. The connecting portion 6 as well as the bolt tip 16 has radially extending contact surfaces 14, 14', which are jointed to the expansion portion in a suitable way such as by friction welding, resistance welding or any other suitable joining method.

The support shoulder 9 is shown having a rounded surface which is intended to co-operate with a vaulted surface of a rock support plate 15 in a per se known manner which is not described in more detail here.

Fig. 3 shows the nozzle 1 and the connecting portion 6 of the rock bolt 5 in an assemble state, wherein the bayonet coupling pins 4, through rotation of the nozzle 1, have been positioned in the end portion of the bayonet grooves 8.

In the embodiment shown in Fig. 4, the nozzle 17 is shown attached to an expansion fluid hose 19 and is provided with an axial channel 18 which communicates over inclined borings 21 with a cylinder chamber 20 wherein a piston 19 is axially moveable.

Upon pressurizing the cylinder chamber 20 the piston 19 moves to the right, as seen in the Figure, whereby an axial force will act on a sealing and clamping ring 22. This results in deformation of the ring 22 radially outwards until it comes into contact with an circular cylindrical inside surface 23 of a cavity 7'in a connecting portion 6'of a rock bolt.

After completed sealing and clamping of the nozzle 17 inside the connecting portion 6'the pressure inside the. channel 18 is rises because of the piston being stopped. Pressure acting on a pressure controlled valve 24 then is great enough to press a valve element 26 inside a valve seat 25 to the right, as seen in the Figure, against the action on the spring 27 until free communication is obtained between the channel 18 and the inside of the cavity of the connecting portion 6'.

This allows fluid to enter into an expansion portion 10'of the rock bolt over an axial channel 12'.

Another modification of a rock bolt is indicated in Fig. 5, wherein the connecting portion includes a fastening sleeve which surrounds an end part of an expansion portion and is fastened thereto by means of a weld.

A further embodiment is shown in Fig. 6, wherein the connecting portion includes a fastening sleeve which surrounds an end part of the expansion portion and is fastened thereto by means of weld. In this embodiment the inside material of the tubular expansion portion is deformed and displaced radially outwards so as to fit on the outside of said fastening sleeve.

The invention can be further modified within the scope of the claims. As an example the nozzle and cavity can have co- operating coupling elements of various kinds besides bayonet coupling elements such as interrupted threads. Locking may be achieved by relative rotation of the nozzle and the connecting part a limited angle of for example 30°.

The locking effect of the nozzle indicated in Fig. 4 can be enhanced by providing a groove or another engagement means in the inside surface of the connecting portion 6'. This is preferred according to the invention. Having the surface of the cavity made as is shown in figs 4,5 and 6 requires strictly frictional engagement, which, however, could be improved by providing the surface with friction increasing means such as serrations etc.

Another possibility is to provide an expandable metallic device coming into locking contact with such a groove or engagement means. Sealing and clamping may, or may not be integrated into the same means.

The features of the rock bolt which are not related to the invention per se are optional and can be of the kind known from the prior art.