The invention concerns a mixing element as stated in the introduction to Claim 1 for use with bolts for reinforc ment bars.

When reinforcement bolts are to be secured in rock, such as in a tunnel roof, the bolts are driven into a plastic mass that can harden which has already been injecte into the drill hole. Providing the diameters of the bolt an the drill hole are suitably adjusted to each other, the rotation of the bolt will ensure that there will normally b adequate mixing of the components in the plastic mass, thereby satisfactory hardening. Usually the diameter of the drill hole should be 6-12 mm larger than the diameter of th bolt. If the diameter of the drill hole is too large in relation to the bolt, the mixing and the hardening of the plastic mass will be incomplete and the bolt will be poorly secured. It is sought, partly on the grounds of cost, to use bolts of 20 mm reinforcement steel, that cannot have drill holes larger than about 30 mm if there is to be adequate mixing of the plastic mass. It is also conceivable that larger drill holes could be used for applications such as dynamite charges where the diameter may be 45 mm. To achie a suitable mixing in this and similar cases, Norwegian Patent Specification 156 620 indicates a way of locating a mixing element at the insertion end of the bolt. The mixin element presupposes continuing rotation of the reinforceme bolt, and can provide a satisfactory mixing as long as the reinforcement bolt rotates at the correct speed.

However, there is a disadvantage with the rotation of the reinforcement bolt, namely that this requires another machine than the one used for drilling the hole. The drill hole has to be drilled by a rig which is unsuitable ^' for rotating the reinforcement bolt.

The main objective of the invention is designing a mixing element of the type indicated that is simpler to use than known mixing elements and is also cheaper to produce. What is required is a mixing element that can be inserted without rotation that nevertheless gives a satisfactory mixing of the plastic mass, even when there is a large difference between the diameter of the bolt and the diameter of the drill hole. Furthermore, it is sought to produce the mixing element in an inexpensive material, preferably plastic.

Principle

The principle of the invention is stated in the characterizing part of Claim 1. This mixing element can be suitably manufactured in an injection moulded plastic. It can be placed on the shaft of the bolt and secured by an easy means such as by a clamping ring. The mixing element in accordance with the invention can easily be adjusted to different drill hole diameters, thereby providin _. g satisfactory mixing irrespective of the application.

Other advantageous features of the invention are indicated in the subsidiary claims.

Example.

The invention is described by reference to the drawings below, where

Fig. 1 shows a front perspective of a first means of designing a mixing element in accordance with the invention, Fig. 2 shows an axial section through a mixing element in accordance with a second means of design, while Fig. 3 shows a partly truncated lateral section of a reinforcement bolt equipped with a mixing element as shown in Fig. 2, with a hardening plastic inserted and a stop plate.

In Fig. 1 a mixing element 10 is shown that consists of a circular disc 11, with axial holes 12 like a sieve in

three rings or another suitable pattern, such as radially elongated grooves. The mixing element 10 is designed to be fitted on the end of a reinforcement bolt, where the cavity 13 is made to adjust the diameter of the bolt. The mixing element is supported on the reinforcement bolt by an axial collar or sleeve 14 around the cavity 13. This sleeve can b used to further support the mixing element, as described in connection with the example below.

The disc 11 is placed at the end of the reinforcement bolt and attached to it. When inserted into a two_component plastic mass that has been placed in a drill hole by a cartridge or the like, the disc 11 will ensure that there i an even redistribution of the mass. This will partly be achieved by forcing the mass to flow through the hoj.es 12 and partly by forcing it to be pressed through the gap between the edge of the disc 11 and the sides of the rock i the drill hole. In favourable circumstances this will be sufficient to provide adequate mixing.

Fig. 2 shows a second design of the invention, with a mixing element 15 that is a further development of the mixing element in Fig. 1. Apart from the circular disc 16 with axial holes 17 that form a strainer, and an axial sleeve 18 around the central cavity 19, the mixing element 15 also has a cup_like collar 20 located on the outer edge of disc 16 facing axially away from the sleeve 18, i.e. facing towards the front of the mixing element. The collar 20 is designed in one unit with the disc 16 and has a heigh that is about the same as the diameter of the cavity 19.

The collar 20 will be able to limit the amount of mass that flows outside the mixing element 15 by pressing the mass outward towards the rock wall thus reducing the circular gap between the mixing element and the rock wall. An important function of the collar 20 is illustrated in Fig. 3, this will be explained below. Close to the edge of the disc 16, there is a circular groove 21 that seats an O-ring (not illustrated) or another appropriate element that can fill the gap between the mixin element 15 and the rock wall.

Fig. 3 shows how the mixing element 15 in Fig. 2 can be fitted and used in a specific context. The mixing element 15 is inserted into the front end 22 of the reinforcement bolt 23. The diameter of the cavity 19 is adjusted to the diameter of the bolt so that the mixing element can be fastened by a press fitting. The element is firmly secured by a clamping ring 24 that is appropriately shaped to be tightly fastened around the sleeve 18. The mixing element 15 can also be secured by shrinking the sleeve 18 by means of a hot air pistol, or the like.

In this example a design of the invention is shown where the mixing element is used actively in the supply of hardener. This is relevant in cases where the plastic mass is injected or placed in the drill hole without any hardening component. A ring 25 with a hardener mass is placed in the circular cavity that is bounded by the collar 20. When the reinforcement bolt 23 with the attached mixing element 15 is pressed into the drill hole, the mixing element 15 and the ring 25 will act like a piston and the plastic mass will be pressed through the hardener and the disc 16. This ensures that there is a effective mixing of the components in the plastic mass. This can be done without any rotation of the reinforcement bolt.

Any run-off of the plastic mass during the hardening phase is prevented by a stop disc 26 on the reinforcement bolt 23 that covers the opening of the hole at an appropriate distance from the end. The stop disc 26 can be made of the same material as the mixing element 15 and have a sleeve 27 with space for a clamping ring 28. The examples that are shown can be modified in different ways. This is particularly with reference to the choice of material and the design of the cavity pattern and cavity dimensions in discs 11 and 16.