The invention relates to a water jet system for cutting away an outer layer of a surface, comprising two parallel guides, a device for keeping the guides parallel to the surface, a feed beam carried by the guides, a carriage with a jet nozzle directed towards the surface, mounted on the feed beam in such a manner that it is movable therealong, and a displacement device for each guide for displacing the feed beam along the respective guide.

It is known to cut away the outer layer of cracked concrete on bridge roadways and to cast a new outer layer in order to maintain the construction. A wheel-mounted unit as shown, e.g. in US 6 877 930 B2 can then be used. However, the outer layer of columns and other vertical and inclined surfaces may also have to be repaired and it is known to use simpler devices. Plastered buildings may also have to be replastered and the old plaster must first be removed. There are many other fields of application where it is necessary to cut away the outer layer of a surface. DE 10 2007 039290 A1 constitutes the closest prior art of the present invention and discloses the features of the preamble of claim 1.

The aim of the invention is to ensure that the feed beam is moved along the guides in steps in an operationally reliable manner.

The aim is achieved in that each displacement device comprises a fixed gripping jaw and a movable gripping jaw for the guide and a device for displacing one gripping jaw in each pair relative to the other along the guide, at least one gripping jaw being assigned a spring for gripping and a hydraulic cylinder for release.

• Figure 1 shows a water jet system according to the invention applied to a vertical concrete surface.
• Figure 2 is an enlarged detail from Figure 1.
• Figure 3 is a diagrammatic view of a stepping device shown in Figure 1.
• Figure 4 is a section along the line 4-4 of Figure 3.
• Figure 5 shows a water jet system designed for a round column.

Figure 1 is a section of a construction which may be of concrete, e.g. a vertical or inclined part of a bridge construction, the surface 11 of which has deteriorated and thus needs to be renewed. A frame is assembled from four tubes 12-15 with four wall supports or braces 16-19. The supports or braces form part of a device for keeping the frame parallel to the wall. The entire frame is shown made up of standard façade scaffolding elements comprising tubes having a diameter of 48.3 mm used worldwide.

The two vertical tubes 12, 13 of the frame form guides for two gripping devices 20, 21 having mountings 36 carrying a feed beam 22. The gripping devices and the feed beam are shown separately as Figure 2. The feed beam has two tubes 30, 31 which form guides for a slide or carriage 33 carrying a water jet lance with a jet nozzle 34 directed towards the concrete surface. The water jet lance receives its high-pressure water from a pump via a hose 35. The slide with the water jet lance executes a cutting pass in one direction with the water jet lance at an angle of attack relative to the concrete surface. The slide then turns and executes a cutting pass in the other direction with the water jet lance at an angle of attack in that direction. The water jet lance is oscillated during the cutting passes transversely to the direction of the slide in order to give a greater cutting width. The oscillation and the speed of the slide are advantageously coupled in a fixed ratio in the manner described in Swedish patent application 0801398-9. The feed beam is moved in steps between the passes so that the water jet strikes a new area upon each cutting pass or after a certain number of cutting passes.

Each gripping device 20, 21 has two gripping jaws 40, 41 which can be displaced relative to one another with the aid of a hydraulic cylinder 47 for stepping. The gripping jaw 40 is fixed on the gripping device 20, while the gripping jaw 41 is movable. Each gripping device 20, 21 has a mounting 36 for the feed beam 22 and the gripping devices are identical to one another.

One of the gripping devices, i.e. the gripping device 20, is shown in diagrammatic form in Figures 3 and 4 and these figures do not correspond entirely to the gripping devices as can be seen in Figure 2, but illustrate the principle. The gripping jaws 40, 41 are controlled by double-acting hydraulic cylinders 43, 44 which moreover also have springs 45, 46 which prevent the gripping device from releasing its grip if it becomes entirely pressureless. Alternatively, the cylinders may be single-acting and used only for release.

The gripping jaw 40 is fixed on the gripping device, while the gripping jaw 41 is controlled in such a manner that it is movable along the gripping device. Figure 4 shows the gripping jaw 40 in section. It has a retainer 49 with a semi-circular gripping surface adapted to the guide/tube 12. The piston rod of the hydraulic cylinder 43 forms a holding-down device and has a point-like holding-down surface 50. This design means that the feed beam can be moved in steps along bent tubes. The design also means that the gripping jaw has such a large opening that such a large part of the periphery of the tube is left free that the jaws can pass the supports of the guides. The hydraulic cylinder 43 has an internal stop 60 which limits the withdrawal of the surface 50 of the holding-down device from the gripping position to a few mm, i.e. 1-3 mm, so that the gripping jaw provides support even when it is not in the gripping position.

A hydraulic cylinder 47 is coupled between the hydraulic cylinders 43, 44, i.e. between the gripping jaws. A stroke length adjuster in the form of an adjustable stop 48, shown as a stop screw, results in accurate adjustment of the stroke length of the hydraulic cylinder 47. Accurate adjustment is important as the feed beam could otherwise become askew after a large number of steps. The stop 48 can take up the entire force of the hydraulic cylinder 47. Alternatively, the stop may be formed of a hydraulic valve which initiates stopping. The gripping devices on both sides always work in parallel and the feed beam can be moved in steps both upwards and downwards.

The feed beam 22 can be moved in steps in that the lower gripping jaw 41 can be displaced along the guide/tube 12 when it is in the gripping position and the upper gripping jaw is in the free position. When the upper gripping jaw 40 is then in the gripping position, the lower gripping jaw 41 can be released and brought back so that it is once again in position for a new stepping operation. Both the upper and the lower gripping jaws are kept in the gripping position during the cutting operation of the feed beam.

Figure 5 shows a water jet system designed for a column having a round cross section and upper and lower guides 51, 52 having a number of supports or mountings 53, 54 or mountings keeping the guides in place parallel to the surface of the column. For the sake of clarity, the column is not shown in the figure. The feed beam 55 is similar to the feed beam 22 shown in Figure 2 and it has gripping devices 56, 57 similar to the gripping devices 20, 21 in Figures 3 and 4. The vertical feed beam 55 is moved in steps around the column. The design of the supports or mounting 53, 54 is adapted to the opening of the jaws so that the jaws can be moved in steps past the supports.

The wall supports or braces 16-19 in Figure 1, like the supports or mountings 53, 54 in Figure 5, form part of carrying devices for keeping the guides 12, 13 or 51, 52 respectively parallel to the surface to be worked. These carrying devices must keep the guides in place and take up the reaction forces from the water jet nozzle. The carrying devices may be, e.g. in the form of a crane carrying the frame 12-19 or 53, 54 respectively. The frame may also be suspended on cables from a winch and the reaction forces can be taken up by scaffolding. The carrying devices are adapted to each site where possible. E.g. a crane can be disposed above the surface to be worked or on the ground below it.