More particularly, the invention concerns a machine tool to shave a surface over a predefined depth, comprising a tool which itself comprises a cylinder drawn in rotation around its longitudinal axis, this cylinder being fitted on the machine tool in such a way that its longitudinal axis is parallel to the surface to be shaved when the machine tool is in operation.

Machine tools of this type are used to eliminate a superficial layer of contaminated wall surfaces in nuclear facilities in course of decommissioning. This superficial layer generally covers about a few millimeters. Thus, only the material corresponding to this superficial layer may be eliminated to be treated as radioactive material and the rest of the walls or ground may be treated in a more traditional manner at less expense.

Machine tools of this type are already well-known.

The tool is made up of a cylinder formed of a succession of disks piled up one over the other along the longitudinal axis of the cylinder, the circumferential edge of each cylinder being equipped with segments made up of shaving material. In fact, these tools, of a former design, are formed of disks initially designed for the cutting of material perpendicular to the rotation plane of these disks. To prevent the segments from eroding too quickly, they must not be spaced too far from each other circumferentially. Thus a large proportion of the cylinder surface is equipped with shaving material. Hence, the power necessary to draw such cylinders in rotation must itself be great. This power can only be supplied by hydraulic motors.

In a contaminated environment, the use of fluids to induce the operation of hydraulic equipment must be avoided so as to minimize the risks of dispersal. Further, these old design machine tools tend to be very bulky and cannot be adapted to the decontamination of confined volumes.

These confined volumes must, therefore, be treated using a smaller man-manipulated tool with the ensuing problems arising from human labor in contaminated environments.

Finally, it is to be noted that disk cooling is hard to ensure.

The aim of this invention is specifically to overcome these inconveniences.

To this effect, the invention provides for a machine tool which, apart from the features already mentioned, is characterized by the fact that the external surface of the cylinder includes shaving material segments, each segment extending longitudinally over this external surface in a direction comprising a component not equal to zero parallel to the rotation axis.

Thanks to these measures, the piling of disks has been replaced by a sole cylindrical surface. Indeed over such a surface, the segments may be indifferently orientated. It is not necessarily the same for all the segments. Preferentially, they are laid out in herringbone pattern, i. e. if the surface of the cylinder is divided in two halves each on the side of a plane perpendicular to the cylinder axis, on one side of this plane the segments are inclined according to a. certain angle in relation to this plane whereas, on the other side, they are inclined at an angle opposite the previous one in relation to this plane.

Thus, it is possible to avoid the asymmetrical stresses of the cylinder longitudinally, i. e. along its shaving rotation axis. In particular, contrary to the case of the old design tools described above, the segments are no

longer solely positioned in accordance with the circumference of each disk.

It is thus possible to decrease the motor power required to draw the cylinder by decreasing the density of the shaving material over its surface, while, however, conserving a contact surface between the cylinder and the surface to be shaved, fully swept by the shaving segments during the course of a cylinder rotation. The cylinder may then be drawn by a compressed air motor.

From another aspect, the invention concerns a tool to shave a surface comprising a cylinder revolving around an axis, characterized by the fact that the external surface of this cylinder is made up of shaving material, each segment extending longitudinally over this external surface in a direction comprising a component not equal to zero parallel to the said axis, the directions of the segments being adapted so as to significantly balance the stresses of the cylinder parallel to this axis when the latter is in rotation and in contact with a surface to be shaved.

From yet another aspect, the invention applies to the decontamination method of a surface by the shaving of a superficial layer of this surface over a predetermined depth wherein a cylinder is displaced in a first direction, the cylinder rotating around an axis perpendicular to the first direction, in contact with the surface to be shaved.

The foregoing is characterized by the fact that segments of shaving material are disposed over the external surface of the cylinder, extending longitudinally over this external surface in a direction comprising a component not equal to zero-parallel to the said rotation axis.

Other aspects, aims and advantages of the invention will be observed on reading a description of one of its embodiments.

The invention will also be better understood using drawings, on which: - Figure 1 diagrammatically represents in perspective (seen from above or upper view) an example of an embodiment example of a machine tool in accordance with this invention; - Figure 2 diagrammatically shows in perspective (seen from below or lower view) part of the machine tool represented in figure 1; - Figure 3a diagrammatically shows in perspective (seen from below or lower view) part of the machine tool represented in figures 1 and 2 ; - Figure 3b diagrammatically shows a roller the height of which is adjustable; - Figure 4 diagrammatically shows in perspective (side view) an example of the mode of constructing a shaving tool intended to equip the machine tool represented in figures 1 to 3 ; - Figure 5 diagrammatically shows in perspective an injection device intended to blow air into the tool represented in figure 4; - Figure 6 diagrammatically shows, in a longitudinal section, the tool represented in figure 4; and - Figure 7 diagrammatically shows, in side elevation perpendicular to its longitudinal axis, the tool represented in figures 4 and 6.

On the different figures, the same references designate identical or similar elements.

An embodiment example of a machine tool in accordance with the invention is described below in relation to 1 to 7.

In this example, the machine tool 1 is essentially made up of a shaving support intended to shave vertical and horizontal concrete walls such as ground or ceiling.

This shavin-g--support comprises fixation means 3, a guide 5, a shaving tool 7 and driving motor 9 of the shaving tool 7.

As represented on figure 2, the fixation means 3 are made up of two vacuum pads 11,13 oblongs of 350X220 mm2 and a vacuum plant 15.

Reverting to figure 1, each vacuum pad 11 or 13 is equipped with handles 17 and a decompression valve 19. Each vacuum pad 11 or 13 is adapted to exercise a tensile strength of 120 to 180 kg on the wall to which it is fixed.

The vacuum plant maintains a vacuum which suffices for the adhesion of vacuum pads 11,13 on a wall. The flow rate of this plant varies between 10.8 to 55.8 m3/hour. This allows for maintaining a pressure in each vacuum pad significantly comprised between 5 and 250 millibars.

Thus, these fixation means 3 make it possible to hold and maintain a shaving support weighing about 30 to 40 kg on vertical walls or on a ceiling while laying a shaving tool pressure on the wall of 5 to 8 bars in normal use and capable of reaching 12 bars.

This makes it possible to mould and absorb the irregularities of the surfaces to be shaved as well as possible warpage of these surfaces. In addition, it makes it possible to position the support in every direction.

Tool 7 and the driving motor 9 move on guide rail 5 thanks to a shaft-free jack, on rollers. The guide extends longitudinally between the fixation means 3. A vacuum pad 11 or 13 is fixed to each of its longitudinal extremities.

The course of tool 7 on guide 5 is about 960 mm. The machine tool according to this invention may comprise automatic back and forth means. Thanks to this automatic back and forth means, the displacement of the shaving tool 7 on guide 5 is such that the shaving tool 7 shaves and grinds the wall surface on one direction, with a shaving

speed, and it comes back, on the opposite direction, without shaving or grinding the wall surface at a return speed higher than the shaving speed. The shaving tool is brought on the wall surface and moved away from this wall, thanks to a pneumatic jack that takes air from air an air supplier which may provide air to the air injection means 33.

As represented on figure 3, tool 7 comprises a cylinder 21 driven by the driving motor 9. This driving motor 9 is a compressed air motor of 4.5 kW with a rotation speed of 6000 revolutions per minute at 7 bars. The cylinder is made to revolve around itself with a tangential speed of cylinder 21 on the surface to be shaved, appreciably exceeding 35 m/s such that any metallic foreign bodies on the surface to be shaved may also be removed.

The driving motor 9 is connected to guide 5 through a support 23 which constitutes a device for adjusting the height of the axis of rotation of the cylinder in relation to the wall with micrometric precision. These adjustment devices, in association with guide 5, make it possible to manage the shaving depth and keep it constant. This depth is specifically adjusted depending on the depth of radioactive contamination.

As shown in figure 3b, this depth is adjusted thanks to a roller 40 attached to a scale 41. The scale 41 is for instance adjusted to 3 mm. Through the jack force, the shaving tool 7 shaves the wall surface until the roller 40 reaches the wall surface. Then the shaving stops, even if the back and forth means continued to move the shaving tool 7 on guide 5.

Cylinder 21 is 130 mm long. It is displaced along guide 5 perpendicularly to its rotation axis. Thus, a displacement of shaving tool 7 on guide 5 corresponds to 0.124 m2 of treated surface.

Cylinder-2-1-is--described-with greater precision in relation to figures 4,6 and 7.

As represented on figure 6, cylinder 21 is hollow and revolves around axis X corresponding to its rotation axis when shaving tool 7 is fitted on machine tool 1. Its cylindrical wall is perforated by orifices 27.

As represented on figure 4, the external surface 29 of this cylinder 21 is formed of segments 31 of shaving material. Each segment 31 extends longitudinally over this external surface 29 in a direction comprising a component not equal to zero parallel to axis X. Segments 31 are laid out on the external surface 29 in herringbone pattern, the branches of the patterns meeting in the median transversal plane of cylinder 21. In a variant, the segments (or certain of the segments) 31 are laid out helicoidally on the external surface 29. However, in all cases, attention must be paid to limit any asymmetrical stresses of cylinder 21 that might draw it too strongly in a direction parallel to its axis X, when it is in rotation in contact with the surface to be shaved. Segments 31 have a flatly developed straight form. In a variant, their flatly developed form is curved. Yet another variant shows segments 31 in both the two above-mentioned forms in the same cylinder 21. Segments 31 may have variable steps.

The segments are made up of shaving material where diamond is present. Diamond of different quality may be used to form the shaving material of the same segment 31 and/or different segments 31 of the same cylinder 21. Thus, segments may comprise several different qualities.

As represented on figure 5, air injection means 33 are fitted inside shaving tool 7, intended to blow air into cylinder 21, allowing for the ventilation and cooling of the latter. The air blown by means of air injection means 33 passes through orifices 27, cylinder 21 being protected

by-casing 35 (cf. figures 1 and 3), the dust-generated by the shaving is kept in casing 35 then sucked up, with the air blown by air injection means 33 through duct 37 connected to an industrial suction machine (not represented).

The shaving support described above makes it possible to work on surfaces of small dimensions and/or surfaces hard to access, being easy to use. It is easily handled by two operators. Its maintenance is simple. All the foregoing reasons allow for decreasing user risks in contaminated environments, allowing for selective shaving which minimizes the production of waste to be treated and/or stored. It may be equipped with man-machine interfaces, jointed or movable arms, visual control tools (camera), etc.

The machine tool, the tool and the shaving method described above may comprise several variants. Thus, for example, shaving tool 7 may comprise several cylinders 21, such as those described above, places side by side along axis X. In this case, the orientation of segments 31 may differ from one cylinder to another when they are fitted to form shaving tool 7 even if the cylinders are identical to each other. All that is needed is that they be placed head to foot. Similarly, cylinder 21 or each cylinder 21 may be full or half-full.

The support described above may be made to greater dimensions.

In accordance with the invention, the tool may also be fitted on a great many shaving tools which may be different from that described above. Equally, in accordance with the invention, the machine tool may receive tools which are different and specifically intended for the surface to be treated.