Device on Kaplan turbines in order to provide the rotor blades with micro ■ ribs and the procedure to make the micro grooves on the rotor blades. The use of the device at a power station.

It is known since long that a surface lowered into water gets a somewhat smaller resistance against a current of water if it has small ribs parallel with the direction of the current than if the surface is totally smooth.

It is true of ship's propellers that less friction makes the propeller more effective. It is also true of a Kaplan type turbine where it is the water which drives the turbine.

In the Swedish patent 530 428 a procedure is mentioned how to make micro ribs on rotor blades in the main circular with the rotor shaft. This procedure can only take place, however, when the blades are assembled on a device made for this purpose and not when the rotor blades (propeller blades) are on their permanent place. Because of pollution in the water, among other things, the surface layer is worn and the ribs are smoothed away in course of time. To renew the ribs the blades must be removed and mounted in the workshop where the device for making the micro ribs is placed. This is hard work and takes long time. This is also true for the rotor blades on a Kaplan turbine.

The present invention aims at making it possible to provide the rotor blades of a Kaplan turbine with in the main circular micro ribs, lying close to each other, with the rotor shaft as a centre while the turbine blades remain in their permanent

places. As a result a long stoppage can be avoided and the heavy expenses that dismantling and assembling would mean can also be avoided.

The ribs separated by grooves (valleys) which can be produced by grinding or milling will certainly not be so favourably shaped as by the procedure with stamping which is described in the above-mentioned patent application but will give a reduction of friction in the surface which with regard to the cost for the procedure is favourable.

The main part of the device needed to make micro ribs on a Kaplan turbine according to this invention can be moved and used for other Kaplan turbines. There are often several similar turbines beside each other in a power station.

The invention has the characteristics that are evident from the patent claims.

In the following, the main principle for a device for making micro ribs on the rotor blades of a Kaplan turbine will be shown by figures.

Figure 1 shows a vertical section on a Kaplan turbine with a device according to the invention.

Figure 2 shows the turbine according to figure 1 in section A-A. Figure 3 shows a vertical section of another Kaplan turbine with a device according to the invention. Figure 4 shows the turbine according to figure 3 in section B-B.

In figures 1 and 2 the shaft of the turbine, the rotor shaft, is indicated with 1 and the hub of the turbine with 2. The water inlet is indicated with 3 and the water outlet, the so called suction pipe, situated under the rotor blades, with 4. The floor above the turbine is indicated with 5. In the floor there is an opening 6, which can be closed with a door 7. Only one rotor blade 8 has been drawn in. It is turned so that its surface becomes in the main horizontal. The device consists of a support 9 which when in use can be attached to the floor. On this support there is a fastening device 10, in which a bar 11 can move vertically. In the lower part of the bar there is a hinged area 12, in which a grinding instrument can move radially. The grinding instrument can consist of a round grinding wheel 13 driven by an electric motor 14. While the rotor shaft turns slowly grinding grooves can be made which are in the main circular with the rotor shaft as a centre. The grinding wheel can make many grooves beside each other so that a total breadth of several centimetres can be made. After that the rotor shaft can be

turned back while the adjacent area is treated. Of course the rotor shaft can be turned so that immediately after a blade has been treated the adjacent blade is treated. It can be arranged so that the treating instrument is moved continuously outward on the arm 12 while the rotor shaft is turned. The bar 11 can be moved vertically during the treatment. If the blades have the shape that they, when turned to an almost horizontal position, somewhat overlap each other, the edge of the lower blade cannot be treated. This means less, however, since the main thing is that the major part of the blade surfaces can get the friction reducing ribs. The most important thing in this connection is that the outer areas of the rotor blades get ribs since the current here is bigger than close to the hub. When grinding or milling no great pressure is needed against the surface which is to be treated. This can be arranged with a tight-fitting hood above the opening 6 through which the bar 11 can move (not in the drawing) so that the treatment can take place also when the turbine room is filled with water.

In figures 3 and 4 a modified device for treatment of the undersides of the rotor blades is shown. The vertical section according to figure 3 is turned 90 degrees in relation to the one in figure 1. Here two rotor blades 15 and 16 have been drawn. The bar 17 is partly movable vertically, partly turnable. A telescopic arm 18 is flexibly fastened to the lower part of the bar so that it can be parallel with the bar when brought down. The arm can be unfolded from the bar when the bar is turned so that the arm has a radial direction. The arm can be unfolded also if the blades overlap each other. In the outer end of the arm there is a grinding tool 19. Since the arm is telescopic and the bar is turnable, the grinding tool can treat a big part of the underside of a blade. By turning the rotor a little, the whole under-surface of a blade can be treated. If the mechanical pressure upwards against the blade surface is not sufficient, greater pressure upwards can be achieved by letting water of high pressure stream out downwards at the grinding instrument. Water can be supplied through a tube along the bar 17. It can be arranged so that when the arm 18 is turned, the grinding instrument 19 always gets such an adjustment that the grooves become at right angles to a radius through the instrument towards the rotor shaft. These devices can be solved by an expert and do therefore not affect the invention whose principle is evident from the patent claims. For treatment of the undersides of the blades, the turbine must be empty of water.