WO2007100281A1

WO2007100281A1 - Procedure to provide a propeller with ridges

Info

Publication number: WO2007100281A1
Application number: PCT/SE2007/000037
Authority: WO
Inventors: Ragnar Winberg
Original assignee: Ragnar Winberg
Priority date: 2006-03-03
Filing date: 2007-01-17
Publication date: 2007-09-07
Also published as: SE530428C2; SE0600499L

Abstract

In order to make a rotor blade provided with ridges where the ridges lie close to each other and have a mainly circular direction with the centre in the rotor axis and where the ridges have a form tapering outward, characterized by the fact that the ridges are formed by a cylinder provided with grooves under strong pressure and under rotation pressing against the rotor blade so that its surface layer flows and, after the cylinder has passed the formed ridges, they remain. Procedure according to Claim 1, characterized by the fact that, at the same time as a cylinder forms one surface of the blade through pressure against its surface, another cylinder forms the opposite side of the blade through pressure directed roughly opposite the direction of pressure of the first cylinder.

Description

Procedure to provide a propeller with ridges

Propellers on big merchant vessels are in most cases made of bronze or of stainless steel. They can be made in only one piece but it is more common that its blades are screwed on to a hub. The blades can then be either immovably bolted or they can be fastened so that they are turnable on the hub. Kaplan turbines have blades resembling propeller blades.

It is known since long that a surface submerged into water will get somewhat less resistance to currents of water if it has small ribs parallel with the current direction than if the surface is totally smooth. Since the cost for fuel for a big ship is very high, also a very small reduction of the friction against the water can give a valuable economic saving.

The present invention concerns a procedure to make a rib pattern directly on a rotor blade intending to reduce the friction against water or air streaming close to the blade surface.

In the following the principle of the invention will be explained in detail by means of figures. Figure 1 shows a ship propeller with four blades.

Figure 2 shows a cross section of a part of a propeller surface.

Figure 3 shows a device for making a ribbed surface.

Figure 4 shows the device according to Figure 3 in another projection.

Figure 5 shows a variant of the device according to Figure 4.

Figure 1 shows a propeller with four blades where the blades 1 , 2, 3 and 4 are screwed on to the hub 5. On blade 1 an area has been marked 6, where the surface has been equipped with small circular ribs. The ribs can be on both sides of the blade.

Figure 2 shows a section of a sector of a propeller where the surface pattern can be seen. Here ribs 7 can be seen which lie close to each other. The ribs have a form tapering outward and can have rounded ridges 8 and rounded valleys 9 between them. The height of the ribs should be less than half a millimetre and the distance between them less than a millimetre. The relationship between the height of the ribs and the distance between them can be different from what can be seen on the figure. With the described process of manufacture it can also be arranged so that the ribs have short interruptions and that they are so close that the length of the ridges between the interruptions are very short. If the length between two interruptions is very small, the term elevation may be more relevant than ridge or rib.

Figure 3 shows a principle for the making of ribs on a propeller blade with a smooth surface. A section of the blade is shown according to the line A - A, marked with lines and dots. A propeller blade 10 is here screwed on to a hub 11 which can be rotated around a firm axis 12. The axis is mounted to a stand with and upper beam 13 and a lower beam 14. The blade 10 can be screwed on to the hub 11 so that the surface of the blade is in the main horizontal. However, the hub can be designed so that the blade is turning while it is rotating around the axis 12. Then the surface which is just to be formed becomes approximately horizontal. 15 and 16 indicate parts which are mobile along the upper beam and the lower beam. On the parts 15 and 16 hydraulic devices 17 and 18 are attached in whose ends rotating cylinders 19 and 20 are mounted. The cylinders can have ten grooves for instance and are made so that its ridges have a very high hardness. It is these ridges which, by pressing hard against the propeller surface, make its surface layer float so that a rib pattern is formed. In this case it is the propeller blade which rotates slowly around the axis 12 while the pressing cylinders 19 and 20 rotate while forming the surfaces of the blade. Depending on the form of the blade the cylinders can follow the form of the blade with unchanged pressure against the blade surfaces by the hydraulic devices 17 and 18. At the same time as the propeller blade rotates around the axis 12, the parts 15 and 16 can move inward towards the axis 12 a cylinder breadth per revolution by the propeller blade. Of course all propeller blades should be screwed on to the hub during the process.

On Figure 4 the device according to Figure 3 can be seen in another projection.

Figure 5 shows a variant of the device according to Figures 3 and 4. Here the parts 21 and 22 are movable also at right angles to the direction along the upper beam and the lower beam. Also the hydraulic devices 23 and 24 are arranged so that their inclination can be changed. The intention is that the forces pressing the forming cylinders against the surfaces of the propeller blades shall be directed against each other. This device may be suitable when the surfaces of the propeller blades cannot be placed in a tolerably horizontal position.

Every cylinder can make many ribs abreast. The cylinder can move entirely circularly around the centre of the hub and after a revolution around it, it is moved a cylinder breadth outward or inward before it marks a new revolution. The cylinder can instead move in a spiral outward or inward so that for every revolution around the hub it moves a cylinder breadth. The cylinder can also be moved more than a cylinder breadth for every revolution around the hub since in this case unprocessed areas result between the areas processed by the cylinder.

Instead of the described device where the propeller is revolved, it can of course be arranged so that the propeller is immovable while the frame with the marking cylinders is turned around the propeller. It can also be organized so that the device is arranged to mark only one propeller blade at a time.

It may be possible to make the corresponding ribs by using a self-rotating milling cutter which at the same time mills many grooves close to each other. Considering that stainless steel wears hard on a cutting tool, the durability will be low for such a milling cutter at the same time as the speed of flow is low and therefore the method is expensive If the propeller is made of bronze the wear is considerably less at the same time as the speed of flow becomes greater. However, the procedure of marking mentioned above is clearly superior.

Claims

1. In order to make a rotor blade provided with ridges where the ridges lie close to each other and have a mainly circular direction with the centre in the rotor axis and where the ridges have a form tapering outward, characterized by the fact that the ridges are formed by a cylinder provided with grooves under strong pressure and under rotation pressing against the rotor blade so that its surface layer flows and, after the cylinder has passed the formed ridges, they remain.

2. Procedure according to Claim 1 , characterized by the fact that, at the same time as a cylinder forms one surface of the blade through pressure against its surface, another cylinder forms the opposite side of the blade through pressure directed roughly opposite the direction of pressure of the first cylinder.