WO1993009027A1

WO1993009027A1 - An elastomeric propeller having a flexible blade core

Info

Publication number: WO1993009027A1
Application number: PCT/DK1992/000313
Authority: WO
Inventors: Nils Oluf EHRENSKJÖLD
Original assignee: Gori Af 1902 As
Priority date: 1991-10-30
Filing date: 1992-10-29
Publication date: 1993-05-13
Also published as: AU2941492A; DK179891D0

Abstract

A propeller for e.g. a ship has a central hub (7) with a plurality of propeller blades (8). Each blade (8) is composed of an elastomer, such as rubber (10), having a flexible core (9), which may e.g. consist of a relatively thin, corrugated plate of spring steel. The core (9) and a hub bushing (11) of e.g. bronze are moulded and vulcanized to an integral unit which, without expensive after-treatment, forms a propeller having a finished smooth surface and a consistency capable of absorbing and damping impact and shock pulses from the reaction forces of the water. The corrugation of the blade is in the form of folds extending outwardly from the hub. Even with a thin plate the blade hereby obtains a sufficiently great rigidity transversely to the direction of rotation of the propeller, while the blade is allowed to twist and bend in response to the load, so that the pitch of the blade is optimally adjusted to the instantaneous state of operation.

Description

An elastomeric propeller having a flexible blade core

The invention concerns a propeller for e.g. a ship and having a central hub with a plurality of propeller blades.

Propellers for e.g. ships are extensively moulded either integrally or with hub and blades separately of metals, such as aluminium alloys, bronze and steel. After moulding the blades often have to undergo a relatively expensive subsequent working to obtain the close accuracy in terms of shape and the smooth surface necessary for the pro¬ peller to work with as low a friction as possible in the water. All the metals used have a great coefficient of elasticity causing the blades to be stiff and maintain their shape unchanged under practically all conceivable conditions of operation. The geometrical design of such metal propellers will therefore necessarily be the result of a compromise where it is attempted to achieve optimum function of the propeller within a specific range of ope- ration, while under other conditions the propeller will work with reduced efficiency and in some cases even with harmful consequential effects in the form of e.g. cavita- tion or noise and vibrations which propagate from the pro¬ peller into the hull to the inconvenience of those on board. If the blades are moreover subjected to impacts beyond the yield point of the metal by striking obstacles in the water or on the bottom during the rotation of the propeller, the blades will be deformed permanently. Then the propeller can no longer work in a quiet and well- balanced manner, but will instead run untrue and transmit shakings and vibrations into the hull. Some of the em¬ ployed metals are moreover not particularly corrosion re¬ sistant to sea water. This applies e.g. to the aluminium alloy used for a ship's propeller known from US Patent 3 744 931, which is therefore protected against corroding attacks by the sea water by means of a thin vulcanized rubber layer.

Today there are also propellers which are made of f bre reinforced plastics with a relatively low coefficient of elasticity and consequently flexible blades. Thus, Norwe¬ gian Published Application 163 090 discloses a plastics propeller having fibre reinforcements which are applied in a manner such that the blades obtain some predetermined anisotropic properties. Furthermore, a rigid beam is mounted at the leading edge of each blade, and this beam together with the anisotropic properties of the blade causes the blade to be deformed elastically in response to the load. For example, the pitch may be changed in inverse ratio to the load, so that the propeller can work with a high efficiency within a much greater operating range than metal propellers. However, the structure is complicated and expensive, and the selected mounting of the fibre re¬ inforcements is an extremely critical operation which it is difficult to perform repeatedly with the required ac¬ curacy under practical conditions of production. If the fibre reinforcements are not completely identical from blade to blade, this will entail that the propeller will operate in a more or less unquiet manner so that it must be considered unuseful for most purposes. Another drawback of these fibre reinforced plastics propellers is that the damage to which the propeller is subjected if striking an object in the water or on the bottom during rotation, is frequently of such a destructive nature that the damage cannot, or only with difficulty, be repaired.

It is common to the metal or plastics materials used for the above-mentioned propeller types that they have a hard consistency which is incapable of damping or absorbing the shock pulses from the reaction forces of the water. The propellers therefore tend to transmit strong propeller noise in the water and convey the shock pulses from the turbulence of the water into the hull in the form of vi¬ brations and shakings.

US Patent 2 473 665 describes a propeller which, within certain limits, is capable of withstanding shocks and im¬ pacts from objects which the propeller might strike in the water during rotation. The blades of this propeller con¬ sist of rubber which merely yields elastically if the blade is struck, and immediately again assumes the origi¬ nal shape. To impart greater rigidity to the rubber than it inherently possesses, the blades are reinforced with some wires. However, this reinforcement is not sufficient to absorb the loads that occur in operation of the great majority of ships, and the reinforcement type cannot be used either for selectively controlling the deformation of the blades in response to the load.

The object of the invention is to provide a propeller of the type mentioned in the opening paragraph which can be moulded to finished size with a smooth and even surface that does not require expensive after-treatment.

Another object of the invention is to provide a propeller of the type mentioned in the opening paragraph which per se is capable of reducing the propeller noise and absorb¬ ing and damping shock pulses from the reaction forces of the water, and which can moreover withstand shocks and impacts from objects in the water or on the bottom to a considerable extent without being permanently deformed.

A third object of the invention is to provide a propeller of the type mentioned in the opening paragraph which is corrosion resistant to e.g. sea water. A fourth object of the invention is to provide a propeller of the type mentioned in the opening paragraph which, by simple means, can safely and effectively adjust the pitch of the blades optimally to any state of operation in re- sponse to the instantaneous load on the propeller.

The novel and characteristic features according to the invention, by which the above-mentioned objects are ob¬ tained, are that at any rate the blades of the propeller are composed of an elastomer having a flexible core which extends from the hub over a considerable portion of the area of each blade and consists of a material having a greater coefficient of elasticity than the elastomer, e.g. fibre reinforced plastics or metal. The elastomer imparts to the blades corrosion resistance and a smooth surface as well as the ability to dampen shock pulses and absorb im¬ pacts without permanent deformations. The core imparts to the blades strength and oriented flexibility to control the pitch of the blades in response to the load.

The elastomer may advantageously be a natural or synthetic rubber which is vulcanized firmly on the core so as to provide an intimate and long-lasting connection between the core and the rubber. To strengthen the blade additio- nally the rubber may moreover be fibre reinforced, and in special advantageous embodiment there may be an inner fibre reinforced layer of rubber to stiffen the blade and an outer soft layer of rubber to improve the impact and shock absorbing properties of the propeller.

When the propeller blades are firmly mounted on the cen¬ tral hub, the rubber covering of the blades may advantage¬ ously continue inwardly as part of the hub, whereby the cores of the blades extend into this elastomeric hub part. The applicant's Danish patent applications No. 1392/91 "a folding propeller having at least three blades" and No. 1393/91 "a folding propeller having at least two blades", both of which are incorporated in the present patent application by reference, describe pivotal propeller blades provided with a rubber covering on the innermost end portion which carries the engagement means for syn¬ chronization of the pivotal movements of the blades. According to the invention, this rubber covering may ad- vantageously be integral with the rubber covering on the rest of the blades, whose core simultaneously extends into the elastomer of the blades to give the blade a suffici¬ ently high bending stiffnes over the swing axis of the blades.

The flexible core may advantageously be constructed as a plate which extends over the area of the blade to a limit curve spaced from the periphery of the blade, thereby forming along said periphery a non-stiffened area having a particularly great flexibility. This entails that the blade edges can easily be bent in the flow direction by the water pressure, thereby reducing the turbulence and the flow resistance which the blade meets in the water.

The flexible plate may e.g. be made of fibre reinforced plastics, which, in a known manner, has obtained the ani¬ sotropic properties necessary to control the pitch of the blade in response to the load, by means of the selective position and orientation of the fibre reinforcement. How- ever, these anisotropic properties can also be obtained by corrugating the plate with folds radiating into the plate from its end positioned closest to the axis of rotation. This entails that the arrangement of the fibre reinforce¬ ment is no longer a critical factor. It is moreover pos- sible to use metals, such as spring steel, which have a great strength and are simultaneously very flexible when the plates employed are thin. With this structure the blade can be given the intended rigidity in the direction of the folds and the intended flexibility transversely to this direction. As regards small and minor propellers, the desired effect can be obtained by means of a single corru¬ gated plate of this type, while in case of larger propel¬ lers and larger loads it may be necessary to stiffen the rubber covering with several plates.

The rubber covering can easily be vulcanized on the plate by means of known methods. To obtain a particularly long- lasting structure and intimate connection between the va¬ rious components of which the blade is composed, the plate may be perforated so as to provide a mutual bond between the rubber coverings on the two sides of the plate through the perforated holes in the plate. When the blade works in the water, the plate edge may tend to cut the rubber co¬ vering. This problem is obviated by providing the plate edge with serrations or waves so as to form an even and soft transition between the rigid plate and the softer rubber.

The invention will be explained more fully by the follow¬ ing description of embodiments which solely serve as ex- amples, and with reference to the drawing, in which

fig. 1- is a partially sectional end view of a fraction of a propeller having three blades, each of which is composed of a fibre reinforced core with a rubber covering on both sides,

fig. 2 shows a section along the line II-II in fig. 1,

fig. 3 shows a section along the line III-III in fig. 1, fig. 4 is a partially sectional end view of a fraction of a propeller having three blades, each of which is composed of a corrugated metal core having a firmly vulcanized rub¬ ber covering on both sides, 5 fig. 5 shows a section along the line V-V in fig. 4,

fig. 6 shows a section along the line VI-VI in fig. 4,

10 fig. 7 is a sectional side view through a folding propel¬ ler blade which is composed of a corrugated metal core having a rubber covering on both sides,

fig. 8 shows a section along the line VIII-VIII in fig. 7,

15 fig. 9 shows a section along the line IX-IX in fig. 7,

fig. 10 is a perspective view of the core shown in fig. 7,

20 figs. 11-16 show various examples of how a propeller blade according to the invention can be constructed,

fig. 17 shows a fraction of an axial section through a propeller blade according to the invention in astern con- 25 figuration,

fig. 18- shows a section along the line XVIII-XVIII in fig. 17,

30 fig- 19 shows the propeller blade of fig. 17 in an un¬ loaded state,

fig. 20 shows a section along the line XX-XX in fig. 19,

35. fig. 21 shows the propeller blade of fig. 7 in forward configuration, and fig. 22 shows a section along the line XXII-XXII in fig. 21.

Figs. 1-3 show a typical structure of an elastomer pro- peller according to the invention for a ship. In this case the propeller, which is generally designated 1, has three propeller blades 3 which are firmly arranged on a hub 2 for the mounting of a propeller on the drive shaft of the ship. The blades are composed of a core 4 and a rubber co- vering 5, which is fixedly adhered or vulcanized on the core. As is the normal case with propellers of this type, the blades are screw-shaped with a radially outwardly de¬ creasing pitch, as appears from figs. 2 and 3, which more¬ over show that the blades have an airfoil profile. How- ever, the selection of blade profile constitutes no part of the present invention, and the blades may therefore equally well have e.g. an ogival profile. As regards all three blades, the core 4 is moulded in one piece of fibre reinforced plastics with a profile following the profile of the blade at a distance corresponding to the thickness of the rubber covering. The core is manufactured in the manner known from the manufacture of fibre reinforced plastics propellers, whose blades have anisotropic proper¬ ties for flexibly changing the pitch in response to the propeller load.

Figs. 4-6 show a second embodiment of a propeller accord¬ ing to the invention. This propeller, which is generally designated 6, has a rubber covering 10 with the same outer shape as the propeller shown in figs. 1-3, but the fibre reinforced plastics core is now replaced by a relatively thin corrugated plate, whose folds radiate outwardly in the plate from that one of its ends which is closest to the axis of rotation. By suitable selection of plate thickness and material and of the shape of the corrugation the blade can be given the intended rigidity transversely to the direction of rotation and also obtain a flexibility permitting the blade to twist and bend in response to the propeller load, so that the pitch of the blade is automa¬ tically adjusted optimally to the instantaneous state of operation. The rubber covering of the blades continues in¬ wardly and forms part of the hub which at the inmost part has a brass bushing 11 with a hole 12 fitting the shaft (not shown) of the ship. As shown, each blade has its se¬ parate core which extends into and is retained by the rub- ber part of the hub. However, as an additional safeguard the core may also be directly connected with the bushing 11 by means of e.g. welding, soldering, glueing, screwing or riveting. The corrugated plate core may be made of any suitable material. Thus, the core shown in figs. 1-3 may be made of plastics with a fibre reinforcement, whose po¬ sition and orientation, however, are not critical since the anisometric properties of the core are primarily established by means of the corrugation. However, the core may also advantageously be made of metal, such a spring steel, which has a very high yield point and can therefore be used for plate-shaped cores which are so thin that in spite of the great coefficient of elasticity of the mate¬ rial the plate is nevertheless extremely flexible.

When the core is of e.g. spring steel, it is typically manufactured by means of punching and pressing operations requiring relatively expensive tools. However, the tool costs can be reduced considerably when, as shown in fig. 4, use is made of separate cores that can be employed for all the blades in the same propeller and for propellers with a different number of blades. When a propeller is to be manufactured, the plate-shaped cores are first posi¬ tioned in a mould together with a bushing, following which the mould is filled with a rubber mass than can be vulca- nized together with the cores and the bushings to an inte¬ grated unit which constitutes the finished propeller, practically without any after-treatment. The surface of the propeller is an accurate cast of the surface of the mould, and for the permanent production of propellers hav¬ ing a fine and smooth surface it is therefore just neces- sary to manufacture a mould once and for all which has such a surface.

When the rubber is vulcanized on a core of e.g. spring steel, it is well-known that a reliable and strong connec- tion is obtained between the two components. When the plate-shaped core is perforated, as shown to the top left in fig. 4, the solidity of the connection is ensured addi¬ tionally, the rubber coverings on the two sides of the plate being now connected directly with each other via the perforated holes 13. To prevent the plate edge from cutt¬ ing the relatively soft rubber, the plate edge is provided with waves 14 to provide a smooth transition between the relatively rigid plate and the softer rubber.

Figs. 7-10 show a folding propeller blade which is gene¬ rally designated 15 and which is constructed in principle in the same manner as shown in figs. 4-6 with a core 16, which is surrounded by a rubber covering 17, but which in this case has a sufficient plate thickness and weight to ensure the deflections of the blades and is provided with waves instead of folds. The blade is intended for folding propellers of the type described in the applicant's pre¬ viously mentioned Danish patent applications 1392/91 and 1393/91. In these propellers the innermost end part 18 of the propeller blades, which is located in the hub and carries the engagement means for synchronization of the pivotal movements of the blades, is provide with a rubber covering which, in the shown embodiment, merges into the rubber covering of the actual plate. The core 16, which is shown in perspective in fig. 10, simultaneously extends in curve-shape into and around a swing axle 19 which is em- bedded in the rubber of the end part. This structure is simple and inexpensive to manufacture and also satisfies all the requirements which must be made with respect to strength and flexibility.

Figs. 11-16 in cross-section show a plurality of examples of how a propeller blade according to the invention can be constructed. The blade in fig. 11 corresponds to the blade shown in figs. 1-3 with a core 4 of fibre reinforced plas- tics and a rubber covering 5. In fig. 12 the fibre rein¬ forced plastics core is replaced by a relatively thick plate-shaped core of e.g. spring steel. The core is sur¬ rounded by a rubber covering 21. This structure is ex¬ tremely simple and inexpensive to manufacture and is suit- able where a relatively stiff blade capable of withstand¬ ing hugh loads is required. A more flexible blade is shown in fig. 13, in which the core 22 consists of a relatively thin plate of e.g. spring steel, in which ribs 24 are pressed to stiffen the blade radially. The core is sur- rounded by a rubber covering 23. A greater rigidity against in particular too great twisting in the profile can be obtained by arranging two thin plate cores 25, 26 mutually spaced in the rubber covering 27, as shown in fig. 14. The plates 25, 26 may be assembled at the ends of the profile as shown. Fig. 15 corresponds to the embodi¬ ment shown in figs. 4-6 with a corrugated core 9 of e.g. spring steel and a rubber covering 10. Fig. 16 shows a structure similar to the one in fig. 15 with a corrugated plate-shaped core 28 which, however, in this case is sur- rounded by an inner relatively stiff rubber layer 29 and an outer relatively soft rubber layer 30. The inner rubber layer 29, which may e.g. be of fibre reinforced rubber, in coaction with the core 28, serves to adapt the bending ri¬ gidity of the blade to precisely the desired magnitude, while the outer soft rubber layer 30 serves to absorb shock pulses from the frequently violently turbulent water flow that surrounds the propeller. This considerably re¬ duces the noise generated by the propeller in operation, and the vibrations which propagate via the propeller and the drive shaft into the hull. It is noted that the inner rubber layer 29 serves as a kind of lattice reinforcement between the folds of the core, which without this rein¬ forcement would not have a sufficiently great bending rigidity transversely to the profile when a thin plate is used. The same applies to the other embodiments using a thin corrugated plate as a core, but in any case the stif¬ fening depends upon the strength of the rubber. A carcass of e.g. canvas (not shown) may be incorporated to streng¬ then the blades additionally.

Figs. 17-22 show how a propeller 31 is deformed in typical situations that occur in operation. The blade 31 has a corrugated, plate-shaped core 32 surrounded by a rubber covering 33 which is moulded firmly around the bushing 34 of e.g. bronze for mounting the propeller on a drive shaft (not shown). Figs. 19, 20 show the propeller in an un¬ loaded state where the blades are not deformed, and the propeller has its original shape as supplied from the fac¬ tory. Figs. 17, 18 show the propeller when going astern where the ship sails in the direction shown by the arrow in fig. 17 and the propeller rotates in the direction shown by the arrow in fig. 18. Consequently, the reaction forces on the propeller act in an opposite direction to the arrows. According to the invention the blade is geome¬ trically designed in a manner such that the centre of gra- vity of the reaction forces is closer to the trailing edge of the profile than the main axis of twist of the blade. Therefore, when going astern the water pressure twists and bends the blade in a manner such that the pitch increases and the shape of the profile is advantageously changed. The propeller blade now has a shape where the propeller can also work with great efficiency when going astern in contrast to propellers having rigid blades, which are primarily adapted for providing satisfactory efficiency when going ahead at relatively great speeds of rotation. Therefore, these propellers must necessarily have a rather small pitch to avoid cavitation. Figs. 21, 22 show the situation during propulsion at a great speed. The water pressure has now twisted and bent the profile such that the blade can rotate at the said great speeds without any danger of cavitation. As will be seen, the trailing edge of the profile is now bent in the same direction as the water flow, thereby greatly reducing the turbulence and flow resistance.

The elastomeric propellers of the invention, in addition to the above-mentioned advantageous properties and ef¬ fects, have the natural corrosion resistance of the rubber to e.g. sea water. Furthermore, the propellers withstand impacts and shocks from objects in the water or on the sea bottom considerably better than the conventional struc- tures without receiving permanent deformations. If de¬ formed, both the rubber covering and the core just deform resiliently and immediately again assume the original shape.

Further advantageous properties and effects are achieved according to the invention by arranging the elastomeric covering in the same manner as stated in the applicant's patent application ^"DK xxxx/91 "elastomeric propeller hav¬ ing a flexible elastomeric covering", which has the same filing date as the present patent application and which is incorporated in the present patent application by refe¬ rence.

The elastomeric propeller of the invention is described above and shown in the drawing as a propeller for a ship. This, however, is just an example, since the propeller may equally well be used for many other purposes within the scope of the invention where the advantageous properties and effects of the propeller can be utilized, e.g. tur¬ bines and ventilators.

Claims

P a t e n t C l a i m s :

1. A propeller for e.g. a ship, having a central hub with a plurality of propeller blades, c h a r a c t e r i z e d in that at any rate the blades are composed of an elasto¬ mer having a flexible core which extends from the hub over a considerable portion of the area of each blade and con¬ sists of a material having a greater coefficient of ela- sticity than the elastomer, e.g. fibre reinforced plastics or metal.

2. A propeller according to claim 1, c h a r a c t e r ¬ i z e in that the elastomer is fibre reinforced.

3. A propeller according to claim 1, c h a r a c t e r ¬ i z e d in that the elastomer is composed of at least two layers, the inner one of which consisting of a relatively stiff, e.g. fibre reinforced, elastomer and the outer one of a relatively soft elastomer.

4. A propeller according to claim 1, 2 or 3, c h a ¬ r a c t e r i z e d in that the elastomer is a natural or synthetic rubber which is vulcanized firmly on the core.

5. A propeller according to one or more of claims 1-4 and of the type where the propeller blades are arranged firmly on the central hub, c h a r a c t e r i z e d in that at any rate partially the hub is composed of an elastomer integral with the elastomer of the blades, and that the cores of the blades extend into or through the elastomer of the hub.

6. A propeller according to one or more of claims 1-4 and of the type where the propeller blades are pivotally arranged on the hub, and the end of each blade located in the hub is composed of an elastomer at any rate in an area which is provided with engagement means for synchronizing the pivotal movements of the blades by engagement with complementary engagement means on the adjacent blades, c h a r a c t e r i z e d in that the elastomer of the blade end located in the hub is integral with the elastomer on the rest of the blade, and that the core of said blade extends into the elastomer of said blade end.

7. A propeller according to one or more of claims 1-6, c h a r a c t e r i z e d in that the core is substan¬ tially plate-shaped.

8. A propeller according to one or more of claims 1-7, c h a r a c t e r i z e d in that the core is corrugated with folds, waves or ribs radiating into the core from its end located closest to the axis of rotation.

9. A propeller according to one or more of claims 1-8, c h a r a c t e r i z e d in that the core consists of two or more plate-shaped parts.

10. A propeller according to one or more of claims 1-9, c h a r a c t e r i z e d in that the core is perforated.

11. A propeller according to one or more of claims 1-10, c h a r a c t e r i z e d in that the contour of the core is serrated or wave-shaped.