PROPELLER MOUNTING

Abstract: A propeller (12) fitted with an internal cast iron sleeve (15) is mounted onto a propeller shaft (10) by being force fitted onto a tapered conical portion (11) on the propeller shaft. The tapered portion (11) of the propeller shaft is roughened prior to assembly by drawing a serrated tool across its surface to provide a high friction coefficient. A recess (61) is formed in the aft end of the propeller hub (12) and accommodates the hydraulic nut (23) which is used for pushing the propeller (12) up the propeller shaft (10). A cover plate (70) is secured over the open end of the recess to enclose the nut (23).

Description: PBOEΕ TiHR MOUNTING The present invention relates to the irounting of propellers on shafts and especially to the irounting of keyless bore propellers on shafts. Keyless bore propellers have been developed with the object of avoiding the effects of stress concentration at the key and keyway and thereby increasing the fatigue resistance of a tailshaft significantly under normal operating conditions. The various Marine Classification Authorities throughout the world have extended the period between tailshaft surveys from 4 years to 5 years for keyless bore propellers in recognition of the improved fatigue performance of keyless bore propellers. In our GB-PS 1276074 we described a keyless method of mounting a propeller on a tapered portion of a propeller shaft in which an internally tapered metallic sleeve is located in a bore in the propeller hub with an annular space between the sleeve and the bore; the ends of the annular space are filled with a hardenable cαπrosition which is maintained under a pressure until set. The assembly of propeller and sleeve is then force-fitting onto the tapered portion of the shaft. The hardenable comt sition consists of an epoxy resin with a filler of carborundum which sets to provide a layer of high friction and high c_n_shing strength. Because the key has been omitted, the drive between tailshaft and the propeller must be achieved by friction alone. The Classification Authorities ..equire a factor of safety against slipping of 2.8 times the rr__ιximum full load torque of the engine. To meet this recruirement there must be a much greater interference - jTE OMP grip between shaft and propeller than is the case with a keyed propeller mounting, which means that unless a high, coefficient of ' friction is achieved between the shaft and the sleeve, the stresses in the sleeve will be very high to achieve the necessary grip. To achieve a. good grip a good bedding contact between sleeve and shaft is obtained before mounting the sleeve in the propeller boss. After rrachiπing, the sleeve is pushed onto the • tailshaft and thai jacked off, any high spots are identified and reπoved from the sleeve by hand grinding. The process may be repeated until bedding contact of at least S5% of the total area of the tapered surface of the propeller shaft is achieved. Prior to final push up the fitting surface are hand rubbed with 100 grit emery cloth and then degreased. We have found that the hand finishing with 100 grit emery tends to cause overall reduction in the shaft diameter and reduction in the bedding contact due to local variation in the amount of metal removed. The present invention in a first aspect provides a method of achieving a high coefficient of friction between propeller and shaft more reliably than has been the case hitherto. According to the invention there is provided a method of πDunting a propeller on a propeller shaft, in which the propeller or an assembly of a propeller with a sleeve secured within an axial bore in the propeller hub, is placed in torque-transmitting frictional engagement with a portion of the shaft, the method including the step of roughening at least one of the engaging surfaces of the hub or sleeve, and propeller shaft, without altering the overall dimensions of the or each surface so roughened, prior ' E O to placing the surfaces in engagement. The roughening may be performed by drawing a serrated 'tool, for example a steel hacksaw blade across the surface of the propeller shaft in a diagonal direction by hand. This treatment performed over substantially the whole of the tailshaft has been formed to produce scratches of a depth of 5 microns. Alternatively the scratches may be formed using 36 grit emery cloth. We have found that using these techniques it has been possible reliably to achieve a coefficient of surface friction of 0.18 to 0.20 or higher, whereas with the known technique using 100 grit emery cloth results of 0.16 to 0.17 are typical. By __mp_.oving the coefficient of friction it is possible to achieve the inquired factor of safety with lower stresses in the propeller boss, or alternatively, if the stresses remain the same, with a smaller area of contact between the propeller and propeller shaft. Thus, according to the invention in a second aspecc there is provided an assembly of a propeller on a tapered portion of a propeller shaft in which an internally tapered sleeve is secured in a bore extending axially through the hub of the propeller and is force fitted on the tapered portion of the propeller shaft so as to be in torque and thrust transmitting connection therewith, the tapered portion of the propeller shaft being roughened by scratching to a depth of 5 microns or greater the length of the engaging surfaces of the propeller shaft and sleeve being between 1.3 and 1.4 •times the shaft diameter. By reducing the length of the engaging surfaces to 1.3 to 1.4 times the shaft diameter the weight of the propeller is reduced and the amount of expensive metal is reduce resulting in considerable cost savings. According to the present invention in a third aspect there is provided an assembly of a propeller on a propeller shaft in which a portion of the propeller shaft is in torα^-transirάtting engagement with a bore within the propeller hub, and wherein the axial length of the engaging portion of the propeller shaft is less than the axial length of the propeller hub. In a preferred form of the invention the length of the engaging surfaces is reduced compared with the length of the propeller hub to form a recess in the aft end of the propeller which accxraπodates the hydraulic nut used for pushing the propeller up the tailshaft. The overall length of the propeller is dete__mined by considerations of the strength reσt_±rements at the roots of the propeller blades and the _-equ__re-rents for good hyd_.odynamic performance in relation to the flow of water over the blade roots. By fonning a recess in the propeller, the amount of metal in the propeller can be reduced whilst at the same time meeting the performance reσuirements of the propeller. There is a corresponding reduction in the length of the propeller shaft with a concoirάtant saving in materials. Providing a recess to accrai-TDdate the hydraulic propeller nut also has the advantage that the conventional fairwater cone which encloses the nut to provide good flow lines can be elininated. The fairwater cone is usually cast from bronze and expensive to manufacture. By recessing the nut completely in the propeller the hydraulic nut can be enclosed with a flat plate of metal or plastics material secured over the open end of the recess. The invention will now be ' further described by way of example with reference to the accompanying drawings in which: Fig. 1 is a longitudinal cross-section of a ship propeller, ready to be assembled on a propeller shaft in accordance with the invention and Fig. 2 shows the propeller of Fig. 1 mounted on the propeller shaft. Be erring to the drawings, a propeller shaft 10 has a tapered portion 11 adjacent its aft end. A bronze propeller 12 has a hub 13 with an axially-extending bore 14 passing through it. A sleeve 15 is cast from pearlitic cast iron. The sleeve 15 has a tapered bore 16 which fits the tapered portion 11 of the shaft. Its outer surface is screw threaded with portions 17 and 18 of opposite hand to provide σircumferentially extending grooves. The bore of the hub is similarly provided with screw threaded portions 19 and 20 of opposite hand. The inside diameter of the bore is 2 mm greater than the outside diameter of the sleeve. Both the sleeve and hub are machine finished. The sleeve 15 is first bedded on the tapered portion of the shaft. The shaft 10 is supported in a horizontal position on two "Vee" block stands. The tapered portion 11 and the tapered bore 16 of the sleeve are hand finished to give a well distributed bedding contact of approximately 60% of the area. After thoroughly degreasing the portion 11 and the bore 16 with carbon tetrachloride, • the sleeve 15, carried by a crane hook and sling, is slid onto the end of the shaft 10. The rearmost part of the shaft 10 has a screw-threaded portion 23. When the sleeve 15 has been slid onto the tapered portion s .) l^draulically-jacked nut 24 is threaded on the screw-threaded portion 23. As can be seen frcm Fig. 1, the nut has an annular cavity 25 in one end into which a hollow rubber ring 26 is fitted. An annular piston 27 is fitted into the cavity over the rubber ring, i^draulic fluid can be pumped into the rubber ring through a conduit in the nut (not shown) to cause the piston to be moved so as to project beyond the end of the nut. The nut is screwed onto the shaft until the piston- bearing end engages the end of the sleeve. Hydraulic fluid, is pumped into the rubber ring 26 and the piston 27 pushes the sleeve 15 up the tapered portion 11. A dial indicator fitted to the shaft 10 measures the travel of the sleeve up the shaft which must not exceed a calculated value. When the travel of the sleeve up the shaft has reached the requi-_ed value the pressure is released and the nut 24 is unscrewed. The hydraulic pump is degreased with carbon tetrachloride and then connected to a conduit in the sleeve which communicates with an array of longitudinal channels 31 interconnected by a circumferential channel 32 in the bore of the sleeve 15. Water is pumped into the 7 -2 channels 31 and 32 to a pressure of about 4000 psi (2.8 x 10 tto ) . The pressure is held to give the watertime to seep across the lands between the groove. After about 5 minutes the sleeve will be jacked off the shaft by the water pressure. By using water rather than oil a high friction coefficient between sleeve and shaft is obtained. The bedding contact of the shaft is thus improved to 75% of the area. The whole process is repeated to produce a bedding contact „ i-.*_ OMPI of about 85%. The sleeve is now ready for location in the bore of the propeller hub. The bore 14 of the hub and the outer surface of the sleeve 15 are carefully degreased with carbon tetrachloride. All holes and channels are blown out with air. The sleeve is placed inside the bore and annular space between the sleeve 15 and the bore 14 is closed by "0" ring seals which are fitted at both ends of the sleeve. A hardenable composition consisting of a synthetic resin, preferably the epoxide resin adhesive sold under the .Registered Trade Mark "Araldite" is injected into the annular space. Grade SW404 resin and SW404C or SW404S hardener is used which includes a carborundum filler to give high sheer and crushing strengths when set. As the resin composition is injected air is bled out until the space is completely filled. The air bleed holes are closed and the pressure is raised to 500 psi (3.5 x 10 Km -1" • ) . This pressue is held until the Araldite has set. The propeller and sleeve is left undisturbed for 24 hours and is then ready for mounting on the shaft. The tapered portion 11 of the shaft is finally prepared to receive the propeller and sleeve by roughening its surface using a hacksaw blade. The blade is drawn by hand diagonally across the surface of the tapered portion in strokes holding the blade at right angles to the direction of movement with its teeth in contact with the conical surface. Gentle pressure is applied to the blade during the operation. Each stroke scratches a diagonal strip of the surface of the cone and the operation is repeated until substantially the whole of the shaft surface has been covered with . scratches. The scratches may be made all in one direction as shown in Fig. 1 or in two crossing directions to produce a cross- hatched pattern as shown in Fig. 2. A blade of high-speed steel , having 32 teeth per inch (12.6 teeth per cm) is preferred. By this means a 5 micron roughening is achieved. Annular portions 22 at each end of the tapered portion are left unscratched so as to provide a seal between the ends of the sleeve and the shaft. The tapered bore of the sleeve may also be scratched in this way if desired. Alternatively the surface roughening of the shaft may be performed using a coarse 36-grit emery cloth. The tapered surfaces 11 and 16 are then thoroughly degreased with carbon tetrachloride and the assembly of propeller and sleeve are then pushed up on the shaft for the last time using the hydraulic nut 24. The technique of roughening described above enables a high coefficient of surface friction of 0.18 to 0.20 or higher to be achieved more reliably than with conventional dry fitting techniques. Because of the iitproved grip the length of the gripping surfaces of the sleeve and propeller shaft can be reduced for a given stress to meet a given factor of safety. With this a__rangement it is possible for the length of the engaging surfaces of the propeller to be reduced,to between 1.3 and 1.4 times the shaft diameter and still meet the safety factor requirements. Reduction in the length of the gripping surfaces means that the weight and hence the cost of the . propeller assembly can be reduced. OMPI The overall length of the propeller hub is determined by considerations of the size of the blade root fillets necessary * for strength and good hydrodynamic performance in relation to the flow of water over the blade roots. The high coefficient of friction achieved by the method described above enables the length of the sleeve to be reduced compared, with the overall length of the propeller boss. As shwon in the drawings the aft end of the propeller may be recessed by means of a counterbore 60 and the sleeve may be shorter than the propeller hub so as to be the same length as the length of the propeller from the forward end to the bottom of the counterbore 60. The length of the gripping surfaces may be less than 75% the overall length of the propeller. The recess 61 defined by the overhanging aft portion 62 of the propeller hub and the aft end of the sleeve serves to accommodate, at least partially, the hydraulic nut 24. This arrangement provides a compact arrangement and also enables the conventional fairway cone which covers the nut on a conventional propeller πounting to be dispensed with as will be described below. The aft end of the propeller hub projects beyond the aft end of the propeller shaft 10 making the mounting of the hydraulic nut 24 on the screw-threaded portion 23 of the shaft difficult using the conventional technique. To facilitate mounting of the nut an arrangement for supporting and aligning the nut is provided. A ' guide bar 63 is screw-threaded at one end to fit in a screw-thread socket 64 located centrally in the aft end of the tailshaft. A guide tube 65 is welded at right angles to a face plate 66 to which the nut 24 may be firmly attached by means of four tap bolts 67. When the plate is mounted on the nut the axis of the nut 24 coincides with the axis of the tube. The bar 63 is a sliding fit in the guide tube. To mount the nut the assembly of nut and plate is slung by a wire rope 68 from a chain block which raises it to the height of the propeller shaft centreline. The guide bar is screwed into the recess 64 and the wire rope 68 is transferred -to the free end 69 of the guide bar to take the load. The propeller nut can be spun on the guide bar by means of the bar 63 so that the heavy propeller nut can be screwed easily onto the screw threaded portion 23. After mounting the plate 66 and guide bar 63 are removed. To cover the nut 23 after the propeller has been mounted, a cover plate 70 of brass or plastic is fitted over the open aft end of the recess 61. Where the nut is completely acc.c_rarodated in the recess the plate may be flat as- shown. To provide additional stiffness to the assembly a forward projecting peripheral lip may be formed on the plate (not shown) which is received in an annular groove in the aft end of the overhanging portion of the propeller. The cover may be secured by screw* 5 (not shown) . To dismantle the propeller, the cover 70 is removed, the guide bar 63 and plate 66 are screwed in place and the hydraulic nut 7 -2 is removed. Hydraulic oil at a pressure of 7500 psi (5.2 x 10 Mπ ) is injected into the grooves and maintained for 5 minutes when jack off should occur. If it does not the pressure may be raised to 10,000 psi (6.9 x 10 7 Nπf 2 ) .

Claims: CLAIMS; ' . 1. A irethod of mounting a propeller on a propeller shaft, in which the propeller or an assembly of a propeller with a sleeve secured within an axial bore in the propeller hub, is placed in to_.que-trans_rιitting frictional engagement with a portion of the shaft, the method including the step of roughening at least one of the engaging surfaces of the hub or sleeve, and propeller shaft, without altering the overall dimensions of the or each surface so roughened, prior to placing the surfaces in engagement. 2. A method according to claim 1 in which the or each surface is roughened by scratching in a non-circumferential direction. 3. A method according to claim 1 in which the surface is scratched to a depth of at least 5 microns. 4. A method according to any preceding claim in which the or each surface is roughened by drawing a serrated tool across it. 5. A method according to claim 4 in which the tool comprises a hacksaw blade. 6. A irethod according to any of claims 1 to 3 in which the surface is roughened by wiping the surface with emery cloth having a coarseness of approximately 36-grit. OMPI 7. A method according to any of the preceding claims in which ■ She engaging surfaces of the hub or sleeve and the propeller shaft are tapered and the frictional engagement is achieved by pushing the propeller or propeller assembly up the tapered portion of the propeller shaft. 8. A method according to any of the preceding cla__ms in which an area free from roughening is left at each end of the engaging surfaces to provide a seal. 9. An assembly of a propeller on a tapered portion of a propeller shaft in which an internally tapered sleeve is secured in a bore extending axially through the hub of the propeller and is force fitted on the tapered portion of the propeller shaft so as to be in torque and thrust transmitting connection therewith, the tapered portion of the propeller shaft being roughened by scratching to a depth of 5 microns or greater the length of the engaging surfaces of the propeller shaft and sleeve being between 1.3 and 1.4 times the shaft diameter. 10. An assembly of a propeller on a propeller shaft, in which a portion of the propeller shaft is in torque-transmitting engagement with a bore within the propeller hub, and wherein the axial length of the engaging portion of the propeller shaft is less than the axial length of the propeller hub. 11. An assembly according to cla-Lm ' 10 in which the propeller hub extends aft beyond the end of the engaging portion of the propeller shaft to define a recess in which a hydraulic nut threaded onto a portion of the propeller shaft aft of the engaging surfaces is at least partially accorrirodated. 12. An assembly according to claim 11 in which the hydraulic nut is wholly accommodated within the recess. 13. , An assembly according to claim 11 or 12 in which a closure irember is secured to the end of the propeller hub over the recess to enclose the hydraulic nut. 14. An assembly according to claim 13 when dependent on claim 12, in which the closure member is a flat plate. 15. An assembly according to any of claims 10 to 12 wherein the bore is defined in a sleeve secured within the propeller hub, the hub extending beyond the end of trie sleeve and of the propeller shaft. 16. An assembly according to any of claims 10 to 15 in which the •length of the engaging-surfaces is less then 75% of the overall length of the propeller. 17. An assembly of a propeller mounted on a propeller shaft according to the method of any of claims 1 to 8.

Inventors: BUNYAN THOMAS, BUNYAN, THOMAS
Applicants: PILGRIM ENG DEV, PILGRIM ENGINEERING DEVELOPMENTS LIMITED
Application year: 1983
Main classification: B63H23
IPC codes: B63H23, F16D1