FR2577672A1 - Methods and devices for static balancing of a ship screw propeller or a similar rotating component - Google Patents

Abstract

The subject of the present invention is methods and devices for static balancing of a ship screw propeller or a similar rotating component. A device for balancing a screw propeller 1 including a mounting cone 3 includes a stationary baseplate 6 placed on a drum (barrel), a counterplate 7, screw jacks 15, three spring balances 9, three jacks 13, three blocks 14 and a centring column 12 which is placed in the mounting cone and whose lower end is engaged in a bore 11 situated at the centre of the counterplate 7. The screw propeller is raised with the jacks 13, it is placed on the blocks 14, the counterplate 7 carrying the spring balances is displaced so as to centre the centring column with respect to the mounting cone. Once this centring has been performed, the screw propeller is placed on the three spring balances and the forces exerted on the screw propeller are measured and from these the position of the centre of gravity is calculated. One application thereof is the balancing of ship screw propellers.

Description

Static balancing methods and devices of a

  ship propeller or similar rotating part.

  The subject of the present invention is methods and arrangements

  static balancing devices of a ship's propeller or of a large rotating part such as a flywheel, a rotor, etc., comprising an axial bore or a fitting cone making it possible to

  mount the propeller or rotating part on a shaft.

  The technical sector of the invention is that of constructions.

mechanical tions.

  In the rest of the presentation, we will refer more particularly-

  ment to methods and devices intended for static balancing of rotary propellers without this choice entailing any limitation

  of the invention, which can be applied without changing the balance

  brage of any other large rotating part intended to be mounted

  on a drive shaft or on a driven shaft.

  Boat propellers are often damaged either by wear or by the meeting of various floating bodies and they require periodic revisions during each of which

  static balancing must be performed.

  The standards in use require that the distance from the center of gravity to the geometric axis of the propeller is less than 0.1 mm,

  regardless of the size of the propeller. To date, the balancing sta-

  propeller ticks are made either on a horizontal axis or on a vertical axis. In a horizontal axis balancing, the propeller is mounted on a horizontal axis by means of two opposite cones

  which are engaged in the fitting cone of the propeller hub.

  The horizontal axis is placed on two horizontal knives or in two ball bearings. If there is an imbalance, the propeller is rotated to the position where the center of gravity is vertical to the axis. The propeller's balance is temporarily restored by loading it with a temporary flyweight opposite the unbalance

  until the propeller remains balanced in all positions.

  Once the unbalance is determined in mass and in position, it is eliminated

  by grinding on the back of the blades a symmetrical mass of ia mass-

temporary balancing monkfish.

  This balancing process lacks precision.

  It is difficult to. use on large propellers which are generally transported in position where the blades are

  horizontal and must be straightened. He lacks loyalty. The-

  Balancing with a horizontal axis must be done by turning the propeller in one direction and then in the other and the results found in both directions are often different and even contradictory. It is an expensive method because it requires a lot of time, qualified personnel and heavy and bulky equipment. In particular, a whole range of cones and shafts is required to balance

different size propellers.

  Finally, the removal of the metal by grinding is generally done without intermediate checks of the residual unbalance and this method risks causing defects in shape on the propeller due

  an exaggerated metal removal.

  The vertical axis balancing process consists of mounting the propeller on a vertical column by means of two direction cones

  opposite which are engaged in the two ends of the cone of emman-

  the propeller hub. This vertical column rests on a film of oil. If there is an imbalance, the propeller leans towards the unbalance side. The position of the propeller is checked by means of levels. If the propeller leans, the balance is temporarily restored by adding temporary weights. A mass is then removed by grinding

  of substantially symmetrical metal of the provisional weights.

  The vertical axis balancing process requires a very expensive balancing machine, which is not universal. This method has the same inaccuracies as the horizontal axis method which are due to centering defects by two cones in opposite directions, which rest on the non-functional edges

  located at both ends of the hub cone of the hub

  running. The objective of the present invention is to provide new methods for static balancing of propellers or other similar heavy rotating parts which involve more precise balancing devices, which are easier to use and which adapt easily to propellers of different size and which allow

  easily perform balance checks during

  metal removal to prevent excess metal from being removed.

  This objective is achieved by a static balancing process.

  tick which comprises the following series of operations: - the propeller or said rotating part is placed in the

  position o the axis of said bore or of the fitting cone is ver-

tical;

  - three scales are placed under the propeller, placed at the top

  dishes of an equilateral triangle which are centered with respect to the axis of said bore or said fitting cone; - the propeller or said rotating part is placed on the three scales; - The forces measured by the three load cells are read and the distance from the center of gravity of the propeller or of the rotating part to the geometric axis of said bore or said fitting cone is deduced therefrom;

  - and, if the center of gravity is eccentric, we grind the-

  said propeller or said rotating part and between the grindings, the forces measured by the three load cells are read again and the grinding is continued until the center of gravity is at a distance

  of the axis less than the tolerances.

  According to a preferred embodiment, first of all

  said propeller or said part rotating horizontally on ca-

  the. Is introduced into said axial bore or said sleeve cone-

  a rectified centering column and the end is engaged.

  of the latter in a housing machined in a counter plate which can slide on a base plate and which carries three load cells

  which are arranged at the three vertices of a perfect equilateral triangle

  tement centered on the axis of said housing. Said plywood is slid onto the base plate until said centering column is perfectly centered with respect to said bore or said fitting cone. Said propeller or said rotating part / said load cells are lowered and the forces measured by

these.

  A device according to the invention for static balancing of a propeller or of a similar rotating part comprising a cylindrical or conical axial bore comprises a horizontal base plate, a counter plate which can slide on said base plate, means p'u.r slide said counter plate, which counter plate carries trols.pesons disposed at the vertices of an equilateral triangle and a central bore and said device further comprises a rectified centering column, the end of which lower is fitted

  in said central bore, which column is positioned ver-

  tically by being centered on the axis of said axial bore of said

  propeller placed in horizontal position.

  Preferably, the counterplate has three radial branches arranged in a star with angular differences of 1206.

between the branches.

  Advantageously, each branch comprises, along its axis, a series of machined holes which are arranged three to three at the vertices of an equilateral triangle perfectly centered on the axis

of the bore of said ring.

  The invention results in new means for static balancing of a ship's propeller or any other heavy rotating part such as a flywheel, a rotor, a pinion, etc., which comprises an ael -axial, cylindrical or conical bore, intended to receive a shaft which requires good balancing with respect to

the axis of said tree.

  The devices according to the invention have the advantage that the propeller blades are arranged horizontally with the back of the blades on top, which facilitates handling and access.

  on the back of the blades for grinding. In addition, the propeller remains fixed during

  during the whole balancing operation.

  Another important advantage of the method and of the devices according to the invention lies in the fact that the position of the center of gravity is calculated from the measurements delivered by three load cells, which makes it possible to produce balancing machines which

  indicate the position of the center of gravity and which can indicate it

  during the whole blade grinding operation.

  A machine according to the invention may include a microprocessor

  sor and a screen on which the position of the center of gravity relative

  port to axis can be displayed graphically on a large scale

  during the whole grinding operation.

  The inventive method is very precise since it does not include cones which are engaged in the fitting cone

  propeller and there is no risk of accumulating errors.

  The centering of the load cells is carried out directly with respect to

  on the lateral surface of the propeller fitting cone - which determines

  do the position of the axis of the drive shaft.

  Because we use a centering column whose

  diameter is significantly smaller than that of the tapered bore of the

  bit and a counterplate which has a series of holes intended to receive the load cells, a device according to the inventon can be used

  to balance propellers of any size.

  The method according to the invention does not require heavy and bulky equipment. For the periodic verification of the propellers, it is possible to envisage a balancing equipment according to the invention

  which could be installed at the bottom of a refit tank and which

  would balance the propellers on site without having to trans-

wear in a workshop.

  The following description refers to the accompanying drawings which

  represent without any limiting character an exemplary embodiment

of a device according to the invention.

  Figure 1 is an axial section of a propeller in progress

balancing.

  Figure 2 is a top view of a device according to the invention.

  Figure I shows the hub 1 of a propeller

  veer which can have a mass of several tons. Mark 2 represents

  shows the birth of the blades, the number of which can be any,

even or odd.

  The hub 1 comprises a cone 3 for fitting the rear

  propeller bre. This cone diverges towards the rear face 4 of the hub

  i.e. the side which is intended to be placed on the side of the ship.

  The propeller is placed in the horizontal position of the blades, that is to say in the position where the x xl axis of the propeller is vertical. The rear face 4 is placed on top, so that the backs 5 of the blades which are the non-active faces on which the metal removals are to be carried out are placed on the top and are

therefore easily accessible.

  The purpose of the static balancing operation is to bring the center of gravity of the propeller to be on the geometric axis x xl

  of the fitting cone, i.e. on the axis of the drive shaft

  or at a distance from it less than a tolerance which is

  generally 0.1 mm regardless of the size of the propeller.

  A balancing device according to the invention comprises a

  fixed base plate 6 which is ground and which is laid horizontally

  lement on a marble or a massif with a very slope tolerance

low, less than 0.08 mm / m.

  The device comprises a movable counter plate 7 which is rectified. The counter plate 7 is placed on the base plate on which it can slide. It has the general shape of a star with three radial branches whose axes make an angle of 120 between them. Each branch comprises, along its axis, holes 8 for positioning a load cell 9 which is an electronic weight sensor, for example a strain gauge sensor intended for

  to measure compression forces of up to several tens

  kilonewtons. Each load cell delivers a voltage proportional to the load exerted on the load cell. The holes 8 are positioned with very high geometric precision and the load cells 9a, 9b, 9c have a centering tip which fits without play in a hole 8, so that the three load cells which are arranged in three

  holes 8, located at the same distance from the axis, are arranged at the

put an equilateral triangle.

  The counter plate 7 comprises a ring 10 which is welded to the center of the upper face of the counter plate. 11l bore

  is machined in this ring to serve as a housing at the end

  lower of a centering column 12 which is fitted without play

in said bore.

  By construction, the three load cells 9a, 9b, 9c placed in

  three homologous holes are located at the vertices of an equilateral triangle

  teral whose center is located on the axis of the bore 11, which coincides with the axis x xl of the centering column 12. The holes 8 for centering the load cells are machined with very high precision which is 0 .01 mm over the distance a between two load cells and with a tolerance between + 0 and + 0.01 mm over the distance between

  the hole axis and the x xl axis of the column.

  Each branch of the counter plate 7 comprises several

  holes 8 and each time we use the three holes which correspond

  tooth at the size of the propeller. Weights 9 are adapted to the weight

  of the propeller to be checked which can go up to 300 KN.

  In practice, three different sets of scales and four holes

  8 are sufficient to obtain a universal device which allows

  free propellers of any size. The base plate supports three

  hydraulic rins 13 and three shims 14 rigorously ground to the same height. Advantageously, the jacks and the shims are placed in three radial counterbores 15 visible in FIG. 2 which form an angle of 1200 between them and which are located in the planes

  bisectors of the branches of the counterplate 7.

  The cylinders 13 and the shims 14 need not be positioned with the same precision as the load cells 9. However, in order to balance the loads, the cylinders and the

  wedges substantially equidistant from the axis.

  The device also comprises three screw jacks 15 which are arranged radially at the ends of the three branches of the counter plate 7 and which make it possible to move the latter on the

base plate.

  The load cells 9 are connected by an electrical conductor 9a to an electronic box 16 which analyzes the signals coming from

  load cells and which displays simultaneously or by switching the

these measured.

  The three jacks 13 are connected by flexible lines 13a to a hydraulic unit or to a hand pump 17. Preferably,

  the three cylinders are operated simultaneously.

  Before making a measurement of the forces exerted on the three load cells, it is necessary to start by centering the propeller relative to

  the counter plate 7 carrying the load cells.

We operate as follows.

  The backplate 7 is centered approximately on the base plate 6, without the load cells or the centering column 12. The positions of the points of tracing are traced on the front face of the propeller.

  contact of the three cylinders located substantially at the vertices of a trian

  equilateral gle. The cylinders 13 fully retracted are arranged on the

  base plate 6. The propeller is brought into a horizontal position

  above the device, the back of the blades being located upwards and

  it descended on the three cylinders, so that these

  approximate to the points plotted on the propeller. By action on the hand pump 17, the three jacks which slightly raise the propeller are actuated and the three wedges are engaged under it. From this moment, the centering column 12 is introduced vertically

  in the fitting cone 3 and the lower end is engaged

bore in bore 11.

  The centering column 12 carries a sliding ring 19

-77672

  which is positioned in height by a needle screw 20 or by any other equivalent means. Column 12 is rectified and a ring

  21 is engaged on the column 12 and rests on the base

  gue 19. The ring 21 carries a comparator 22, the feeler of which rests on the inside contour of the fitting cone 3.

  By rotation of the ring 21, the compa-

  erator the inner contour of the fitting cone and we note the

diameter measurements.

  If it appears that the column is not centered relative to the fitting cone, the counterplate 7 is moved by means of the screw jacks 15 until the centering difference is less than

    0.01 mm. A deu-

  xth position of the sliding ring at another level of the colon-

  born. A centering check is carried out at this second level to verify that the x xl axis of the column is correctly merged with the axis of the fitting cone. If this is not the case, place under the load cells 9 shims to bring the propeller into a position where the axis of the fitting cone is vertical and coincident.

  with the x xl axis of the centering column.

  Once the column has been perfectly centered with respect to

  port to the propeller, the propeller is slightly raised using the jacks,

  we put the load cells 9, possibly on shims of thick-

  To restore the verticality of the centering column, we

  raise the wedges 14 and slowly lower the propeller to put it

  be supported on the three load cells 9 which are then theoretically perfectly centered relative to the geometric axis of the propeller which

  coincides with the axis of the centering column.

  A check of correct centering is carried out by means of the comparator 22. If the centering proves to be defective, the propeller is reassembled on the jacks and the counterplate 7 is again moved until the propeller is centered be satisfactory. When the centering is good, the forces FA, FB and FC measured by the

three scales.

  The distance OG between the center of gravity of the propeller and the x xl axis is given by the formula:

  OG 3 (FA + FB + BC). A2 + FB2 + FC2- (FB.FC + FA.FB + FA.FC),

  a being the distance between two scales.

  The distance 0G can be calculated from the measured values of FA.FB and FC. Alternatively, the electronic box 16 can include a microprocessor programmed to calculate the distance

  OG from the values transmitted to it by the three load cells.

  If the distance OG is less than 0.1 mm, the propeller is balanced. Otherwise, metal is removed by grinding

  easily accessible from the back of the blades.

  The grinding operation can be done while the propeller is resting on the three scales, which allows you to check the

  result as metal is removed.

  You can determine where the grinding should be done

  killed by first adding temporary masses on the blades until the three forces FA, FB, FC are equal and

  then grinding in diametrically opposite places.

  It is also possible to determine by calculation the coordinates of the center of gravity with respect to an axis Y YI coincident with the axis of one of the three branches of the counterplate b for example the

  branch carrying the load cell 9a and to an axis X XI which is perpendicular thereto

  cular. The values of X and Y are given by the formulas: X a. (FC-FB) y = aVI (FB + EC-2FA)

2 (FA + FB + FC 6 (FA + FB + FC)

  from which we deduce the angular position a of the center of gravity by X relative to the Y axis YI by the formula tga = X

  Once the balancing is completed, the hi-

  running on the three cylinders, we remove the scales and the column

  centering and the propeller is removed from the device.

  The balancing of a propeller by a method according to the invention is much more precise than that which can be obtained by the methods used to date. In the end, it only depends on the accuracy of the load cells which can be of the order of 0.5% and of the good

  geometric centering, which can be achieved with very good accuracy

  due to the fact that we do not have to move the mass of the propeller.

  The process according to the invention does not cause an accumulation

  tion of geometric errors or mechanical play. Geometric centering

  Weighing of the load cells is carried out using the comparator with respect to

  lateral surface of the fitting cone which is a functional surface

  which determines the position of the axis of the drive shaft by

  ratio at which the propeller must be balanced.

  The centering of the load cells relative to the axis of the eme cone

  sleeving is achieved by using a centering column whose diameter is much smaller than that of the fitting cone, so that the same centering column is used for propellers of

different size.

  The process according to the invention makes it possible to use a micro-

  which processor / directly calculates the distance to the axis of the center of gravity and its coordinates, so that the process is

  easy to implement even by personnel without great skill-

  tion. The propeller handling is limited, since the center-

  ge is done by leaving the propeller fixed.

  As you can leave the propeller on the scales while removing metal by grinding, it is easy to make checks during this removal, which avoids

  risk of excessive metal removal.

he

Claims (10)

R E V E N D I C A T I 0 N S   1. Static balancing method for a ship's propeller (1) or a similar rotating part comprising an axial bore or a fitting cone (3), characterized by the following operations: - place l propeller or said rotating part in the position where the axis (x xl) of said bore or of the fitting cone is vertical; - Three weights (9) are placed under the propeller, placed at the vertices of an equilateral triangle which is centered relative to the axis (x xl) of said bore or of said fitting rod; - the propeller or said rotating part is placed on the three load cells (9); - The forces measured by the three load cells are read and the distance from the center of gravity of the propeller or of the rotating part to the geometric axis of said bore or said fitting rod is deduced therefrom; - And, if the center of gravity is eccentric, the said propeller or the said rotating part is ground and between the grindings, the forces measured by the three load cells are read again and the grinding is continued until the center of gravity is at a distance   of the axis less than the tolerances.   2. Method according to claim 1, characterized in that: - first said propeller or said rotating part is placed horizontally on wedges (13); - A rectified centering column (12) is introduced into said axial bore or said fitting rod (3) and the lower end of the latter is engaged in a housing (11) machined in a countersink (7) which can slide on a base plate (6) and which carries three load cells (9) which are arranged at the three sqmmets of an equilateral triangle perfectly centered on the axis of said housing (11); - sliding said counter-plate (7) on the base plate (6) until said centering column (12) is perfectly centered with respect to said bore or said fitting cone (3); - And said propeller or said rotating part is allowed to descend on said load cells (9) and the forces measured are read by these.   3. Method according to claim 2, characterized in that said centering column (12) has a diameter less than the smallest diameter of said bore or said fitting cone (3) and the centering and parallelism of said column are checked. centering with respect to said bore (3) by means of a comparator which is mounted on a rotating ring, which is engaged on said centering column and is positioned in height by a second ring which is fixed to said column successively to several different heights.   4. Static balancing device for a propeller (1) or a similar rotating part comprising an axial bore (3) cylindrical or conical, characterized in that it comprises a fixed horizontal base plate (6), a counter plate (7) which can   slide on said base plate, means (15) for sliding   ser said counterplate, which counterplate carries three load cells (9) arranged at the vertices of an equilateral triangle and a central bore (11) and said device further comprises a column   centering (12) rectified, the lower end of which is fitted   located in said central bore (11), which column is positioned   born vertically while being centered on the axis of said axial bore   (3) of said propeller placed in a horizontal position.   5. Device according to claim 4, characterized in that said counter-plate comprises three radial branches arranged   in a star with angular differences of 120 between the branches.   6. Device according to claim 5, characterized in that each branch comprises along its axis a series of machined holes (8) which are arranged three to three at the vertices of an equilateral triangle perfectly centered on the axis of the bore (11) of said ring (10).   7. Device according to Claim 5, characterized in that the said means for sliding the counter-plate consist of three screw jacks (15) arranged at the ends of the   say radial branches of the counterplate (7). -   8. Device according to any one of claims   4 to 7, characterized in that it further comprises three hydraulic cylinders (13) which are placed on said base plate (6) and 257767t   which are used to lift said propeller (1).   9. Device according to claim 8, characterized in that it further comprises shims (14) which are placed on said base plate (6) and which serve to support the propeller (1) during the operations of centering.   10. Device according to any one of the claims   4 to 9, characterized in that said centering column (12) has a diameter less than the smallest internal diameter of the bores (3) of the propellers to be balanced and it comprises a first ring (19) which is engaged on said centering column (12) and which is provided with means (20) enabling it to be fixed at different heights and a second rotating ring (21) which is also engaged on said centering column and which can receive a comparator (22)   the feeler of which follows the internal contour of said bore.