Description:FIELD OF THE INVENTION:
The present invention relates to a device for elongation of studs. Particularly, the present invention relates to a device employed in elongation of studs of heavy machinery.
BACKGROUND OF THE INVENTION:
Large public utility power plants produce electricity by coupling a generator to a mechanical power source such as a steam turbine. The generator comprises a rotor journaled in a stator, the rotor containing copper coil windings which carry a direct current for producing a magnetic flux. The power source spins the rotor at high speeds, causing the magnetic flux to sweep across copper coil windings in the stator and generate an electric current.
In the manufacture of stator or rotor cores for dynamoelectric machines, which may exceed 300 inches in length, it is a common practice to build these cores from a series of punched laminations. The laminations are assembled in abutting relationship to each other in a stack that runs axially along the dynamoelectric machine. The axial ends of the stack of laminations, as called core, are closed off by ring shaped end plates called core press rings which provide compression forces to the laminations. The laminations are typically provided with a plurality of through holes which also extend through the end plates. Through bolts or core studs typically pass through the through holes of the stacked laminations and the end plates. The core studs have end portions which extend beyond the end plates. The core stud end portions are usually threaded to receive nuts and other washers which when tightened using a device or fixture with high levels of torque, it presses against the end plates to provide axial tightness of the core assembly.
Referring to figure 1(a) and 1(c), there is provided a dynamoelectric machine 10 comprising a rotor 12 having a shaft 14. The shaft 14 may extend either horizontally or vertically along axis 16. The rotor 12 also comprises a rotor core structure 17. It should be understood that while the details of the present invention are being described with reference to a rotor, that the insulated core studs of the present invention are also applicable to use in a stator core.
The rotor core structure 17 has a plurality of magnetic laminations 18 which may comprise either an iron or steel material and may be coated with an insulation paint or epoxy. The magnetic laminations 18 are spaced closely adjacent to each other and axially along the stator core structure 17. Adjacent the outer ends of the magnetic laminations 18 are stepped laminations 20. The stepped laminations 20 reduce in steps the outside diameter of the laminations 18 of the core structure 17 to have a diameter corresponding to the outside diameter of supporting core press ring 22 located on axially outer sides of the stepped laminations 20. The ring 22 provide axial clamping pressure to the stepped laminations 20 and thereby to the laminations 18. Each of the end plates or flanges 24 is positioned axially on the outer sides of a respective core press ring 22. The end plates provide clamping pressure to the finger plates.
Each of the magnetic laminations 18, stepped laminations 20, core press ring 22 and end plates 24 have through holes 26 that extend there through. The through holes 26 are shown in figure 3 to be radially spaced about axis 16 of the rotor 12.
As shown in figure 1(b), an insulated core stud 30 passes through each of the through holes 26. The ends 36 of the insulated core stud 30 extend beyond the end plates 24 and are adapted through threads to receive nuts 32. In between the nuts 32 and the end plates 24 are locking washers 34 which also may be insulated. The nuts 32 are secured to the threaded ends 36 of the insulated core studs 30 so that the nuts 32 and core studs 30 provide an axial tightness against the end plates 24 to axially tighten the laminations 18 and 20 within the rotor core structure 17.
Referring to figure 1(d), the insulated stud 30 comprises opposing threaded ends 36 and a central shaft portion 38.
These nuts 32 may be torqued to a predetermined setpoint, but friction in the threads may result in a lower tensioning force being transmitted to the studs 30. As the laminations 18 must be held in precise alignment with each other to provide a uniform air gap between the rotor core structure 17 and stator member, a slight distortion of the air gap created because of lesser stud tension may cause a reduction in starting torque and output power, and a misaligned rotor may cause an increase in bearing wear. Misalignment and radial shifting may occur when the rotor core structure 17 is subjected to unbalanced torsional loading as the rotor core structure 17 is bolted down to a planar mounting surface.
Moreover, the assembly of bolted joints on heavy engineering equipment like turbine housings, generators etc., requires high clamping forces at the bolted joints.
Therefore, there is felt a need for development of a device to perform stud stretching post nut tightening and thereby minimize uncertainties in residual loads on the studs caused by variations in the actual pressure applied to the studs by the tensioner, high friction in the stud threads and possibly operator error.
OBJECTS OF THE INVENTION:
An object of the present invention is to provide a simple and compact device for elongation of studs.
Another object of the present invention is to provide a device which can adapt to any type of bolt flange surface.
One more object of the present invention is to provide an efficient device for elongation of studs.
Still another object of the present invention is to provide a reliable device for elongation of studs.
Further another object of the present invention is to provide a device for elongation of studs having less weight.
SUMMARY OF THE INVENTION:
A pressure fluid connection is provided for the chamber formed by the piston and cylinder, application of fluid pressure causing the cylinder to rise. This will cause the nut to be lifted due to the upward component of force acting on the tapered nut surface, and the stud will thus be tensioned so that the stud nut may be tightened.
The radially outward force on the nut created by the stud thread surfaces will be counteracted by the inner cylinder wall and the cylinder fluid pressure, and the radially inward force of the fluid pressure on the inner cylinder wall will be likewise counteracted by the nut. The tapered interfitting surfaces of the nut and cylinder will thus not only enable a decrease in total overall height in the unit by acting as vertical force-transmitting surfaces, but will enable a decrease in radial dimensions as well, since the wall thickness requirements of the nut and of the cylinder will be reduced.
Briefly, the illustrated embodiment of the invention comprises a base having a prismatic upper surface and supporting a piston in the form of a cylindrical member with a lower partially spherical surface and an upper piston head. The piston fits in a cylinder which also comprises an annular member having a downwardly facing annular cylinder chamber within which the piston slides. The inner surface of the inner cylinder wall is flared upwardly and outwardly, and a nut is threadable on the stud and has a downwardly tapered outer surface complementary to the flared cylinder surface.
BRIEF DESCRIPTION OF THE DRAWINGS:
The invention will now be described with reference to the accompanying drawings in which:
Figure 1(a) illustrates a sectional view of a rotor core structure of a dynamoelectric machine with a core stud passing therethrough according to the prior art;
Figure 1(b) illustrates an enlarged view of one end of the rotor core structure of figure 1(a);
Figure 1(c) illustrates a side view of the rotor core structure of figure 1(a) with a plurality of core studs extending through the rotor core structure;
Figure 1(d) illustrates a sectional view of the core stud of figure 1(a);
Figure 2 illustrates a cross-sectional of a device for elongation of a stud, in accordance with an embodiment of the present invention;
Figure 3 illustrates a front view of a socket of figure 2;
Figure 4 illustrates a front view of a top plate of figure 2; and
Figure 5 illustrates a front view of a puller of figure 2.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS:
A preferred embodiment will now be described in detail with reference to accompanying drawings. The preferred embodiment does not limit the scope and ambit of the invention. The description provided is purely by way of example and illustration.
Referring to fig 2, in accordance with the present invention, there is provided a device 40 for elongation of a stud 30 comprising a base plate 41, a piston 42, a cylinder 43, a socket 50, a puller 60 and a top plate 80.
The piston 42 is likewise of circular, square or annular shape, having an upright portion 44 and a piston push surface 45 at the upper end of the upright portion 44. The lower end of base plate 41 has a surface 46 with a configuration complementary to that of stud-nut flange surface, so that these surfaces may rest upon each other.
The socket 50 is annular and stepped as shown in detail in the figure 3. The socket 50 comprises an upper socket portion 51 and a bottom socket portion 52 above and below a step 53 respectively. An antechamber space 54 in the bottom socket portion 52 leads to an annular space 55 of larger diameter. A plurality of handle-receiving apertures 56 secured to the upper socket portion 51 receives a handle bar 57 for rotating the socket 50. The interior of antechamber space 54 is adapted to rest on nut 32. The stud 30 extending through the nut 32 remains concentric with the annular space 55.
As shown in the figure 4, the top plate 80 with an annular space 82 is placed over the piston 42 in such way that a bottom surface 81 of the top plate 80 rests on the piston push surface 45.
Referring to the figure 2 and 5, the puller 60 is of annular shape and internally threaded. The puller 60 passes through the annular space 82 of the top plate 80 and is rotated to insert into the annular space 55 to ensure a tightened threaded kinematic connection with extending threaded ends 36 of the stud 30. As the puller 60 is tightened with the stud 30, a bottom surface 62 an upper collar portion 61 of the puller 60 makes a collar connection with a top surface 83 of the plate 80.
A pressure fluid port 72 is provided in an outer surface of the cylinder 43, and a conduit 74 connects this port with the cylinder 43. A working fluid motor 73 provides the required pressure to activate the piston 42 to move upwards and elongate the length of the stud. Such pressure through the working fluid motor 73 can be adjusted through a check valve lever 76 and a pressure gauge 78.
Fluid pressure will then be applied to the pressure fluid port 72, and the pressure created will cause the upright portion 44 of the piston 42 to rise. The downward pressure on the piston 42 will be transmitted through the base 41 to the stud-nut flange surface, and the upward force on the piston 42 will be transmitted through the plate 80 to the puller 60 and then to the nut 32 itself through threaded connection, and thus to the stud 30, which will be tensioned and elongated.
This elongation will continue to the desired extent, after which the fluid pressure will be held in while the socket 50 is rotated by the handle bar 57 inserted into the plurality of handle-receiving apertures 56. When the nut 32 is sufficiently tightened, pressure will be released from hydraulic system which will draw the piston 42 downward to relieving the pressure on the nut 32.
In order to remove the nut 32 from the stud 30, the operation will be the same except that the nut 32 will be rotated in the opposite direction while fluid pressure is applied.
It will be observed that the radially outward camming force of the threads of the stud 30 on the puller 60 while the stud 30 is being tensioned will be counteracted by the engagement of inner cylinder wall threads of the puller 60, and also by the fluid pressure. These combined actions result in the ability to achieve a relatively high degree of tensioning force with much smaller wall thicknesses of both the piston 42 and the puller 60 than would otherwise be possible.
The overall radial size of the unit may thus be materially decreased as compared with previous constructions, permitting the tensioner to be used in confined spaces. The total height of the unit may also be considerably smaller than previous constructions because of the novel configuration of the parts, and especially the use of the wall portion of the nut both to threadably engage the stud and to receive the vertical lifting forces from pressure system.
Although the invention has been described herein above with reference to the embodiments of the invention, the invention is not limited to the embodiments described herein above. It is to be understood that modifications and variations of the embodiments can be made without departing from the spirit and scope of the invention.

Claims:1) A device (40) for stretching of a stud (30) comprising:
atleast one piston (42) having a base (41) to rest over a stud-nut flange surface and a piston push surface (45) to hold a bottom surface (81) of a top plate (80);
a socket (50) of annular shape having an upper socket portion (51) and a bottom socket portion (52) above and below a step (53) and adapted to fit over a nut (32) with the stud (30) extending therein, said upper socket portion (51) provided with a plurality of handle receiving apertures (56);
a puller (60) adapted to insert into an annular space (82) of said top plate (80) to establish a tightened kinematic connection with the threads of said stud (30); and
a cylinder (43) in hydraulic connection with said piston (42) pushes said piston push surface (45) which in turn pushes said puller (60) thereby resulting in the stretching of said stud (30) and subsequently a handle bar (57) inserted into said plurality of handle receiving apertures (56) of the socket (50) rotates said socket (50) which in turn tightens said nut (32).
2) The device (40) as claimed in claim 1, wherein said puller (60) is provided with a plurality of threads on its inner circumference complementary to the threads of said stud (30).
3) The device (40) as claimed in claim 1, wherein a bottom surface of an upper collar portion (61) of said puller (60) makes a collar connection with a top surface (83) of said top plate (80).
4) The device (40) as claimed in claim 1, wherein a pressurized fluid port (72) is provided on the outer surface of said cylinder (43), and a conduit (74) connects said pressurized fluid port (72) with said cylinder (43).
5) The device (40) as claimed in claim 1, wherein a working fluid motor (73) controlled by a check valve lever (76) and a pressure gauge (78) provides the required pressure to activate said piston (42).
6) The device (40) as claimed in claim 1, wherein said handle bar (57) rotates said socket (50) in opposite direction with said piston (42) in activated position to loosen said nut (32).