FIELD OF THE INVENTION
The present invention relates to an improved device for accurately core machining core press ring corresponding to large size turbogenerator exciters. The invention further relates to a method for accurately machining core press ring corresponding to large size turbogenerator exciters.
BACKGROUND OF THE INVENTION
Turbogenerators have three major assemblies Stator, Rotor and Exciter. Exciter is required for the supply of the electric current to the field circuit which generates magnetic field. Exciters are mounted on the same shaft. With increase in the capacity, exciters of larger size were required. Exciter has two major parts, shaft mounted armature housed in the exciter core and a stator providing magnetic field known as Magnetic System.
The armature winding is housed in the laminated core. For the symmetrical rotation of the exciter armature, it is essential to have high accuracy in the verticality and eccentricity of the exciter armature core.

While the core is built up layer by layer, for compacting the core, it is pressed at many stages during stacking. After complete stacking on both side a Core press-ring is assembled with core packed. Core Press Ring provides a surface for mounting of Support Ring. This whole assembly is finally mounted on Exciter Rotor.
It was observed that in the higher rating exciters, there exists an unbalance during the balancing of exciters. Any misalignment during assembly of Armature core with core press ring or winding Support ring will cause eccentricity and the resulting increase in vibration hampering to achieve the balancing of the exciter. This results ing enormous amount of rework and time as the exciter is required to be taken back to shop from balancing tunnel. So, there exists the need to have high degree of precision and alignment in matching components to have it proper balanced.
Once the core is built up layer by layer and then core press ring is mounted on the armature core on both ends, i.e. driving end and non-driving end, for pressing the core and also for providing the seating surface for mounting the Support Ring.
Since the outer dia of core press rings of both side are machined separately i.e. before their assembly with armature core, this creates problem since matching is done separately therefore core press ring axis alignment and symmetricity cannot be maintained with respect to axis of armature core and when in this condition support

ring is mounted over core press ring vibration and balancing issues comes up because of poor matching in assembly of support ring with core press ring.
However, instead of machining both the core press ring separately and beforehand, machining should be done after its assembly on the armature so that it can be ensured that axis alignment of armature and core press ring is within zero tolerance i.e. both are having same coincidental axis and that there will be no eccentricity thus eliminating the problem during balancing of exciter.
However, since the core press ring is assembled on both the sides of armature, this becomes a difficult situation, as no facility exists to keep core press ring-armature assembly in vertical position during machining. Neither the armature can be vice pressed during clamping as armature is not a mono block component but made up of thin stamping which cannot be pressed as solid cylinder. Hence, there existed a need of improved means capable of setting, clamping and machining of the armature in vertical position with core press ring intact.
OBJECT OF THE INVENTION
It is therefore an object of the invention to propose a device and method for machining core press ring corresponding to large size turbogenerator exciters having low initial cost and un- keep, great and continuing accuracy inherent in its

configuration and operation, ruggedness and simplicity in its construction and operation, all to the ultimate end of consistently reproducing the desired manufacturing quality and balancing required.
SUMMARY OF THE INVENTION
Accordingly, there is provided an improved device for accurately machining core press ring corresponding to large size turbogenerator exciters, said device comprising a mounting base acting as the base of the device; a plurality of equispaced and internally recessed threaded hole arranged towards and outer edge of mounting base and in a circular array; a plurality of block weldably attached on a peripheral face of the mounting base through a plurality of threaded holes to secure in standard machine bed and a plurality of threaded holes for facilitating lifting of the device; a plurality of Structural Block weldably mounted on the mounting base , having a flat work contact surface, provided in the mounting base over which a job W to be accommodated; a plurality of flexible means provided between the structural block for adjusting the vertical position of the device to maintain a parallel relation between the top and bottom ring; a plurality of L-Blocks 40 with fastening means provided on the mounting base 10 for securely holding an armature W from its base in order to machine the ring at top end; a saddle clamp

tightened end; a saddle clamp tightened over a rubber cushioning, provided over the circumference job W, through threaded flexible connection; at least one pull stud for pressing an U-clamp downwards upon tightening a hexnut; a plurality of equispaced threaded hole 11 on the mounting base to threadedly receive a plurality of said pullstud; an adjustable support means to provide shoulder support to the U-clamp through top surface of a nut, received by an internally recessed threaded hole in said support means , which can be threadedly adjusted for tightening or loosening; a plurality of through holes in the nut in which a solid slender rod can be inserted to facilitate rotation for height adjustments; a groove on the nut to provide air passage avoid vacuum lumps in order to reduce lifting force; and protrusions on the clamp to upside rotate the job W using an over-head crane.
BRIEF DESCRIPTION OF THF ACOMPANYING DRAWINGS
The foregoing and other features of the invention, comprising the improved means and method for machining core press ring corresponding to large size turbogenerator exciters together with the construction and relative arrangement of the several parts, will be apparent from the following more particular description of the invention, as illustrated in the accompanying drawings, in which like reference

characters refer to the same parts throughout the different figures and subsequently incorporated in the subjoined claims. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.
Fig. 1 is line representation of front view of proposed mechanism for machining core press ring corresponding to large size turbogenerator exciters and wherein it may be noted that minor changes with respect to the object of the invention may be present in the cross-sectional view.
Fig. 2 is line representation of top view of proposed mechanism for machining core press ring corresponding to large size turbogenerator exciters and wherein it may be noted that minor changes with respect to the object of the invention may be present in the cross-sectional view.
Rg. 3 is line representation of armature core held together by core press ring and the machining to be performed.
Rg. 4 is line representation of top and front view of nut 62 used in proposed mechanism for machining core press ring corresponding to large size turbogenerator exciters and wherein it may be noted that minor changes with respect to the object of the invention may be present in the cross-sectional view.

Fig. 5 is line representation of top and front view of clamping arrangement done using U-clamp 66 and pullstud 67 used in proposed mechanism for machining core press ring corresponding to large size turbogenerator exciters and wherein it may be noted that minor changes with respect to the object of the invention may be present in the cross-sectional view.
DETAILED DESCRIPTION OF THE PREFERED EMBODIMENT OF THE
INVENTION
Before describing in detail, means for manufacturing core press ring machining corresponding to large size turbogenerator exciters in accordance with the present invention, it should be observed that the present invention resides primarily in a novel and non-obvious combination of hardware elements and method steps. Accordingly, these elements and steps have been represented by conventional elements and steps in the drawings, showing only those specific details that are pertinent to the present invention so as not to obscure the disclosure with details that will be readily apparent to those skilled in the art having the benefit of the description herein.

The present invention is directed to solve the above-described problems of the prior art and to provide means for manufacturing core press ring machining corresponding to large size turbogenerator exciters in accordance with the present invention and to enable to accurately machine exciter core press ring with enhanced balancing that too in short time.
Referring now to figure 3 wherein details have been drawn to represent the exact machining requirements for which the proposed device has been developed to rectify the defects in prior art. As discussed earlier, armature core is build of numerous thin stamping L stacked over each other. In any electrical machine, the development of eddy currents is influenced by the resistance of the material in which they flow. For any magnetic material, there is an inverse relationship between the material's cross-sectional area and its resistance, meaning that a reduction in area causes an increase in resistance, and in turn, a decrease in eddy currents. One way to achieve a reduction in cross-sectional area is to make the material thinner. This is why armature cores are made up of many thin pieces of iron, rather than a large, solid piece. These individual, thin pieces have a higher resistance than one solid piece, and therefore, produce less eddy currents and experience lower eddy current loss. The individual iron pieces that make up the armature are referred to as laminations. To make the core a monolithic mass, the stamping L are tightened

with long insulated studs S and insulated washer IW passing through the stampings as well as core press ring R at both the ends. After this assembly, core press ring is being machined in vertical position. The machining area is shown thorough a bold profile M.
Referring now figure 1 and 2 in detail, the disc like mounting base 10 acts as the base of the fixture F wherein mounting base 10 comprises of plurality of equispaced and internally recessed threaded hole 11 disposed towards outer edge of mounting base 10 and arranged in a circular array while maintaining a concentric relationship with L-block 40 and structural bloc 20, both welded on mounting base 10, and threaded hole 22. Provisions of fixing the fixture machine bed is provided through securing means 30.
Entire fixture is first secured in standard machine bed 50 through plurality of block 30 weldedly attached on peripheral face of mounting base 10. Block 30 have on it threaded holes 31 for making threaded connection with machine bed T-slot and threaded holes 32 for facilitating the need of lifting the entire device Das per requirement.
Plurality of Structural Block 20, weldedly mounted on mounting base 10 and having a flat work contact surface, are provided in mounting base 10 over which the job

W, unfinished core press ring assembled on both ends of a cylindrical exciter armature core and wherein machining of these core press rings is to be performed one after another, will rest. Job W is first placed on flat work contact surface of Plurality of Structural Block 20 and parallelism of top ring is maintained with respect to machine bed 50. To maintain such parallelism, plurality of flexible means 22 are also provided in between Structural Block 20, which are used for adjusting vertical position of armature during machining.
As the armature is placed on structural block 20, the armature core is held secured by fastening means 40. Plurality of L-Blocks 40 with fastening means 41, 42 are weldedly provided on mounting base 10 for securely holding armature from its base in order to machine ring at top end.
To secure the armature from vibrations, machining forces or the likes, downward securing forces are applied upon the armature. For this, clamping means 70 are provided towards the center part of the armature wherein said clamping means comprises of saddle clamp 70, provided in two C-halves, being adequately tightened over rubber cushioning 73 provided over job W circumference, through threaded flexible connection 74. As tightening a hexnut 68 on pullstud 67 results in pressing U-clamp 66 downwards, the downward motion is resisted as U-clamp 66 is mechanically shouldered at its ends by Saddle clamp 70 and adjustable support

means 60 and thereby generating securing forces required to compensate for machining forces and provide structural stability to the job W. Plurality of pullstud 67 is being threadly received by plurality of equispaced threaded hole 11 on mounting base 10.
The adjustable support means 60 is a height adjustable support system wherein the shoulder support to U-clamp 66 is provided as the U-clamp rests on top surface of a nut 62, received by internally recessed threaded hole 61 in support means 60, which can be threadedly adjusted for tightening or loosening. To rotate the nut 62 for said height adjustments, plurality of through holes 63, 64 are used in which a solid slender rod can be inserted to facilitate rotation. Nut 62 also grooved 65 so as to provide air passage and therefore avoid vacuum lumps in order to reduce lifting efforts.
It is to be noted here that since both top and bottom rings are required to be machines initially, plurality of flexible means 22 are also provided in between structural block 20 will only be used for adjusting vertical position of armature when both the ring ends are unfinished. However, once one end of the ring is machined, all clamping means are removed to upside rotate the job using an over-head crane whose slings or the likes would use protrusions 71 for the same. Here forth, the

finished ring will perfectly rest on structural block 20 and flexible means 22 will not be required for adjusting vertical position of armature W.
Also the clamp 70 angular position in horizontal plane is to be decided on the basis of which threaded hole 11 on mounting base 10 will receive the pull stud 67. Referring to figure 2, plurality of threaded hole 11 are positioned on mounting base 10 in a way that either they are radially behind structural block 20 or behind flexible means 22. Whichever of the two, i.e. structural block 20 or behind flexible means 22 will support armature W, stud shall be received by corresponding radially positioned threaded hole 11.
Although the present discussion relates to means for manufacturing core press ring machining corresponding to large size turbogenerator exciters, it will be appreciated that the device and methods discussed may be readily adapted for use with other similar procedures. Not only the methods and the tools devised thereof for enabling accurate machining of exciter core press ring with enhanced balancing is cheap and easy to manufacture but also will provide safer and ergonomic means for the operators to deal with the machining operation. It will be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described or shown herein, embody the principles of the invention and are included within its scope.

Furthermore, all examples recited herein are principally intended expressly to be only for pedagogical purposes to aid the reader in understanding the principles of the invention and the concepts contributed by the inventor(s) to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. Also, the various embodiments described herein are not necessarily mutually exclusive, as some embodiments can be combined with one or more other embodiments to form new embodiments.

WE CLAIM
1) An improved device for accurately machining core press ring corresponding to large size turbogenerator exciters, said device comprising:-
- a mounting base 10 acting as the base of the device;
- a plurality of equispaced and internally recessed threaded hole 11 arranged towards and outer edge of mounting base 10 and in a circular array;
- a plurality of block 30 weldably attached on a peripheral face of the mounting base 10 through a plurality of threaded holes 31 to secure in standard machine bed 50 and a plurality of threaded holes 32 for facilitating lifting of
the device;
- a plurality of Structural Block 20 weldably mounted on the mounting base
10, having a flat work contact surface, provided in the mounting base 10
over which a job W to be accommodated;
- a plurality of flexible means 22 provided between the structural block 20 for adjusting the vertical position of the device to maintain a parallel relation between the top and bottom ring;
- a plurality of L-Blocks 40 with fastening means 41, 42 provided on the mounting base 10 for securely holding an armature W from its base in order to machine the ring at top end;

- a saddle clamp 70 tightened over a rubber cushioning 73, provided over the circumference job W, through threaded flexible connection 74;
- at least one pullstud 67 for pressing an U-clamp 66 downwards upon
tightening a hexnut 68;
- a plurality of equispaced threaded hole 11 on the mounting base 10 to threadly receive a plurality of said pullstud 67;
- an adjustable support means 60 to provide shoulder support to the U-clamp 66 through top surface of a nut 62, received by an internally recessed threaded hole 61 in said support means 60, which can be threadly adjusted for tightening or loosening;

- a plurality of through holes 63, 64 in the nut 62 in which a solid slender rod can be inserted to facilitate rotation for height adjustments;
- a groove 65 on the nut 62 to provide air passage to avoid vacuum lumps in order to reduce lifting force ; and
- multiple protrusions 71 on the clamp 70 to upside rotate the job W using an
over-head crane.
2) A method for accurately machining core press ring corresponding to large size turbogenerator exciters, said method comprising :

- securing a device as claimed in claim 1, in standard machine bed 50 through a plurality of threaded holes 31 disposed on the plurality of block 30 attached on peripheral face of the mounting base 10;
- placing the armature W on flat work contact surface of the Plurality of Structural Block 20 or plurality of flexible members 22 used for adjusting vertical position of the armature during machining and securing the same using fastening means 41, 42 in the plurality of L-Blocks 40;

- securing armature clamping means 70 towards the center part of the armature W wherein adequately tightening of said clamping means 70 over the rubber cushioning 73 provided over the job W circumference, through the threaded flexible connection 74;
- freely placing the U-clamp 66 in a way for being mechanically shouldered by the saddle clamp 70 and the adjustable support means 60;
- adjusting height of the adjustable support means 60 to bring u-clamp 66 in horizontal plane by rotating the nut 62 received by the threaded hole 61 in the support means 60;
- generating securing forces by tightening the hexnut 68 on the putlstud 67
received by the plurality of equispaced threaded hole 11 radially adjacent to
the flexible means 22 on the mounting base 10 resulting in downwards

pressing of the U-clamp 66, wherein the downward motion is resisted by saddle clamp 70 and adjustable support means 60;
- machining the core press ring R mounted on one end of the armature core;
- removing all clamping to upside rotate the job using an over-head crane by using the protrusions 71;
- placing the job on the structural block 20; and
- clamping the job for top ring and reiterate the process for machining the other ring.