FIELD OF THE INVENTION
This invention relates to an improved arrangement of thrust bearing spring assembly system formed of pre-stressed springs adaptable to Hydro Generators.
BACKGROUND OF THE INVENTION
In prior art hydrogenerators, spring support type thrust bearing is used, in which thrust pad is supported on a number of helical springs such that each spring is enabled to share a portion of the total load. The springs are uniformly distributed under the pads. Sudden variations in the load due to water flow through the turbine may result in substantial variations in axial thrust leading to tilting and jumping of the rotor of the generator and turbine. With a free spring, this jumping and tilting is accentuated and causes damage to the white metal surfaces of the bearing pads. This effect is reduced according to prior art to a safe level by pre stressing each spring by means of a central screw adjustable to tighten washer plates fitted at each end of the spring. Conventional process of manufacturing pre-stressed thrust bearing spring is as follows :-
• Springs are pre-stressed to a given value of pre-load by means of a central screw.
• After pre-loading, the springs are locked in position by means of a grub screw.
• Then, machining of the top and bottom retaining plate is carried-out to a given dimension 'H'. Projected length of the central screw is used for fixing. Refer figure 1A.

In spring support type bearing assembly, a number of holes are made in the spring plate for fixing the thrust bearing spring. Refer figure IB.
Number of thrust bearing springs depends on the design load which takes into consideration rotor weight, turbine rotating components weight and hydraulic :hrust. Number of springs varies from 100 to 1000 as per load requirement, for Which number of holes are to be drilled in the spring plate. For complete thrust Dearing arrangement refer figure 1C.
OBJECTS OF THE INVENTION :-
It is therefore, an object of the present invention to propose an improved thrust tearing system formed of pre-stressed springs adaptable to a hydrogenerator.
mother object is to propose an improved arrangement of thrust bearing spring ssembly system formed of pre-stressed springs adaptable to a hydrogenerator, which reduces manufacturing cycle by eliminating operation of drilling of a lurality holes for spring fixing.
still another object of the invention is to propose an improved arrangement of lrust bearing spring assembly system formed of pre-stressed springs adaptable ) a hydrogenerator, which avoids deformation of surface around the holes hich leads to unlevelled surface.
further object of the invention is to propose an improved arrangement of rust bearing spring assembly system formed of pre-stressed springs adaptable a hydrogenerator, which simplifies the pre-stressing of the springs.

SUMMARY OF THE INVENTION
Accordingly, there is provided an improved thrust Bearing spring system formed with pre-Stressed springs, adaptable to a Hydro Generator, comprising: a plurality of springs pre-stressed to a given value of pre-load by means of a central screw; a hole reamed through a bottom portion of a retaining plate to lock the pre-stressed springs via the central screw; a shear pin rigidly locking the sub-assembly of the retainer plate and springs; a spring plate having a plurality of holes to accommodate corresponding number of pad stops; the sub-assembly of the pre-stressed springs and the retainer plate disposed over the spring plate and interlocked by said plurality of pad stops; and a thrust pad disposed over the :hrust bearing spring assembly.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS ;
Figure 1A : Shows a thrust Bearing Spring Assembly of prior art
Figure IB : Plan view showing holes in spring plate for fixing of the spring
assembly according to prior art. Figure 1C : Thrust Bearing Arrangement according to prior art. Figure 2A : Thrust Bearing Spring Assembly according to the invention. Figure 2B : Retaining Plate of the invention Figure 2C : Plan view showing holes in the spring plate according to the prior
art. Figure 2D : Thrust Bearing Arrangement according to the invention.

DETAIL DESCRIPTION OF THE INVENTION
In the improved system, the thrust bearing spring assembly (1A) is modified as follows :-
• Springs (1) are pre-stressed to a given value of pre-load by means of a central screw (5).
• A hole is reamed through a bottom retaining plate (2B) and a central screw (5) is provided for locking of the pre-stressed springs (1), a shear pin (6) being positioned to lock the spring (1) in position.
• Top and bottom retaining plates (2T, 2B) are machined to a given dimension 'H'.
• Projected portion of the central screw (5) is machined out.
Refer figure 2A. For fixing of these springs (1), a retaining plate (2) is used. In the retaining plate (2), a plurality of holes (2a) are made with a clearance of 0.5 mm with reference to the outside diameter (D) of the thrust bearing spring (1). Refer figure 2B. The retaining plate (2) is placed over a spring plate (4) and is locked in position by modified pad stops (3). Refer figure 2C. The thrust bearing springs (1) are further positioned in the spring plate (4) and a complete assembly is done. For complete assembly refer figure 2D.

The invented design has the following advantages :-
• Pre-Loaded spring is locked by replacing a grub screw.
• Making of holes for fixing the springs in the spring plate is completely eliminated thus, saving cost and manufacturing cycle time.
• Assembly/Dismantling of the thrust bearing is simplified and faster.
• Leveling of the thrust bearing is more accurate as the surface of the spring plate is more leveled.

WE CLAIM :
1. An improved thrust Bearing spring system formed with Pre-Stressed springs,
adaptable to Hydro Generator, comprising :-
a plurality of springs (1) pre-stressed to a given value of pre-load by means of a central screw;
a hole reamed through a bottom portion of a retaining plate to apply a pre-determined pre-load on the pre-stressed springs via the central screw;
a shear pin rigidly locking the sub-assembly of the retainer plate and springs;
a spring plate having a plurality of holes to accommodate corresponding number of pad stops;
the sub-assembly of the pre-stressed springs and the retainer plate disposed over the spring plate and interlocked by said plurality of pad stops; and
a thrust pad disposed over the thrust bearing spring assembly.
2. The system as claimed in claim 1, wherein the retaining plate comprises a top
portion.

3. The system as claimed in claim 1 or 2, wherein the top portion and the
bottom portion of the retaining plate is configured to a pre-determined
dimension through a machining process.
4. The system as claimed in claim 1, wherein a portion of the central screw
projected out of the sub-assembly is machined out.
5. The system as claimed in claim 1, wherein the holes on the retaining plate is
drilled with a clearance of at least 0.5 mm with reference to the outside
diameter of the springs.

ABSTRACT

The invention relates to an improved thrust Bearing spring system formed with Pre-Stressed springs, adaptable to Hydro Generator, comprising: a plurality of springs (1) pre-stressed to a given value of pre-load by means of a central screw; a hole reamed through a bottom portion of a retaining plate to apply a pre-determined pre-load on the pre-stressed springs via the central screw; a shear pin rigidly locking the sub-assembly of the retainer plate and springs; a spring plate having a plurality of holes to accommodate corresponding number of pad stops; the sub-assembly of the pre-stressed springs and the retainer plate disposed over the spring plate and interlocked by said plurality of pad stops; and a thrust pad disposed over the thrust bearing spring assembly.