FIELD OF INVENTION
The invention relates to a device for assembly and machining of grid flats in a
steam generator. The invention further relates to a process for the assembly of
grid flats to a grid pattern of the Steam generator in the device. The invention
also relates to a process of machining an assembled grid flats of a steam
generator in the device.
BACKGROUND OF INVENTION
Steam Generators for 500 MWe capacity for nuclear power plants have a number
of tube supports called "grid". It is possible to use the same support system in
higher capacity steam generators also. These grids are similar to the baffles
except that these supports permit steam to pass through them in the axial
direction apart from supporting the tubes. The manufacture of these grids
involve assembling of the gird flats (SG flats of varying width depending on the
type (ie) main grid flat or small grid flat) to the grid pattern meeting the
accuracy requirement of forming rhombus in the correct location and fixing them
in position through peripheral support rings during machining. Presently, there is
no single device which allows assembly of the grid flats to different grid patterns,
and enables machining of the assembled grid flats.

OBJECTS OF INVENTION
It is therefore the object of the invention is to propose a device for assembly
including machining of main grid flats and small grid flats to a desired grid
pattern in a steam generator.
A still further object of the invention is to propose a device for assembly
including machining of main grid flats and small grid flats to a desired grid
pattern in a steam generators, which enables assembly of the main and small
grid flats to the specific pattern and further enables machining of the assembled
grid flats.
Another object of the invention is to propose a device for assembly including
machining of main grid flats and small grid flats to a desired grid pattern in a
steam generator, which allows positioning of the spacer ring concentric to the
centre of the grid pieces to be introduced at the periphery including pasting of
the spacer pieces.
A further object of the invention is to propose a device for assembly including
machining of main grid flats and small grid flats to a desired grid pattern in a
steam generator, which allows machining of the assembly including the grooves
in a single set-up.

A still another object of the invention is to propose a process for the assembly of
grid flat in a device.
Yet another object of the invention is to propose a process of machining an
assembled grid in a device.
SUMMARY OF THE INVENTION
Accordingly, there is provided in a first aspect of the invention, a device for
assembly and machining of a grid assembly in a steam generator, the grid
assembly comprising a plurality of main grid flats, each having angular slots in
several locations for establishing an interconnection among them, the angular
slots accommodating a corresponding number of small grid flats; a man-hole grid
assembly disposed on top of the assembly of the main grid flats and the small
grid flats, and aligned to a basic pattern and clamped; a plurality of spacer
blocks insertable between the grid flats and pastable around the periphery of the
grid flats assembly; and a plurality of frame rings joining the spacer pieces, the
frame rings being clamped together using welding pins, the device comprising a
base plate having a housing and at least four support legs, an annular clamping
ring for clamping the grid flats near the periphery, and accommodating a
plurality of segmented top rings; a plurality of side rings clamped via around the
base plate

to support the grid during the machining, a first type of studs including rollers at
the intersection of the main grids for positioning the main grids and retaining the
main grids by clamp plates; a plurality of clamps for clamping the top rings over
the grids; a second type of studs provides the required force for the clamps; and
a step pin for centering the spacer ring which is disposed between the top and
bottom main grid flats. In a second aspect, the invention provides a process for
the assembly of grid flats in a device. The process comprising the steps of
disposing the main grid flats on the base plate such that the bottom main grid
flats are enabled to slide on the base plate supported by the roller and stud
means provided at the intersection location of the top main grid flats; placing the
spacer ring on the periphery of the bottom main grid flats duly centralized by
providing step pins, the top main grid flats resting on the spacer rings;
intertwining the top and bottom main flats using the slots in them at the
functions supported by the rollers; and inserting the small grid flats into the slots
of the main grid flats, the small grid flats being pasted at the periphery using the
spacer pieces.
The invention further provides in a third aspect, a process for machining an
assembled grid in a device as claimed in claim 1, the process comprising the
steps of, loading the assembled grid on the device and placing the device with
assembled grid on a vertical turning lathe for machining the outside diameter
(OD) including the grooves; clamping the main grid flats to the base plate
through the studs and the clamp plate; joining an annular clamp ring over the
grid assembly including clamping all around a first top ring in segments by using

clamps and the studs; screwing around the base plate a plurality of peripherial
ring to support the grid flats and the spacer pieces; and carrying out the OD-
machining; replacing the first top ring with a second top ring during a top groove
machining; and replacing back the first top ring and removing the peripherial
ring and the second top ring during the bottom groove machining.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure - 1 shows a plan view of a grid assembly according to invention.
Figure - 2 shows the device of the invention.
DETAILED DESCRIPTION OF INVENTION
Component-GRID
As shown in figure 1, a 'Grid' is a supporting member for tubes in the Steam
Generator. There are totally 2489 U-tubes in 500 Mwe steam generator and
hence 4978 support location each having rhombus shape in the grid assembly.
As shown in the Figure 1, the main grid flats (A) have angular slots at crossing
locations for assembly of one into the other. The main grid flats (A) crossing at
number of locations, and the angular slots in them accommodate the small gird

flats (B). A man-hole grid assembly (C) is a separate sub-assembly which can be
kept over the grid assembly (A and B) and gets aligned to a basic pattern by
proper location and clamping. A plurality of spacer pieces (D) is inserted between
the grid flats (A and B) and pasted in a position over the spacer rings (D) around
the periphery. Several frame rings (E) are used to clamp the grid flat end along
with the spacer pieces (D) using a number of grooves machined on the faces.
These frame rings (E) are in turn clamped together using weld pins.
Device
As shown in figure - 2, a base plate (1) houses all the constituent components of
the device and supports the grid flats in assembly. An annular clamping ring (2)
clamps the grid flats (A, B) near the periphery and also accommodates a plurality
of top rings (8). Several side rings (3) which are segmental rings are clamped
around the base plate (1) to support the grids during machining of the outside
diameter (OD) and the top grooving operations. During bottom groove
machining, the side rings (3) are removed. A first type of studs (4) and rollers
(5) at the intersections of the main grids (A) are provided to ensure positioning
of the main grids (A) in the exact locations and also to support them by clamping
to the base plate (1) using clamp plates (6). Four support legs (7) are provided
to the base plate (1) to aid the approach of the tool during bottom grooving
operation and also to clamp the base plate (1) to the machine table/chuck. The

top rings (8) have variants "a" and "b" for the purpose of clamping the grids (A,
B) very near the machining area to avoid destabilisation of the assembly due to
cutting force. Clamps (9) are provided to clamp the segmented top rings (8a, 8b)
over the grids. A second-type of studs (10) emanating from the base plate (1)
provides the force for the clamps (9). A step pin (11) is used for centering the
spacer ring (D) of the grid assembly (A, B) coming between the top and bottom
main grid flats (A).
ASSEMBLY OF GRID FLATS
Figure 1 shows a plan view of the device for assembly and machining, of the
grid. The bottom main grid flats (A) are made to slide on a base plate (1)
supported by rollers and stud (4 and 5) provided on the base plate (1) at the
intersection locations of the top main grid flats (A). The spacer ring (D) is kept
on the periphery over the bottom grid flat end centralized using step pins (11),
over which the top main grid flats (A) are supported. The top main grid flats are
inter twined with bottom main grid flats (A) using slots in them at the junctions
supported by the rollers (5).
The small grid flats (B) are inserted into the slots of the main grid flats (A),
finally, resulting in rhombus supports for the tubes. These grid flats (A, B) are
supported/spaced at the periphery using a plurality of spacer pieces (D) and the
spacers (D) are pasted to the grid flats using adhesive.

Machining of the assembly
Machining involves (1) outside diameter (OD) machining 2) Top and bottom
groove machining. The whole assembly in the device is loaded on a vertical
turning lathe for machining the OD and grooves. At the crossing of the main grid
flats (A), they are clamped to the base plate (1) through the studs (12) and the
clamped plate (6). Annular clamp ring (2) is assembled over the grid assembly,
and a first top ring in segments (8a) meant for OD machining operation is
assembled and clamped all around using clamps (9) and the studs (12). A
plurality of segmental peripheral rings (3) are screwed around the base plate (1)
to support the grid flats (A) and the spacers (D) during OD machining operation
as shown in Figure 2. The base plate (1) is supported using four support legs (7)
for clamping to the machine table. Peripheral support arrangement is provided in
the fixture in the form of dismantling type segmented rings for OD machining
and grooving.
During the top groove machining, a second top ring (8b) replaces the first top
ring (8a) to give room for machining and at the same time clamping the
assembly very near to the groove. The bottom groove machining is taken up
later removing the segmental peripherial ring (3), and again putting back the
first top ring 8(a).
Thus the device helps in assembly and machining for the manufacture of grids.

WE CLAIM
1. A device for assembly and machining of a grid assembly in a steam
generator, the grid assembly comprising a plurality of main grid flats (A),
each having angular slots in several locations for establishing an
interconnection among them, the angular slots accommodating a
corresponding number of small grid flats (B); a man-hole grid assembly
(C) disposed on top of the assembly (A, B)of the main grid flats (A) and
the small grid flats (B), and aligned to a basic pattern and clamped; a
plurality of spacer rings (D) insertable between the grid flats (A and B)
and pastable around the periphery of the grid flats assembly (A and B);
and a plurality of frame rings (E) joining the spacer pieces (D), the frame
rings (E) being clamped together using welding pins, the device
comprising:
- a base plate (1) having a housing and at least four support legs
(7);
- an annular clamping ring (2) for clamping the grid flats (A, B) near
the periphery, and accommodating a plurality of top rings (8);
- a plurality of side rings (3) clamped around the base plate (1) to
support the grid (A,B,C) during the machining;

- a first type of studs including rollers (4,5) at the intersection of the
main grids (A) for positioning the main girds (A) and retaining the
main grids (A) by clamp plates (6);
- a plurality of clamps (9) for clamping the segmented top rings (8a,
8b) over the grids;
- a second type of studs (10) providing the required force for the
clamps (9); and
- a step pin (11) for centering the spacer rings (D) which are
disposed between the top and bottom main grid plates (A).
2. A process for the assembly of grid flats in a device as claimed in claim 1,
the process comprising the steps of:
- disposing the main grid flats (A) on the base plate (1) such that the
bottom main grid flats (A) are enabled to slide on the base plate
(1) supported by the roller and stud means (4 and 5) provided at
the intersection location of the top main grid flats (A);
- placing the spacer ring (D) on the periphery of the bottom main
grid flats (A) duly centralized by providing step pins (11), the top
main grid flats (A) resting on the spacer rings (D);

- intertwining the top and bottom main flats using the slots in them
at the junctions supported by the rollers (5); and
- inserting the small grid flats (B) into the slots of the main grid flats
(A), the small grid flats (B) being pasted at the periphery using the
spacer pieces (D).
3. A process for machining an assembled grid in a device as claimed in claim
1, the process comprising the steps of:
- loading the assembled grid on the device and placing the device
with assembled grid on a vertical turning lathe for machining the
outside diameter (OD) including the grooves;
- clamping the main grid flats (A) to the base plate (1) through the
studs (12) and the clamp plate (6);
- joining an annular clamp ring (2) over the grid assembly including
clamping all around a segmented first top ring (8a) by using clamps
(9) and the studs (12);
- screwing around the base plate (1) a plurality of peripherial ring (3)
to support the grid flats (A, B) and the spacer pieces (D); and

- carrying out the OD-machining;
- replacing the first top ring (8a) with a second top ring (8b) during a
top groove machining; and
- replacing back the first top ring (8a) and removing the peripherial
ring (3) and the second top ring (8b) during the bottom groove
machining.
4. A device for assembly and machining of a grid assembly in a steam
generator as substantially described and illustrated herein with reference
to the accompanying drawings.
Dated this th Day 2008


- carrying out the OD-machining;
- replacing the first top ring (8a) with a second top ring (8b) during a
top groove machining; and
- replacing back the first top ring (8a) and removing the peripherial
ring (3) and the second top ring (8b) during the bottom groove
machining.
4. A device for assembly and machining of a grid assembly in a steam
generator as substantially described and illustrated herein with reference
to the accompanying drawings.
Dated this 23rd Day MAY 2008

The invention relates to a device for assembly and machining of a grid assembly in a steam generator, the grid assembly comprising a plurality of main grid flats (A), each having angular slots in several locations for establishing an interconnection among them, the angular slots accommodating a corresponding
number of small grid flats (B); a man-hole grid assembly (C) disposed on top of the assembly (A, B)of the main grid flats (A) and the small grid flats (B), and aligned to a basic pattern and clamped; a plurality of spacer rings (D) insertable between the grid flats (A and B) and pastable around the periphery of the grid
flats assembly (A and B); and a plurality of frame rings (E) joining the spacer pieces (D), the frame rings (E) being clamped together using welding pins, the device comprising a base plate (1) having a housing and at least four support
legs (7); an annular clamping ring (2) for clamping the grid flats (A, B) near the
periphery, and accommodating a plurality of top rings (8); a plurality of side rings (3) clamped around the base plate (1) to support the grid (A,B,C) during the machining; a first type of studs including rollers (4,5) at the intersection of the main grids (A) for positioning the main girds (A) and retaining the main grids (A) by clamp plates (6); a plurality of clamps (9) for clamping the segmented top
rings (8a, 8b) over the grids; a second type of studs (10) providing the required force for the clamps (9); and a step pin (11) for centering the spacer rings (D) which are disposed between the top and bottom main grid plates (A).