FIELD OF INVENTION
The present invention relates to clamping device for surface grinding of non-magnetic
material piston ring of IP (Intermediate Pressure) control valve of a steam turbine
governing system. More particularly, the present invention relates to development of
special device which provides clamping force to withstand the cutting forces during
grinding of piston ring ensuring the required dimensional accuracy.
BACKGROUND OF THE INVENTION
In Steam Turbine Governing system, IP (intermediate pressure) control valve is
connected through IV and CV valve (intercepter valve and control valve) casing to
regulate the flow of steam in IP (Intermediate Pressure) turbine. In IP control valve,
the piston rings are fitted on the valve cone inside the valve cover assembly to properly
guide the valve cone and seal the leakage of steam. These Piston rings have very less
thickness and also have very controlled dimensional accuracy on thickness which can be
achieved only through grinding.
In the past, these piston rings were made of magnetic materials which were easily
clamped on magnetic base of surface grinding machine. Now the new piston rings are
made of non-magnetic cobalt based alloy satellite which is also very hard. Therefore it
is very difficult to clamp the non-magnetic piston rings on magnetic base of surface
grinding machine which also generates lot of cutting forces. Hence, there was a need of
a special clamping device for surface grinding of piston ring which also ensures the
required dimensional accuracy.

OBJECTS OF THE INVENTION
An object of the present invention is to provide a clamping device for surface grinding
of piston rings of IP control valve of steam turbine governing system which can
eliminate the disadvantages of prior art.
Another object of the invention is to provide a clamping device for surface grinding of
piston rings of IP control valve of steam turbine governing system which provides the
positive and uniform clamping of very thin non-magnetic piston ring on the surface
grinding machine.
Yet another object of the invention is to provide a clamping device for surface grinding
of piston rings of IP control valve of steam turbine governing system which ensures the
required dimensional accuracy during grinding of piston ring, thus improving the
quality.
A further object of the invention is to provide a clamping device for surface grinding of
piston rings of IP control valve of steam turbine governing system which ensures rigid
clamping of piston ring withstanding the cutting forces during surface grinding.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig.1: Clamping device for surface grinding of IP control valve of steam turbine
governing system
Fig.2: Section AA of fig 1 showing resting of piston ring on base plate as well as
clamping
Fig.3: Section BB of fig 1 showing clamping of piston ring along with taper bush and
taper wedges

Fig. 4: Base plate showing different diameters
Fig. 5: taper bush and taper wedge.
BRIEF DESCRIPTION OF DIFFERENT EMBODYMENT OF THE INVENTION
Fig 1 shows the clamping device for surface grinding of IP control valve of steam
turbine governing system which comprises of:-
a) Base plate (1)
b) Taper bushes (2)
c) Taper wedges (3)
d) Allen bolts (4)
e) Clamps (5)
f) Screws (6)
Fig 2 shows the section-AA of fig 1 and fig 3 shows the section-BB of fig. 1 according to
present invention. In section-AA, (fig 2) the piston ring is rested at its location on the
top face of base plate (1) and clamped on top surface by plurality of clamps (5) with
Allen bolt (4) through holes H3, The screws (6) are also tightened through clamps (5)
to hold them horizontal. In section-BB of figure 3, the piston ring having is uniformly
clamped through taper bushes (2), taper wedges (3) and Allen bolts (4) such that the
Allen bolts (4) is rotated, the Taper bushes (2) pushes the Taper wedges (3) towards
the piston ring and thus ensuring the positive clamping. After the clamping is uniformly
done at 6 different locations, the clamps (5) are removed.
Fig 4 shows the Base plate (1) having outer diameter D7 and inner diameter D8 with
plurality of holes H2 on pitch circle diameters D3 and D4 for fastening of Taper bush (2)

and plurality of holes H3 on pitch circle diameter D3 fort fastening of clamps (5)
according to an embodiment of the present invention. The base plate (1) also has
plurality of counter-bored holes H4 having depth T2 on pitch circle diameters D3 and
D4 which have pockets machined with width Wl as shown. The pockets having width
Wl are machined such that it has dimension D5 and D6 from centre line of holes H2 as
shown. The base plate (1) also has 4 no. of slots having width W3 to measure the
thickness of piston ring during the grinding.
Fig. 3 shows the Taper Bush (2) with hole HI, height T3 & taper angle A2 and Taper
wedge (3) with width W2, height Tl and taper angle Al according to an embodiment of
the present invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
Accordingly, there is provided a clamping device for surface grinding of IP control valve
of steam turbine governing system which comprises of:-
a) Base plate (1)
b) Taper bushes (2)
c) Taper wedges (3)
d) Allen bolts (4)
e) Clamps (5)
f) Screws (6)

Fig. 1 shows the clamping device for surface grinding of IP control valve of steam
turbine governing system according to present invention The whole method of clamping
of piston ring on the device is as follows:-
1. Firstly the Piston ring having outer diameter D1, inner diameter D2 and thickness T is
located on the top face of Base plate (1) such that it is located inside the pockets Wl
on both outer diameter and inner diameter. The dimensions D5 and D6 have been
selected such that outer diameter Dl and inner diameter D2 of the face piston ring lies
in the pockets Wl of counter-bored holes H4. Both the top face and bottom face of the
Base plate (1) are grounded to ensure that parallelism of surface on which piston ring is
rested.
2. Then the piston ring is clamped at this location by plurality of clamps (5) with Allen
bolt (4) through holes H3 on base plate (1) section -AA, fig 2. The screws (6) are .also
tightened through clamps (5) to hold them horizontal. The purpose of these clamps (5)
is to hold the piston ring at its location while tightening the Taper Bushes (2) and Taper
wedges (3).
3. Then the Taper wedges (3) having width W2 and height Tl with taper angle Al on
one surface are inserted inside the pockets with Wl of counter-bored holes H4 having
depth T2 on pitch circle diameters D3 and D4 (section -BB, fig 3, Tl> T2). The height
Tl of Taper wedges (3) is kept more than the depth T2 of counter-bored hole H4 and
less (below the level of) than the thickness T of piston ring so that they does not
interfere with the grinding wheel.
4. Now the Taper bushes (2) having height T3 with taper angle A2 on one surface are
tightened by Allen bolts (4) with Base plate (1) through holes H1/H2 that tapered angle
surface A2 of taper bushes (2) butt with tapered angle surface Al of Taper wedges (3)
and pushes the Taper wedges (3) towards the piston ring when tightened by Allen bolts
(4) (section -BB, fig 3 T3