FIELD OF INVENTION
The present invention relates a three blade segment fixture for end profiles and throat
gap checking of banana type hollow guide blade of low pressure steam turbine. More
particularly the invention relates to a three blade segment fixture for checking the end
profiles of the blades within the specified tolerances and the throat gap between two
blades as per requirement.
BACKGROUND OF THE INVENTION AND PRIOR ART
As this banana type of hollow guide blades are being designed and developed in the
recent past only, the methods established for the above inspection are not reported
readily. The patent search has been carried out on this subject, but the information
related to this invention is not directly available. The following patents
(US20050186045A1, EP1790826A1, US006558115B1, US2006008347A1 etc..) related to
the present invention were checked and found there is no mention of this kind of
fixture. Normally the Steam or Gas Blades are designed with prismatic blade roots, such
as T-root, Fir-Tree root, Fork Root etc., but in case of Banana type hollow guide blades
there is no prismatic root available to hold the blade. Hence the methods available are
not suitable to assemble the blades and to check the throat gaps of the blades of the
banana type hollow guide blades.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a 3-blade segment fixture for end
profiles and throat gap checking of banana type hollow guide blade of low pressure
steam turbine which is capable of checking the both ends aerofoil sections of the blades
for meeting the assembly requirement along with throat gap between two consecutive
blades within the specified tolerances, at the time of manufacturing the blades.
Another object of the invention is to propose a 3-blade segment fixture for end profiles
and throat gap checking of banana type hollow guide blade of low pressure steam
turbine which is able to accommodate three blades at a time to facilitate checking of
throat gaps and the outer end profiles of the blades, all in a single setting.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig.1 - shows the fixture for checking the aerofoil end profiles of the blades according
to the invention.
Fig.2 - shows the fixture for checking the throat gap between the blades.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
For manufacturing technology of the Banana type hollow guide blades of Steam Turbine
Low Pressure (LP) modules, the end aerofoil sections of the blades are to be maintained
within the specified tolerances and also the throat gaps between two blades, as it is
done at the time of assembly of the blades in the inner and outer casings of the Guide
Blade carrier, as part of assembly fit-up requirements, for which the assembly and
checking methods are very much essential at the time of manufacturing the blades. The
invention is giving a way to design and develop the 3-Blade segment Fixture suitable for
the measurement of the end aerofoil sections of the banana type hollow guide blades
along with the throat gaps between blades.
Banana type hollow guide blade is a stationery blade of Low Pressure (LP) module of
the Steam Turbines of power generating equipment. This guide blade has typically
designed geometrical aerofoil profiles with bent stacking axis. Moreover these blades do
not have any prismatic root such as T-Root, Fir Tree, Fork Type etc. which will be
normally found in all the other types ST/GT blades. During the assembly, these blades
are to be positioned between the inner and outer casings of the guide blade carrier and
checked for the throat gaps in adjacent blades for further welding to be carried out.
While manufacturing of these blades, checking of outer profiles and the throat gaps is
essential to satisfy the assembly conditions. This needs a special fixture to facilitate the
above requirements.
The 3-Blade Segment Fixture (A) and the operation of the fixture against the assembly
requirements, which is main claim of this invention, is described with the help of line
diagrams (Fig.1 and Fig.2). The banana type hollow guide blade (1), which is to be
checked, has got suction (2) and pressure (3) aerofoil surfaces and also the outer (7)
and inner end profiles (8). At the time of assembly, the outer and inner profiles are to
be matched butted against the Outer (5) and Inner (6) casings of the guide blade
carrier of Low Pressure Module of the Steam Turbine. During the assembly of these
blades in the guide blade carrier, in a circular form, the pitch between two side by side
is very much important. To ensure the pitch, the throat gap values are to be checked at
two locations of the blade length with the help of two throat gap checking gauges (10
and 11).
Since it is cumbersome and time consuming to check the above assembly fit up
requirements at the time of manufacturing these turbine blades, the 3-blade segment
fixture is designed. This fixture can accommodate three blades at a time to facilitate
checking of throat gaps and the outer end profiles matching to the casings of guide
blade carrier, all in one setting.
The fixture is designed with a base plate (4) to fix the Outer (5) and Inner (6) casing
segments in specified positions as per the assembly. These segments are fixed with the
help of locating pins (9) and fasteners. The butting surfaces of the above segments (5,
6) are part of the conical surfaces of the inner and outer casings of the guide blade
carrier assembly. To hold the banana type hollow guide blades (1) in position by
matching the Outer end profile (7) and inner end profile (8) of the blade with the casing
segments (5 and 6), the locating pins (9) are used at four butting points of the blade.
These pins (9) will ensure the blade to be held properly. Once three blades are
mounted in the fixture, the throat gaps between two consecutive blades can be
checked with the help of Outer and Inner throat checking gauges (10 and 11). These
gauges are taper in nature to match the gap between blades and also to measure the
actual gaps.
Based on the above functional requirements a 3-blade segment fixture (A) has been
designed and manufactured to inspect the blade end profiles butting on to the inner (6)
and outer (5) casings and also the throat gaps at two places-similar to the checking
procedure being followed at the time of actual assembly. The blades are held in the
fixture with the help of locating pins fixed on inner and outer casing inserts. This will
simulate and also ensure the assembly conditions and the same inspection can be
carried out in advance, before sending the blades for assembly.
WE CLAIM
1. A 3-blade segment fixture (A) for end profiles and throat gap checking of banana
type hollow guide blade of low pressure steam turbine comprising:
a base plate (4) for fixing the outer (5) and inner (6) casing segments at the
required position according to the assembly;
two segments (5 and 6) fixed with locating pins (9) and fasteners;
locating pins (9) disposed at four butting points of the blade for holding the
banana type hollow guide blades (1) in position;
characterised in that,
the fixture accommodates three blades at a time (A) for checking the blade outer
(7) and inner (8) end profiles butting on to the inner and outer casing (5,6) and
also the throat gaps at two places between two consecutive blades, all in one
setting.
2. A 3-blade segment fixture, as claimed in claim 1, wherein the locating pins are
fixed on inner and outer casing inserts.
3. A 3-blade segment fixture, as claimed in claim 1 and 2, wherein the butting
surfaces of the segments (5,6) are part of the conical surfaces of the inner and
outer casings of the guide blade carrier assembly.

This invention relates to a 3-blade segment fixture for end profiles and throat gap
checking of banana type hollow guide blade of steam turbine low pressure module. The
fixture consists of a base plate (4) for fixing the outer (5) and inner (6) casing
segments at the required position according to the assembly. Two segments (5 and 6)
are fixed with locating pins (9) and fasteners. The locating pins (9) are disposed at four
butting points of the blade for holding the banana type hollow guide blades (1) in
position. The fixture accommodates three blades at a time and checks the blade outer
(7) and inner (8) end profiles butting on to the inner and outer casing and also the
throat gaps at two places between two consecutive blades, all in one setting.