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FIELD OF INVENTION
The invention relates to fabrication of connecting plate assembly for rotary
regenerative air preheaters in general and to a fixture for fabricating the connecting plate
assembly in a shop floor in particular.
BACKGROUND AND PRIOR ART
A rotary regenerative air preheater (APH) is a boiler auxiliary used in power
plants.
The Regenerative Air Preheater absorbs waste heat from flue gas, and then transfers
this heat to incoming cold air by means of continuously rotating heat transfer elements of
specially formed metal plates through air and gas streams.
Air preheater mainly consists of rotor assembly connected to central rotor post with
support & guide bearings, octagonal shaped rotor housing connected to connecting plate
assemblies at both the ends, sealing and drive arrangement.
The housing surrounding the rotor is provided with duct connections at both the ends
and is adequately sealed by radial and axial sealing members forming an air passage
through one half of the preheater and the gas passage through the other. As the rotor
slowly revolves the mass of the elements alternatively pass through the air and gas
passages, heat is absorbed by the element surfaces passing through the hot gas stream,
then as the same surfaces are carried through the air steam, they release the stored up
heat thus increasing the temperature of the incoming combustion or process air.
Connecting plate assemblies (CPA) are used to house both ends of on APH. Fixtures are
needed for the manufacture of the CPA on the shop floor. The size of an APH depends on

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the rating of the boiler of which the APH would form an auxiliary. Therefore there are many
sizes of APH which are made. Consequently, the CPA sizes are also several. So, depending
upon the requirement, different sizes of CPA must be fabricated.
In the prior art, fixture for manufacture of the CPA are known. Every CPA must
be fabricated with the help of a fixture which is dimensioned and manufactured to suit the
fabricational requirement of the particular size of the CPA. Therefore, in the prior art, based
on production requirement, a variety of sizes of fixtures are made throughout the
year.Welded construction fixtures made out of rolled beams for manufacture of connecting
plate assembly are used presently. These welded fixtures are laid on concrete floors in shop
in octagonal shape to accommodate the bottom flanges of connecting plate assembly.
A rotary regenerative air preheater has an octagonal flange hole at one end and
rechangular flanges at the other end.
In the prior art, the layout of the bottom flange of the required size of APH is
marked on the ground to get the location and size of fixture beams. Rolled beams are then
cut to suit the layout at the comers and are tack-welded to form the octagonal shape and
levelled before welding. This octagonal arrangement is centrally connected by the rolled
angles as spiders, which are welded to the beams and center block at each end. After
welding, the entire arrangement is levelled before using it for assembly.
The rough concrete shop floor invariably has level difference, due to which the
entire fixture is levelled with wedges and packed with metal strips. After levelling the
fixture, it is lifted from the floor and made to rest primarily on the packing strips only. Since
the fixture is not resting on the floor, the instability of the fixture and distortion due to
assembly welding is inevitable. After dismantling of each connecting plate assembly, the

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fixture has to be verified for the level and if needed, the entire process of levelling is to be
repeated. This process is painstaking and consumes a lot at time.
As mentioned earlier, the size of the fixture needs to be frequently modified,
depending on the size of the APH. Very often totally new fixtures are called for. If the
available fixture can accommodate the required size of APH, some modifications in the same
existing fixture is done otherwise a new fixture is fabricated. This modification is done by
adding short length beams (500mm) of same size radialy to the existing beams inside or
outside depending on APH size. But in the prior art, in the case of making a new fixture for
new size of APH it needs cutting and removing the entire existing fixture beams, spiders &
extended beams.
The present invention seeks to overcome some of the major shortcomings of the
prior art described above.
Objects of the invention:
One object of the invention is to eliminate welding of various beams, center
block etc. needed in prior art.
Another object of the invention is to eliminate levelling of the fixture which is a
very time-taking process.
Yet another object of the invention is to provide fixtures which are re-usable with
only minor touch-up operations.
A further object of the invention is to eliminate the hazards due to unstable
fixtures.
Yet another objective of the invention is to make the factory floor space available for
manufacture of the next size air preheater at once.

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A still further objective is to reduce the time of manufacture and
requirement of manpower for the manufacture of connecting plate assembly.
Description of the invention:
The invention will be described in details with the help of the following
accompanying drawings.
Fig. 1 shows the line diagram of the fixture in accordance with the invention
Fig. 2 shows the perspective view of fitter's bar.
Fig. 3 shows cross- sectional details of fitter's bar
Fig. 4 shows the sectional view through section AA of Fig. 1
Fig. 5 shows the sectional view through section BB of Fig. 1
The fixture for manufacture of connecting plate assembly (CAP) is made with
fixture beams (01), stiffeners (02), fitter's bar (03), clamps (04), T-bolts (05) and nuts (06).
The fixture for the manufacture of any particular CPA has to be tailored to suit the
dimensions of the CPA. The CPA in turn has to match the air preheater (APH). As disclosed
earlier the APH can be of various sizes, which means that the corresponding CPAS will have
various different sizes. For optimum saving, the sizes of the APH s and therefore the CPAS
are grouped in a few ranges. A fixture therefore is made for a range of CPAS.
Initially, the layout of bottom flanges of a range of APH is marked. From these
markings, the positions for the fitter's bars (03) are determined on these layouts, as shown
in Fig. 1. Positioning of the fitter's bars has to be made in such way that each fixture beam
(01) should rest at least on three fitter's bars (03), so that it shall be held firmly. Next,
stiffener plates (02) are located based on the length of the beam. These fitter's bars (03)
are to be grouted on the concrete shop floor after levelling the entire arrangement within a

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tolerance range of ±1 mm. A set of fixture beams for a particular range of APH is connected
so that the entire range of APH with minimum number of fixture is achieved.
The fixture beams (01) lengths are calculated to accommodate a range of APH size
so that at least 80% of the flange area rests on these beams. By such grouping we can
arrive at a minimum number of fixtures for the entire range of APH size. Each set of beams
for a range of APH size is to be differently colour- coded to have better traceablity, and
since we have minimum number of sets, we need minimum space for storage.
To form the fixture in accordance with the invention, the fixture beams (01) with adequate
stiffeners (02) at both sides of the web are placed on the grouted and levelled fitter's bars
(03) and firmly secured by clamp (04 ) with T- bolt (05) & nut (06) on the layout of required
APH size. The details are depicted in Figs 1-5.
To change the fixture for next range of APH, one has only to remove the clamps and
repeat the exercise as above.
In the prior art, changing the fixture involved a labour-intensive and time-consuming
procedure of cutting numerous weld joints, machining, removing of tack-welds etc. In
comparison the fixture in accordance with the present invention earn easily be dismantled
through loosening of nuts, bolts and clamps. This feature of the invention results in saving
of considerable manpower and time, which directly leads to cost saving.
The fixture in accordance with the invention has the following main advantages over the
prior art.
Fabrication time for a new fixture is reduced very appreciably. While the fabrication time as
per present practice is typically about 24 man-days, it is reduced to about 2 man-days in the
ease of a new fixture according to the invention.

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As the fixture is laid on fitter's bars which have been levelled, the levelling operation, which
is very elaborate and painstaking, is not required to be performed at all for every new
fixture fabrication.
The fixture according to the invention eliminates all welding activity,
resulting in time and material saving.
Modification of the Fixture to suit the next size of APH is very fast and easy.
Storage of Fixture beams takes up less storage space.
The shop-floor area can be quickly made available for some other job once a
fabrication job is over.
The fixture is re-usable, unlike in prior art.

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WE CLAIM:
1. Fixture (A) for manufacturing connecting plate assembly of air preheaters comprising a
plurality fitter's bars (03) which are grouted on the concrete shop floor and levelled, a
plurality of fixture beams (01) with adequate stiffners (02) being positioned on said fitter's
bars and firmly secured to the fitter's bars by clamps (04), T- bolts (05) and nuts (06),
characterized in that the fixture (A) is fabricated without any welding to facilitate its easy
dismantling or modification.
2. The fixture as claimed in claim 1, wherein the length of the fixture beams (01) are so
calculated that a range of air precheater (APH) sizes are accommodated and it is ensured
that at least 80% of the flange area nests on these beams.
3. The fixture as claimed in 1, wherein the fitter's bars (03) are levelled within a
tolerance range of ±lmm before they are grouted on the concrete shop floor.
4. The fixture as claimed in claim 1, wherein fitter's bower (03) are levelled within a
tolerance range of ±lmm before grouting on the concrete shop floor.

Fixture (A) for manufacturing connecting plate assembly of air preheaters comprising a
plurality fitter's bars (03) which are grouted on the concrete shop floor and levelled, a
plurality of fixture beams (01) with adequate stiffners (02) being positioned on said fitter's
bars and firmly secured to the fitter's bars by clamps (04), T- bolts (05) and nuts (06),
characterized in that the fixture (A) is fabricated without any welding to facilitate its easy
dismantling or modification.