Note: Descriptions are shown in the official language in which they were submitted.
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EXPLOSIVELY WELDED RADIANT HEAT SHIELD
FOR A SUPERCONDUCTING GENERATOR ROTOR
BACKGROUND AND SUMMARY OF THE INVENTION
The present invention relates generally to a
superconducting generator rotor and more particularly to
the radiant heat shield thereof.
Typically, a superconducting generator has a
supercooled rotor which includes a superconducting field
winding and a structure for supporting the winding. The
rotor is supercooled to a cryogenic temperature by a fluid
refrigerant, such as helium, which is contained within the
rotor. During normal operation of the generator, the
liquid helium within the rotor is transformed into a vapor
or gas through a relatively slow but continuous boil off.
The function of the radiant heat shield is to
intercept heat radiated from the rotor's ambient surround-
ings, which are typically at room temperature, so as toprevent the radiated heat from warming the cryogenic cold
zone within the rotor. A radiant heat shield typically
consists of a tubular, or cylindrical, structure disposed
radially outward from the superconducting rotor coils.
This tubular structure is provided with a p~urality of
coolant channels therein along with a means for the re-
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frigerant to pass radially into the radiant heat shield,
pass axially through it and exit, via another radial
passageway, toward the internal portion of the super-
conducting rotor. U. S. Patent No. ~,250,~18 issued to
Eckels on February 10, 1981 and U. S. Patent 4,319,149
issued March 9, 1982 to Eckels ~md assigned to the
present assignee disclose, inter alia, particular designs
of radiant heat shields. One object of the present
invention is to provide a radiant heat shield for a
superconducting generator which is designed to be manu-
factured in a reliable and yet economical manner.
In a typical superconducting generator, the size
of the radiant heat shield could exceed 130 inches in
length and 30 inches in diameter and, since the radiant
heat shield must be cooled with a plurality of coolant
passages located within its cylindrical walls, these
design parameters essentially require that it be made of a
two-shell construction. The bonding of these two coaxial
shells must provide an effectively sealed coolant channel
network and must not distort the radiant heat shield nor
weaken its structural integrity.
A radiant heat shield made in accordance with
the present invention comprises an inner cylindrical tube
and an outer cylindrical tube associated in coaxial and
concentric relation. The inner tube has two circumferen-
tial grooves formed in its outer cylindrical surface.
These two circumferential grooves are formed in the inner
tube a predetermined axial distance apart from one anoth-
er. A plurality of axially extending grooves are formed
in the outer cylindrical surface of the inner tube, with
each axial groove intersecting and connec-ting the two
above-described circumferential grooves. Each circumfer-
ential groove is also provided with at least one radial
hole which intersects it and provides fluid communication
between it and the internal portion of the inner tube. An
outer cylinder is disposed radially outward from the inner
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tube and metallurgically bonded to the inner tube to form
a unitary radiant heat shleld structure. The outer tube
encloses the radially outward portion of each of the above
mentioned grooves and thus provides an enclosed coolant
channel network which, in turn, provides fluid communica-
tion between the radial hole which intersects one of the
circumferential grooves and the radial hole which inter-
sects the other circumferential groove.
In accordance with the present invention, the
inner and outer tubes are explosively welded together. In
order to prevent the potential collapsing of the outer
tube into the grooves of the inner tube during the ex-
plosive welding operation, the grooves may be filled with
a removable substance prior to the expl~sive welding
process to provide local support for the outer tube during
the explosive welding process. Depending on the relative
thicknesses of the inner and outer tubes, the use of this
substance may not be required. However, in order to
assure that no collapse occurs in the region of the above
mentioned grooves, a radiant heat shield made in accord-
ance with the present invention incorporates within its
scope a solid which can be disposed in the grooves and
which is removable after completion of the explosive
welding. This substance may be either meltable, such as a
low melting metal or sulfur, or combustible, such as
polystyrene. Experimental work has been done using a low
melting alloy, Cerrotru, which can be melted and removed
from the coolant channels following the explosive welding
procedure. Also, carbon steel inserts have been used to
provide local support in the region of the coolant chan-
nels and were later removed by etching with acid. Of
course, it should be apparent that this acid etching
technique is practical only when the radiant heat shield's
structural tubes are acid resistant, such as in the case
when Inconel 706 or Inconel 718 is used for their manu-
facture. After providing the localized support described
above, tne meltable, etchable or combustible substance is
removed through the above-described radial holes.
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The present invention provides a radiant heat
shield which has good contact between the adjacent sur-
faces of the inner and outer tubes to provide excellent
thermal conductivity ~herebetween and prevents leakage of
coolant either between adjacent axial grooves or between
the coolant channel network and its surrounding environ-
ment which is generally a vacuum.
Prior to assembly, the inner and outer tubes can
be initially oversized so that they may be machined exact-
ly to size following the explosive welding procedure.Also, the radial holes may be remachined following the
explosive welding process in order to correct for any
minor distortions incurred during the metallurgical bond-
ing process
It should be apparent that the present invention
provides a radiant heat shield, for use with superconduct-
ing rotors, that is manufacturable in a manner which
results in a structure of high mechanical integrity and
which also provides a reliable fluid containment for the
superconducting rotor's refrigerant.
BRIEF DESCRITION OF THE DRAWING
Figure 1 shows an exemplary sectioned view of a
radiant heat shield made in accordance with the present
invention; and
Figure 2 illustrates a cross section view of the
radiant heat shield shown in Figure 1.
DES~RIPTION OF THE PREFERRED EM~ODIMENT
The present invention relates generally to
superconducting rotors and, more specifically, to the
manufacture of the radiant heat shield utili7ed therein.
Figure 1 shows an exemplary illustration of a
radiant heat shield made in accordance with the present
invention. It comprises an inner tube 10 and an outer
tube 12 disposed in coaxial and concentric relation. The
inner cylindrical tube lO has a first 14 and a second 16
circumferential groove formed in its outer cylindrical
surface. A plurali~y of axial grooves 18 intersect these
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circumferential grooves and provide fluid communication
therebetween. Circumferential groove 14 has a radial hole
intersecting it and pro~riding fluid communication
between it and the internal portion of the inner tube 10.
The second circumferential groove 16 has a radlal hole 22
intersecting it and providing fluid communication between
it and the internal portion of the inner tube 10. The
combination of the first 14 and second 16 circumferential
grooves along with the plurality of axial grooves 18 and
radial holes, 20 and 22, provide fluid communication
between the internal portion of the inner tube 10 pro~i-
mate the radial tube 20 and the internal portion of the
radial tube 10 proximate the radial hole 22. Both the
inner 10 and outer 12 tubes are made of a high s~rength
material, such as one of those referred to as superalloys,
which has a yield strength sufficient for use in super-
conducting~ These materials include, but are not limited
to, Inconel 706 and Inconel 718. The material used should
have a yield strength equal to or greater than 130,000 psi
and retain its high strength at cryogenic temperatures of
approximately 4K.
The outer tube 12 is explosively welded to the
inner tube lO to form a radially outward seal for the
above mentioned circumferential, 14 and 16, and axial 18
grooves. This construction provides a coolant channel
network which carries liquid or gaseous refrigerant be-
tween components which are disposed inside the inner tube
lO proximate the radial hole 20 and other components
disposed within the inner tube 10 and located proximate
the radial hole 22.
Prior to the outer tube 12 being explosively
welded to the inner tube lO, the circumferential grooves,
14 and 16, and the axial grooves 18 can be filled with a
substance in order to prevent the outer tube 12 from
locally collapsing into the grooves in the outer surface
of the inner tube 10. This substance, of course, must be
removable following the explosive welding process. A
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radiant heat shield made in accordance with the present
invention can utilize either a meltable substance such as
a low melting metal or sulfur, or a combustible substance,
such as polystyrene. It has been found that a 15w melting
alloy, such as Cerrotru, is suitable. Also, carbon steel
has been experimentally used to provide this local support
and later be etched away by acid. Acid etching is practi-
cal when the inner lO and outer 12 cylinders are made of a
material which is acid resistant, such as Inconel 706 or
Inconel 718. These specific removable substances, or
other suitable substances, provide local support for the
outer cylinder 12 in the region of the grooves in the
outer cylindrical surface of the inner tube 10 during the
explosive welding operation and are later removed through
lS the radial holes, 20 or 22, following that procedure.
Explosively welding the inner 10 and outer 12
tubes together provides a reliable fluid seal in the
axially outboard regions, 30 and 32, which are between the
circumferential grooves, 14 and 16, and the surrounding
environment and also provides a reliable fluid seal in the
regions 40 between adjacent axial channels 18.
Figure 2 is a section view of Figure l showing
the inner 10 and outer 12 tubes. Also, the relative
radial positions of the axial grooves 18 and the circum-
ferential groove 14 is shown. The radial hole 20 is shownintersecting the circumferential groove 14 and providing
fluid communication between it and the internal portion of
the inner tube lO. Figure 2, viewed in conjunction with
Figure 1, illustrates how a coolant could travel radially
outward through radial hole 20, circumferentially around
the inner tube in circumferential groove 14, axially
between the inner 10 and outer 12 tubes in channels 18,
circumferentially around circumferential channel 16 and
radially inward through radial hole 22, to provide a
network for the coolant to travel through, and reduce the
temperature of, the radiant heat shield.
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Referring again to F:igure 1, it should be under-
stood that a seal weld could also be provided at the
interface of the inner 10 and outer 12 tubes at their
axial ends 50 in order to provide an added measure of
S fluid sealing reliability between the coolant channel
network and the environment surrounding the radiant heat
shield which is typically a vacuum. However, it should be
understood that, in most applications, the explosive
welding of the inner tube 10 to the outer tube 12 provides
a sufficient fluid seal in the regions, 30 and 32, between
the circumferential grooves and the environment surround-
ing the radiant heat shield, and that the above-mentioned
seal weld wou.ld therefore generally not be rec;uired.
It should be apparent that t~e present invention
provides a radiant heat shield for use in a superconduct-
ing rotor which is mechanically strong and which provides
a coolant network therein. It should further be apparent
that, although the present invention has been described
with considerable detail, it should not be considered tc
be so limited.
