Note: Descriptions are shown in the official language in which they were submitted.
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REPEATING TEMPERATURE SENSING
IMMERSION PROBE
Background Of The Invention
This invention relates generally to temperature
sensing devices which are suitable for repeated immersions
into molten metal. In particular this inventions relates
to improvements to a molten metal temperature sensing
device which includes a high temperature protection tube
of a fiberous refractory material.
As shown by Kraus, U.S. Patent Number 3,816,183, and
Falk, U.S. Patent Number 4,521,639, it is known to surround
a ~emperature sensing device with a cylindrical sleeve of
refractory ~aterial for aohieving repeated immersions into
a molten metal bath. The oorresponalng U.g. Patent Number
4,645,865 referred to above shows a refractory ~leeve havlng a
generally cylindrlcal bore lnitlatlng at one end and
termlnatlng at an inwardly projectlng shoulder and a tapered
or trunoated cone shaped cyllndrical bore whlch extends from
the choulder through the opposlte end of the sleave.
The construction of the repeating device includes a
support tube surrounding a thermocouple unit which is in-
serted into the cylindrical bore of the refractory sleeve.
A projecting portion of the thermocouple unit extends
through the cone shaped bore and away from the end of the
sleeve by a predetermined distance. The refractory sleeve
is secured to the support tube by filling the end of the
sleeve with a refractory cement.
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The invention described herein is an improvement
over the structures shown and described in the previous
mentloned patents and U.S. Patent 4,645,865 so as to further
.
increase the number of immersions that the sensing device
may be utilized prior to failure.
Summarv Of The Invention
In accordance with the present invention, a pre-formed
refractory sleeve, preferably having a generally cylindrical
bore therethrough, is provided for receiving a support tube
having a thermocouple unit inserted therein. This structure
is further provided, first, with a reflective metal foil
which is wrapped around the exterior of the support tube
prior to insertion into the pre-formed refractory sleeve.
Second, the quartz tube of the thermocouple unit within
the device, which surrounds the hot junction of the ther-
mocouple wire, is provided with an alumina coating. These
individual features on a repeating type sensing device or
each feature, in conjunction with the other improvement,
permit the device to be immersed into a molten metal bath
for temperature measurements for an increased number of
readings prior to failure, as compared to known structures.
The reflective foil wrap around the, typically,
paperboard tube reflects radiant heat prior to and during
immersion into the bath. Additionally, the foil wrap pro-
tects the paperboard tube such that the temperature seen
by the tube is substantially uniform across the length of
the tube which is inserted within the refractory sleeve.
The foil wrap also seals the outer surface of the paper-
board tube so as to limit the amount of oxygen that is in
contact with the paperboard tube during immersion. Since
the presence of oxygen is removed combustion of the tube
at elevated temperatures in basically eliminated.
The alumina coating on the quartz sleeve of the
thermocouple unit is provided to eliminate degradation of
the ~uartz material after repeated immersions into the
molten metal environment. A common mode of failure in the
typical repeating type immersion sensing devices is the
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failure of the quartz material of the thermocouple tube.
It was previously known to coat a thermocouple tube with
an alumina coating in a non-repeating device for use in
conjunction with a oxygen sensing electrochemical cell
which was also mounted on the immersion end of the probe.
An examPle of this type immersion probe is described in
Cure, U.S. patent Number 4,342,633. The
coating found on the oxygen and temperature measuring type
device is generally heavier than that contemplated by the
present invention. The purpose of the alumina coating on
this oxygen and temperature type probe is to prevent dis-
sociation of the oxygen in the area of the oxyen sensing
electrochemical cell from the quartz material such that
the cell provides a more accurate reading of the oxygen
content of the molten metal bath. An oxygen an~ temDerature
sensing probe is not utilized repeatedly as in the p.esent
invention. Additionally, the relatively heavier coating
of alumina on the quartz material of the oxygen and tempera-
ture type probe slows the time required to make an accurate
temperature reading by the thermocouple and, therefore,
is undesirable for purposes of a repeating ty~e temperature
probe. A repetitive type probe must provide a temperatu.e
reading as quickly as possible in order to prevent exces-
sive degradation of its entire structure during a lengthy
immersion. The faster the response time of the thermo-
couple unit the more likely that the number of immersions
of the probe will increase prior to failure.
Further advantages of the invention will become
apparent to those skilled in the art by particularly
pointing out and describing a preferred embodiment of the
invention.
For the purpose of illustrating the invention, there
is shown in the drawings a form which is presently pre-
ferred; it being understood, however, that this invention
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is not limited to the precise arrangements and instrumen-
talities shown.
Brief Descrintion of The Drawings
Figure 1 shows a cross sectional view of a reneating
high temperature immersion probe of the invention.
Figure 2 shows a cross sectional view of the immer-
sion probe in Figure 1 taken along line 2-2.
Detailed Description Of The Invention
Referring to the drawings wherein like numerals indi-
cate like elements, there is shown in Figure 1 a cross
section of a temperature sensing device 10 which is adapted
to be mounted on the immersion end of the lance ~not shown).
The structure of the device 10 is designed for repeated im-
mersion into a bath of molten metal such as steel or iron.
The device 10 includes a support tube 12 which is
typically made of a paperboard or like material. The SUD-
port tube 12 is inserted into and surrounded by a high
temperature protection sleeve 14. Positioned within the
interior of the support tube 12 is a temperature sensing
unit 16 having a body portion 18 and a thermocouple exten-
sion portion 20. The bodv portion 18 is positioned within
the interior of the support tube 12 while the thermocouple
extension portion 20 projects through and out of the end of
the protection sleeve 14.
The protection sleeve 14 shown in the drawings is
simllar to that described in applicantl 6 U. S. Patent
4,645,865. The sleeve 14 i preferably vacuum
casted from a fine refractory fiberous type material such
as a ceramic type fiber as disclosed in U.S. Patent number
3,816,183. However, the sleeve 14 may take any specific
form and is not limited to that shown by the drawing or by
the patents discussed herein. The outer surface 22 of the
protection sleeve -14 is preferably smooth. The interior
of the protection sleeve 14 is provided with a generally
cylindrical shaped bore 24 which extends from one end of
the sleeve and terminates in a radial, inwardly projecting
shoulder 26 which is formed adjacent to the immersion end
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28 of the protection sleeve 14. ~etween the shouid~r '~
and the immersion end 28 of the sleeve 14 is provi~ed an
inwardlv tapering cylindrical surface 30 which ta~ers
toward the immersion end ~8 of the sleeve 14. This surface
30 forms a generally truncated cone shaped bore. A second
shoulder 32 may be provided on the sleeve 14 which is open
to the immersion end 28. The second shoulder 32 is in
communication with the narrow end of the cone shaped bore 30.
The assembly of the device 10 is such that the body
18 of the temperature sensing unit 16 is inserted into
the support tube 12 with the thermocouple extension portion
20 of the unit projecting away from the end of the tube
12. The support tube 12 and sensing unit 16 are inserted
into the cvlindrical bore 24 of the protection sleeve 14
such that the protection sleeve 14 and sensin~ unit 16
abut the inwardly projectiong shoulder 26. This arran~e-
ment prepositions the projecting end of the sensing unit
extension 20 beyond the immersion end 28 of the protection
sleeve 14 by a predetermined amount. The cone shaped bore
30 and the second shoulder ~ortion 32 of the protection
sleeve 14 are filled with a refractory cement 34. The
combination of the shoulder 26 and the cement fill 34 in
the tapered bore 30 provides a positive locking of the
temperature sensing unit 16 and the support tube 12 within
the protection sleeve 14. Additionally, this arrangement
provides an increased insulation of the temDerature sensing
unit 16 and permits the use of less refractory cement 34.
The refractory sleeve 14 is typically a better insulator
than the refractory cement 34, therefore the thermocouple
unit 16 may be embedded in the sleeve at a relatively
shallower depth. Additional advantaqes of this type struc-
ture are discussed in U.8. Patent 4,645,865.
In accordance with the present invention the support
tube 12 is provided with a reflective foil wrap 36. The
reflective wrap 36 is provided in substantially direct
contact with the exterior surface of the support tube 12.
Additionally, the wrap 36 is folded over the end of the
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support tube i2 and is ?ositioned around the leas ~2 of the
thermocouple extension 20 and over the top of the tempera-
ture sensing unit 16. The wrap 36 may be applied in any
convenient manner and is preferably of an aluminum material
approximately .004 inches thick, although other thicknesses
may be utilized depending on design conditions. The out-
side surface of the wrap 35 is reflective of heat radiated
from the protection sleeve 14 prior to and during immersion.
The foil wrap 36 also acts as a heat sink for the heat
transfered by conductin~ or convection from the sleeve 14
during immersion. The wrap 36, because of its relatively
high conductivity, will also disperse absorbed heat from
within the interior of the protection sleeve 14 substantially
over its entire surface.
A common problem in the repeating temperature sensing
devices 10 is the combustion of the paperboard material of
the support tube 12 after a number of immersions. ~fter
repeated immersion of the device, the paperboard material
of the tube 12 reaches its combustion point and combines
with the oxygen within the interior of the cylindrical
bore 24 to cause the paper to smolder or char. By provid-
ing a reflective foil wrap 36 of a non-combustible material
in surrounding contact with the paperboard material the
oxygen present within the cylindrical bore 24 is not directly
exposed to the paperboard tube. Therefore, the wrap 36
prevents combustion of the tube 12 even at elevated temper-
ature above its flash or burning point.
The body portion 18 of the temperature sensing unit
16 generally includes contacts 38 which extend from the
end opposite from that of the thermocouple extension 20.
The contacts 38 are adapted to mate with corresponding
contacts on a lance tnot shown) which is inserted through
the support tube 12. The body portion 18 contains cold
compensation joints between the thermocouple wire and the
contacts 38 (structure not shown). In Figure 2, a cross
section of the body portion 18 is shown including a refrac-
tory cement fill 40. This refractory cement 40 acts to
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support ~he ~lermocoup ~ e.Ytension portion 2n on he
body portion 13 anc protect tne thermocouple lires and
the cold joints ~ithin ~he body 18. Th2 refractorv cement
fill 40 is, oreferably, of the same material as refractory
cement 34.
The thermocouole extension portion 20 of the sensing
unit 16 typically comprises a U-shaped quartz type tube ~2
which contains the hot junction of the thermocouple wire
at the projecting end of the U-shape. A primary reason
for failure of known variations of a repeating i~mersion
device is due to the failure of the quartz material of
this U-shaped tube 42. As part of the invention, the
quartz tube 42 was modified by coating 44 the quartz
~aterial with an alumina (AL2~3) material which is then
force-dried. The alumina coating 44 of the quartz tube '2
acts to strengthen t~e quartz material and prevent degreda-
tion during repeated i~mersions. Typically, the environ-
ment of the molten metal bath causes the quartz material
to become soft and eventually fail. It has been discovered
that by coating 44 the quartz material with the alumina in
diluted strength (260 grams AL2O3 with 340cc of a polyvinyl
alcohol solution) that the failure of the quartz ~-shaped
tube is eliminated as a mode of failure of the device 10.
As stated previously, it was known to use an alumina
coating on a quartz thermocouple tube on an oxygen and
temperature type measuring device having an electro-
chemical cell for measuring the oxygen content in the
bath. The application of the alumina coating in this type
temperature and oxygen device is to prevent dissociation
of the oxygen from the quartz which may effect the measure-
ments of the oxygen sensing cell. In the present applica-
tion, the alumina coating is provided in diluted strength
as compared to previous uses 1000 grams AL2O3 with 400cc
polyvinyl alcohol) so that the alumina does not effect the
response time of the thermocouple. By providing this
coating on a repeating immersion temperature sensing device
1~, the molten metal bath will not cause degredation of
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the quartz material after repeated immersions. The tempera-
ture and oxygen sensing type probes are not utilized for
repeated immersions.
The structure of the immersion device 10 as shown in
the drawings and as described herein substantially increases
the useful life of the temperature sensina devi~ described
ln U.S. Patent 4,645,865. Each of the lmprove-
ments as described herein substantially increase this
useful life. However, each improvement may be utilized
individually as desired.
Optional structure which may be added to the device
10 includes a cap located at the immersion end 28 of the
sleeve to protect the thermocouple extension portion 20
during initial immersion of the device 10 through the slag
on the top of the molten metal bath. Additionally, ribs
48 may be provided within the sleeve 14 which project
inwardly from the cylind.ical bore 24 so as to maintain
the support tube 12 and temperature sensing unit 16 within
the protection sleeve 14 in a fixed relationship. The
cylindrical bore end of the sleeve 14 ~ay be sealed by a
refactory material (not shown). However, the device 10
contemplated by this invention is generaly not immersed
into the bath beyond the level of the non-immersion end.
The invention as described herein substantially
increases the useful life of a temperature sensing device
such that the number of immersions, providing accurate
temperature readings, may be increased. Testing has shown
that the invention as described increases the number of
immersions by two-fold.
The present invention may be embodied in other
specific forms without departing from the spirit o essen-
tial attributes thereof and, accordingly, refe.ence should
be made to the appended claims, rather than to the foregoing
specification, as indicating the scope of the invention.
