Note: Descriptions are shown in the official language in which they were submitted.
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"Method, device and probe for measuring a gas
content of a bath of liquid metal".
The invention relates to a method for measuring
a gas content, in particular a hydrogen content, of
a bath of liquid metal with a low partial pressure
of oxygen, according to which method a probe with a
gas supply line and a gas removal line, the lowermost
ends of which are situated near each other, is immersed
in the bath, a carrier gas is supplied via a gas line
to the gas supply line, said carrier gas is collected
again after exchanging with the bath the gas whose
content is to be measured, and it is fed via the gas
removal line of the probe and a gas line connected
thereto through a gas detector in which the gas content
is measured. A metal which a low partial pressure of
oxygen is a metal with high H2/H20 ratio, such as,
for example, steel.
A method of this type is described in the Belgian
Patent No. 1,004,013 on November 22, 1988.
In said method, as indeed in other known methods
for determining the hydrogen content, fairly large
correction factors, which cannot always be clearly
justified theoretically, have to be made in the actual
measurement based on the hydrogen content which is
obtained by exchange in the carrier gas. Although these
correction factors produce a satisfactory result at
high hydrogen concentrations, this is no longer so
at low hydrogen concentrations.
The object of the invention is to remedy this
defect and to provide a method which makes a more accurate
measurement possible of the gas content, in particular
of the hydrogen content, without such correction factors
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having to be used, which method can also be used at
very low gas concentrations, in particular hydrogen
concentrations, in the metal.
For this purpose, the carrier gas is dried.
Surprisingly, it has been found that water or
moisture which is liberated when the probe is immersed
in the bath from materials from which the probe is
constructed can cause interferences in the measurement.
Liberated moisture can start to decompose at the high
temperatures in the bath so that consequently, when
the hydrogen content is measured, not only the hydrogen
from the bath, but also the hydrogen produced from
the moisture is measured.
The moisture liberated from the probe also proves
to have a disadvantageous effect on the precision of
the measurement in measuring other gas contents, such
as nitrogen content.
By removing the moisture from the gas which is
passed through the probe, a very correct measurement
is obtained.
In a particular embodiment of the invention, the
gas is passed during the measurement in a closed circuit
through the probe and the gas detector, the drying
being carried out during this circulation of the gas.
The drying may be carried out both in the probe
and upstream or downstream of the probe.
The drying can be carried out in the usual man-
ners, either by drying agents such as silica gel, or,if
the drying is carried out outside the probe, by cooling
and condensing the moisture.
The invention also relates to a device for measuring
a gas content of a bath of liquid metal with a low
partial pressure of oxygen, which device is particularly
suitable for carrying out the method according to one
of the preceding embodiments.
The invention thus relates to a device for measur-
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ing a gas content, in particular a hydrogen content,
of a bath of liquid metal with a low partial pressure
of oxygen, which device contains a probe which is designed
to be immersed in the liquid metal and which, in its
turn, has a gas supply line, which debouches with an
end on the end of the probe designed to be situated
at the bottom, a gas removal line for collecting the
gas which flows out of the gas supply line and has
picked up a gas, whose content is to be measured, from
the bath, the end of which removal line is situated
in the vicinity of the lowermost end of the gas supply
line, which device furthermore contains a gas circuit,
one end of which connects to the gas supply line of
the probe and the other end of which connects to the
gas removal line of the probe, a gas detector installed
in said circuit and means installed in or on said circuit
for passing carrier gas around the circuit through
the gas detector and the probe, characterized in that
it contains drying means which is installed in or on
the entity formed by the gas supply line of the probe,
the gas removal line of the probe, the gas circuit
and the gas detector.
In a particular embodiment of the invention, the
drying means are installed in one of the gas lines
in the probe.
Preferably, the device contains a lance and the
probe is a throw-away probe which is installed on the
lance by means of a quick-connection coupling, of which
quick connection coupling a section is installed on
the probe and a section on the lance, and which quick-
connection coupling connects the gas supply line and
the gas removal line of the probe in a gastight manner
to both ends of the gas circuit, the drying means are
installed in one of the gas lines in the probe, the
lowermost end of at least one of the gas lines in the
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probe is sealed in a moisture-tight manner by a seal
which is opened when the probe is immersed in the metal
bath and the uppermost end of said gas line in the
probe is likewise sealed in a moisture-tight manner
by a seal which is opened by coupling the sections
of the quick-connection coupling to each other.
The invention finally also relates to a throw-
away probe obviously designed to be used in the device
according to one of the preceding embodiments.
The invention therefore also relates to a throw-
away probe for measuring a gas content, in particular
a hydrogen content, of a bath of liquid metal with
a low partial pressure of oxygen, which probe has a
gas supply line, which debouches with one end on the
end designed to be situated at the bottom, and a removal
line for collecting a gas which flows out of the gas
supply line, the end of which is situated in the vicinity
of the lowermost end of the gas supply line, and which
is characterized in that it contains drying means in
at least one of the gas lines and said gas line is
sealed in a moisture-tight manner at both ends by breakable
seals.
Other features and advantages of the invention
will emerge from the description, which follows below,
of a method, device and probe for measuring a gas content
of a bath of liquid metal according to the invention;
this description is given solely as an example and
does not restrict the invention; the reference numerals
relate to the accompanying drawings.
Figure 1 represents a block diagram of a device
for measuring the hydrogen content of liquid steel
according to the invention.
Figure 2 is partly a section and partly a front
view of the lowermost section of the probe from the
device according to figure 1.
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Figure 3 is partly a section and partly a front
view of the uppermost section of the probe from figure
1, but drawn on a larger scale than figure 2.
In the three figures, the same reference numerals
relate to the same elements.
The device in figure 1 contains essentially a
probe 1 , a gas circuit 2, both ends of which connect
to the probe and in which a filter 4, a katharometer
5,a pump 6, a four-way stopcock 7 and a flow meter
8 are installed consecutively in the flow direction
of the gas which is indicated in figure 1 by the arrow
3.
The probe 1 is a throw-away probe, is connected
by means of a quick-connection coupling 9, 10 detachably
to a lance 11 through which ends of the gas circuit
2 extend, and is connected by means of the same quick-
connection coupling 9, 10 to said two ends of the circuit
2.
A bottle 12 containing pressurized nitrogen is
connected by means of a supply line 13 to the four-
way stopcock 7.
Said four-way stopcock 7 closes, in one position,
the gas circuit 2, the supply line 13 being connected
to the open atmosphere. The bottle 12 is, of course,
then closed. In another position, the four-way stopcock
interrupts the gas circuit 2 and it connects, on the
one hand, the supply line 13 to the section of the
gas circuit 2 which connects to the probe 1 via the
flow meter 8 and it connects, on the other hand, the
section of the gas circuit 2 which comes from the pump
6 to the open atmosphere.
The katharometer 5 is also of a construction known
per se and is not described in detail here. Said katha-
rometer determines the hydrogen content of the inert
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carrier gas by measuring the thermal conductivity of
the gas.
The probe 1 contains, as depicted in figures 2
and 3, at one end a gas collection section which is
formed by a bell 14 of porous refractory stone and
at the other end, one section 9 of the quick-connection
coupling 9, 10 mentioned above.
The opening of the bell 14 is directed away from
the section 9 and the bell is held at a distance from
said section 9 by a quartz tube 15, to the ends of
which the bell 14 and the section 9 are attached by
means of cement 16.
Extending axially through the quartz tube 15 is
a narrow quartz tube 17 which, on the one hand, projects
into the section 9 and, on the other hand, extencls
through the bell 14 and is attached to said bell 14
with cement.
A limb of a narrower fine quartz tube 18, bent
through 180 , is attached by means of the cement 19
in the open end of the narrow quartz tube 17 extending
outside the bell 14. The other limb of said fine quartz
tube 18 is directed with its free end towards the open-
ing of the bell 14. Said end is sealed by a plug 38
of a material which melts at the temperature of the
steel bath and which seals the gas supply line 17,
18, 27 in a moisture-tight manner before the probe
1 is immersed in the metal bath. The cement 19 seals
the narrow tube 17 around the fine tube 18 in a gastight
manner.
In the quartz tube 15, the narrow quartz tube
17 is additionally surrounded by a tube 20 of A12O3.
The end of the quartz tube 15 remote from the
bell 14 and especially the section 9 of the quick-connec-
tion coupling 9, 10 are surrounded by a sheath consisting
of three concentric tubes adjacent to each other, namely
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an innermost tube 21 of paperboard, a middlemost tube
22 of paperboard and an outermost tube 23 of resin-
bonded sand.
The tubes 22 and 23 of said sheath are attached
to the quartz tube 15 by means of cement 24.
The sheath 21, 22, 23 extends at the side facing
away from the bell 14 to appreciably beyond the section
9. The inside diameter of the innermost tube 21 corres-
ponds to the outside diameter of the lance 11 whose
end projects into said sheath when the lance is connected
to the probe 1.
The sheath 21, 22, 23 forms a thermal shield for
this lowermost end of the lance 11 and particularly
for the quick-connection coupling 9, 10.
As is especially evident from figure 3, the section
9 of the quick-connection coupling 9, 10 consists of
a body which, on the immersion side, i.e. the side
directed towards the bell 14 is provided with a collar
25 in which the quartz tube 15 is secured and is centrally
provided with a hole 26 into which an end of the narrow
quartz tube 17 projects.
An axial hole 27, which forms a gas supply line
together with the quartz tubes 17 and 18, extends through
said body.
The uppermost end of the axial hole 27 is sealed
by a rubber stopper 39 which seals the hole 27 and
therefore the gas supply line 17,18, 27 in a moisture-
tight manner before the sections 9 and 10 of the quick-
connection coupling are coupled and therefore before
the probe 1 is installed on the lance 11.
Next to the axial hole 27, there extend through
the body of the section 9 four holes 28 which debouch
into the space between the quartz tube 15 and the narrow
quartz tube 17 and which together with the last-mentioned
space form a gas removal line which is closed at the
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immersion side by the porous bell 14 which forms a
diaphragm, allows gas through but holds back liquid
metal.
The diameter of the body of the section 9 of the
quick-connection coupling 9, 10 decreases stepwise
in the direction facing away from the quartz tube 15
and, specifically, in a manner such that three inwardly
indented collars 29, 30 and 31 are formed.
The innermost tube 21 of the sheath 21, 22, 23
are up against the collar 29 situated most outwardly
and nearest the quartz tube 15 and is also up against
the outside of the cylindrical section of the section
9 which is situated between the collars 29 and 30.
The section of the body with a smaller diameter
which is situated between the collars 30 and 31 is
surrounded by an O-ring 32 partially recessed therein.
The abovementioned holes 28 debouch in the collar
31.
The cylindrical section extending outside the
collar 31 is also surrounded by an O-ring 33 partially
recessed therein.
The collars 30 and 31 and the O-rings 32 and 33
interact with parts of the section 10 of the quick-
connection coupling 9, 10, which section 10 forms a
piece which is installed on the end of the lance 11.
This section 10 is provided at its end with an
axial circular hole 34 into which the cylindrical section,
situated between the collars 30 and 31, of the section
9 fits and is provided with a smaller axial hole 35
which,on the one hand, debouches at the base of the
hole 34 and, on the other hand, connects to the end
of the gas circuit 2 which is situated downstream of
the flow meter 8.
Around the hole 35 there extends, in the section
10, a channel 36 which, on the one hand, debouches
at the base of the hole 35 and, on the other hand,
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connects to the other end of the gas circuit 2 which
just like the previous end, is attached in said section
10 .
These two ends of the gas circuit therefore ex-
tend through the metal lance 11.
In the smallest hole 35 of the section 10 of thequick-connection coupling 9, 10 there is attached a
mechanical connecting piece 37 which has four sprung
legs 41 provided at their ends with thicker parts which,
when the lance 11 is pushed into the sheath 21, 22,
23, snap in a sprung manner over the thickened head
on the end of the section of the section 9 projecting
outside the collar 31.
Connected to the connecting piece 37 is a hollow
needle 40 which extends axially between the legs 41
and whose hollow part connects to an axial channel
42 transversely through the connecting piece 37.
When installing the probe 1 on the lance 11, the
needle 40 is forced through the rubber stopper 39 into
the hole 27 of the section 9 so that if the legs 41
of the section 10 are snapped over the thickened head
of the section 9, the needle 40 projects through the
stopper 39 and connects the hole 35 of the gas supply
line 17, 18, 27 with one end of the circuit 2 situated
in the centre of the lance and downstream of the flow
meter 8.
As is especially evident from figure 2, the narrow
quartz tube 17 of the gas supply line 17, 18, 27 is
partly filled with silica gel 43.
Because said gas supply line are sealed in a moisture-
tight manner at both ends, respectively by the fusible
plug 38 and the rubber stopper 39 by mounting the probe
1 on the lance 11, the drying means formed by the silica
gel 43 does not absorb any moisture from the air.
The entity formed by the quartz tube 15 with possibly
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the bell 14, the projecting end of the narrow quartz
tube 17 and the fine quartz tube 18 may also be surrounded
by a cap of metal which, for the sake of simplicity,
is not depicted in the figures and is attached to the
sheath 21, 22, 23 and which is surrounded by a cap
of paperboard, likewise not shown in the figures.
To carry out a measurement, the probe 1 is installed
by means of the quick-connection coupling 9, 10 on
a lance 11, which lance is therefore pushed into the
sheath 21, 22, 23 of the probe 1, as a result of which
the seal formed by the rubber stopper 39 of the uppermost
end of the gas supply line 17, 18, 27 is opened by
the needle 40 as described above.
The four-way stopcock 7 is set in the position
in which the supply line 13 connects to the gas circuit
2 so that nitrogen flows from the bottle 12 to the
probe 1.
Because the lowermost end of the gas supply line
17, 18, 27 is still sealed by the fusible plug 38,
nitrogen will no longer flow once said line has been
filled and a relatively high pressure, which corresponds
to the pressure of the gas bottle 12, will prevail
in said line.
As soon as the probe 1 is immersed in the bath
of liquid steel, the plug 38 melts and nitrogen bubbles
through the liquid metal, which nitrogen is collected
in the bell 14 and is drawn off via the gas removal
line 14, 15, 28 and the circuit 2 via the filter 4
and the katharometer 5 by the pump 6 which has been
started in the meantime.
For a few seconds, the gas drawn off escapes at
the position of the four-way stopcock 7 into the open
atmosphere as a result of which any impurities which
when the probe 1 is immersed in the metal bath, for
example by combustion of the constituents of the probe,
are removed.
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After flushing for ten seconds, when the catharo-
meter no longer measures any impurities, the position
of the four-way stopcock changes to that depicted in
figure 1, and the nitrogen therefore flows in a closed
circuit around the circuit 2 and the probe 1, and the
actual measurement begins.
Already during the flushing, but also still while
nitrogen is circulating, any moisture which is still
released, for example, from the probe 1, is absorbed
by the silica gel 43 in the narrow tube 17 so that
no moisture is fed into the metal bath with the nitrogen
and neither is any additional hydrogen consequently
produced by liberated moisture.
After the dried nitrogen which has exchanged hydrogen
with the metal bath has been pumped round for a short time,
an equilibrium is established in relation to the hydrogen
and the katharometer 5 indicates the correct hydrogen
content.
As a result of the absence of additional hydrogen
which has been formed by moisture, no correction factor
has to be applied and it is also possible for very
low hydrogen contents to be measured.
The invention is by no means restricted to the
embodiment described above and within the scope of
the patent application, many alterations on the described
embodiment may be made, inter alia, in relation to
the shape, the structure, the arrangement and the
number of the components which are used to implement
the invention.
In particular, the silica gel does not necessarily
have to be located in the gas supply line of the probe
and the drying means do not necessarily have to be
formed by silica gel.
The drying means may, for example, also be provided
in the gas removal line of the probe or in both gas
lines of the probe.
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The said gas lines in which the drying means are
present should always be sealed in a moisture-tight
manner at both ends before the probe is installed on
the lance in order to avoid absorption of moisture
from the atmosphere.
The drying means may, however, also be provided
outside the probe in the gas circuit. For example,
the filter from the circuit may be filled with silica
gel or another drying means instead of with filter
material.
The drying means may also be provided, for example
in the katharometer.
Insofar as drying means are provided in the circuit,
they may also, for example, be formed by cooling means
which remove the moisture from the gas in the circuit
by condensation.
