Note: Descriptions are shown in the official language in which they were submitted.
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. APPARTUS FOR DETERMINING THE ACTIVE OXYGEN
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~ CONTENT OF MOLTEN METAL
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Background
In some cases, practical use of prior art devices
has resulted in incorret measurements, for which no ex-
planation could initially be found. The object of the
invention is to ensure that incorrect measurements are
reliably avoided.
The invention is based on the finding that the
malfunctions that have occurred are due to the presence
of moisture in the cell, particularly in the reference
material. The cell absorbs moisture because of the por-
osity of the zirconium oxide tube or zirconium oxide disc,
and via the filler material, which usually consists of
A1203. Other moisture originates, for example, from the
cement by means of which the measuring head is filled and
secured.
Summary Of The Invention
Starting from apparatus of the kind described here-
inbefore, and on the basis of the above finding, which
must be regarded as surprising, the solution to the pro-
blem as provided by the invention is that the electro-
chemical cell is completely provided with a jacket which
prevents the penetration of moisture during manufacture
and storage.
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This invention relates to apparatus for determining
the active oxygen content of cast iron, iron or steel
melts. A measuring head is secured to the end of a sup-
porting tube. The head includes a ceramic material in
which there is disposed an electrochemical cell comprising
a zirconium oxide material and a reference electrode. The
cell is provided with a metal shock shield which shields
the electrochemical cell from the melt and is destroyed
on immersion of the measuring head into the molten metal.
In one embodiment of the apparatus the zirconium
oxide material is in the form of a tube projecting from
the body of ceramic material- The reference material is
disposed in the tube. The shield is also in the form of
a tube and having at least the same length as that portion
of the tube of zirconium oxide material which projects
from the ceramic material. The shield is adapted to be
pushed on to the tube of zirconium oxide material and the
inside diameter of the shield corresponds practically
to the outside diameter of the cell tube so that the shield
bears tightly against the electrochemical cell.
In another embodiment of this apparatus known from
German Offenlegungsschrift 2 824 143, of June 24, 1982 to
Electro-Nite Company the zirconium oxide material is in the
form or a disc which rests on the reference material in a front
opening in the ceramic material. In this case the shield is of
disc-shaped construction, rests on the top surface of the zir-
conium oxide disc, and is secured by a suitable bonding agent,
preferably refractory cement. Thermal shocks can be avoided by
means of apparatus of this kind, which is very simple in
construction.
Of course the air contained in the cell should con-
tain as little moisture as possible. To this end, the
reference material and the zirconium oxide material can be
dried beforehand. It has also been found advantageous for
the air contained in the cell to be removed after the
jacket has been fitted, and for it to be replaced, possibly
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by an inert gas, e.g. argon. In this way, the reference
material is protected from the oxidizing action of the
i, air during storage. To this end, according to the inven-
tion, the jacket and/or the closure is/are provided with
an extraction means, preferably an extraction spigot, via
- which the air is sucked out of the cell and which after
the suction or after introduction of an inert gas is
3 closed by pinching and/or heating.
1 By means of the apparatus according to this inven-
tion it is possible to avoid the penetration of moisture
to the interior of the cell and to protect the reference
material therefrom so as to reliably preclude incorrect
measurements due to the penetration of moisture.
Three exemplified embodiments of the invention are
illustrated diagrammatically in the drawing wherein:
For the purpose of illustrating the invention, there
is shown in the drawing a for which is presently pre-
ferred; it being undertsood, however, that this inven-
tion is not limited to the precise arrangements and
instrumentalities shown.
Figure 1 is a section through a measuring head in
accordance with one embodiment.
Figure 2 is also a section showing another type of
jacketing of the zirconium oxide tube in accordance with
another embodiment.
Figure 3 is a vertical section through the top por-
tion of a measuring head in accordance with another em-
bodiment wherein the zirconium oxide material is in the
form of a disc.
De~ailed Description
The bottom part of the measuring head 1 shown in
Figure 1 contains a plug system for connection to a
measuring lance in a known manner. Reference 11 denotes
the ceramic body accommodating the actual measuring cell 2
and a thermocouple 9. The electrochemical cell 2 com-
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prises a zirconium oxide tube 3. The reference material
4 is disposed in the top closed portion of tube 3. The
remainder of the tube 3 is filled with a filler 5, pre-
ferably of aluminum oxide (A1203).
A conductor 6, e.g. a molybdenum wire, which ter-
minates inside the reference material 4, extends through
the filler 5 as far as the plug system. The zirconium
oxide tube 3 is surrounded by a metal shock shield 8,
which bears tightly against the tube 3 and is a metal such
as low carbon steel which melts on immersion into the
molten metal bath. At its bottom open end the shield 8
projects slightly beyond the zirconium oxide tube 3 and is
provided with a moisture prevention closure 7, through
which the conductor 6 is tightly passed and which tightly
seals the bottom end of the zirconium oxide tube 3.
In the embodiment illustrated in Figure 1 of the
drawing, a reduced-diameter portion of the closure 7
projects slightly into the zirconium oxide tube 3 while
the larger-diameter portioh bears tightly against the inner
surface of the shield 8. Reference 10 denotes a protective
cap which is conventionally used in measuring devices of
this kind and which may be, for example, of cardboard or
alternatively of metal. Closure 7 is preferably silicone
rubber but other materials may be used.
The zirconium oxide tube may alternatively be en-
cased in the manner shown in Figure 2, in which like or
primed reference numerals are used for like parts with
respect to the above-explained device shown in Figure 1.
In the second embodiment, the zirconium oxide tube 3 is
again surrounded by a metal shield 8' bearing tightly
against it but the shield 8' does not extend as far as the
bottom open end of the zirconium oxide tube 3. For
example, shield 8' extends over only two-thirds of the
length of tube 3. The bottom portion of the tube 3 is
surrounded by a jacket 12, e.g. of plastics, to prevent
the penetration of moisture. The jacket 12 extends
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slightly above the open end of the shield 8' to give a
perfect seal. Closure 7' seals the bottom end of the
zirconium oxide tube 3 and preferably is made of silicone
rubber.
Figure 3 illustrates an embodiment in which the
zirconium oxide compound is in the form of a disc 13 dis-
posed in a front opening 17 in the ceramic member 11'.
A metal shield 14, which is also of disc-shaped construc-
tion, rests on the top surface of the zirconium oxide disc
13 and is secured to the ceramic member 11' by a suitable
bonding agent, preferably refractory cement or lute. The
front opening of ceramic member 11' also contains the
reference material 15 in which the conductor 16 terminates.
The entire front opening 17 of the ceramic member 11' is
provided with a jacket or lining 18 which completely
surrounds the electrochemical cell and prevents the pene-
tration of moisture.
In each embodiment the air in each cell has prefer-
ably been evacuated and replaced with an inert gas as
described above.
The present invention may be embodied in other spe-
cific forms without departing from the spirit or essential
attributes thereof and, accordingly, reference should be
made to the appended claims, rather than to the foregoing
specification, as indicating the scope of the invention.
