Batteries: thermoelectric and photoelectric – Thermoelectric – Having housing – mounting or support
Patent
1993-01-22
1997-10-07
Jordan, Charles T.
Batteries: thermoelectric and photoelectric
Thermoelectric
Having housing, mounting or support
136230, 136232, 136233, 374179, 374208, H01L 3502
Patent
active
056751184
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the continuous temperature measurement of liquid steels, but also to all high temperature thermo-couples with an outer metal protective tube, and an inner ceramic protective tube.
2. Description of the Related Art
State of the art are thermo-couple tips made of platinum-rhodium-platinum that indicate, when submerged into liquid steel, the temperature of the melt for several seconds and afterwards dissolve in the steel.
Furthermore state-of-the-art are thermo-couples according to the U.S. Pat. Nos. 4,746,534, 4,721,534, 4,721,533.
They describe a thermo-couple with three protective tubes: stabilizers) that can be submerged directly into the liquid steel. This protective tube is exchangeable. two hole insulation rod and thermowires.
The outermost protective tube is relatively inexpensive, but only lasts for one casting sequence. In other words it only lasts for one heating and cooling process, less than one day.
The two hole insulation rod is as pure and thick as possible, because the temperatures of 1530.degree.-1550.degree. C. are so high, that, as is commonly known, a thin insulation would start to conduct electricity and thereby cause a too low indication.
Said thermo-couples were the first, that made a continuous measurement of the temperature of liquid steel possible. This is very important with continuous casting devices. At a too low temperature the casting operation has to be stopped.
The problem of the above described continuous thermo-couple is however, that it falsely starts to indicate the too low temperature already after about three days, although the temperature is still sufficiently above the liquidus temperature (i.e. around 3K). This drift increases according to an exponential function as is shown in FIG. 1 according to an actual measurement. The thermo voltage collapses at an increasing speed.
The drift at temperatures that high is something natural. It can easily be checked through submerge-measurements in intervals of 10 minutes. If t is the time in hours, the Delta T drift according to an exponential function
The accuracy of measurement in the beginning is of particular advantage. The drift remains almost immeasurably small.
After several days, however, a clearly negative drift appears. After having shown up for the first time, it becomes more and more severe. FIG. 1 shows, that the apparent change of temperature of the liquid steel amounts to over 1 Kelvin per hour after the thermo-couple has been in use for 90 hours. The thermo-couple had to be exchanged. Thus the staff was exposed to the strong temperature radiation and to the danger of injury.
Therefore, the advantage of the small drift in the beginning is only of value for a short time. The drift becomes the more uncalculable the longer the thermocouple is in use. The drift curve according to FIG. 1 can depend on metal vapors, reactions within the ceramic and on the natural Rhodium diffusions within the thermo-wires.
SUMMARY OF THE INVENTION
The drift curve shows a process, which takes place faster and faster; for example, a collapse of the insulation resistance. The solution to this problem was achieved through a surprisingly simple way, namely through a measure that surely no expert could have foreseen: increased--as every expert would have recommended--to prevent the collapse of the termo voltage. On the contrary: the insulation layer was reduced very much; namely to only 0.2 mm (max. 0.5 mm).
Even only one thermo wire was electrically insulated namely through a one hole insulation rod, while the other thermo wire was freely located in the fitting ceramic protective tube.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a graph showing drift over time;
FIG. 2 is a schematic elevational view of a thermo-couple provided in accordance with the present invention.
DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EXEMPLARY EMBODIMENT
Experiments showed, that it is better to keep the old molybdenum protective tube, than to adapt it to the new, very thi
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Carroll Chrisman D.
Jordan Charles T.
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