Device for measuring the temperature of a molten metal

Abstract

A device for measuring the temperature of a melt, particularly of a molten metal, includes an optical fiber and a guiding tube having an immersion end and a second end opposite to the immersion end. The optical fiber is partially arranged in the guiding tube. An inner diameter of the guiding tube is larger than an outer diameter of the optical fiber. A first plug is arranged at the immersion end of or within the guiding tube proximate the immersion end of the guiding tube. The optical fiber is fed through the first plug and the first plug reduces a gap between the optical fiber and the guiding tube.

Claims

1. A device for measuring the temperature of a melt comprising: a guiding tube having an immersion end and a second end opposite to the immersion end, an optical fiber partially arranged in the guiding tube, an inner diameter of the guiding tube being larger than an outer diameter of the optical fiber, and a first plug having a first end and an opposing second end, an inner diameter of the first plug being reduced from the second end of the first plug toward the first end of the first plug, wherein the first plug is arranged at the immersion end of the guiding tube or within the guiding tube proximate the immersion end of the guiding tube, and wherein the optical fiber is fed through the first plug and the first plug reduces a gap between the optical fiber and the guiding tube.

2. The device according to claim 1, wherein the first plug is elastic.

3. The device according to claim 1, wherein a second plug is arranged at the second end of the guiding tube or within the guiding tube proximate the second end of the guiding tube, wherein the optical fiber is fed through the first and second plugs, and wherein the first and second plugs reduce a gap between the optical fiber and the guiding tube.

4. The device according to claim 3, wherein at least one of the first plug and the second plug is elastic.

5. The device according to claim 3, wherein the second plug is arranged within the guiding tube between the first plug and the second end of the guiding tube.

6. The device according to claim 1, wherein at least the first plug has a conical shape at least at its immersion end, and wherein a wall thickness of the first plug is reduced toward the immersion end.

7. The device according to claim 1, further comprising a fiber coil and a feeding mechanism for feeding the optical fiber and the guiding tube, the feeding mechanism comprising at least two independent feeding motors, one for feeding the optical fiber and one for feeding the guiding tube.

8. The device according to claim 7, wherein the two independent feeding motors are each combined with a separate speed control.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) The foregoing summary, as well as the following detailed description of the invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there are shown in the drawings embodiments which are presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown.

(2) In the following the invention is described by way of an example.

(3) FIG. 1 shows a prior art consumable optical fiber;

(4) FIG. 2A shows the leading section of a metal coated optical fiber with guiding tube;

(5) FIG. 2B shows an alternate leading section of a metal coated optical fiber with guiding tube;

(6) FIG. 2C shows a further alternate leading section of a metal coated optical fiber;

(7) FIG. 3 shows the leading section of a metal coated optical fiber with adapted guiding tube;

(8) FIG. 4A shows an immersion device before immersing the optical fiber;

(9) FIG. 4B shows the immersion device after immersing the optical fiber;

(10) FIG. 4C shows the immersion device according to FIG. 3B with a different melt container such as a molten metal ladle or tundish; and

(11) FIG. 5 shows a view of both the position of the immersion end of the outer tube and the immersion end of the optical fiber during immersion.

DETAILED DESCRIPTION OF THE INVENTION

(12) One embodiment of the device of the present invention is described as follows, by way of example. FIG. 1. shows a prior art consumable optical fiber 10, typically employed in the measurement of liquid metals comprising an optical fiber, a jacket covering the optical fiber and a protective metal tube covering the surface of the plastic jacket. The optical fiber 10, typically a graded index multimode fiber made of quartz glass with an inner core 11, diameter of 62.5 m and an outer cladding 12, diameter of 125 m covered with a polyimide or similar material 13. The protective metal tube 14 is typically stainless steel 1.32 mm outer diameter (OD) and 0.127 mm wall thickness. Although a metal covered optical fiber is preferred, additional embodiments where protective metal tube 14 and/or polyimide or similar material 13 are replaced by a singular plastic material do not depart from the intended invention.

(13) FIG. 2A shows the leading section 10 of a metal coated optical fiber 10, as fed from spool 20 through a first gas retaining elastic plug 32, affixed to an outer disposable guiding tube 40. The first gas retaining plug 32 is proximate the immersion end 50 of tube 40.

(14) FIG. 2B shows the leading section 10 of a metal coated optical fiber 10, as fed from spool 20 through a second gas retaining elastic plug 30, affixed to the opposite immersion end 50 of an outer disposable guiding tube 40. A first gas retaining plug 32 is proximate the immersion end 50 of tube 40.

(15) Fiber 10 and outer disposable guiding tube 40 are not in a fixed arrangement and, as such, can move independent of each other and thus can be independently inserted through the slag layer 51 and into the molten bath 52 at different velocities while maintaining a gas volume 31 between plugs 30 and 32. Disposable guiding tube 40 is preferably low carbon steel having a wall thickness of 0.8 to 1 mm, but may be selected from a variety of metal materials as well as ceramics and glasses, cardboard and plastics or a combination of materials. In the case that disposable guiding tube 40 is selected from a material that reacts with the molten bath, the immersion portion 50 is preferably prepared in a way that it does not splash molten metal on the inside of the disposable guiding tube 40 by the application of coating or coverings of a material known in the art for the purpose of splash reduction.

(16) Immersing the open ended outer disposable guiding tube 40 in the steel through the slag layer 51 without plug 30 will result in ingress of slag and steel in this tube. Molten slag resulting from the refining process is preferably high in oxides, such as iron oxide which is easily absorbed into the optical fiber structure. The fiber 10 fed through the outer disposable guiding tube 40 containing slag and steel will be damaged before reaching the open end of the outer disposable guiding tube 40. For the preferred outer disposable guiding tube 40, of 2 m long with an immersion depth of 30 cm and being open at both ends, the upwelling of molten material inside the outer disposable guiding tube 40 can be up to 30 cm. In case of a closed end outer disposable guiding tube 40, the upwelling will be approximately 16 cm. This is calculated ignoring the gas expansion of the enclosed air which will undergo expansion due to an increase in its temperature. Tests show that the steel ingress can be minimized by reducing the air gap between the inner diameter (ID) of the outer disposable guiding tube 40 and the OD of the optical fiber 10 metal covering. Preferably, the air gap is reduced to the minimum. However, practically for tubes with an ID of 10 mm, this gap is preferably less than 2 mm.sup.2, more preferably less than 1 mm.sup.2. It can even be closed. Tubes with a smaller ID would allow a bigger gap due to the faster heating rate of the enclosed air.

(17) One of the preferred features of the present invention is to avoid molten ingress utilizing the thermal expansion of a volume of gas contained between a pair of gas retaining plugs affixed on or within in the disposable guiding tube 40. The use of elastic plugs 30 and 32 to effectively seal the end opposite the immersion end of a certain sealing quality ensures that expanding gas retains a positive pressure against the filling pressure of the liquid steel during immersion, thus keeping the disposable guiding tube 40 clear. Notwithstanding, any means of creating an overpressure in the disposable guiding tube 40 while immersing also avoids steel ingress such as an internal coating of a material vaporous at minimal temperatures, such as a galvanized coating (for example Zn). A prominent concept towards creating a positive pressure in the outer disposable guiding tube 40 is to avoid the upwelling and intrusion of metal, slag or other contaminants inside the disposable guiding 40 tube that could impede the free feeding of the optical fiber 10.

(18) Plugs 30 and 32 preferably have a feed through hole having a diameter (non-operated) which his less than the outer diameter of the optical fiber and should be suitably elastic in order to compensate for an un-ideal optical fiber end resulting from the prior immersion. The thermo elastic material Santoprene (Santoprene is a trademark of Exxon Mobile) is one such material that has been found to both remain elastic and surprisingly intact during the duration of the measurement. However, it can also be a different material, such as wood or another suitable plastics. In one embodiment, plugs 30 and 32 are preferably replaced with each outer disposable guiding tube 40. Each replacement assures a proper seal, however plug 30 could be constructed in such a way as to be reused with multiple outer disposable guiding tubes and replaced as a matter of maintenance. The preferred location of the plug 30 at the terminal end of outer disposable guiding tube 40 in FIGS. 2B and 2C is selected for ease of installation. However, placing plug 30 closer to the immersion end is equally acceptable. The design of plugs 30 and 32 in FIG. 2B facilitates their placement at the extremities of disposable guiding tube 40 showing lips that rest upon the tube ends. Other configurations are possible as well as means molded or embossed on the external surface of the plug to aid in the fixation of the plugs to tube 40 by tabs or adhesives. The exact embodiment of plug 32 should reflect the ease of positioning, location and fixation of its position without departing for the main purpose of the plug to restrict the escape of air from the outer tube, thus ensuring a build-up of inner pressure. FIG. 2C shows an alternate position for gas retaining plug 32 approximate the immersion end of tube 40. In this embodiment, the preferred distance between the immersion end of tube 40 and the exit location of the optical fiber from plug 32 is not more than 5 times the internal diameter of tube 40. Opposite the immersion end of plug 32, the internal contour of the plug tapers towards the internal wall of tube 40 such that the thickness of the plug 32 at its extremity is not more than one third the diameter of the optical fiber, thus insuring a consistent guide towards the immersion end during feeding. Plug 32 also may be configured with means molded or embossed on the external surface of the plug to aid in the fixation of the plugs to tube 40 by tabs or adhesives. The plugs have a conical shape, whereby the wall thickness of the plugs is reduced towards the immersion end.

(19) Similar to FIG. 2C, a reduction of the diameter or of the cross-section area of the guiding tube 40 at or close to its immersion end can be used (FIG. 3) instead of plug 32.

(20) The steel ingress in the steel tube while immersing in the steel tube preferably increases with an increase of the immersion depth, an increase of the tube length, an increase of the air gap (at the other end), a lower bath temperature, a thicker wall thickness and a higher oxygen content of the steel bath.

(21) The immersion device is shown in FIGS. 4A-4C. Machine 100 is suitably constructed and instrumented in such a manner that assembly of plugs 30 and 32 to outer disposable guiding tube 40 are aligned so optical fiber 10 can be inserted through plug 30 into the interior of the outer disposable guiding tube 40 and just exit plug 32. Notwithstanding, tube 40 and plugs 30 and 32 can be preassembled and loaded on machine 100 without departing from the scope of the invention. Both the outer disposable guiding tube 40 and optical fiber 10 are fed at approximately 3,000 mm/s through the side wall of an EAF through suitable access panels 80. These panels 80 are not part of the machine 100. The machine 100 has independent 100% reversible drive or feeding motors 25; 45. Motor 25 drives the optical fiber 10 and motor 45 drives the disposable guiding tube 40, so that the velocity of the outer disposable guiding tube 40 in either direction is independent of the velocity of the optical fiber 10 in either direction.

(22) The machine 100 is preferably capable of independent feeding of optical fiber 10 into the bath with a speed less, equal or higher than the speed of the outer disposable guiding tube 40. Preferably, the optical fiber 10 is fed faster so that both the immersion end 50 of the outer disposable guiding tube 40 and leading section 10 of optical fiber 10 arrive at the predetermined surface of the metal at approximately the same time. Once the bath level position is reached, the outer disposable guiding tube 40 is decelerated to a nearly stationary position in the molten metal 52. The leading section 10 of optical fiber 10 continues to move slowly deeper in the steel at about 200 mm/s for approximately 0.7 s. Both the outer disposable guiding tube 40 and the optical fiber 10 are constantly moving at unequal speeds to avoid welding the two metal surfaces together, thereby solving a problem stated in the prior art.

(23) The problem of the acceleration and deceleration of the optical fiber 10 is more complicated than moving the outer disposable guiding tube 40. The optical fiber 10 is constantly de-coiled and recoiled from a coil or spool 20 with its coil weight that is constantly changing due to fiber consumption. The feeding machine must be adapted with additional mechanics to avoid the elastic spring back effect from the coil or spool 20 itself, as well as the weight of the pyrometer connected to the coil. This is solved by using a servo motor or feeding motor 25 to control the fiber movement. One feeding motor 25 takes care of the de-coiling and recoiling of the fiber 10 and pre-feeds fiber 10 in such a way that the feeding motor 25 can accelerate very fast.

(24) The consumable optical fiber 10 receives the radiation light emitted from the molten metal, conveys such to a photo-electric conversion element mounted on the opposite end of the coiled consumable optical fiber and combined with associated instrumentation measures the intensity of the radiation, using this to determine the temperature of the metal. The optical fiber coil or spool 20 and instrumentation are located at a distance away, and separated from the EAF but are suitably robust to withstand the harsh conditions of the steel making environment. The location of the immersion end of the optical fiber 10 is preferably constantly known and monitored by machine instrumentation throughout the immersion, measuring and removal portions of the immersion cycle. The machine is preferably equipped with position encoders that determine the passage of fiber length and inductive switches that register the fiber end.

(25) After the measurement is complete, both the consumable optical fiber 10 and the outer disposable guiding metal tube 40 are withdrawn from the steel with different speeds in such a way that the optical fiber 10 stays relatively deeper in the bath. During this movement, it is capable to determine the bath-level due to a change in the light intensity when correlated with the length of optical fiber 10 extracted between predetermined positions. The post measurement bath level determination is subsequently used for the next immersion. It is also contemplated that the bath level could be determined during immersion using various techniques well described in the literature without departing from the method of the present invention.

(26) Once the optical fiber 10 is clear of the EAF interior, the direction of the outer disposable guiding tube 40 is preferably reversed toward the furnace interior. The outer disposable guiding metal tube 40 is then ejected, disposed and consumed in the furnace interior. A new outer disposable guiding tube 40 and gas plugs 30 and 32 are positioned to receive the optical fiber 10 for the next measurement. The remaining optical fiber 10 is preferably recoiled during removal and returned to a starting position.

(27) Key abilities of embodiments of the present invention are:

(28) accurate payout and recoil of fiber,

(29) detection of fiber end,

(30) loading of outer disposable guiding tube,

(31) load and position of gas plugs,

(32) guide fiber at starting position into gas plugs,

(33) fully reversible drives for both fiber and outer disposable guiding tube,

(34) independent speed profiles for fiber and outer disposable guiding tube,

(35) registration of fiber output for level detection, and

(36) attachable to furnace shell for tilt compensation of bath level.

(37) The method of one embodiment of the present invention is described by way of example of a total cycle description. This concept preferably involves an operator free control of EAF's. It is envisioned that the best operation is to take multiple temperature immersions in quick succession (about 5). Each immersion is preferably approximately 2 s; the total cycle time is preferably less than 20 s during a single heat.

(38) The schematic of FIG. 5 gives a view of both the position of the immersion end 50 of the outer disposable guiding tube 40 and the immersion end or leading section 10 of the optical fiber 10 during 2 immersions of a measurement cycle. For fiber movement, the end position of the fiber is preferably tracked.

(39) With tube movement is indicated the position of the immersed end of the disposable guiding tube 40. At or near the immersion end of tube 40 is gas plug 32. At the opposite of the immersion end 50 of the outer disposable guiding tube 40 is the gas plug 30. For the purpose of this schematic, the outer disposable guiding tube 40 is already in ready to immerse position. Gas plugs 30 and 32 are already attached to the back end and the optical fiber 10 is slightly extended from the gas plug 32 towards the molten metal. The relative dimensions shown are for descriptive purposes understanding that the absolute distances are predicated upon the actual furnace size which is a variable from steel shop to steel shop.

(40) The starting position 1 at time 0 of the fiber within the outer metal tube set at 350 cm above molten metal/bath-level. The starting position 1 at time 0 of the immersion end of the outer metal tube is located at 150 cm above the bath-level. The optical fiber 10 is fed from position 1 to 2 while the outer disposable guiding tube 40 remains nearly stationary. Between time 0.8 s and 1.2 s covering positions 2 through 4 both optical fiber 10 and outer disposable guiding tube 40 advance to a location just above the molten slag 51. At 1.2 s and position 4, the fiber is advanced slightly faster than the outer disposable guiding metal tube 40 passing through the slag 51 and into the molten metal 52. The outer disposable guiding metal tube 40 slows while the optical fiber 10 advances at approximately 200 mm/s reaching the maximum immersion at position 6 and 1.5 s into the immersion. Both optical fiber 10 and outer disposable guiding tube 40 are extracted within 0.1 s. The optical fiber 10 continues to be withdrawn and recoiled returning to its load position 8 while the remains of the outer disposable guiding metal tube 40 direction is reversed at position 7 and discarded. The optical fiber 10 is still protected by the remaining portion of the discarded outer disposable guiding tube 40.

(41) It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims.