US3816183A

US3816183A - High temperature molten metal thermocouple

Info

Publication number: US3816183A
Application number: US00292352A
Authority: US
Inventors: M Kraus
Original assignee: Electro Nite Co
Current assignee: M-R OHIO Inc A OHIO CORP; MRC ACQUISTION CORP NO 3 A CORP OF DE
Priority date: 1972-09-26
Filing date: 1972-09-26
Publication date: 1974-06-11
Anticipated expiration: 1991-06-11

Abstract

A non-splash temperature measuring device for repeated immersion in molten metal is disclosed. The immersion end includes a vacuum cast sleeve of refractory fibers having low density and a low rate of thermal conductivity, while having high temperature stability and being capable of resisting thermal shock.

Description

1 Unite States atet 11 1 1111 3,816,383 Kraus June 11, 1974 HIGH TEMPERATURE MOLTEN METAL 3,398,027 8/1968 Lajurrige et al. 130/234 O OU 3,467,542 9/1969 Nordlie 136/234 X 3,580,744 5/1971 Shingo lnouye et a], 136/234 Inventor: Max Kr k1ns Park, Pa. 3,698,954 10/1972 Jones, Jr. 136/234 [73] Assignee: Electro-Nite Co., Philadelphia, Pa.

Primary ExammerLeland A. Sebastlan [22] Flled? P 26, 19/2 Assistant ExaminerE. A. Miller 211 App] NO: 292 352 Attorney, Agent, or Firm-Seidel, Gonda &

Goldhammer 1521 us. (:1 136/234. 136/232, 136/242 1511 1111.01 HOlv 1/02 [57} ABSTRACT 58 Field of Search 130/233. 234. 232, 230, A non-splash temperature measuring device for 13 242; 73 359 peated immersion in molten metal is disclosed. The

immersion end includes a vacuum cast sleeve of re- 5 References Ci fractory fibers having low density and a low rate of UNITED STATES PATENTS thermal conductivity, while having high temperature I stability and being capable of resisting thermal shock. 2.993.944 7/[961 Silver [36/234 3,374,122 3/1968 Cole 73/359 x 13 Claims, 4 Drawing Figures Li e,

. 26 i $124 i 2/ l 22 2 9 2 37" 3Q HIGH TEMPERATURE MOLTEN METAL THERMOCOUPLE A non-splash lance in accordance with the present invention is adapted for repeated immersions in molten metal tomeasure the temperature of the same. A temperature measuring device adapted for repeated immersion is, per se, known. The present invention is directed to a temperature measuring device which is lighter in weight and capable of better withstanding high' temperatures of about 2,4003,IOOF, while at the same time materially simplifyingassembly and production techniques.

In accordance with the present invention, a support tube has a thermocouple unit supported within one end of the tube which is the immersion end of the tube. The tube may be made from any high temperature resistant material while being light in weight, such as wound paper. A preformed sleeve surrounds the immersion end portion of the tube and also surrounds the body of the thermocouple unit.

The sleeve is preferably vacuum cast from fine refractory fibers such as ceramic fibers (about 90-98 percent alumina-silica), to which may be added colloidal' silica, and a binder. The sleeve has high temperature stability, low thermal conductivity, is light in weight, resists thermal shock, etc. Such a sleeve preferably has a density of to pounds per cubic foot, a thermal conductivity of 0.5 to 1.6 at 1,500F, and a melting point in excess of 3,200F.

The sleeve is preferably a cast sleeve so that it need only be telescoped over the tube during assembly. A preformed sleeve of this nature increases the rate of production, is easy to handle, and is a sufficient barrier to molten metal such as steel, cast iron, copper, etc., whereby the device may be repeatedly immersed in the molten metal to obtain temperature readings thereof.

It is an object of the present invention to provide a temperature measuring device adapted for repeated immersion in molten metal to detect the temperature of the molten metal.

It is another object of the present invention to provide a temperature measuring device which has its immersion end surrounded by a vacuum cast sleeve of fine refractory fibers.

It is another object of the present invention to provide a non-splash lance which is lighter in weight and provides for greater thermal insulation at the junction of the free ends of the thermocouple wires of the temperature measuring unit at the immersion end of the lance.

Other objects will appear hereinafter.

For the purpose of illustrating the invention, there is shown in the drawings a form which is presently preferred; it being understood, however, that this invention is not limited to the precise arrangements and instrumentalities shown.

FIG. I is a perspective view of the immersion end of a temperature measuring device in accordance with the present invention.

FIG. 2 is a plan view of the temperature measuring device of FIG. I on an enlargedscale and partly in section.

FIG. 3 is a sectional view taken along the line 33 in FIG. 2.

FIG. 4 is a partial sectional view similar to FIG. 2 but illustrating another embodiment.

Referring to the drawing in detail, wherein like numerals indicate like elements, there'is shown in FIGS. 1 and 2 a temperature measuring device in accordance with the present invention designated generally as 10. The device 10 is in the form of a non-splash lance for immersion pyrometry. The device 10 is immersed into the bath of molten metal by means of a metal pole 12 which may be straight or curved. A support tube 14 is telescoped over the immersion end of the pole 12. The tube 14 is preferably made from a lightweight, high temperature resistant material having low thermal conductivity such as wound paper. Tube 14 protects pole 12 from radiant heat. The ability of tube 14 to perform its function may be enhanced by a heat reflective coating such as aluminum, on its outer surface.

A temperature measuring unit 16 is mounted in and supported by one end portion of the tube 14 which is the immersion end thereof. The temperature measuring unit 16 preferably includes a body 18 in the form of a cylinder which may be a cast ceramic cylinder. The body 18 is filled with a refractory material 20 which may be of the castable type. One end of the body 18 is closed by an end wall 22 which partially telescopes thereinto and may be made from a wide variety of materials including polymeric plastics. The end wall 22 has axially extending

contact supports

24 and 26 adapted to cooperate with mating structure, not shown, on the end of the metal pole 12.

A U-shaped tube 2 8 of refractory material such as quartz or the equivalent is supported by the refractory material 20 and projects from the end face of the body 18 in an axial direction. Thermocouple wires are connected together at a hot junction in the bight of the tube 28. The other ends of the thermocouple wires are metallurgically joined to short pieces of compensating lead wires within material 20. The individual lead wires are supported at their free ends by the contact supports 24 and 26. If desired, a metal cap 30 may be used to protect the tube 28 during initial storage or handling and during passage through any slag. Cap 30 is perforated and is readily consumable by the bath. Cap 30 is optional and may be eliminated if desired.

.Unit 16 is inserted into tube 14 and body 18 is adhesively bonded thereto. A preformed sleeve 32 is telescoped over the tube 14. Sleeve 32 surrounds the immersion end portion of the device 10 and is in surrounding relationship to the body 18. It will be noted that the end face 34 on the sleeve 32 projects beyond the adjacent end face of the tube 14. A layer of heat insulating refractory material 36, preferably of the airdry type is applied over the end face of body 18, the end face of tube 14, and may overlie the end face 34 on sleeve 32. The refractory material 36 bonds the temperature measuring unit 16, tube 14 and sleeve 32 into an integral unit, with a layer 37 of said refractory material 36 disposed between tube 14 and sleeve 32.

The sleeve 32 is preferably vacuum cast from fine refractory fibers such as ceramic fibers (about -98 percent alumina-silica), to which may be added a colloidal silica, and a binder. The sleeve 32 may suitably be cast by coating an aqueous slurry of the ceramic fibers, a high temperature binder, and any desired fillers on a vacuum former of appropriate size and shape, removingthe water by applying a vacuum, and then curing or setting the binder. Sleeve 32 has high temperature stability with a melting point in excess of 3,200F, low

' thermal conductivity, is light in weight with a density of between to 40 pounds per cubic foot and is resistant to thermal shock. A comparison of thermal conductivity is as follows:

K coefficient of thermal conductivity at l,500F in Refractory castables are a poor insulator when compared with the material from which sleeve 32 is made. Assuming a certain maximum allowable temperature in the body 18, the thickness of a protective sleeve would be proportional to the various K factors. Thus, a refractory castable at best would require four to five times the wall thickness of sleeve 32. At the same time, refractory castables have a density which is between five and times as great as the density of the material from which sleeve 32 is made.

Suitable ceramic fibers of this type are commercially available, for example, from the Carborundum Company under the trademark Fibe'rfrax. Such commercially available materials have a K of about 0.9 to 1.3. Suitable binders for the ceramic fibers include, for example, aqueous colloidal silica sols, which are commercially available, for example, from 13.1. duPont de Nemours and Co. under the trademark Ludox.

Sleeve 32 when made from materials referred to above are superior over sleeves made from asbestos mortar since the asbestos ablates below 2,000F whereby the asbestos covering disappears. Further, asbestos does not have the low thermal conductivity of the material referred to above and is a definite health hazard.

Entry of heat thorugh the end face of the device 10 is a major avenue of heat transfer. Refractory material 36 is preferably made from the same material as sleeve 32 whereby a layer one-quarter inch thick would have the same thermal conductivity as a castable refractory cement 1 inch thick. Refractory material 36 reduces heat transfer into the body 18, while bonding the sleeve 32 to the tube 14 and the temperature measuring unit 16. It will be noted that the body 18 is preferably a straight cylinder rather than having an end flange which would provide a greater area for heat transfer to take place. Body 18 may be made from polymeric plastics, wound paper, etc., if desired. lf body 18 were made from a suitable insulating material, such as the material of sleeve 32, then it may have a flange which overlies the end face of tube 14.

The sleeve 32 has a length whereby the upper end face 38 will be above the level of molten metal in the bath in which the device 10 is immersed. Depending upon the type of bath involved, sleeve 32 may have a length between 3 inches and 48 inches. By way of example and not by way oflimitation, the tube 14 in one embodiment has an OD of about 1% inches and a radial wall thickness of about A inch. Likewise, the sleeve 32 for that tube has an OD of 1% inches and a radial wall thickness of A inch. When measuring temperature of a molten metal bath in a furnace, tube 14 preferably has a length substantially greater than the length of sleeve 32. When measuring temperature of a molten metal bath in a full ladle, tube 14 may have a length substantially equal to the length of sleeve 32.

The tube 14 and sleeve 32 are both good heat insulators. The ID of tube 14 is abrasion resistant so that pole 12 easily slides to a position wherein contact may be attained with

supports

24 and 26. When tube 14 is longer than sleeve 32, the exposed length of tube 14 provides a handle for gripping and sliding the device 10 over the pole 12. The tube 14 may be made of an inexpensive material such as wound paper or of insulating plastic thereby contributing to thermal insulation of pole 12 while being made from material less expensive than that of the sleeve 32.

In some applications, it is desirable for the immersion end of the device to be buoyant. The free ends of

supports

24 and 26 in an operative embodiment are about 2 inches from the exposed face of refractory material 36. The said operative embodiment had an OD of 2 inches, and the initial 2 inches of the immersion end of device 10 weighed 0.14 lbs. with a volume of 6.3 in An equivalent steel bar 2 inches long and 2 inches OD weighed 1.7 lbs. Hence, there would be an upward force of about 1.6 lbs. on the terminal 2 inches of the immersion end of the device 10 by the diplaced steel. Since the downward force of the remainder of device 10 was 1.6 lbs., the entire device floated in the molten bath while being submerged for adepth of 2 inches measurement its immersion end. This is an optimum position for measurment of temperature.

Since only sleeve 32, layer of refractory material 36, and tube 28 contact the bath, there is a minimal thermal effect on the bath. This provides for greater accuracy, and also enables tube 28 to be shorter in length with the thermocouple hot junction closer to the exposed face of refractory material 36.

Since sleeve 32 does not burn, does not chemically react with the bath, and does not absorb moisture, there is no boiling or splashing phenomenon when in contact with a bath of molten metal. Hence, device 10 is a non-splash lance which provides a safety feature not readily attained by a device wherein paper or other material contacts the bath.

In FIG. 4, there is illustrated a portion of another device in accordance with'the present invention designated generally as 10'. The device 10 and the device 10 are identical except as to be made clear hereinafter.

ln device 10', a spacer 40 is attached to the immersion end of the tube 14 so as to provide an air gap between the OD of tube 14' and the ID of sleeve 32. Refractory material 36' is used to join the upper end of sleeve 32 (not shown) to the outer periphery of tube 14. The air gap 42 is a sealed space which provides additional insulation. As contrasted with the air gap 42, thesleeve 32 is a snug fit over the OD of tube 14.

The present invention may be embodied in other specific 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.

1 claim:

1. A temperature measuring device suitable for immersion into molten metal at temperatures of about 2,400-3,l0() F., comprising a non-metallic support tube, a thermocouple unit having a main portion supported by said tube within one end thereof, a thermal insulating sleeve carried by said tube, said sleeve surrounding said tube at said one end of the tube and surrounding said main portion of said thermocouple unit, said thermocouple unit having a hot junction supported beyond said one end of said tube, said sleeve being formed from refractory fibers said sleeve having a density of to 40 pounds per cubic foot and a thermal conductivity of between 0.5 and 1.6 BTU in./F. hr. ft. at 1,500F. and a layer of thermal insulating refractory material bonding said tube and said sleeve and overlying the end face of said one end of said tube and said main portion.

2. A device in accordance with claim 1 wherein said tube is made of paper material and is at least as long as said sleeve.

3. A device in accordance with claim 1 wherein said sleeve projects beyond said one end of said tube for a distance corresponding generally to the thickness of said refractory material.

4. A device in accordance with claim 1 wherein said sleeve is a vacuum cast preformed sleeve shorter in length than the length of said tube.

5. A device in accordance with claim 1 wherein said tube has a thermal coefficient of conductivity of between 0.9 and 1.3 BTU in/F-hr ft at l,500F.

6. A device in accordance with claim 1 wherein said refractory material is made from the same refractory fibers used in said sleeve.

7. A device in accordance with claim 1 wherein said sleeve has a snug fit over said tube.

8. A device in accordance with claim 1 including a spacer between said tube and sleeve to define an air gap between the outer periphery of the tube and the inner periphery of the sleeve, and means for preventing molten metal from entering said air gap.

9. A temperature measuring device suitable for immersion into molten metal at a temperature of about 2,4003, IOOF., comprising a non-metallic support tube, a thermocouple unit having a main portion supported by said tube within one end thereof. a sleeve carried by said tube, said sleeve surrounding said main portion of said thermocouple unit, said sleeve being formed from refractory fibers of which about -98 percent are alumina-silica held together by a binder, and thermal insulating means bonding said tube and said sleeve at said one end of said tube and overlying the end faces of said one end of said tube and said main portion.

10. A device in accordance with claim 9 wherein said means is a layer of refractory material.

11. A.device in accordance with claim 10 wherein said sleeve projects beyond said one end of said tube for a distance corresponding generally to the thickness of said refractory material.

12. A device in accordance with claim 9 wherein said sleeve is a vacuum cast sleeve having a density of 10 to 40 pounds per cubic foot, a melting point in excess of 3,000F, and a thermal conductivity of 0.5 to 1.6 BTU in/F-hr ft at 1,500F.

13. A device in accordance with claim 9 wherein said tube is of paper material and is at least as long as said sleeve.

Claims

2. A device in accordance with claim 1 wherein said tube is made of paper material and is at least as long as said sleeve.
3. A device in accordance with claim 1 wherein said sleeve projects beyond said one end of said tube for a distance corresponding generally to the thickness of said refractory material.
4. A device in accordance with claim 1 wherein said sleeve is a vacuum cast preformed sleeve shorter in length than the length of said tube.
5. A device in accordance with claim 1 wherein said tube has a thermal coefficient of conductivity of between 0.9 and 1.3 BTU in/* F-hr ft2 at 1,500*F.
6. A device in accordance with claim 1 wherein said refractory material is made from the same refractory fibers used in said sleeve.
7. A device in accordance with claim 1 wherein said sleeve has a snug fit over said tube.
8. A device in accordance with claim 1 including a spacer between said tube and sleeve to define an air gap between the outer periphery of the tube and the inner periphery of the sleeve, and means for preventing molten metal from entering said air gap.
9. A temperature measuring device suitable for immersion into molten metal at a temperature of about 2,400*-3,100* F., comprising a non-metallic support tube, a thermocouple unit having a main portion supported by said tube within one end thereof, a sleeve carried by said tube, said sleeve surrounding said main portion of said thermocouple unit, said sleeve being formed from refractory fibers of which about 90-98 percent are alumina-silica held together by a binder, and thermal insulating means bonding said tube and said sleeve at said one end of said tube and overlying the end faces of said one end of said tube and said main portion.
10. A device in accordance with claim 9 wherein said means is a layer of refractory material.
11. A device in accordance with claim 10 wherein said sleeve projects beyond said one end of said tube for a distance corresponding generally to the thickness of said refractory material.
12. A device in accordance with claim 9 wherein said sleeve is a vacuum cast sleeve having a density of 10 to 40 pounds per cubic foot, a melting point in excess of 3,000*F, and a thermal conductivity of 0.5 to 1.6 BTU in/*F-hr ft2 at 1,500*F.
13. A device in accordance with claim 9 wherein said tube is of paper material and is at least as long as said sleeve.