JP2013019735A - Molten metal detection sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a molten metal detection sensor capable of knowing proper timing for re-coating a coating agent.SOLUTION: The molten metal detection sensor includes an electrode rod 22 which detects existence of a molten metal by contacting. A first protective coating film 26 is formed on a surface of the electrode rod. And a second protective coating film 28 different from the first protective coating film in color is formed on a surface of the first protective coating film. The first protective coating film gradually disappears when the electrode rod is repeatedly immersed in a high-temperature molten metal. A surface color of the electrode rod changes if the first protective coating film disappears and the second protective coating film is exposed. A point of time when the surface color of the electrode rod changes is suitable timing for re-coating a coating agent of the second protective coating film.

Description

  The present invention relates to a molten metal detection sensor. This detection sensor is used, for example, for a molten metal supply device of a casting apparatus.

  The molten metal supply device supplies a fixed amount of molten metal to the cavity of the casting device or the plunger sleeve each time. In such a molten metal supply apparatus, a molten metal detection sensor is used. For example, in a molten metal supply device of a type that scoops molten metal with a ladle, the molten metal detection sensor is attached in the vicinity of the ladle that is moved by the arm, and is used to check the relative distance between the ladle and the liquid level. In this case, the molten metal detection sensor functions as a so-called liquid level sensor that detects the position of the liquid level of the molten metal. Also, in a molten metal supply device called a “waist mat” that applies pressure to the space above the molten metal in the molten metal tank and pushes the molten metal in the tank to the plunger sleeve, the metal molten metal detection sensor supplies the molten metal to the plunger sleeve. It is attached to the road and used to check whether the molten metal is flowing.

  The structure of the molten metal detection sensor is extremely simple. A typical molten metal detection sensor has an electrode bar made of iron (SKD material) or stainless steel. A thermocouple is charged inside the electrode rod. When the electrode rod touches the molten metal and one end of the thermocouple in the electrode rod becomes hot, the current (or resistance) flowing through the thermocouple changes, and this change detects that the electrode rod is in contact with the molten metal. This type of molten metal detection sensor is a kind of thermocouple sensor. Examples of the molten metal detection sensor used in the molten metal supply device are disclosed in Patent Document 1 and Patent Document 2.

JP 2006-88182 A JP-A-8-261813

  High-temperature molten metal has a strong effect of eroding other substances. For example, molten aluminum reaches about 700 ° C. Therefore, the electrode rod of the molten metal detection sensor is also eroded while contacting the molten metal many times (the electrode rod is melted). The surface of the electrode rod may be provided with a protective coating made of a release agent so that the electrode rod is protected from melting damage and the attached molten metal (typically aluminum) is easily removed (for example, patents). Document 1) and the protective coating disappear due to melting damage. When the protective coating disappears and the bare metal of the electrode rod is exposed, the molten metal melts at an accelerated rate. In addition, since the surface becomes rough due to melting damage, the attached molten metal is more difficult to fall off, and the phenomenon that the adhered molten metal begins to solidify as it is may occur, and finally the molten metal may hang down like an icicle. There is even (see Patent Document 1). Furthermore, the melting of the electrode rod and the adhesion of the molten metal may cause a change in the thermal conductivity of the entire electrode rod, which may reduce the detection accuracy of the molten metal. Therefore, it is necessary to replace the electrode rod from which the protective coating has disappeared or to recoat the coating agent before the metal bar of the electrode rod is exposed. It is more economical to recoat the coating agent than to replace the electrode rod. However, it is difficult to measure the timing for recoating the coating agent. If the timing of repainting is late, the bare metal of the electrode rod will be exposed, and the adhered molten metal will be fixed. It is uneconomical if the timing of repainting is early. Moreover, if the timing of recoating is early, that is, if a coating agent is further applied while a sufficient protective coating remains, the coating becomes thick. It is costly to scrutinize the electrode rod surface to measure the timing of recoating the coating agent.

  The present invention was created in view of the above problems. The present invention provides a molten metal detection sensor capable of easily knowing an appropriate timing for recoating a coating agent.

  In the molten metal detection sensor disclosed in this specification, two different types of protective coatings are stacked on the surface of the electrode rod. In a preferred embodiment of the molten metal detection sensor disclosed in the present specification, a first protective film is formed on the surface of the electrode rod of the molten metal detection sensor, and the first protective film is formed on the surface of the first protective film. The 2nd protective film from which a color differs from is formed. The protective film may be two or more layers.

  By overlaying at least two types of protective coatings of different colors on the electrode rod surface, the user can easily visually confirm that the upper protective coating (second protective coating) has disappeared due to the color change of the electrode rod surface. Can know. When the user visually recognizes the color of the lower protective coating (first protective coating), the user may apply a coating agent for the second protective coating. That is, the timing at which the color of the electrode rod surface changes from the color of the second protective coating (upper protective coating) to the color of the first protective coating (lower protective coating) is suitable for recoating the coating agent for the second protective coating. Is the right timing. Even if the second protective film disappears, the first protective film remains, so that the electrode bar body is protected from melting. In addition, since the second protective coating disappears when the color of the electrode rod surface changes, the thickness of the second protective coating does not increase significantly even if the second protective coating is repeatedly applied. Since the coating agent of the second protective coating is reapplied each time the color of the first protective coating is exposed, the thickness of the second protective coating does not increase as the reapplying is repeated. (For example, if the coating of the second protective coating is repeated at regular intervals, the remaining second protective coating gradually increases in thickness.) The molten metal detection sensor disclosed in this specification is The timing suitable for recoating the second protective coating can be easily known visually.

  Particularly suitable as the first protective film is a protective film mainly composed of carbon oxynitride nanofibers. The carbon nanofiber has high thermal conductivity and does not impair the function of the electrode rod including the thermocouple. Further, the nitrosulfurizing layer enhances the resistance to melting of the electrode rod itself. Furthermore, since the carbon nanofibers adhere firmly to the surface of the electrode rod that has been subjected to nitrosulphurizing treatment, it is possible to expect high fusing resistance to the first protective coating. Carbon nanofibers are deposited on the surface of the electrode rod that has been subjected to nitrosulphurizing treatment. By such treatment, it is possible to form a protective film in which carbon nanofibers grow from the surface of the electrode rod (this situation will be further described in the embodiment section). In addition, since the carbon nanofibers have low wettability to the molten metal (aluminum) (because of low affinity with the molten metal), the first protective coating can be expected to have an effect that the molten metal runs out. In addition, the color of the 1st protective film of carbon nanofiber is a true black.

  Particularly suitable as the second protective film is a protective film containing at least one of fullerene, boron nitride (BN), and silicon oxide (SiO2) as a main component. The size of the carbon nanofiber is on the order of 100 nm (nanometer), and the size of fullerene is on the order of 1 nm. When fullerene is used as the coating agent for the second protective coating, the fullerene adheres so as to cover the entire carbon nanofiber (the state of attachment will be further described in the examples). Because of carbon and carbon, fullerene forms a strong protective coating on the gaps and upper layers of carbon nanofibers. That is, the fullerene on the carbon nanofiber forms a second protective film having a relatively high resistance to melting. The fullerene before application is dark gray or dark blue. When the second protective film mainly composed of fullerene is formed on the first protective film (true black) mainly composed of carbon nanofibers, the surface of the electrode rod looks dark gray. This dark gray is the color of the second protective coating.

  When the electrode rod repeatedly touches a high-temperature molten metal (for example, an aluminum melt of about 700 ° C.), the fullerene second protective film gradually disappears. When the second protective film almost disappears, the color of the electrode rod changes from dark gray to true black (color of the first protective film). When the surface of the electrode rod becomes black, this corresponds to the time when the second protective coating disappears and the carbon nanofibers as the first protective coating are exposed. The coating agent (fullerene) for the second protective coating may be applied again at this timing. If it does so, a new 2nd protective film can be formed, while there is almost no melting loss of the 1st protective film of carbon nanofiber. Since the electrode rod can be returned to its original state, the life of the electrode rod is extended.

  In addition, if the electrode rod is used as it is after the surface of the electrode rod changes to black, the surface changes to brown next. If it is used further, it changes to light gray. Brown has shown that the carbon nanofiber of the 1st protective film burned and discolored. Light gray indicates that the color of the electrode rod base material (SKD or stainless steel) has been seen through. Therefore, if the color of the electrode rod changes from the original dark gray and the second protective coating is repainted between true black and brown (preferably before changing to brown), the electrode rod body may be melted. The second protective coating can be repaired before inviting.

  Boron nitride (BN) or silicon oxide (SiO2) has the same particle size as fullerenes and is likely to bind to carbon like fullerenes, so the same effect as fullerenes is expected. Boron nitride (BN) and silicon oxide (SiO2) are white before coating, but appear gray when coated on the first black protective coating. That is, gray is the color of the second protective coating.

  The technology disclosed in the present specification can also be embodied in a maintenance method for a molten metal detection sensor. As described above, the molten metal detection sensor targeted by the method has the first protective film formed on the surface and the second protective film having a color different from that of the first protective film on the surface of the first protective film. It has an electrode bar formed. This maintenance method is characterized in that a coating agent for the second protective coating is applied when the electrode rod changes from the color of the second protective coating to the color of the first protective coating. As described above, according to this maintenance method, since the second protective film disappears but the second protective film is applied while the first protective film remains, the second protective film is applied before the electrode rod is melted. 2 The protective coating can be repaired. In addition, since the second protective coating disappears when the color of the electrode rod surface changes, the thickness of the second protective coating does not increase significantly even if the second protective coating is repeatedly applied.

It is a schematic diagram of the molten metal supply apparatus containing a metal easy detection sensor. It is a typical sectional view of an electrode bar. FIG. 3 is a schematic microscopic cross-sectional view of a portion surrounded by reference numeral III in FIG. 2.

  First, with reference to FIG. 1, an example of the utilization form of a molten metal detection sensor will be described. FIG. 1 is a schematic diagram of a molten metal supply device 2 including a molten metal detection sensor 22. The molten metal supply device 2 is a waist mat type, and the gas pressure in the molten metal tank 6 is increased by the pressurizing pump 4 to push out the molten metal W. From the molten metal tank 6 to the sleeve 30 of the casting apparatus, a molten metal guide tube 7 is connected, and a molten metal detection sensor 22 is disposed in the middle thereof. The output of the molten metal detection sensor 22 communicates with the controller 21. The controller 21 determines whether or not the molten metal is passing through the molten metal guide tube 7 by the molten metal detection sensor 22. When a predetermined amount of molten metal has passed through the molten metal guide pipe 7, the controller 21 reverses the pressure pump 4 to lower the pressure in the tank and stops the molten metal supply. Here, the controller 21 measures the amount of molten metal passing through the molten metal guide tube 7 based on the output of the molten metal detection sensor 22.

  The molten metal detection sensor 22 is a rod-shaped member made of SKD material, and a thermocouple is charged therein. One end of the thermocouple (joint point of two kinds of metal wires) is located at the inner lower end of the rod-shaped member. When the temperature at the lower end of the molten metal detection sensor 22 rises by touching a high temperature molten metal (in the case of aluminum, the temperature of the molten metal is about 700 ° C.), a current flows through the thermocouple according to the difference in the characteristics of the two types of metal wires. (Or the electrical resistance changes). The controller 21 detects that the molten metal is passing through the molten metal guide tube 7 by this current change (resistance change). In other words, the molten metal detection sensor 22 is a sensor that detects the presence of the molten metal by contact. Hereinafter, for the sake of simplicity, the molten metal detection sensor 22 is referred to as an electrode rod 22.

  A lower end cross section of the electrode rod 22 is shown in FIG. In FIG. 2 (and FIG. 3), illustration of the thermocouple inserted into the electrode rod 22 is omitted. The surface of the end region, which is the lower end of the electrode rod 22 and is expected to touch the molten metal, is covered with two types of protective coatings. The surface of the base material of the electrode rod 22 is covered with a first protective coating 26 mainly composed of carbon oxynitride carbon nanofibers. On the surface of the first protective film 26, a second protective film 28 containing fullerene as a main component is formed.

  FIG. 3 shows a state near the surface layer of the electrode rod 22. FIG. 3 is a diagram schematically showing a microscopic cross section of a portion surrounded by reference numeral III in FIG. The first protective film 26 is formed as follows, for example. After the nitronitriding process is performed to form the oxynitride layer 22a on the surface of the electrode rod 22, the electrode rod 22 is heated together with a carbon-containing gas (for example, acetylene gas) in a nitriding atmosphere. Then, carbon contained in the acetylene gas becomes carbon nanofibers, and is deposited so as to grow from the surface 22b of the oxynitride layer 22a. Here, the precipitation means that the gasified carbon is solidified on the surface 22b of the nitrosulfuration nitride layer 22a without passing through the liquid phase, and further grows in a fiber shape. A curve like a whisker indicated by reference numeral 26a in FIG. 3 schematically shows the carbon nanofibers that grow from the surface 22b. A layer formed of the carbon nanofibers 26 a extending from the surface 222 b corresponds to the first protective coating 26. Acetylene gas is often used as a raw material for nanocarbon.

  Regarding the deposition of carbon nanofibers on the metal surface, refer to, for example, Japanese Patent Application Laid-Open Nos. 2010-137155 and 2010-036194. In addition, nitronitriding is a process in which an iron or stainless steel material is heated to 400 ° C. to 600 ° C., and mainly nitrogen is diffused on the surface of the material to diffuse carbon, sulfur, etc. (Sulfur nitride layer). Note that the shaded area indicated by reference numeral 22a in FIG. 3 schematically shows the oxynitride layer. This oxynitride layer improves the hardness of the material and improves the wear resistance (melting resistance) and seizure resistance. Since the nitronitriding treatment is well known as a treatment for improving the wear resistance (melting resistance) and the like of the metal, further detailed explanation is omitted.

  The second protective coating (the coating agent) is typically fullerene. The particle size of fullerene is about 1 nm (nanometer). On the other hand, the carbon nanofiber has a size of about 100 nm. When fullerene is applied onto the first protective film 26 of the carbon nanofiber, as shown in FIG. 3, the surface of the fiber of the carbon nanofiber is schematically shown as understood from the ratio of the sizes. Fullerene adheres to the whole. A large number of circles indicated by reference numeral 28a in FIG. 3 schematically represent fullerenes. Carbon nanofibers and carbon of fullerene attract each other by the action of van der Waals bonds, so they are firmly connected to each other. A layer formed by many fullerenes corresponds to the second protective film 28. As shown in FIG. 3, since fullerene adheres around the carbon nanofibers, the surface layer of the first protective coating 26 and the lower layer of the second protective coating 28 partially overlap each other. As described above, fullerenes enter between the fibers of the carbon nanofibers, and both are firmly bonded by van der Waals bonding, so that the second protective film mainly composed of fullerenes can be expected to have high resistance to melting.

  The 1st protective film 26 should just have carbon nanofiber as a main component, and an additive etc. may be mixed in addition. Similarly, the second protective coating 28 may be fullerene as a main component, and may contain other additives.

  The color of the surface of the electrode rod 22 on which the first protective film 26 mainly composed of carbon nanofibers is formed is true black. When the second protective film 28 mainly composed of fullerene is formed thereon, the color of the surface of the electrode rod 22 becomes dark gray. By the above processing, the electrode rod 22 in which two types of protective coatings (first protective coating 26 and second protective coating 28) having different colors are superimposed is completed.

  An experiment was conducted to confirm the effect of the double protective coating. As a simulated electrode rod, a SKD steel rod was prepared. After carbon nanofibers were deposited on the simulated electrode rod, fullerene was applied. The surface of the simulated electrode bar on which the two-layer protective film was formed was dark gray in the initial state. After immersing the simulated electrode rod in a molten aluminum at 700 ° C., two types of experiments were conducted to visually confirm the color of the surface.

  (First Experiment) The simulated electrode bar in the initial state was immersed in a molten aluminum at 700 ° C. for 1 minute and then pulled up. At this time, the surface of the simulated electrode rod was changed to brown. Thereafter, the simulated electrode bar having a brown surface was again dipped in molten aluminum at 700 ° C. for 1 minute and pulled up. At this time, the surface of the simulated electrode rod was changed to light gray. In the first experiment, the simulated electrode rod was immersed in molten aluminum at 700 ° C. for a total of 2 minutes.

  (Second Experiment) A simulated electrode rod in the initial state (having a dark gray surface) was immersed in a molten aluminum at 700 ° C. for 30 seconds and then pulled up. The surface color was changed to black. The fullerene was then reapplied to the surface. After reapplication, the surface color changed to dark gray. Subsequently, the simulated electrode bar after fullerene re-application was dipped in molten aluminum at 700 ° C. for 30 seconds and pulled up. The surface of the simulated electrode bar was changed to black. Next, fullerene was applied again to the surface. After re-application, the surface color changed to dark gray. Next, the simulated electrode bar after re-application of fullerene was immersed in molten aluminum at 700 ° C. for 30 seconds and pulled up. Even at this time, the surface was changed to black. Further, fullerene was applied again on the surface. The surface after application again changed to dark gray. Next, the simulated electrode bar after repeated application of fullerene was immersed in molten aluminum at 700 ° C. for 30 seconds and pulled up. The surface was turned black. So far, it has been immersed in molten aluminum at 700 ° C. for a total of 2 minutes. Thereafter, the simulated electrode was immersed in a molten aluminum at 700 ° C. for 30 seconds four times. The fullerene was not applied between the immersions for 30 seconds. The surface of the simulated electrode was light gray after being immersed in the molten aluminum at 700 ° C. for 2 minutes from the re-application of fullerene for a total of 4 minutes from the initial state.

  (Experimental Consideration) In the first experiment, the change to brown after immersion for 1 minute was caused by the disappearance of the fullerene of the second protective coating, and the first protective coating (carbon nanocarbon directly contacting the 700 ° C. molten aluminum). This is caused by the burning of the fiber). In addition, the light gray after immersion for a total of 2 minutes in the first experiment almost disappears the first protective film, and the color of the bare metal of the simulated electrode rod (SKD material) is visible. In the second experiment, fullerene is repeatedly applied, so that the original state (dark gray) can be maintained even after immersion in the molten metal for 2 minutes in total. As described above, the black color is black after the first protective film is formed, and the color is dark gray after the second protective film is formed. The time when the surface color of the electrode rod changes from dark gray to true black during repeated immersion in the molten metal is a suitable timing for recoating fullerene. In addition, even if it is not immediately after the surface has changed to black, it is a period suitable for re-coating fullerene (coating agent) from when it becomes black to brown. Until the surface becomes brown, the first protective film remains, so that the electrode rod itself does not melt. If possible, it is preferable to re-apply the coating agent for the second protective coating before the color changes to brown, that is, while the surface of the electrode rod is black.

  As in the second experiment, when the surface of the electrode rod changes from the color of the second protective coating to the color of the first protective coating, a maintenance method for the electrode rod (metal melt detection sensor) is reapplied with the coating agent for the second protective coating. Is advantageous in that recoating can be performed before the electrode rod begins to melt, and the film thickness does not increase even if recoating is repeated.

  Points to note about the technology disclosed in this specification will be described. When forming the first protective coating of the carbon nanofiber, a nitronitriding treatment is performed to form a nitronitriding layer on the surface of the electrode rod. The nitrosulfurized layer has not only high resistance to melting damage (wear resistance) itself, but also has an advantage that carbon nanofibers are easily fixed to the nitrosulfurized layer. That is, a high resistance to melting can be expected for the second protective coating layer. Furthermore, since the fullerene of the second protective coating enters the gaps between the carbon nanofibers and the fullerene is firmly fixed to the van der Waals force, the second protective coating can be expected to have high resistance to melting.

  Moreover, both carbon nanofibers and fullerenes are carbon and have high thermal conductivity. Therefore, the protective coating containing them as a main component has little influence on the heat transfer characteristics of the electrode rod itself. Therefore, a protective coating mainly composed of carbon is suitable as a coating agent for an electrode rod in which a thermocouple is charged.

  As a main component of the second protective film, boron nitride (BN) or silicon oxide (SiO 2) may be used instead of fullerene. Boron nitride (BN) and silicon oxide (SiO 2) have the same particle size as fullerenes and can be easily combined with carbon elements, so that the same effects as fullerenes can be expected.

  Conventionally, as a coating agent for protecting a metal object such as an electrode rod from the melting damage of molten aluminum, a mixture of a ceramic fine particle (for example, titanium oxide TiO) and a binder is often used. It is also known that graphite is also used as a coating agent. When these conventional coating agents are used, the effect is as high as the combination of the first protective coating mainly composed of carbon nanofibers and the second protective coating composed mainly of fullerene (or boron nitride, silicon oxide). Cannot be expected. For example, in a combination in which a coating agent mainly composed of a ceramic system is used as the first protective coating and graphite is applied as the second protective coating, both may be mixed when applying the graphite. In this combination, the second protective film made of graphite is more easily peeled off than the combination of carbon nanofiber + fullerene.

  For example, when graphite is applied on the first protective film mainly composed of carbon nanofibers, the carbon nanofibers may be oxidized first under the graphite. This is because graphite has a larger particle size than fullerene. It is presumed that the graphite particles do not enter the gaps between the carbon nanofibers but only cover the carbon nanofibers, resulting in a steamed state.

  After the application of the second protective film composed mainly of fullerene, the surface of the electrode rod is dark gray. When the second protective coating disappears and the first protective coating of the carbon nanofibers is exposed, the surface becomes black. Thus, when “two types of protective coatings with different colors” are referred to, in this specification, even when the density is different, such as dark gray and light gray, or true black, it is included in the expression “different colors”. Please note that.

  In the embodiment, a waist mat type molten metal supply device using a molten metal detection sensor is taken as an example. The molten metal detection sensor disclosed in the present specification can also be used in a molten metal supply apparatus using a ladle. In this case, the molten metal detection sensor is installed as a ladle or in the vicinity of the ladle, and is used as a sensor for detecting the height of the molten metal surface (liquid level) relative to the ladle.

  Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above. The technical elements described in this specification or the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology exemplified in this specification or the drawings can achieve a plurality of objects at the same time, and has technical usefulness by achieving one of the objects.

2: Molten metal supply device 4: Pressurizing pump 6: Molten metal tank 7: Molten metal guide tube 21: Controller 22: Molten metal detection sensor (electrode bar)
26: First protective coating 28: Second protective coating 30: Sleeve W: Molten metal

Claims (4)

It is a molten metal detection sensor equipped with an electrode bar that detects the presence of molten metal by contacting it,
A molten metal detection sensor characterized in that a first protective film is formed on the surface of the electrode rod, and a second protective film having a different color from the first protective film is formed on the surface of the first protective film. .   The molten metal detection sensor according to claim 1, wherein the first protective coating is mainly composed of carbon oxynitride nanofibers.   3. The molten metal detection sensor according to claim 1, wherein the second protective coating contains at least one of fullerene, boron nitride, and silicon oxide as a main component. A maintenance method for a molten metal detection sensor having an electrode bar having a first protective coating formed on the surface and a second protective coating having a different color from the first protective coating on the surface of the first protective coating. Yes,
A maintenance method comprising applying a second protective coating when the electrode rod changes from a color of the second protective coating to a color of the first protective coating.

Images