JPH0218317B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a sliding member made of a high-density silicon carbide sintered body for a hydrodynamic seal, and a method for machining grooves on the sliding end surface of the sliding member. It is related to. [Prior Art] As is well known, high-density sintered bodies of silicon carbide (hereinafter referred to as SiC sintered bodies) have excellent heat resistance, wear resistance, and corrosion resistance. Ceramic materials are highly anticipated as materials for gas turbines, for example, and the earliest material to be put into practical use was as a sliding member for mechanical seals, and is now considered the best material due to its excellent properties. It is positioned as a sliding member that exhibits the following performance. On the other hand, along with the development of technology, the usage environment for this type of mechanical seal is becoming more and more severe day by day. There is a tendency for things to become even more complex. At this time, the structure of the so-called hydrodynamic seal, in which grooves were machined on the sliding end face with the intention of improving lubricity on the sliding end face and promoting cooling performance, was developed. It is attracting attention as a cutting-edge seal design technology, and the use of SiC sintered bodies, which are currently the highest-grade sliding components, in hydrodynamic seals is of course the highest-grade mechanical component. It is nothing more than providing a seal. [Problems to be solved by the invention] However, this type of commonly used SiC sintered body is a material with extremely high hardness and excellent wear resistance, so machining is not easy. Although it has high hardness, it is also a brittle material, so aggressive machining that ignores these properties can result in machining scratches and other defects.
There is a risk of destruction, and furthermore, since it is corrosion resistant, it is difficult or almost impossible to perform etching processes using chemical agents. Therefore, the present invention provides a sliding member made of high-density silicon carbide sintered body for hydrodynamic sealing, and a sliding end face of the sliding member in order to use the sliding member for hydrodynamic sealing. It is an object of the present invention to provide a method by which groove machining can be performed accurately and easily. [Means for Solving the Problems] In order to achieve the above object, the present invention provides a sliding member made of a high-density silicon carbide sintered body, in which a groove for lubrication is formed in a required portion of the sliding end surface. This is a sliding member made of high-density silicon carbide sintered body for hydrodynamic seals. In addition, this method of machining grooves on the sliding end face of a sliding member made of high-density silicon carbide sintered body for hydrodynamic seals has a high density The sliding member is coated with a decomposition inhibitor having a melting point higher than the decomposition point of the silicon carbide sintered body, and then the coated sliding member is coated at a temperature higher than the decomposition point of the high-density silicon carbide sintered body and without the decomposition inhibitor. Heat treatment is performed at a temperature lower than the melting point to sublime and decompose the groove-forming portion to be processed to a predetermined depth by heat treatment at a temperature lower than the melting point, and then the coating is removed by oxidation, chemical treatment, or mechanical treatment. The coating is removed. [Example] Hereinafter, a sliding member made of a high-density SiC sintered body for a hydrodynamic seal having a sliding end groove according to the present invention, and a method of machining the sliding end groove of the sliding member are shown in Fig. 1a. This will be explained in detail with reference to d to d. Generally, high-density SiC sintered bodies are made by adding a predetermined amount of a boron-based compound and/or an aluminum-based compound as a sintering accelerator to a finely powdered raw material of highly purified silicon carbide. It is constructed by adding and mixing a predetermined amount of carbon as a material, molding, and firing in an inert atmosphere at a high temperature of 2000°C or higher. When the high-density SiC sintered body configured in this way is used as a sliding member of a mechanical seal,
The sliding end surface is lapped for use. On the other hand, the sliding member of this type of mechanical seal has certain sealing characteristics under high load usage conditions, that is, under high pressure and high speed.
To improve the PV value and the PVT value at high temperatures, mere boundary lubrication between the seal sliding end faces is insufficient, and even if some seal leakage is allowed, the sliding It uses a so-called hydrodynamic seal structure with grooves for lubrication formed on the end face, but as mentioned earlier, this high-density SiC sintered body as a sliding member is
Secondary processing after sintering is extremely difficult, and the formation of lubrication grooves on the sliding end surface for the hydrodynamic seal structure is no exception. Therefore, the inventors conducted intensive studies on forming grooves in order to make the sliding member made of the high-density SiC sintered body into a hydrodynamic seal structure, and as a result, they discovered the following means. In other words, once fired, the high-density SiC sintered body is
Normally, self-sublimation decomposition occurs at temperatures above 2000℃, and decomposition starts at around 1900℃ under vacuum and reduced pressure.Using this sublimation decomposition reaction (SiC-→Si↑+C), desired unevenness can be created on the sliding end surface. In order to effectively utilize the sublimation decomposition reaction in this way, the entire surface of the sliding end surface, except for the groove forming part, is made of high-density SiC sintered material. After coating with a decomposition inhibitor that has a melting point higher than the decomposition point of the high-density SiC sintered body, heat treatment is performed at a temperature higher than the decomposition point of the high-density SiC sintered body and lower than the melting point of the decomposition inhibitor, so that the material is not coated. This is a novel technical means for forming grooves by sublimating and decomposing the groove-forming portion to be processed over a predetermined depth range. Next, regarding a preferred embodiment of this invention, the first
This will be explained in detail with reference to figures a to d. In this embodiment, a high-density SiC sintered body formed into a predetermined sliding member shape and fired at a predetermined sintering temperature is used. First, as shown in Figure 1a, high-density SiC molded into a predetermined shape
The entire surface of the sliding member 1 made of a sintered body, in this case, a predetermined surface including at least the sliding end surface 2, is lapped. Next, as shown in Figure b, the entire surface of the sliding end surface 2 except for the groove forming portion 2a has a high melting point and is heated at a sintering temperature of, for example, 2000°C. In the following, a decomposition inhibitor 3 made of a substance having a low vapor pressure and not causing a sublimation decomposition effect is coated. Here, as the decomposition inhibitor 3, carbon, carbide such as B ₄ C, TiC, etc., or boride such as TiB ₂ , ZrB _2, etc.
Furthermore, tungsten, molybdenum, etc. can be used, and the coating method may be a spray coating method, a dipping method, a printing deposition method, a CVD method, a PVD method, or the like. Next, the coating-treated sliding member 1 is placed in a vacuum furnace at 1900°C under reduced pressure.
Heat treatment is performed at a temperature higher than that. That is, by this heat treatment, as shown in FIG. A concave groove 4 is formed in the same portion 2a.
Here, the heat treatment temperature is preferably controlled at 1900°C or higher, preferably so as not to exceed the sintering temperature of the high-density SiC sintered body as the sliding member 1; This is to avoid the risk of causing changes in the internal structure of the sintered body if it exceeds this range. Furthermore, the depth of the concave groove 4 can be freely adjusted by controlling the heat treatment temperature and heat treatment time. Thereafter, as shown in FIG. Thus, a sliding member 1 having a groove 4 for lubrication formed therein is obtained. In this case, it is effective to use carbon as the decomposition inhibitor 3 that forms the coating.When using this carbon, it is effective for masking action during heat treatment, and it can also be removed after heat treatment by oxidation treatment. It is easy to perform and, if necessary,
If the uneven grooves 4 are processed by sublimation and decomposition of only the sliding end surface 2, mechanical removal can be easily performed even by a simple lapping process. In addition, since this sliding member 1 is a hydrodynamic seal, when the fluid to be sealed is oil-based, in order to more stably retain the lubricating oil in the groove 4, the lubricating oil is generated by sublimation and decomposition. Since the carbon layer in groove 4 is lipophilic, it is better to leave it as is.If the fluid to be sealed is aqueous, conversely, the carbon layer in groove 4, which is generated by sublimation and decomposition, is hydrophobic. Therefore, after the decomposition process, the carbon layer in the groove 4 is removed by oxidation treatment, etc., and an oxide film such as hydrophilic SiO ₂ is formed in the groove 4. It is preferable to improve the effectiveness of water lubrication. Next, more specific examples will be described. Example 1 α-SiC powder (1000 g) with an average particle size of 0.7 μm,
B ₄ C (5 g) with an average particle size of 0.5 μm was placed in a ball mill, and 40 g of phenolic resin with a residual carbon content of 50% was added.
20 g of PEG and 10 g of stearic acid were added and mixed as a methanol solvent. Then, after drying and granulating with a spray dryer, 10 molded bodies of 70φ×50φ×10 ^t were manufactured using a mold at a molding pressure of 1500Kg/cm ² . After setting this compact in a firing furnace, the temperature was raised to 1600°C under vacuum (below 10 ^-1 Torr), then Ar gas was introduced, the temperature was raised to 2100°C under atmospheric pressure, and the temperature was maintained for 1 hour. Firing has finished. After cooling, this high-density SiC
All of the sintered bodies had a density of 3.15 to 3.16 g/cm ³ and exhibited a linear shrinkage rate of about 18%. Moreover, the internal structure of this high-density SiC sintered body is 5
It was composed of crystal grains of ~10 μm, and no particularly large grain growth structure was observed. The high-density SiC sintered body was polished into a 54φ x 41φ x ^7t seal ring, and the sliding end surface was lapped and polished with diamond paste. In order to form grooves 4 on the sliding end surface obtained in this way, such as those formed on the sliding end surface 2 shown in FIG. Carbon paste was printed on the sliding end surface, and the other surfaces were coated with carbon paste by brushing. The above treated product was subjected to decomposition heat treatment under the conditions shown in Table 1 below.

[Table] As mentioned above, the decomposition treatment conditions for the sliding end face groove processing method are preferably 1900°C to 2000°C under vacuum.
If the temperature exceeds 2000℃, decomposition will be accelerated and some decomposition will occur from the coating, making accurate groove machining difficult. On the other hand, at temperatures below 1900°C, decomposition is almost suppressed and grooving cannot be performed. In particular, when the treatment temperature is raised to the firing temperature of a high-density SiC sintered body, as shown in Comparative Product 3, not only is the decomposition significant, but grain growth occurs in the structure of the sintered body, making it undesirable as a sliding material. Experimental Example 2 Seal rings based on the above-mentioned products 1, 4, and 5 of the present invention were installed in a mechanical seal tester and a rotation test was performed under the following conditions. As a result, as shown in Table 2 below,
In both cases, the amount of leakage increased slightly, but the coefficient of friction decreased significantly, and almost no wear was observed. [Conditions] Fluid (fresh water), pressure (10Kg/cm ² ), rotation speed
3600rpm (8.9m/s), flushing amount (3/
min)

[Table] (Effects of the Invention) As described above, according to the present invention, in the sliding member made of high-density silicon carbide sintered body, a groove for lubrication is formed in the required portion of the sliding end surface, so that the heat resistant Hydrodyna not only has excellent wear resistance, wear resistance, and corrosion resistance, but also has significantly improved lubricity and cooling performance on the sliding end surface, making it suitable for use even under high load conditions. It is possible to provide a sliding member made of high-density silicon carbide sintered body for a mix seal. Further, according to the method of grooving the sliding end face of a sliding member made of a high-density silicon carbide sintered body for a hydrodynamic seal of the present invention, in the sliding member made of a high-density SiC sintered body, the sliding end face is covered. The entire surface except the part where the processed grooves are formed is coated with a decomposition inhibitor having a melting point higher than the decomposition point of the high-density SiC sintered body, and then the coated sliding member is
Grooving is performed by heat treatment at a temperature higher than the decomposition point of the high-density SiC sintered body and lower than the melting point of the decomposition inhibitor to sublimate and decompose the groove-forming portion to be processed that is not coated over a predetermined depth. and
After that, the coating was removed by oxidation, chemical treatment, or mechanical treatment, so it was difficult to create grooves for lubrication on sliding members made of high-density silicon carbide sintered body, which was extremely difficult in the past. It is characterized by being extremely easy to perform, and by controlling the temperature and time during heat treatment, the depth of the processed groove can be precisely adjusted.

[Brief explanation of drawings]

FIGS. 1a to 1d are enlarged sectional views of essential parts showing, in order of steps, an embodiment of the method for machining sliding end grooves of a high-density SiC sintered sliding member having sliding end grooves according to the present invention; FIG. 2 is a plan view showing an example of a hydrodynamic sliding member. 1...Sliding member made of high-density silicon carbide sintered body, 2...
...Sliding end face of the sliding member, 2a... Processed groove forming portion of the sliding end face, 3... Anti-decomposition agent coated, 4... Groove formed in the sliding end face.

Claims (1)

[Claims] 1. Regarding a sliding member made of high-density silicon carbide sintered body,
A sliding member made of a high-density silicon carbide sintered body for a hydrodynamic seal, characterized in that a groove for lubrication is formed in a required portion of the sliding end surface. 2 A sliding member made of a high-density silicon carbide sintered body is used, and the entire surface of the sliding end face of the sliding member except for the groove forming part is heated to a temperature higher than the decomposition point of the high-density silicon carbide sintered body. The sliding member coated with a decomposition inhibitor having a melting point is then heat-treated at a temperature higher than the decomposition point of the high-density silicon carbide sintered body and lower than the melting point of the decomposition inhibitor. The groove forming portion to be machined which is not covered with the coating is sublimated and decomposed over a predetermined depth to form the groove, and then the coating is removed by oxidation, chemical treatment, or mechanical treatment. A method for machining grooves on the sliding end face of a sliding member made of high-density silicon carbide sintered body for dynamic seals.