JPS63120897A - Ceramic pump for melted metal - Google Patents

Abstract

PURPOSE:To prevent a pump for metal from abnormalities like cracks or the like generated by thermal shock while improving anti-wear property and corrosion resistance by forming portions contacting liquid such as impeller, shaft, column and discharge pipe of silicon nitride ceramic according to atmospheric sintering process. CONSTITUTION:a pump used for transferring and circulating melted metal in a furnace receives a column 4 having the upper end mounted to a frame bed 8 by flanges 6, 7 and an impeller 3 having a casing 1 mounted on the lower end of a discharge pipe 5 and the lower end of a shaft 2 fixed to the interior of the casing. The upper end of shaft 2 is connected to the output shaft 11a of a drive motor 11 through shaft joints 9a, 9b and a universal joint 10. Then, the shaft 2, impeller 3, column 4 and discharge pipe 5 of portions contacting liquid for example are molded of silicon nitride ceramic according to atmospheric shintering process. Also, the casing 1 is made of carbon, and a discharge vent pipe 13 of ceramic fiber.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention is applicable to industries that handle molten metal such as molten aluminum;
For example, the present invention relates to improvements in molten metal pumps used for transporting molten metal or circulating it in furnaces in the smelting or scouring industry, plating industry, die casting industry, and the like.

[Prior technology] Originally, molten metal was transferred by hand, but from the viewpoint of improving work efficiency, economy, and ensuring safety, automatic, continuous, and large-scale transfer was made possible. There was a high demand for a dedicated pump.

For this reason, pumps made of low carbon steel or carbon have been developed and used as pumps for transporting molten metal. is corrosion caused by molten metal,
It had the disadvantage of being subject to significant wear and having an extremely short service life. Even when made of carbon, which has relatively corrosion resistance, rotating parts such as impellers and shafts only have a service life of about 480 to 720 hours at most, while low carbon steel has a service life of about 8 to 10 hours. Ta. In other words, it is used almost as a consumable item, and although it is expected that efficiency will be improved by using a pump, there are major problems in terms of economic efficiency and maintenance work, and the effectiveness of using a pump is not recognized. However, due to the lack of dedicated pumps with a long service life, there are still many sites where transport is still carried out manually.

Therefore, in order to deal with this current situation, the applicant proposed the following:
We have previously developed and provided a hanging type and molten metal immersion type molten metal pump made of ceramic paulownia material, especially silicon nitride ceramic made by the reaction sintering method. This was based on the recognition that silicon nitride produced by reactive sintering is superior in terms of corrosion resistance, thermal shock resistance, and resistance to wetting, compared to silicon nitride produced by atmospheric pressure forming. . Structurally, it consists of a column and discharge pipe whose upper ends are attached to an upper frame, a casing supported by the lower ends of the column and discharge pipe, and a suction port installed in the casing at the top or bottom. The impeller is composed of a substantially cylindrical impeller having a large number of discharge ports on its circumferential surface, and a shaft that supports the impeller and is connected to a drive motor at its upper end on a pedestal. The shaft is molded from silicon nitride ceramic material using a reaction sintering method.

[Problems to be Solved by the Invention] Using the molten metal pump having the above configuration, the molten metal temperature is 505.
When tested on an actual machine by immersing it in a molten zinc furnace at a temperature of ~540°, there was almost no zinc adhesion, no cracking due to thermal shock, and no phenomena such as corrosion or wear. The time period was also significantly extended, and very favorable results were obtained.

However, new problems arose in subsequent research.

That is, when the above pump was used for molten aluminum alloy castings, adhesion and growth of molten metal was observed on the outer surface of the ceramic material, especially near the gas-liquid interface, and metal adhesion to the peripheral wall of the impeller outlet or foreign matter clogging the outlet. Unexpected accidents occurred due to this, such as inability to pump the liquid, and breakage of the shaft due to the shaft being crushed due to contact between the drain of the vortex chamber and foreign matter adhering to the discharge port.

After intensive research into these causes, we found that the problem was that on the moon phase surface using silicon nitride using the reactive sintering method, silicon nitride reacts with molten aluminum to form extremely hard aluminum nitride. It turns out that there is something.

For example, a metal object that has grown on the shaft is strongly bonded to the ceramic base material, and when an attempt is made to remove it, the ceramic itself eats away, resulting in the surface being chipped. When this peeled piece was observed and analyzed using an optical microscope, EPMA analysis, and X-ray diffraction, aluminum nitride, a product compound with extremely high hardness, was detected. This aluminum nitride was also detected in leaf outlet obstructions.

Therefore, silicon nitride ceramics produced by the reaction sintering method are unsuitable for applications such as molten aluminum alloy castings, and there is a need for further improvements.

Therefore, it is an object of the present invention to prevent the occurrence of cracks due to thermal shock, to prevent the adhesion and growth of molten metal, and to prevent the occurrence of cracks due to thermal shock, not only in molten zinc but also in molten aluminum or molten aluminum alloy castings. It is an object of the present invention to provide a molten metal pump which can be operated in good condition for a long period of time without any self-eating phenomenon.

[Means for solving the problems] In order to achieve the above objectives, we reexamined the pump material and pump structure. Since ceramic materials are preferred as pump materials that require corrosion resistance, we went back to the basics and explored the applicability of silicon nitride ceramics, one of the silicon nitride ceramic materials, by pressureless sintering.

That is, a test piece in the shape of a discharge pipe was made from silicon nitride ceramic using the pressureless sintering method, and the
A thermal shock resistance test was conducted by immersing the lower part in a molten aluminum alloy casting whose temperature was raised to . When the temperature of the upper part of the test piece reached 150° due to heat conduction and radiant heat (humidity difference: 505°), molten metal was passed through the tube and visually observed. No other abnormalities were observed.

Silicon nitride produced by pressureless sintering has a lower porosity and is denser than silicon nitride produced by reaction sintering, and has higher hardness, so it has superior wear resistance. Furthermore, it has excellent bending strength and mechanical strength. Looking at thermal conductivity, silicon nitride produced by pressureless sintering is superior, and is predicted to have high thermal shock resistance. In addition, although difficulty in wetting or non-reactivity with molten aluminum or molten aluminum alloy castings is a problem, satisfactory test results were obtained in this regard as well, confirming the suitability of the material as a molten metal pump material. be.

Therefore, this invention is characterized by selecting silicon nitride ceramic, especially silicon nitride ceramic made by pressureless sintering method, as the material for the molten metal pump, and also improves the pump structure, especially the structure of the impeller. The structure is such that blockage is unlikely to occur.

That is, the ceramic molten metal pump of the present invention is
The casing is supported by the column whose upper end is attached to the frame and the lower end of the discharge pipe, and the impeller is attached to the lower end of the shaft connected to the output shaft of the drive motor at the upper end. The shaft and column are located in the vortex chamber of the casing and are made of silicon nitride ceramic by pressureless sintering and are made of ceramic, including at least the impeller and the shaft, more preferably the column and the discharge pipe. It is formed into a hollow shape.

As mentioned above, the structure of the impeller is semi-oven-shaped with blades on the bottom surface to avoid clogging of molten metal as much as possible. In consideration of improving thermal shock resistance, it is preferable to avoid the presence of a thick solid part, similar to making the column and shaft hollow. Therefore, the structure of the impeller is preferably a cashier oven type with blades on the bottom, and is fastened to the shaft at the central boss, and the impeller is attached to the inner peripheral surface of the impeller installation hole formed in the casing. It is desirable to have a structure in which a recess for reducing wall thickness is provided between the opposing outer circumferential surface and the boss portion.

[Function] As described above, in the present invention, in a molten metal pump, the entire wetted part including the impeller and shaft, more preferably the column and the discharge pipe, and even more preferably the casing, which are exposed to extremely severe conditions. Since it is molded with silicon nitride ceramic, especially silicon nitride ceramic made by pressureless sintering, there is no abnormality such as cracking due to thermal shock, and it has excellent corrosion resistance against molten metal, as well as wear resistance and wetness resistance. In particular, compared to silicon nitride ceramics made using the reactive sintering method, it has no reactivity to molten aluminum or molten aluminum alloys, and is highly effective against molten zinc as well as molten aluminum and molten aluminum. A molten metal pump that can be applied to alloys, etc. has been achieved.

In addition, since the impeller has a semi-oven structure with blades on the bottom surface, it is possible to avoid clogging the impeller with molten metal, resulting in a favorable operating condition over a long period of time.

[Embodiment] Fig. 1 is a longitudinal cross-sectional view showing an embodiment of the molten metal pump according to the present invention, in which symbol @1 is a casing, 2 is a shaft,
3 is an impeller, 4 is a column, and 5 is a discharge pipe.

The casing 1 is supported by inserting the upper ends of the column 4 and the lower ends of the discharge pipe 5, which are respectively attached to a frame 8, through set flanges 6 and 7, and solidifying them with heat-resistant mortar. The impeller 3 is supported by a shaft 2 screwed into a central boss portion 3a, and is installed in the casing 1 through the impeller installation hole 1a so that the blades 3b on the bottom surface are located in the swirl chamber 1b of the casing 1. As shown in the figure, the upper end of the shaft 2 has @lI joints 9a and 9b.
and is connected to an output shaft 11a of a drive motor 11 via a universal joint 10.

12 is a motor stand mounted on the pedestal 8.

Reference numeral 13 denotes a discharge vent pipe connected to the upper end of the discharge pipe 5. Nuts are screwed to both ends of the bolt passed through the flange portion, the frame 8, and the set flange 7, and the set flange 7 is connected to the discharge vent pipe 13.
Both are fixed to a pedestal 8.

Both set flanges 6 and 7 have a two-part structure, and are held so as to hold the upper ends of the column 4 and discharge pipe 5 with bolts and nuts fastened to the mating flanges 6a and 7a. Reference numeral 14 uses ceramic paper in the gaskets 1 to 1 installed between the discharge pipe 5 and the discharge vent pipe 13.

In this example, the shaft 2, impeller 3, column 4
The discharge pipe 5 is made of silicon nitride ceramic made by pressureless sintering, the casing 1 is made of carbon, and the discharge vent pipe 13 is made of ceramic fiber. In order to improve thermal shock resistance, the column 4 and shaft 2 are also hollow.
A heat insulating tube 15 made of ceramic fiber is attached to the inner surface of the discharge pipe 5 above the gas-liquid interface.

In addition, the semi-oven-shaped impeller 3 with blades 3b provided on the bottom has a recess 3C for reducing wall thickness between the outer circumferential surface facing the inner circumferential surface of the impeller installation hole 1a formed in the casing 1 and the boss portion 3a. is poorly formed. 16 is heat-resistant mortar that fills this recess 3C. In addition, the inner peripheral surface of the impeller installation hole 1a in the casing 1 and the opposing surface in the vortex chamber 1b, where the lower end surface of the blade 3b is opposed, are each lined with silicon nitride ceramic made by pressureless sintering to prevent wear. Parts 17.18 are installed. 19 is a suction hole, and 20 is a baffle plate attached to the lower end of the casing 1.

Figure 5 shows the other side of the impeller 3, which has a horizontal protruding edge 3d on the outer periphery of the upper surface that protrudes along the upper surface of the casing 1, making the gap passage between the casing and the impeller as long as possible. This provides a pressure loss and suppresses leakage from the inside of the casing as much as possible, and also prevents blow-out in the vertical direction when the molten metal level drops during pump operation.

Using the molten metal pump based on Fig. 1 above, the molten metal temperature is 7.
Molten metal was pumped from molten aluminum alloy castings at a temperature of 20 to 750°C.

Prior to pump operation, the pump was preheated as follows.

Suspend the pump using the lifting device and raise it approximately 5 to 1 cm above the molten metal surface.
The sample was held at the 0# position and first incubation was performed for about 30 minutes. Then 30-40uvn/4Hin.

The sample was gradually immersed into the molten metal at a rate of descent of 30 minutes, and was preheated in a stationary state for 30 minutes. At this point, the upper part of the discharge pipe is about 1
The temperature was raised to 50°C. At this point, the pump was operated and the liquid was pumped out, and the molten aluminum alloy castings were smoothly pumped out.

Once the specified meter has been pumped out, it will remain immersed in the molten metal until the next pumping.
The equipment was repeatedly started and stopped by pulling it out of the melter and preheating it again before starting work. As a result, smooth operation continues even after several months have passed, with almost no adhesion of molten aluminum alloy castings, and even the slightest adhesion of molten aluminum alloy castings can be easily scraped off by rubbing.
No self-eating phenomenon was observed. Of course, there was no occurrence of cracks due to thermal shock, no corrosion of the parts in contact with the liquid, and no clogging phenomenon was observed inside the casing.

[Effects of the Invention] As described above, the ceramic molten metal pump according to the present invention has excellent corrosion resistance, abrasion resistance, and heat rain shock resistance even when used with molten zinc, molten aluminum, and molten aluminum alloy. This pump is ideal for transporting molten metal or for circulating inside the furnace, as it has superior properties such as durability, carbon resistance, and reaction resistance, and can effectively avoid blockage accidents due to its structure. It could have been provided.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view showing an embodiment of the ceramic molten metal pump according to the present invention, FIG. 2 is an enlarged vertical cross-sectional view of only the impeller in the same pump, FIG. 3 is a bottom view of the pump, and FIG. FIG. 4 is a longitudinal cross-sectional view of the casing, and FIG. 5 is a longitudinal cross-sectional view of the main parts showing the other features of the impeller.

Claims (4)

[Claims] (1) The casing is supported at the lower end of the column and discharge pipe, the upper end of which is attached to the pedestal, and the impeller is attached to the lower end of the shaft connected to the output shaft of the drive motor at the upper end. A shaft located in a vortex chamber of a casing having a suction hole, including at least an impeller and a shaft, more preferably a column and a discharge pipe, made of silicon nitride ceramic by pressureless sintering and made of ceramic. A ceramic molten metal pump formed by forming a column into a hollow shape. (2) The impeller having blades on the bottom is fastened to the shaft at the central boss, and there is a recess for reducing wall thickness between the boss and the outer circumferential surface facing the inner circumferential surface of the impeller installation hole formed in the casing. A ceramic molten metal pump according to claim 1. (3) On the inner circumferential surface of the installation hole where the opposing surface of the lower end surface of the blade in the vortex chamber of the casing and the outer circumferential surface of the impeller face,
The ceramic molten metal pump according to claim 1 or 2, which is provided with a lining member made of silicon nitride ceramic made by pressureless sintering. (4) The ceramic molten metal pump according to claim 3, wherein the impeller has a horizontal protrusion on the outer periphery of the upper surface that projects along the upper surface of the casing.