Cementless pump for pumping molten metal

In a cementless pump for pumping molten metal, support structure is suspended above the molten metal. A motor is supported by the support structure. A shaft is fastened to the motor. An impeller is mounted to a lower end of the shaft. A refractory base is supported in the molten metal and includes at least one impeller chamber in which the impeller is rotated and at least one discharge passageway. The base includes through holes. Support posts are each fastened to the support structure and to the base. Refractory sleeves are each disposed in one of the through holes. Post fastening members fasten the lower ends of the posts to the base without cement. A portion of each of the post fastening members is located inside the refractory sleeve. Also featured is a method of replacing posts in a cementless pump for pumping molten metal.

TECHNICAL FIELD

The technical field is pumps for pumping molten metal and, in particular, the posts used in such pumps to connect a base in which the impeller rotates to a motor support structure.

BACKGROUND

Due to the oxidizing effects of molten metal, components of pumps in the molten metal inevitably wear out. Such components that wear out include the shaft for driving the rotor and the pump posts that support the base in the molten metal. When assembling a pump, a fixture may be used for aligning the posts relative to the base especially when cement is used. Cement is used to secure the posts to the base or to cap a bolt on the bottom of the base to prevent intrusion of molten metal. Once the pump is lifted from the molten metal to replace the posts, the usage of cement becomes problematic. The cement needs to be removed with a chisel since it is harder than the surrounding graphite of the base and resists machining After chiseling to remove the cement, the shapes of the holes that receive the posts become distorted. Thus, preparing the base to receive new posts becomes a labor intensive, drawn out process. Chiseling out the cement and possibly drilling new holes to receive replacement posts, aligning the posts and curing the cement holding the posts or caps in place can take two days. Thus, an improved pump and method for replacing posts without the need for cement would be advantageous.

TECHNICAL SUMMARY

This disclosure features a cementless pump for pumping molten metal. Support structure (e.g., a motor mount plate) is suspended above a bath of molten metal. A motor is supported by the support structure. A shaft is fastened at an upper end thereof to the motor and has a lower end. An impeller is mounted to a lower end of the shaft. A refractory base is supported in the bath of molten metal. The base includes at least one impeller chamber in which the impeller is rotated and at least one discharge passageway leading from the impeller chamber. The base includes through holes. Support posts are each fastened at an upper end thereof to the support structure and at a lower end thereof to the base. Refractory sleeves are each disposed in one of the through holes. Each of the support posts is connected to the base without cement by post fastening members, wherein a portion of each of the fastening members is located inside the refractory sleeve. For example, the fastening member can be a nut outside the base and a threaded bolt portion of the post extending through the through hole of the base, which is threaded to the nut. Alternatively, the fastening members can be formed wherein each post includes an internally threaded opening at the lower end. Another portion of the fastening member can be a bolt that includes a head, a shank extending from the head and an exteriorly threaded portion at an end of the shank. The shank is disposed inside the refractory sleeve and the threaded portion of the bolt is threaded to the internally threaded opening of the post so that the head engages the base. The posts are fastened to the base without use of any cement.

Turning now to specific features of the cementless pump, a refractory (e.g., fiber) gasket can be disposed between a lower surface of each of the posts and the base and between each of the post fastening members and the base (e.g., between the base and the nut or the head of the bolt). The posts, bolts and nuts can be made of refractory material such as ceramic or graphite. The base can be made of suitable refractory material such as graphite. The refractory sleeves are softer than graphite. For example the refractory sleeves are made of ceramic, such as an aluminum boron oxide. A density of the refractory sleeves can be not greater than 0.60 g/cm3, more particularly, not greater than 0.50 g/cm3, and specifically about 0.48 g/cm3.

Each of the refractory sleeves is configured and arranged to have an outer diameter and length that are the same as a diameter of the through holes and a length of the through holes, respectively.

In a method of replacing the posts of a molten metal pump, after the pump has been operated for awhile and the posts, shaft and/or rotor have become worn, it is desired to replace the posts, among other components of the pump. When the pump has been operated for an extended period of time, wherein the base and posts have been submerged in the molten metal bath, molten metal may enter the through holes of the base. This can be resisted by the use of gaskets between the posts and an upper surface of the base and between the post fastening member and the lower surface of the base but may not be altogether prevented. As a result, once the pump has been removed from the molten metal and cooled, the metal can form a crust inside the through holes. When cement is used to fasten or cap the bolts or posts to the base, as in conventional pumps such as the Tensor Post™ pump by Pyrotek Inc., it forms a very hard material on the base that requires chiseling to remove, which damages the shape of the through holes in the base. The cement is harder than the graphite material of the base, which causes deflection of the chisel or a drill when attempting to remove the cement. In contrast, when using the relatively soft refractory sleeves of this disclosure in the through holes, the refractory sleeves are easily removed without significant damage to the shape of the through holes. All that might remain is a thin crust of metal on the surface of the holes after the refractory sleeves have been removed, which can easily be scraped out.

In summary, the method of replacing the posts of a molten metal pump includes the following steps. After the pump has been operated and it is desired to replace the posts, the posts are cut near the upper surface of the base (e.g., through the bolts or through the elongated portion of the posts). For example, the cutting may occur through the threads of the bolt and any remaining piece of the post may be chiseled off the top of the bolt. The remainder of the bolt is removed from the through hole, such as by tapping a rigid rod into the through hole having a diameter somewhat less than the diameter of the through hole. The remaining refractory sleeve and any remaining metal adhered to the surface of the base that forms the hole can then be removed such as by scraping (e.g., without any need of machining) Then, replacement posts can be installed in the pump, along with the post fastening members, to form the cementless pump as described above.

The cementless pump of this disclosure is advantageous because it avoids the time and expense of applying cement to connect the posts to the base. To the inventors knowledge there are no pumps today for pumping molten metal that do not use cement to fasten or cap the posts, or bolts used with them, to the base. More importantly, once the posts need replacement in the cementless pump of this disclosure, the through holes that were formed in the base can be reused, because there is no problematic hardened cement that deflects drills and chisels and damages the through holes when removing the posts from the base. This will enable posts to be replaced efficiently and easily. Instead of at least two days of post rebuilding during which the cement is removed with difficulty, the base has new holes drilled in it to accommodate the damage of chiseling, and the cement is cured, the cementless pump and method of this disclosure will enable the posts to be replaced in a few to several hours without the need for chiseling, machining or curing of cement. When using the Tensor Post™ system of Pyrotek, an assembly fixture is needed to properly align the posts because there is play between the post and post holes for cement clearance. In contrast, an assembly fixture for aligning the posts during post replacement will not be needed in the cementless pump of this disclosure. The posts of this disclosure will be self positioning because of the snug fit of the post fastening member against the refractory sleeve and the machined through hole surface of the base.

Another advantage is that the cementless pump and method of this disclosure will minimize the investment in spare parts. Typically, to accommodate the expected need to replace the posts during every 2 weeks to three months, molten metal processors keep 2 replacement pumps on hand. Therefore, while a pump is being repaired a replacement pump is being used and a spare replacement pump remains. The device and method of this disclosure can eliminate one of the replacement pumps due to the substantially faster time to repair the posts of the pump and reduced pump down time in the event of failure of the replacement pumps. Occasionally, a major problem occurs during molten metal processing in which both replacement pumps are damaged or defective while a pump is having its posts replaced over a two day duration. This will require adding heat to maintain the temperature of the molten metal in the furnace while the pumps are being repaired. In contrast, if such a major problem occurs during the repair of the cementless pump of this disclosure, there is only at most several hours of down time. Thus, the cementless pump of this disclosure could result in savings of energy costs during such a major multiple pump failure problem.

The cementless pumps of this disclosure may include two, three or more stacked impeller chambers and associated impellers or impeller portions and discharge passageways, for various functions of transfer and circulation, as disclosed in U.S. Pat. Nos. 7,687,017 and 7,507,365, which are incorporated herein by reference in their entireties, and/or may be used for various functions of scrap submergence, circulation and transfer using a vortexer apparatus as disclosed in U.S. Pat. No. 7,497,988, which is incorporated herein by reference in its entirety. The cementless pump of this disclosure may also be used with the vortexer system disclosed in U.S. patent application Ser. No. 12/787,556, which is incorporated herein by reference in its entirety. Also, the cementless pump may include only a single impeller, a single impeller chamber and a single discharge passageway.

Many additional features, advantages and a fuller understanding of the invention will be had from the accompanying drawings and the detailed description that follows. It should be understood that the above Technical Summary describes the invention in broad terms while the following Detailed Description describes the invention more narrowly and presents preferred embodiments that should not be construed as necessary limitations of the broad invention as defined in the claims.

DETAILED DESCRIPTION

This disclosure features a cementless pump10for pumping molten metal. A motor mount plate12is suspended above a bath of the molten metal. A motor14is supported by the motor mount plate. A pump shaft16is fastened at an upper end17thereof to a drive shaft18of the motor. An impeller19is mounted to a lower end20of the pump shaft. A refractory base22is supported in the bath of molten metal. In the particular example shown, the base includes one upper transfer impeller chamber24and associated transfer discharge passageway26leading to a riser28for transfer to another location and one lower circulation chamber30and associated circulation discharge passageway32leading to an exterior opening34of the base. An impeller positioning device36, including various types of actuators and optional programmable logic controller, can be used for moving the impeller into alignment with the transfer discharge passageway only, the circulation discharge passageway only, or both the transfer discharge passageway and the circulation discharge passageway, as disclosed in the U.S. Pat. Nos. 7,687,017 and 7,507,365 . The base22includes an upper inlet opening38leading to upper inlet openings40of the impeller19and a lower inlet opening42leading to lower inlet openings44of the impeller. The impeller19includes vanes46and cavities48between the vanes on a side of the impeller forming outlet openings50of the impeller that communicate with the upper and lower impeller inlet openings and are aligned with one or both of the discharge passageways26,32. The impeller and base include suitable bearing rings52. Exterior threads54on the pump shaft16are screwed to a central threaded opening56of the impeller. The base22includes through holes58. Support posts60are each fastened at an upper end thereof62to the motor mount plate12such as using one or more clamps64and at a lower end thereof66to the base to suspend the base in the molten metal. Refractory sleeves68are each disposed in one of the through holes. Each of the support posts60is connected to the base22without cement by post fastening members70, wherein a portion72of each of the post fastening members is located inside the refractory sleeve.

In one aspect, the post fastening members70can be formed by each post including an internally threaded opening74at the lower end66. Another portion of the post fastening member70can be a bolt76that includes a head78, a shank80extending from the head and an exteriorly threaded portion82at an end of the shank. The shank is disposed inside the refractory sleeve and the threaded portion82of the bolt is threaded to the internally threaded opening74of the post so that the head78engages the base22. The through hole58would typically extend between upper surface84and lower surface86of the base22. The bolt head78would ordinarily be located near (e.g., in contact with) the lower surface86of the base. The posts60are fastened to the base without use of any cement. The posts60and bolts76are ideally made of a refractory material. The refractory sleeves68have an outer diameter and length that approximate the diameter and length of the through holes58in the base. For example, each of the refractory sleeves68can have an outer diameter of 2-4 inches and a thickness of 3/16-¼ inch. The outer diameter of the shank80of the bolt76can approximate the inner diameter of the refractory sleeve so as to minimize the intrusion of molten metal inside the through holes58. The heads78can be countersunk into the base.

Referring toFIG. 2B, in another aspect each of the post fastening members70can be a threaded nut88and a threaded elongated bolt portion90of the post60extending through the through hole of the base, which is threaded to the nut. The nut would ordinarily be located near the lower surface of the base. The nut can be countersunk into the base.

A refractory fiber gasket92can be disposed between a lower surface of each of the posts and the base and between each of the post fastening members and the base (e.g., between the lower surface of the base and the nut or bolt head). The fiber gasket can be a Fiberfrax® gasket by Carborundum. The post, including any elongated portion, the bolts and the nut are ideally made of refractory material such as graphite or ceramic. The base can be made of suitable refractory material such as graphite.

The refractory sleeve is softer than graphite. For example the refractory sleeve is made of ceramic, such as an aluminum boron oxide. A density of the refractory sleeve can be not greater than 0.60 g/cm3, more particularly, not greater than 0.50 g/cm3, and specifically about 0.48 g/cm3.

In a method of replacing the posts of a molten metal pump, after the pump has been operated for awhile and the posts, shaft and/or rotor have become worn or damaged, it is desired to replace the posts, among other components of the pump. When the pump10has been operated for an extended period of time, wherein the base22and posts60have been submerged in the molten metal bath, molten metal may enter the through holes58of the base. This can be resisted by the use of the gaskets92between the posts and the upper surface84of the base and between the post fastening members70and the lower surface86of the base but may not be altogether prevented. As a result, once the pump has been removed from the molten metal and cooled, the metal can form a crust inside the through holes. When using the relatively soft refractory sleeves68of this disclosure in the through holes, the sleeves are easily removed without significant damage to the shape of the through holes58. All that might remain is a thin crust of metal on the surface of the through holes after the refractory sleeves have been removed, which can easily be scraped out.

The method of replacing the posts of a molten metal pump includes the following steps. After the pump has been operated and it is desired to replace the posts60, the pump10is removed from the molten metal and cooled. The posts60are removed from the clamps64on the bottom surface of the motor mount. The riser28is also unclamped. The posts60are cut near the upper surface of the base (e.g., through the bolts or through the elongated portion of the posts as shown by the dotted line ofFIG. 2A). For example, the cutting may occur through the threads of the exterior threaded portion82of the bolt and any remaining piece of the post may be chiseled off the top of the bolt. The remainder of the bolt is removed from the through hole, such as by tapping a rigid rod into the through hole having a diameter somewhat less than the diameter of the through hole. The remaining refractory sleeve and any remaining metal adhered to the surface of the base that forms the hole can then be removed such as by scraping (e.g., without any need of machining)

Replacement posts60can be installed in the pump, along with the post fastening members, to form the cementless pump as described above. The base22includes the through holes58extending between the upper and lower surfaces of the base. The refractory sleeves68are inserted in each of the through holes so that there is a snug fit. The post fastening members70extend inside the refractory sleeves and can be in contact with the refractory sleeves. In the case of using an elongated portion90of the posts, the posts are positioned so that the elongated portions extend inside the refractory sleeves68out the bottom of the base22. A refractory nut88is threaded to the threaded end portion of the refractory sleeve. In the other aspect of the post fastening members70, the posts60are positioned over the through hole58containing the refractory sleeve. Each of the bolts76is positioned inside the opening94of the refractory sleeves and are threaded to the interior threaded opening74in the post60. The bolts are tightened until the heads78contact the lower surface86of the base. The refractory gaskets92can be positioned between the posts60and the upper surface84of the base and between the lower surface86of the base and the nut88or bolt head78, to minimize intrusion of molten metal into the through holes.

Many modifications and variations of the invention will be apparent to those of ordinary skill in the art in light of the foregoing disclosure. Therefore, it is to be understood that, within the scope of the appended claims, the invention can be practiced otherwise than has been specifically shown and described.