HK1079266B - Shaft and post assemblies for molten metal pumping apparatus - Google Patents

Description

Background of the Invention

This invention relates to the construction of a post for a molten metal pump according to the preamble of claim 1.

Such a post is for example known from US-A-5 558 505.

In the processing of molten metals, it is often necessary to pump molten metal from one place to another. When it is desired to remove metal from a vessel, a so called transfer pump is used. When it is desired to circulate molten metal within a vessel, a so called circulation pump is used. When it is desired to purify molten metal disposed within a vessel, a so called gas injection pump is used. In each of these pumps, a rotatable impeller is submerged, typically within a pumping chamber, in the molten metal bath contained in the vessel. Additionally, the motor is suspended on a superstructure over the bath by posts connected to the base. Rotation of the impeller within the pumping chamber forces the molten metal as desired in a direction permitted by the pumping chamber design.

Mechanical pumps for moving molten metal in a bath historically have a relatively short life because of the destructive effects of the molten metal environment on the material used to construct the pump. Moreover, most materials capable of long term operation in a molten metal bath have relatively poor strength which can result in mechanical failure. In this regard, the industry has typically relied on graphite, a material with adequate strength, temperature resistance and chemical resistance, to function for an acceptable period of time in the harsh molten metal environment.

While graphite is currently the most commonly used material, it presents certain difficulties to pump manufacturers. Particularly, mechanical pumps usually require a graphite pump housing submerged in the molten metal. However, the housing is somewhat buoyant in the metal bath because the graphite has a lower density than the metal. In order to prevent the pump housing from rising in the metal and to prevent unwanted lateral movement of the base, a series of vertical legs are positioned between the pump housing and an overhead structure which acts simultaneously to support the drive motor and locate the base. In addition to functioning as the intermediate member in the above roles, the legs, or posts as they are also called, must be strong enough to withstand the tensile stress created during installation and removal of the pump in the molten metal bath.

Similarly, the shaft connecting the impeller and the motor is constructed of graphite. Often, this shaft component experiences significant stress when occluding matter in the metal bath is encountered and sometimes trapped against the housing. Since graphite does not possess as high a strength as would be desired, it would be helpful to reinforce the leg and shaft components of the pump.

In addition, graphite can be difficult to work with because different stock may have different thermal expansion rates and/or different grain orientation. This may result in a post and base having divergent and conflicting thermal expansion rates in the molten metal environment. This problem is compounded by the fact that pump construction has historically required cementing the graphite post into a hole in the graphite base. This design provides no tolerance between the components to accommodate divergent thermal expansion. Unfortunately, this can lead to cracking of the base or the post. Accordingly, it would be desirable to have a molten metal pump wherein the mating of a post and a base is achieved in a manner which accommodates divergent thermal expansion tendencies.

An example of a submergence device is described in U.S. Patent 4,598,899, herein incorporated by reference.-An exemplary degassing apparatus is described in U.S. Patent 4,898,367, herein incorporated by reference. In both devices, a vertically oriented shaft having a impeller/rotor disposed at one end in the molten metal bath is employed. Similar problems arise in these apparatus wherein the components are usually constructed of graphite, and would benefit from an increase in strength.

Summary of the Invention

Accordingly, it is a primary advantage of this invention to provide a new and improved.

Additional advantages of the invention will be set forth in part in the description which follows and in part will be obvious from the description, or may be learned by practicing the invention. The advantages of this invention may be realized and attained by means of the instrumentalities and combinations pointed out in the appended claims.

A molten metal pump comprises a pumping member (such as an impeller or rotor), at least partially enclosed within a housing. A power device is seated on a support above the housing and pumping member. A shaft connects the power device and the pumping member to provide rotation thereof according to the invention at least one, and preferably two to four posts, suspend the housing from the support. Said posts are constructed according to the features of claim 1.

Further embodiments are defined by the dependent claims.

Preferably, the outer member is comprised of a graphite, refractory, or ceramic material and the housing is comprised of graphite. Preferably, the rod will be comprised of a heat resistant alloy.

In a particularly preferred form of the invention, the outer member is comprised of a plurality of generally cylindrically shaped units, aligned along their longitudinal axis. The rod runs down a central bore of each unit to provide a stacked arrangement. Preferably, the lower most unit will include a circumferential protrusion shaped to mate with a recess formed in the top surface of the housing to create a fluid tight seal.

Brief Description of the Drawings

The accompanying drawings, which are incorporated in and constitute a part of the specification illustrate one embodiment in the invention and, together with the description, serve to explain the principles of the invention. Of the Drawings:

• FIG. 1 is a front elevation view, partially in cross-section, of a molten metal pump which is not part of the present invention;
• FIG. 2 is a side elevation view, also partially in cross-section, of Fig. 1;
• FIG. 3 is a front elevation view, partially in cross-section, of the rod of Fig.1;
• FIG. 4 is a front elevation view, in cross-section, of the inventive sheath of Fig. 1;
• FIG. 5 is a front elevation view, in cross-section, of an alternative post embodiment;
• FIGS. 6, 7 and 8 are front elevation views, in cross-section, of alternative post and base seating arrangements;
• FIG. 9 is a front elevation view, in cross-section, of a segmented post design;
• FIG. 10 is a front elevation view, in cross-section, of an alternative segmented sheath design;
• FIG. 11 is an exploded side elevation view, in cross-section, of an alternative post/base joining arrangement;
• FIG. 12 is an exploded view of section A of Fig. 11 showing the fluid tight joint;

Detailed Description of the Invention

Reference will now be made in detail to the present preferred embodiment of the invention, an example of which is illustrated in the accompanying drawings. While the invention will be described in connection with a preferred embodiment, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications and equivalents as may be included within the scope of the invention defined by the appended claims.

Referring now to Figs. 1 and 2, molten metal transfer pump 1 is provided. The molten metal pump includes a base assembly 3 having a pumping chamber 5 with an impeller 7 disposed therein. Bearing rings 9 provide mating surfaces between the impeller 7 and the base assembly 3. Rotation of the impeller 7 forces molten metal 11 through outlet 13 and up riser tube 15 for transport to another location.

Rotation of impeller 7 is achieved when motor 17 rotates shaft 19 by turning shaft coupling 21 provided therebetween. The motor is positioned above the base assembly 3 on a platform assembly 22 having an insulation layer 23, a motor mount bracket 25 and a motor mount plate 26.

Two post assemblies 27, comprised of a rod 29 constructed of a heat resistant alloy material disposed within a refractory sheath 31 suspend the base assembly 3 below the platform 22. Preferably, the rod will be constructed of an alloy such as MSA 2000 or MSA 20001 available from Metaullics Systems Co., L.P., 31935 Aurora Road, Solon, Ohio, 44139. The refractory sheath also includes a ceramic shield 33 for additional protection against oxidation. The lower end of rod 19 includes cap 35. Cap 35 is disposed within a cavity 37 in base assembly 3. A graphite or refractory plug 39 is cemented into the lowermost portion of the cavity to seal the area from molten metal. The upper end of the rod 29 extends through the insulation layer 23 and is secured with nut 41 to the motor mount plate 26. A disc spring 43 or other compression spring is disposed between the motor mount platform 25 and insulation layer 23. Preferably, an insulating washer (not shown) will be positioned between motor mount plate 26 and spring 43. Tightening of nut 41 results in compression of the spring 43 and a bias on the rod 29 and sheath 31.

- Advantageously this assembly provides a high strength alloy rod connection between the base and motor mount. Of course, it also protects the otherwise degradable rod from the molten metal environment. A further advantage is that the thermal expansion mismatch resulting from divergent grain orientations in a graphite post and a graphite base is eliminated because a graphite post is not rigidly cemented into a hole in the base. Furthermore, the strength of the graphite sheath is increased because it is retained under compression as a result of being squeezed between a socket 45 and the upper surface of base assembly 3.

Turning now to Figure 3, a detailed depiction of rod 29 is provided. In this embodiment, cap member 35 is welded at weld lines 47 to the lower most end of the rod. Of course, other mechanisms of attachment, including but not limited to, threaded or swaged, are appropriate joining techniques. Figure 4 provides a detailed cross-sectional view of the graphite sheath 31.

Referring now to Figure 5, an alternative post embodiment is depicted. In this embodiment, the post 101 again includes rod 103 protected from the molten metal environment by sheath 105. Rod 103 passes through a bore/cavity 106 in a base member 107 and is retained by the cap 109 containing a snap ring 111 having corresponding retaining grooves 113 and 115 in the cap 109 and rod 103, respectively. Again a disk spring 117 and nut 118 are provided, which in concert with the platform 119 create a bias on rod 103 and a compressive force on sheath 105.

Turning now to Figures 6, 7, and 8, alterative post and base joining techniques are depicted. For example, in Figure 6, rod 201 extends through base 205 and includes a threaded end 202 on which graphite cap 203 is secured. In Figure 7, the embodiment of Figure 6 is modified to include seal members 207 and 209 constructed of boron nitride, silicon carbide, or other suitable material. In Figure 8, an alternative embodiment is depicted wherein a threaded bore 301 is provided in the end of graphite post 303 and a threaded graphite post 305 extends upwardly through base member 307 and is mated to the end of the post 303. An advantage of each design is the ability to create a tension on the post to provide a self-alignment mechanism without the need for a structural use of cement. In this regard, a thermal expansion gap can be provided (see Fig. 11) where cement has been historically required.

Furthermore, the use of a protrusion 211 on the end cap post/bolt 203/205 in a combination with recesses 213 on the top and bottom surfaces of the base 205/307 create a fluid tight joint. Accordingly, molten metal does not enter this joint, allowing the post to be removed from the base if a rebuild of the pump is required.

It should be noted that while the present joining mechanisms in Figures 6 through 8 are generally depicted as coinciding to the utilization of a steel alloy rod, these mechanisms for joining a post to a base are equally applicable to a graphite post arrangement. Moreover, the arrangements depicted in Figures 6 through 8 can equally be considered as being constructed of all elements comprised of a combination of steel and graphite/ceramic or graphite/ceramic alone. The advantage provided by these assemblies is that there is no necessity for a cement joint between the post and the base which better accommodates thermal expansion mismatches.

Turning now to Figure 9, an alternative embodiment of the present invention is provided wherein the post 401 includes a rod 403 and a sheath 405. However, in this embodiment sheath 405 is comprised of the plurality of segmented units. This design is particularly desirable because of the relative ease of forming individual segmented units (A-E) as opposed to an elongated tube. Again, the post 401 is provided with a spring 407 and a metallic coupling unit 409, which in combination with the motor mount (not shown) creates a compressive force on the sheath segments (A-E). A fluid tight seal is created between each of the individual units as a result of the compressive force, and, may be enhanced by the inclusion of a gasket material (not shown) therebetween. The lower most unit E includes a circumferential protrusion 411 which is seated in a recess 413 in the top surface of the base 415. Accordingly, a fluid tight seal is achieved. As in any of the other designs herein, a bead of cement-or sealant may be placed around the seated protrusion 411 to further protect against unwanted metal seepage.

Referring now to Figure 10, an alternative embodiment of a segmented sheath 501 is depicted. In this embodiment, the end surfaces of the individual units A-E are cooperatively contoured to facilitate achieving an appropriate mating arrangement. In this regard, a verifiable seating arrangement is provided to assure a metal tight seal is formed between each individual segment.

Turning now to Figure 11, a detailed view of an arrangement mating a graphite post to a graphite base is provided to demonstrate both the desired tolerance for thermal expansion and a desirable configuration for achieving a fluid tight seal. More particularly, graphite post 601 passes through a hole 603 in a base assembly 605. Threaded graphite cap member 607 is attached to the lowermost portion of post 601. At both of the top and bottom interface of post 601 and/or cap -member 607 to the base assembly 605, a cooperative protrusion 609 and recess 611 are provided to create a fluid tight if seal. Referring now to Figure 12, the angled surfaces of the protrusion and recess are depicted. In this manner, a fluid tight mating surface achieved. The mating surfaces may be filled with a gasket material (not shown). A further advantage of the present invention is the tolerance provided by gap 613 for thermal expansion.

Claims (9)

1. A molten metal pump post comprising:

   an elongated rod (29);

   a sheath (31) receiving the elongated rod such that a first end and a second end of the rod extends from the sheath;

   a coupling unit (41) at least partially surrounding a first portion of the sheath member proximal the first end of the rod; characterised in that

   a biasing member (43) at least partially surrounding a portion of the rod adjacent the first end of the rod.
2. The post of claim 1, wherein the coupling unit (41) comprises a nut.
3. The post of claim 1, wherein the sheath (31) comprises a refractory material.
4. The post of claim 1, wherein the sheath (31) further comprises a ceramic shield (33).
5. The post of claim 1, wherein the rod (29) comprises a heat resistant alloy.
6. The post of claim 1, wherein the biasing member (43) comprises a disc spring.
7. The post of claim 1, wherein the sheath (41) includes a circumferential protrusion disposed at one end.
8. The post of claim 1, wherein the sheath comprises a plurality of segmented units (405).
9. The post of claim 8, wherein an end surface of adjacent segmented units are contoured.