US20170204862A1 - Riserless recirculation/transfer pump and mixer/pre-melter for molten metal applications - Google Patents
Riserless recirculation/transfer pump and mixer/pre-melter for molten metal applications Download PDFInfo
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- US20170204862A1 US20170204862A1 US15/426,407 US201715426407A US2017204862A1 US 20170204862 A1 US20170204862 A1 US 20170204862A1 US 201715426407 A US201715426407 A US 201715426407A US 2017204862 A1 US2017204862 A1 US 2017204862A1
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- impeller
- molten metal
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
- F04D—NON-POSITIVE-DISPLACEMENT PUMPS
- F04D7/00—Pumps adapted for handling specific fluids, e.g. by selection of specific materials for pumps or pump parts
- F04D7/02—Pumps adapted for handling specific fluids, e.g. by selection of specific materials for pumps or pump parts of centrifugal type
- F04D7/06—Pumps adapted for handling specific fluids, e.g. by selection of specific materials for pumps or pump parts of centrifugal type the fluids being hot or corrosive, e.g. liquid metals
- F04D7/065—Pumps adapted for handling specific fluids, e.g. by selection of specific materials for pumps or pump parts of centrifugal type the fluids being hot or corrosive, e.g. liquid metals for liquid metal
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
- F04D—NON-POSITIVE-DISPLACEMENT PUMPS
- F04D1/00—Radial-flow pumps, e.g. centrifugal pumps; Helico-centrifugal pumps
- F04D1/14—Pumps raising fluids by centrifugal force within a conical rotary bowl with vertical axis
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
- F04D—NON-POSITIVE-DISPLACEMENT PUMPS
- F04D13/00—Pumping installations or systems
- F04D13/02—Units comprising pumps and their driving means
- F04D13/021—Units comprising pumps and their driving means containing a coupling
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
- F04D—NON-POSITIVE-DISPLACEMENT PUMPS
- F04D29/00—Details, component parts, or accessories
- F04D29/40—Casings; Connections of working fluid
- F04D29/42—Casings; Connections of working fluid for radial or helico-centrifugal pumps
- F04D29/44—Fluid-guiding means, e.g. diffusers
- F04D29/445—Fluid-guiding means, e.g. diffusers especially adapted for liquid pumps
Abstract
A pump for processing molten metal having an enlarged tubular body which houses a centrifugal lifting pump at its bottom end. The bottom end has a curved shape that aids in the formation and sustainability of: a) a forced vortex; b) a highly forced vortex; and c) a super forced vortex, depending on the application when it which receives the ejected molten metal from the lifting pump's impeller. The lifting pump is controlled to cause the vortex to climb up the inner wall of the body up to and out of an outlet formed in the upper end of the body. A recirculation centrifugal pump is mounted coaxially to and rotates with the lifting impeller.
Description
- This application is a continuation-in-part of U.S. patent application Ser. No. 12/604,000 filed Oct. 22, 2009 which claims priority of U.S. Utility Patent Application filed Oct. 29, 2008 having Ser. No. 61/109,352.
- The present invention relates to lifting, mixing, and recirculating molten metals and, more particularly, to a pump creating a vortex within a lift tube to elevate and mix molten metal.
- A typical molten metal facility includes a furnace with a pump for moving molten metal. During the processing of molten metals, such as aluminum and zinc, the molten metal is normally continuously circulated through the furnace by a centrifugal circulation pump to equalize the temperature of the molten bath. These pumps contain a rotating impeller that draws in and accelerates the molten metal creating a laminar-type flow within the furnace.
- To transfer the molten metal out of the furnace, typically for casting the metal, a separate centrifugal transfer pump is used to elevate the metal up through a discharge conduit that runs up and out of the furnace. As shown in
FIG. 1 , a typical prior art transfer pump includes abase 5, two to three support posts 6 (only one shown), a shaft-mountedimpeller 7 located within a pumping chamber or volute 5 a in thebase 5, amotor 8 andmotor mount 9 which turn the impeller,bearings 10 that support the rotating impeller (and shaft), and a riser tube orconduit 11 located at the outlet of the base. Theriser 11 is provided to allow the metal to lift upward over the sill edge of the furnace in order to transfer some of themolten metal 12 out of furnace into ladles or molds. - A well-known problem with previous transfer pumps, however, is that the relatively
narrow riser tube 11 becomes clogged as small droplets of the molten metal accumulate in the riser each time the pump stops transferring and the metal stops flowing through the riser. Initially, the metal accumulates in the porosity of the riser tube material (typically graphite or ceramic) and then continues to build upon the hardened metal/dross until aclog 13 occurs. As a result of this problem, furnace operators must frequently replace the transfer pump's riser tube as they are too narrow to effectively clean. This replacement typically requires the furnace to be shut down for an extended period to remove the clogged riser tube. - Several treatments have been used to alleviate this riser-clogging in transfer pumps. Including impregnating, coating, and inert gas pressurization of the riser to reduce the build-up within the tube. Another method pump manufacturers employ is to simply increase the diameter of the riser to delay the blockage. These treatments have varying degrees of success, but still only delay the inevitable clogging of the riser.
- Another common operation in a molten metal facility is to add scrap metal, typically metal working remnants or chips, to the molten bath within a furnace. The heat of the bath melts the chips. Currently, the added chips are simply allowed to fall into the bath or may be mixed into the molten metal by a circulation pump. The current process(es), however, is not effective to fully immerse the solid chips into the molten bath resulting in a longer melt time. As shown in
FIG. 2 , prior art systems utilizing adedicated mixing pump 14 directsmolten metal 12 into avessel 15 resulting in a nearlyfree vortex 16 to be formed. Scrap metal, such aschips 17, are deposited into thevortex 16 to mix and melt thechips 17 within themolten metal bath 12. As will be discussed in greater detail below, these nearly free vortex-based systems do not provide sufficient residence times within the bath to efficiently melt and mix the newly deposited chips into the bath. A nearlyfree vortex 16, such as the type formed by prior art systems are governed by the following equations ω=Cr−2, Vr=C, P/γ=C/2gr+h, where ω is the angular velocity, V is the peripheral velocity, P/γ is the pressure distribution (pressure energy) and h is the static energy. Then the maximum velocity would be at the center axis of the vortex, expelling the chips upward and outwards. Consequently, any metal particles introduced therein will float at the top of the metal and exit without being melted at the top exit outlet, generating a large amount of dross instead of liquid metal. The resulting shape ofvortex 16 is shown inFIG. 12 . - Presently, molten metal facilities have limited furnace footprints with relatively small pump wells and charge wells. The limited space available typically prevents furnace operators from having permanently installed transfer pumps and/or mixer/pre-melter systems within a furnace (in addition to the recirculation pump). There is therefore a need for a system that can combine two or more of the transfer/pre-melt/recirculation processes within a single pump.
- Another drawback of conventional molten metal pumps is the highly inefficient use of very large/high horsepower motors which are stepped down in velocity electronically with a frequency converter that maintains the torque constant, thus reducing the output horsepower when running the equipment at a safe RPM. The present invention provides for a mechanical gear box which provides for the desired reduction in RPMs, while boosting the torque and permitting the motor to operate at or near its optimal speeds to further increase efficiency. The gear box necessitates another improvement to existing molten metal pumps to avoid the undesirable transfer of heat from the molten bath into the gear train and pump motor. This further improvement is a coupling that operates as a thermal barrier between the drive shaft that is submerged within the bath to rotate the pump impeller and the upper portion of the shaft that is driven by the gear train.
- In view of the current inefficient use of molten metal transfer and mixing pumps, there is a need for a molten metal pump that overcomes all of the above-indicated drawbacks.
- The present invention provides a molten metal pump including an elongated body or vessel having an elongated bowl or tube that terminates in a curved bottom end. A centrifugal impeller is seated in an inlet opening formed in the center of the bottom end. The shape of the vessel's bottom end provides a smooth upward transition for metal ejected from the impeller to the inner walls of the tube. The rotation of the impeller centered in the curved lower walls results in the ejected flow of molten metal to create an uplifting vortex which climbs the inner walls of the vessel to an outlet opening in an upper portion wall. The pump is preferably a hybrid-drag turbine type disclosed in my U.S. Pat. No. 8,033,792 which is incorporated herein.
- Further, the, present molten metal pump includes a second centrifugal impeller mounted coaxially to the vortex lifting impeller. The second centrifugal impeller is a recirculation pump and is preferably a turbine impeller such as the ones disclosed in my U.S. Pat. No. 7,896,617 (turbine) which is incorporated herein and which provides a very high outlet peripheral velocity.
- The vessel's shape (i.e., the curvature of the inner wall and bottom end) is a function of the type of vortex required by the particular application. Particularly, I have determined that the optimum vortex for transfer-only applications maintains a constant angular velocity using an internally curve-shaped vessel that concurs with the following equations ω=CTE (constant, i.e., ω=Cro with Vr−1=C), P/γ=Cr2/2g+h. The constant angular velocity of the liquid metal moves like a solid, while twisting and turning upwards in the vessel without each molecular layer sliding with respect to the adjacent layer minimizing the possibility of turbulence, loss of heat and viscous windage losses.
- Further, I have determined that the optimum vortex for a mixing/pre-melting application requires an internally curve-shaped vessel when flows greater than 1500 GPM are required follow the equations ω=Cr, Vr−2=C, P/γ=Cr4/4g+h. A curve that follows the equations ω=Cr1/2 with Vr−3/2=C, P/γ=Cr3/3g+h will suffice for lower flow rates. The vortex created in a mixing/pre-melting application should be a highly forced or super forced vortex to assure the penetration of the particles of added material into the matrix of partially combined material. To ensure adequate churning or slipping between adjacent molecular layers the angular velocity is higher toward the periphery of the vortex. At higher flow rates a hyperbolic-shaped vessel creates a super forced vortex requiring a hybrid-drag turbine type impeller such as the type disclosed in my U.S. Pat. No. 8,033,792. At lower flow rates a turbine impeller may be used to generate the flows and velocities necessary, such as the type disclosed in my U.S. Pat. No. 7,896,617.
- The present invention further provides an improved system for transmitting the requisite torque to the combined impellers. The present power transmission includes a mechanical gear train which reduces the revolutions per minute from the pump's electric motor, while also boosting the torque being applied along the output shaft.
- The present invention still further provides a self cooling thermal barrier coupling which transmits the torque from the motor/gear box, while limiting the conduction of heat from the molten metal bath to the motor and gear box.
- It is an advantage of the present invention to provide a pump which creates a forced, highly forced or super forced vortex of molten metal within a generally vertical tube body of the pump to lift the whirling molten metal for transferring, mixing, and/or pre-melting applications.
- It is another advantage of the present invention that the lifting cavity has a relatively large internal diameter allowing the inner walls to be readily accessed for cleaning and removal of accumulated metal and dross. Preferably, the vessel internal diameter being between 1.5 to 4 times the impeller outside diameter.
- It is still another advantage of the present invention that two coaxial impellers are driven by a common drive motor-shaft design to simultaneously provide the lifting vortex flow and the recirculation flow. An upper impeller being mounted within the tubular lifting vortex cavity, while the lower impeller is mounted within a volute to recirculate a bath of molten metal.
- It is still yet another advantage of the present invention that the lifting vortex cavity has a curved shape and size that complements the intended vortex formed therein. That is, in a transfer application, the lifting cavity has a particular curvature shape, while in a pre-melting/mixing application the lifting vortex cavity has at least a third degree curved shape as described above (e.g., has a pressure distribution following P/γ=C2r3/3g+h or P/γ=C2r4/4g+h).
- An advantage of the present invention over prior art transfer-type pumps is that the present invention eliminates the support posts, riser tube, and one impeller bearing thereby reducing the complexity of the pump system and reducing the number of components subject to deterioration due to the molten metal environment and which must eventually be replaced.
- It is an additional advantage of the present invention when mixing or pre-melting to provide an upper impeller having a plate with a plurality of radial vanes facing into the tubular body. When metal scrap chips are inserted into the pump's tubular cavity, the plurality of radial vanes on the upper impeller causes the metal chips to be directed radially outwardly into the pump-generated uplifting vortex of molten metal. The rotational velocity of the impeller causes the chips to further penetrate the surface of the vortex to fully immerse the chips within the molten metal.
- It is yet another advantage of the present invention that the dual impellers are driven by the motor through a mechanical gear train which increases the torque transmitted to the output shaft and permits the motor to run near its optimal operating speed by reducing the rotational speed of the output shaft to a desired amount.
- These and other objects, features and advantages of the present invention will become apparent from the following description when viewed in accordance with the accompanying drawings.
- The description refers to the accompanying drawings in which like reference characters refer to like parts throughout the several views, and in which:
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FIG. 1 is a side sectional view of a prior art transfer pump having a riser tube; -
FIG. 2 is a side section view of prior art mixer producing a nearly free vortex; -
FIG. 3 is a side sectional view of a transfer pump embodiment of the present invention; -
FIG. 4 is a partial side sectional view of the transfer embodiment and the curved lower portion of the lifting vessel; -
FIG. 5 is a partial side sectional view of the transfer pump embodiment generating a forced vortex with constant angular velocity; -
FIG. 6 is a partial side sectional view of a mixing/pre-melting embodiment of the present invention;FIGS. 5 and 6 provide a side by side comparison of the vessel profile and differing impellers generating the two applications; -
FIG. 7 is a side sectional view of the mixing/pre-melting embodiment generating a super forced vortex produced within a lifting vessel with hyperbolic-shaped inner wall; -
FIG. 8 is a top sectional view through line 8-8 inFIG. 7 showing the radially accelerated metal particles penetrating the impeller induced vortex; -
FIG. 9 shows the minimum and standard transfer pump requirement curves for head and flow for a 7.5 inch impellers operating at 600 rpms; -
FIG. 10 shows the head to flow rate curves for ten inch impellers of various configurations; -
FIG. 11 shows the vortex velocity distribution for different forced vortices; -
FIG. 12 shows the vortex pressure distribution between different vortex types generated with a lifting vessel; -
FIG. 13 is a side sectional view of an alternate pump embodiment having both a lifting pump impeller and recirculation pump impeller driven by a common drive shaft; -
FIG. 14 is a side partial cut-away view of an alternate drive motor having coaxially mounted drive shafts; a mechanical gear train connects the two coaxial drive shafts; -
FIG. 15 is a side partially exploded view of a coupling having self-cooling feature and a thermally resistive configuration; -
FIG. 16 is a top view of the lower portion of the thermal coupling shown inFIG. 15 ; and -
FIG. 17 is a side sectional view of a recirculation pump throat including an inert gas injection port. - Referring now to
FIG. 3 , the present invention ismolten metal pump 20 which creates a forced vortex of acceleratedmolten metal 21 within avertical tube 22 in the pump to lift or raise the molten metal to anoutlet 24 in the upper end of the pump. -
Pump 20 includes an elongated tubular pump body orvessel 26 having a generally verticalinner tube wall 27 and a curved or dome-shapedbottom end 28. As will be discussed in greater detail below, the cavity-defining profile of thebottom end 28 and inner wall are a consequence of the type of vortex selected, ω=Crm, where m is based on a design criteria that depends on the lifting application. For a transfer pump, I have selected m=0. In other embodiments, the profile may be spherical or perhaps elliptical. An inlet opening 30 is formed in the center of the concavelower end 28. Acentrifugal impeller 32 is mounted withinopening 30 and is rotated by anelongated output shaft 34 which runs concentrically down through the center oftube body 26.Shaft 34 is driven by a conventional motor 35 (such as the motor illustrated inFIG. 14 ). In the embodiment illustrated, inlet opening 30 and the impeller's inlets are suspended above thefurnace floor 36 to ensure an adequate amount of molten metal is pulled intopump 20. -
Impeller 32 rotates onbearings 37 disposed between the impeller andbody 26 to draw in molten metal from bath/matrix 12, which is accelerated in the radial and tangential directions and is upwardly lifted by the Coriolis force that with the assist of the transition angle α, denoted 43, overcomes the g-forces at very high peripheral velocities. Since the condition of equilibrium requires that the centrifugal force must be balanced by the static liquid column at the same point it follows that: dP/dr=γV2/gr=γω2r/g. The rotatingimpeller 32 expels the accelerated molten metal out of the impeller and intobottom end 28 of the pump body.Impeller 32 is preferably a type to generate the molten metal lifting vortex withinpump 20, such as the impeller configurations disclosed in: a) my issued U.S. Pat. No. 7,326,028 patent, hereinafter referred to as a dual inducer impeller; b) my issued U.S. Pat. No. 7,896,617, hereinafter referred to as a turbine impeller; both with very high peripheral velocities and which are each incorporated herein by reference. - The
pump body 26 is preferably formed from a material suitable for molten metal applications, such as a boron nitride impregnated refractory material. It should be appreciated that since most transfer-type molten metal pumps typically only need to lift the metal three to seven feet vertically, the lifting cavity portion of the pump body has a similar overall length/height. - In the embodiment illustrated in
FIGS. 3-5 ,tube 26 terminates in a curved-shapedend 28, which provides the contour necessary for the impeller to generate the forced-type vortex required by the application at hand. - In this embodiment, a transferring application is illustrated where the curved shape of
end 28 has its curvature focus proximate to its vertex. Further in this transferring application, the forcedvortex 40 has a constant angular velocity, ω=Cr0, (i.e., where there is little to no shear in the fluid such that the fluid essentially rotates as a solid body) generated by the rotating impeller. - Importantly, I have determined that the profile of the
inner surfaces vortex 40 is generated where thefree surface 40 a is nearly a square (or second degree curve) curve resulting in a varying radial thickness or depth of the molten metal, which narrows as the flow rises up thetube walls 27. That is, more molten metal can be found proximate to thelower end 28 inpump body 26 than at the upward end of the vertical tube. - As described above, a forced
vortex 40 exhibits little to no internal shear within the liquid. The forcedvortex 40 having a constant angular velocity, ω=Cr0 wherein C=Vr−1. This assures the liquid metal is moving like a solid, while twisting and turning upwards in the vessel without each adjacent molecular layer sliding with respect each other, thereby minimizing the possibility of turbulence, loss of heat and viscous windage losses. The pressure distribution is then given by: P/γ=C2r2/2g+h, which is theoretically a square parabola curve. I have determined that the vertical cross section configuration of a lifting vessel for a transfer application with a parabolic curve plus the assist of a two degree to a fifteen degree starting lift angle α (43) beginning at the inlet opening 30 of the vessel is the optimal configuration. Optimally, the angle 43 is between two and ten degrees. - In the preferred embodiment of a transferring pump,
body 26 includes anexit volute 44 in the upper end of the body.Exit volute 44 is a channel recessed inbody 26 which redirects the whirlingvortex 40 of molten metal out throughoutlet opening 24. - In a transferring application, the outlet opening 24 leads onto a conventional
molten metal sluice 45 to move the exiting molten metal away from the furnace. - The maximum lift, “Hmax”, (i.e., the maximum vertical distance a given
pump 20 will elevate a given molten metal from the inlet of the impeller) will depend on: a) theinternal diameter 27 a of the pump body's tube; b) the impeller'souter diameter 30 a; and c) the speed (in rpm) at which theimpeller 32 is rotated. For optimum transfer lift the impeller'souter diameter 30 a is preferably within the range of one-third to one-half theinternal diameter 27 a of thepump body tube 27. The minimum lift, “Hmin”, is the vertical distance between themolten metal line 12 a in the furnace and the height to theoutlet opening 24, which results in sufficient material exiting thepump 20 to maintain the desired vortex formed by the incoming/accelerating molten material. - Referring now to
FIG. 9 , the distribution curves of the necessary flow to lift requirements for transfer pumps with traditional impeller configurations (such as a mixed flow impeller) and a turbine impeller are shown for the same sized impellers running at the same speeds. As shown, the flow rates, Q, for my turbine impeller far exceed the rates of more traditional impellers at any desired lifting heights. -
Pump 20 further preferably includes an annular lid or splashprotector 46 which substantially covers the upper open end of thetube body 26 while leaving a central opening to allow access for thedrive shaft 34. In one embodiment, pump 20 includes a gas injection tube orconduit 48, which passes intocavity 42 to introduce an inert gas into the molten metal, such as injecting nitrogen gas to flux/clean molten aluminum and prevent the formation of aluminum oxide (Al2O3). - Referring now to
FIGS. 6-8 , in an alternate embodiment thepump 20′ is used as a metal mixer or pre-melter, chips orparticles 50 of various materials are introduced intobody 26 through the upper end. In one embodiment, the curved shape of cavity bottom 28 andinner wall 27 has a wider nearly hyperbolic configuration than the transferring pump above, with the focus being as far as practicable from the vertex. In the mixing application, the height of the lifted metal should be maintained at a minimum to ensure proper dispersion of theparticles 50 added for mixing with the metal matrix/bath 12. This will depend on: a) the materials being mixed; b) the particles' size; c) the wetability of the particles; d) the mixing speed (rpm); and e) the impeller configuration and tip velocity. In a preferred embodiment of this mixing application, highly forcedvortex 40′ or even a super forcedvortex 40″ is generated where thefree surface 40 a′ is a cubic curvature of the type P/γ=C2r3/3g+h resulting in a near constant radial thickness or depth of the molten metal, which remains uniforms as the flow rises up thetube walls 27 and the angular velocity i9 s higher toward the periphery and slower at the center axis ω=Cr1/2. Note that r is to the third p[ower and V=C/r3/2, generating a very strong upper lift. - When the resulting flow and exit velocities are large enough, the resulting vortex within the vessel takes the shape of what I have termed a “super forced vortex”, where the
vortex 40″ of fluid forms a near constant or uniform depth/thickness and thefree surface 40 a″ of the fluid has substantially the same curved shape as the underlying cavity 42 (defined bytube 27 and dome-shaped end 28) in pump body 26 (FIG. 4 ). - As shown in
FIG. 7 , while mixing, the flow out of thepump 20′ returns the lifted molten metal to the furnace until the mixing is completed, then casting can start. Preferably, theoutlet 24 is located proximate to thefurnace metal line 12 a to reduce turbulence and dross formation. - In a pre-melting system the conditions are similar to the mixing application described above, except the particles' 50 residence time in the
vortex 40′ orvortex 40 a″ and the vortex's outlet flow should be such as to guarantee the complete melting of the material 50 added to the vortex to assure sufficient heat is available to cause the solid particles to melt without overcooling either the melting or the melted flow. - In the mixing and pre-melting applications, the highly forced/super vortex(s) 40 a′, 40″ would be optimally generated by means of my turbine impeller or hybrid-drag impeller. These impellers generate a very balanced flow versus head performance curve assuring high melting flow and moderate to high recirculation (residence time). In general, it can be stated that the ratio of molten metal flow to required melting pounds of chips is given by
-
- producing a ratio of pounds of flow per pound of chips. Therefore a successful design must rely not only in the pre-melt recirculation system but on how well the furnace/pre-melt/recirculation combination has been optimized for maximum efficiency, something rarely done at present times.
- or optimum mixing or pre-melting applications the
internal diameter 27 a of the liftingcavity 42 is preferably between 1.5 to four times the impeller outsidediameter 30 a to guarantee larger flows and longer residence times of the particles to be melted within or dispersed throughout the metal matrix/bath 12. - Referring now to
FIGS. 7 and 8 pump 20′ having animpeller 32′ which is substantially the same asimpeller 32 described above, except thatimpeller 32′ has a much thicker back plate portion 52 (i.e., the face of the impeller opposite to the surface bearing the molten metal inlets 35) thanimpeller 32. Within the thickened backplate 52 is a plurality of spacedchannels 54 which form a plurality of spaced mixingvanes 56 that extend radially outwardly from a central driveshaft mounting hub. These spaced vanes cooperatively form another impeller which directs anymaterial entering channels 54 in a substantially radial outward direction away from the rotating impeller. As shown, when theimpeller 32′ is inserted within inlet opening 30 of thepump body 26, theinlets 54 a ofchannels 54 are open to theinternal cavity 42 facing in the opposite direction of liftingimpeller inlets 35, while thechannel outlets 54 b face toward theinner wall 27. - In another embodiment, the
integrated mixing vane 56 formed withinback plate 52 may be replaced with a separate second impeller mounted to the back plate of liftingimpeller 32′. Like the integrated vanes, this second impeller would includeopen channels 54 andvanes 56 substantially the same as those described above. - In a mixing or pre-melting operation,
solid particles 50 are introduced intocavity 42 through the upper end of thebody 26. As discussed above, when theimpeller 32′ is turning at rated speed, the flow of molten metal exiting the impeller forms either a highly forced orsuper-forced vortex 40 a′, 40″ which travels up thetube walls 27. Thesolid particles 50 fall in the axial direction into theinlets 54 a of therotating channels 54 formed in the upper surface ofback plate 52 and due to theradially extending vanes 56 are re-directed or thrown in a substantially radial direction out ofchannel outlets 54 b into the vortex of molten metal. Importantly, the rotational speed of theimpeller 32′ which is necessary to lift the molten metal up alongwalls 27 causes theparticles 50 being ejected by theradial vanes 56 in the back plate to have sufficient velocity to fully penetrate into the liquid vortex, i.e., beyond the inward-facingsurface 40 a of the vortex, thereby allowing the molten material to fully engulf thesolid particles 50 to maximize heating/melting efficiency. - Although the
riserless pump 20 has several applications, the general design remains substantially the same except only the lifting capability of the forcedvortex 40 is utilized in the transfer application, while the lifting, mixing and recirculation capabilities of the highly forcedvortex 40′ and super forcedvortex 40″ are used in conjunction to achieve the ultimate requirements for mixing and pre-melting. - Referring now to
FIG. 10 , the distribution curves of the necessary flow to lift requirements for mixing and pre-melting pumps with traditional impeller configurations (such as a mixed flow impeller), my turbine impeller, and my hybrid-drag turbine impeller are shown for the same sized impellers running at the same speeds. As shown, the flow rates, Q, for my impellers far exceed the rates of more traditional impellers at any desired lifting heights. These increased flows and high pressures from my impellers allows the formation of the desired highly forced and super forcedvortices 40′, 40″ in these applications. Particularly, these forcedvortices 40′, 40″ having an angular velocity which increases toward the periphery of the vortex (i.e., ω=Cr1/2 to Cr and v=C/r2), also the velocity assures a slip between metal layers (shear) that act in a “churning” motion on the unmelted particles and accelerate the mixture to the top outlet. These vortices have ω=Cr1/2 wherein C=Vr−3/2. The pressure distribution is then given by: P/γ=C2r3/3g+h, which is a theoretical hyperbolic curve. I have determined that the vertical cross section configuration of the lifting vessel for a mixing/pre-melting application will require a third degree curve (notice P/γ above) shaped vessel depending on how “highly” forced the vortex is. Like the forcedvortex 40 above, the highly forced and super forced vortices have between a two degree to a fifteen degree starting lift angle α (43) beginning at the inlet opening 30 of the vessel. Optimally, the angle 43 is between two and ten degrees. - It should be appreciated that the above described highly forced and super forced vortices are not easy to generate with molten metals if using standard centrifugal mixed flow pumps or impellers. For that reason I rely upon my hybrid-drag turbine type impeller with total tip velocities generating more than 35% higher flow and shut-off pressures obtained by increasing the peripheral outlet velocity as well as the shut-off coefficient. For example, standard mixed flow pumps have a shut-off pressure coefficient, Kso≦0.69, while my hybrid-drag turbine has Kso≧0.90.
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FIG. 11 illustrates the vortex velocity distribution between a highly forced vortex and a super forced vortex. Similarly,FIG. 12 shows the vortex pressure distribution of various types of vortices, including a free vortex, a constant energy vortexfree vortex 16, a constant angular velocity forcedvortex 40, a highly forcedvortex 40′, and a super forcedvortex 40″. The primary difference between the highly forced and super forced lifting vortices being the velocity of the vortex itself. Thereby distinguishing between the highly forced—closer to a parabolic and super forced—closer to a hyperbolic distribution. - Referring now to
FIG. 13 an alternate embodiment of the invention is illustrated. In this embodiment, denotedpump 120, two impellers are mounted coaxially upon acommon drive shaft 34. Theupper impeller 132 is substantially the same as either of the liftingimpellers pump 120 shown inFIG. 13 , the mixing/pre-melting hybrid-drag turbine impeller 32′ is shown generating avortex 40′, 40″ within a third degree curvaturevortex lifting cavity 42. -
Pump 120 differs from the embodiments discussed above in that a secondcentrifugal impeller 150 is mounted to and rotates with theupper impeller 132. -
Pump 120 has an extended orelongated drive shaft 134 which couples the twoimpellers Pump 120 includes apump housing 152 which supports the liftingvessel 26 and includes avolute 154 within which thesecond impeller 150 rotates. As shown in the FIG.,housing 152 has twoinlet manifolds molten metal 12 to one of the two impellers.Inlet manifold 156 is in fluid communication with the inlet opening 30 of the liftingvortex vessel 26 to supply molten material to be lifted along theinner walls 27 of thevessel 26. A plurality of manifold apertures passing generally horizontally through the side walls ofhousing 152 permit the molten bath the be pulled into thevessel 26. Similarly, thelower inlet manifold 158 is in fluid communication with both theinlet openings 150′ of theimpeller 150 and the surroundingbath 12 by additional side apertures. In addition, theoutlet 162 from thepre-melt vessel 26 joins the incoming flow from the surroundingbath 12 adding additional melting residence time before the mix is recirculated through thepump impeller 150 into the furnace hearth. - In the preferred embodiment the
second impeller 150 is a recirculation impeller of a type such as my dual inducer impeller or my turbine impeller. The outlet ofvolute 154 may include a narrowing passage orthroat 160, which operates to further increase the outlet velocity from the recirculation pump portion ofpump 120. This increase velocity may be beneficial to allow for the ready injection of Nitrogen or Chlorine gas into the recirculating bath ofmolten metal 12 to clean the bath. - As shown, the
upper outlet exit 24 for the liftingvessel 26 is in fluid communication with apassage 162 that passes down into thehousing 152 and into the recirculation pump's manifold 158 wherein the molten metal that is lifted up (and ostensibly mixed with other materials, such as chips 50) withinvessel 26 is immediately accelerated into the pool ofmolten metal 12 by thecentrifugal impeller 150. - Referring now to
FIG. 14 , the present invention further provides for an improved power transmission system orgear train 170, which mechanically transmits the rotational energy from aconventional motor 35 suitable for a molten metal furnace-environment to thedrive shaft 34 of a molten metal pump, such aspumps motor 35 has a fixedstator 172 andwindings 174 which surround arotor 176. Therotor 176 is fixed to atubular motor shaft 178 which turns freely onbearings 180. - Importantly,
tubular motor shaft 178 is linked at one end ofgear train 170. Thegear train 170 is configured in a conventional manner and is linked to and rotates thedrive shaft 34. It should be appreciated thatgear train 170 will be configured to reduce the motor's specific speed, while simultaneously increasing its torque in the same ratio. In one non-limiting embodiment,motor 35 is configured to rotate at 1800 RPM at its optimal efficiency, while the motor output shaft is geared down to rotate at 750 RPM. In the preferred embodiment,output shaft 34 is arranged to be concentric to and telescopically received within the tubular opening ofmotor shaft 178. In this manner, the packaging constraints of the pump/furnace can be limited, while setting the speed and torque of therotating pump shaft 34. In the preferred embodiment,shaft 34 is formed from a solid bar of stainless steel to transmit the torque to the impeller. To avoid degradation of the steel shaft in the molten metal environment, conventional techniques of protecting the torque-transmittingshaft 34, such as encasing the shaft in a suitable ceramic shell/tube 34′ (as best seen inFIG. 4 ) is preferred. - While in some non-limiting embodiments,
shaft 34 may be directly passed down to the pump impeller, the present invention also discloses a thermalresistive coupling 190 which interconnects a split drive shaft, denoted 34 a and 34 b inFIG. 15 . Coupling 190 is preferably formed from a ceramic low thermal conductivity material (e.g., alumina titanate or zirconium silicate) and includes a stainlesssteel top plate 192 which is fixed to theupper drive shaft 34 a by means of abolt 215, which is driven bymotor 35. In theexemplary coupling 190 ofFIG. 15 , thedrive shaft 34 a is similarly fastened to a complementary fitting withintop plate 192. - Coupling 190 also includes a
lower plate 194, which has a generally round andflat base 196 and a plurality of radially spaced monolithic low conductivity ceramic vanes orspacers 198 extending vertically from thebase 196. Opposite of thespacers 198 is another fitting formed in the lower face of the base 196 which permits thelower plate 194 to be fixed to thelower drive shaft 34 b. - Each
vane 198 includescoupling apertures 200 formed into thetop surface 202. A plurality of complementary apertures are formed intop plate 192 allow the top and lower plates to be coupled together bydrive pins 204 and mechanical fasteners, such asbolts 206, to assemble thecoupling 190. In addition to thecoupling apertures 200, the top andlower plates air passages 208 formed between the spacedvanes 198. As shown best inFIG. 16 , when thecoupling 190 is assembled and joins theshafts passages 208 and out between thevanes 198. In this manner, there is little to no heat transferred from thelower drive shaft 34 b (extending out from the molten bath 12) to theupper drive shaft 34 a and thetransmission 170 and/ormotor 35. In other non-limiting embodiments, the lower portion of theshaft 34 can be made from graphite with a ceramic sleeve to protect it from burning at the metal line. Further embodiments may also be nitrogen gas impregnated through the upper shaft portion. - Referring now to
FIGS. 13 and 17 ,throat 160 is shown receiving the flow ejected from the recirculation pump (impeller 150 and volute 154) portion of the pump. To facilitate the effective introduction an inert gas into the flow of molten metal, the flow from a recirculation-type impeller, such asimpeller 150, must be accelerated to between twenty-eight and thirty feet per second to achieve an ideal sonic ratio which creates a suction force within the throat, thereby pulling the injected inert gas, viainjection port 230 formed in thethroat 160. To accelerate the flow, a narrowing orrestriction 232 is formed within the tubular throat. The restriction preferably decreases the cross-sectional area of the throat gradually by narrowing gradually at a slight angle, less than eight degrees and preferably between five and eight degrees. Thethroat 160 may also include adiffuser portion 234, which is formed downstream of the inertgas injection port 230.Diffuser 234 gradually increases the cross-sectional area of the throat to slow the flow of molten metal to a more acceptable rate (e.g., between fourteen and twenty feet per second). In one non-limiting embodiment, the diffuser gradually angles outwardly between seven and ten degrees to limit the turbulence and/or cavitation from the slowing of the flow. - The present invention, by increasing the flow rates and combining a lifting pump (mixing and/or pre-melting) with a recirculation pump increases the amount of molten metal which flows through the furnace thereby improving the overall efficiency of the furnace by maintaining desirable recirculation velocities while at the same time providing a pre-melting apparatus having increased dwell time for chips melt.
- From the foregoing description, one skilled in the art will readily recognize that the present invention is directed to an improved molten metal pump system that rotates the molten metal within an internal cavity creating a vortex of molten metal along the vertical cavity wall, which rises up to an outlet at the upper end of the wall. Further, a pump including both a lifting impeller and a recirculation impeller are provided which reduces the footprint within the furnace wells. The present invention, through its novel use of a mechanical transmission to boost torque while reducing output speeds allows the pump's motor to operate at or near peak efficiency and eliminates the necessity to employ over powered motors to generate the necessary torques at the relatively low speeds required of molten metal pumping operations.
- While the present invention has been described with particular reference to various preferred embodiments, one skilled in the art will recognize from the foregoing discussion and accompanying drawing and claims that changes, modifications and variations can be made in the present invention without departing from the spirit and scope thereof.
Claims (28)
1. A molten metal pump comprising:
an elongated body defining an internal cavity defined by an inner wall which terminates in a bottom end; and
a first centrifugal impeller seated in an opening formed in the center of said bottom end, wherein molten metal ejected from the impeller is received by the bottom end;
whereby rotation of the impeller results in the ejected flow of molten metal creating an uplifting momentum which climbs the inner wall to an outlet opening passing through an upper portion of said body.
2. A pump as defined in claim 1 , wherein said internal cavity has a curvature which aids in the formation and sustaining of one of the following vortices: a forced vortex; a highly forced vortex; and a super forced vortex.
3. (canceled)
4. (canceled)
5. A pump as defined in claim 1 , wherein the diameter of the vessel inner wall is from 1.5 to 4 times the outer diameter of the first impeller.
6. A pump as defined in claim 1 , wherein the outlet opening of said vessel is at least three feet to seven feet above the bottom end of the internal cavity.
7. A pump as defined in claim 1 , wherein the impeller is a centrifugal pump generating a high velocity mixed flow with a specific speed ranging from 1,000 to 3,000.
8. A pump as defined in claim 1 , further comprising:
a pump motor which rotates a tubular motor shaft;
a gear box coupled to said motor shaft, which reduces the output speed of the motor and increases the torque from the motor; and
a drive shaft coupled at one end to said gear box and receiving said increased torque and extending concentrically down through the tubular motor shaft and fixed to said impeller.
9. A pump as defined in claim 1 , further comprising:
a pump motor which rotates a first drive shaft;
a second drive shaft which is fixed to said impeller; and
a thermally resistive coupling mounted between and interconnecting said first and second drive shafts, wherein said coupling includes a plurality of radially spaced vanes which draw ambient air into and then out of said coupling as said coupling is rotated.
10. A pump as defined in claim 2 , wherein said forced vortex has a constant angular velocity.
11. A pump as defined in claim 10 , wherein said forced vortex has a curved shaped pressure distribution given by P/γ=C2r2/2g+h.
12. A pump as defined in claim 2 , wherein said highly forced vortex and said super forced vortex have a curved shaped pressure distribution given by P/γ=C2r3/3g+h; wherein said highly forced vortex has a flow rate of less than 1,000 gallons per minute and said super forced vortex has a flow rate greater than 1,000 gallons per minute.
13. (canceled)
14. (canceled)
15. (canceled)
16. (canceled)
17. (canceled)
18. (canceled)
19. (canceled)
20. (canceled)
21. (canceled)
22. (canceled)
23. (canceled)
24. (canceled)
25. A powertrain for a molten metal pump having drive motor which rotates a centrifugal impeller, comprising:
a hollow tubular motor shaft which rotates with a rotor of said drive motor;
a mechanical gear train coupled at a first end to said motor shaft, wherein said gear train reduces the output speed of said drive motor and increases the torque transmitted; and
a cylindrical output shaft which is coupled to a second end of said gear train, wherein said output shaft rotates at said reduced output speed and receives said increased torque, wherein said output shaft is passes through said hollow motor shaft and is fixed to said impeller.
26. A molten metal pump comprising:
an elongated body defining an internal cavity defined by an inner wall which terminates in a bottom end; and
a first centrifugal impeller seated in an opening formed in the center of said bottom end and mounted upon a rotatable shaft, wherein molten metal ejected from the impeller is received by the bottom end;
a flow influencing element mounted above the first centrifugal impeller and in rotational engagement with the shaft; and
whereby rotation of the impeller results in the ejected flow of molten metal creating an uplifting momentum which climbs the inner wall to an outlet opening passing through an upper portion of said body.
27. The molten metal pump of claim 1 , further including a mechanism for introducing inert gas to said internal cavity.
28. The molten metal pump of claim 1 , further comprising a splash protector.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
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US15/426,407 US20170204862A1 (en) | 2008-10-29 | 2017-02-07 | Riserless recirculation/transfer pump and mixer/pre-melter for molten metal applications |
Applications Claiming Priority (4)
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US10935208P | 2008-10-29 | 2008-10-29 | |
US12/604,000 US8246295B2 (en) | 2008-10-29 | 2009-10-22 | Riserless transfer pump and mixer/pre-melter for molten metal applications |
US13/285,766 US9599111B2 (en) | 2008-10-29 | 2011-10-31 | Riserless recirculation/transfer pump and mixer/pre-melter for molten metal applications |
US15/426,407 US20170204862A1 (en) | 2008-10-29 | 2017-02-07 | Riserless recirculation/transfer pump and mixer/pre-melter for molten metal applications |
Related Parent Applications (1)
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US13/285,766 Continuation US9599111B2 (en) | 2008-10-29 | 2011-10-31 | Riserless recirculation/transfer pump and mixer/pre-melter for molten metal applications |
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US20170204862A1 true US20170204862A1 (en) | 2017-07-20 |
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US13/285,766 Active 2034-07-15 US9599111B2 (en) | 2008-10-29 | 2011-10-31 | Riserless recirculation/transfer pump and mixer/pre-melter for molten metal applications |
US15/426,407 Abandoned US20170204862A1 (en) | 2008-10-29 | 2017-02-07 | Riserless recirculation/transfer pump and mixer/pre-melter for molten metal applications |
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US13/285,766 Active 2034-07-15 US9599111B2 (en) | 2008-10-29 | 2011-10-31 | Riserless recirculation/transfer pump and mixer/pre-melter for molten metal applications |
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Families Citing this family (27)
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US20070253807A1 (en) | 2006-04-28 | 2007-11-01 | Cooper Paul V | Gas-transfer foot |
JP4874243B2 (en) * | 2004-07-07 | 2012-02-15 | パイロテック インコーポレイテッド | Molten metal pump |
US9205490B2 (en) | 2007-06-21 | 2015-12-08 | Molten Metal Equipment Innovations, Llc | Transfer well system and method for making same |
US9409232B2 (en) | 2007-06-21 | 2016-08-09 | Molten Metal Equipment Innovations, Llc | Molten metal transfer vessel and method of construction |
US9643247B2 (en) | 2007-06-21 | 2017-05-09 | Molten Metal Equipment Innovations, Llc | Molten metal transfer and degassing system |
US9410744B2 (en) | 2010-05-12 | 2016-08-09 | Molten Metal Equipment Innovations, Llc | Vessel transfer insert and system |
US8337746B2 (en) | 2007-06-21 | 2012-12-25 | Cooper Paul V | Transferring molten metal from one structure to another |
US9156087B2 (en) | 2007-06-21 | 2015-10-13 | Molten Metal Equipment Innovations, Llc | Molten metal transfer system and rotor |
US8366993B2 (en) | 2007-06-21 | 2013-02-05 | Cooper Paul V | System and method for degassing molten metal |
US8535603B2 (en) | 2009-08-07 | 2013-09-17 | Paul V. Cooper | Rotary degasser and rotor therefor |
US8524146B2 (en) | 2009-08-07 | 2013-09-03 | Paul V. Cooper | Rotary degassers and components therefor |
US10428821B2 (en) | 2009-08-07 | 2019-10-01 | Molten Metal Equipment Innovations, Llc | Quick submergence molten metal pump |
US8444911B2 (en) | 2009-08-07 | 2013-05-21 | Paul V. Cooper | Shaft and post tensioning device |
US9108244B2 (en) | 2009-09-09 | 2015-08-18 | Paul V. Cooper | Immersion heater for molten metal |
US9903383B2 (en) | 2013-03-13 | 2018-02-27 | Molten Metal Equipment Innovations, Llc | Molten metal rotor with hardened top |
US9011761B2 (en) | 2013-03-14 | 2015-04-21 | Paul V. Cooper | Ladle with transfer conduit |
US10052688B2 (en) | 2013-03-15 | 2018-08-21 | Molten Metal Equipment Innovations, Llc | Transfer pump launder system |
US9057376B2 (en) | 2013-06-13 | 2015-06-16 | Bruno H. Thut | Tube pump for transferring molten metal while preventing overflow |
US9011117B2 (en) | 2013-06-13 | 2015-04-21 | Bruno H. Thut | Pump for delivering flux to molten metal through a shaft sleeve |
US10138892B2 (en) | 2014-07-02 | 2018-11-27 | Molten Metal Equipment Innovations, Llc | Rotor and rotor shaft for molten metal |
US10947980B2 (en) | 2015-02-02 | 2021-03-16 | Molten Metal Equipment Innovations, Llc | Molten metal rotor with hardened blade tips |
US10267314B2 (en) | 2016-01-13 | 2019-04-23 | Molten Metal Equipment Innovations, Llc | Tensioned support shaft and other molten metal devices |
TWI617376B (en) * | 2017-06-20 | 2018-03-11 | 財團法人金屬工業研究發展中心 | A pump device for casting process |
US11149747B2 (en) | 2017-11-17 | 2021-10-19 | Molten Metal Equipment Innovations, Llc | Tensioned support post and other molten metal devices |
US11858036B2 (en) | 2019-05-17 | 2024-01-02 | Molten Metal Equipment Innovations, Llc | System and method to feed mold with molten metal |
EP4226045A1 (en) * | 2020-10-05 | 2023-08-16 | Pyrotek, Inc. | Low pressure molten metal transfer pump |
US11873845B2 (en) | 2021-05-28 | 2024-01-16 | Molten Metal Equipment Innovations, Llc | Molten metal transfer device |
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US9599111B2 (en) | 2017-03-21 |
US20120163959A1 (en) | 2012-06-28 |
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