Sheet metal casing for multistage pump and method for manufacturing the same

Information

  • Patent Grant
  • 6267555
  • Patent Number
    6,267,555
  • Date Filed
    Wednesday, January 12, 2000
    24 years ago
  • Date Issued
    Tuesday, July 31, 2001
    23 years ago
Abstract
A sheet metal casing for multistage pump and its manufacturing method, the casing includes an outer shell and an inner shell. The outer shell is integrally formed and includes a front end ring, a step positioning ring, an outer shell surface and a positioning end. The inner shell is fixed to the inner side of the outer shell and includes an inner end, an inner shell surface and a step positioning rim. The step positioning rim forms a closed holding space with the outer shell surface for holding and squeezing a seal ring therein. When a plurality of casings being serially mounted on a spindle, the positioning end of a front casing may make contact with the step positioning ring of a rear casing, and the positioning rim of the front inner shell may make contact with the front end ring of the rear outer shell for axially positioning the casings on the spindle.
Description




BACKGROUND OF THE INVENTION




1. Field of the Invention




This invention relates to sheet metal casing for multistage pump and its manufacturing method, and particularly to a sheet metal casing for multistage submerged pump that has simple structure to facilitate fabrication and assembly at low cost, and has improved sealing and pumping efficiency.




2. Description of the Prior Art




Conventional multistage centrifugal pumps (such as submerged pumps) usually includes a plurality of casings with passages and impellers housed therein and mounted serially on a rotationable spindle for pumping fluid by adding pressure. The multistage pump made by casting in the past is heavy and bulky and has lower pump efficiency. It is generally replaced by sheet metal casing pump nowadays.




In the design of multistage sheet metal casing pump, the main considerations include: manufacturing and assembly cost, pump efficiency and passage design, pressure resistance, leakage prevention, etc. These factors are rarely totally met by conventional sheet metal casing multistage pump. For instance, European Pat. Application No. 81110541.0 discloses a sheet metal casing structure for multistage pump shown in FIG.


1


. It has a casing


11


made by punching and a partition member


12


to form a stage


2


for housing an impeller


3


and baffles


20


therein. The casing


11


has a curved portion


19


for engaging a front stage with a rear stage. At the juncture of the engagement, a seal ring


14


is provided. The dimension and precision of the curved portion


19


is difficult to control. When more than one stage being fastened axially, the positioning of the curved portion


19


is even more difficult and is prone to deform. The seal ring


14


tends to malfunction and result in leakage under pressure or vibration. Moreover there is no smooth passage inside the casing


11


and the impeller


13


. It is easy to produce turbulence around the front end


112


during pumping operation and result in lower pump efficiency. In short, it has the drawbacks of poor axial positioning, easy leaking and low pump efficiency.





FIG. 2

illustrates another prior art disclosed in U.S. Pat. No. 5,234,317. It has a pump casing


21


made by punching and pressing. The pump casing


21


has an end rim


211


formed in a U-shaped member for engaging securely with a next stage pump casing. However it has a smaller contact area (sealing surface). The end rim


211


is prone to deform and open outwardly under strong pumping pressure or vibration. Leaking is still not avoidable. Furthermore the pump casing


21


cannot be made by merely punching operation. It needs pressing operation to finish all the fabrication work required. The cost is higher. And there is also no smooth passage inside the casing and may result in turbulence and lower pump efficiency. When two stage pumps are connected, the connection portion forms an S-shaped structure. While it helps to prevent deformation and leakage, it increases production cost.





FIG. 3

shows a still another technique seen in the market place. The pump casing


4


includes a front outer shell


41


, a rear outer shell


42


, a front inner shell


43


, a rear inner shell


44


, a hub


46


, a front seal ring


47


and an impeller (not shown in the figure). The front outer shell


41


includes a front side ring


413


, an axial positioning ring


411


and a radial positioning ring


412


. The rear outer shell


42


includes an axial positioning end


421


and a radial positioning end


422


mating respectively with the rings


411


and


412


. The rear inner shell


44


has a positioning end


441


at the rear end.




For assembly of a single casing


4


, the vane


45


is firstly soldered to the front inner shell


43


. Then the front outer shell


41


, rear outer shell


42


, front inner shell


43


and rear inner shell


44


are assembled together (otherwise the inner shells


43


and


44


cannot be put into the outer shells


41


and


42


). Then circular soldering is made on the solder spots


48


around the outer shell.




For assembly of a multistage pump casing


4


, the positioning end


44


of a front casing


4


will be made contact with the front side ring


413


of a rear casing. The axial and radial positioning end


421


and


422


of the front casing will be made contact with the axial and radial positioning rings


411


and


412


which may couple with a seal ring to prevent leakage. The front and rear inner shells


43


and


44


have curved inside surface to smooth flow passage and enhance pump efficiency.




However there are still disadvantages in this technique, notably:




1. It has too many components and costs too much to produce. Eight components are required, including the front and rear outer shells


41


and


42


front and rear inner shells


43


and


44


, vane


45


, hub


46


, front seal ring


47


and the impeller. The molding cost and assembly time increase greatly. The hub


46


and front seal ring


47


also add to the cost.




2. It needs secondary machining that increases cost and production time. The axial and radial positioning ring


411


and


412


, and the axial and radial positioning end


421


and


422


need high precision machining work to get the accurate dimension for making the required connection. An usual punching operation cannot produce that kind of precision. The machining also unavoidably reduces shell thickness and weaken the structural strength.




3. The circular soldering of the solder spots


48


are much more expensive and time-consuming than conventional spot soldering. It also tends to produce notsightly casing and lower dimension accuracy. Positioning for assembly is more difficult. The soldering property and strength is difficult to control. A secondary machining is needed after the soldering and may reduce casing thickness.




The prior arts set forth above thus cannot totally meet all the design factors such as production and assembly costs, pump efficiency and passage streamline, pressure resistance, leak control and prevention, etc. There are still a lot of room for improvement.




SUMMARY OF THE INVENTION




It is an object of this invention to provide a sheet metal casing for multistage pump and manufacturing method that has lower production and assembly cost, enhanced pressure resistance and improved leakage prevention.




The pump according to this invention consists of a plurality of pump unitsserially mounted on a rotationable spindle. Each pump unit includes a casing, an impeller and a hub. The casing includes an outer shell and an inner shell. The outer shell is integrally formed and includes a front end ring, a step positioning ring, an outer shell surface and a positioning end. The inner shell is located inside the outer shell and includes an inner end, an inner shell surface and a step positioning rim. The positioning rim and the outer shell surface form a holding space inside for holding a seal ring. When a plurality of casings are serially connected, the positioning end of a front casing may contact with the step positioning ring of a rear casing, and the positioning rim of the front casing may contact with front end ring of the rear casing for positioning the casings on the spindle and securing the seal ring in the closed holding space. The front end ring and the inner end are bent and extended forward and are parallel with the spindle with a gap formed therebetween to mate against inlet of the impeller. It also serves sealing function.




The manufacturing method of this invention includes more than one punching operation on a metal sheet to produce the front end ring, step positioning ring and outer shell surface. Then the inner shell is formed by more than one punching operation to form a front half and a rear half sections.




The front half section includes the inner end and about a half of the inner shell surface. The rear half section includes about a half of remaining inner shell surface and the positioning rim. Then the front half section, vane and rear half section are soldered serially to the outer shell. Finally a punching operation is performed on the outer shell to form the positioning end.











BRIEF DESCRIPTION OF THE DRAWINGS




This invention, as well as its many advantages, may be further understood by the following detailed description and drawings, in which:





FIG. 1

is a sectional view of a conventional sheet metal casing for a multistage pump.





FIG. 2

is a fragmentary sectional view of another conventional sheet metal casing for a multistage pump.





FIG. 3

is a fragmentary sectional view of a further conventional sheet metal casing for a multistage pump.





FIG. 4

is a fragmentary sectional view of this invention for a single pump casing.





FIG. 5

is fragmentary sectional view of this invention for a two-stage pump.





FIG. 6

is a fragmentary sectional view of a positioning end for holding a seal ring.











DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT




Referring to

FIGS. 4 and 5

, the sheet metal casing of this invention consists of a plurality of pump casings


6


serially mounted on a rotationable spindle


5


. Each of the pump casings


6


includes a casing, an impeller


7


and a vane


8


. The structure of the spindle


5


, impeller


7


and vane


8


, and their constructional relationship are known in the art and form no part of this invention, thus will be omitted hereinafter.




This invention mainly focuses the pump casing structure and will be described in the following.




The pump casing includes an outer shell


61


, an inner shell


62


and a seal ring


9


. The outer shell


61


is made by punching a sheet metal (such as stainless steel) with more than one operation to form an integrated annular shell shape. It includes (from left to right in

FIG. 4

) a first front end


611


which extends approximately parallel with the spindle


5


for a selected length, a front end ring


612


extending outward and normal to the spindle


5


, a step positioning ring


613


extending outward from the front end ring


612


, an outer shell surface


614


extending parallel with the spindle


5


and a positioning end


615


extending inward and nearly normal to the spindle


5


as shown in FIG.


6


). The step positioning ring


613


also has a normal or near normal angle.




The inner shell


62


is fixed inside the outer shell


61


and houses the vane


8


therein. The inner shell


62


includes a second front end


621


approximately parallel with the spindle


5


, an inner end


622


extending outward and normal to the spindle


5


, an inner shell surface


623


approximately parallel with the spindle


5


below the outer shell surface


614


and forms a step elbow inward toward the spindle


5


at a fist curved bend


627


, and a positioning rim


624


parallel with the spindle


5


. The positioning rim


624


and positioning end


615


form a holding space for holding the seal ring


9


therein. The juncture between the inner end


622


and inner shell surface


623


also forms a second curved bend


626


which couples with the first curved bend


627


to form a smooth fluid passage guide to enable pumping fluid to flow smoothly from the impeller


7


to the vane


8


without producing turbulence.




Referring to

FIG. 5

, when a plurality of pump casings


6


are assembled serially, the front casing


6


(at the left side in

FIG. 5

) has its positioning end


615


making contact with the step positioning ring


613


of the rear casing (at the right side in FIG.


5


). The positioning rim


624


of the front casing makes contact with the front ending


612


of the rear casing, so that the pump casing


6


may be positioned on the spindle


5


and the space


625


may become closed. The seal ring


9


held in the closed space


625


is squeezed and may prevent leakage effectively. As the positioning end


615


of the front casing engages with a slightly tilted step positioning ring


613


of the rear casing, the deformation of the positioning end


615


under pressure may be minimized and may further prevent leakage from taking place. Furthermore the first front end


611


and second front end


621


form a gap mating with the inlet


71


of the impeller


7


and may also provide impeller sealing function.





FIG. 6

shows another embodiment of the positioning end


615


of this invention. Same or similar components will be marked by same numerals suffixed with a character. The positional end


615




a


is bent slightly larger than 90 degree for wedging with the step positioning ring


613




a


. It forms a more secured sealing and anti-leaking effect than the one shown in FIG.


5


. However it needs more precise machining.




The manufacturing method of this invention may include the following steps:




a. punching a sheet metal more than once to form the outer shell


61


, including the first front end


611


, front end ring


612


, step positioning ring


613


and outer shell surface


614


;




b1. Punching two metal sheets more than once to form the front and rear half section of the inner shell


62


. The front half section includes the second front end


621


, inner end


622


and about a half of the inner shell surface


623


. The rear half, section includes about a half of the inner shell surface


623


and positioning rim


624


.




b2. Placing the front half section of the inner shell


62


and the vane


8


into the outer shell


62


from a rear end thereof, soldering the vane


8


to the front half section.




b3. Placing the rear half section of the inner shell


62


into the outer shell


61


from the rear end thereof;




Soldering the front and rear half section together to form a complete inner shell


62


and fixing the inner shell


62


to the inner side of the outer shell surface


614


.




c. punching the outer shell surface


614


to form the positioning end


615


.




According to this invention, the outer shell


61


and inner shell


62


have relatively simple form. They are simpler to produce and assemble at lower cost. The positioning end


615


is formed after the inner shell


62


is fixed in the outer shell


61


. It may be made with simpler mold at higher precision. It thus can sustain high pressure without deformation or leakage. The engagement of the positioning end


615


with the step positioning ring


613


is also more secure, and can effectively prevent leakage under high pressure even with less than perfect fabrication precision of the pump casing. The seal ring


9


held in a closed space


625


can further improve anti-leaking effect. The curved bend


626


and


627


provide smooth passage guide to streamline fluid flow without generating turbulence and thus may enhance pump efficiently. Almost all the shortcomings resulting from conventional pump casing thus may be overcome by means of this invention. In summary, this invention offers the following advantages:




1. Small number of components.




As shown in

FIGS. 4 and 5

, the pump casing


6


of this invention includes an outer shell


61


, an inner shell


62


(with a front and a rear section), a vane


8


and an impeller. It takes only five components comparing with eight in the conventional pump casing mentioned before. Positioning and assembly become much easier. At least four molds may be saved for producing the components. Production cost thus may be greatly reduced. The sealing between the hub and the front seal ring may be done without additional features. It also helps to drive cost down.




2. No need for secondary high precision machining.




The sealing effect from the positioning end


615


and step positioning ring


613


and the seal ring


9


is simple and effective with no need of precision machining. The production cost becomes lower.




3. No need for circular soldering.




The outer shell


61


is one piece made integrally. Spot soldering is sufficient to accomplish required bonding strength. It costs lower, makes sightly appearance and stronger structural strength. Spot soldering also has less impact on pump casing deformation and mechanical strength of the material, it thus makes secondary machining for the step positioning ring


613


and positioning end


615


unnecessary.




It may thus been seen that the objects of the present invention set forth herein, as well as those made apparent from the foregoing description, are efficiently attained. While the preferred embodiment of the invention has been set forth for purpose of disclosure, modifications of the disclosed embodiment of the invention as well as other embodiments thereof may occur to those skill in the art. Accordingly, the appended claims are intended to cover all embodiments which do not depart from the spirit and scope of the invention.



Claims
  • 1. A sheet metal casing for multistage pump which consists a plurality of pump casings serially mounted on a rotationable spindle, the pump casing includes a casing, an impeller and a vane, the casing comprising;an annular outer shell made by integral forming including at least, starting from one end thereof, a front end ring approximately normal to the spindle and extending outward, a step positioning ring having one end thereof connecting with the front end ring, an outer shell surface extending nearly parallel with the spindle and a positioning end connecting with an end of the outer shell surface and extending toward the spindle; an inner shell fixedly located in the outer shell and housed the vane therein, including at least, starting from an end adjacent the front end ring, an inner ring approximately normal to the spindle and extending outward, an inner shell surface approximately parallel with the spindle, and a step positioning end connection with inner shell surface at one end thereof, the step positioning end forming a holding space with the outer shell surface; and a seal ring held in the holding space; wherein the front end ring has a first front end bent parallel with the spindle and extending forward, the inner end has a second front end bent parallel with the spindle and extending forward, the first and second front ends form a gap therebetwen mating with an inlet of the impeller for sealing the impeller.
  • 2. The sheet metal casing for multistage pump of claim 1, wherein the positioning end of a front pump casing makes contact with the step positioning ring of a rear pump casing, and the positioning rim of the front pump casing makes contact with the front end ring of the rear pump casing to form a closed space to hold the squeezed seal ring therein for preventing leakage.
  • 3. The sheet metal casing for multistage pump of claim 1, wherein the positioning end has a surface formed an approximately ninety degree angle radially against the outer shell surface for mating and contacting with the step positioning ring of the rear adjacent pump casing to prevent leaking under high pumping pressure.
  • 4. The sheet metal casing for multistage pump of claim 1, wherein the inner shell surface forms respectively with the inner end and positioning rim a first and a second curved bend to become curved passage guide to streamline fluid flow from the impeller to the vane for preventing turbulence.
  • 5. The sheet metal casing for multistage pump of claim 1, wherein the positioning end forms an angle with the outer shell surface larger than ninety degree, the step positioning ring has a bending angle less than ninety degree for mating and contacting with the positioning end so that the positioning end wont deform outward under high pumping pressure.
  • 6. The sheet metal casing for multistage pump of claim 1, wherein the vane is fixedly located on the inner end within the inner shell.
  • 7. A manufacturing method for fabricating the sheet metal casing of claim 1, comprising the following steps:a. punching a sheet metal more than once to form the front end ring, step positioning ring and the outer shell surface; b. placing the inner shell which has the vane located therein into the outer shell through a rear end thereof and soldering the inner shell to the outer shell; and c. punching a rear end of the outer shell surface to form the positioning end.
  • 8. The manufacturing method of claim 7, wherein the step b further includes the following:b1. Punching more than once two separate metal sheets to form a front and a rear section of the inner shell, the front section including at least the inner end and approximately a half of the inner shell surface, the rear section including at least approximately a half of the inner shell surface and the positioning end; b2. Placing the front section and a front end of the vane into the outer shell at a selected location behind an inside end of the outer shell, the vane being soldered to the front section before being moved into the outer shell; and b3. Placing the rear section into the outer shell to connect with the front section by soldering to form the inner shell, fixing the inner shell to an inner side of the outer shell surface.
  • 9. A sheet metal casing for multistage pump which consists a plurality of pump casings serially mounted on a rotationable spindle, the pump casing includes a casing, an impeller and a vane, the casing comprising;an outer shell engaged with an inner shell; an annular outer shell made by integral forming including at least, starting from one end thereof, a front end ring approximately normal to the spindle and extending outward, a step positioning ring having one end thereof connecting with the front end ring, an outer shell surface extending nearly parallel with the spindle and a positioning end connecting with an end of the outer shell surface and extending toward the spindle; an inner shell fixedly located in the outer shell and housed the vane therein, including at least, starting from an end adjacent the front end ring, an inner ring approximately normal to the spindle and extending outward, an inner shell surface approximately parallel with the spindle, and a step positioning end connection with inner shell surface at one end thereof, the step positioning end forming a holding space with the outer shell surface; and wherein the front end ring has a first front end bent parallel with the spindle and extending forward, the inner end has a second front end bent parallel with the spindle and extending forward, the first and second front ends form a gap therebetwen mating with an inlet of the impeller for sealing the impeller.
  • 10. The sheet metal casing for multistage pump of claim 9 further having a seal ring located in the holding space, the seal ring being squeezed when the pump casings being serially mounted for preventing leakage.
  • 11. The sheet metal casing for multistage pump of claim 9 wherein the positioning end has a surface formed an approximately ninety degree angle radially against the outer shell surface for mating and contacting with the step positioning ring of the rear adjacent pump casing to prevent leaking under high pumping pressure.
  • 12. The sheet metal casing for multistage pump of claim 9, wherein the inner shell surface forms respectively with the inner end and positioning rim a first and a second curved bend to become curved passage guide to streamline fluid flow from the impeller to the vane for preventing turbulence.
  • 13. The sheet metal casing for multistage pump of claim 9, wherein the positioning end forms an angle with the outer shell surface larger than ninety degree, the step positioning ring has a bending angle less than ninety degree for mating and contacting with the positioning end so that the positioning end wont deform outward under high pumping pressure.
  • 14. The sheet metal casing for multistage pump of claim 9, wherein the vane is fixedly located on the inner end within the inner shell.
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Number Name Date Kind
5234317 Kajiwara et al. Aug 1993
5256033 Kajiwara Oct 1993
5318403 Kajiwara et al. Jun 1994
5352089 Tokunaga et al. Oct 1994
5358380 Arkawa Oct 1994
5385444 Kobayashi et al. Jan 1995