Rotary kinetic fluid motors or pumps – Working fluid passage or distributing means associated with... – Specific casing or vane material
Reexamination Certificate
2001-02-08
2003-03-25
Look, Edward K. (Department: 3745)
Rotary kinetic fluid motors or pumps
Working fluid passage or distributing means associated with...
Specific casing or vane material
C415S213100
Reexamination Certificate
active
06537024
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a sheet metal pump casing and its fabrication method and particularly to a pump casing made by roll forming of sheet metal, and having a flange reinforced structure to enhance pump casing strength, and having a guide plate for forming more effective volute.
2. Description of the Prior Art
Conventional methods for fabricating a pump casing for a centrifugal pump generally include casting and sheet metal working. The pump casing made by casting usually is relatively bulky and heavy. It takes more material and space. Because of material characteristics (cast iron), it has poor erosion resistantance and low stiffness. It is therefore less durable and is mostly used in relatively low value and price products. The pump casing made by sheet metal stamping may use high strength and high erosion resistant metal (such as stainless or alloy steel). It is lighter and smaller and more durable. However due to pump casing made by sheet metal is relatively thin, it is prone to deform under external force. Furthermore during stamping process, high stress concentration often happens at some spots of the pump casing and results in strength reduction, uneven thickness, deformation or even fracture.
In general, a pump connects with a piping system at the inlet and outlet. The piping system constantly subjects to heat expansion and cold contraction effects. The fluid pressure has wide variation. The pump impeller will generate torque during rotation. All these factors will create dynamic loads acting upon the inlet and outlet, and could result in deformation of pump casing at the inlet and outlet sections. It is therefore a constant studying subject in pump design on how to increase the strength of the inlet and outlet sections to withstand those internal and external forces and stress. PCT (Germany) patent No. PCT/DE86/00188 discloses a sheet metal pump design (shown in FIG.
1
). The centrifugal pump
10
has a sheet metal pump casing
11
which is formed by a sheet metal working piece or by welding a plural number of sheet metal working pieces together. The sheet metal working pieces are made by stamping processes. The pump casing
11
near the inlet
12
is formed in ravine shape for reinforcement. However there is still some deficiencies in such construction. For instance, it is generally known that the centrifugal pump usually has a wear ring
15
located at the front end of the impeller
14
near the inlet
12
. It is to keep clearance between the impeller tip and the inside wall of the pump casing
11
so that when the impeller rotates in high speed, the severe friction that might otherwise happen between the impeller and the pump casing may be avoided. The degree of clearance directly affects pump efficiency, noise level and working life of the pump. Although the pump
10
shown in
FIG. 1
has reinforcement structure for the pump casing
11
, the maximum force receiving location is still at the inlet
12
section. When the pump
10
subjects to high stress, torsion or torque, the pump casing
11
near the inlet
12
is easily deformed. The wear ring
15
clearance is prone to change. It could result in lower pumping efficiency or increasing noise level, or even damage the pump. It is also known that a volute will be formed between the impeller
14
and the inside wall of the pump casing
11
. The volute will produce better pumping effect with increasing crosssection dimensions starting from the outlet along the rotor
14
rotation direction. This variating dimension shape is easily made by casting method but is difficult to form by stamping sheet metal working process. Therefore, in
FIG. 1
, the volute has a constant dimension rather than variation that is more desirable. The pumping efficiency will be lowered because of such deficiency.
European patent No. EPO-0442070A1 (Ghiotto) discloses another centrifugal pump
20
with sheet metal pump casing
21
(shown in FIG.
2
). Around the inlet
22
is a flange
23
. Near the flange
23
at the inlet section, there is a reinforced member
26
formed in a passage shape and relatively greater thickness than the pump casing. The reinforced member
26
is welded to the inside wall of the pump casing
21
to support high stress at the inlet section. However when the flange
23
is subjected to great external force, the wear ring clearance at the front end of the impeller
25
tends to change. Hence it will cause dropping of pumping efficiency, increasing noise level and reducing working life. Furthermore it also does not cover detailed description about the volute
27
improvement.
There have been prior cases which tried to employ multiple stamping processes on sheet metal along the volute of the pump casing for producing increasing crosssections volute. They usually need a plural number of dies and stamping operations. The total fabrication time is long and the cost is higher. Moreover excessive stamping processes could result in harmful effect on material property and structure of the pumping casing.
SUMMARY OF THE INVENTION
In view of aforesaid disadvantages, it is therefore an object of this invention to provide a sheet metal pump casing and its fabrication method for producing sheet metal pump casing with greater strength. It can also result in stable wear ring clearance at the front of the impeller and volute with increasing crosssections at low cost. The sheet metal working method according to this invention can form a pump casing with stable and steady strength without undue stress concentration or downgrade the pump casing material.
The sheet metal pump casing according to this invention includes a body, an impeller, an inlet flange and an outlet flange. The body has an inlet engaging with the inlet flange, and an outlet engaging with the outlet flange. At the inlet flange, there is provided with a first flap flange which has one end located from the peripheral of the inlet flange and another end extending to the outside wall of the body and spaced from the inlet. Around the outlet flange, there is also a second flap flange with one end extending to the outside wall of the body and connecting with the inlet flange. Because of such construction, the stress, torque and torsion applying on the inlet flange and outlet flange will not directly transmit to the body near the inlet and outlet. The first and second flap flange will receive and disperse the stress and forces to other parts of the body remote from the inlet and outlet. Therefore the wear ring clearance at the front end of the impeller will be least affected by external force.
According to one aspect of this invention, the first and second flap flange are respectively made in a double flange form and welded to body in opposite direction between the inlet (or outlet) flange and the body. The flap flange has a flap foot fixed to the body. The flap foot has the contour mating with the shape and form of the body so that the stress and force may be dispersed more evenly.
In another aspect of this invention, there is provided with a guide plate formed in an arched shape and being fixed to the inside wall of the body. The guide plate has a joint section mating and welded to the inside wall near the outlet, a cut water section and a spread section. The cut water section bridges between the joint section and the spread section with a cut water end projecting toward the impeller but spaced from it. The spread section is an elongated narrow strip with a head end connecting with the cut water section and a tail end fixing to the inside wall of the body. The middle section of the spread section is formed in curved shape around the impeller with a narrow gap at the cut water end and wider gap at the tail end. Therefore the impeller and the guide plate form a volute with increasing crosssection from the cut water end to the tail end. When the impeller rotates and pumps fluid, fluid flows in the volute and being discharged out from the outlet more smoothly. The cut water section also helps to smooth out fluid discharge
Chien Huan-Jan
Pen Char-Lie
Tang Kou-Yu
Industrial Technology Research Institute
Liauh W. Wayne
Look Edward K.
McAleenan James M
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