[0001] The present invention relates to an open bladed impeller, particularly for a centrifugal
pump, comprising a supporting element which substantially has the shape of a planar
disk and a plurality of blades rigidly affixed to said supporting element at regularly
angularly spaced locations thereof, wherein each blade is formed by a longitudinal
core extending transversely of the main plane of the supporting element and having
a back longitudinal edge which is affixed to the supporting element and a front longitudinal
edge adapted to cooperate with a stationary facing wall of the pump casing; the back
longitudinal edge has a profile which is substantially parallel to the inner surface
of the stationary wall of the casing with a substantially uniform axial clearance
to provide a free frontal skimming surface providing a partial seal against the stationary
casing wall.
[0002] Bladed impellers of the foregoing type are commonly termed open impellers, since
the blading of the impeller is inwardly delimited by the back plate of the hub and
outwardly delimited by the stationary wall of the casing, unlike ordinary impellers
wherein the blading is closed along the outer edge by the front plate of the hub.
[0003] In order to improve the sealing action between the open blading of the impeller and
the stationary wall of the scroll casing, an adequate surface roughness is to be provided
on this stationary wall, possibly by lapping, to enable small assembly clearances
therebetween.
[0004] The efficiency of these known impellers obviously depends, to a large extent, on
the external profile of the blades, which has to follow as precisely as possible the
internal profile of the fixed wall in order to provide the minimum required clearance.
[0005] The advantage offered by these open impellers resides in the simplified machining
operations and results in improved surface smoothness of the rotation blades, which
generally leads to improved efficiency due to reduction of losses.
[0006] Various attempts have been made to manufacture high-efficiency open impellers in
an economical way. In particular, known impellers are obtained from cast-iron castings
or from steel or light-alloy forgings which have walls of considerable thickness in
order to provide open bladed structures with front skimming surfaces of suitable extension.
[0007] Though said known impellers have shown satisfactory operating conditions, they have
a first limitation in the fact that the blade vanes have a reduced width due to the
intrinsic thickness of the blades.
[0008] A further disadvantage of the known impellers made of cast-iron castings or steel
forgings resides in their considerable weight, which is a negative factor especially
for very large pumps. Though they fulfill optimum requirements from many viewpoints,
light-alloy castings are difficult and expensive to produce and machine.
[0009] In order to obviate the afore mentioned drawbacks, an attempt has been made to provide
impellers made of metal plate which have the features stated in the preamble of the
accompanying claim 1 and which involves a number of constructional and economical
advantages.
[0010] In said prior impellers, a problem arises in the limited front surface of the outer
skimming edges of the blades which are adapted to cooperate with the fixed wall of
the pump casing, due to the limited thickness of the metal plate forming the blades.
[0011] Manufacturers are evidently interested in providing impellers which offer the advantages
of metal plate products but have skimming surfaces interacting with the stationary
wall of the casing which are larger than is allowed by the limited thickness of the
metal plate itself, so as to obtain higher efficiency in spite of the same constructive
clearance. As an alternative, larger frontal coupling surfaces could be used which
would allow the adoption of smaller constructive clearances involving lower production
costs.
[0012] Unfortunately, current metal plate impellers have sets of stamped blades exhibiting
rather wide tolerances, which when combined with the tolerances for assembly on the
supporting frames lead to considerable variations of clearance with respect to the
fixed walls of the casing. In order to reduce said variations, subsequent surface
finishing operations are to be effected, which reduce the competitiveness of this
kind of sheet metal impellers with respect to the conventional ones.
[0013] It is an object of the present invention to obviate the foregoing disadvantages by
providing an open bladed impeller permitting to obtain high efficiency with low fabrication
costs.
[0014] A further object of the present invention is to provide an open bladed impeller which
has a simplified structure and can be easily obtained starting from commonly commercially
available raw materials.
[0015] These and other objects which will become apparent hereinafter are achieved by an
open bladed impeller, particularly for a centrifugal pump, according to the preamble
of claim 1, characterized in that at the front longitudinal edge of each blade there
is provided a substantially planar, longitudinal flange formation which projects laterally
from said longitudinal core to extend parallel to the facing surface of the stationary
wall, to thereby increase extension of the front skimming surfaces and improve their
sealing action relative to the inner casing wall.
[0016] Further characteristics and advantages will become more apparent from the following
description of some preferred but not exclusive embodiments of open bladed impellers,
illustrated only by way of non-limitative example in the accompanying drawings, wherein:
figure 1 is a partially sectional side view, taken along an axial plane, of a centrifugal
pump with open impeller according to the invention;
figure 2 is a partially sectional front view, taken along the plane II-II, of a first
embodiment of the impeller of figure 1;
figure 3 is a partially sectional partial front view, taken along the plane III-III,
of a second embodiment of the impeller of figure 1;
figure 4 is a sectional view of a blade of the impeller illustrated in figure 3, taken
along the plane IV-IV;
figure 5 is a sectional view of a blade of the impeller illustrated in figure 2, taken
along the plane V-V;
figures 6, 7 and 8 are front views respectively of a third, fourth and fifth embodiment
of impellers according to the invention.
[0017] With reference to the above figures, the open impeller according to the invention,
generally indicated by the reference numeral 1, is rotatably mounted inside a stationary
case 2 and is drivably connected to a shaft 3 which is rigid with the rotor 4 of the
motor.
[0018] The impeller 1 is formed by a supporting element 5 which is substantially disk-shaped
and whereupon a plurality of blades 6 of the radial centrifugal type are fixed. The
supporting element 5 comprises a central portion or hub 7 for rigid connection with
the motor shaft 3, optionally keyed by means of per se known elements not illustrated
in the drawing, and is generally obtained from blanked and stamped steel plate. Blades
6 are rigidly attached at 8 to element 5 by means of weldings, rivets or other similar
connecting elements.
[0019] Figure 2 is a front view of the impeller of figure 1, wherein the blades 6 are obtained
monolithically from an element 9 made of blanked and stamped plate which is subsequently
rigidly attached on the supporting element 5. In particular, the bladed element 9
is formed by a frusto-conical shaped, raised central portion 10 having a central hole
for the passage of coupling elements for connection with the drive shaft 3, from which
central portion blades 6 extend in a radial pattern at regularly spaced locations.
[0020] The impeller of figure 3 differs from the one of figure 2 exclusively in that the
blades 6 consist of separate members which are individually coupled to the supporting
element 5 at predetermined locations. Blades 6 may be obtained from stamped plate
or from sections of extruded profiled elements which are subsequently curved.
[0021] In both embodiments set forth before, the blades 6 have an elongated core 15 which
extends along a suitable profile to provide a centrifugal radial flow. The core 15
has an inner longitudinal edge 11 which is contacting the supporting element 5 and
an outer longitudinal edge 12 which is parallel to the inner surface of the fixed
wall 13 of the stationary case 2.
[0022] When the impeller 1 is assembled in case 2, the outer edges 12 are spaced from the
inner surface of the fixed wall 13 by an axial clearance
d of relatively small value enabling free rotation of the impeller, to thereby limit
the laminar leakage of the fluid between the edges and the fixed wall, in order to
convey the fluid to be pumped into the blade vanes.
[0023] The clearance
d is usually a few percent of the axial height
h of the core 15 of the blades. Obviously, the smaller are the values of axial clearance
d, the better will be the sealing conditions of the blade skimming and the operating
efficiency of the impeller.
[0024] According to the invention, the blades 6 have, at the outer edge 12, a substantially
planar longitudinal flange 14 extending laterally from the core 15 of the blades so
as to increase the front skimming surface, improving sealing conditions thereof with
respect to the fixed wall. In the embodiment illustrated in figure 1, the fixed wall
13 of the stationary case 2 is substantially perpendicular to the axis of the pump;
however, the wall could have different shapes and inclinations, and consequently the
outer edge 12 of the blades should match these orientations and inclinations.
[0025] The width
b of the longitudinal flange 14 can be comprised between 2 and 10 times the thickness
s of the core 15 of the blades.
[0026] Advantageously, the transverse cross section of the blades may be C-shaped, as illustrated
in figure 4, or X-shaped, as illustrated in figure 5.
[0027] These embodiments are particularly advantageous since they can be obtained by stamping
or extrusion, in a separate form or as a monolithic assembly, and besides the advantages
of greater sealing described above they have high rigidity and stiffness with a very
limited increase in weight.
[0028] According to a further aspect of the present invention, the free edge of the longitudinal
flange 14 can assume various shapes in order to cooperate with the wall of the stator
case so as to act like a shredding or jam-preventing blade. Figures 6, 7 and 8 depict
three exemplary embodiments of the outer edge of the longitudinal flange 14 having
this purpose. In particular, in figure 6 the edge is defined with trapezoidal teeth,
in figure 7 the teeth are semicircular protrusions, and in figure 8 the teeth are
semicircular recesses alternated with linear portions.
[0029] The fact is stressed that both the supporting element 5 and the set of blades 6 are
preferably obtained starting from sheet metal, by means of blanking and cold forging
process. With particular reference to the blades 6, this embodiment permits axial
span of the blades with high precision and repeatable processes, due to the presence
of the upper and lower blades which are normal to the central core. As an alternative,
by providing wider skimming surfaces it is possible to use larger axial clearances
d obtaining the same efficiency.
[0030] However, the same components can be obtained with other materials and by means of
other processes such as for example light-alloy casting or injection of thermoplastic
resins.
[0031] From the foregoing description it appears that the invention achieves the proposed
aim and objects and in particular the fact is underlined that though the open impeller
according to the invention has a simplified and lightweight structure it however implies
the same efficiency and performances as prior more complicated and expensive impellers.
[0032] The impeller according to the invention is susceptible to numerous modifications
and variations, all of which are within the scope of the inventive concept. Furthermore,
all the details may be replaced with other technically equivalent elements. By way
of example, mention is made of possible flattening operations and/or thermal or surface
treatments carried on the flange portions of the blades in order to improve the resistance
of said regions.
[0033] In practice, the materials employed, so long as compatible with the specific use,
as well as the contingent shapes and dimensions, may be any according to the requirements.
Where technical features mentioned in any claim are followed by reference signs, those
reference signs have been included for the sole purpose of increasing the intelligibility
of the claims and accordingly, such reference signs do not have any limiting effect
on the scope of each element identified by way of example by such reference signs.
1. Open bladed impeller (1), particularly for a centrifugal pump, comprising a substantially
planar disk-like supporting element (5) having a central hub (7) adapted to be keyed
to a drive shaft (3) and a plurality of blades (6) which are rigidly attached to the
front surface of said supporting element (5) in regularly angularly spaced locations
thereof, each of said blades (6) being formed by a longitudinal core (15) extending
transversely of the main plane of said supporting element, said blades having a back
longitudinal edge (11) affixed to said supporting element (5) and a front longitudinal
edge (12) adapted to cooperate with an adjacent stationary wall (13) of the pump casing
(2), said front longitudinal edge (12) having a profile which is substantially parallel
to the inner surface of said stationary wall (13) with such a substantially uniform
axial clearance (d) to provide a free frontal skimming surface providing partial sealing
with said stationary wall, characterized in that said blades (6) have, at said front
longitudinal edge (12), a longitudinal flange formation (14) which is substantially
planar and projects laterally from said longitudinal core (15) to extend parallel
to the facing surface of said stationary wall (13), to thereby increase extension
of the front skimming surfaces and improve their sealing action relative to said wall.
2. Open bladed impeller according to claim 1, characterized in that said blades (6)
consist of longitudinal members, made of stamped plate or extruded elements, which
have a substantially constant transverse cross section along their longitudinal extension.
3. Open bladed impeller according to claim 2, characterized in that said transverse
cross section is substantially C-shaped.
4. Open bladed impeller according to claim 2, characterized in that said transverse
cross section is substantially X-shaped.
5. Open bladed impeller according to any one of the preceding claims 3 and 4, characterized
in that said longitudinal flange (14) is defined by one of the end wings of said transverse
cross section, whereas the other end wing of said cross section defines an attachment
portion for connection with said first supporting element (5).
6. Open bladed impeller according to claim 1, characterized in that said plurality
of blades (6) are monolithically formed in a second metal plate element (9) adapted
to be coupled to said first supporting element (5).
7. Open bladed impeller according to one or more of the preceding claims, characterized
in that the average width (b) of said longitudinal flange (14) is comprised between
2 and 10 times the average thickness (s) of the core (15) of the blades.
8. Open bladed impeller according to claim 1, characterized in that the free edge
of said longitudinal flange formation (14) is substantially continuous and parallel
to the curved profile of the longitudinal core (15) of the blades.
9. Open bladed impeller according to claim 1, characterized in that the free edge
of said longitudinal flange (14) has a ragged profile suitable for shredding debris
or other solid materials possibly present in the fluid to be pumped.
10. Open bladed impeller according to claim 9, characterized in that said ragged shape
is substantially saw-toothed.
11. Open bladed impeller according to claim 9, characterized in that said ragged shape
comprises semicircular protrusions or recesses alternated with substantially continuous
portions.