Device for transmitting torque to brittle impellers of fluid flow machines

A centrifugal pump wherein the back shroud of a brittle impeller of ceramic or glass is coupled to the radially outwardly extending disc of a metallic adapter whose hub receives torque from the pump shaft. The adapter has a flange which surrounds the peripheral surface of the impeller or it has a collar which surrounds a complementary collar of the back shroud. The arrangement is such that the coupling between the adapter and the impeller does not subject the impeller to any tensional or other stresses which would be likely to affect the integrity of the brittle impeller. The disc of the adapter is adjacent the rear side of the back shroud so that the adapter does not interfere with the flow of conveyed material to, in and from the impeller.

BACKGROUND OF THE INVENTION 
The invention relates to fluid flow machines in general, and more 
particularly to improvements in means for transmitting torque from the 
driving element (such as a motor-driven shaft) to one or more impellers of 
a centrifugal pump or another fluid flow machine. Still more particularly, 
the invention relates to improvements in means for transmitting torque to 
brittle impellers. 
German Offenlegungsschrift No. 29 15 292 discloses a ceramic rotor which is 
secured to a metallic shaft by means of two star-shaped discs each of 
which has a hub and a set of radially outwardly extending prongs or arms. 
The discs flank the rotor which is provided with slightly conical surfaces 
abutting the respective sets of prongs. These prongs are elastic and 
engage the respective surfaces of the rotor in stressed condition. At 
least one of the discs is form-lockingly connected with the rotor. 
The purpose of the just described mounting of the rotor is to ensure that 
the rotor will be acted upon by compressive stresses but will be subjected 
to the action of negligible forces which could cause the development of 
tensional stresses, i.e., of stresses which cannot be readily withstood by 
a brittle material (such as a ceramic or glass). A drawback of the discs 
which are proposed in the Offenlegungsschrift is that their initial cost 
is substantial. Moreover, such discs can properly engage only a rotor 
which is of special design so that it can cause at least some stressing of 
the prongs and can be maintained in requisite form-locking engagement with 
one or both discs. Still further, at least one of the discs interferes 
with the flow of conveyed material toward, in and from the rotor if the 
latter constitutes an impeller. This holds true especially for the suction 
side of an impeller because the suction side is normally adjacent several 
indispensable or optional component parts of the pump, such as devices for 
engaging the periphery of the impeller. 
OBJECTS AND SUMMARY OF THE INVENTION 
An object of the invention is to provide a novel and improved device which 
can connect a brittle impeller to a driving element without interfering 
with the flow of conveyed material. 
Another object of the invention is to provide a simple, compact and 
inexpensive adapter which can secure a brittle impeller to a pump shaft 
and occupies little room in a fluid flow machine. 
A further object of the invention is to provide a fluid flow machine which 
embodies one or more adapters of the above outlined character. 
An additional object of the invention is to provide a adapter which can be 
coupled to an impeller in such a way that the impeller is subjected to 
negligible tensional and/or other stresses which would be likely to result 
in breakage of an impeller consisting of glass or a ceramic substance. 
Another object of the invention is to provide a novel and improved method 
of mounting brittle impellers on the shafts of centrifugal pumps or other 
fluid flow machines. 
The invention is embodied in a fluid flow machine, such as a centrifugal 
pump. The fluid flow machine comprises a rotary impeller having a back 
shroud with a peripheral surface, and an adapter which connects the 
impeller to a driving component, such as the pump shaft. The adapter 
includes means for engaging the impeller in the region of the peripheral 
surface of the back shroud in such a way that the impeller is not 
subjected to any, or is subjected to negligible, tensional stresses. This 
is important when the back shroud or the entire impeller contains or 
consists of a brittle material (such as glass or a ceramic). The adapter 
preferably comprises or consists of a ductile material, such as a suitable 
metallic substance. 
The adapter can further include a hub which can be non-rotatably mounted on 
the shaft of a centrifugal pump, and a disc which is adjacent the back 
shroud. The aforementioned engaging means is provided on the disc. Such 
engaging means can comprise a flange or an analogous member which 
surrounds at least a portion of the peripheral surface of the back shroud. 
Alternatively, the back shroud can be provided with a first collar and the 
disc of the adapter can be provided with a second collar, which 
constitutes or forms part of the engaging means and surrounds or is 
surrounded by the first collar. The disc can be in large-area 
surface-to-surface contact with the back shroud; alternatively, the back 
shroud can contact only the hub and the engaging means of the adapter. 
The novel features which are considered as characteristic of the invention 
are set forth in particular in the appended claims. The improved fluid 
flow machine itself, however, both as to its construction and the mode of 
mounting the impeller on its adapter, together with additional features 
and advantages thereof, will be best understood upon perusal of the 
following detailed description of certain specific embodiments with 
reference to the accompanying drawing.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 shows a portion of a centrifugal pump which comprises a motor-driven 
shaft 6, a closed impeller 1 which spacedly surrounds the shaft and is 
made of a brittle material (e.g., a ceramic or glass), and an adapter 2 
which serves to transmit torque between the impeller 1 and the shaft 6. 
The impeller 1 includes an inner coverplate or back shroud 3 and a front 
or outer coverplate 7. The peripheral surface 8 of the back shroud 3 is 
surrounded by a flange-like engaging portion 10 of a disc 9 forming part 
of the adapter 2 and being integral with a hub 5 which can be provided 
with internal splines cooperating with axially parallel teeth of the shaft 
6 in order to ensure that the shaft 6 and the adapter 2 invariably rotate 
as a unit. The adapter 2 is made of a ductile material, preferably of a 
metallic material, and the adapter is configurated and mounted in such a 
way that it can subject the impeller 1 to permissible compressive stresses 
but only to negligible tensional or any other stresses of the nature which 
cannot be readily withstood by a brittle material. The flange-like 
engaging portion 10 can be replaced with a set of circumferentially spaced 
apart discrete claws which can extend into complementary recesses or 
notches in the peripheral surface 8 to even more reliably ensure that the 
impeller 1 will be compelled to share all angular movements of the shaft 6 
and adapter 2. Alternatively, the engaging portion 10 can be provided with 
a set of radially inwardly extending claws or prongs (one indicated by 
broken lines, as at 11) which are received in complementary recesses 12 
provided in the peripheral surface 8 of the back shroud 3 to establish a 
combined form-locking and force-locking connection between the impeller 
and the adapter. 
The engaging portion 10 and/or its claws 11 exert a certain pressure upon 
the peripheral surface 8 of the back shroud 3 so as to properly center and 
entrain the impeller 1 when the shaft 6 rotates. The forces which act at 
the periphery of the back shroud 3 are relatively small so that they 
cannot affect the integrity of the impeller 1, even if the latter is made 
entirely of a brittle material, such as glass or a ceramic substance. The 
transmission of torque between the hub 5 of the adapter 2 and the shaft 6 
does not affect the forces acting between the adapter and the impeller 1. 
In FIG. 1, the disc 9 of the adapter 2 is in large surface-to-surface 
contact with the outer side of the back shroud 3. FIG. 2 shows an 
embodiment wherein the disc 9' of the adapter 2' is spaced apart from the 
outer side of the back shroud 3' of the impeller 1' save for the contact 
between an engaging and entraining collar 10' at the periphery of the disc 
9' and a collar 4 at the outer side of the back shroud 3' close to the 
peripheral surface 8'. The manner in which the hub 5' of the adapter 2' is 
mounted on the shaft 6' is or can be the same as described in connection 
with FIG. 1. The area of contact between the adapter 2' and the impeller 
1' is limited to that between the abutting surfaces of the collars 10', 4 
and those of the back shroud 3' and hub 5'. 
The improved adapter can be used in single-stage or multi-stage fluid flow 
machines, and it can be impellers. 
An important advantage of the improved adapter is its simplicity. In 
addition, the adapter does not interfere with the flow of fluid media 
toward, in or away from the impeller. The hub 5 or 5' can be designed to 
enable the respective adapter to mount a brittle impeller in an existing 
fluid flow machine. 
Without further analysis, the foregoing will so fully reveal the gist of 
the present invention that others can, by applying current knowledge, 
readily adapt it for various applications without omitting features that, 
from the standpoint of prior art, fairly constitute essential 
characteristics of the generic and specific aspects of my contribution to 
the art and, therefore, such adaptations should and are intended to be 
comprehended within the meaning and range of equivalence of the appended 
claims.