SPECIFICATION
Vane wheels, and equipment and processes for producing them by moulding The present invention relates to vane wheels i and to equipment and processes for making them by moulding.
There are three distinct types of vane wheels:
those called centrifugal (or centripetal) radial vane wheels, where the paths of the fluid particles are i contained in planes perpendicular to the axis of rotation, except in the immediate vicinity of the latter; those called axial vane wheels, in which the fluid particles remain substantially at a constant distance from the axis of rotation; and those called helico-centrifugal (or helico-centripetal) vane wheels, which come between the two preceding cases, and in which the vanes are shaped so that the fluid particles follow a path which has both a radial component and an axial component. It is this last type of wheel which the invention improves.
The outline of the vanes of these wheels is governed by hydraulic factors which define, in particular, their angle of entry, angle of exit, length, height, leading edge and profile. The vane which results from this has a complicated skew shape. It cannot be removed from a mould. To produce it in a foundry, sand cores are made by assembling sectors which are held together by bonding and by tying. These assemblies give a casting which has many burrs, thus making it necessary to remove these burrs subsequently, and its dimensions are neither exact nor reproducible and its surface state is very mediocre. When the curves of the vanes are slight, a one-piece core is used, and the core maker loosens the fins of the core case to move then from the core during preparation of the latter.Consequently, not only do the cores no longer comply with the dimensions fixed by the hydraulic engineer and differ from one another, but also the hydraulic engineer does not know of this difference in dimension, and it varies in an unforeseen manner from one vane to another on the same wheel, according as the movement of the caster is more or less abrupt. The manufacturer of helico-centrifugal vane wheels does not know the actual profile of the vanes, although he has determined the theoretical profile with a great degree of accuracy, and because of this uncertainty in production he is prompted to adopt larger tolerances.
The invention overcomes these disadvantages by means of a helico-centrifugal vane wheel, the surface state of which, when obtained from casting or moulding, is flawless, the dimensions of which are accurate and can correspond exactly to the plans given to the caster, without insuperable difficulties facing him, and the production of which is quicker than in the past and can be automated. Experience has shown that this vane wheel gives at least the same performances as conventional helico-centrifugal wheels and often performances higher than these.
The subject of the invention is a wheel with helico-centrifugal vanes, with an axis of repetition, characterised in that the lower face and upper face of a vane extend respectively over portions of surfaces of revolution with the same axis which is different from the axis of repetition and is not perpendicular thereto.
Since the axis of the portions of surfaces of revolution is not perpendicular to the axis of repetition, it is possible to have vane exits inclined relative to the axis and therefore different angles of exit for the trickles of water flowing along each web, this being more consistent with the calculation of the vane than if this axis were perpendicular to the axis of repetition.
Preferably, the axis is at the intersection of a plane parallel to the plane tangent to the vane at a point on the leading edge and a plane perpendicular to this tangent plane.
The invention relates to a core case which comprises helico-centrifugal vanes, with an axis of repetition, the lower face and upper face of each vane extending respectively over portions of surfaces of revolution with the same axis which is different from the axis of repetition.
The process for moulding wheels with metallic vanes according to the invention consists in producing a sand core in which cavities are made with the shape of the vanes of the wheel to be moulded, filling these cavities with liquid metal, leaving the metal to solidify into a piece, and destroying the sand core to release the piece, and it is characterised in that it consists in filling the core case according to the invention with sand, hardening the sand in it into a core and removing the core from the case, taking the blades of the case out of the core by giving them a rotational movement about the axis of the surfaces of revolution.
In the attached drawings given solely by way of example: Figure 1 is a partial perspective view of a vane wheel according to the invention, shown with the front web removed.
Figure 2 is a sectional view of a mould for moulding the wheel of Figure 1. Figure 3 is an exploded view, with a partial cutaway, of a core case making it possible to obtain the core used in the mould of Figure 2. Figure 4 is a sectional view of a vane of the core case. Figure 5 is a perspective view illustrating the production of a vane wheel, and Figure 6 illustrates an automated installation for producing the vanes of the core case.
The wheel of Figure 1 comprises six helicocentrifugal vanes 1, the lower face 2 and the upper face 3 of which extend respectively over portions of surfaces of revolution of the same axis which is different from the axis of repetition X, X' of the vanes 1. The axis of revolution is at the intersection of a plane parallel to the plane tangent to the vane at a point on the leading edge and a plane perpendicular to this tangent plane.
The wheel is produced, in casting, by means of two frames 9, 10, one lower and one upper, filled with sand and matching the outer shapes of the wheel, and, between the two frames, a sand core 8 reproducing the inner shape of the wheel (Figure 2). After the metal has been cast and cooled, the sand is destroyed, and the rough-cast wheel is obtained.
To produce the two frames and the core, it is necessary to have: - two model plates reproducing the front face and the rear face of the wheel, a core case (Figure 3) for making the core.
The model plates are obtained in a conventional way without difficulty. The core case consists essentially of a case bottom 11, an assembly of vanes 12 and a cap 13.
The bottom 11 and the cap 13 are made without difficulty. These are turned parts. To make the assembly of vanes 12, the following procedure is adopted (Figure 5):
1. Production of a part called a "top" 15 (Figure 5).
This is a former made of wood, which is turned according to the definition of the profile of the surface of revolution; the axis of this former is called the "mould-release axis" (K-L).
2. Production of a core former 14. This is a wooden piece which is also turned and which represents the shapes between the front web and the rear web of the wheel.
3. Carrying out the penetration operation.
After a notch has been made without precision in the core former 14: -the axis of the top 15 is positioned, - the top 15 is positioned on this axis KL; - an imprint (casting of resin) taken between the "core former 14 and the top 15" defines exactly the skeleton of the vane perfectly positioned on the core former.
4. Production of the negative of the vane.
a) a calibrated wax of a thickness equal to half the thickness of the vane and representing the upper face is applied to the skeleton of the vane. b) an imprint of the upper face of the vane is taken by means of a casting resin. c) a calibrated wax of a thickness equal to the thickness of the vane is applied to the imprint of the upper face of the vane. d) an imprint of the lower face of the vane is taken by means of a casting resin.
By means of a succession of resin moulding operations, the negative of the vane 12 positioned in the core former 14 is thus obtained. This negative will make it possible to obtain final vanes and to position these vanes 12 on the case bottom 11.
The vanes 12 are made either of resin cast in the negative or of metal by the moulding in sand of a model obtained from the negative.
In both of these cases, it is appropriate to add to the actual vane a portion called a locating stud 19 (Figure 4).
This "locating stud" is embedded in the case bottom 11 1 like a tenon in a mortice and will make it possible to put the vane 12 in place on the case bottom 11 and remove it from this.
The core case makes it possible to produce as many sand cores 11 as it is desired to make vane wheels. Each core 11 is located between the two frames 9, 10. The metal is cast. The cast wheel is released by removing the sand.
To take the vanes 12 out from the core 11, the edge of each vane 12 is integral with two levers 20 which rotate integrally with a shaft 21 located on the axis KL and which are driven by a motor (not shown). The removal of the vanes from the core case is thus mechanised (Figure 6).