Method for the manufacture of a pump rotor for a coolant pump in a motor vehicle

A method for the manufacture of a closed plastic pump rotor is described. The mold comprises two outer casting mold shells and an intermediate core, whose shaping determines the shape of the guide vanes and flow channels of the rotor. The core is made from a material, whose melting point is below that of the plastic to be cast. The core is melted following the curing of the plastic.

The present invention relates to a method for the manufacture of a rotor 
for a coolant pump in a motor vehicle, for example a water pump rotor for 
a cooling water pump or a fan rotor, the rotor having a metal hub for 
mounting on a shaft, a metal reinforcing disk coaxially shaped on to one 
end of the metal hub and surrounded by plastic and guide vanes shaped from 
plastic located in the outer circumferential area of the pump rotor. 
Pump rotors or impellers of the aforementioned type are fundamentally known 
in connection with their use in internal combustion engines. Due to the 
thermal loads which can occur in this particular use, where there can be 
temperatures ranging from approximately -40.degree. C. to +130.degree. C., 
special demands are made on the materials and the construction. The use of 
grey cast-iron or brass for such a pump rotor has the disadvantage that 
such materials have a cavitation tendency leading to the destruction of 
the rotor. Apart from the high weight and high costs, the further 
disadvantage arises that the surface is rough, so that the flow resistance 
is increased. 
In addition, water pumps are known, in which the water pump rotor is 
completely made from plastic. However, due to the high hot and cold loads, 
this construction is not suitable for motor vehicles, because the rotors 
bend in such a way that they run up against the casing wall. It has also 
not hitherto been possible to manufacture closed pump wheels from plastic. 
Furthermore, U.S. Pat. No. 3,251,307 discloses an open water pump rotor for 
use in connection with internal combustion engines, which has a metal hub 
and a metal reinforcing disk oriented substantially at right angles to the 
hub axis and coaxially shaped on to the hub. Together with the outer 
surface of the hub, the reinforcing disk is embedded in a plastic body. 
Here again, during the operation of the rotor, a deflection is unavoidable 
due to the resultant axial force. The axial thrust produced leads to the 
risk of the rotor being destroyed on the casing. If for safety reasons 
large spaces are provided,the efficiency of the rotor or pump is 
correspondingly low. 
The problem of the present invention is to provide a method for the 
manufacture of a rotor of the aforementioned type, in which the 
disadvantageous effects of axial forces are reduced. 
This problem is solved by arranging the reinforcing disk is arranged in a 
first casting mold shell, whose shaped out parts define that surface of 
the rotor opposite to the flow channels of said rotor. A core is placed 
over the reinforcing disk and the shaping thereof defines the shape of the 
rotor blades and the flow channels. The first casting mold shell and the 
core are tightly sealed in the outer circumferential region thereof. The 
core is made from a material, whose melting point is below that of the 
plastic to be cast. A second casting mold shell is mounted on the core and 
in its outer circumferential region and on the openings of the flow 
channels issuing in the axial direction is tightly sealed with the core. 
The second casting mold shell is constructed for forming a cover located 
over the flow channels. The cavities formed between the first and second 
casting mold shells and the core are then filled with plastic, and finally 
the core is melted. 
The invention has the advantage that now also closed pump rotors or 
impellers can be made from a plastics material. Through the melting of the 
core, it is possible to manufacture the cavities of a closed pump rotor. 
According to a preferred development of the invention, on either side of 
the reinforcing disk are provided stampings, whose height corresponds to 
the thickness of the plastic subsequently to be applied. These stampings 
permit a dimensionally accurate arrangement of the reinforcing disk 
relative to the first casting mold shell and to the core, because during 
the casting of the plastic, the two moldings are supported on the 
stampings and maintained with the desired spacing. 
It is particularly advantageous to produce the stampings by stamping out 
circular openings and deep drawing the opening rims. It is alternatively 
possible to produce the stampings by stamping out and bending tongues. 
It is also advantageous to widen the free end of the hub. This offers the 
advantage that the pump rotor can be mounted without difficulty on a 
driving shaft, because the widening acts in the manner of a funnel. 
It is also advantageous to provide the reinforcing disk with at least one 
adjusting opening and to pass therethrough an adjusting mandrel located in 
the core and/or the first mold shell. This makes it possible to increase 
the dimensional accuracy of the pump rotor. If the mandrel leads to an 
opening in the pump rotor, this can be useful for compensating the axial 
thrust. 
According to another preferred embodiment, prior to casting, a metal ring 
is mounted on the hub and cast in the plastic. This ring reinforces the 
hub, so that it is possible to absorb powerful stresses caused by heat 
action. It also makes it possible to compensate any material fatigue which 
occurs. 
Both for the casting process and for the adhesive action of the plastic, it 
is advantageous to provide the reinforcing disk with a plurality of 
openings, which permit the penetration of plastic. 
It is advantageous to stagger the openings in the circumferential 
direction. As a result the supporting effect of the reinforcing disk is 
maintained and the plastic can be uniformly distributed within the mold 
cavity. 
The assembly and adjustment of the two casting mold shells is facilitated 
in that the hub is mounted on a shaft during casting. The shaft can form 
the boundary of the mold cavity in the extension of the hub. 
It can be advantageous for the shaft to extend up to the hub and to engage 
a pin in the latter. The differing external diameters of shaft and pin 
ensure that the plastic extending axially over the hub has in the radial 
direction a predetermined spacing from the driving shaft which, on 
inserting the pump rotor, is engaged in dimensionally accurate manner in 
the hub. This ensures that the different expansion coefficients of the 
metal hub and the plastic parts do not have disadvantageous effects and 
cannot damage the pump rotor. 
Further developments of the invention and preferred materials for the core 
are given in the subclaims.

A first embodiment of a pump rotor or impeller shown in FIG. 1 comprises a 
hub 1, by means of which the pump rotor is mounted on a not shown driving 
shaft. A coaxially arranged, circular disk part 7, on which are shaped 
guide vanes 3, which is at right angles to the hub axis is connected to 
the hub by means of a revolution-paraboloid reinforcing region 2. Guide 
vanes 3 may also be referred to as rotor blades. Reinforcing region 2 and 
disk part 7 together form a reinforcing disk 4, which is sprayed with 
plastic on either side and passes into hub 1. Plastic is only applied on 
one side to the outer surface of hub 1, so that the pump rotor with its 
metal inner surface of hub 1 can be mounted on the driving shaft. 
For better anchoring of the plastic with reinforcing disk 4, openings 6 are 
distributed over the surface of reinforcing disk 4. Said openings 6 can 
cover roughly 40 to 70% of the surface of reinforcing disk 4. As is 
illustrated by a partial section through the pump rotor, the openings 6 
are circular in the presently represented embodiment. Other shapes of 
openings 6 are described in FIGS. 6 to 13. In the present embodiment there 
are also four adjusting openings 5, which are parallel to the hub axis and 
whose significance will be explained relative to FIG. 5. Hub 1 of 
reinforcing disk 4 extends over at least 40% of the hub length of the pump 
rotor. Disk part 7 is only slightly smaller than the external diameter of 
the water pump rotor, so that the guide vanes 3 are located entirely in 
the vicinity of reinforcing disk 4. 
In the outer circumferential region of the rotor, the flow channels 9 
between the guide vanes 3 are closed at the top by a cover 8, so that a 
closed rotor with a rotor intake 10 running roughly parallel to the hub 
axis and rotor outlets 11 directed radially outwards is formed. In the 
left-hand, upper part of FIG. 1, a partial section illustrates in 
exemplified manner the path of a flow channel 9 with rotor intake 10 and 
rotor outlet 11. 
In the cross-section through a pump rotor according to FIG. 2, different 
cross-sections for covers 8, 8' are provided on the left and right-hand 
sides for illustrating two different rotors. Unlike in the presently 
chosen representation, the cover 8, 8' for a rotor has an all-round 
identical construction. It can also be gathered that plastic parts 13, 15 
in the axial direction of the hub are shaped over and beyond the metal hub 
1. These two plastic parts 13, 15 terminate in the radial direction at a 
given distance from the inner surface of the hub, so as to ensure that the 
plastic can come into contact with the driving shaft. In the gap between 
reinforcing region 2 and plastic part 13, in the present embodiment 
radially directed plastic reinforcing ribs 17 are formed. For embedding 
reinforcing disk 4 and hub 1 use is made of an abrasion-resistant, stable 
plastic. On either side, the plastic support typically has a thickness of 
1 to 2 mm. 
As is illustrated in exemplified manner on the left-hand side of FIG. 2, 
the cover 8 for flow channel 9 is provided on the outside with an annular 
groove 18, into which engages a casing 20 in such a way that an axial 
clearance 19 and a radial clearance 21 remain free, so as not to impede 
the rotation of the rotor. FIG. 2 clearly shows that an axial thrust of 
the rotor, which can occur in operation, merely modifies the cross-section 
of the radial clearance 21, whereas the axial clearance 19 remains 
cross-sectionally identical. As the axial clearance 19 determines the flow 
of coolant between casing 20 and the pump rotor, the efficiency of a pump 
provided with such a closed pump rotor is particularly high, because the 
axial clearance 19 can be made relatively narrow. FIG. 3 illustrates 
further details of an embodiment of the pump rotor. Unlike in the 
embodiment according to FIG. 2, the reinforcing region 2 of the 
reinforcing disk is at an acute angle to hub 1. The rotor blades are in 
this embodiment formed on the concave side of the reinforcing disk 4 (not 
shown). 
The free end of hub 1 is widened in a roughly trumpet-shaped manner, in 
order to facilitate the mounting of the rotor on a driving shaft. The 
plastic part 13 extended axially over hub 1 terminates at a radial spacing 
A from the inner surface of the hub. On the front face of the here 
cylindrically shaped plastic part 13 is mounted a packing ring 22. 
In the embodiment according to FIG. 3, on one side hub 1 is sealed by an 
outwardly streamlined plastic part 15, which is rotationally symmetrical 
to the hub axis and has the function of preventing vortexing of the 
coolant upstream of the pump rotor center. Here again, it is obviously 
necessary to avoid contact between the driving shaft and plastic part 15, 
so as to prevent the disadvantageous consequences of the different 
expansion coefficients. 
FIG. 4 shows in cross-section another detail of an embodiment of the pump 
rotor. Unlike in the embodiment according to FIG. 3, the pump rotor 
additionally has a metal ring 23, which is mounted from the outside on the 
hub and is cast in the plastic. This supports the hub e.g. against cold 
flow. Following the mounting of ring 23, as in the embodiment of FIG. 3, 
the free end of hub 1 can be widened. 
FIG. 4 also shows a shaft 24 with a pin 25, but it is not a driving shaft. 
FIG. 4 merely illustrates the way in which the spacing A can be produced 
during the actual casting of the pump rotor. During the casting of the 
rotor, shaft 24 determines the internal diameter of the plastic part, pin 
25 being inserted in hub 1. As can be gathered from the description 
relative to FIG. 5, shaft 24 can also be used for the centering of the 
casting molds. 
FIG. 5 diagrammatically illustrates the way in which the pump rotor can be 
manufactured. The mold for the pump rotor comprises a first mold shell 51 
and a second mold shell 52, as well as an intermediate core 53. In 
accordance with FIG. 4, a not shown shaft can be used for shaping in the 
vicinity of hub 1. The first casting mold shell 51 determines the shape 
and surface of the rotor on the side remote from the guide vanes. In this 
first shell 51, reinforcing disk 4 is positioned with the aid of spacers, 
which determine the thickness of the plastic coating. 
The spacers can be constructed in different ways. They can e.g. comprise 
cones 54 or pins, which project from the surface of the first casting mold 
shell 51. However, it is particularly advantageous for the spacers to be 
formed by tongues 55, which are stamped from the reinforcing disk 4 and 
then bent. A particularly preferred possibility consists of making 
openings 56 in the reinforcing disk 4 and to draw the rims or edges 57 of 
openings 56 outwards, so that the height of the rims corresponds to the 
thickness of the plastic to be subsequently poured in. FIG. 5 illustrates 
in cross-section opening 56 with downwardly drawn edges 57. Only the 
upwardly drawn rim 57' of a further opening position behind it can be 
seen. 
Spacers can also be formed on core 53 from core material, e.g. in that 
further cones 58 or the like are constructed. These cones are melted 
together with the core 53. 
Core 53 is arranged on the first mold shell 51 in such a way that it is 
tightly sealed with the latter in the outer circumferential region. By 
means of reinforcing disk 4, it is held by the spacers, which in the 
present embodiment comprise stampings formed by tongue 55 and rim 57', as 
well as cone 54. Core 53 determines the shape of the flow channels, the 
rotor intake 10 and the rotor outlets 11 (cf.) FIG. 1). It is made from a 
material having a melting point below that of the plastic to be cast. The 
material used for core 53 is a low-melting metal, whose melting point is 
in the range 50.degree. to 150.degree. C. and is preferably a bismuth 
alloy. 
The second casting mold shell 52 is mounted on the core and through its 
mold cavity 59 essentially determines the external shape of cover 8. The 
second mold shell 52 is tightly sealed with core 53. In order to ensure 
the association of the individual mold components, an adjusting mandrel 60 
is provided, which is passed through a not shown adjusting opening in the 
reinforcing disk 4 and is connected at predetermined points by its ends to 
the first casting mold shell 51 and core 53. It can also extend up to the 
second casting mold shell 52. Through the passage of adjusting mandrel 60 
through reinforcing disk 4 and through the plastic of the rotor are 
obtained the through openings in the rotor referred to as "adjusting 
opening 5" in FIG. 1. The concentric alignment of the first and second 
shells 51, 52 and reinforcing disk 4 takes place by a shaft 24'. 
If the casting mold is arranged in this way, the cavities thereof are 
filled with an abrasion-resistant, stable plastic. Following the curing of 
the latter, core 53 is melted away to leave the rotor blades 3 and flow 
channels 9. This preferably takes place in a bath of liquefied core 
material. 
FIGS. 6 to 13 show various examples for the openings 6 in reinforcing disk 
4 and as are diagrammatically shown in FIG. 1. The stampings for producing 
the spacers can be produced in that the tongues are stamped and bent with 
the shapes shown in FIGS. 6 to 13 and simultaneously passage openings for 
the plastic are formed. 
When molding plastic, preference is given to an injection molding process, 
which is known per se and need not therefore be described in detail here.