TITLE
Rotary Blower With Corrosion-Resistant Abradable Coating.
FIELD OF THE INVENTION
The present invention relates in general to a rotary blower, such as a
Roots-type rotary blower, typically used as an automotive supercharger, with an
abradable coating for increasing the volumetric efficiency of the rotary blower, and,
in particular, to a corrosion-resistant rotary blower rotor having an abradable
coating.
BACKGROUND OF THE DISCLOSURE
Rotary blowers of the Roots type typically include a pair of meshed,
lobed rotors having either straight lobes or lobes with a helical twist with each of the
rotors being mounted on a shaft, and each shaft having mounted thereon a timing
gear. Rotary blowers, particularly Roots blowers are employed as superchargers
for internal combustion engines and normally operate at relatively high speeds,
typically in the range of 10,000 to 20,000 revolutions per minute (rpm) for
transferring large volumes of a compressible fluid like air, but without compressing
the air internally within the blower.
It is desirable that the rotors mesh with each other, to transfer large
volumes of air from an inlet port to a higher pressure at the outlet port. Operating
clearances to compensate for thermal expansion and/or bending due to loads are
intentionally designed for the movement of the parts so that the rotors actually do
not touch each other or the housing. Also, it has been the practice to epoxy coat
the rotors such that any inadvertent contact does not result in the galling of the
rotors or the housing in which they are contained. The designed operating
clearances, even though necessary, limit the efficiency of the rotary blower by
allowing leakage. This creation of a leakage path reduces the volumetric efficiency
of the rotary blower.
One known approach to improving pumping efficiency of a rotary blower
is the use of a coating with an abradable material. While known supercharger
rotor abradable coatings provide, among other things, increased volumetric
efficiency of the rotary blower and sufficient lubricating properties, they have been
found to exhibit relatively poor corrosion resistance, limiting their use to
supercharger applications in which the supercharger is not be exposed to a
corrosive environment. For example, known supercharger abradable coatings are
generally incompatible with marine engines that operate in a salt water
environment, as the relatively high salt content ambient air may corrode the rotors.
BRIEF SUMMARY OF THE INVENTION
A rotary blower rotor is disclosed that includes a rotor body having a
corrosion-resistant coating covering the rotor body. An abradable coating covers at
least a portion of the corrosion-resistant coating for providing an essentially zero
operating clearance for increasing a volumetric efficiency of the rotary blower. The
corrosion-resistant coating inhibits corrosion of the rotor body during exposure to a
corrosive environment.
In an embodiment of the present invention, the corrosion-resistant coating
comprises an electrolytic ceramic coating that exhibits excellent resistance to
various corrosive environments, and forms a foundation exhibiting excellent
adhesion to the abradable coating.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side elevation view of an exemplary Roots-type rotary blower
of the type with which the present invention may be utilized;
FIG. 2 is a cross-sectional view of the exemplary Roots-type rotary
blower of FIG. 1, showing a pair of rotors according to an embodiment of the
present invention;
FIG. 3 is a cross-sectional view of a rotor shown in FIG. 2;
FIG. 4 is a photograph of a rotor according to an embodiment of the
present invention shown after an ASTM-B117 salt spray test; and
FIG. 5 is a photograph of a prior art rotor having only an abradable
coating shown after an ASTM-B117 salt spray test.
DETAILED DESCRIPTION
Referring now to the drawings, which are not intended to limit the present
invention, and first in particular to FIGS. 1 and 2, there is shown an exemplary
rotary pump or blower of the Roots type, generally designated 11. Rotary blower 11
may be better understood by reference to U.S. Pat. Nos. 4,828,467; 5,118,268; and
5,320,508, all of which are assigned to the Assignee of the present invention and
hereby incorporated by reference.
As is well known in the art, rotary blowers are used typically to pump or
transfer volumes of a compressible fluid such as air from an inlet port opening to an
outlet port opening without compressing the air in the transfer volumes prior to
exposing it to higher pressure air at the outlet opening. Rotary blower 11 comprises
a housing assembly 13 which includes a main housing member 15, bearing plate
17, and the drive housing member 19. The three members are secured together by
a plurality of fasteners 21.
Referring next to FIG. 2, the main housing member 15 is a unitary
member defining cylindrical wall surfaces 23, 25 which define parallel transverse
overlapping cylindrical chambers 27 and 29, respectively. Chambers 27, 29 have
rotor-shaft subassemblies 31, 33, respectively mounted therein for counter-rotation,
with axes substantially coincident with the respective axes of the blower 11 as is
known in this art. Subassembly 31 has a helical twist in a counterclockwise
direction as indicated by the arrow adjacent reference numeral 31 in FIG. 2. The
subassembly 33 has a helical twist in the clockwise direction as shown by the arrow
adjacent reference numeral 39 in FIG. 2. For purposes of explaining the use of the
corrosion-resistant coating and abradable coating in accordance with the present
invention, the subassemblies 31 and 33 will be considered identical, and only one
will be described in reference to the use of the coatings hereinafter.
Referring also to FIG. 3, there is shown a cross-sectional view of a rotor
39. Rotor 39 comprises a body 40 having three separate lobes 43, 45, and 47
which connect together, or preferably are formed integrally, to define a generally
cylindrical web portion 49. A shaft 37, 41 is disposed within a central bore portion
51. Each of the lobes 43, 45, and 47 may define hollow chambers 53, 55, 57,
respectively therein, although the present invention is equally applicable to both
solid and hollow rotors.
To facilitate a better understanding of the structure in accordance with
the present invention and for ease of illustration FIG. 3 depicts rotor 39 as a straight
lobed rotor. It should be understood that the present invention is equally applicable
to any shaped rotor whether it is helical or straight lobed.
[00*8] In FIG. 3, there is shown an abradable coating 61 preferably covering the
entire outer surface of rotor 39. Coating 61 may include a mixture of a coating
material base or matrix which is preferably an epoxy polymer resin matrix in powder
form and a solid lubricant. Exemplary coatings 61 are described in U.S. Patent No.
6,688,867, which is owned by the Assignee of the present invention and
incorporated by reference herein in its entirety.
Referring still to FIG. 3, a corrosion-resistant coating 63 is disposed
between the rotor 31 and the abradable coating 61. In an embodiment of the
present invention, corrosion-resistant coating 63 is an electrolytic ceramic material,
such as the electrolytic titanium ceramic coating Alodine® marketed by Henkel
KGaA. The corrosion-resistant coating 63 may be deposited over the rotor 31 at a
controlled thickness of approximately 5-7 microns (µm) with a tolerance of less than
+/- 0.5 microns (nm). The corrosion-resistant coating 63 may be applied with an
electrostatic or air atomized spray process, but may also be applied with a liquid
process such as a liquid spraying or immersion process. The adhesion of the
corrosion-resistant coating 63 on the rotor surface may be improved with surface
preparation of the substrate by mechanical means such as machining, sanding, grit
blasting or the like, or alternatively with chemical means for surface treatment such
as etching, degreasing, solvent cleaning or chemical treatment such as an alkaline
or phosphate wash.
It is desirable for the corrosion-resistant coating 63 to maintain its
structure without peeling at contact areas, and to have good adhesion to aluminum
or other lightweight metals employed in the rotor 39. Also, the corrosion-resistant
coating 63 should not be harmful to the catalytic converter or the heat exhaust gas
oxygen (HEGO) sensor if any particles become entrained into the engine after the
break-in period. As such, the corrosion-resistant coating 63 particles do need to be
combustible. In addition, the corrosion-resistant coating 63 also has compatibility
with gasoline, oil, water (including salt water), alcohol, exhaust gas, and synthetic
lubricating oils.
In the development of the blower which uses the corrosion-resistant
coating material of the present invention, a variety of coating materials were
investigated. Table 1 lists the results of several of these coating materials.

The abradable coating 61 is deposited over the corrosion-resistant
coating 63 so that the abradable coating 61 and the corrosion-resistant coating 63
havea collective thickness ranging from about 80 microns (µm) to about 130 (µm).
The coated rotors can have clearances due to manufacturing tolerances that may
range from rotor to rotor from about 0 mils to about 7 mils, and rotor to housing that
may range from about 0 mils to about 3 mils. Preferably, the thickness of the
abradable coating material on the rotors is such that there is a slight interference fit
between the rotors and the housing. During the assembly process, the rotary
blower is operated on line for a brief break-in period. The term "break-in" as used
herein is intended to refer to an operation cycle which lasts as a minimum
approximately two minutes where the rotary blower undergoes a ramp from about
2000 rpm to about 16,000 rpm, and then back down. Of course, the break-in period
can include but is not limited to any operation cycle employed to abrade the coating
to an essentially zero operating clearance.
The invention has been described in great detail in the foregoing
specification, and it is believed that various alterations and modifications of the
invention will become apparent to those skilled in the art from a reading and
understanding of the specification. It is intended that all such alterations and
modifications are included in the invention, insofar as they come within the scope of
the appended claims.
We claim:
1. A rotary blower rotor, comprising:
a rotor body;
a corrosion-resistant coating covering the rotor body; and
an abradable coating covering at least a portion of the corrosion-resistant
coating for providing an essentially zero operating clearance for increasing a
volumetric efficiency of the rotary blower.
2. The rotory blower rotor of claim 1, wherein the corrosion-resistant coating
has a thickness ranging from about 5 microns to about 7 microns.
3. The rotory blower rotor of claim 1, wherein the corrosion-resistant coating
comprises an electrolytic ceramic coating.
4. The rotory blower rotor of claim 3, wherein the electrolytic ceramic coating
includes a titanium ceramic.
5. The rotory blower rotor of claim 1, wherein the abradable coating and the
corrosion-resistant coating have a collective thickness ranging from about 80
microns to about 130 microns.
6. The rotory blower rotor of claim 1, wherein the abradable coating is a
mixture of a coating matrix and a solid lubricant.
7. A rotary blower rotor, comprising:
a rotor body;
an electrolytic ceramic coating adhered to and covering the rotor body;
and
an abradable coating adhered to and covering at least a portion of the
corrosion-resistant coating for providing an essentially zero operating clearance
for increasing a volumetric efficiency of the rotary blower.
8. The rotory blower rotor of claim 7, wherein the electrolytic ceramic coating
has a thickness ranging from about 5 microns to about 7 microns.
9. The rotory blower rotor of claim 7, wherein the electrolytic ceramic coating
includes a titanium ceramic.
10. . The rotory blower rotor of claim 7, wherein the abradable coating and
electrolytic ceramic coating have a collective thickness ranging from about 80
microns to about 130 microns.
11. The rotory blower rotor of claim 7, wherein the abradable coating is a
mixture of a coating matrix and a solid lubricant.
12. A rotary blower, comprising:
a pair of rotors, each rotor including a corrosion-resistant coating covering
the rotors and an abradable coating covering at least a portion of the corrosion-
resistant coating for providing an essentially zero operating clearance for
increasing a volumetric efficiency of the rotary blower.
13. The rotory blower of claim 12, wherein the corrosion-resistant coating has
a thickness ranging from about 5 microns to about 7 microns.
14. The rotory blower of claim 12, wherein the corrosion-resistant coating
comprises an electrolytic ceramic coating.
15. . The rotory blower of claim 14, wherein the electrolytic ceramic coating
includes a titanium ceramic.
16. The rotory blower of claim 12, wherein the abradable coating and
corrosion-resistant coating have a collective thickness ranging from about 80
microns to about 130 microns.
17. The rotory blower of claim 12, wherein the abradable coating is a mixture
of a coating matrix and a solid lubricant.
ABSTRACT
Title : rotary blower with corrosion-resistant abradable coating
A rotary blower rotor (39) includes a rotor body having
a corrosion-resistant coating (63) covering the rotor
body. An abradable coating (61) covers at least a
portion of the corrosion-resistant coating for
providing an essentially zero operating clearance for
increasing a volumetric efficiency of the rotary
blower. A rotary blower including such a rotor is also
provided.
Figure : 3

A rotary blower rotor (39) includes a rotor body having
a corrosion-resistant coating (63) covering the rotor
body. An abradable coating (61) covers at least a
portion of the corrosion-resistant coating for
providing an essentially zero operating clearance for
increasing a volumetric efficiency of the rotary
blower. A rotary blower including such a rotor is also
provided.