TITLE: A rotary vane machine.
European Patent Application EP0019605 A1

ABSTRACT:
A rotary vane machine having vanes with a three component wear
resistant material. The matrix is a fluorocarbon polymer, e.g. PTFE.
Furthermore, there are hard phases whose hardness deviates less than
20% from that of the counterface. Glass or carbon is preferable against
steel or cast iron. Furthermore an inorganic solid lubricant has been
added to the wear resistant material. Lead and lead oxides are
particularly good.

INVENTORS:
Cooper, George Anthony
Berlie, Jacques

APPLICATION NUMBER: EP19800850073
PUBLICATION DATE: 11/26/1980
FILING DATE: 05/12/1980

ASSIGNEE: Cerac, Inst SA. (CH)
INTERNATIONAL CLASSES: F04C18/344; F01C21/08; F04C2/344; (IPC1-7): F01C1/34; F01C21/08
EUROPEAN CLASSES: F01C21/08B

FOREIGN REFERENCES:
FR1574999A
GB1324248A
GB1213552A
FR2250904A
GB1324443A
GB1336128A

CLAIMS:
1. Claims A rotary vane machine comprising a cylinder having two
opposite end plates, inlet and outlet means for a compressible working
medium, a rotor eccentrically journalled in the cylinder, and a number
of vanes slidable in substantially radial slots in the rotor to
maintain sealing contact with the cylinder during rotation of the
rotor, c h a c r a c t e r i z e d t h e r e b y that each vane at
least at the surface in sealing contact with the cylinder is provided
with a portion which is formed of a wear resistant material comprising
a matrix with hard phases having a hardness on the Vickers scale
deviating less than 20 % from the hardness of the cooperating cylinder
material, and an inorganic solid lubricant.
2. A rotary vane machine according to claim 1, c h a r a c t e r i z e
d t h e r e b y that the matrix is a fluorocarbon polymer.
3. A rotary vane machine according to claim 1 or 2, c h a r a c t e r i
z e d t h e r e b y that the wear resistant material contains between 5
and 30 Z by volume of hard phases.
4. A rotary vane machine according to claim 1, 2 or 3, c h a r a c t e
r i z e d t h e r e b y that said hard phases comprise glass or carbon.
5. A rotary vane machine according to any of the preceding claims, c h
a r a c t e r i z e d t h e r e b y that the hard phases are in form of
fibres which are systematically oriented to increase vane stiffness.
6. A rotary vane machine according to claim 5, c h a r a c t e r i z e
d t h e r e b y that the fibres are woven.
7. A rotary vane machine according to any of the preceding claims, c h
a r a c t e r i z e d t h er e b y that the inorganic solid lubricant
is chosen from a group of materials which do not react chemically with
the cooperating cylinder material.
8. A rotary vane machine according to claim 7, c h a r a c t e r i z e
d t h e r e b y that the inorganic solid lubricant is lead or a
compound of lead and that the cooperating surface of the cylinder is of
steel or cast iron.
9. A rotary vane machine according to any of the preceding claims, c h
a r a c t e r i z e d t h e r eb y that the wear resistant material
contains between 5 and 30 % by volume of inorganic solid lubricant.
10. A rotary vane machine according to claim 9, c h a r a c t e r i z e
d t h e r e b y that the wear resistant material contains from 10 to 20
% by volume of inorganic solid lubricant.

DESCRIPTION:
A rotary vane machine The present invention relates to a rotary vane
machine particularly suitable for operation with a dry and oilfree
compressible working medium, e.g. compressed air, at high speeds.
A considerable amount of experiments has been made during several
decades in order to find out how a vane machine should be designed in
order to operate without oil lubrication oVer a substantial period of
time. So far no solution has been found having a service life directly
comparable with the service life of oil lubricated machines . In US
patent 3 335 944 it has been suggested to use a vane material
consisting of a mixture of polytetrafluoroethylene and ground glass.
The main object of the present invention has been to find a material
combination which is sufficiently hard to make it wear resistant
without being brittle so that pieces are broken away from the vanes.
Since a working medium which is believed to be dry and oil-free often
contains small amounts of moisture and oil, the vane machine accord
ing, to the invention should be capable of operation also under these
circumstances without any serious effects on the service life.
As mentioned above nobody has found a suitable material combination for
the vanes of a rotary vane machine before the present invention was
made, in spite of all the efforts that have been made during several
decades. One important problem has been the high sliding speeds which
often exist between the vanes and the cylinder housing. The sliding
speed can for instance be up to and even above 20 m/sec.
in a rotary vane motor for a hand-held grinder. Since the contact
pressure between the substantially radially movable vanes and the
cylindrical countersurface is approximatively proportional to the
square of the sliding speed it is obviously desirable to make the vanes
as light as possible in order to counteract the effect of high sliding
speeds.
According to the present invention a rotary vane machine is created in
which the substantially radially movable vanes are provided with
portions, at least at the surface in sealing contact with the cylinder
housing, of a wear resistant material comprising a matrix with hard
phases having a hardness on the Vickers scale deviating less than 20 %
from the hardness of the cylinder, and an inorganic solid lubricant.
The matrix should preferably be a fluorocarbon polymer, particularly
polytetrafluoroechylene, fluorinated ethylene-propylene, or poly fluor
alkoxy resin.
The wear resistant material should preferably contain between 5 and 30
Z by volume of hard phases. Glass or carbon is preferred as hard
phases, which advantageous- ly could be in form of particles of fibres.
The fibres should preferably be systematically oriented, e.g. woven, in
order to increase vane stiffness.
The inorganic solid lubricant should preferably be chosen from a group
of materials which do not react chemically with the cooperating
cylinder material. Particularly good performance has been obtained with
lead or lead oxides as solid lubricant in the wear resistant material
when the cylinder is made of steel or cast iron. It is reasonable to
suppose, outgoing from these findings, that other compounds of lead
would perform satisfactorily because no significant difference in
performance has been found between non-oxidised lead metal,
semi-oxidised lead metal and lead oxide.
In bearing technology lead and tin are recommended because they are
soft and ductile metals. However, these recommendations cannot be
applied in the present case because the addition of tin to a mixture of
polytetrafluoroethylene and glass seriously impairs the performance.
The wear rate is about three times as high with 10 % by volume of tin
in the material than without. As mentioned above lead does not have to
be in its metal form. Furthermore, as mentioned above, it is desirable
to make the vanes as light as possible. The addition of lead
constitutes a considerable step away from this idea. It is, therefore,
quite surprising that the addition of lead decreases the wear rate of
the vanes.
Improvements by about a factor ten have been observed in high speed
tests with lead or lead oxide as solid lubricant. Tests have shown that
the wear rates obtained with the invention, under dry and oil-free
conditions, are as low as the wear rates obtained with conventional
phenolic vanes with full oil lubrication.
Fig. 1 is a longitudinal section through an air motor according to 1-1
in fig. 2. Fig. 2 is a cross-section through the motor according to 2-2
in fig. 1. Fig. 3 shows the wear rates obtained in a series of tests
with different amounts of lead. Fig. 4 shows the wear rate as a
function of the amount of lead.
The air motor shown in figs. 1 and 2 comprises a cylinder housing 11
provided with two end plates 13. A rotor 16 having an outgoing shaft 12
is eccentrically journalled relative to cylinder 11 in the end plates
13 by means of bearings 14. The rotor is further provided with a number
of vanes 20 which are movable in substantially radial slots 19.
Substantially radial in this context means that the slots may deviate
from the radial direction with up to 300. The housing is provided with
an inlet port 30 for compressed air and outlet ports 31.
Fig. 3 shows the wear rates obtained with different amounts of
semi-oxidised lead metal. These tests have been made with an air motor
operating unloaded at 10000 rpm, corresponding to a sliding speed of 20
m/sec. The ratio of glass fibre, cut into short pieces, to
polytetrafluoroethylene (PTFE) has been kept konstant at one to three.
All amounts are given in percent by volume (V/o).
In fig. 4 the wear rates in Mm/hr are shown as a function of the amount
of lead. The wear rate obtained without lead is the wear rate
obtainable with the combination of materials disclosed in the above
mentioned U.S. patent 3 335 944. The wear rate obtained with one
percent of lead (18 fm/hr) has been deleted when fig. 4 was plotted
because it is very unlikely that there should be a peak value in that
position. This value is probably wrong and no efforts have been made to
obtain the correct value since it is not, from a practical point of
view, interesting to know this value precisely. As can be seen in figs.
3 and 4 the wear resistant material should contain between 5 and 30 %
by volume of inorganic solid lubricant.
The wear rates obtained with from 10 to 20 % by volume of inorganic
solid lubricant are particularly interesting. In applications where the
demand for quick speed changes is particularly high an amount of 5 %
would be very interesting even though the wear rate is considerably
higher than the optimum value. However, the wear rate is in this case
only about 50 % of the value obtained without the inorganic solid
lubricant.
Tests have also been made, at the above mentioned operating speeds,
with carbon fibre instead of glass as the hard phase material. In these
tests two varieties commonly known as type I (high modulus, moderate
strenght) and type II (high strength, moderate modulus) were used. As
in the above mentioned tests with glass the ratio of carbon fibres to
PTFE was kept constant at one to three. Tests were made with up to 20
lo of lead with the type II fibres. A wear rate of 4 Fm/hr was obtained
with 60 /o PTFE, 20 /o carbon fibre type II and 20 /o lead. With a
composition comprising 60 v/o V PTFE, 20 /o carbon fibre type I and 20
/o lead a wear rate of 1.5 fm/hr was obtained.
It can be seen from these results that very good performance is
obtainable with carbon fibres as hard phases. The best value obtained
with type I fibres is as good as the value obtained with glass.
The above description gives examples only of preferred alternatives and
must not be regarded as limiting the cope of the invention which is
defined by the subsequent claims. The matrix could be a phenolic resin.
In some cases it could be advantageous to use graphite or
molybdenumdisulfide as inorganic solid lubricant.