[0001] The present invention relates to a rotary vane machine according to the prior art
part of claim 1; it is intended for operation with a dry and oil-free compressible
working medium, e.g. compressed air, at high speeds.
[0002] A considerable amount of experiments has been made during several decades in order
to find out how a vane machine shoud 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 PTFE and ground glass. FR-A-1 574 999 describes a rotary vane
machine where the vanes comprise a matrix of PTFE reinforced with glass fibre and
having molybdenumdisulfide as lubricant. No figures are given regarding the amounts
of the materials. GB-A-1 336 128 describes a material, example 2, comprising PTFE
and carbon and glass fibres and furthermore it is compression moulded under the conventional
conditions pertaining for PTFE followed by sintering. 1596 by weight of bronze powder.
Since bronze is much denser than the other
'- materials in the example the figure is much lower when calculated according to volume.
GB-A-1 324 248 describes for dry operation a vane material having a matrix of lead
oxide and not more than 20% of PTFE and also another one having a matrix of PTFE and
a filler of lead oxide; it describes furthermore that bronze may be substituted for
lead.
[0003] 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
according to the invention should be capable of operation also under these circumstances
wihout any serious effects on the service life.
[0004] As mentioned above nobody has found a suitable material combination for the vanes
of a rotary vane machine before the present invent
ion 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.
[0005] 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 according
to the prior art part of claim 1 and characterized thereby that the material comprises,
between 5 and 3096 by volume of glass or carbon as hard phases and from 10 to 2096
by volume of lead or lead oxide as inorganic solid lubricant whereas the cooperating
surface of the cylinder is made of steel or cast iron.
[0006] 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. No significant difference in performance has been found between non-oxidised
lead metal, semi-oxidised lead metal and lead oxide.
[0007] 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 1096 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.
[0008] 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 rates as a function of the amount of lead.
[0009] 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 30°. The housing is provided with an inlet port 30
for compressed air and outlet ports 31.
[0010] 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 constant at one to three.
All amounts are given in percent by volume (v/o). In Fig. 4 the wear rates in ,um/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
,um/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 from 10 to 20% by volume of lead.
[0011] 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 strength). 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 v/o
of lead with the type II fibres. A wear rate of 4 µm/hr was obtained with 60 v/o PTFE,
20 v/o carbon fibre type II and 20 v/o lead. With a composition comprising 60 v/o
PTFE, 20 v/o carbon fibre type I and 20 v/o lead a wear rate of 1.5,um/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.
A rotary vane machine comprising a cylinder (11) having two opposite end plates (13),
inlet (30) and outlet means (31) for a dry and oil-free compressible working medium,
a rotor (16) eccentrically journalled in the cylinder (11), a number of vanes (20)
slidable in substantially radial slots (19) in the rotor (16) to maintain sealing
contact with the cylinder (11) during rotation of the rotor (16), each vane being
provided with wear resistant material at least at the surface in sealing contact with
the cylinder, said wear resistant material comprising a matrix of a fluorocarbon polymer,
glass or carbon as hard phases and an inorganic solid lubricant, characterized thereby
that the wear resistant material comprises from 10 to 20% by volume of lead or lead
oxide as inorganic solid lubricant and between 5 and 30% by volume of glass or carbon,
whereas the cooperating surface of the cylinder is made of steel or cast iron.
Drehschieberverdichter, bestehend aus einem Zylinder mit zwei gegenüberliegenden Stirndeckeln,
Einlaß und Auslaß für ein trockenes und ölfreies komprimierbares Arbeitsmedium, mit
einem exzentrisch im Zylinder gelagerten Rotor mit in im wesentlichen radial verlaufenden
Rotorschlitzen und einer Anzahl von darin verschieblichen Schiebern zur Aufrechterhaltung
eines Dichtkontaktes mit dem Zylinder beim Umlauf des Rotors, wobei jeder Schieber
zumindest an seiner Dichtfläche zum Zylinder mit verschleißfestem Werkstoff versehen
ist, welcher aus einer Grundmasse aus einem Fluorkarbonkautschuk, Glas oder Kohlenstoff
als Hartphase und einem anorganischen festen Schmierstoff besteht, dadurch gekennzeichnet,
daß der verschleißfeste Werkstoff 10-20 Vol.% Blei oder Bleioxid als anorganischen
festen Schmierstoff und 5-30 Vol.% Glas oder Kohlenstoff enthält, während die mit
ihm zusammenwirkende Zylinderfläche aus Stahl oder Gußeisen hergestellt ist.
Machine à aubes tournantes comprenant un cylindre (11) ayant deux plaques extrêmes
opposées (13), une entrée (30) et des sorties (31) pour un agent actif compressible,
sec et sans 'hûïle, un rotor (16) tourillonné excentriquement dans le cylindre (11),
un certain nombre d'aubes (20) capables de coulisser dans des fentes (19) pratiquement
radiales dans le rotor (16) pour maintenir un contact étanche avec le cylindre (11)
pendant la rotation du rotor (16), chaque aube étant couverte d'un matériau résistant
à l'usure au moins sur sa surface en contact étanche avec le cylindre, ce matériau
résistant à l'usure comprenant une matrice en un polymère fluoro-carbone, verre ou
carbone résistant à l'usure et un lubrifiant solide, et caractérisée en ce que le
matériau résistant à l'usure comprend de 10 à 2096 en volume de plomb ou d'oxyde de
plomb sous la forme d'un lubrifiant solide inorganique et entre 5 et 30% en volume
de verre ou de carbone, tandis que la surface coopérante du cylindre est en acier
ou en fonte.
