SELF-LUBRICATED COATING AND METHOD
BACKGROUND
TECHNICAL FIELD
Embodiments of the subject matter disclosed herein generally relate to methods
and systems and, more particularly, to mechanisms and techniques for providing a
self-lubricated coating.
DISCUSSION OF THE BACKGROUND
During the past years, with the increase in price of fossil fuels, the interest in
various aspects related to the processing of the fossil fuels has increased. In
addition, there is an increased interest in producing more efficient and reliable
motors, turbines, compressors, etc. to facilitate a better production and distribution
of oil and gas based products.
Such machines generally include a fixed part, the stator, and a rotating part, the
rotor. The rotor is configured to rotate relative to the stator to achieve one of
compressing a medium, producing electrical energy, or transforming electrical
energy into mechanical energy. The rotor needs to rotate relative to the stator with
minimum friction and in a certain temperature range. Because of the continuous
rotation of the rotor and its weight (which might be between 20 and 20,000 kg and
increases the friction}, a large amount of heat is produced. The heat appears
mainly in the bearings that support the rotor.
Thus, various mechanisms for cooling the bearings may be used. One such
mechanism is to continuously circulate a medium, oil for example, between the
rotor and the bearings and to remove the excessive heat by cooling the oil. A
pump may be used to force the circulation of the oil. However, if the pump fails,
the oil stops flowing and consequently, stops removing the heat developed at an
interface between the rotor and the bearing. Under these circumstances, no oil
may be present at the interface between the rotor and the bearing, which
determines an increase of the temperature of the bearing up to a point that will
result in damages to the rotor and/or the bearing or other component of the
machine.
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If this abnormal condition is not rapidly identified by the operator of the machine or
by a dedicated system so that the machine is stopped, the entire machine may be
severely damaged, resulting in the interruption of the whole process in which the
machine is involved, which is costly and undesirable in the oil and gas industry.
Even if the failed condition of the machine is quickly identified, sometimes it may
be impossible to immediately stop the affected machine as the machine is part of a
process in which multiple machines are coordinated and the quick shut down of
one machine is not possible without interfering with the safety of the other
machines.
Accordingly, it would be desirable to provide systems and methods that offer the
operator of the machine a time buffer between the instant when the machine has
failed to work properly and the instant when the machine is damaged due, for
example, to the high temperature that appears when the oil pump fails.
SUMMARY
According to one exemplary embodiment, there is a method for providing a selflubricated
coating on a substrate. The method includes spraying with an inert gas
at least a layer of liquid metal on the substrate; adding a compound to the liquid
metal while being sprayed on the substrate; forming a porous layer on the
substrate that includes the metal and the compound, where the porous layer has
plural pores; heating the porous layer to open the pores; flooding the open pores
with a greasing substance such that part of the greasing substance is stored in
one or more pores; and cooling the porous layer to close the pores and trap the
greasing substance inside the pores.
According to still another exemplary embodiment, there is a method for operating
a turbo-machinery having a safety mechanism for a bearing. The method includes
rotating a rotor relative to a stator of the turbo-machinery; supporting the rotor with
a bearing that includes at least a porous layer, the at least a porous layer including
a metal and a compound that form plural pores and a greasing substance stored in
the pores; and providing a lubricant to the bearing while the rotor rotates such that
an operation temperature of the bearing is substantially constant.
According to yet another exemplary embodiment, there is a turbo-machinery that
includes a stator configured to be fix; a rotor configured to rotate relative to the
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stator; a bearing configured to support the rotor and facilitate a rotation of the
rotor; and a self-lubricated coating provided on the bearing or the rotor. The selflubricated
coating includes at least a porous layer, the at least a porous layer
including a metal and a compound that form plural pores and a greasing
substance stored in the pores, and the pores are closed trapping the greasing
substance when an operational temperature of the bearing is below a
predetermined value.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are incorporated in and constitute a part of the
specification, illustrate one or more embodiments and, together with the
description, explain these embodiments. In the drawings:
Figure 1 is a schematic diagram of a machine having a rotor and a stator;
Figure 2 is a schematic diagram of a substrate having a self-lubricated coating
according to an exemplary embodiment;
Figure 3 is an illustration of a porous layer according to an exemplary
embodiment;
Figure 4 is a flow chart illustrating a method for providing a self-lubricated coating
on a substrate according to an exemplary embodiment; and
Figure 5 is a flow chart illustrating a method for operating a turbo-machinery
having a safety mechanism for a bearing according to an exemplary embodiment.
DETAILED DESCRIPTION
The following description of the exemplary embodiments refers to the accompanying
drawings. The same reference numbers in different drawings identify the same or
similar elements. The following detailed description does not limit the invention.
Instead, the scope of the invention is defined by the appended claims. The following
embodiments are discussed, for simplicity, with regard to the terminology and
structure of a compressor. However, the embodiments to be discussed next are not
limited to compressors, but may be applied to other systems that include a rotor
supported by bearings.
Reference throughout the specification to "one embodiment" or "an embodiment"
means that a particular feature, structure, or characteristic described in connection
with an embodiment is included in at least one embodiment of the subject matter
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disclosed. Thus, the appearance of the phrases "in one embodiment" or "in an
embodiment" in various places throughout the specification is not necessarily
referring to the same embodiment. Further, the particular features, structures or
characteristics may be combined in any suitable manner in one or more
embodiments.
According with an exemplary embodiment, part of the rotor, the bearing or both of
them are coated with a self-lubricated coating that is configured to store a greasing
material while the machine operates at a normal temperature and to release the
greasing material when the temperature of the machine increases over a certain
threshold temperature.
According to an exemplary embodiment shown in Figure 1, a compressor 10
includes, among other things, a rotor 12 that is configured to rotate relative to a
rotor 14. The rotor 12 is supported, for example, at both ends, by one or more
bearings 16. Various bearings are known in the art and any of these bearings may
be used to support the rotor 12. One example of a bearing is a journal bearing,
which is described in U.S. Patent No. 6,361 ,215, the entire content of which is
incorporated herein by reference.
A journal bearing 16 uses one or more pads 18 that support the rotor 12 and oil is
injected between the pads 18 and the rotor 12 at an interface 20 to reduce friction
and/or to cool the interface. A pump (not shown) may be used to pump the oil
through a channel 22 in each pad at the interface 20 between the pad 18 and the
rotor 12. If the oil fails to be delivered at the interface 20, the temperature at this
interface would increase beyond an acceptable value, which may damage the
bearing 16, the rotor 12 or both of them.
According to an exemplary embodiment shown in Figure 2, a portion of either the
rotor 12, or the bearing 16, or both of them may be coated with a self-lubricated
layer 24. The self-lubricated layer 24 may be deposited, as shown in Figure 2, on
a substrate 26, which may be one of the rotor 12 and/or the bearing 16. When the
self-lubricated layer 24 is deposited on the rotor 12, it is desired that this layer be
deposited to directly face the bearing 16.
Layer 24 may include a base material 28 that is deposited on the substrate 24.
The base material may include a metal used for the bearing, e.g., gray cast iron,
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stainless steel, carbon steel, non-ferrous alloys, etc. In one application, the base
material is plastic, e.g., includes a material with a low carbon content and high
content of Fe, Ni or Cobalt. In another application, the base material does not
includes Cr. In still another application, the base material may include a nonferrous
metal so that the base material is plastic. The base material may be
deposited by methods known in the art. For example, the base material may be
sprayed on the substrate. However, in one application the base material layer 28
is not part of the layer 24. Base material layer 28 is deposited to ensure a better
adherence between the self-lubricated layer 24 and the substrate 26.
A porous layer 30 that provides the self-lubricated functionality is formed on the
base material layer 28 or directly on the substrate 26. Porous layer 30 may
include a metal and a compound that promotes the formation of pores in the
porous layer 30. The metal may be one or more of a metal used for the bearing,
e.g., gray cast iron, stainless steel, carbon steel, etc., depending on the
application, the desired hardness of the layer, the load of the bearings. The
compound may be one or more of graphite powder, Molybdenum disulfide (MoS2),
Tungsten sulfide (WS2). The metal is sprayed as a liquid on the base material
layer 28. For example, electric arc or plasma spray may be used for spraying the
liquid metal and compound. An inert gas under pressure may be used to not only
deliver the melted metal from the gun or other device used for coating the
substrate but also to insert the compound into the melted metal. For example, the
inert gas may be nitrogen (N).
Porous layer 30 is shown in Figure 3 to have plural pores 32 distributed through
the metal and compound mixture 34. The number of the plural pores 32 depends
on many variables. For example, the number of pores may depend on the
temperature at which the liquid metal is sprayed on the substrate, the pressure of
the inert gas, the distance between the gun that sprays the liquid metal and the
substrate, the specific metal used, the specific compound used, etc. In one
application, the thickness of the self-lubricated layer 30 is between micrometers
and millimeters.
Once the porous layer 30 has been formed on the substrate 26 and the
temperature of the assembly is lowered around room temperature (e.g., 25 °C),
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the pores are closed, e.g., if the porous layer 30 is immersed in a bath of liquid, an
insignificant amount of that liquid enters the pores of layer 30. However, if the
layer 30 together with the substrate 26 are exposed (e.g., immersed) into an oil
bath at a high temperature , the pores 32 of layer 30 open up and the oil starts
flooding the pores. The high temperate range may be from 80 to 500 °C,
depending for example, on the type of oil (synthetic or not, etc.). The oil is used as
an example but any greasing material may be used to partially fill part or all of the
pores of the layer 30.
The substrate 26 and layer 30 are then cooled down to the room temperature to
seal the pores such that the absorbed greasing material is stored inside the pores
32. Such substrate having the self-lubricated layer 30 is then used in one or more
of the machines discussed above. Thus, when such a machine fails to provide oil
at an interface between the rotor and the bearing, the temperature at the interface
increases past the temperature for opening the pores of the self-lubricated layer
30, which determines the porous layer 30 to start releasing the greasing material
at the interface between the rotor and the bearing.
Such a self-lubricated layer 30, depending on its size and distribution on the
bearing and/or rotor, may provide the operator of the machine with minutes if not
hours of safe operation although the main oil supply mechanism of the machine
has failed. In this way, the operator has the necessary time to shut down the
entire processing line in a controlled manner without impairing the safety of the
other machines making up the processing line.
While it may be intuitive to provide a thick self-lubricated layer 30 in order to
provide a longer supply of the greasing material, it has been found that a thick
layer is prone to cracks, and thus, a shorter life. Further, the cracks in the thick
layer allow the greasing material to escape earlier than desired and also may
compromise the adherence of the porous layer to the substrate. On the contrary,
a thin layer is not desirable as not enough greasing material may be stored. Thus,
an appropriate thickness of the self-lubricated layer 30 depends on the type of
machine, the weight of the rotor, the number of pads and the number of bearings,
etc.
According to an exemplary embodiment illustrated in Figure 4, there is a method
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for providing a self-lubricated coating on a substrate. The method includes a step
400 of spraying with a gas at least a layer of liquid metal on the substrate; a step
402 of adding a compound to the liquid metal while being sprayed on the
substrate; a step 404 of forming a porous layer on the substrate that includes the
metal and the compound, where the porous layer has plural pores; a step 406 of
heating the porous layer to open the pores; a step 408 of flooding the open pores
with a greasing substance such that part of the greasing substance is stored in
one or more pores; and a step 41 0 of cooling the porous layer to close the pores
and trap the greasing substance inside the pores.
It is noted that the gas used to deposit the liquid metal may be an inert gas.
However, for depositing ferrous layers, a N2 gas may be used as N2 is cheaper.
Also, the N2 gas may provide more plasticity to the porous layer, which is
desirable. The N2 gas is better than the Argon or compressed air as this gas
avoids oxidation of alloying elements in the liquid metal and also does not alter the
composition of the deposited layer.
According to an exemplary embodiment shown in Figure 5, there is a method for
providing a safety mechanism for a bearing in a turbo-machinery. The method
includes a step 500 of rotating a rotor relative to a stator of the turbo-machinery; a
step 502 of supporting the rotor with a bearing that includes at least a porous
layer, the at least a porous layer including a metal and a compound that form
plural pores and a greasing substance stored in the pores; and a step 504 of
providing a lubricant to the bearing while the rotor rotates such that an operation
temperature of the bearing is substantially constant.
The disclosed exemplary embodiments provide a system and a method for
providing a greasing material when a dedicated supply of the greasing material
fails. It should be understood that this description is not intended to limit the
invention. On the contrary, the exemplary embodiments are intended to cover
alternatives, modifications and equivalents, which are included in the spirit and
scope of the invention as defined by the appended claims. Further, in the detailed
description of the exemplary embodiments, numerous specific details are set forth
in order to provide a comprehensive understanding of the claimed invention.
However, one skilled in the art would understand that various embodiments may
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be practiced without such specific details.
Although the features and elements of the present exemplary embodiments are
described in the embodiments in particular combinations, each feature or element
can be used alone without the other features and elements of the embodiments or in
various combinations with or without other features and elements disclosed herein.
This written description uses examples of the subject matter disclosed to enable any
person skilled in the art to practice the same, including making and using any
devices or systems and performing any incorporated methods. The patentable
scope of the subject matter is defined by the claims, and may include other examples
that occur to those skilled in the art. Such other examples are intended to be within
the scope of the claims.

CLAIMS:
1. A method for providing a self-lubricated coating on a substrate, the method
comprising:
spraying with a gas at least a layer of liquid metal on the substrate;
adding a compound to the liquid metal while being sprayed on the
substrate;
forming a porous layer on the substrate that includes the metal and the
compound, wherein the porous layer has plural pores;
heating the porous layer to open the pores;
flooding the open pores with a greasing substance such that part of the
greasing substance is stored in one or more pores; and
cooling the porous layer to close the pores and trap the greasing substance
inside the pores.
2. The method of Claim 1 , wherein the liquid metal is one of a metal used for a
bearing, gray cast iron, stainless steel, carbon steel, or non-ferrous alloys.
3. The method of Claim 1 or Claim 2, wherein the compound is one of graphite
powder, Molybdenum disulfide (MoS2), Tungsten sulfide (WS2), or a combination
thereof.
4. The method of any preceding Claim, further comprising:
providing a base material that includes a low carbon content and high
content of Fe, Ni or Cobalt or a plastic non-ferrous metal on the substrate prior to
spraying so that the porous layer is formed on the base material to better adhere
to the substrate.
5. The method of any preceding Claim, wherein the heating is achieved by
immersing the porous material in the greasing substance at a predetermined
temperature.
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6. The method of any preceding Claim, wherein the substrate is a bearing of a
compressor.
7. The method of any preceding Claim, wherein the gas includes nitrogen (N).
8. A method for operating a turbo-machinery having a safety mechanism for a
bearing, the method comprising:
rotating a shaft relative to a stator of the turbo-machinery;
supporting the shaft with a bearing that includes at least a porous layer, the
at least a porous layer including a metal and a compound that form plural pores
and a greasing substance stored in the pores; and
providing a lubricant to the bearing while the shaft rotates such that an
operation temperature of the bearing is substantially constant.
9. The method of Claim 8, further comprising:
failing to provide the lubricant;
increasing an operation temperature of the bearing; and
opening the pores of the at least a porous layer such that the stored
greasing substance exits the pores and lubes the bearing.
10. A turbo-machinery, comprising:
a stator configured to be fix;
a shaft configured to rotate relative to the stator;
a bearing configured to support the shaft and facilitate a rotation of the
shaft; and
a self-lubricated coating provided on the bearing or the shaft,
wherein the self-lubricated coating includes at least a porous layer, the at
least a porous layer including a metal and a compound that form plural pores and
a greasing substance stored in the pores, and
the pores are closed trapping the greasing substance when an operational
temperature of the bearing is below a predetermined value.