Patent Application
20180245638
The present disclosure generally relates to coatings. More particularly, the present disclosure relates to a method of forming a coating having a surface roughness below a predefined surface roughness value.
Thermal spray coatings are frequently used to impart new property to a component's surface. For example, spray coatings may be used on worn components to restore their dimensions, sealing ability, and/or other material properties. All spray coating techniques have a common characteristic wherein they define some internal porosity within the coatings.
Subsequent to deposition of the coating on the component, the coating may be subjected to finishing processes such as lathe turning, milling, honing, grinding, polishing, etc. These finishing processes may expose internal pores of the coating, thereby creating valleys or depressions of large sizes on the final external surface of the coating. Such large size valleys and depressions may impact the performance of the coating or of the component.
For example, in salvaging journal bearing surfaces, too high of an Rz (the difference between the deepest depression and the tallest peak) value is often thought to lead to failure via cavitation erosion when oil is trapped in the valleys and is subjected to cyclic liquid pressure fluctuations, which generate cavitation. In other applications such as hydraulic cylinder rods, coatings with too high of Rz can damage polymeric seals, leading to catastrophic leakage. Accordingly, for optimal operation of the components, it is necessary to reduce the size and frequency of these peaks-to-valley dimensions.
U.S. Pat. No. 6,305,459 discloses thermally spraying bulk material on a target surface. U.S. Pat. No. 6,305,459 further discloses that subsequent coatings of different materials are applied on the target surface to reduce porosity levels in the sprayed layers. This results in the need for multiple coatings to be applied in multiple steps, thus increasing costs.
In an aspect of the present disclosure, a method for coating a component is disclosed. The method comprising the steps of depositing, by a thermal spraying process, simultaneously a first material and a second material on a surface of the component to form a rough coating, wherein the first material is of higher hardness than the second material and removing a layer of the rough coating such that the second material plastically deforms and produces a finished coating having a finished surface with an Rz value of less than 2 μm.
In another aspect of the present disclosure, a component is disclosed. The component includes a coating including a first material mixed with a second material, the first material being of higher hardness than the second material, wherein the coating has a finished surface having an Rz value of less than 2 μm.
In another aspect of the present disclosure, a journal bearing having a coating is disclosed. The coating is formed by a process comprising the steps of depositing, by a thermal spraying process, simultaneously a first material and a second material on a surface of the journal bearing to form a rough coating, wherein the first material is of higher hardness than the second material and removing a layer of the rough coating such that the second material plastically deforms and produces a finished coating having a finished surface with an Rz value of less than 2 μm.
Reference will now be made in detail to embodiments of the disclosure, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.
The component 100 may be subjected to wear and tear during operation. The present disclosure provides for a method of enhancing the wear resistance and enhancing life of the component 100 by depositing a coating on the surface 104 of the component 100 via a thermal spray system 102, as illustrated in
As illustrated in
The spray gun 106 may include feed rollers 125, 126 configured to pull the first wire 118 and the second wire 122 from the first spool 114 and the second spool 116 respectively. The first wire 118 and the second wire 122 fed to the spray gun 106 may be coupled to the energy source 108. The energy source 108 may be configured to energize the first wire 118 and the second wire 122 such that opposing polarities may be developed in the first wire 118 and the second wire 122.
The control console 110 may be operatively coupled to the feed rollers 125, 126. The control console 110 may be configured to control the wire feed rate, i.e., the speed at which the first wire 118 and the second wire 122 may be fed into channels 176 of the spray gun 106. The control console 110 may further be operatively coupled to the energy source 108 and may be configured to actuate the energy source 108 such that current is passed by the energy source 108 to the first wire 118 and the second wire 122.
Upon being actuated, the energy source 108 causes opposing polarities to develop in the first wire 118 and the second wire 122. Due to the opposing polarities, an arc may be struck between the first wire 118 and the second wire 122 at an arc point 130, i.e., location at which the first wire 118 and the second wire 122 come into contact and electrically arc based on electric current therein. The arc generated causes the first wire 118 and the second wire 122 to melt and form a mixture of first material 120 and second material 124 at the arc point 130. At the arc point 130, the mixture of first material 120 and the second material 124 commingle to form a blend/mixture of coating material. Further, at the arc point, the first material 120 and the second material 124 mix such that the first material 120 and the second material 124 are uniformly distributed in the mixture of coating material.
The thermal spray system 102 may further include a propelling gas 134 stored in a propelling gas source 136. The propelling gas 134 may be configured to propel the mixture of coating material generated at the arc point 130 to the surface 104 of the component 100 to form a rough coating 138. In an embodiment, the propelling gas 134 may include a compressed gas, for example argon. However, in another example, the propelling gas 134 may take the form of a combustion-based gas such as that created by a high velocity oxygen fuel (HVOF) process using hydrogen gas or a liquid fuel like kerosene.
In the embodiment, illustrated in
The rough coating 138 applied/deposited to the surface 104 of the component 100 may be configured to impart a new functionality/property or improve the wear resistance to a component's 100 surface 104. For example, the rough coating 138 may be applied on a comparatively softer component 100 thereby imparting strength and hardness to the component 100. In an alternate example, the component 100 may be used in harsh environments of high temperature (more than 300 degrees Celsius). Layer of heat resistant rough coating 138 may be applied over the component 100 to prolong component 100 life and prevent the negative effects of the harsh temperatures on the component 100.
The rough coating 138 as deposited by the thermal spray system 102 of
The first material 120 of the rough coating 138 has a comparatively higher hardness value as compared to the second material 124. For example, in the embodiment illustrated in
The first wire 118 (made of the first material 120) may have a Vickers hardness value of more than 500 HV300 (Vickers microhardness measured with a 300 g load) and may for example be any one of Inconel 625, 420 stainless steel, Tafa 90 MXC, Tafa 95 MXC, Tafa 96 MXC, Tafa 140 MXC, nanosteel SHS 9193W16, Nanosteel SHS 717, Nanosteel SHS 9192W16 and Oerlikon Metco 8222. Further, the second wire 122 (made of comparatively softer second material 124) may have a Vickers hardness of not more than 250 HV300 and may for example be any one of Tafa 01T (Al) Tafa O1A (Al-12Si), Tafa O2Z (Zn), Tafa 80T (304 stainless), Tafa 85T (316 stainless), Tafa O5T (copper), babbit, brass, nickel and aluminium.
Referring to
The finishing process includes removal of a layer of the rough coating 138.
The rotating grinding roller 152 comes in contact with the rough coating 138, as illustrated in
Rz={(P1+P2+P3+P4+P5)−(D1+D2+D3+D4+D5)}/5
FIG.7 illustrates the finished surface 156 of the finished coating 154 (in this example made of 50 percent Stellite and 50 percent brass). The finished coating 154 has an Rz value of 1.6 μm over a length of 5.797 mm. This low Rz value provides a finished surface 156 configured to prevent accumulation of oils within the gaps on the surface of the finished coating 154 and prevents breakage of seals. The low Rz value is achieved by smearing of the second material 124 within the pores 140 exposed to the external surface of the machined rough coating 138. The smearing/plastic deformation within the pores 140 reduces the difference between the peaks and the depressions on the finished surface 156 of the finished coating 154 and produces a finished surface with Rz less than 2 μm.
As illustrated in
The thermal spray system 102 as illustrated in
The powder feeding device 166 may be a reservoir having a mixture of first powder made of first material (depicted by solid circles) and a second powder made of a second material (depicted by hollow squares). The first material is of higher hardness than the second material. The first material powder may be a powder of any one of tungsten carbide (WC), chromium carbide (Cr2C3), aluminium oxide (Al2O3), zirconium Oxide (ZrO2), chromium oxide (Cr2O3), Stellite alloys and high-Cr/Ni stainless steel alloys such as NAH 3.5, Ni-based alloys containing Cr, Si & B such as Diamalloy 2001 and tool steel powders like M2. The second material powder may be a powder of any one of Co, Ni, Cu, bronze, brass, monel or NiCr.
The controller 180 may be operatively coupled to the carrier gas source 162, and the powder feeding device 166. The controller 180 may be configured to control the amount of powder mixture (mixture of first material and second material) and the amount of carrier gas sent to the burner system 164. Thus, when actuation signals from the controller 180 are transmitted to the carrier gas source 162, and the powder feeding device 166, the burner system 164 is fed with the powder (mixture of first material and second material) from the powder feeding device 166 and with a carrier gas and a burnable gas mixture (from the carrier gas source 162). When the carrier gas along with the powder and the burnable gas mixture are ignited in the burner system 164, the hot combustion gases together with the propelling gas are accelerated to a supersonic velocity. At the same time the hot combustion gases partially melt the powder particles (i.e. the mixture of first material and the second material) and mix them together to form a coating material. When this partially melted coating material hits the surface 104 of the component 100 it adheres to the surface 104 to form a rough coating 138. The coating process is carried out until the rough coating 138 attains a desired thickness.
The rough coating 138 deposited on the surface 104 of the component 100 may have a thickness of not less than 50 μm. A thickness value of at least 50 μm of the rough coating 138 ensures that even after the removal of a layer of rough coating 138 during a finishing operation of the rough coating 138, an adequate thickness of the finished coating 154 remains.
The rough coating 138 formed by the thermal spray system 102, as illustrated in
The component 100 may be subjected to wear and tear during operation. This degradation of the surface 104 due to wearing of the component 100 may decrease the life of the component 100 and may also lead to breakdown of the component 100, thereby leading to machine downtime and loss of productivity. One such method of enhancing the wear resistance and enhancing life of components is to deposit a coating on the surface 104 of the component 100 via the thermal spray system 102.
In an aspect of the present disclosure, a method 800 (illustrated in
The finished coating 154 as disclosed in the present disclosure has an Rz value of less than 2 μm. The finished coating 154 has a smooth surface finish with depressions of low magnitude (as illustrated in
In another example, the method may be used to coat a journal bearing. The low surface roughness value of the finished coating deposited over the journal bearing ensures that the finished surface of the coating, deposited over the journal bearing, has depressions of low magnitude. Further, a low surface roughness prevents fluid from being captured/accumulated within the depressions present in the finished coating, thereby preventing the erosion of the finished coating via cavitation during operation of the journal bearing. Accordingly, the wear resistance and the life of the journal bearing may be enhanced. Hence, coating the component 100 by the method 800 as described in the present disclosure provide significant cost savings for both the manufacturer and the user.
While aspects of the present disclosure have seen particularly shown and described with reference to the embodiments above, it will be understood by those skilled in the art that various additional embodiments may be contemplated by the modification of the disclosed machines, systems and methods without departing from the spirit and scope of what is disclosed. Such embodiments should be understood to fall within the scope of the present disclosure as determined based upon the claims and any equivalents thereof.
