Patent Application
20090304519
The present invention relates to a gas-compressor impeller for compressing gas containing solid particles and to a gas compressor having the same.
Gas compressors designed to mainly compress gas such as air sometimes need to compress gas contaminated with solid particles, depending on the use. For example, gas compressors for compressing air used in ironworks sometimes compress air contaminated with iron oxide.
Thus, if gas is contaminated with solid particles, damage to impellers due to solid particles cannot be ignored. To prevent damage from solid particles, Patent Document 1 discloses a technique in which a compressor member is plated with a nickel-phosphorus alloy.
On the other hand, though not directed to a gas compressor, Patent Document 2 discloses a technique in which cermet particles containing tungsten carbide are thermally sprayed on a water wheel or pump for pumping liquid to form an abrasion-resistant thermal-spray film to prevent abrasion by hard particles (slurry erosion).
Patent Document 1: Japanese Unexamined Patent Application, Publication No. 2001-200390
Patent Document 2: Japanese Unexamined Patent Application, Publication No. 2005-187890 ([0002], [0003], [Table 1], etc.)
However, because the technique disclosed in Patent Document 1 forms an abrasion-resistant film by plating, the durability is not sufficient.
In addition, because the aforementioned document does not disclose the region where the abrasion-resistant film is formed, it is assumed that the entire compressor member is plated. However, because gas-compressor impellers, among others, have three-dimensional shapes, in the case of electrolytic plating, it is difficult to form a film whose thickness is adjusted to a desired value. Thus, sufficient durability may not be obtained.
Patent Document 2 discloses an abrasion-resistant thermal-spray film composed of a cermet material mainly containing tungsten carbide. However, Patent Document 2, in every respect, relates to a water wheel or pump intended for liquid or slurry, which does not compress gas. Therefore, as disclosed in Table 1 of Patent Document 2, although a slurry erosion evaluation is conducted, the adhesiveness of the abrasion-resistant film with respect to solid particles that collide at a higher speed than slurry (for example, solid particles floating in gas) is not taken into consideration at all.
When an abrasion-resistant film is used for a gas-compressor impeller, solid particles collide with the abrasion-resistant film at various angles. At this time, when the solid particles collide with the abrasion-resistant film at a substantially right angle (for example, a collision angle of 60° or greater), the impact force during the collision is great. When this impact force is great, the abrasion-resistant film may peel off. That is, no matter how high the abrasion resistance of the abrasion-resistant film, if the adhesiveness thereof is low, it cannot withstand the impact force during the collision of the solid particles and may peel off. Accordingly, abrasion-resistant films for gas-compressor impellers need to exhibit not only abrasion resistance but also adhesiveness.
In addition, similarly to Patent Document 1, Patent Document 2 does not disclose the region where the abrasion-resistant film is provided at all.
The present invention has been made in view of such circumstances, and the object thereof is to provide a gas-compressor impeller which has excellent durability even when gas containing solid particles is compressed and which does not increase the cost, and a gas compressor having the same.
Another object of the present invention is to provide a gas-compressor impeller provided with an abrasion-resistant film having not only abrasion resistance but also adhesiveness, and a gas compressor having the same.
To overcome the above-described problems, the present invention employs the following solutions.
A gas-compressor impeller according to a first aspect of the present invention is installed in a gas compressor that compresses gas containing solid particles. The impeller has a hub portion and a plurality of blades extending substantially radially from an outer circumferential surface of the hub portion. The hub portion and the blades are rotated about a central axial line to compress gas. The blades have abrasion-resistant films only at gas inlet portions.
As a result of intensive study, the present inventors have found that, in impellers used in gas compressors that compress gas containing solid particles, damage to the gas inlet portions of the blades is significant but there is comparatively no advancement of damage to the other portions. Thus, in the first aspect of the present invention, the abrasion-resistant films are provided only at the gas inlet portions of the blades. Accordingly, because the abrasion-resistant films need to be only locally provided, the durability of the impeller can be easily improved at low cost.
Furthermore, in the gas-compressor impeller according to the first aspect of the present invention, formation regions of the abrasion-resistant films provided only at the gas inlet portions may be provided from connecting positions of the blades to the hub portion in a height direction of the blades, and the size of the formation regions in the height direction of the blades may be gradually reduced from leading edges of the blades toward a downstream side.
The damage from the solid particles contained in the gas is significant on the hub portion side of the blades, i.e., the base side of the blades. Therefore, the formation regions of the abrasion-resistant films are provided from the connecting positions of the blades to the hub portion in the height direction of the blades.
The damage from the solid particles contained in the gas gradually decreases from the leading edges of the blades toward the downstream side. Thus, it is preferable that the size of the formation regions of the abrasion-resistant films in the height direction of the blades be gradually reduced from the leading edges of the blades toward the downstream side.
Furthermore, in the gas-compressor impeller according to the first aspect of the present invention, the formation regions of the abrasion-resistant films provided on ventral sides of the blades may be larger than the formation regions of the abrasion-resistant films provided on back sides of the blades.
Because the ventral sides of the blades are the pressure faces, they are more severely damaged than the back sides of the blades. Thus, it is preferable that the formation regions of the abrasion-resistant films on the ventral sides of the blades be larger than the formation regions of the abrasion-resistant films on the back sides of the blades.
Furthermore, in the gas-compressor impeller according to the first aspect of the present invention, the abrasion-resistant films may be composed of a cermet material formed by thermally spraying a composite mainly containing tungsten carbide.
In a gas compressor that compresses gas containing solid particles, collision energy is great because of the high-speed solid particles. Accordingly, the abrasion-resistant films need to have not only abrasion resistance but also adhesiveness so as not to be peeled off upon collision of the solid particles. In the first aspect of the present invention, by making the abrasion-resistant films from a cermet material formed by thermally spraying a composite mainly containing tungsten carbide, not only abrasion resistance but also adhesiveness can be ensured.
Examples of the composite mainly containing tungsten carbide (WC) include WC—NiCr, WC—Co, and WC—CoCr.
A preferable thermal spraying method is ultra high-speed flame thermal spraying because it provides a great particle-flying speed to improve adhesiveness.
A gas compressor according to a second aspect of the present invention includes any one of the above-described gas-compressor impellers.
Because the gas compressor according to the second aspect of the present invention includes any one of the above-described gas-compressor impellers, a gas compressor having excellent durability can be provided even when gas containing solid particles is compressed.
A centrifugal compressor is suitable as the gas compressor.
According to the present invention, because the abrasion-resistant films are provided only at the gas inlet portions of the blades, a gas-compressor impeller having excellent durability can be provided at low cost.
In addition, in the present invention, by using a cermet material formed by thermally spraying a composite mainly containing tungsten carbide as the abrasion-resistant films, not only abrasion resistance but also adhesiveness of the abrasion-resistant films can be improved.
An embodiment of the present invention will be described below with reference to the drawings.
The centrifugal compressor 1 is used to compress air containing solid particles P such as, for example, iron oxide. The centrifugal compressor 1 has an impeller 3, an air-intake flow path 5 provided upstream of the impeller 3, and a discharge flow path 7 provided downstream of the impeller 3.
The impeller 3 is rotated about a central axial line L by a driving source (not shown). The impeller 3 has a hub portion 10, a plurality of blades 12 extending substantially radially from the outer circumferential surface of the hub portion 10, and a shroud 14 connected to the upper edges of the blades 12 and forming a flow path between the blades 12 and the hub portion 10.
The impeller 3 is made of low-alloy steel (for example, JIS SNCM431) or stainless steel (for example, SUS630).
In
As shown in
A formation region of the abrasion-resistant film 20 is provided from a connecting position of the blade 12 to the hub portion (i.e., the base of the blade 12) in the height direction of the blade 12. The size of the formation region of the abrasion-resistant film 20 in the height direction of the blade 12 is gradually reduced from the leading edge 12a of the blade toward the downstream side of the gas flow. More specifically, it is preferable that the size, h, of the formation region of the abrasion-resistant film 20 in the blade's height direction at the leading edge 12a of the blade be set to about ¾H, where H is the height of the leading edge 12a of the blade. It is also preferable that the formation region of the abrasion-resistant film 20 be formed such that the formation region is gradually reduced from the leading edge 12a of the blade to a position around LL=h/2 on the downstream side.
As shown with hatching in
The formation region of the abrasion-resistant film 20 is provided from the connecting position of the blade 12 to the hub portion (i.e., the base of the blade 12) in the height direction of the blade 12. The size of the formation region of the abrasion-resistant film 20 in the height direction of the blade 12 is gradually reduced from the leading edge 12a of the blade toward the downstream side of the gas flow. More specifically, it is preferable that the size, h, of the formation region of the abrasion-resistant film 20 in the blade's height direction at the leading edge 12a of the blade be set to about ¾ H, where H is the height of the leading edge 12a of the blade. It is also preferable that the formation region of the abrasion-resistant film 20 be formed such that the formation region is gradually reduced from the leading edge 12a of the blade to a position around LH=h on the downstream side.
As described above, the formation region of the abrasion-resistant film 20 provided on the ventral side of the blade 12 is larger than the formation region of the abrasion-resistant film (refer to
The abrasion-resistant film 20 is a cermet material formed by thermally spraying a composite mainly containing tungsten carbide (WC). Examples of a suitable composite mainly containing tungsten carbide include WC—NiCr, WC—Co, and WC—CoCr. A preferable thermal spraying method is ultra high-speed flame thermal spraying.
As shown in
The abrasion-resistant films 20 according to this embodiment have abrasion resistance and adhesiveness (peel resistance). Test results of the evaluation of their performances are shown below.
As shown in
The abrasion-resistant film was formed by thermal spraying. As thermal spraying materials according to this embodiment, tungsten carbide (WC) cermet materials, namely, WC-27% NiCr, WC-10% Co-4% Cr, and WC-12% Co, were used. As comparative examples, Cr3C2-25% NiCr, Al2O3-3% TiO2, and Cr2O3 were used. Their composition ratios are expressed in percentage by weight.
First, each sample was degreased by trichloroethylene vapor degreasing. Then, using an alumina grid of #60, blasting was performed at a gas pressure of 4 kgf/cm2. Then, thermal spraying was performed under the following conditions to form an abrasion-resistant film.
(i) The present invention: WC cermet materials (WC-27% NiCr, WC-10% Co-4% Cr, and WC-12% Co)
After the abrasion-resistant films were formed by thermal spraying under the above-described conditions, grinding was performed using a diamond wheel.
As shown in
As shown in
As is clear from
As shown in
The fabrication processes of the abrasion-resistant films and of the samples were the same as those of the above-described abrasion resistance test. However, in the adhesiveness test, the grinding step performed in the abrasion resistance test after formation of the abrasion-resistant film was not performed.
Using a bending test apparatus shown in
The bending test apparatus had a bending jig base 30 for supporting each sample 27 from below at two points and a bending jig 32 for pressing the sample 27 downward at a single point. The sample 27 with a coating surface 29 having the abrasion-resistant film facing down was placed on the bending jig base 30, and a pressure was applied to the sample 27 from above with the bending jig 32. Thus, three-point bending was performed.
The tip portion, which served as the pressing portion of the bending jig 30, had three radii, namely, 5 mm, 10 mm, and 25 mm. The bending speed, i.e., descending speed, of the bending jig 30 was 1 mm/s or less. Regarding the number of samples, one sample was used under each condition, and a total 15 samples (three bend radii×five types of abrasion-resistant film) were used.
The presence or absence of peeling was determined by carrying out observation at 20 times magnification with a microscope.
As is clear from
As has been described, the abrasion-resistant films composed of the WC cermet materials according to this embodiment have not only abrasion resistance but also adhesiveness. The reason for the improved adhesiveness may be as follows.
The abrasion-resistant films composed of the WC cermet materials according to this embodiment were formed by “ultra high-speed flame thermal spraying” using combustion gas flames as a heat source. On the other hand, the abrasion-resistant films composed of alumina-titania and chromium oxide ceramic according to the comparative examples were formed by “plasma thermal spraying” using plasma as a heat source. In the ultra high-speed flame thermal spraying, the particle-flying speed is 500 m/s or more, which is much faster than the particle-flying speed in the plasma thermal spraying (from 100 m/s to 200 m/s). Therefore, in the ultra high-speed flame thermal spraying, the collision energy of the thermal spraying particles with the base material is great, whereby the adhesiveness is greater compared to that obtained in the plasma thermal spraying.
In addition, the WC powders according to this embodiment have larger specific gravities than the Cr3C2 powder according to the comparative example that employs the ultra high-speed flame thermal spraying similarly to this embodiment. Therefore, with the WC powders according to this embodiment, the thermal spraying particles have greater collision energy with the base material than the Cr3C2 powder according to the comparative example, thus giving greater adhesiveness.
Accordingly, the abrasion-resistant films according to this embodiment, which are composed of the WC cermet materials and formed by the ultra high-speed flame thermal spraying, have the best adhesiveness.
As has been described, according to this embodiment, the following advantages are obtained.
Because the abrasion-resistant films 20 are provided only at the gas inlet portions of the blades 12, that is, the abrasion-resistant films 20 are provided locally, the durability of the impeller 3 can be easily improved at low cost.
Damage from the solid particles contained in gas is severer at portions of the blades 12 closer to the hub portion 10, i.e., the base side of the blades 12. Therefore, in this embodiment, the abrasion-resistant films 20 are provided from the bases of the blades 12 in the height direction of the blades. Damage from the solid particles contained in gas is smaller at portions farther from the leading edges 12a of the blades 12 toward the downstream side. Therefore, in this embodiment, the size of the formation regions of the abrasion-resistant films 20 in the blade's height direction is gradually reduced from the leading edges 12a of the blades toward the downstream side. Furthermore, the ventral sides of the blades 12 are pressure faces, which are damaged more severely than the ventral sides of the blades. Therefore, in this embodiment, the formation regions of the abrasion-resistant films 20 on the ventral sides of the blades 12 are larger than the formation regions of the abrasion-resistant films on the back sides of the blades 12. Thus, according to this embodiment, because the abrasion-resistant films 20 are formed only at the necessary portions, the durability of the impeller 3 can be improved without increasing the cost.
Because the abrasion-resistant films 20 according to this embodiment are composed of a cermet material formed by performing ultra high-speed flame thermal spraying of a composite containing tungsten carbide, not only abrasion resistance but also adhesiveness can be ensured. In a gas compressor that compresses gas containing solid particles, because the collision energy is great due to the high-speed solid particles, the abrasion-resistant films need to have not only abrasion resistance but also adhesiveness. Accordingly, the abrasion-resistant films are particularly useful.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-005852 | Jan 2007 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2007/074527 | 12/20/2007 | WO | 00 | 1/23/2009 |
