Method for manufacturing flow path forming member of liquid pump, and liquid pump
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2026-02-05
- Publication Date
- 2026-08-13
Smart Images
Figure JP2026004133_13082026_PF_FP_ABST
Abstract
Description
Method for manufacturing a flow path forming member of a liquid pump and a liquid pump
[0001] The present technology relates to a method for manufacturing a flow path forming member of a liquid pump and a liquid pump.
[0002] Pure aluminum and aluminum alloys are widely used in various products because of their light weight and high specific strength. Such aluminum parts and aluminum products are often subjected to an anodic oxidation treatment (alumite treatment) to form an oxide film on the surface for the purpose of improving various properties such as corrosion resistance and wear resistance. In this treatment, the target aluminum substrate is used as an anode and electrolyzed in an electrolytic bath to oxidize the substrate surface, gradually generating an aluminum oxide (Al2O3) film excellent in corrosion resistance, wear resistance, etc. The aluminum oxide constituting this film is also called alumite. The alumite film is known to have a honeycomb structure (cell structure) with a large number of pores elongated in the thickness direction due to its formation process (see FIG. 3). For an alumite film having such a structure, it is common to perform pore sealing in order to sufficiently obtain corrosion resistance. Methods of the sealing treatment include a method of exposing the alumite film to pressurized steam, a method of immersing it in high-temperature water, a method of immersing it in a high-temperature metal salt aqueous solution, a method of using a special chemical at room temperature, and the like.
[0003] On the other hand, various performances are required for the components of a pump used for pumping a liquid from a tank. For example, wear resistance is required for components that are severely rubbed by the liquid existing between rotating components such as an impeller. In addition, a pump generates cavitation due to a rapid pressure fluctuation of the liquid flowing inside. Cavitation refers to a phenomenon in which when a locally low-pressure portion occurs in a liquid, the liquid vaporizes there to generate bubbles (cavities). It is known that these bubbles collapse with a very large shock wave when the pressure rises again. Therefore, pump components are required to have erosion resistance and impact resistance so that the surface is not eroded by the impact of cavitation collapse. In addition, corrosion resistance (corrosion resistance) is also required depending on the type of liquid to be pumped, such as when fuel is used as the liquid.
[0004] Japanese Patent Publication No. 2010-77532 discloses a method for sealing pores in parts having an anodized coating using a treatment solution containing lithium ions, with a pH of 10.5 or higher and a temperature of 65°C or lower. In this sealing method, the anodized coating is exposed to high-temperature water, causing anodized hydrate (Al2O3・H2O, AlO(OH)) mainly composed of boehmite to form on the surface of the anodized coating, which causes the walls of the pores to grow and ultimately seals the pores. However, in order to apply this to liquid pump parts as described above, it is desirable to form a sealing anodized coating with even better corrosion resistance or impact resistance.
[0005] One aspect of this technology is a method for manufacturing a flow channel forming member that faces the impeller of a liquid pump, comprising the steps of forming an anodized film on the surface of a substrate made of pure aluminum or an aluminum alloy, and occluding the pores of the anodized film by immersing the substrate in hot water, wherein the pH value of the hot water is 4.5 to 5.5. In some embodiments, the conductivity of the hot water is 7 to 25 μS / cm.
[0006] Depending on the embodiment, the above configuration makes it possible to seal pores with hydrates while leaving a certain thickness in the wall of the anodized coating. Therefore, the balance between the filling of pores and the contribution of the thickness of the anodized coating wall to strength is optimized, improving cavitation resistance (impact resistance).
[0007] In some embodiments, the process of forming the anodized film is carried out in a weak acid bath of oxalic acid. As a result, the wear resistance of the anodized film, which forms a honeycomb structure, is superior to that of anodized films formed by other anodic oxidation treatments such as sulfuric acid anodizing, and a larger wall thickness of the anodized film becomes more effective.
[0008] Depending on the embodiment, the degree of porosity of the anodized coating determined by immersion test in an aqueous phosphoric acid-chromic acid solution is 30 to 80 mg / dm 2 This ensures that the balance between pore filling and the contribution of the thick anodized coating walls to strength is optimally maintained.
[0009] Another aspect of the present technology is a liquid pump comprising a housing, a rotatable impeller disposed within the housing, and a flow channel forming member facing the impeller and made of pure aluminum or an aluminum alloy, wherein the impeller and the flow channel forming member form at least partially a flow channel for a liquid, and the rotation of the impeller causes the liquid to be pumped through the flow channel, wherein the flow channel forming member has an anodized coating on its surface, the pores of the anodized coating are blocked with hydrate from the bottom to the opening, and the hydrate is denser at the bottom than at the opening.
[0010] In some embodiments, the above configuration results in the pore sealing not being completely completed, leaving a difference in density from the bottom to the opening. This optimizes the balance between the filling of pores and the contribution of the thick anodized coating wall to strength, thereby improving cavitation resistance (impact resistance).
[0011] This is a partial cross-sectional view of a fuel pump consisting of a vortex pump as one embodiment. This is an exploded perspective view of the pump body, impeller, and pump cover. This is a schematic diagram of a general anodized coating having multiple pores. This is a schematic diagram of an anodized coating where the sealing has progressed completely and the hydrate that closes the pores is homogeneous from the bottom to the opening. This is a schematic diagram of an anodized coating where the sealing has progressed partway and there is a difference in density from the bottom to the opening of the pores. This is an SEM image of the cross-section of an unsealed test piece. This is an SEM image of the cross-section of a test piece that has been sealed with hot water at a pH of 4.02. This is an SEM image of the cross-section of a test piece that has been sealed with hot water at a pH of 4.04. This is an SEM image of the cross-section of a test piece that has been sealed with hot water at a pH of 4.58. This is an SEM image of the cross-section of a test piece that has been sealed with hot water at a pH of 4.94. This is an SEM image of the cross-section of a test piece that has been sealed with hot water at a pH of 5.27. This is an SEM image of a cross-section of a test specimen that was sealed with hot water at a pH of 5.34. This is an SEM image of a cross-section of a test specimen that was sealed with hot water at a pH of 6.16. This is a graph plotting the degree of sealing of the anodized coating, measured by an immersion test of phosphoric acid-chromic acid solution, which is an indicator of the degree of sealing, against the conductivity of the hot water used. This is a graph plotting the degree of sealing against the pH of the hot water. This is a graph plotting the percentage of damaged area of the anodized coating, which is an indicator of corrosion resistance to cavitation collapse, against the conductivity of the hot water used. This is a graph plotting the percentage of damaged area against the pH of the hot water.
[0012] Various embodiments will be described below with reference to the drawings.
[0013] [Fuel Pump] As shown in Figures 1 and 2, one embodiment of the liquid pump is a fuel pump 1 consisting of a vortex pump. However, the features described below are also applicable to fuel pumps other than vortex pumps and liquid pumps other than fuel pumps. The fuel pump 1 is provided, for example, as part of a fuel pump module in the fuel tank of a vehicle equipped with an engine, such as an automobile. The fuel pump 1 comprises a metal pump housing 10 and a pump section 3 inside the pump housing 10. The pump section 3 comprises a pump cover 40, a pump body 20 arranged opposite to the pump cover 40, and an impeller 30 rotatably arranged between the pump cover 40 and the pump body 20. The impeller 30 can be made of plastic. The pump body 20 is secured to the pump cover 40 by a crimped portion formed by crimping the edge of the pump housing 10. The impeller 30 is generally a disc and has a plurality of blade grooves 31 (see Figure 2) arranged circumferentially on the peripheral edges of both sides thereof. The pump cover 40 and the pump body 20 have arc-shaped passage grooves 21 and 41 that are less than one full circumference and face the blade grooves 31 of the impeller 30 (see Figure 2). These passage grooves 21 and 41, together with the blade grooves 31 of the impeller 30, form a fuel flow path 4. Therefore, both the pump cover 40 and the pump body 20 are flow path forming members that face the impeller 30.
[0014] The fuel pump 1 is equipped with an electric motor 2 located on top of the pump housing 10, and an impeller 30 is coupled to the tip of the output shaft 12 of the electric motor 2. The output shaft 12 is coupled to the rotor 11 of the electric motor 2 and is rotatably supported by the pump cover 40 via a bearing 13. The flow path 4 communicates with an intake port 22 formed in the pump cover 40. A filter (not shown), which forms part of the fuel pump module, is attached to the intake port 22, and fuel from the fuel tank is drawn up through this filter. The flow path 4 also communicates with the discharge port 24 of the pump housing 10 through a through hole formed in the pump body 20 and the inside 14 of the electric motor 2. To pump fuel, the electric motor 2 is energized and the impeller 30 is rotated. As a result, fuel is drawn in from the intake port 22 into the flow path 4, pressurized while being created as a vortex by the action of the blade grooves 31, and finally pumped out to the outside from the discharge port 24.
[0015] [Anodizing treatment of pump body and pump cover] The pump cover 40 and pump body 20 are subjected to intense friction from the impeller 30 itself and the fuel present between the impeller 30 and the pump body 20 in the passage grooves 21, 41 or other areas. For this reason, the pump cover 40 and pump body 20 are formed from pure aluminum or an aluminum alloy containing Mg, Mn, Cu, Si, Zn, etc., and are further subjected to anodizing treatment. This provides the pump cover 40 and pump body 20 with wear resistance, erosion resistance, or impact resistance.
[0016] As shown in Figure 3, the anodized coating 102 formed on the surface of the substrate 100 has numerous pores 104. These pores give the anodized coating a honeycomb structure (cell structure). The internal space of the pores 104 is isolated from other pores by walls 110 (also called cell walls) and isolated from the substrate 100 by a barrier layer 112.
[0017] Anodizing can be applied to only a portion of the surfaces of the pump cover 40 and pump body 20, rather than to the entire surface. For example, an anodized coating can be formed on at least the surface facing the impeller 30. This can be achieved by masking the parts that do not require treatment.
[0018] Before anodizing, surface impurities and native oxide films can be removed by degreasing or etching as needed. Anodizing is performed by immersing the pump cover 40 and pump body 20 as part of the anode in an acidic electrolytic bath. Oxalic acid, sulfuric acid, etc., can be used as the electrolytic bath, but oxalic acid can be used as an example. The anodizing process itself can be carried out by a well-known method. The thickness of the anodized coating can be set appropriately according to the performance required for each product, but can be, for example, 5 to 50 μm, 10 to 30 μm, or 15 to 25 μm.
[0019] [Sealing Treatment] The pump cover 40 and the pump body 20 are subjected to the impact of cavitation collapse in the fuel in the passage grooves 21, 41 or other areas. For this reason, as shown in Figures 4 and 5, a sealing treatment is performed on the anodized coating 102 formed as described above. This sealing treatment is performed by immersing the pump cover 40 and the pump body 20 in hot water and depositing and filling the pores 104 of the anodized coating 102 with a hydrate 120 mainly composed of boehmite.
[0020] As shown in the grayscale density in Figure 5, the hydrate 120 seals the pore 104 from the bottom 106 to the opening 108, but it is dense at the bottom 106 and sparse at the opening 108. This means that the hydrate has not completely filled the pore until the density is uniform from the bottom 106 to the opening 108, as shown in Figure 4, and that the sealing is still in progress. When the sealing is complete (Figure 4), dense hydrate is formed along the entire length of the pore, but the thickness of the anodized aluminum wall 110 of the base material that forms the honeycomb structure (the radial dimension of the pore) is reduced, making the wall 110 more susceptible to breaking at the base due to the impact of cavitation collapse. On the other hand, when the sealing is still in progress (Figure 5), the balance between the effect of preventing the wall 110 from collapsing due to the pore being adequately filled and the strength provided by the anodized aluminum wall 110 maintaining an adequate thickness is optimal. As a result, the pump cover 40 and the pump body 20 achieve optimal erosion resistance or impact resistance.
[0021] The pH value of the hot water at room temperature can be between 4.5 and 5.5, and can be adjusted by adding an appropriate acid, such as oxalic acid. The temperature of the hot water can be, for example, 70°C or higher, 75°C or higher, 80°C or higher, 85°C or higher, or 90°C or higher. The immersion time in the hot water can be determined according to the thickness of the anodized coating, the temperature of the hot water, the degree of sealing to be achieved, and can be, for example, 10 minutes or more and 60 minutes or less, 10 minutes or more and 30 minutes or less, or 15 minutes or more and 25 minutes or less.
[0022] Although specific embodiments have been described above, this technology is not limited to these embodiments, and those skilled in the art can make various substitutions, improvements, and modifications without departing from the purpose of this technology.
[0023] [Manufacturing Example] The flow path forming member of the fuel pump was formed by aluminum die casting. After degreasing and cleaning the flow path forming member, an anodized coating was formed on the surface by anodic oxidation in a weakly acidic oxalic acid bath. Multiple test flow path forming members (hereinafter referred to as "test pieces") were prepared in this manner. The average thickness of the anodized coating on the test pieces was 19.8 μm.
[0024] Next, the test specimens were immersed in hot water to perform a sealing treatment. The pH value of the hot water at room temperature was adjusted to the values shown in Table 1 below by adding oxalic acid to pure water (pH value 0.72). The table also shows the conductivity at room temperature, which serves as an indicator of the pH value. Other treatment conditions, such as temperature and immersion time, were kept the same. Test specimens without sealing treatment were also prepared for comparison.
[0025] [SEM Image Observation] As shown in Figures 6 to 13, the prepared test specimens were cut and cross-sectional images were obtained using a field emission scanning electron microscope. In each of these figures, the upper row (labeled "a" in Figure 8) shows a cross-section near the surface of the coating (pore opening), and the lower row (labeled "d" in Figure 8) shows a cross-section near the interface with the substrate (pore bottom). The magnification of the images in the right column is 3.3 times that of the images in the left column (left and center columns in Figure 8).
[0026] In the unsealed specimen shown in Figure 6, the presence of pores is clearly visible. The cell wall thickness was approximately 134 nm, and the barrier layer thickness was approximately 95 nm.
[0027] In the specimen with a pH of 4.02 shown in Figure 7, the cell wall thickness was approximately 136 nm, and the barrier layer thickness was approximately 103 nm. As can be seen from the two images in the upper row, the hydrate is present only on the wall surface in the immediate vicinity of the opening (the region from approximately 0.6 to 0.9 μm from the surface) and is coarsely deposited.
[0028] On the other hand, in the specimen with a pH of 4.04 shown in Figure 8, the average thickness of the cell wall was approximately 113 nm, and the average thickness of the barrier layer was approximately 92 nm. Image "a" in the figure shows the surface of the coating, and image "d" shows a cross-section at the bottom of the pore (18.4 μm from the surface). No lines indicating unfilled pores are seen at the bottom, and the pores are relatively densely packed, but cavities are observed near the surface, indicating that the pores are not sealed. Images "b" and "c" are cross-sections of different regions of the coating at different depths, with "b" at approximately 3.8 μm from the surface and "c" at approximately 7.4 μm from the surface. Both "b" and "c" show cavities at the top of the image and are filled at the bottom, indicating that the hydrate fills up to 79% of the pore from the bottom in "b" and up to 60% in "c". Thus, it was found that even if hydrates accumulate on the wall surface near the opening in the initial stage of sealing (Figure 7), as sealing progresses further, the hydrates fill from the bottom of the pore toward the opening. This can be attributed to the fact that, compared to sealing methods using, for example, metal salt aqueous solutions, hydrothermal fluids can penetrate more easily to the bottom of the pore.
[0029] In the specimen with a pH of 4.58 shown in Figure 9, the average thickness of the cell wall was approximately 95 nm, and the average thickness of the barrier layer was approximately 85 nm. Therefore, it can be seen that the thickness of the cell wall and barrier layer decreases as pore sealing progresses. In the specimens in Figures 9 and 10 (pH 4.94), the pores are densely packed near the bottom, but noticeable streaks are visible near the surface. In the specimens in Figures 11 (pH 5.27) and 12 (pH 5.34), the pores are also densely packed near the bottom, but only faint streaks are visible near the surface. In summary, in Figures 9 to 12, the hydrate fills the pores from the bottom to the opening, and although the pores are blocked, quantitatively the hydrate is denser at the bottom and more sparse towards the opening. Figure 5 schematically shows this difference in density using grayscale.
[0030] In the specimen with a pH of 6.16 shown in Figure 13, no pore lines are visible near the surface or bottom, indicating that pore sealing has progressed almost completely. This is also confirmed by the deposition of hydrates on the surface of the anodized coating. The average thickness of the barrier layer is approximately 81 nm, which is a further decrease compared to Figures 9 to 12. (Note that the thickness of the cell wall at the bottom of the pores, including the area outside the range of the SEM image in the lower right of Figure 13, is less than approximately 100 nm on average, indicating an overall decrease.) Figure 4 schematically shows, with a more concentrated and homogeneous density than Figure 5, that pore sealing has progressed to the maximum extent and the difference in density between the bottom and opening of the pores has disappeared.
[0031] [Sealing Degree Test] The degree of sealing was evaluated by immersion testing in a chromate-phosphate aqueous solution as specified in the standard JIS H 8683-2 on the prepared test specimens. First, the mass of the test specimen was measured. Next, the test specimen was immersed in a chromate-phosphate aqueous solution. At this time, the exposed parts of the anodized aluminum dissolved violently due to the acid, but the parts covered by the sealing process could withstand prolonged immersion as the degree of sealing progressed. The immersion time was set to 15 minutes as per the standard. Next, the test specimen was dried to remove the aqueous solution, and the mass was measured again. The degree of sealing was then obtained by dividing the difference in mass (decrease) before and after immersion by the total surface area of the test specimen. The results of the degree of sealing of the test specimen against the conductivity and pH value of the hot water are shown in Figures 14 and 15, respectively. Note that a higher value indicates a lower degree of sealing. From the results, it was found that the higher the pH value of the hot water (closer to neutral), the higher the degree of sealing. This is consistent with the observation results of the SEM images mentioned above.
[0032] [Cavitation Test] The erosion resistance of the test specimen to cavitation collapse was evaluated. First, the test specimen was fixed in a sufficient amount of water (deionized water), and vibration (sound waves / ultrasound) was generated by a transducer on the test specimen in the water, thereby forcibly generating cavitation near the surface of the test specimen. The distance from the transducer to the test specimen was 0.5 mm, the transducer frequency was 19 ± 1 kHz, and the amplitude was 30 μm. A certain evaluation range was set on the surface within the range facing the transducer, and the damaged area in the evaluation range was measured based on a binarized image created from a photograph of the test specimen surface. The damaged area ratio was calculated by dividing the damaged area by the area of the evaluation range. Therefore, a larger damaged area ratio means lower erosion resistance. The results of the damaged area ratio of the test specimen against the conductivity and pH value of the hot water are shown in Figures 16 and 17, respectively.
[0033] The results showed that the minimum damage area ratio, i.e., the point at which corrosion resistance is best, appears around a pH of 5 in the hydrothermal water (specifically, about 4.9 to 5.3). In the region of high acidity of the hydrothermal water, corrosion resistance increases significantly as the pH value decreases, but conversely, corrosion resistance also decreases slightly in the neutral region. Considering this in conjunction with the observation results of the SEM images, it is thought that when pore sealing is at its maximum, as shown in Figure 4, dense hydrates are formed along the entire length of the pores in the anodized coating, and corrosion resistance improves as the pores are blocked (filled with hydrates). On the other hand, the walls 110 of the anodized base material, which form a honeycomb structure, become thinner, and the walls 110 become more prone to breaking at the base due to the impact of cavitation collapse. On the other hand, when the sealing is in an intermediate stage (Figure 5), it is considered that the optimal balance is achieved between the effect of preventing the wall from collapsing due to the moderate filling of the pores and the strength provided by the anodized coating wall 110 maintaining a moderate thickness. Specifically, the degree of sealing of the anodized coating is approximately 20 to 80 mg / dm 2 , or approximately 30-80 mg / dm 2 It would be preferable if this were the case.
[0034] [Corrosion Test] The prepared test specimens were subjected to the CASS test specified in the standard JIS H 8681-2 to evaluate their corrosion resistance. To accelerate the corrosion rate, a test solution with a pH of 3.0 was prepared by adding Cu ions and acetic acid to saline solution (NaCl aqueous solution). This test solution was sprayed for 16 hours in a 50°C test chamber containing the test specimens, exposing the measurement surface to the mist of the test solution. After spraying, the state of pitting corrosion that occurred on the measurement surface of the test specimens was examined, and the area of pitting corrosion exceeding a certain size was measured. The corrosion area ratio was calculated by dividing the total pitting area by the area of the measurement surface. Therefore, a larger corrosion area ratio indicates lower corrosion resistance. Although not shown in the figures, the test results showed that the corrosion area ratio had a positive correlation with the conductivity of the hot water used for sealing. In other words, the higher the pH of the hot water and the closer it is to neutral (i.e., the higher the degree of sealing), the higher the corrosion resistance. However, in applications where corrosion resistance is not a particularly high requirement, as mentioned above, having the pores partially sealed is preferable in terms of cavitation resistance.
Claims
1. A method for manufacturing a flow path forming member that faces the impeller of a liquid pump, comprising the steps of: forming an anodized coating on the surface of a substrate made of pure aluminum or an aluminum alloy; and occluding the pores of the anodized coating by immersing the substrate in hot water, wherein the pH value of the hot water is 4.5 to 5.
5.
2. The method according to claim 1, wherein the conductivity of the hot water is 7 to 25 μS / cm.
3. The method according to claim 1 or 2, wherein the step of forming the anodized film is carried out in a weak acid bath of oxalic acid.
4. A method according to any one of claims 1 to 3, wherein the degree of porosity of the anodized coating determined by an immersion test in an aqueous phosphoric acid-chromic acid solution is 30 to 80 mg / dm 2 The way of doing so.
5. A liquid pump comprising: a housing; a rotatable impeller disposed within the housing; and a flow path forming member facing the impeller and made of pure aluminum or an aluminum alloy, wherein the impeller and the flow path forming member form at least partially a flow path for a liquid, and the rotation of the impeller causes the liquid to be pumped through the flow path, wherein the flow path forming member has an anodized coating on its surface, and the pores of the anodized coating are blocked with a hydrate from the bottom to the opening, and the hydrate is denser at the bottom than at the opening.