Closed impeller and welding manufacturing method thereof

Abstract

The invention provides a closed impeller and a welding manufacturing method thereof. The welding manufacturing method of the closed impeller comprises the steps that a wheel disc and a wheel cover are manufactured, and welding process grooves in one-to-one correspondence with blades of the wheel disc are formed in the wheel cover; according to the method, the wheel cover and the wheel disc are assembled and welded together, finish machining is conducted on the whole formed after the wheel cover and the wheel disc are welded, the welding deformation is greatly reduced while the connecting strength and reliability of the closed impeller are guaranteed, the leakage risk is eliminated, and the service life of the closed impeller is prolonged. And the manufacturing requirements of high precision, high efficiency, low vibration and high reliability of the closed impeller are met.

Description

Technical Field

[0001] This application relates to the technical field of impellers, and further relates to a closed impeller and a welding manufacturing method thereof. Background Art

[0002] A centrifugal pump is a pump that relies on the centrifugal force generated by the rotation of an impeller to transport fluids. Before starting the centrifugal pump, the pump casing and the suction pipe are filled with fluid, and then the motor is started, causing the pump shaft to drive the impeller and the fluid to rotate at a high speed. The fluid undergoes centrifugal motion and is thrown towards the outer edge of the impeller, flowing into the pressure water pipeline of the centrifugal pump through the flow channel of the volute pump casing, and finally the fluid is output from the pressure water pipeline. As the fluid inside the impeller is continuously discharged, a low-pressure area gradually forms at the center of the impeller, even reaching a vacuum. At this time, the fluid at the inlet of the centrifugal pump flows continuously into the impeller through the suction pipe under the action of atmospheric pressure and is then thrown out by the impeller. It can be seen that the impeller is the key of the centrifugal pump.

[0003] The closed impeller is a commonly used impeller structure for centrifugal pumps, with technical advantages such as small overflow loss and high compression efficiency. Currently, as the requirements for vibration and noise indicators and energy consumption indicators of centrifugal pumps become increasingly strict, the design of the impeller has become more and more refined, resulting in complex and narrow internal flow channels of the closed impeller. The processing and welding method of the impeller generally adopts one-piece processing, but this method has high requirements for processing tools and is difficult to apply to impellers with complex and narrow internal flow channels. For this reason, combined welding manufacturing has been proposed. By using machining methods, the internal flow channel of the closed impeller is transformed into a semi-open impeller flow channel. However, there are many problems with the current combined welding method, such as low connection strength and inability to ensure the connection strength and reliability of the closed impeller.

[0004] Therefore, the present invention is committed to providing a closed impeller and a welding manufacturing method thereof to solve the above technical problems. Summary of the Invention

[0005] Aiming at the above technical problems, the purpose of this application is to provide a closed impeller and a welding manufacturing method thereof, which while ensuring the connection strength and reliability of the closed impeller, also significantly reduce the welding deformation amount and eliminate the leakage risk, meeting the manufacturing requirements of high precision, high efficiency, low vibration, and high reliability of the closed impeller.

[0006] To achieve the above purpose, this application provides a welding manufacturing method for a closed impeller, including:

[0007] S1: Prepare a wheel disc and a wheel cover;

[0008] S2: Open welding process grooves on the wheel cover corresponding to the blades of the wheel disc one by one;

[0009] S3: Perform welding at the welding process groove, the inlet of the blade, and the outlet of the blade, so that the machined wheel cover and the wheel disc are assembled and welded together;

[0010] S4: Finish machining the whole after welding the wheel cover and the wheel disc.

[0011] In some embodiments, the welding process groove includes a groove body and a welding notch communicating with the groove body. The welding notch is arranged on one side of the groove body away from the wheel disc, and the welding process groove penetrates through the wheel cover.

[0012] In some embodiments, a machining allowance is machined along the outer extension of the side of the wheel cover away from the wheel disc, and the width of the welding process groove is not greater than the thickness of the blade.

[0013] In some embodiments, the performing welding at the welding process groove, the inlet of the blade, and the outlet of the blade, so that the machined wheel cover and the wheel disc are assembled and welded together specifically includes the steps of:

[0014] S31: Use a tooling fixture to make the wheel disc and the wheel cover closely and correspondingly fit;

[0015] S32: Perform laser circumferential welding on the wheel cover and the blade along the groove body;

[0016] S33: Perform laser fillet welding at the inlet and outlet of each blade;

[0017] S34: Use argon arc welding to layer by layer build up and fill the welding process groove to complete the welding of the wheel cover and the wheel disc.

[0018] In some embodiments, the included angle between the groove body and the meridian of the wheel cover is 85°≤α≤95°, and the depth of the groove body is 2.5mm≤d≤3mm.

[0019] In some embodiments, when using argon arc welding to layer by layer build up and fill the welding process groove, a cooling device injects coolant from the inlet of the blade to the outlet of the blade.

[0020] In some embodiments, the finish machining of the whole after welding the wheel cover and the wheel disc specifically includes the following steps:

[0021] S41: Perform heat treatment on the impeller to eliminate the stress generated after welding;

[0022] S42: Finish machining and remove the machining allowance of the thickness of the wheel cover along the outer contour of the side of the wheel cover away from the wheel disc.

[0023] A closed impeller is manufactured by using the manufacturing method for welding a closed impeller described in any one of the above.

[0024] In some embodiments, the closed impeller includes:

[0025] A hub, on one side of which there are a plurality of blades provided.

[0026] A shroud, on which there are welding process grooves provided corresponding to the blades one by one. The welding process grooves penetrate through the shroud, and the width of the welding process grooves is not greater than the thickness of the blades. An annular weld is provided in the welding process grooves to connect and fix with the blades. Fillet welds are formed at the welding joints at the inlet and outlet of the blades on the shroud.

[0027] In some embodiments, a ring port is provided on the side of the shroud away from the hub, and the ring port communicates with the inlet of the blade to form the water inlet of the impeller. A hub is provided at the center of the hub.

[0028] Compared with the prior art, the closed impeller and its welding manufacturing method provided by the present application have the following beneficial effects:

[0029] 1. For the closed impeller and its welding manufacturing method provided by the present invention, through the setting of the welding process grooves, welding is carried out at the welding process grooves, the inlet of the blades, and the outlet of the blades to realize the connection and fixation of the shroud and the hub, which can effectively improve the welding strength of the shroud and the hub and reduce the deformation amount of the impeller.

[0030] 2. For the closed impeller and its welding manufacturing method provided by the present invention, laser circumferential welding is carried out on the edge of the groove body of the shroud and the hub in the groove body, and laser fillet welding is carried out at the inlet and outlet of the blades, which can realize the welding of the shroud and the hub, making the welding process grooves physically isolated from the internal flow passage of the impeller. Moreover, under the fixing action of the laser welds, then the welding process grooves are filled layer by layer with argon arc welding, which can effectively control the deformation amount generated during the argon arc welding process. In this way, by using a welding method combining laser welding and argon arc welding, the defects of limited welding range, insufficient welding penetration depth, and low connection strength of single laser welding are made up, and at the same time, it is prevented that there are small gaps in the un-welded area inside the impeller, thus causing leakage.

[0031] 3. For a closed impeller and its welding manufacturing method provided by the present invention, when welding is carried out by argon arc welding in the welding process groove, a cooling device is used to inject coolant into the interior of the impeller through the inlet of the blade, and the coolant flows out through the outlet of the blade, which can quickly export the heat generated by argon arc welding, significantly reduce the welding heat affected area, thereby greatly improving the welding efficiency. Moreover, with the combined action of the fixation of the laser weld, the layer-by-layer surfacing of argon arc welding and the control of the welding sequence, and the cooperation of coolant cooling, the welding deformation amount of argon arc welding is greatly reduced, thus ensuring the manufacturing accuracy of the finished closed impeller. Description of the Drawings

[0032] The above characteristics, technical features, advantages and their implementation manners of the present application will be further described below in a clear and understandable manner in combination with the drawings in the preferred embodiments.

[0033] Figure 1 is a flowchart of a welding manufacturing method of a closed impeller provided by the present invention;

[0034] Figure 2 is a structural schematic diagram of a closed impeller provided by the present invention;

[0035] Figure 3 is a structural schematic diagram of a hub cover of a closed impeller provided by the present invention;

[0036] Figure 4 is a structural schematic diagram of a hub plate of a closed impeller provided by the present invention;

[0037] Figure 5 is a sectional view of a hub cover of a closed impeller provided by the present invention;

[0038] Figure 6 is provided by the present invention Figure 5 Partial enlarged schematic diagram of A;

[0039] Figure 7 is a bottom view of a closed impeller provided by the present invention.

[0040] Explanation of the reference numerals in the drawings:

[0041] Hub plate 1, blade 11, hub 12, hub cover 2, welding process groove 21, welding section 211, groove body 212, ring opening 22. Detailed Embodiments

[0042] To more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will describe the specific embodiments of the present application with reference to the accompanying drawings. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings, and other embodiments can also be obtained.

[0043] To make the drawings concise, only the parts related to the application are schematically shown in each drawing, and they do not represent their actual structures as products. In addition, to make the drawings concise and easy to understand, in some drawings, components with the same structure or function are only schematically shown for one of them, or only one of them is marked. In this document, "one" not only means "only this one", but also means "more than one" situation.

[0044] It should also be further understood that the term "and / or" used in the description of the present application and the appended claims refers to any combination and all possible combinations of one or more of the related listed items, and includes these combinations.

[0045] In this document, it should be noted that unless otherwise clearly specified and limited, the terms "install", "connect", and "couple" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to specific situations.

[0046] In the description of the present application, it should be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. is based on the orientation or positional relationship shown in the accompanying drawings. It is only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation to the present application.

[0047] In addition, in the description of the present application, the terms "first", "second", etc. are only used for distinguishing descriptions, and cannot be understood as indicating or implying relative importance.

[0048] In this embodiment, a method for welding and manufacturing a closed impeller is described. While ensuring the connection strength and reliability of the closed impeller, it greatly reduces the welding deformation and eliminates the risk of leakage, meeting the manufacturing requirements of high precision, high efficiency, low vibration, and high reliability for the closed impeller.

[0049] In one embodiment, referring to the attached drawings of the specification Figures 1 to 7 , a method for welding and manufacturing a closed impeller provided by the present invention includes:

[0050] S1: Prepare the hub 1 and the shroud 2;

[0051] First, prepare the hub 1 and the shroud 2 required for the closed impeller respectively. The hub 1 has a plurality of blades 11, and the size and shape of the shroud 2 match those of the hub 1 to ensure the accuracy of subsequent assembly and welding. The hub 1 and the shroud 2 can be made of suitable metal materials, such as stainless steel, etc., to meet the strength and corrosion resistance requirements of the impeller during actual operation.

[0052] S2: Open welding process grooves 21 on the shroud 2;

[0053] On the prepared shroud 2, open welding process grooves 21 corresponding one-to-one to the blades 11 on the hub 1, that is, a plurality of welding process grooves 21 are opened on the shroud 2, and each welding process groove 21 is arranged corresponding to one blade 11.

[0054] S3: Weld at the welding process grooves, the inlets and outlets of the blades;

[0055] It can be understood that before welding, carefully check the dimensions, shapes and relative positions of the welding process grooves with the blades to ensure they meet the design requirements. At the same time, clean the oil stains, rust and other impurities in the welding area to ensure the welding quality.

[0056] S4: Finish machine the whole after welding the shroud and the hub.

[0057] It should be noted that by opening the welding process grooves 21 on the shroud 2, the welding of the shroud 2 and the blades 11 of the hub 1 can be realized within the welding process grooves 21, thus realizing the in-channel welding. Then, the parts at the inlets of the blades 11 and the parts at the outlets of the blades 11 are welded to the hub 1, thereby completing the welding and fixing of the shroud 2 and the hub 1. After the welding of the shroud 2 and the hub 1 is completed, finish machine the whole after welding the shroud 2 and the hub 1 to obtain the finished product of the closed impeller.

[0058] In this embodiment, the welding process grooves 21 are further described in this embodiment. Referring to the attached drawings of the specification Figure 5 and Figure 6, the welding process groove 21 includes a groove body 212 and a welding groove 211 connected and communicating with the groove body 212. The welding groove 211 is arranged on the side of the groove body 212 away from the wheel disc 1, and the welding process groove 21 penetrates through the wheel cover 2, so that when welding is carried out through the welding process groove 21, the edge of the welding process groove 21 can be directly welded and fixed to the blade 11. Further, a machining allowance is formed by following the shape on the side of the wheel cover 2 away from the wheel disc 1.

[0059] When milling the welding process groove 21 corresponding to the blade 11 on the wheel cover 2, the bottom width value of the welding process groove 21 is determined according to the thickness value of the welded blade 11. Among them, the width of the welding process groove 21 (bottom width value) is not greater than the thickness value of the blade 11, so that when welding is carried out through the welding process groove 21, the edge of the welding process groove 21 can be better connected to the blade 11 to ensure the welding effect.

[0060] In one embodiment, this embodiment further describes step S3: welding at the welding process groove, the inlet of the blade, and the outlet of the blade, so that the processed wheel cover and the wheel disc are assembled and welded together:

[0061] S31: Use a tooling fixture to make the wheel disc and the wheel cover closely fit: Place the prepared wheel disc and wheel cover on a special tooling fixture. Through the action of the tooling fixture, the wheel disc and the wheel cover are closely and correspondingly fitted together to ensure the accuracy and stability of the welding position and avoid misalignment or loosening during the welding process.

[0062] It can be understood that when welding the wheel cover 2 and the wheel disc 1, a tooling fixture is used to clamp and fit the wheel cover 2 and the wheel disc 1. The wheel cover 2 and the wheel disc 1 are correspondingly arranged, and each welding process groove 21 corresponds to a blade 11 to ensure the welding effect between the two.

[0063] S32: Perform laser circumferential welding on the wheel cover and the blade along the groove body.

[0064] Adopt a laser welding device to perform laser circumferential welding on the blade 11 on the wheel cover 2 and the wheel disc 1 along the groove body 212 part of the welding process groove 21. Laser circumferential welding has the advantages of fast welding speed, small heat affected zone, and high weld quality, which can ensure the connection strength and sealing performance between the wheel cover 2 and the blade 11, and reduce welding deformation at the same time.

[0065] S33: Perform laser fillet welding at the inlet and outlet of each blade.

[0066] After completing the laser circumferential welding of the welding process groove, laser fillet welding is performed at the inlet and outlet of each blade 11 using a laser welding device. The laser fillet welding further strengthens the connection between the blade 11 and the hub 2, improving the reliability of the welded structure.

[0067] S34: Use argon arc welding to layer by layer build up and fill the welding process groove to complete the welding of the hub and the disk.

[0068] Based on laser welding, using an argon arc welding device, layer by layer build up and fill the welding process groove 21 until the hub 2 and the disk 1 are completely welded together. Argon arc welding has the advantages of stable welding quality and easy control. By means of layer by layer build up, it can ensure that the weld in the welding process groove is full and dense, further improving the strength and stiffness of the welded structure. When performing argon arc welding, use a cooling device to inject coolant from the inlet of the blade 11 to the outlet of the blade 11, so that the coolant fills the internal flow passage of the impeller and keeps flowing, which can quickly take away the heat generated by the argon arc welding, significantly reduce the welding heat affected area, avoid deformation of the impeller due to high temperature during welding, and at the same time greatly improve the welding efficiency. Preferably, after building up one layer of the welding process groove 21, it is necessary to wait for the built-up layer to cool completely before implementing the next layer of build up. On the other hand, it is also necessary to control the welding sequence. When building up each layer of multiple welding process grooves 21, a symmetric welding sequence should be adopted to further reduce the small deformation caused by weld stress.

[0069] It can be understood that in this embodiment, the combined welding process of laser welding and argon arc welding is used. On the one hand, it effectively solves the problems such as limited welding range, insufficient welding penetration depth, and low connection strength when using laser welding alone, and at the same time prevents the occurrence of leakage caused by small gaps in the un-welded parts inside the impeller. On the other hand, under the fixing action of the weld formed by laser welding, it can effectively control the deformation amount generated during the argon arc welding process.

[0070] Preferably, the included angle α between the meridian of the groove body and the hub satisfies 85° ≤ α ≤ 95°, and the depth d of the groove body 212 satisfies 2.5 mm ≤ d ≤ 3 mm. In addition, the side of the hub away from the disk is subjected to conformal extension processing with appropriate machining allowance left.

[0071] It can be understood that when performing backing welding on the welding process groove and the blade by argon arc welding, the welding nozzle cannot extend into the welding groove due to the width of the welding nozzle of the welding torch. Therefore, preferably, the angles between the two side walls and the bottom of the welding process groove are both 85°≤α≤95°, so that the welding nozzle of the welding torch can smoothly extend into the welding process groove 21. Preferably, the angles between the two side walls and the bottom are both 90°. Further, on the wheel disc, the side of the groove body 212 away from the blade 11 is milled to form a welding section 211 on the side of the welding process groove 21 away from the blade 11. After only filling the welding process groove 21, in the state where the welding section 211 is not filled, the base metal allowance formed by the welding section 211 and the welding filling line filled into the welding process groove 21 can increase the strength of the impeller.

[0072] In this embodiment, a further description is made on the overall finishing of the welded wheel cover and wheel disc in this embodiment:

[0073] S41: Heat-treat the impeller to eliminate the stress generated after welding. Heat-treat the entire welded impeller. Through processes such as heating, heat preservation, and cooling, eliminate the internal stress generated during welding, stabilize the organizational structure of the impeller, and improve the dimensional stability and service life of the impeller. The specific process parameters of the heat treatment can be set according to the characteristics of the material used for the impeller to ensure the best heat treatment effect.

[0074] S42: Finish machining to remove the machining allowance of the thickness of the wheel cover along the outer contour of the side of the wheel cover away from the wheel disc. After the heat treatment is completed, perform finish machining on the impeller. Specifically, perform finish machining along the outer contour of the side of the wheel cover away from the wheel disc to remove the previously left machining allowance, so that the thickness of the wheel cover 2 reaches the design requirements, ensuring the dimensional accuracy and surface quality of the impeller's outer shape, and thus guaranteeing the performance and reliability of the closed impeller in actual operation.

[0075] Through the above steps, this embodiment has successfully realized a method for manufacturing a welded closed impeller. This method can effectively control welding deformation, improve welding quality and the manufacturing accuracy of the impeller through reasonable welding processes and subsequent finish machining, meeting the high-performance requirements of the closed impeller in actual applications.

[0076] In this embodiment, a closed impeller provided in this embodiment is manufactured by using the method for manufacturing a welded closed impeller described in any one of the above embodiments.

[0077] Specifically, a closed impeller has a structure including a hub plate 1 and a shroud 2. On one side of the hub plate 1, there are a number of blades 11, which are evenly distributed at a certain angle and spacing to meet the hydrodynamic performance requirements of the impeller during operation. The hub plate 1, as the basic component of the impeller, is used to support and connect the blades 11. The shroud 2 is provided with welding process grooves 21 corresponding one-to-one with the blades 11. These welding process grooves 21 penetrate through the shroud 2, and the width of the welding process grooves 21 is not greater than the thickness of the blades 11. The design of the welding process grooves 21 enables a firm connection between the shroud 2 and the blades 11 through welding. A circumferential weld is provided in the welding process grooves 21, which is connected and fixed to the blades 11 to ensure the sealing performance and strength between the shroud 2 and the blades 11. In addition, fillet welds are formed at the welding joints at the inlet and outlet of the blades 11 on the shroud 2, further strengthening the connection between the shroud 2 and the blades 11, improving the reliability of the welding structure, and preventing leakage when the cooling medium flows in the internal flow passage of the impeller.

[0078] Furthermore, the closed impeller in this embodiment further includes a hub 12. The hub 12 is provided at the center of the hub plate 1, and an annular opening 22 is provided on the side of the shroud 2 away from the hub plate 1. The annular opening 22 is communicated with the inlet of the blades 11 to form the water inlet of the impeller, so that the coolant of the cooling device is injected into the impeller through the annular opening 22 and then discharged out through the water outlet.

[0079] Through the above structural design, this embodiment provides a closed impeller with good welding structure and cooling performance, which can meet the high-performance requirements of the impeller in actual operation. The design of the welding process grooves, circumferential welds and fillet welds between the shroud and the blades ensures the structural strength and sealing performance of the impeller; the design of the hub, water inlet, shaft hole and keyway enables the impeller to be effectively connected with external transmission devices and cooling systems, realizing the normal operation and cooling of the impeller.

[0080] It should be noted that the above embodiments can be freely combined according to needs. The above is only the preferred embodiment of the present application. It should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present application, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present application.

Claims

1. A closed impeller welding manufacturing method, characterized in that Including: S1: Prepare the wheel disc and the wheel cover; S2: Open welding process grooves on the wheel cover that correspond one-to-one with the blades of the wheel disc; S3: Weld at the welding process grooves, the inlets of the blades, and the outlets of the blades, so that the wheel cover and the wheel disc are assembled and welded together; S4: Finish machining the whole after welding the wheel cover and the wheel disc.

2. A method for manufacturing a closed impeller by welding according to claim 1, characterized in that, The welding process groove includes a groove body and a welding section connected to the groove body. The welding section is arranged on the side of the groove body away from the wheel disc, and the welding process groove penetrates through the wheel cover.

3. A method for manufacturing a closed impeller by welding according to claim 2, characterized in that, There is a follow-shaped extension machining allowance on the side of the wheel cover away from the wheel disc, and the width of the welding process groove is not greater than the thickness of the blade.

4. A closed impeller welding manufacturing method according to claim 3, characterized in that, The welding at the welding process grooves, the inlets of the blades, and the outlets of the blades, so that the machined wheel cover and the wheel disc are assembled and welded together, specifically includes the steps: S31: Use a tooling fixture to make the wheel disc and the wheel cover closely correspond and fit; S32: Perform laser circumferential welding on the wheel cover and the blade along the groove body; S33: Perform laser fillet welding at the inlets and outlets of each blade; S34: Use argon arc welding to layer by layer build up and fill the welding process groove to complete the welding of the wheel cover and the wheel disc.

5. A method for manufacturing a closed impeller by welding according to claim 2, characterized in that The included angle between the groove body and the meridian of the wheel cover is 85° ≤ α ≤ 95°, and the depth of the groove body is 2.5 mm ≤ d ≤ 3 mm.

6. A method for manufacturing a closed impeller by welding according to claim 4, characterized in that, When using argon arc welding to layer by layer build up and fill the welding process groove, the cooling device injects coolant from the water inlet of the impeller to the water outlet of the impeller.

7. A method for manufacturing a closed impeller by welding according to claim 6, characterized in that, The finish machining of the whole after welding the wheel cover and the wheel disc specifically includes the following steps: S41: Perform heat treatment on the impeller to eliminate the stress generated after welding; S42: Finish machining and remove the machining allowance of the thickness of the wheel cover along the outer contour of the side of the wheel cover away from the wheel disc.

8. A closed impeller, characterized in that, Manufactured by using the closed impeller welding manufacturing method according to any one of claims 1-7.

9. The closed impeller according to claim 8, characterized in that, The closed impeller includes: A wheel disc, on one side of the wheel disc, there are several blades arranged; A wheel cover, on the wheel cover, there are welding process grooves arranged corresponding one-to-one with the blades. The welding process grooves penetrate through the wheel cover, and the width of the welding process grooves is not greater than the thickness of the blades. There is a circumferential weld arranged in the welding process grooves to connect and fix with the blades, and fillet welds are formed at the welding positions of the inlets and outlets of the blades on the wheel cover.

10. A closed impeller according to claim 9, characterized in that, On the side of the wheel cover away from the wheel disc, there is an annular opening, and the annular opening is connected to the inlet of the blade to form the water inlet of the impeller. At the center of the wheel disc, there is a hub.

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