Method for vacuum brazing impeller containing main disc with blades and cover disc

Abstract

FIELD: soldering of metal products.SUBSTANCE: invention relates namely to vacuum soldering of parts of impellers of blade machines containing a main disk with blades and a cover disk. The method involves placing a 0.08–0.15 mm thick ribbon solder on the end surfaces of the main disk blades. The width of the ribbon solder exceeds twice the thickness of the blade by 8–12 mm. The solder is placed in separate sections without mutual overlap, while the gap between adjacent sections is no more than 1 mm. The solder pieces are fixed by spot welding along the blade axis in 10–15 mm increments. A piece of solder intended for soldering a vertical section of a blade is fixed to an adjacent horizontal section of the same blade, and its free part is placed along the transition radius and vertical sections without additional fixation by spot welding. After this, the cover disk is installed, the solder sections on the vertical sections of the blades are evenly aligned, and a gap of no more than 0.04 mm is ensured between the ends of the blades and the mating surface of the cover disk.EFFECT: improving the quality of the soldered joint between the end surfaces of the main disk blades and the mating surface of the impeller cover disk, as well as in increasing the uniformity of the solder distribution in the soldering zone, reducing the likelihood of the formation of local solder build-ups and increasing the stability of the geometry of the inter-blade channels of the impeller after soldering.1 cl, 2 tbl

Description

[0001] The invention relates to the field of brazing metal products, specifically to methods for vacuum brazing of impeller components for turbomachines, pumps, compressors, and other bladed machines, comprising a main disk with blades and a cover disk. More specifically, the claimed invention relates to a technology for preparing, assembling, and vacuum brazing an impeller, in which a brazing ribbon is applied to the end surfaces of the main disk blades, secured by spot welding, followed by installation of the cover disk and brazing in a vacuum furnace.

[0002] The claimed method is designed to produce a brazed joint between the end surfaces of the main disk blades and the mating surface of the impeller cover disk. The method can be used in the manufacture of impellers requiring a strong, uniform, and reproducible connection between the blades and the cover disk while maintaining the geometry of the interblade channels. Such a connection is especially important for impellers operating under centrifugal loads, vibrations, and changes in temperature and pressure of the working medium. The claimed technical solution is aimed at improving the quality of the brazed joint by controlled placement of ribbon solder on the blade ends, eliminating overlapping solder sections, limiting the gaps between adjacent sections, fixing the solder by spot welding, and ensuring a specified gap between the blade ends and the mating surface of the cover disk.

[0003] Technical solutions are known for the production of impellers for centrifugal machines, in which the main disk, cover disk and blades are connected to each other by soldering, welding or other methods of permanent connection.

[0004] Russian Federation Patent RU2459980C1 discloses a method for manufacturing centrifugal compressor impellers by joining the main and cover disks using brazing followed by heat treatment. In this method, the blades are installed in an assembly fixture, the mating surfaces of the blades are machined to accommodate the main and cover disks, the mating surfaces are pre-treated with brazing material, the cover disk is applied, and the brazing is performed simultaneously in a vacuum. To reduce warpage of the disks, annular grooves are made in the area of ​​the manufacturing allowance.

[0005] This solution is close to the claimed invention in terms of manufacturing a centrifugal compressor impeller, joining the main and cover disks by hard soldering, and performing the brazing in a vacuum. However, this solution does not disclose the placement of 0.08–0.15 mm thick ribbon solder in separate sections on the end surfaces of the blades, does not disclose limiting the gap between adjacent solder sections to no more than 1 mm, and does not disclose fixing the solder sections by spot welding along the blade axis in 10–15 mm increments. This solution also does not disclose the specifics of fixing the solder section for brazing a vertical blade section to an adjacent horizontal section of the same blade or brazing the impeller with the cover disk facing down.

[0006] Patent document CN101406977A discloses a method for vacuum brazing a pump impeller. The known method involves cutting brazing plates to a shape corresponding to the impeller blade cross-sections, cleaning the impeller and brazing plates, checking the smoothness of the blade surfaces to be brazed, placing the brazing plates on the blade surfaces to be brazed, installing the pump cover, securing the cover using positioning pins, assembling with clamping devices, and then heating in a vacuum furnace. The document's specific features indicate that the brazing plates may have a thickness of less than 0.12 mm and be 0.5–1 mm larger than the blade cross-section.

[0007] This solution is similar to the claimed invention in that it relates to vacuum brazing of the impeller by placing solder on the blade surfaces before installing the cover element. However, this solution requires the use of solder plates corresponding to the blade cross-section, as well as flux and positioning holes. It does not disclose the placement of ribbon solder in separate sections without overlapping, with a gap between adjacent sections of no more than 1 mm. It does not disclose fixing the solder by spot welding at 10-15 mm increments along the blade axis. It also does not disclose the special placement of solder on the transition radius and vertical sections of the blade without additional fixation by spot welding.

[0008] Patent US9815134B2 discloses a method for brazing an impeller, in which a thermal cycle is performed on an impeller assembly with solder located in the joint zone between at least two impeller components. This prior art solution places particular emphasis on the heating, holding, and cooling regime, as well as the use of a heating element that heats the assembly from the inner circumference to reduce temperature unevenness and solder defects.

[0009] This solution is similar to the claimed invention in that it relates to brazing of an impeller and is aimed at reducing defects in the brazed joint. However, it primarily covers the thermal cycle and heat distribution during brazing, rather than the technology for pre-applying ribbon brazing to the blade end surfaces. It does not cover features related to the geometry and placement of individual ribbon brazing sections, their fixation by spot welding at a specified pitch, the elimination of overlap, the limitation of the gap between sections, the alignment of the brazing on the vertical sections of the blades, and brazing with the impeller facing down.

[0010] European patent EP2047938B1 discloses a method for welding an impeller comprising multiple blades, a disk, and an outer element including a cover element. In the known solution, grooves are formed on the surface of the disk or outer element, after which the bottom of each groove is irradiated with a laser beam and joined to the end of the corresponding blade by penetration welding. This design reduces stress concentration and simplifies subsequent processing of the welded joint.

[0011] This solution relates to the same general area of ​​manufacturing impellers with blades and a cover plate, but is based on welding rather than vacuum brazing with pre-placement of a ribbon of solder. It lacks any indication of solder placement on the blade end surfaces, solder fixation by spot welding, control of the spacing between solder strips, or ensuring a specified clearance between the blade ends and the mating surface of the cover plate before brazing.

[0012] The closest technical approach to the claimed invention is a method for manufacturing an impeller according to patent document CN102625881B, in which the impeller comprises a disk, a cover, and a plurality of blades between them, and the connection is achieved by soldering, with solder placed between the blade edge and the mating surface of the cover or disk. This solution discloses the use of solder divided into several sheet parts in the longitudinal direction, which facilitates the placement of solder along the curved joining surface, and also discloses the fixation of the sheet parts of the solder to the blade, including by spot welding.

[0013] Common features of the prototype and the claimed invention are the production of an impeller containing a disk, a covering element and blades, the placement of solder in the area of ​​connection of the blades with the covering element, the production of solder in the form of separate parts located along the surface to be connected, fixing the solder on the blade and subsequent soldering to connect the disk and the covering element through the blades.

[0014] A disadvantage of the prototype is that it does not disclose the technologically specified set of operations that ensure stable placement of ribbon solder on the end surfaces of the blades prior to vacuum brazing of the impeller. Specifically, the prototype does not disclose the ribbon solder thickness of 0.08–0.15 mm, the solder width, which exceeds twice the blade thickness by 8–12 mm, the placement of solder sections without mutual overlap with a gap between adjacent sections of no more than 1 mm, fixation by spot welding along the blade axis at 10–15 mm increments, or the specific fixation of a section of solder for brazing a vertical blade section to an adjacent horizontal section of the same blade.

[0015] Furthermore, the prototype does not disclose the placement of the free portion of the said solder section along the transition radius and vertical sections without additional fixation by spot welding, the subsequent uniform alignment of the solder sections on the vertical sections of the blades after installing the cover disk, ensuring a gap of no more than 0.04 mm between the ends of the blades and the mating surface of the cover disk, as well as performing vacuum soldering with the impeller positioned with the cover disk down.

[0016] As a result, the prototype does not provide a fully controlled position of the solder on sections of blades of different spatial orientations and does not solve the problem of increasing the reproducibility of the formation of a soldered joint between the ends of the blades of the main disk and the mating surface of the cover disk due to the declared set of operations.

[0017] The technical objective of the claimed invention is to develop a method for vacuum brazing of an impeller containing a main disk with blades and a cover disk, ensuring controlled placement and retention of ribbon solder on the end surfaces of the blades, including on horizontal, transition radius and vertical sections of the blades, with the subsequent installation of the cover disk and the performance of vacuum brazing.

[0018] An additional objective is to reduce the likelihood of solder displacement, overlaps, gaps between solder sections, localized dry joints, and areas of excess solder accumulation in the area where the blades connect to the cover disc.

[0019] The technical result achieved by implementing the claimed invention is an increase in the quality and reproducibility of the soldered joint between the end surfaces of the main disk blades and the mating surface of the impeller cover disk.

[0020] An additional technical result is an increase in the uniformity of the solder distribution in the soldering zone, a reduction in the likelihood of the formation of dry spots and local solder build-ups, as well as an increase in the stability of the geometry of the inter-blade channels of the impeller after soldering.

[0021] The specified technical result is achieved due to a combination of features of an independent claim, including the specified dimensions of the ribbon solder, its placement in separate sections without overlapping, limiting the gap between adjacent sections, fixing by spot welding, special placement of a section of solder in the transition area from the horizontal to the vertical section of the blade, alignment of the solder after installation of the cover disk, ensuring a gap of no more than 0.04 mm and performing vacuum soldering with the impeller positioned with the cover disk facing down.

[0022] In the claimed method, the use of a tape solder with a thickness of 0.08–0.15 mm makes it possible to form a layer of solder sufficient to fill the gap between the end surfaces of the blades and the mating surface of the cover disk, without the formation of excess accumulations of molten solder in the inter-blade channels.

[0023] Making the solder ribbon 8–12 mm wider than the blade thickness ensures that solder is present on both sides of the blade end. This allows the solder to flow across the blade-cover disc contact area during heating and melting, forming a bond across the entire width of the joint, improving the uniformity of the solder joint.

[0024] Placing solder in separate sections without overlapping each other prevents localized increases in solder thickness. This reduces the likelihood of laps and uneven gap filling in the soldering area.

[0025] Limiting the gap between adjacent solder sections to no more than 1 mm ensures continuous solder flow along the blade end surface. When melted, adjacent solder sections can merge into a single solder joint, reducing the likelihood of dry joints.

[0026] Spot welding solder sections along the blade axis at 10–15 mm intervals maintains the solder in position during impeller assembly and cover plate installation. This precise fixation allows for subsequent solder spreading during heating.

[0027] Clamping a solder rod for brazing a vertical blade section to an adjacent horizontal section of the same blade ensures that the rod is held in place without the need for additional welds at the transition radius and vertical sections. This reduces the risk of damage or deformation of the solder rod in a complex geometry, and the free solder rod can be evenly distributed across the transition radius and vertical sections.

[0028] Placing the free portion of the solder strip along the transition radius and vertical sections without additional spot welding allows for subsequent alignment after installing the cover disc. This compensates for possible localized solder displacement during assembly and ensures a more uniform solder position in the future joint area.

[0029] Installing the cover disk after placing and securing the solder ensures the formation of an assembly in which the solder is positioned between the end surfaces of the blades and the mating surface of the cover disk. Subsequent uniform alignment of the solder sections on the vertical sections of the blades ensures the desired solder position in areas most susceptible to displacement under their own weight and contact forces during assembly.

[0030] Maintaining a gap of no more than 0.04 mm between the blade ends and the mating surface of the cover disk allows for capillary filling of the joint zone with molten solder. This gap reduces the likelihood of unfilled areas and ensures uniform formation of the soldered joint.

[0031] Vacuum brazing with the impeller facing down helps maintain the brazing position in the blade-to-cover-disc contact area and reduces the likelihood of it shifting from the brazing zone during heating and melting. This improves the stability of the brazed joint formation along the blade ends.

[0032] Thus, the claimed combination of features ensures controlled preparation of the soldering zone, stable position of the solder during assembly and heating, uniform filling of the gap between the blades and the cover disk, which leads to an increase in the quality and reproducibility of the soldered joint of the impeller.

[0033] The essence of the claimed invention is that in the method of vacuum brazing of an impeller containing a main disk with blades and a cover disk, before installing the cover disk, a ribbon solder with specified geometric parameters is placed on the end surfaces of the blades, it is fixed by spot welding in specified zones, a controlled position of the solder is provided on the horizontal, transition radius and vertical sections of the blades, after which the cover disk is installed, the solder is aligned on the vertical sections, a specified gap is provided in the connection zone and vacuum brazing is carried out in the position of the impeller with the cover disk down.

[0034] Ribbon solder with a thickness of 0.08–0.15 mm is used as solder. This thickness ensures sufficient solder to form a brazed joint between the blade ends and the mating surface of the cover disc, without causing excessive filling of the interblade channels with molten solder.

[0035] The width of the solder ribbon is selected so that it is 8-12 mm greater than twice the blade thickness. This ratio ensures that the solder extends beyond the sides of the blade end surface. When heated during vacuum brazing, the solder melts and distributes in the blade-to-cover disc mating area, ensuring the formation of a soldered joint across the width of the contact.

[0036] Ribbon solder is applied to the blade end surfaces in separate sections. The sections are placed without overlapping each other. This lack of overlap eliminates localized solder buildup and reduces the likelihood of burrs that could disrupt the impeller's interblade channel geometry.

[0037] The gap between adjacent solder sections is no more than 1 mm. This limitation ensures that adjacent solder sections are closely spaced, resulting in a continuous or nearly continuous gap filling zone along the blade end face when the solder melts.

[0038] After the solder pieces are placed on the blade end surfaces, they are spot welded along the blade axis at 10-15 mm intervals. Spot welding holds the solder pieces in position during subsequent impeller assembly and installation of the cover disc. This spacing ensures sufficient solder retention without excessive weld spots, which could hinder uniform solder distribution during heating.

[0039] A solder rod intended for soldering a vertical blade section is secured to an adjacent horizontal section of the same blade. The free portion of this rod is positioned along the transition radius and vertical sections without additional spot welding. This arrangement prevents the solder rod from shifting by securing it to the horizontal section and simultaneously allows for alignment of the free portion of the solder rod along the transition radius and vertical sections after installation of the cover disc.

[0040] After the solder has been placed and secured, a cover disk is installed. The cover disk is positioned relative to the main disk so that the end surfaces of the blades face the mating surface of the cover disk, and the solder is located in the area of ​​the future soldered joint.

[0041] After installing the cover disk, evenly align the solder sections on the vertical sections of the blades. This operation is necessary to prevent localized solder displacement and ensure uniform solder distribution in the contact area between the vertical sections of the blades and the cover disk.

[0042] A gap of no more than 0.04 mm is maintained between the blade ends and the mating surface of the cover disk. This gap allows for capillary filling of the joint zone with molten solder during vacuum brazing and promotes the formation of a strong soldered joint.

[0043] Vacuum brazing is performed with the impeller facing downward. In this position, the impeller is oriented so that the cover disk is located below the main blade disk. This orientation helps maintain solder in the contact area between the blade end surfaces and the cover disk during heating, melting, and solder spreading.

[0044] The combination of these features ensures controlled placement of the ribbon solder, its retention in a given position during assembly, uniform filling of the soldered gap and the formation of a high-quality soldered joint between the blades of the main disk and the cover disk of the impeller.

[0045] To confirm the feasibility of the claimed method, impeller samples were manufactured, each containing a main disc with blades and a cover disc. In each sample, ribbon solder was applied to the blade end surfaces in separate sections without overlapping each other, with a gap of no more than 1 mm between adjacent sections. The solder sections were spot-welded along the blade axis. The cover disc was then installed, the solder sections were uniformly aligned on the vertical sections of the blades, the gap between the blade ends and the mating surface of the cover disc was maintained at no more than 0.04 mm, and vacuum brazing was performed with the impeller facing downward.

[0046] The samples differed in the thickness of the solder ribbon, the excess of the solder width over twice the blade thickness, the spacing between adjacent solder sections, the spot weld pitch, and the gap between the blade ends and the mating surface of the cover disc. These parameters were selected within the stated ranges.

[0047] Table 1 - Sample manufacturing parameters

[0048] Parameter Unit of measurement Sample 1 Sample 2 Sample 3 Solder tape thickness mm 0,08 0,10 0,15 Exceeding the width of the solder over twice the thickness of the blade mm 8 10 12 The gap between adjacent pieces of solder mm 0,8 0,5 1,0 Step of fixing solder by spot welding mm 10 12 15 The gap between the ends of the blades and the mating surface of the cover disk mm 0,03 0,02 0,04 The presence of mutual overlap of solder sections - absent absent absent Laying a piece of solder for soldering a vertical section - fixation on an adjacent horizontal section fixation on an adjacent horizontal section fixation on an adjacent horizontal section Placing the free part of the solder - along the transitional radius and vertical sections along the transitional radius and vertical sections along the transitional radius and vertical sections Position of the impeller during soldering - cover disk down cover disk down cover disk down

[0049] Sample 1 utilizes lower solder thickness, solder width offset, and spot welding pitch. This design ensures a reduced amount of solder injected and frequent placement of solder strips on the blade end surfaces.

[0050] Sample 2 uses average process parameter values. This design is preferred because it ensures a balanced amount of solder, stable solder retention during assembly, and uniform filling of the joint area.

[0051] Sample 3 utilizes the upper values ​​for solder thickness, solder width excess, spacing between adjacent segments, and spot weld pitch. This design confirms the feasibility of the method at the upper limits of the stated ranges while maintaining the absence of overlap, the specified gap, and the impeller position with the cover disc facing down.

[0052] Table 2 - Solder joint control parameters

[0053] Controlled indicator Sample 1 Sample 2 Sample 3 The gap between the ends of the blades and the mating surface of the cover disk before soldering, mm 0,03 0,02 0,04 Average thickness of the soldered layer after soldering, mm 0,055 0,065 0,075 Variation of soldered layer thickness along the length of the controlled section, mm ±0,015 ±0,010 ±0,018 Maximum length of a single unfilled section in the soldered layer zone, mm no more than 0.20 not identified no more than 0.25 Maximum pore size in the soldered layer, mm no more than 0.06 no more than 0.04 no more than 0.06 Solder leakage into the interblade channel does not violate the flow cross-section not identified does not violate the flow cross-section Deviation of the width of the interblade channel after soldering from the specified value, mm no more than 0.08 no more than 0.05 no more than 0.09

[0054] The gap between the blade tips and the mating surface of the cover disc was checked before brazing during impeller assembly. This measurement confirms that all test samples provided adequate conditions for capillary filling of the joint zone with molten solder.

[0055] The brazed layer thickness after brazing, the variation in brazed layer thickness, the presence of unfilled areas, and pores were assessed using macrosections of control specimens manufactured and brazed simultaneously with the experimental impeller assemblies. These parameters confirm the quality of the brazed joint formation, the uniformity of the brazed solder distribution within the brazing zone, and the reduced likelihood of dry joints.

[0056] Solder leakage into the interblade channel and interblade channel width deviation after brazing were assessed by visual and dimensional inspection of the impeller. The absence of burrs that disrupt the flow area and limited interblade channel width deviation confirm the stability of the impeller geometry after brazing.

[0057] As follows from Table 2, in all experimental samples, the claimed method ensures the formation of a soldered layer in the mating zone of the end surfaces of the blades with the cover disk, a limited spread in the thickness of the soldered layer, the absence of pronounced non-soldering spots and the absence of solder beads that disrupt the flow section of the inter-blade channels.

[0058] The most preferable indicators were obtained in sample 2, which used the average values ​​of the declared process parameters: tape solder thickness of 0.10 mm, excess of solder width over double blade thickness of 10 mm, gap between adjacent solder sections of 0.5 mm, spot welding fixation step of 12 mm and gap between the ends of the blades and the mating surface of the cover disk of 0.02 mm.

[0059] Samples 1 and 3 confirm the feasibility of the claimed method at the lower and upper limits of the stated ranges, respectively. In both cases, the formation of a soldered joint is ensured without visible dry spots, without localized solder buildup that disrupts the geometry of the interblade channels, and with the preservation of the channel cross-section after vacuum brazing.

[0060] Thus, the given indicators confirm the achievement of the declared technical result, which consists in improving the quality and reproducibility of the brazed joint between the end surfaces of the main disk blades and the mating surface of the impeller cover disk, as well as in increasing the uniformity of the solder distribution, reducing the likelihood of the formation of dry joints and local solder build-ups, and increasing the stability of the geometry of the inter-blade channels after brazing.

Claims

A method for vacuum brazing of an impeller containing a main disk with blades and a cover disk, characterized in that a ribbon solder with a thickness of 0.08–0.15 mm, the width of which exceeds twice the thickness of the blade by 8–12 mm, is placed on the end surfaces of the blades in separate sections without mutual overlap with a gap between adjacent sections of no more than 1 mm and fixed by spot welding along the axis of the blade with a step of 10–15 mm, wherein a section of solder for brazing a vertical section of the blade is fixed on an adjacent horizontal section of the same blade, and its free part is placed along the transition radius and vertical sections without additional fixation by spot welding, after which the cover disk is installed, uniform alignment of the solder sections on the vertical sections of the blades is performed, a gap of no more than 0.04 mm is provided between the ends of the blades and the mating surface of the cover disk, and vacuum brazing is carried out in position of the impeller with the cover disk facing down.