RU2533892C1 - Method to manufacture composite heat exchanger - Google Patents

Abstract

FIELD: heating.

SUBSTANCE: on steel plates they form ledges of conical shape, pierce holes in tops of ledges with their subsequent flanging, plates are assembled into a package so that ledges of one plate enter holes of the other one to form a tubular cavity, the package of plates is submerged into a bath, containing copper carbonate-based powder dissolved in a solution, with its continuous mixing, the package of plates treated in the solution is withdrawn from the bath, and prior to sintering the packet is placed into a tight jacket, where inert gas is supplied under pressure, at the same time the packet is dried in the same tight jacket by removal of pressure and passage of nitrogen flow via its inner volume, and the nitrogen flow is heated to temperature of 60-80°C, then the packet of plates is placed into a furnace with recovery atmosphere at temperature of 1100-1150°C. As ledges are generated on steel plates, a domain crystalline steel structure is activated by an electromagnetic pulse for levelling of domains in areas of plates coupling.

EFFECT: increased strength of a heat exchanger due to high-quality even sintering of plates along the entire area of their coupling.

Description

The invention relates to a technology for the production of plate heat exchangers that can be used as automobile radiators, cooling towers of reduced volume, heat recovery complexes of metallurgical industries, gas turbine engines, any high-potential heat sources, radiators in a residential heating system, heat exchangers for refrigeration machines, compact railway locomotives and etc.

A known method of manufacturing a plate-tube heat exchanger by forming protrusions in the form of a truncated cone in the form of a truncated cone in the form of a truncated cone by multi-stamping and punching holes at the tops of the protrusions with subsequent flanging, assembling the plates into a bag and soldering in a continuous furnace at a temperature of 1100 ° C, a brass layer is a solder for brazing plates in a bag (RU 2038563, 1995, F28F 3/04).

The disadvantage of this method is that with this technology it is difficult to ensure the same thickness of the clad layer due to the possible formation of folds and tears of the coating film and, as a consequence, the fragility of the heat exchanger.

There is a known method of manufacturing a plate heat exchanger, according to which the plates are stamped, at least one protrusion in the form of a hollow truncated cone is made in each of them, the surfaces of the plates are cleaned, the plate package is formed by sequentially installing the protrusion of one plate in the hole of an adjacent plate with a predetermined gap between adjacent surfaces of the plates and with the formation of a channel for the passage of coolant. Next, a solder paste solution based on copper bicarbonate and nickel salts is prepared by diluting the solder paste with water and binders, one of which is ethylene glycol, and immerse the plate pack in the prepared solder paste solution, and then dry the applied solder paste solution. Then, the plate package is placed in a high-temperature continuous conveyor furnace, in which a protective medium with free hydrogen is created and two temperature zones are formed along the plate package, in the first of which the plate package is annealed, and in the second, the plate package is brazed and coated with alloy based on copper, while setting the speed of the package of plates sufficient to anneal the package of plates in the first zone and soldering and coating the package of plates with an alloy based on copper in the second zone (RU 2419755, IPC F28F 3/00, 05.27.2011).

The disadvantage of this method is the complexity of the process and the insufficiently high strength of the heat exchanger.

Closest to the proposed method is a method of manufacturing a plate-tube heat exchanger, in which conical protrusions are formed on metal plates, holes are punched at the tops of the protrusions, followed by their flanging, then the plates are assembled in such a way that the protrusions of one plate enter the holes of another, forming tube cavities, after assembly, the package of plates is immersed in a bath containing copper-carbonate-based powder diluted in solution with the addition of nickel acetic acid, while it is continuously mixing, and grinding the solid powder components of the solution is carried out using a jet mill, while a mixture of water and ethylene glycol is used as the solution, the package of plates processed in the solution, after removing it from the bath, is placed in a sealed casing, into which an inert gas is supplied under pressure, drying the package plates is made in the same casing by relieving pressure and passing through the internal volume of the casing a stream of nitrogen heated to a temperature of 60-80 ° C, then the package of plates is placed in a furnace with recovery atmosphere at a temperature of 1100-1150 ° C (RU 2380211 C1, IPC V23P 15/26, B21D 53/04, 01/27/2010).

The known method provides the production of heat exchangers capable of operating at a temperature of 700 ° C and above and withstand a pressure of 100 kg / cm ² or more.

However, this method does not take into account the fact that steel has a domain crystal structure, and the most uneven deposition of solder flux occurs at the domain boundary, as a result of which heat exchangers made in a known manner have insufficient strength and quality.

The objective of the invention is to increase the strength and durability of manufactured heat exchangers by creating on the surface of their mating parts a protective multilayer composite coating formed directly in the manufacturing process of the product.

The specified technical problem is solved by the fact that in the method of manufacturing a composite heat exchanger, conical protrusions are formed on metal plates, holes are punched at the tops of the protrusions with their subsequent flanging, then the plates are assembled in such a way that the protrusions of one plate enter the holes of another, forming tube cavities, after assembly, the package of plates is immersed in a bath containing powder diluted in solution based on copper carbonate, with continuous stirring, the package of plates processed in solution, last removing it from the bath, it is placed in a sealed casing, into which an inert gas is supplied under pressure, the plate package is dried in the same casing by depressurizing and passing through the internal volume of the casing a stream of nitrogen heated to a temperature of 60-80 ° C, then a plate package placed in a furnace with a reducing atmosphere at a temperature of 1100-1150 ° C.

Distinctive features of the claimed method is that when the protrusions are formed synchronously with an electromagnetic pulse, the domain crystal structure of the steel is activated, aligning the domains in the interface zones of the plates.

The grinding of the solid powder components of the solution can be carried out using a jet mill.

In a solution, for high-quality surface preparation and conditioning before soldering, use a mixture of water and surface-active substances (surfactants).

This solution to the method allows you to create on the surface of the mating parts protective multilayer composite coating formed directly in the manufacturing process of the heat exchanger.

The technical result of the claimed method consists in increasing the strength of the heat exchanger by increasing the strength of the connection of the plates in the package, high-quality volumetric uniform sintering of the material with an absolutely uniform composition over the entire area of the mating plates.

A method of manufacturing a composite heat exchanger is as follows.

Conical protrusions are formed on metal plates, holes are punched in the tops of the protrusions with their subsequent flanging. On the edge of the cone of the plate, sealing cylindrical bands are formed, which create toroidal cavities at the place of mating of the plates. The thickness of the cavity is 50-100 microns. This cavity during subsequent heating creates a vacuum that “draws” the reduced copper into the cavity with a certain pressure. The thickness of the composite layer at the junction of the plates reaches 40-50 microns.

At the same time, an electromagnetic pulse in the form of a damped sinusoid (remagnetizing pulse) activates the domain crystal structure of steel, aligning the domains in the interface zones of the plates, thereby reducing the surface effect of the domains.

Then each plate is subjected to a degreasing process, which takes place in three stages: the actual degreasing - removal of sulfur and dust from stamping; surface treatment with a surface-active substance (surfactant) for uniform conditioning, which ensures good wettability of molten copper during soldering; Coated with wax film for short-term protection against corrosion and lubrication during assembly.

The heat exchanger package is assembled in an anti-dust room with on-board suction and filters, with a strictly defined “tightness” (force), in which the cylindrical belts undergo plastic deformation of at least 90% in height, but not leading to the formation of “barrel-like” cones. When assembling the plates in the package, a gap of 50-100 microns is maintained.

After assembly, the package of plates is immersed in a bath containing copper carbonate-based powder diluted in the solution with continuous stirring, and, depending on the composition of the flux used, according to preliminary chemical analysis, the missing components nickel, phosphorus, and others are introduced into the solution. The solid powder components are further crushed using a jet mill to a particle size of not more than 20 microns before being introduced into the solution.

When preparing a solution in a bath, a mixture of water and a surfactant is used as a solvent in a ratio that creates and automatically maintains a certain density of the solution. After removal from the bath, the package of plates processed in the solution is placed in a sealed casing before sintering in a soldering furnace, into which an inert gas with a predominance of nitrogen is supplied under a pressure of 1.05-1.1 atm, the package of plates is dried in the same casing by depressurizing heating the inert gas stream to a temperature of 60-80 ° C, while the package is placed with cones down, which makes it possible to form a toroidal influx of flux around the place where the plates meet (the entrance of one cone to another), which provides the necessary supply of copper at soldering. Drying is carried out using the utilized heat of the soldering furnace. The time and drying mode is controlled by a humidity sensor to the required moisture content in the coating of the plates. Next, the package of plates is placed in a furnace with a reducing atmosphere at a temperature of 1100-1150 ° C. The reducing atmosphere in the furnace is created using catalysts and a system for automatically maintaining the composition of the atmosphere no worse than +/- 1%. These retort-type catalysts are built into process furnaces with the ability to adjust the composition of the protective-reduction atmosphere. The atmosphere is created from natural gas of low pressure. The parameters of the content of hydrogen, nitrogen and other gases depend on the thickness of the plates and the composition of the flux.

Product strength is determined by the number of thin-film layers formed in the surface layer of steel. In this case, the effect of thin-film structures works: each layer has a different composition of copper and steel, and therefore the layers do not "mix", but form clearly over the entire surface in the surface layer. With a thickness of each thin-film layer of approximately 0.8 μM, a composite layer with a total thickness of 40–50 μM, which is approximately 50–65 thin-film layers, is formed at the interface between the plates.

The optimal conditions for the formation of a large number of thin-film layers are determined by the temperature-time technological modes:

- preheating mode;

- soldering mode;

- cooling mode.

Each of the modes affects the final composition of the composite layer and, as a consequence, the overall strength of the product.

Claims (1)

A method of manufacturing a composite heat exchanger, including forming conical-shaped protrusions on steel plates, punching holes at the tops of the protrusions, and then flanging them, assembling the plates into a packet so that the protrusions of one plate enter the holes of another plate to form a tube cavity, immersing the plates in a bath containing diluted in a solution powder based on copper carbonate, with continuous stirring, removing the package of plates processed in the solution from the bath, and before sintering the package of plates they are replaced in a sealed enclosure into which an inert gas is supplied under pressure, while the package of plates is dried in the same sealed enclosure, and in a sealed enclosure, the pressure is reduced and a stream of nitrogen heated to a temperature of 60-80 ° C is passed through its internal volume, and then a plate pack is placed in a furnace with a reducing atmosphere at a temperature of 1100-1150 ° C, characterized in that when the protrusions are formed on the steel plates with an electromagnetic pulse, the domain crystal structure of the steel is simultaneously activated to break winding domains in the zones of pairing plates.