Preparation method of aluminum alloy surface brazing coating and end plate machining method

Abstract

The invention discloses a preparation method of an aluminum alloy surface brazing coating and an end plate machining method. The method comprises the steps that S1, NOCOLOK brazing flux and absolute ethyl alcohol are blended according to the weight ratio of 1: 4, and a binding material is prepared; s2, a binding material is sprayed on the surface of the brazing filler metal foil, and then drying is conducted; s3, the surface of the aluminum alloy with the fence arranged on the edge is covered with the brazing filler metal foil sprayed with the binding material; and S4, the aluminum alloy covered with the brazing filler metal foil is heated, so that the brazing filler metal foil is evenly spread on the surface of the aluminum alloy within the enclosure range after being molten. The pressure bearing capacity and the use range of the tubular radiator can be greatly improved.

Description

Technical Field

[0001] The invention belongs to the technical field of processing aluminum alloy workpieces, and specifically relates to a method for preparing a brazing coating on the surface of an aluminum alloy and a method for processing an end plate. Background Art

[0002] In the processing of aluminum alloy shell and tube radiators, in order to obtain a radiator with good pressure-bearing capacity of more than 10MPa (gauge pressure), it is necessary to optimize the design structure of the shell and tube radiator end plate to improve the overall pressure-bearing capacity of the radiator. Therefore, a bimetallic sheet with a special-shaped structure (the special-shaped structure refers to bimetallic sheets of unequal thickness) and a thickness of not less than 10mm (one layer of the bimetallic sheet is an aluminum alloy substrate, and one layer is an aluminum alloy brazing filler metal layer) is required. Since the bimetallic sheet with a large thickness of the special-shaped structure cannot be manufactured, the development of the shell and tube radiator with this high pressure-bearing structure is limited, causing stagnation of this series of technologies. Therefore, it is urgent to solve the problem that bimetallic sheets with a special-shaped structure and a large thickness of aluminum alloy cannot be manufactured.

[0003] According to the traditional processing method, only bimetallic sheets of equal thickness available on the market can be purchased, which has great restrictions on the product structure, and the thickness of the brazing material layer of the bimetallic sheets available on the market cannot meet the requirements of filling the brazing seam of the product. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing a brazing coating on an aluminum alloy surface and a method for processing an end plate. The present invention facilitates the processing and use of the end plate parts of a shell-and-tube radiator and can greatly improve the pressure bearing capacity and application breadth of the shell-and-tube radiator.

[0005] The technical solution of the present invention is: a method for preparing a brazing coating on the surface of an aluminum alloy, comprising the following steps: S1. NOCOLOK brazing flux and anhydrous ethanol are mixed in a weight ratio of 1:4 to prepare a bonding material;

[0006] S2. Spray the binder on the surface of the solder foil and then dry it;

[0007] S3. The solder foil after spraying the binder is covered on the aluminum alloy surface with a fence at the edge;

[0008] S4. Heat the aluminum alloy covered with the brazing foil, so that the brazing foil melts and spreads evenly on the surface of the aluminum alloy within the enclosure.

[0009] In the aforementioned method for preparing the brazing coating on the surface of the aluminum alloy, in step S1, after the binder is prepared, it must be used within 4 hours.

[0010] In the aforementioned method for preparing the brazing coating on the surface of the aluminum alloy, in step S2, before spraying the binder, the surface of the brazing foil is cleaned.

[0011] In the aforementioned method for preparing the brazing coating on the surface of aluminum alloy, in step S2, the drying temperature is 60°C to 80°C.

[0012] In the above-mentioned method for preparing the brazing coating on the surface of the aluminum alloy, in step S3, before spraying, the surface of the aluminum alloy is cleaned according to the following method:

[0013] S31. Chemical degreasing: immerse the aluminum alloy in an alkaline degreasing solution at a temperature of 70°C to 90°C for 5 to 15 minutes;

[0014] S32. Warm water washing: The degreased aluminum alloy is placed in running warm water at 30°C to 50°C for 5 to 10 minutes;

[0015] S33. Rinse with running cold water: Rinse in running cold water at 10℃~25℃ for 5~10min;

[0016] S34. Alkali corrosion: Place the washed aluminum alloy in an alkali solution for corrosion at a temperature of 40℃~50℃ for no more than 2 minutes;

[0017] S35. Flowing warm water washing: wash the alkali-corroded aluminum alloy in flowing warm water at 30°C to 50°C for 3 to 5 minutes;

[0018] S36. Flowing cold water washing: The aluminum alloy after warm water washing is washed in flowing cold water at 10°C to 25°C for 3 to 5 minutes;

[0019] S37. Nitric acid polishing: After rinsing with warm water, polish the aluminum alloy in nitric acid at 40℃~60℃ for 3~5min;

[0020] S38. Flowing cold water washing: wash the aluminum alloy after nitric acid glazing in flowing cold water at 10°C to 25°C for 3 to 5 minutes;

[0021] S39. Drying: Dry the aluminum alloy with hot air at 60℃~70℃.

[0022] In the aforementioned method for preparing the brazing coating on the surface of the aluminum alloy, in step S4, the heating process is as follows:

[0023] S41. The aluminum alloy after assembling the solder foil is dried at 170 ℃ ~ 190 ℃ for 20 min;

[0024] S42. After drying, brazing is performed in a nitrogen atmosphere with an oxygen partial pressure of not more than 100 ppm and a dew point of not more than -30 ° C. The brazing temperature is 595 to 610 ° C and the time is 300 s.

[0025] S43. After brazing, cool to 150℃ and take out of the oven to complete the brazing coating.

[0026] The processing method of the heat exchanger end plate is as follows: processing the aluminum alloy into the end plate shape according to the requirements; preparing the brazing coating on the surface of the end plate by using the above-mentioned preparation method; processing the part hole on the surface of the end plate with the brazing coating.

[0027] In the aforementioned method for processing the end plate of the heat exchanger, when processing the outer shape of the end plate, one end surface of the end plate is in the form of an arc.

[0028] The advantages of the present invention are: the method for manufacturing the special-shaped structure variable thickness aluminum alloy bimetallic material is not limited by the shape and thickness of the sheet material, and can manufacture bimetallic plates of various structures and thicknesses according to design requirements to meet the high strength requirements of the end plate of the aluminum alloy shell and tube radiator.

[0029] In order to verify the beneficial effects of the present invention, the inventors conducted the following experiments:

[0030] 1. Determination of binder ratio

[0031] The flux in the binder mainly plays the role of breaking the oxide film, wetting the molten solder, increasing the fluidity of the solder, and ensuring the uniform spreading of the solder during the brazing process, so as to achieve the purpose of an ideal brazing surface. Too little flux will result in the solder not spreading when it melts, and too much flux will result in more compounds on the formed brazing surface, which will fall off during use and form excess matter.

[0032] In order to determine the exact ratio of the binder, NOCOLOK flux and anhydrous ethanol were mixed in a weight ratio of 1:3, 1:4, and 1:5 respectively. The test results are as follows:

[0033] The test was conducted at a ratio of 1:3. Due to the small amount of brazing material, the wetting effect could not be fully achieved, resulting in poor fluidity of the molten brazing material and poor brazing surface formation. Figure 2 shown.

[0034] The test was carried out at a ratio of 1:4. The amount of brazing flux was appropriate, the brazing surface was well formed, and there was no excess potassium fluoride compound. Figure 3 shown.

[0035] The test was conducted at a ratio of 1:5. Due to the large amount of brazing flux, a thicker potassium fluoride composite was formed on the brazing surface. Figure 4 shown.

[0036] Therefore, NOCOLOK flux and anhydrous ethanol were selected and mixed in a weight ratio of 1:4.

[0037] 2. Determination of brazing parameters

[0038] This method uses a nitrogen protection furnace to heat the solder foil to melt and spread to form a uniform thickness solder layer. The key brazing parameters are temperature and time. If the temperature and time are not enough, the solder foil will not melt or spread. If the temperature and time are too high or too long, the solder grains will be coarse and dissolution will occur. It will also cause the composition of the prepared coating to change and cannot play an ideal role in subsequent use.

[0039] In order to determine the appropriate brazing temperature and time, multiple sets of data were used to prepare the test pieces, as shown in Table 1. Through the quality inspection of the test pieces, it was confirmed that the quality of test piece 5 met the requirements, that is, the brazing temperature was 595-610℃ and the time was 300s.

[0040] Table 1 Brazing temperature and time test results

[0041] Test piece number Brazing temperature / ℃ Brazing time / s Specimen quality Specimen 1 580～595 240 Most of the solder does not melt Specimen 2 580～595 300 Most of the solder does not melt Specimen 3 580～595 360 The solder part does not melt Specimen 4 595～610 240 The solder part does not melt Specimen 5 595～610 300 The solder melts and spreads evenly Specimen 6 595～610 360 Larger solder melting flow area

[0042] 3. Confirmation of the consistency of solder layer thickness

[0043] The brazing material coating prepared according to the above-mentioned binder configuration and determined brazing parameters is cut into multiple sections to measure the coating thickness, see Figure 5 As shown, the coating thickness range is (0.3-0.4) mm, which meets the requirements of coating thickness consistency.

[0044] To sum up, the present invention fundamentally solves the problem that the production of bimetallic plate materials is limited by the shape and thickness of the plate materials. It can well produce bimetallic plates of various shapes and thicknesses as required, which is convenient for the processing and use of the end plate parts of the shell and tube radiator, and can greatly improve the pressure bearing capacity and application range of the shell and tube radiator. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 It is a schematic diagram of the production of surface coating of a special-shaped structure variable thickness aluminum alloy part, namely, a heat exchanger end plate;

[0046] Figure 2 It is the brazing surface obtained by the ratio of 1:3;

[0047] Figure 3 It is the brazing surface obtained by the ratio of 1:3;

[0048] Figure 4 It is the brazing surface obtained by the ratio of 1:3;

[0049] Figure 5 It is a schematic diagram showing that the solder coating of the present invention has uniform thickness. DETAILED DESCRIPTION

[0050] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0051] The features and illustrative embodiments of various aspects of the present invention will be described in detail below. In the detailed description below, many specific details are proposed to provide a comprehensive understanding of the present invention. However, it is obvious to those skilled in the art that the present invention can be implemented without the need for some of these specific details. The following description of the embodiments is only to provide a better understanding of the present invention by illustrating examples of the present invention. The present invention is by no means limited to any specific settings and methods proposed below, but covers any improvements, replacements and modifications of structures, methods, devices without departing from the spirit of the present invention. In the accompanying drawings and the following description, known structures and technologies are not shown to avoid unnecessary ambiguity in the present invention.

[0052] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other, and the embodiments can refer to and quote each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0053] Example 1. A method for preparing a brazing coating on an aluminum alloy surface and a method for processing an end plate, see Figure 1-5 The processing method of the heat exchanger end plate comprises the following steps:

[0054] (A) End plate shape processing: Process the end plate shape into a special-shaped structure with variable thickness according to the drawing requirements;

[0055] (B) Cleaning: Clean the parts according to the aluminum alloy cleaning method;

[0056] (C) Brazing foil processing: Process the shape of the brazing foil according to the part structure, and prepare the quantity of brazing foil according to the thickness of the bimetallic plate brazing layer;

[0057] (D) Flux coating: The flux is mixed according to certain requirements and coated on the surface of the processed parts and both sides of the solder foil;

[0058] (E) Assembling solder foil: Lay the solder foil coated with solder flux on the required surface of the part.

[0059] (F) Brazing: Place the parts in a nitrogen-protected brazing furnace for brazing.

[0060] (G) Machining: According to the use requirements, it is necessary to process part holes on the manufactured parts. The part holes need to be processed in coordination with the outer diameter of the heat pipe, and the gap must not be larger than the gap required for brazing.

[0061] In the step (A), the parts may be of a special-shaped structure with a variable thickness, but the mounting holes required for processing the tube-in-tube radiator are not processed.

[0062] The step (B) comprises the following steps:

[0063] (b1) Chemical degreasing: immerse the parts in an alkaline degreasing solution at a temperature of 70℃ to 90℃ for 5 to 15 minutes;

[0064] (b2) Warm water cleaning: Place the degreased parts in running warm water at 30℃ to 50℃ for 5 to 10 minutes;

[0065] (b3) Rinse with running cold water: rinse in running cold water at 10℃ to 25℃ for 5 to 10 minutes;

[0066] (b4) Alkali corrosion: Place the washed parts in an alkali solution for corrosion at a temperature of 40°C to 50°C for no more than 2 minutes;

[0067] (b5) Flowing warm water washing: wash the alkali-corroded parts in flowing warm water at 30℃~50℃ for 3~5min;

[0068] (b6) Flowing cold water rinse: wash the parts after warm water rinse in flowing cold water at 10℃~25℃ for 3~5min;

[0069] (b7) Nitric acid polishing: After rinsing with warm water, polish the parts in nitric acid at 40℃~60℃ for 3~5min;

[0070] (b8) Flowing cold water washing: wash the parts after nitric acid glazing in flowing cold water at 10℃~25℃ for 3~5min;

[0071] (b9) Drying: Blow the parts dry with hot air at 60℃~70℃.

[0072] In the step (C), the shape of the solder foil is processed according to the part structure, and laser cutting equipment or a dedicated mold can be used. Since the thickness of the solder foil is generally 0.15 mm, the amount of solder foil used can be prepared according to the thickness requirement of the bimetallic plate solder layer.

[0073] The step (D) comprises the following steps:

[0074] (d1) Preparation of flux: NOCOLOK flux and anhydrous ethanol are prepared in a weight ratio of 1:4 and stirred evenly. The flux needs to be used within 4 hours after preparation, otherwise it needs to be prepared again.

[0075] (d2) Use flux spraying equipment to spray the prepared flux on both sides of the solder foil. Ensure that the spraying is even. Do not touch the solder foil with bare hands. Wear clean white gauze gloves.

[0076] (d3) Dry the solder foil in a drying furnace at a temperature of 60°C to 80°C until it is dried.

[0077] The flux is proportioned according to certain requirements and coated on the surface of processed parts and both sides of the solder foil.

[0078] In the step (E), the solder foil coated with solder flux is laid on the required surface of the part to make it fit.

[0079] The step (F) comprises the following steps:

[0080] (f1) Place the parts after solder foil assembly in a drying oven for drying at a temperature of 170°C~

[0081] 190℃, time: 20min.

[0082] (f2) Put it into a nitrogen-protected brazing furnace and braze it under the conditions that the oxygen partial pressure in the brazing furnace is not more than 100 ppm and the dew point is not more than -30°C. The brazing temperature is 595-610°C and the time is 300S.

[0083] (f3) After the temperature of the welded part in the furnace drops to 150°C, it is taken out of the furnace, and the production of the bimetallic plate is completed.

[0084] In the step (G), according to the part drawing, a special drilling jig is used to process the aperture on the manufactured part. The aperture needs to be processed in coordination with the outer diameter of the heat dissipation pipe, and the gap must not be larger than the gap required for brazing.

[0085] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the field can easily think of various equivalent modifications or substitutions within the technical scope disclosed by the present invention, and these modifications or substitutions should all be covered within the protection scope of the present invention.

Claims

1. A method for preparing a brazing coating on an aluminum alloy surface, characterized in that: The method comprises the following steps: S1. NOCOLOK flux and anhydrous ethanol are mixed in a weight ratio of 1:4 to prepare a binder; S2. Spray the binder on the surface of the solder foil and then dry it; S3. The solder foil after spraying the binder is covered on the aluminum alloy surface with a fence at the edge; S4. Heat the aluminum alloy covered with the brazing foil, so that the brazing foil melts and spreads evenly on the surface of the aluminum alloy within the enclosure.

2. The method for preparing a brazing coating on an aluminum alloy surface according to claim 1, characterized in that: In step S1, after the binder is prepared, it must be used within 4 hours.

3. The method for preparing a brazing coating on an aluminum alloy surface according to claim 1, characterized in that: In step S2, before spraying the binder, the surface of the solder foil is cleaned.

4. The method for preparing a brazing coating on an aluminum alloy surface according to claim 1, characterized in that: In step S2, the drying temperature is 60°C to 80°C.

5. The method for preparing a brazing coating on an aluminum alloy surface according to claim 1, characterized in that: In step S3, before spraying, the surface of the aluminum alloy is cleaned according to the following method: S31. Chemical degreasing: immerse the aluminum alloy in an alkaline degreasing solution at a temperature of 70°C to 90°C for 5 to 15 minutes; S32. Warm water washing: The degreased aluminum alloy is placed in running warm water at 30°C to 50°C for 5 to 10 minutes; S33. Rinse with running cold water: Rinse in running cold water at 10℃~25℃ for 5~10min; S34. Alkali corrosion: Place the washed aluminum alloy in an alkali solution for corrosion at a temperature of 40℃~50℃ for no more than 2 minutes; S35. Flowing warm water washing: wash the alkali-corroded aluminum alloy in flowing warm water at 30°C to 50°C for 3 to 5 minutes; S36. Flowing cold water washing: The aluminum alloy after warm water washing is washed in flowing cold water at 10°C to 25°C for 3 to 5 minutes; S37. Nitric acid polishing: After rinsing with warm water, polish the aluminum alloy in nitric acid at 40℃~60℃ for 3~5min; S38. Flowing cold water washing: wash the aluminum alloy after nitric acid glazing in flowing cold water at 10°C to 25°C for 3 to 5 minutes; S39. Drying: Dry the aluminum alloy with hot air at 60℃~70℃.

6. The method for preparing a brazing coating on an aluminum alloy surface according to claim 1, characterized in that: In step S4, the heating process is as follows: S41. The aluminum alloy after assembling the solder foil is dried at 170 ℃ ~ 190 ℃ for 20 min; S42. After drying, brazing is performed in a nitrogen atmosphere with an oxygen partial pressure of not more than 100 ppm and a dew point of not more than -30 ° C. The brazing temperature is 595 to 610 ° C and the time is 300 s. S43. After brazing, cool to 150℃ and take out of the oven to complete the brazing coating.

7. A method for processing a heat exchanger end plate, characterized in that: Processing the aluminum alloy into the shape of the end plate as required; preparing a brazing coating on the surface of the end plate using the preparation method described in any one of claims 1 to 6; and processing part holes on the surface of the end plate with the brazing coating.

8. The method for processing the heat exchanger end plate according to claim 7, characterized in that: When the end plate is processed in shape, one end surface of the end plate is curved.

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