A furnace welding method for a feedback spring assembly

Abstract

This invention relates to a furnace welding method for a feedback spring assembly, using a box-type electric furnace and tooling. The steps are as follows: (1) Set the furnace temperature to 1000℃ and hold it for a period of time until the temperature stabilizes; (2) Wipe the inner and outer surfaces of the graphite tooling clean with a damp white cotton cloth and dry it; (3) Magnetically grind the spring wire, spring sheet, and sleeve and dry them; (4) Adjust the solder paste to a constant concentration as flux; (5) Assemble the feedback spring assembly, place the silver solder sheet, put it on the graphite crucible tooling, and add an appropriate amount of flux to the feedback spring assembly; (6) Put the feedback spring assembly and crucible into the furnace and quickly close the furnace door, holding it at the temperature for 45-46 seconds; (7) After the holding period, remove the crucible and quickly place it in ice water to cool for 30 seconds; (8) After cooling, remove the feedback spring assembly from the tooling or water and transfer it to the next process. This invention solves the problem of difficult control of flame brazing process parameters and unstable welding quality of feedback components.

Description

Technical Field

[0001] This invention relates to the field of hydraulic servo valve manufacturing technology, specifically to a furnace welding method for a feedback spring assembly. Background Technology

[0002] The feedback spring assembly is a key component in jet-tube electro-hydraulic servo valves, consisting of three parts: a spring plate, a spring wire, and a sleeve, all made of C17300 and C17200 beryllium bronze. The design of the feedback spring assembly imposes strict requirements on the spring wire deflection and the hardness of each part of the component, while ensuring uniform solder distribution on the welding contact surface. The technical performance of the feedback spring assembly can change significantly with even slight variations in welding process parameters. For example, the humidity of the welding environment, the temperature at the welding point, and the ratio of flux to water all affect the welding quality, hardness, solder flowability, and uniformity of the feedback assembly. Therefore, strict control of all process parameters during welding is necessary. Currently, the feedback spring assembly is welded using flame brazing, with welding points including the spring plate and spring wire, and the spring plate and sleeve, requiring simultaneous welding of both points in one operation. Flame brazing is characterized by simple equipment and convenient operation, but process parameters are difficult to control, and welding quality is significantly affected by human factors.

[0003] Furnace welding provides a relatively stable welding environment. The temperature inside the high-temperature furnace can be set and maintained at a constant level; furthermore, the uniform temperature distribution within the furnace ensures consistent weld quality. Simultaneously, the entire feedback component furnace welding device and process are carried out in a dedicated heat treatment room, where the temperature and humidity of the welding environment are well controlled. Furnace welding has been widely used in the mass production of various small stainless steel parts. However, feedback spring components have high requirements, and various process parameters require significant time and effort to explore and research. Currently, there is no research data on the furnace welding process for feedback spring components.

[0004] Traditional flame brazing processes for welding feedback spring assemblies only allow for the adjustment of oxygen and acetylene pressures. Factors such as the nozzle-to-workpiece distance, welding angle, flame size, ambient temperature, and humidity are uncontrollable, resulting in numerous variables that significantly impact weld quality stability. Therefore, a furnace brazing method for feedback spring assemblies is needed to address the challenges of controlling flame brazing process parameters and ensuring consistent weld quality. Summary of the Invention

[0005] To address the problems of difficult control of flame brazing process parameters and unstable welding quality, this invention proposes a furnace welding method for feedback spring assemblies.

[0006] To achieve the above objectives, the technical solution of the present invention is: a furnace welding method for a feedback spring assembly, employing a box-type electric furnace, brazing filler metal, solder paste, and tooling, the steps of which are as follows:

[0007] (1) Set the furnace temperature to 1000℃ and keep it at that temperature for a period of time until the temperature stabilizes;

[0008] (2) Wipe the inner and outer surfaces of the graphite tooling clean with a damp white cotton cloth and blow dry;

[0009] (3) Magnetically grind and dry the spring wire, spring sheet, and sleeve;

[0010] (4) Adjust the solder paste to a constant concentration to serve as flux:

[0011] (5) Assemble the feedback spring assembly, place the silver solder sheet, put it on the graphite crucible fixture, and add an appropriate amount of flux to the feedback spring assembly using a burette.

[0012] (6) Place the feedback spring assembly along with the crucible into the furnace and quickly close the furnace door, and keep it warm for 45-46 seconds;

[0013] (7) After the heat preservation is completed, remove the crucible and quickly put it into ice water to cool for 30 seconds;

[0014] (8) After cooling, remove the feedback spring assembly from the tooling or water and transfer it to the next process.

[0015] Furthermore, the flux concentration is solder paste:water, 10:10 to 10:7.5.

[0016] Furthermore, the solder paste is 50 mL of 1802PF solder paste.

[0017] Furthermore, the tooling uses a graphite crucible with a lid. The lid has a groove, which allows the melted solder paste to fall into the sealed container during welding, forming a reducing atmosphere and preventing the feedback spring assembly from oxidizing due to furnace welding. This eliminates the need to purchase furnace brazing or gas-shielded welding equipment separately.

[0018] Furthermore, the volume of the box-type electric furnace is not less than 120 mm (length) x 180 mm (width) x 250 mm (height). 3 Extreme temperature: 1000℃; furnace temperature uniformity: ±8℃.

[0019] The present invention has the following beneficial effects:

[0020] 1. Using graphite sheets to prevent adhesion, placing the feedback spring assembly on the graphite sheet avoids the need to pry the spring sheet off the tooling and reshape it after welding;

[0021] 2. The temperature of furnace welding is guaranteed by the uniformity of furnace temperature. The temperature is controllable and the heating is uniform and stable, which greatly reduces welding deformation and welding stress, and provides a good reference for the bending angle of the subsequent control feedback spring assembly.

[0022] 3. It greatly shortens the welding time and avoids post-weld annealing of parts, which would lead to a significant decrease in the fatigue strength of the parts;

[0023] 4. By setting the furnace temperature and controlling the furnace temperature uniformity during furnace welding, the high consistency of the welding of the feedback spring assembly is ensured;

[0024] 5. Keep the non-welded parts of the feedback spring assembly in a closed space (within the tooling) to reduce their exposure to heat annealing;

[0025] 6. A groove is left on the cover of the tooling so that the solder paste melts and falls into the sealed container during welding, forming a reducing atmosphere and preventing the feedback spring assembly from oxidizing due to furnace welding. Therefore, it is not necessary to purchase furnace brazing or gas shielded welding separately.

[0026] 7. To prevent oxidation of parts, vacuum furnace brazing requires placing the parts in first, then drawing a vacuum, and then heating from room temperature to 1000℃; while gas-shielded welding requires placing the parts in first, then filling with gas, and then heating from room temperature to 1000℃. Both welding methods are complex and require long heating times, making short-time heating welding impossible. The above-mentioned fixture cleverly avoids these drawbacks and can truly achieve short-time heating welding.

[0027] 8. Due to the uniformity and stability of the furnace temperature, multiple feedback spring assemblies can be welded at once, which greatly improves production efficiency and reduces labor costs;

[0028] 9. Compared with vacuum furnace brazing, it does not change the material supply state and preserves the mechanical properties of the material to the greatest extent. Attached Figure Description

[0029] Figure 1 This is a metallographic image of the feedback spring assembly welded together. Detailed Implementation

[0030] Embodiment of the present invention: A furnace welding method for a feedback spring assembly, comprising:

[0031] I. Preparations before the experiment:

[0032] 1. Box-type electric furnace: Dimensions not less than 120*180*250mm 3 (H*B*L), extreme temperature 1000℃, furnace temperature uniformity: ±8℃;

[0033] 2. Solder: 80 DHAg50B silver solder sheets of each size;

[0034] 3. Flux: 50mL of 1802PF solder paste

[0035] 4. Tooling: A set of graphite crucibles including a lid, with dimensions of 30*22*60mm. A circular groove with a diameter of 16mm and a depth of 2mm needs to be machined on the lid, and holes of 1.5mm and 3mm need to be drilled. The form and position tolerances are as per the feedback spring assembly sleeve and spring wire.

[0036] 5. 150 spring wires, 150 spring sheets, and 150 sleeves. All parts must have the same batch number and must be marked with the raw material batch number and the processing batch number for traceability.

[0037] 6. One bucket of ice-water mixture is 3-5 liters;

[0038] 7. A pair of clean white cotton gloves.

[0039] II. Implementation Steps:

[0040] 1. Wear white cotton gloves;

[0041] 2. Set the furnace temperature to 1000℃ and maintain it for a period of time until the temperature stabilizes;

[0042] 3. Wipe the inner and outer surfaces of the graphite tooling clean with a damp white cotton cloth and blow dry;

[0043] 4. Magnetically grind and dry the spring wire, spring sheet, and sleeve;

[0044] 5. Adjust the flux to a constant concentration (solder paste:water, 10:10 to 10:7.5). Use it immediately after use and close the cap when not in use.

[0045] 6. Assemble the feedback spring assembly, place the silver solder sheet, put it on the graphite crucible fixture, and add an appropriate amount of flux to the feedback spring assembly using a burette.

[0046] 7. Place the feedback spring assembly along with the crucible into the furnace and quickly close the furnace door (closing time is limited to 1-4 seconds), and keep it warm for 45-46 seconds;

[0047] 8. After the heat preservation is complete, remove the crucible and quickly place it in ice water to cool for about 30 seconds;

[0048] 9. After cooling is complete, remove the feedback spring assembly from the tooling (or water) and proceed to the next process.

[0049] The feedback spring assembly is one of the core components of a servo valve, and its quality affects the service life of the servo valve. Welding quality is crucial to the quality of the feedback spring assembly. To solve the brazing problem of the feedback spring assembly, after extensive review of domestic and international literature, furnace welding was determined as the process solution for ensuring the stability of the welding process.

[0050] 1. The following is a comparison table of hardness between furnace welding and flame brazing:

[0051]

[0052]

[0053] Table 1 Comparison of Welding Hardness of Feedback Spring Components

[0054] The comparison shows that the overall hardness uniformity of the feedback component after furnace welding is high, meeting the design requirements, while the overall hardness uniformity of flame welding is low and does not meet the design requirements.

[0055] 2. Gold ratio comparison chart as shown Figure 1 As shown, the furnace-welded metallographic structure contains fewer gray precipitates, indicating that it is less affected by welding, resulting in higher strength and hardness.

Claims

1. A furnace welding method for a feedback spring assembly, characterized in that: Using a box-type electric furnace, brazing filler metal, solder paste, and tooling, the steps are as follows: (1) Set the furnace temperature to 1000℃ and keep it at that temperature for a period of time until the temperature stabilizes; (2) Wipe the inner and outer surfaces of the graphite tooling clean with a damp white cotton cloth and blow dry; (3) Magnetically grind and dry the spring wire, spring sheet, and sleeve; (4) Adjust the solder paste to a constant concentration as flux, wherein the flux concentration is solder paste:water, 10:10~10:7.5; (5) Assemble the feedback spring assembly, place the silver solder sheet, and put it on the graphite crucible fixture. Add an appropriate amount of flux to the feedback spring assembly using a burette. The fixture is a set of graphite crucibles with a lid. The lid has a groove so that the solder paste melts and falls into the sealed container during welding, forming a reducing atmosphere and preventing the feedback spring assembly from oxidizing due to furnace welding. Therefore, it is not necessary to use furnace brazing or gas-shielded welding. (6) Place the feedback spring assembly along with the crucible into the furnace and quickly close the furnace door, and keep it warm for 45~46 seconds; (7) After the heat preservation is completed, remove the crucible and quickly put it into ice water to cool for 30 seconds; (8) After cooling is complete, remove the feedback spring assembly from the tooling or water and transfer it to the next process.

2. The furnace welding method for the feedback spring assembly according to claim 1, characterized in that: The solder paste is 50 mL of 1802PF solder paste.

3. The furnace welding method for the feedback spring assembly according to claim 1, characterized in that: The volume of the box-type electric furnace shall not be less than 120 mm (length) x 180 mm (width) x 250 mm (height). 3 Extreme temperature: 1000℃; furnace temperature uniformity: ±8℃.

Images