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Vacuum heat treatment of corrugated spring bayonet connector

Corrugated spring is the key part for locking bayonet electrical connector. 65Mn thin wall corrugated spring is widely used in various bayonet electrical connectors because of its good elasticity and simple forming process. Hydrogen embrittlement always exists in the electroplating of this part, especially for thin-walled elastic parts with thickness less than 0.5mm. Generally, cyanide cadmium plating or cyanide zinc plating is prohibited in the national and industrial standards to prevent brittle fracture. However, in order to improve the protection performance, it is sometimes necessary to do so. Although the hydrogen removal treatment is carried out, the effect is often not ideal.

65Mn thin wall corrugated spring, in the state of quenching and tempering strengthened II steel strip (YB/T5063-93), with thickness of 80.3~0.5mm and tensile strength of 1579~1863MPa. In order to improve the corrosion resistance of its parts, cyaniding cadmium plating or cyaniding zinc plating was used before. Although hydrogen permeation was avoided and hydrogen was removed in the process of pretreatment, electroplating and post-treatment, due to the limitations of the geometric dimensions and mechanical properties of the parts and the objective impact of electrolytic oil removal, strong acid washing, and hydrogen evolution from cyaniding cadmium (zinc) plating, the quality problem of hydrogen embrittlement is still difficult to solve, Finally, the corrugated spring will break prematurely and lose its locking effect. At the same time, the friction coefficient of zinc cadmium coating is too large and the wear resistance is poor, so the protection performance is difficult to meet the requirements.

In addition, in order to reduce hydrogen embrittlement, mechanical galvanizing or chemical oxidation processes are also used. Although these methods can relatively reduce hydrogen evolution, their adhesion, wear resistance, protection and fatigue resistance are still insufficient and cannot meet the requirements of practical application.

In view of the above conditions, the following processes can be adopted: the vacuum heat treatment purification of corrugated spring, ultrasonic cleaning with active agent solution, ultrasonic activation with neutral salt solution, electroless nickel plating and vacuum heat treatment after plating, in order to reduce the hydrogen embrittlement of corrugated spring, enhance self lubrication and wear resistance, and improve its service life and reliability.

Technological process

Aviation gasoline – anhydrous ethanol – 100 ℃ drying – vacuum heat treatment purification – ultrasonic cleaning – hot water washing – tap water washing two courses – sodium chloride aqueous solution ultrasonic activation – pure water washing two courses – chemical nickel plating – tap water washing two courses – pure water washing two courses – drying – drying – vacuum heat treatment after plating – dip coating DJB-823 solid lubricant – curing.

Process performance analysis

In the bayonet electrical connector, the elastic deformation of the corrugated spring is used to absorb the impact energy and play a buffering role, so that the connector can maintain a constant interface pressure during long-term use, and prevent the electrical connector from breaking instantaneously during vibration and impact. It generally works under alternating stress, and the maximum stress appears on the surface when working, so attention must be paid to prevent decarburization, surface roughness, cracks and corrosion.

The original heat treatment process of corrugated spring was carried out in an ordinary box furnace, and the surface was easy to be oxidized and decarburized. If the grease on the surface cannot be completely cleaned, the surface is easy to deposit carbon after heating, which will lead to an increase in the amount of pickling before plating, and it is easy to cause a large amount of hydrogen permeation in the cleaning process of the corrugated spring substrate. The vacuum purification heat treatment can not only eliminate the processing stress caused by cold forming, but also avoid the oxidation and decarburization of the part surface. The principle of purification and degassing of the parts due to the decomposition and volatilization of the organic pollutants on the part surface under high vacuum can be used. After the heat treatment, the surface of the parts is clean and bright white. In this way, strong alkaline degreasing and strong acid washing can be avoided during electroplating pretreatment, and only combined surfactant degreasing and neutral salt solution activation can be used, thus greatly improving the problem of serious hydrogen permeation in the matrix of high-strength thin-walled elastic parts.

Electroless nickel plating is a chemical treatment method that uses hypophosphite as reducing agent to make Ni and P co deposit on the surface of parts activated by catalyst to form a nickel phosphorus alloy coating.

After electroless nickel plating, we conducted high vacuum heat treatment on the corrugated spring to eliminate the residual hydrogen and internal stress in the substrate and coating. At the same time, the metal atoms of the coating and the substrate diffuse, and the bonding mode gradually transits from the bonding of the composite layer to the metal bond bonding between atoms, thus improving the bonding force between the coating and the substrate.

To sum up, in the whole process flow, new processes such as vacuum heat treatment purification, organic oil removal, neutral salt activation, electroless nickel plating and post plating vacuum heat treatment are adopted, which completely avoid the traditional hydrogen evolution processes such as strong alkaline oil removal, strong acid washing and electrochemical plating. Therefore, the amount of hydrogen permeation in the process is greatly reduced, and theoretically, the probability of hydrogen embrittlement is very small, The possibility of hydrogen embrittlement of corrugated spring is greatly reduced.

Main process parameters and formula

Vacuum degree of vacuum purification heat treatment 4 × 10~3Pa, heating temperature 270 ℃, heating time 30min, holding time 50min, cooling in furnace.

Ultrasonic cleaning: 5% “Amway” Lexin multi-purpose concentrated detergent aqueous solution, the temperature increases with the extension of cleaning time, and the time is uncontrolled, 15~20min.

Ultrasonic activation: 5% sodium chloride aqueous solution, the temperature increases with the extension of cleaning time, not controlled, and the time is 15-20min.

Electroless nickel plating: open the cylinder, PPF-500A 80ml/L, PPF-500B135ml/L, total nickel content 5.6g/L, temperature 82~91 ℃, pH 4.6~5.0 (for every 1g of nickel ion consumed, add 14.3ml/L of PPF-500A, 14.3ml/L of PPF-500C14, and adjust the pH value with 10% ammonia and 20% sulfuric acid solution).

Post plating vacuum heat treatment: vacuum degree 4 × 10~° Pa, heating temperature 270 ℃, heating time 45min, holding time 50min, cooling in the furnace to below 80 ℃, discharging, dipping DJB-823 solid lubricant, and curing.

Heat treatment equipment selection: The RVGQ series vacuum heat treatment furnace produced by SIMUWU is a high-quality product for vacuum heat treatment process of precision parts. Good temperature control accuracy and uniformity ensure the effective implementation of vacuum heat treatment process. SIMUWU focuses on the manufacturing of vacuum furnaces, has more than ten years of relevant experience, and has a good reputation in the field of vacuum furnace manufacturing. The product line includes vacuum gas quenching furnace, vacuum oil quenching furnace, vacuum brazing furnace, etc., which are widely sold in developed and developing countries.