This invention relates to the field of flux technology, in particular, to a flux used for air - condition refrigeration, for welding environmental-friendly welding ring of energy-efficient copper-aluminum composite pipe and its preparation method thereof.

Flux can be broadly devided into resin flux, water-soluble flux and inorganic flux. The resin flux is a flux in which an active agent is added to rosin and insoluble resin such as synthetic resin; The water-soluble flux is a flux that add active agent to resins dissolved in water such as Polyethylene glycol, Tween emulsifier; Inorganic fluxes made of inorganic acid such as hydrochloric acid and inorganic salts such as zinc chloride. The water-soluble and inorganic flux must be cleaned residue after soldering , because the residue of both at room temperature is also corrosive. Therefore, the welding flux of copper-aluminum wire mainly use resin flux, but its active ingredient and composition is different from the resin-core flux used for electronic packaging and solder wire. Therefore, studying a new type of flux used in the environmental welding of welded copper-aluminum wire has become one of the major urgent topics to be solved.

This invention also discloses a flux preparation method, which comprises the following steps:

(1) Organic acid activators, surfactants, wettijng agents, corrosion inhibitors and film-forming agents shall be accurately weighing according to the weight percentage of each component.

(2) ) The film-forming agent was added to a reaction kettle having a heating function, heated to 110℃, to mix;

(3) When temperature is slowly warmed up to 140℃, organic acid activator, wetting agent, surfactant and corrosion inhibitor shall be added at once according to the ratio , and to be stirred 0. 5h;

(4)Cooling, then get the finished flux.

The advantages of welding flux

This solder ring flux used in welding air conditioning and refrigeration industry with energy efficient copper and aluminum composite wires, developed according to the characteristics of the solder and welding technology developed, which has scientific design, reasonable formula, and strong technology. Its advantages are as follows:

1. The film-forming agent in the flux is consisted of one or more of disproportionated rosin, polymerized rosin and hydrogenated rosin. The rosin shows certain activity and a certain ability to deoxidize the film at the soldering temperature, increasing the fluidity of the soldering fluid, showing solid state when cooled to room temperature after soldering, which is inert and wrapped the active residue, good gas tightness, good protective properties, solving the problem of corrosion after flux soldering.

2. It use two or even a variety of organic hydroxy acid active agent to compound. Hydroxyl in the organic acid is electron-withdrawing group, with the electron-induced effect that increase the degree of dissociation of the carboxy group and is more acidic than the corresponding carboxylic acid, because the boiling point of these organic acids and the decomposition temperature of the active agent exhibit a large interval distribution that makes the flux maintaining a high activity in the entire welding process, access to good welding results.

3. The addition of wetting agent can quickly remove the oil on the surface of the weldment and oxide, reducing the surface tension of the weld liquid, changing the surface materialized balance conditions, so that the solder and copper-aluminum composite pipe mutual wetting, to achieve the best welding effect;

4. The surfactant can reduce the surface tension of the molten solder and the metal surface energy of welded aluminum-aluminum composite pipe to improve the welding effect, leaving no residue after welding;

5. Tetrazole and its derivatives are selected as corrosion inhibitors for this soldering ring. These kind of materials can only hinder the unilateral reaction of carboxyl groups and copper ions, thereby inhibiting the production of metallic soap of green copper and also having the ability to prevent corrosion caused by organic acids or active agents, increases the reliability of the product.