A kind of flux paste for brazing and preparation method thereof

Abstract

The invention discloses flux paste for hard brazing and a preparation method of the flux paste. The flux paste is formed by brazing flux and finished paste according to the mass ratio being 1:1-1.5:1.The brazing flux comprises boric acid, potassium tetrafluoroborate and anhydrous potassium fluoride. The boric acid accounts for 30%-50% of the total mass of the brazing flux, the potassium tetrafluoroborate accounts for 10%-30% of the total mass of the brazing flux, and the anhydrous potassium fluoride accounts for 25%-45% of the total mass of the brazing flux. In the finished paste, a surface active agent accounts for 0.5%-10% of the mass of the finished paste, a cosurfactant accounts for 0.25%-7.5% of the mass of the finished paste, a carbon residue free polymer accounts for 7.5%-17.5% ofthe mass of the finished paste, and an organic solvent accounts for 65%-92.5% of the mass of the finished paste. The flux paste has the beneficial effects that high storage stability and excellent welding performance are achieved, carbon residues are low after welding, and layering is not prone to happening after brazing filler metal is mixed.

Description

technical field [0001] The invention relates to the technical field of welding, in particular to a soldering flux paste for brazing and a preparation method thereof. Background technique [0002] Brazing refers to the brazing process in which the brazing temperature is greater than 400°C, and the main components of the flux used in brazing are borax, boric acid and their mixtures. In addition, in order to adjust and reduce the melting temperature and activation temperature of the flux, some alkali metal or alkali metal fluorine and chlorine compounds are often added to the system. For example, adding chloride can improve the flux wetting ability, adding calcium fluoride can improve The ability of brazing flux to remove oxides on the surface of stainless steel, adding potassium fluoride can reduce its melting temperature and surface tension, and improve the activity of brazing flux. In addition, adding a certain amount of potassium fluoroborate can further reduce the melting...

AI Technical Summary

Problems solved by technology

[0003] However, the brazing flux powder is very easy to absorb moisture and agglomerate during storage, which makes subsequent use difficult. At the same time, the moisture absorption of each component is different, resulting in the separation of phases during storage and changes in actual components, thereby further Lead to deterioration of welding effect

And by dissolving flux in water to make paste flux, although the problem of flux absorption and agglomeration can be solved, there is a new problem: the water solubility of each component in the flux is different, and even some components (such as Fluoroborate) is insoluble in water, and after a certain period of storage, it will be layered to form a saturated solution on the upper layer and a pasty insoluble solid on the lower layer, resulting in a change in the composition of the flux

In the brazing paste described in CN106514044, alcoholic organic solvents are mixed with silicone oil or glyceryl caprylate and ammonium triacetate as a paste, but the viscosity of the paste is too low to effectively inhibit the flux and Layering of solder

And the soldering paste described in CN158679A becomes the paste body with fatty acid glyceride as surfactant to guarantee the compatibility of inorganic brazing flux and paste body, add benzotriazole, unsaturated fatty acid ester and animal and vegetable oil simultaneously as Additives to further improve the anti-delamination stability of the solder paste. In the actual brazing process, fatty acid glycerides, animal and vegetable oils, and unsaturated fatty acid esters are very easy to form carbon residues under the combined action of high temperature and flux, which will deteriorate the soldering. Effect

However, the solder paste described in CN105643148A does not add a surfactant component that promotes the compatibility of the inorganic flux and the organic paste, and cannot guarantee the storage stability of the solder paste