Polish version

Volatile brazing flux

The object of the offer is a technology for producing volatile flux for brazing steel, copper, brass and zinc bronze with a gas torch (burner). The active substance of the flux is trimethyl borate, obtained in the form of its azeotrope with methanol. The flux in liquid form is fed into the brazing zone with a flammable gas supplying the torch. The gas flame saturated with the flux vapours exhibits a reductive effect on the most metal oxides and provides an effective screening of the brazing zone from atmospheric oxygen, thus safeguarding metallic purity of the joint, required anti-corrosiveness and aesthetics of the product. Such a way of brazing eliminates the burdensome necessity to clean joints from slag, what is characteristic of using classical fluxes in the form of powder or paste. The preparation is a uniform, colorless, clear liquid with a characteristic, acrid smell. It contains about 70 % azeotrope of trimethyl borate with methanol. Remaining ingredients are potassium fluoride with its stabilizing and activating influence and ethylene glycol.

A brief description of the technology

Synthesis of trimethyl borate proceeds according to the simple equilibrium reaction scheme:


In order to ensure reaction progress in the expected direction to create the product it is necessary to separate the product from the reaction mixture. The synthesis is performed at the boiling temperature of the reaction mixture (72–78 °C). The distillate of azeotrope of trimethyl borate with methanol (about 70 wt. %) is separated from the reaction environment by the rectification method in the range of temperature 53–57 °C.

In order to separate the azeotrope enriched with trimethyl borate, there is a necessary to apply a rectification column. Depending on the technical parameters of the applied apparatus set (including the resolution capacity of the fractioning column) there can be different: speed of the process to separate from the reaction environment the azeotrope of trimethyl borate with methanol of required composition, the time to bring the system to the equilibrium state and the yield of the synthesis. Water created in the synthesis slows down the trimethyl borate creation process, until the equilibrium of the reaction is shifted to the substrates. Then the synthesis should be treated as completed, despite the fact that the reactor still contains unreacted boric acid and methanol.

Advantages of the technology offered

The offered technology allows to obtain, in a simple and a safe way, a home-made preparation of a quality comparable to foreign ones.


The base of the installation is a periodic rectification apparatus set. The rectification tub acts at the same time as a reactor and it should be fitted with a stirrer and a drain valve. The rectification system consists i.a. of a column with filling, a condenser, a cooler and a receptacle.

The installation should be equipped with a control-measuring apparatus, allowing to keep technological parameters i.a.: temperature of the reactor, temperature of the rectification column and temperature of the column's top.

Installations of all electric devices, mechanical ventilation and lighting should be explosion-protected and non-sparking.


pat. PL 210 201 (2011) „Method to obtain volatile brazing flux”.

Market competitiveness

The technology allows to obtain the product from cheap constituents (boric acid and methanol) and it enables to separate the product from the reaction environment by the rectification of azeotrope of trimethyl borate with methanol. The price of the product is competitive to offers of foreign companies, e.g. German Company Chemet and characteristics of trimethyl borate in the brazing process is comparable with other foreign products.


Based on brazing tests, the preparation received a positive opinion by the Welding Institute in Gliwice – ruling No ZT/227/06.


Lidia Lewicka, M.Sc., Chem. Eng.

phone: + 48 22 568 21 93