RU1828796C - Brazing flux for metal structures - Google Patents

Abstract

Usage: the flux is designed for brazing steel products and dissimilar materials by medium-melting brazes on a copper basis at high shutter speeds and a heating temperature of up to 1100 ° C, mainly when brazing. The inventive flux contains components in the following ratio, wt.%: Boric acid 60 ... 75, potassium carbonate 13 ... 22. sodium fluoride 7 ... 10. silicon dioxide 5 ... 8. 3 tab.

Description

The invention relates to brazing, in particular to fluxes for brazing metal structures by copper-based smelters.

The aim of the invention is to improve the technological properties of brazed joints and to improve the range of fluxing action.

This goal is achieved in that the flux for brazing by medium-melting brazing alloys based on copper, consisting of boric acid, potassium carbonate and a fluorine-containing component, additionally contains silicon dioxide, and sodium fluoride is used as a fluorine-containing component in the following composition, wt. .%:

Boric acid 60 ... 75

Sodium fluoride 7 ... 10

Potassium carbonate 13 ... 22

Silicon dioxide 5 ... 8

Sodium fluoride and potassium carbonate are added to the slag to reduce the viscosity of borates and metabolites resulting from the interaction of boric acid with base metal oxides and solder, and silicon dioxide is added to increase the maximum temperature of the active flux. It was established by experiments that the best properties of the slag system are possible only with a certain ratio of these components introduced into the flux base. It corresponds to: 2NaF.K2C03 4 SiOa1

or one part of the total content of sodium fluoride and potassium carbonate should use four parts of silicon dioxide

The solubility limit of sodium fluoride in the system under consideration is within the range not exceeding 10%. With a higher content of sodium fluoride, it precipitates. Crystallized flux forms on the surface.

0)

ate with

from u to v u o

a strong white crust with a melting point of more than 900 ° C. Hence, the maximum content of sodium fluoride in the proposed system will correspond to 10%.

The minimum sodium fluoride content was determined by studies on the spreading of silver-free solders under experimental fluxes. It corresponds to 7%. With less sodium fluoride, the fluxing properties of the slag deteriorate. The surface of the solders becomes bumpy and the spreading area decreases.

The highest content of potassium carbonate was established by the appearance of porosity in the welded joints due to the excessive release of CO2 during thermal decomposition of the component. The indicated amount corresponds to 22%. The lowest content of potassium carbonate is determined by the fact that when its content in the proposed flux decreases below 13%, the technological properties of the molten slag deteriorate, in particular, the viscosity increases.

Outcome from. of formula I and taking into account the established amounts of sodium fluoride and potassium carbonate, the limits of the content of silicon dioxide (SlOa) are determined:

10-f22

Si02max Si02mln

4 7 + 13

 %; ---5 %

The basis of the flux - boric acid - is defined as the difference

100% SNaF, K2CO3, SI02 and for the inventive flux will be in the range of 60 to 75%. The viscosity of the developed flux was investigated. In fig. Figure 1 shows the curves of the variation of the coefficient of internal friction / (pascal. Sec.) Versus temperature during furnace heating. Curve 1 shows the change in viscosity of the prototype, curve 2 shows the proposed slag system. Practice shows that the optimal t) values for blast fluxes should be in the range t, 2 ... 0.4 Pa-s. From this, I compared curves 1 and 2, it follows that the flux we are offering starts to work from about 780 ° C, while the prototype at this temperature already reduces its active effect, darkens and becomes loose.

A standard spreading test methodology was used to evaluate the experimental fluxes. In this case, PAN-12 grade silver-free solder based on a copper-tin base with a full melting temperature of 810 ° C was used as a base, as well as industrial grade PSr 40 silver alloy.

Spreading experiments were carried out on

steel substrates 40x40x2 mm in a muffle furnace with adjustable heating. At least 6 samples were used for each flux composition. Evaluation of the quality of the flux

the spreading area of the solder and the appearance of the crystallized slag, the adhesion to the substrate, and the like.

Selected fluxes were used for furnace brazing of steel, brass and copper

samples heated in a furnace without any protective atmosphere. The appearance of fillets, strength test results and fracture analysis data were taken into account.

in table Figure 1 shows the compositions of the five studied fluxes. Moreover, compositions 2, 3 and 4 fall within the scope of the claimed flux, compositions 1 and 5 contain, respectively, fewer and more components specified in the claims of the present invention.

In the table. 2 shows the results of flux tests of the above five compositions. Has the best qualities

flux of an average composition (1st 3). It also has good fluxing properties even at a temperature of 1100 ° C, which allows it to be used for brazing.

The compositions of fluxes 2 and 4 are quite accessible from the point of view of the quality of the soldered compounds, which indicates the correct choice of the limits of the content of components. It should be noted that the proposed flux showed good results with induction and gas heating, as evidenced by the data in table. 3.

Claims (1)

SUMMARY OF THE INVENTION A flux for brazing metal structures containing boric acid, potassium carbonate and a fluorine-containing component, characterized in that, in order to improve the technological properties of the steam compounds and increase the range of the fluxing action, it additionally contains silicon dioxide, and as the fluorine-containing component sodium fluoride in the following ratio, wt.%: Boric Acid 60-75 Potassium carbonate 13-22 Sodium Fluoride 7-10 Silicon dioxide 5-8. Table Composition number during spreading tests The flux turns black and loses its properties at 850 ° C. Spreading solder has an uneven, bumpy surface. Solder spreading is satisfactory when heated to 920 ° C. The surface is flat. The flux provides good spreading of solder when heated to 1100 ° C. The surface is flat. In some areas of the surface, the solders have a tubercle. The number of defects is permissible and amounts to no more than 3% of the total area. Due to its high viscosity, the flux does not spread well on the substrate. A strong white crust is present on the surface. Table 2 Characterization of flux compositions when soldering with lap heating Solder only wets the front edge of the solder joint. After breaking, most of the edges are oxidized. Do not drink. A reverse fillet is formed with an overlap of not more than 3 mm. Seams have smooth concave fillets. The solder satisfactorily flows into the gaps with an overlap of up to 4 mm. Separate pores appear on the back fillet. Durability of soldered joints is acceptable. The seam formation is poor, the fillets are uneven, many pores. Tables a 3