CS264730B1 - Non-corrosive flux for capillary brazing - Google Patents

Abstract

The non-corrosive (powder or paste) flux is intended for capillary hard soldering of materials and parts made of copper and its alloys, of austenitic and unalloyed steels and their combinations with AgCuZnSn and AgCuP type solders with a particularly low Ag content, using common soldering methods. The essence of the non-corrosive flux is that it consists of 40 to 60% by mass. boric acid, 20 to 28 wt.% of sodium fluoride and potassium fluoride individually or in combination and 15 to 22% by mass. of potassium fluoroborate, as well as from 20 to 30% by mass. of denatured ethyl alcohol in a combination of 40 to 50% by mass.

Description

264730 2

The present invention relates to a non-corrosive flux for capillary brazing of materials from its alloy, austenitic and non-alloy steels and their combinations.

For the soldering of the medium and its alloy, especially for electrical purposes, low electrical transfer resistance and excellent conductivity are required, often in conjunction with high strength soldering, and in the soldering of austenitic and unalloyed steels and their combinations, respectively. Further combination with meSa and its alloys requires a high mechanical strength which is closely related to the fullest possible utilization of the diffusion possibilities of the article material and the actual solder. In the last time widespread use of the properties of AgCuZn, AgCuZnCd and AgCuZnSn type solders, as well as the increased requirements of electrical conductivity and higher mechanical strength of soldered joints, influenced the development of a new flux, which allows higher utilization of diffusion properties and currently non-corrosive. In practice, a number of melts for capillary soldering are known, but do not achieve a satisfactory degree of corrosion. Many of them contain chlorides that release toxic substances and cause corrosion, and their necessary complete removal after soldering is complicated and challenging. The working acceptable quartz is based on sodium tetraborate, boric acid, fluoridoammonium acid, potassium hydroxide, sodium fluorosilicate, sodium fluoroborate, potassium fluoride, sodium fluoride and boron trifluoride.

Known earlier, still used melts include a similar solder melting, such as a brazing filler for stainless steel, or a medium and its alloys, or both, boric acid, crystalline borax, acid fluoride, sodium, or both. and based on potassium fluoroborate or sodium, or both, with a high carbon content and containing one or more components of the group of alkali silicates, lithium aluminum, sodium, etc. (CS AO No. 158 443). The great dependence of this flux on imported raw materials has become a drawback. This flux allows solder soldering with an Ag content of 25% by weight. above. The development of solders went intermediate to lower Ag, down to 5% by weight, and lower. In these cases, the fusing feature no longer performs.

An older boric acid, crystalline borax, alkali metal fluoride, potassium fluoroborate, or sodium and ethyl alcohol, and glycerine or monoethylene glycol and sodium potassium double silicate, or sodium or potassium acid silicate are known. (CSN AO No. 227 108) The flux allows soldering with Ag 15% by weight solders and higher, the dependence on the import of foreign exchange raw materials (up to 25% w / w) and the hygienic production conditions have been improved. In the period of this developmental phase, there were generally melting effects of corrosion around the soldered joint.

The essence of the novel, non-corrosive flux for the capillary brazing of the medium and its alloys, austenitic and unalloyed steels and their combinations, consisting of boric acid, sodium fluoride, potassium fluoroborate and denatured ethyl alcohol, consists in containing 40 % to 60 wt. boric acid, 20 to 28 wt. sodium fluoride and potassium fluoride, individually or in combination with 15 to 22 wt. potassium boroborate. Furthermore, it contains 20 to 30 wt. % denatured ethyl alcohol at a concentration of 40 to 50 wt.

The main advantages of the new, non-corrosive flux are that it is designed, tested and proven to work with complete new types of solders, especially AgCuZnSn and for AgO, 5CuP solders, for which types are known to be unusable. Further advantages are to a large extent the usability of the new flux in soldering methods and means, in the wide range of solderability of various types of materials and their combination 3 264730 using AgCuZnSn based solders. The flux is characterized by excellent capillarity, high activation capability and an extraordinary property of rapid removal of oxide layers, inclusions and the like, at very low aggressiveness to the metal skeleton, has excellent adhesion and thixotropic properties, reduced toxicity in the production of the flux, and especially technological applications. The flux slag is glassy, easily removable by washing with water. Tests have shown that where slag residues do not worsen the aesthetic appearance, or if they do not. where they are not exposed to observation, as well as where it would be difficult to remove, for example, in inaccessible places, not leaving it at fault for its corrosive effects, decay, etc., as the residues behave as non-corrosive.

Tests in one case were carried out under the following conditions and showed the following results: flux with a chemical composition of 54.3 wt. boric acid, 25.9 wt. sodium fluoride and 19.8 wt. Potassium fluoroborate was used for brazing Cu 99.5 by solder

Ag40CuZnSn in the form of a wire in a warm electric spiral furnace at a temperature of 660-685 ° C. The flow rate was 1400 mm, the tensile strength was 224 MPa. In another case, the flux was 45% by weight. boric acid, 20 wt. % fluoride, 15 wt. % potassium fluoroborate, 20 wt. of denatured alcohol at a concentration of 50 wt. used in soldering process in warm neutral oxygen-acetylene flame when soldering parts from combined materials Cu99,5 and ČSN 17 246, resp. Ms and ČSN 17 246, Ag40CuZnSn solder in the form of wire. Reachability on Cu side - 1 310 mm22 on side 17 246 - 508 mm. Total tensile strength of 224 Mpa. In case of combination with Ms, in heat resistance soldering furnace, working temperature 650 to 680 ° C, solder in foil shape: 2 2 achieved flowability on Ms side - 1 090 mm, on side 17 246 - 502 mm, tensile strength of tensile strength 305 MPa . In another case, flux tests were carried out in a heat resistance furnace at 780 ° C, 5 ° C, Ag4CuP solder in foil form: the flow rate reached 508 mm 2, the bond strength at 360 MPa. In the case of a further test with a flux of 59% by weight. boric acid, 20% sodium fluoride, 21% wt. Potassium fluoroborate, using AglOCuP solder to combine Ms - 17 246 materials in a warm neutral oxygen-acetylene flame, yielded the following 2 results: the highest flow rate of 1 210 mm (Ms), the lowest flow rate of 512 mm (17 246), bond strength thrust of 315 MPa.

For comparison, some of the flux test results according to CS AO No. 227 108: in the condition of an electric resistance furnace on Ms material, using an Ag40CuZnCd solder, the flow rate was 680 mm, under the conditions of a neutral oxygen-acetylene flame the flow rate was about 590 up to 720 mm. Under the same conditions, the flow rate on the material was 17,246,2,250 mm (resistance furnace) and 217 mm (flame).

The non-corrosive (powder or paste) flux can be utilized in capillary soldering by AgCuZnSn type solders, respectively. type AgCuP, materials from media and its alloys, from asutenitic and unalloyed steels and their mutual combinations, especially in engineering, in the production of instrumentation, in electrical engineering, in chemical, energy, refrigeration and freezing industry, etc.

The widest use is in the production of soldering machine parts and medical equipment, in the electrical industry, in food production.

Claims (2)

1. A non-corrosive flux for capillary brazing by media and its alloys, austenitic and non-alloyed steel, and combinations thereof, consisting of boric acid, sodium or potassium fluoride, potassium fluoroborate and denatured alcohol, characterized in that: It contains 40 to 60 wt. % boric acid, 20 to 28 wt. % sodium fluoride and potassium fluoride, singly or in combination, and 15 to 22 wt. potassium fluoroborate. 2. A non-corrosive flux as claimed in claim 1, wherein the salt contains 20 to 30 wt. % denatured ethyl alcohol at a concentration of 40 to 50 t.