The paper presents research conducted for the development of precursors and wrapped rods for brazing, that deposit, through melting, two different alloys, with respect to the level of silver alloying and the melting temperature. The alloy with the high silver content is introduced under the form of powder, in the coating of the brazing rods, in a participation proportion that assures a buffer layer, with advance proprieties of diffusion in the base metal and in the core alloy of the coated rod. The participation ratio of the silver rich powder alloy is established within the following limits 8-12%, depending on their melting point, the grinding degree and mixing with the deoxidizer coat. The development of the precursors was made by homogeneous melting and spraying on a oblique plan, the grains obtained were grounded, the grist obtained is considered optimum to be introduced in the coating mixture after it successfully passed through a sieve with a mesh of 0.1 mm. The alloyed precursors with 45% silver, grounded between the above mentioned limits, were introduced in the deoxidizer coat mixture af the bare rods type Ag30 according to SR EN 1044/1999. The resulted mixture was used to manufacture experimental lots of covered rods for brazing, which were used for testing, in order to achieve highly important joints. The melting temperature of the precursors was established through micro-alloying so that it will be 10-15°C higher than that of the deoxidizer coat, which in turn has a lower melting temperature, by 56-60°C, than the melting temperature of the core alloy. The deoxidizer coat is usually fluoroboric type, conforming to SR EN 1045/2001. Representative joints made with the new experimental rods, after testing, presented results consistent with the requirements, which allowed the authors to appreciate this method as appropriate for cost reduction with brazing materials in the use of composite coated rods.
Impurity effects in thermal regelation
