Composite Materials for Mechanized Brazing

Abstract

The productivity of large scale process manufacturing, of mill cutters for removing the asphalt, is significantly influenced by the deep joint brazing process, by wolfram cable stiffeners sintered in supports made of low alloy steel with chromium. Unanimously accepted solutions of brazing in oven with controlled conditions or in CIF, requires brazing material in shape of pastille having well defined properties of deoxidiser of basic materials, of lifting and complete filling through capillarity of brazing joint and of assurance a good resistance to thermo-mechanical fatigue. The experiments made in CIF with economical materials type Ag140+Ag156+Cu-Sn-Si, in couple with boron-fluorine flows, have underlined a good behaviour to brazing and complete joints filling characteristics. These materials can easily be done by powder technology. The shape and position of the inductor, corroborate with heating-cooling parameters of the brazing assembly, ensure a good resistance to thermal shock of stiffeners made of sintered carbides. Metallographic analysis and hardness tests have revealed structures with defects like: decarburization, oxidizing corrosion and white spot, in the limit allowed by the product norms.

Brazing Behaviour of Ag-Cu Filler Materials

“…In the case of austenitic stainless steels, the holding in the 600-800°C temperature range is critical to avoid the inter-crystalline corrosion. In the case of very thin components, the effects of high temperatures are more critical [6].…”

“…At higher temperatures, between 700 and 800°C, the second ceramic coating, containing a mixture of silver particles, starts to melt, completing the final chemical composition of the filler material. In this way, the filler metal can spread rapidly and it can completely fill the gap between the joined components [3][4][5][6]. The most used filler material brands are 244 Ag, 134 Ag and 145 Ag, which are designed to perform connections for drinkable water pipes a) b) The operating conditions involve corrosive effects and oxidation at high temperatures (300°C), tensions and contractions in the joint.…”