Investigation of induction brazing on circular pipes: An detailed investigation of an induction brazing process

Abstract

This master’s thesis was done at the department of Industrial and Materials Science at Chalmers University of Technology in Gothenburg. A company with relating interests initiated the project, and helped with setup and experiments. They have required to remain anonymous, and are referred to as “the company” in this report. Some withdrawal of details are done to protect their business case. This thesis project was an investigation of induction brazing on circular pipes and a detailed investigation of an induction brazing process station. The background for the project was problems with not fulfilling quality requirements for induction brazed joints at a specific induction brazing station. The different quality defects were the presence of voids and other non-metallic inclusion inside the joints. The purpose of the project was to identify the main influencing parameters for the unfulfilled quality requirements. The investigation was done by a combination of a theoretical study and an experimental study. The theoretical study was carried out to understand the fundamentals of brazing and potential influential parameters for a brazing process. At the experimental part of the project, the influence of different parameters were investigated. Different induction machine programs were used in combination with different filler materials tested. The way and the amount the flux was applied was examined, and how different surface preparations affect the quality of the induction brazed joints. The manual flame brazing of the same joints was set as a reference for the results. Combining the theory from the theoretical study and the examined parameters in the experimental part, conclusions could be drawn that the main quality issue most likely is that the gaps are too big for the joints. The current design of the joints is adjusted to manual flame brazing that provides joints with high-quality joints. However, when it comes to induction brazing smaller gaps are required to achieve sound joints. Proposed solutions were based on reducing the gaps for the investigated joints. Reduced gaps will, according to the theory, increase the capillary flow of the filler material during the brazing operation. In combination with smaller gaps and better flow, the risk for voids and other inclusions will probably be reduced. Another influencing process parameter discovered through the project was the lack of centering of the pipes in the connections. Proposed solutions related to the lack of centering were based on chamfers in the joint design of the pipe connections.