Papers by Keyword: Brazing

Abstract: Diamond tools are fabricated by brazing and used to machine dental ceramics in this paper. The morphology, grinding ratio, wear and grinding force of the brazed tools are investigated in comparison with that of the electroplated ones. The results show that the brazed alloy forms a hill-like structure around the diamond grits, and the protrusion of the brazed diamond grits is higher than that of the electroplated one. The grinding ratio of the brazed diamond tool is higher than the electroplated one. Many fall-off diamond pits of the electroplated tool and only few micro-crack diamond grits of the brazed tool are observed after grinding, and the brazed one remains well process capability. The grinding force of the electroplated tool is larger than that of the brazed one.

Abstract: Increasing performances of thermal engines and the emission reduction requirements force the functioning point of the engines to have higher temperatures, recirculation of a fraction of exhaust gases, and also higher pressure in the engine compartment. These requirements have an impact on the technical and corrosion resistance characteristics of the aluminum heat exchangers that equip these engines. Brazing technology of aluminum alloys is the most energetically effective method, having a low impact on the environment; it consists of a controlled atmosphere binding using NOKOLOK fluxes. The first downside of this method is the flux which even if is chemically inert at ambient temperature, necessitates cleaning operations at the surface of the material, the powders can become an environmental problem if they are not handled carefully; the second downside is the residual flux that resides at outlet and inlet surfaces of the brazed structure can react with the hot cooling agents giving birth to some kind of gel which can alter the heat exchanger’s functionality; the flux particles, in solid state, may detach from the surfaces and may be driven into the cooling loop leading to corrosion of the parts of which the cooling loop is composed of. This paper presents some experimental methods which reduce the flux consumption carried out at RAAL S.A. in their horizontal and vertical controlled atmosphere brazing ovens. These methods point out a significant consumption drop of flux. As a direct consequence we obtained a significant reduction of the residual flux and also the next direction of experimental investigations for obtaining a minimum flux quantity required for the brazing process to run.

Abstract: 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.

Abstract: The principal objective of the paper is to modify the conventional vapor compression refrigeration system by connecting heat exchangers thereby heating and cooling of water is done simultaneously. The vapor refrigerant is supplied to the hermetic sealed compressor where the refrigerant gets compressed to a temperature of 100-120^◦ C. The compressor is connected to a counter flow heat exchanger. Experimentation is carried out to design and manufacture a modified vapor compression refrigeration system. The main parameters considered during the design are connection of a compressor to a hermetically sealed compressor, keeping polyurethane foam as insulating material, adjusting the capillary tube and finned evaporators. The operations carried during the fabrication of equipment are bending, brazing and arc welding process. After the experimental setup has been fabricated the system is checked for the performance by using refrigerants R-22 and R-407.The results are plotted between heating temperatures, cooling temperatures with respect to time in minutes.

Abstract: The purpose of this research is focused on developing a reliable plate heat exchanger made by Incoloy 800 (IN-800) alloy featured with high corrosion resistance in order to replace the current Cu brazed plate heat exchanger made by the 316 stainless steel. A Ni-based filler, MBF-51, was applied to braze the plate heat exchanger made by IN-800. According to the brazing optimizing experiments, the successful brazed joint was made by brazing at 1170 °C for 1800 s. Better shear strength is achieved from the specimen brazed at 1120 °C for 1800 s.

Abstract: This study investigated actively brazing Alumina-to-Alumina with Ag-Cu-Ti as the filler metal system and Alumina-to-Copper with Cu-Ti-Co as the filler-metal system. The research was conducted on four samples, two of which were alumina brazed to alumina (Samples 1 & 2), and the other two were alumina brazed to copper (Samples 3 & 4). The filler metal composition for each sample was as follows: Sample 1 consisted of Cu-96%, and Ti-4%; Sample 2 consisted of Ag-70%, Cu-26%, and Ti-4%; Sample 3 consisted of Cu-85%, Ti-10%, and Co-5%; and Sample 4 consisted of Cu-55%, Ti-40%, and Co-5%. The phase transformations between the filler and base metal of each brazed joint were studied using EDS, SEM, optical microscopy, and X-ray diffraction.

Abstract: Some aluminium alloys with Mg-Si age-hardening are used in vehicle radiators. For cost reasons they are preferably delivered in a naturally aged temper. Estimated minimum time of natural ageing between brazing and when the radiator is taken into service is 14 days. At the service temperature of 95°C, the radiator material will continue to age harden. For accelerated durability testing it is vital to use a radiator with the strength and ageing response of a service radiator. We investigated whether the full 14 days of natural ageing were needed, or if the time could be shortened. Since a vehicle is not in constant use, the radiator temperature will vary over time. We therefore compared cyclic ageing between ambient temperature and 95°C to continuous ageing at 95°C. The Sapa Heat Transfer alloys FA7870 (for headers) and FA7850 (for tubes) were subjected to different ageing times at different temperatures. Tensile and hardness were performed to assess the ageing effect. It was found that natural ageing reduced hardening during the subsequent ageing at service temperature ageing effect, an effect that was most pronounced for the first four days. There was no difference between continuous and cyclic ageing.

Abstract: Brazing of commercially pure titanium to low carbon steel by using the Ag72Cu28 interlayer at different conditions was carried out in the present work in order to investigate the tensile-shear strength, microstructure and the fracture morphology of brazed joint. The results show that different intermetallic compounds such as CuTi,CuTi₂,Cu₄Ti₃ and FeTi were formed at the bonding area. It was observed that the microstructure of joint has a considerable effect on tensile-shear strength of the brazed samples and the maximum tensile-shear strength was achieved at “750°C-10min→850°C-5min”.All the fracture paths after tensile-shear tests occurred in the interface between titanium and silver-based interlayer in spite of the different fracture morphology.

Abstract: As part of the EU/SME project SafeFlame (www.safeflameproject.eu ) the heating of a Cu pipe by a H₂/O₂ flame has been modeled and the results are compared to experiments. CFD (Computational Fluid Dynamics) modeling has been utilized to study the flow and combustion in the flame and the heat transfer from the flame to the pipe. The simulation results are compared with the measured temperature history of the pipe at different locations and with the visual flame. The influence of distance between the burner and the pipe and of using two opposite H₂/O₂ flames on the heating rate of the pipe has been investigated. Reasonable agreement between modeling and experiments has been obtained. The reasons for differences between modeling and experimental results are discussed.

Abstract: The enhanced demands made to safety and comfort for vehicle occupants have, in recent years, resulted in a steady increase of the vehicle weight. The achievement of a good vehicle performance has been accompanied by the development of more effective combustion motors. However, all this entailed the increased out-put of detrimental exhaust fumes. More restrictive environmental requirements demand the future reduction of the vehicle weight. In order to follow those requirements, different lightweight concepts are currently being followed. The application of higher-strength steel materials allows the reduction of the vehicle weight with, at the same time, increase of the part strength. A further possibility is composite construction which, depending on local demands on the material, means the application of the proper material at the proper position in the vehicle. The highest importance is attached to the combination of steel and aluminium. The development of modern, digitally controlled arc processes has rendered the process-reliable reproducible joining of steel to aluminium possible. Within the framework of a publicly sponsored project, the joining of vehicle-relevant materials with different short-arc processes using low-melting zinc-based brazing solders is currently investigated.