Beryllium copper/palladium alloy electron beam welded sliding contacts
The advantages and process limitations of the latest generation of electron-beam-welded materials are reviewed. The study of metallurgical properties in the weld zone utilizes scanning electron microscopy and metallographic techniques. Various material and weld parameters are evaluated at they relate to final mechanical properties. The relationships of design criteria to metallurgical characteristics and to the effects of heat treatment are discussed.<<ETX>>
Electron-Beam Technology in Switch Contacts
The original concept was to develop a composite strip of material for switch contacts, such that the silver portion is suitably bonded to the base metal such as copper, phosphor bronze, or beryllium copper. The requirements were a metallurgically sound reproducible-nonporous uniform ductile bond. Electron-beam welding technology meets these requirements for joining switch contact materials. Fine silver, coin silver, silver cadmium oxide, and other wrought contact materials can be continuously electron-beam welded to the base metal switchblade member and then subsequently stamped and formed to the necessary switch configuration. This manufacturing technique is an improvement over the alternate joining methods of resistance welding, brazing, tungsten inert gas welding, thermocompression bonding, and the more recent laser welding.
Effect of superficial gas velocity on the particle temperature distribution in a fluidized bed with heat production
The heat transfer behavior of particles and gas in an olefin polymerization fluidized bed was numerically analyzed using an in-house developed 3-D computational fluid dynamics discrete element model (CFD-DEM). First the implementation of the model was verified by comparing simulation results with analytical results. A constant volumetric heat production rate was implemented in the particle energy equation to mimic the heat production due to the polymerization reaction. It was found that the probability density function (PDF) of the particle temperature becomes more homogeneous with increasing superficial gas velocity. Furthermore, instantaneous snapshots of the thermal driving force (the difference between the single particle temperature and bed-average gas temperature, Tp− ) for different heat production rates provide detailed insight in the particle temperature distribution inside the fluidized bed. The time- and bed-averaged particle convective heat transfer coefficient, which was calculated by Gunn׳s correlation, was found to be independent of the superficial gas velocity. This is explained by the fact that the relative velocity of gas and particles in the emulsion phase, where most of the particles and gas interact, is hardly influenced when increasing the gas superficial velocity. From the spatial distribution of Nusselt number, it becomes apparent that the high heat transfer regions are found in the wake of rising bubbles, whereas low heat transfer rates are found in the clouds of the bubbles.