| Summary: | The electron beam remelting process is used extensively for the refining and
recycling of titanium and its alloys. The success of the process relies on its ability to
provide a thermal environment capable of removing impurities and deleterious particles
while allowing control of chemical composition and solidification. These aspects of the
process hinge on the accurate control of power input to the melt stock. Over the years,
the effects of various parameters (such as chamber pressure) on the power delivery to the
melt stock have largely been ignored.
In this work, a series of laboratory scale experiments using instrumented
cylinders was conducted. In parallel, a finite element model of the electron beam heating
process was developed to analyze the experimental results.
The experimental results show that the temperature regime within a target
cylinder is affected by variations in chamber pressure. The magnitude of the temperature
changes measured as a result of pressure changes was on the order of two to three times
the intrinsic error in the thermocouples. Thus these perceived temperature changes were
close to the limit of our ability to measure them. The experimental results are self
consistent in that a pressure variation produced a
similar trend at each thermocouple
location.
Analysis with the model has shown that the effect of pressure is to alter the power
distribution within the beam and not the efficiency of power transfer. The model can be
made to reproduce both qualitatively and quantitatively the measured temperature
response by varying the beam spreading parameter with chamber pressure. Such a
claim
cannot be made when varying the power transfer efficiency with chamber pressure.
By fitting the model to the experimental thermocouple results it has been shown
that that the beam power distribution is adequately represented by a Gaussian or normal
distribution. Additional analysis has led to empirical relationships for the effect of chamber pressure on beam focusing characteristics under the conditions used in the
laboratory. -
The indirect link between chamber pressure and beam power distribution is
reinforced using careful and self-consistent experiments, a mathematical model that can
reproduce both quantitatively and qualitatively the results of the experiments and the
physics of beam -
gas particle interactions.
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