Intelligent Sensors for Atomization Processing of Molten Metals and Alloys
ABSTRACT We briefly introduce the principles of atomization processing of molten metals and alloys, discuss potentially applicable instrumentation, and propose opportunities for developing intelligent sensors for monitoring and control of the process. Particle size and velocity are considered the two most important variables to monitor and control the atomization process. Several on-line sensors suitable for atomization of molten metals and alloys are compared: laser light scattering methods using small angle scattering analysis, moderate angle scattering analysis, and doppler analysis, electrical methods using surface ionization and triboelectric charging, and image analysis. The isokinetic sampling probe is introduced as a direct method to sample powders at the desired point in the atomized spray. Prospects and problems of integrating instruments based on these principles into intelligent processing of materials (IPM) scenarios are discussed.
High speed imaging and Fourier analysis of the melt plume during close coupled gas atomisation
Abstract A high speed digital analysis technique has been used to study the atomisation plume of a superheated sample of Ni–Al in a close coupled gas atomiser. The atomisation, incorporating a generic melt nozzle and die design was captured using a Kodak high speed digital analyser at a frame rate of 18 k frames per second. The resulting 65 536 frames were then analysed using a specially designed routine, which calculates values of optical brightness and position of the intensity maximum for all frames and performs Fourier analysis on the sequence. The data produced from this analysis show that the plume, pulses at low frequencies (<25 Hz) and precesses at higher frequencies (∼360 Hz) around the atomiser's centreline. To aid investigation into the origins of this precession and other phenomena it was decided to conduct further experiments using an analogue system. The analogue atomiser reproduces the important features of the full atomiser but instead of atomising molten metal, the analogue system atomises water, providing a quick and easy way of testing the effects of changing parameters. Using this system it was found that the precession of the melt plume is independent of the atomiser's gas inlet pressure but strongly dependent on both the die and melt nozzle's geometry.
Response characteristics of the multiple-ratio single-particle counter
Abstract The importance of aerosols and aerosol processes has prompted considerable research into techniques for particulate characterization. As batch sampling probe techniques often introduce unacceptable perturbations into the flow and can have serious uncertainties associated with possible alterations of the aerosol in the sample line, in situ optical methods have received much interest. This paper is concerned with a laser light-scattering technique for in situ analysis of individual particles, the multiple-ratio single-particle counter (MRSPC). In particular a thorough study of the response characteristics of the MRSPC was completed, including both experimental and theoretical analyses of nonideal effects associated with particle size distribution measurements. The effects of unknown refractive index, nonspherical particle shape, size-selective sampling bias, and instrument resolution were considered. Theoretical predictions of MRSPC performance for these nonideal conditions were found to agree quite well with experiments performed here. The overall analysis indicates that the MRSPC can make in situ measurements of volume-equivalent size distributions of moderately nonspherical particles of unknown refractive index with uncertainties on the order of 50%.