Semakan pada 05:06, 10 November 2009 sunting Yosri (bincang \| sumb.) Birokrat, Penyelia 245,308 suntingan →‎Bahan Kerja Biasa ← Suntingan sebelumnya		Semakan pada 05:08, 10 November 2009 sunting batalkan Yosri (bincang \| sumb.) Birokrat, Penyelia 245,308 suntingan →‎Atomization Suntingan berikutnya →
Baris 65: === ~~Atomization~~Pengatoman (“Pengatoman”) === Pengatoman dicapai dengan memaksa aliran cecair logam melalui bukaan dengan tekanan serdahana. Gas dimasukkan dalam aliran logam sejurus sebelum ia meninggalkan muncung, yang bertindak untuk menghasilkan golakan apabila gas yang disuntik mengembang (akibat pemanasan) dan keluar ke dalam pengumpul isipadu besar diluar bukaan. Isipadu pengumpul diisi dengan gas bagi menggalakkan pergolakan lanjut jet logam cair. Di [[Bumi]], aliran udara dan serbuk dipisahkan menggunakan graviti atau [[pemisah siklon\| pemisah siklon (“cyclonic separation”)]]. Kebanyakan serbuk diatomkan merupakan sepuh lindap (“annealed”), yang membantu mengurangkan pengoksidaan dan kandungan karbon. Partikel air diatomkan adalah lebih kecil, bersih, dan tidak telap dan mempunyai saiz jarak lebih besar, yang membenarkan pemampatan lebih baik. Atomization is accomplished by forcing a molten metal stream through an orifice at moderate pressures. A gas is introduced into the metal stream just before it leaves the nozzle, serving to create turbulence as the entrained gas expands (due to heating) and exits into a large collection volume exterior to the orifice. The collection volume is filled with gas to promote further turbulence of the molten metal jet. On Earth, air and powder streams are segregated using gravity or [[cyclonic separation]]. Most atomized powders are annealed, which helps reduce the oxide and carbon content. The water atomized particles are smaller, cleaner, and nonporous and have a greater breadth of size, which allows better compacting. Simple atomization techniques are available in which liquid metal is forced through an orifice at a sufficiently high velocity to ensure turbulent flow. The usual performance index used is the [[Reynolds number]] R = fvd/n, where f = fluid density, v = velocity of the exit stream, d = diameter of the opening, and n = absolute viscosity. At low R the liquid jet oscillates, but at higher velocities the stream becomes turbulent and breaks into droplets. Pumping energy is applied to droplet formation with very low efficiency (on the order of 1%) and control over the size distribution of the metal particles produced is rather poor. Other techniques such as nozzle vibration, nozzle asymmetry, multiple impinging streams, or molten-metal injection into ambient gas are all available to increase atomization efficiency, produce finer grains, and to narrow the particle size distribution. Unfortunately, it is difficult to eject metals through orifices smaller than a few millimeters in diameter, which in practice limits the minimum size of powder grains to approximately 10 μm. Atomization also produces a wide spectrum of particle sizes, necessitating downstream classification by screening and remelting a significant fraction of the grain boundary.

Metalurgi serbuk: Perbezaan antara semakan