The Effect of the Gas Outlet on the Gas Velocity Field in Mass-Production of HFCVD Diamond-Coated Drills

Abstract

In the present study, the¯nite volume method (FVM) is adopted to investigate the e®ect of gas outlet on the°uid¯eld generated by a hot¯lament chemical vapor deposition (HFCVD) setup that is designed for the mass-production of diamond coated drills. The temperature¯eld is calculated simultaneously such that its e®ect on the gas°ow can be included in the resulted gas velocity¯eld. First, the e®ect of outlet radius (R out Þ is investigated using a 2-outlets arrangement. The results show that the gas¯eld obtained with R out ¼ 10 mm is superior to R out ¼ 5 mm or 15 mm, which not only can produce higher gas velocity, but also a more uniform gas¯eld in¯lament plane. To further re¯ne the uniformity of gas¯eld outside the¯lament area, four 4-outlets arrangements with di®erent combinations of the distance between gas outlets and worktable and gas inlets coverage are proposed and a comparative study on their e®ect on the gas¯eld is conducted. The simulation results show that allocating two additional outlets near the worktable is bene¯cial for enhancing the uniformity of gas velocity¯eld outside the¯laments but slightly worsen it near the¯laments. Finally, actual deposition experiments are conducted to justify the simulation results and the results suggest that the gas velocity in the drill region plays critical role on the growth rate of diamond¯lm and the 4-outlets arrangement could provide more uniform growth environment than the 2-outlets arrangement.