INERT GAS ATOMIZATION
The technological scheme of leading fine metal powders manufacturers, such as Schlenk (Germany), Alkan (Canada), Alcoa (USA) and others, were critically analyzed. Their advantages and problem were noted.
On the basis of leading companies data and or own calculations unique technological scheme was developed. Its main feature is vertical atomization plant with close couple atomizing nozzle and closed nitrogen supply system with its purification and recirculation. Also, it was determined that melting of initial metal is possible to realize at open air crucible.
To provide high output of fine fraction less than 30 mkm special atomizing nozzle was calculated and developed with using supersonic nitrogen jet speed.
Pre-heating of the nitrogen before nozzle with its temperature regulating up to 400°C provides spherical shape of the final metal powder particles.
Nitrogen closed supply system with its purification and recirculation allows significantly decrease its consumption during atomization and provide full independence of atomizing process to produce fine metal powder.
Regulating of oxygen content in nitrogen before atomizing nozzle provides passivation of the metal powder during its atomization.
On the basis of the technological scheme non standard equipment was developed and designed to produce fine metal powder. Main non standard equipment includes atomizing plant, which consists of atomization chamber, atomizing nozzle, tundish, powder container. There are all assembly drawings, all overall dimension is precisely established for general layout and building construction design. Manufacturers and suppliers of standard equipment are recommended. To control process parameters and certification of the produced powders analytic devices were selected and several commercial proposals were obtained.
WHAT HAD BEEN DONE?
Detailed manufacturing documentation of the whole technological route and atomizing unit have been done. Here above of technological scheme of the inert gas atomizing plant is shown. Here are:
1- Induction furnace
2 – Atomizer
3 – Compressor
4 – PSA plant
5 – Compressor
6 – Vacuum pump
7 – Filters
8 – Receivers
9 – Receiver
10 – Pre-heater
11 – Argon manifold
12 – Pressure regulator
13 – Cut-off valves
14 – Valves
15 – Water valves
16 – Coarse cyclone
17 – Fine cyclone
Experimental testing of pre-calculated nozzles was conducted with using of two nozzle variants at the pilot atomization plant. Predicted theoretical and experimental characteristics of the nozzles are very close.
Shape factor of the powder atomized with cold nitrogen pointed on slight deviation from spherical shape, so it was recommended to regulate nitrogen temperature before atomizing nozzle to provide more spherical shape of the powder particles.
Study of HSS (R6M5) atomization at pilot unit URS-40 of National Academia of Ukraine with our nozzle design. Cold nitrogen at 6 Bar was applied. It is small unit of 35 kg crucible volume of induction furnace.
Fraction composition:
less 63 mkm = 40.1 % 63-160 mkm = 35.3 %
160-315 mkm = 18.7 %
> 315 mkm = 6.2 %
Total = 100.0%
AS RESULTS
The nitrogen supply system is our own “know-how” and fully automated. Actual scheme depends on what type of metal will be atomized and volume of molten metal batch. Close nitrogen supply scheme with nitrogen recirculation
PSA nitrogen unit produces nitrogen and supplies it into accumulating receivers. Compressor booster increases pressure up to 2.5 – 4.0 MPa and through receiver-buffer supplies it into nozzle. Vacuum-compressor sucks nitrogen from the atomizing chamber and returns into the cycle
.
A unique design of the close couple nozzle has been developed:
– Metal is fed through central calibrated orifice; Gas is fed through special super sonic Laval nozzle with internal body; Annular nozzle has special angle to attack the metal stream in focal point.
To determine these parameters is our “know-how” and key factor of atomization.
THE TECHNOLOGY CAN BE REALIZED WITH MODERNIZATION AND MODIFICATION AGAINST AN ORDER.