Meaning
Spatial offset representing the axial setback of the liquid delivery tube relative to the gas nozzle exit plane in gas atomization systems. The melt tip recess determines the local pressure field and the flow patterns that develop at the nozzle face. This geometric parameter is adjusted to prevent the molten metal from freezing prematurely or splashing back onto the nozzle.
Geometric Configuration
Positioning the delivery tube behind the exit plane of the gas nozzle shields the liquid stream from the direct impact of the expanding gas. This recessed position creates a small chamber where a low-pressure area forms. The depth of this chamber must be carefully controlled, as even sub-millimeter changes can alter the gas expansion behavior.
A greater recess increases the volume of the recirculation zone and can alter the gas flow path.
Pressure Variation
Suction pressure at the exit of the delivery tube increases as the recess depth is increased up to a critical limit. This suction assists the flow of molten metal by drawing it out of the tube and into the atomization zone. However, if the recess is too deep, the suction can turn into a positive pressure that forces the molten metal backward.
An uncontrolled reversal disrupts the continuous pour and can lead to severe equipment damage.
Operational Benefit
Stable atomization with minimal nozzle clogging is achieved by maintaining the correct balance of this recess. It keeps the high-temperature liquid metal from contacting the cold surfaces of the gas nozzle, which prevents nozzle freeze-off. Properly configured nozzles run longer and yield powders with more consistent particle size distributions.
