of the remaining molten metal when the inert gas flow rate through tube 34 is set at a fixed level any decrease in the level of molten metal within crucible 12 will reduce the backpressure exerted against said inert gas flow backpressure sensor 36 detects this change in backpressure and sends a pneumatic signal to central control unit 38 which converts the pneumatic signal into an electronic signal this electronic signal is relayed to electronic servo valve 28 the electronic signal causes electronic servo valve 28 to allow sufficient additional gas to flow through line 24 into the upper volume of crucible 12 in order to increase the gas overpressure in crucible 12 this additional gas pressure over the molten metal returns the effective backpressure against the flow of gas through tube 34 to its original pre set pressure in the apparatus of fig1 backpressure sensor 36 produces a pneumatic signal however an electronic backpressure sensor can also be used such a backpressure sensor sends an electronic signal directly to the central control unit which relays it to the electronic servo valve because the backpressure exerted against the inert gas from gas supply 30 through ceramic tube 34 correlates with the ejection pressure of the molten metal through orifice 14 in crucible 12 means to keep the backpressure constant will maintain the ejection pressure constant and thus the flow rate of the molten metal through orifice 14 will be maintained at a fixed value the maintenance of a constant flow rate of molten metal through orifice 14 will produce metal foil having a uniform thickness by uniform thickness it is meant that the thickness variation is less than u00b1 10 from start to finish in summary the molten metal delivery rate can be kept.