Method of Producing a Metal Foam by Oscillations

Abstract

This disclosure relates to a method of producing a bubbled metal foam, wherein adjusting the size of the bubbles takes place simultaneously with forming the bubbles by the use of oscillations induced by longitudinal waves within a formation region of the bubbles. In this way, a decrease in bubble size which can be caused in an uncontrolled or chaotic manner after the bubbles are created can be avoided. The oscillations are produced along a free surface of a metal melt to provide surface foaming.

What is claimed is: 
     
         1 . A method for producing a block of metal foam having monomodal pore sizes, the method comprising:
 arranging a melt of a foamable material within a container so as to provide a free surface of the melt;   bringing a bubble forming end of a device into mechanical interaction with the melt in an interaction region of the melt, the interaction region being located on the free surface of the melt, and creating bubbles at the bubble forming end to be released at the interaction region;   introducing longitudinal waves into the interaction region to induce oscillations within the interaction region when the bubbles are being created; and   controlling the size of each of the bubbles to a controlled monomodal size value simultaneous to formation of the bubbles by using the oscillations induced by the longitudinal waves within the interaction region, thereby forming a metal foam with monomodal bubbles.   
     
     
         2 . The method of  claim 1 , wherein controlling the size of each of the bubbles further comprises:
 detaching the bubbles from the bubble forming end only when the bubbles reach the desired monomodal size, the oscillations of the longitudinal waves acting to force bubbles to release from the bubble forming end only after reaching the desired monomodal size and without breaking the bubbles into smaller sizes.   
     
     
         3 . The method of  claim 2 , wherein introducing the longitudinal waves into the interaction region further comprises:
 generating longitudinal waves with a generator coupled to the bubble forming end; and   introducing the longitudinal waves from the generator through the bubble forming end to induce oscillations within the interaction region when the bubbles are being created.   
     
     
         4 . The method of  claim 3 , wherein the bubble forming end defines a nozzle with an inner gas passage that is connected to an external gas source, and the method further comprises:
 assisting with the creation of bubbles at the bubble forming end by injecting gas from the external gas source from the nozzle, wherein the longitudinal waves are introduced in parallel to the inner gas passage of the nozzle and within the bubble forming end.   
     
     
         5 . The method of  claim 3 , wherein the longitudinal waves are generated by an acoustic radiation source. 
     
     
         6 . The method of  claim 3 , wherein a frequency range of the oscillations falls into the ultrasonic frequency domain. 
     
     
         7 . The method of  claim 6 , wherein the ultrasonic frequency domain corresponds to a range extending from 20 kHz to 10 MHz. 
     
     
         8 . The method of  claim 6 , wherein the ultrasonic frequency domain corresponds to a range extending from 24 kHz to 2 MHz. 
     
     
         9 . The method of  claim 3 , further comprising:
 solidifying the metal foam.   
     
     
         10 . The method of  claim 9 , further comprising:
 shaping the metal foam before, simultaneously with, or subsequent to solidifying the metal foam.   
     
     
         11 . The method of  claim 3 , wherein the oscillations are less than the cavitation limit. 
     
     
         12 . The method of  claim 3 , wherein the bubbles detached from the bubble forming end remain at the controlled monomodal size and are not broken apart into different sized bubbles by the longitudinal waves or other forces following detachment from the bubble forming end.