Method and apparatus for manufacturing tubes or tubular bodies with inner walls having cross sections of irregular shapes

Abstract

There are disclosed herein a method and an apparatus for manufacturing tubes or tubular bodies by means of hydrostatic extrusion, which tubes or tubular bodies have axially running holes therethrough having cross-sections of irregular shapes. The method and apparatus utilize a mandrel of novel construction which comprises a conical tip portion having a smooth peripheral surface, a cut or grooved intermediate portion with a sloped groove starting at a peripheral edge and a body portion formed with a flange and adapted to move longitudinally of a pressure chamber, as necessary. The conical tip portion is specifically intended to seal against the conical end of a metallic billet. Unless there is such a provision, there would be leakage of a fluid through the grooved portion because of direct contact of the grooved edge with the inner end surface of the billet. Thus, this method and the apparatus for performing the method enables one-step extrusion of tubes or tubular bodies having inner fins or inner walls having irregularly shaped cross-sections, with the accompanying advantages of providing complete sealing among the die, the billet and the mandrel, particularly in the initial stage of the extrusion.

What is claimed as new and desired to be secured by Letters Patent of the United States is: 
     
       1. A method of manufacturing tubes or tubular bodies with inner walls having cross-sections of irregular shapes by means of hydrostatic extrusion, comprising the steps of: placing a tubular billet having a pre-shaped, tapered tip portion against a die in a pressure chamber with a mandrel positioned in an axially extending hole of said billet, said mandrel having a conical tip portion and a grooved portion, said conical tip portion of said mandrel being so shaped as to be similar to a corresponding, conically shaped inlet hole of said .[.die.]. .Iadd.billet;.Iaddend.   introducing a pressure medium under pressure into said chamber so as to advance said mandrel toward the inner end surface of said billet, such that the conically shaped tip portion and the grooved portion of the mandrel may provide complete sealing between the inner surface of said billet and the tip portion of said mandrel and between the outer surface of said billet and the inner wall of the inlet opening of said die; and   raising the pressure of the pressure medium to a required value thereby effecting the extrusion of said tubes or tubular bodies.   
     
     
       2. A method according to claim 1, wherein the application of pressure to said pressure chamber effects the advancement of said mandrel and the extrusion of said tubes or tubular bodies in a single step. 
     
     
       3. A method according to claim 1, wherein said tubular billet is pre-shaped so that the inner end surface of said billet may be in register with the conical tip portion of said mandrel prior to placing said tubular billet in said pressure chamber.