Method and apparatus for hot forming elongated metallic bars

Abstract

A hot stretch wrap forming apparatus includes a die having a work surface formed of a thermally and/or electrically insulative material, and a set of spaced jaws for stretching and wrapping the metal form around the work surface. A preferred insulative material is a flexible blanket of woven ceramic fibers. A heat source is used to heat the metal form prior to stretching and wrapping. The metal form is preferably heated resistively to maintain a uniform temperature throughout the metal form. The die is typically formed primarily of metal and thus the insulative material thermally insulates the metal form from the metal of the die to prevent the formation of hot spots which would otherwise occur therebetween. The insulative material also electrically insulates the metal form from the metal of the die to prevent shunting therebetween.

1 . An apparatus comprising: 
 a die having a work surface which is formed of at least one of a thermally insulative material and an electrically insulative material; wherein the work surface is adapted for wrapping a metal form there around during hot stretch wrap forming of the metal form;    a set of first and second spaced jaws adapted for gripping the metal form;    wherein the jaws are movable away from one another whereby the jaws are adapted to apply a stretching force to the metal form; and    wherein at least one of the set and the die is movable relative to the other of the set and die between a pre-wrapping configuration and a post-wrapping configuration whereby the relative movement between the set and die is adapted to wrap the metal form around the work surface of the die.    
   
   
       2 . The apparatus of  claim 1  wherein the work surface is formed of a thermally and electrically insulative material.  
   
   
       3 . The apparatus of  claim 1  wherein the insulative material comprises a ceramic material.  
   
   
       4 . The apparatus of  claim 1  wherein the insulative material comprises a flexible blanket of fibrous refractory material.  
   
   
       5 . The apparatus of  claim 1  wherein the die includes a body having a die face and a cover which includes the work surface; and wherein the cover is positionable adjacent the die face whereby the cover is adapted to be positioned between the die face and the metal form.  
   
   
       6 . The apparatus of  claim 1  wherein the die has a metal outer surface and a first layer of thermally insulative material positionable in abutment with or adjacent the metal outer surface whereby the first layer is adapted to reduce heat transfer between the metal form and the metal outer surface of the die during the hot stretch wrap forming of the metal form.  
   
   
       7 . The apparatus of  claim 6  wherein the material forming the first layer is electrically insulative whereby the first layer is adapted to prevent electrical communication between the metal form and the metal outer surface of the die during the hot stretch wrap forming of the metal form.  
   
   
       8 . The apparatus of  claim 6  wherein the die includes a second layer of electrically insulative material positionable at one of a first location between the metal outer surface and the first layer and a second location in which the first layer is disposed between the metal outer surface and the second layerwhereby the second layer is adapted to prevent electrical communication between the metal form and the metal outer surface of the die during the hot stretch wrap forming of the metal form.  
   
   
       9 . The apparatus of  claim 1  further including a heat source adapted for heating the metal form to a forming temperature.  
   
   
       10 . The apparatus of  claim 9  wherein the heat source includes an electric power source and a pair of electrical conductors in electrical communication with the power source; the electrical conductors adapted for electrical communication with the metal form for resistively heating the metal form.  
   
   
       11 . A method comprising the steps of: 
 heating a metal form;    applying a stretching force to the heated metal form; and    wrapping the heated metal form around a working surface which is formed of at least one of a thermally insulative material and an electrically insulative material.    
   
   
       12 . The method of  claim 11  wherein the step of wrapping includes the step of wrapping the heated metal form around a surface of a metal die with a layer separating the surface of the metal die from the heated metal form wherein the layer is formed of at least one of a thermally insulative material and an electrically insulative material.  
   
   
       13 . The method of  claim 11  wherein the step of wrapping includes the step of wrapping the heated metal form around an outer surface of a metal die with a layer of electrically insulative material separating the outer surface of the metal die from the heated metal form to prevent electrical communication between the metal form and the metal die.  
   
   
       14 . The method of  claim 11  wherein the step of wrapping includes the step of wrapping the heated metal form around a working surface which is formed of a material which is both thermally and electrically insulative.  
   
   
       15 . The method of  claim 11  wherein the step of wrapping includes the step of wrapping the heated metal form around a working surface which is formed at least partially of a ceramic material.  
   
   
       16 . The method of  claim 11  wherein the step of wrapping includes the step of wrapping the heated metal form around a working surface which is formed at least partially of a blanket of fibrous refractory material.  
   
   
       17 . The method of  claim 11  wherein the step of heating includes the step of passing an electrical current through the metal form to heat the metal form resistively.  
   
   
       18 . The method of  claim 11  further including the step of positioning a cover which includes the working surface between the metal form and a die face of a body of a die; and wherein the step of wrapping includes the step of wrapping the heated metal form around the cover and the die face.  
   
   
       19 . The method of  claim 11  further including the step of inserting the metal form into a die cavity to press a flexible layer against a cavity-bounding surface which bounds the die cavity to conform the flexible layer to the cavity-bounding surface and to a mating outer surface of the metal form wherein the flexible layer is formed of at least one of a thermally insulative material and an electrically insulative material.  
   
   
       20 . The method of  claim 11  wherein the step of heating includes the step of heating the metal form to a temperature which is substantially uniform throughout the metal form; and further including the step of maintaining the substantially uniform temperature throughout the step of wrapping.