Thermal shock resistant apparatus for molding thixotropic materials

In an apparatus for processing a metallic material feed stock into a molten or semisolid state exhibiting thixotropic properties, the apparatus including a rotatable screw located within a barrel and heating means located about the barrel whereby feed stock material is received into the barrel at a colder temperature than material discharged from the barrel such that the barrel is subjected to thermal cycling as a result of the introduction of additional feed stock into the barrel, the improvement comprising:

• a barrel having a first section, a second section, and a nozzle section having a tip, connecting means for connecting said first section to said second section and for connecting said second section to said nozzle section, said first, second and nozzle sections including internal surfaces cooperatively defining a central passageway through said barrel, said first section further having portions defining an inlet into said passageway and said nozzle section having portions defining an outlet out of said passageway, said first section being constructed of a first material, said second section being constructed of a second material, and said nozzle section being constructed of a third material, said first material having a greater thermal conductivity and a lesser coefficient of thermal expansion than said second material thereby providing said first material with greater resistance to thermal fatigue and thermal shock than said second material, a nozzle bushing engaging said tip of said nozzle, said nozzle bushing having a thermal conductivity being less than said third material.