in accordance with the novel aspects of the present invention an extruder die is provided that is capable of both cooling a hot extrudate as well as expanding the extrudate to form a spongy type product . more specifically , this expanded , spongy product is produced by injecting a gas directly into the mass of the hot extrudate substantially parallel to the flow of the hot mixture through the extruder die . expansion produced in this manner would be highly beneficial in the formation of expanded plastic products and food products such as puffed cereals . if desired , the pressure of the gas injected into the mixture may be low enough so that it will merely have a cooling effect and yet not expand the hot extrudate . the figure illustrates a cross - sectional view of a novel extruder die 11 . this die is made up of three basic structures ; the inner housing , the heating means , and the gas - injection means . at each end of the inner housing 12 is an opening . these openings are interconnected by a longitudinal bore . the opening at the upper portion of the housing acts as an inlet 13 while the opening at the lower portion of the housing acts as an outlet 14 . typically the inner housing would be composed of a one - section hollow pipe capable of engagement with means used to blend a mass of material , i . e . an extruder . engaged about the inner housing 12 is heating means 15 capable of maintaining the temperature within the die equal to that within the extruder . as shown in the figure the heating means may be an outer jacket sealingly engaged about the inner housing . the outer jacket is provided with an inlet for the introduction of steam into said jacket , and an outlet for the discharge of condensation . protruding through both the heating means and the inner housing are gas injection means 16 . the gas injection means 16 is connected to a pressurized gas source , such as a pressurized air tank , not shown . either one or a plurality of gas injection means spaced equidistant , or longitudinally spaced and coaxial , to one another may be employed . preferable gas injection means comprise an air injection nozzle composed of stainless steel . the extruder die operates in the following manner . when the inlet 13 is connected with a screw conveyor a hot mixture is forced through the inner housing 12 . the inner housing may be heated to an elevated temperature by the introduction of steam into these outer jackets . as the hot mixture flows through the housing 12 , air is injected through the gas injection source 16 so that the hot mixture undergoes expansion before exiting through outlet 14 . if it is desired to cool the hot extrudate before its leaving the die , cooling water may be introduced into the outer jacket in lieu of steam . furthermore , cool air or air at ambient temperature may be injected through the gas injection means 16 to further cool the mixture . the pressure of such injection should be low enough to prevent expansion of the extrudate if expansion is not desired . obviously modifications of this invention are possible . it is understood , therefore , that this application is intended to cover any variations , uses , or adaptations of the invention as may be considered to be known or customary practice in the art to which the invention pertains .
an apparatus for use as an extruder die is disclosed . the die comprises a cylindrical housing surrounded by heating means . within the die is provided gas injection means which can be used to expand the hot extrudate .