temperature of the material 12 also prevents thermal degradation of the resin and aramid constituents and eliminates the explosion hazards that can result from heat buildup since the liquid nitrogen bath 20 of the immersion freezer 16 is enclosed from above much of the evaporating nitrogen from the bath will enter the interior of cutter 26 through exit chute 22 and throat 24 the rotating portions of mill 26 enhance this flow by creating a partial vacuum drawing the gaseous nitrogen into the mill this use of cold gaseous nitrogen is an important aspect of the process since the gaseous nitrogen that is supplied to the cutter 26 reduces the milling temperature to a level assuring adequate product consistency mill and screen longevity and processing efficiency a thermocouple 36 is used to monitor the temperature at the exit from cutter 26 thermocouple 36 controls a gas regulator 38 which in turn regulates a valve 40 in a conduit 42 coupled to the exit duct 22 conduit 42 may simply be a flue for diverting gaseous nitrogen from throat 24 or if desired may be a line coupled to a separate supply not shown of cold gaseous nitrogen valve 40 is regulated in such a manner as to maintain the exit temperature in cutter 26 below 75 u00b0 f with a 3 8 inch sieve the fibrous end product 32 has an average fiber length of one inch an analysis of the distribution of fiber lengths appears in the following table ______________________________________ wet sieve amount______________________________________ bss sup 1 7 68 50 bss sup 1 14 2 60 bss sup 1 25 2 65 bss sup 1 50 14 50 uss sup 2 200 7 25 uss sup 2 200 4 50 total.