Extrusion tread band compound

Experimental study. Using short dies of various L/Dq ratios (Dq= 6.35 mm L/Djj 1.088, 2.828 and 5.704 entry angle 90 ), experiments were performed at 121 C with the Monsanto Processability Tester, on a tread band compound ( ). Results are given in Table V, in terms of extrusion pressure and 60 sec. relaxed extrudate swell versus the various shear rates used. 

Table V Extrusion of a tread band compound through short dies at -T = 121 C...

The tread is also formed by extrusion, but different rubber compounds are used for sidewall and tread (see Appendix AlO). When making the side-wall and the tread in two separate extrusion lines, it is useful to take the extruded sidewall to the second extruder, which would deliver the tread to the sidewall. To simplify the tire-building operation, the sidewall and the tread may also be produced as a single unit by simultaneous extrusion of the two compounds in a single band-the tread over the sidewall-with two extruders arranged head-to-head with a common double die. The band is rapidly cooled to avoid scorching and then cut to the appropriate length. The tread receives its characteristic pattern from the mold when the subsequently huilt tire is vulcanized. 

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