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Mix <br /> 300 PROCESS AND CONTROL HotFaciliiteshalt <br /> ous mixture of uniformly distributed and properly coated aggregates of Batch Mixing <br /> unchanging appearance. If the mixing is inadequate, the mixing time must be Time <br /> extended.' <br /> If mineral filler is required, it should be weighed separately and added Mineral <br /> directly into the center of the pugmill. Mineral filler usually consists of Filler <br /> very fine particles of crushed rock, limestone, hydrated lime, Portland <br /> cement, or other nonplastic mineral matter.' <br /> Batch mix facilities fall into three categories, manual, semi-automatic, and <br /> fully automatic. In a manual operation, each phase of the batching is performed <br /> by a manipulation of a lever, switch, or button? <br /> In a semi-automatic operation, only a portion of the several phases of batch- <br /> ing is accomplished automatically. Most semi-automatically operated facili- <br /> ties are arranged so that the operations of the weigh-box discharge and mixing <br /> time are included in the automatic cycle control? <br /> In a fully automatic operation, all phases of batching are performed <br /> automatically by using a starter switch, which is pre-programmed to a control- <br /> ler. Automatically operated facilities proportion the material, discharge the <br /> material from the weigh hoppers into the pugmill, control the mixing time, <br /> discharge the completed mix into the hauling units,print out batch weights, and <br /> cycle subsequent batches' <br /> Most facilities today are of the fully automatic type. The fully automatic <br /> facility provides greater efficiency of operation, including a more uniform <br /> product. The fully automatic facility also frees the operator to coordinate other <br /> facility operations' <br /> 301.2 DRUM MIX FACILITIES <br /> In a drum mix facility, see figure 301.5, aggregate is not only dried and heated <br /> within the drum, but also mixed with the asphalt cement. <br /> In a drum mix facility, controlled gradations of aggregate are carefully metered Basic <br /> from the cold feed bins in exact proportions on to a cold-feed conveyor. An Operation <br /> August 1990 Page 300 - 7 <br />