World Grain - September 2011 - 78

MILLINGOPERATIONS

tle and reduce the lifespan of the ﬂutes. Smooth rolls are not meant to be shiny rolls. Smooth rolls with a matte ﬁnish or frosted ﬁnish need regular inspection. Shiny spots on the rolls are an indication of excessive wear. SETTING THE GRIND Setting the grind of the rolls takes experience and training. Where the break rolls are typically set using a target release, smooth rolls are set using the miller’s sense of touch, hearing and even smell. Break release is the measure of the amount of work performed during a speciﬁc break grinding passage. Break release is stated as the percentage of material passing through a speciﬁc size testing sieve. Each break roll or passage in the milling ﬂow has a predetermined target break release based on the capacity of the equipment feeding and being fed by that roll passage. A change

in load can overload downstream rolls, transport lines, and affect the quality and quantity of ﬂour produced. Changes in the break release may be the result of many different variables including the type of wheat, the tempering time or ﬁnal moisture of the wheat, feed rate to the grinding passage and distribution of product across the grinding roll. Roll wear is another factor that affects break release and energy consumption of the roller mills. The impact of roll wear can be measured by monitoring the amp load of the motor and calculation of a granulation curve. As roll wear increases, the rolls must be adjusted closer together to achieve the same target break release. As this occurs, the motor load increase is measurable by the increased amp load on the motor. For mills that use line shafts, increased belt slippage can be a sign of

the increased load on the rolls. A granulation curve is an illustration of the distribution of the particle size for a ground product. The granulation curve can be used in addition to the break release to get a better picture of the distribution of product for the roll passage. Whereas break release only measures one separation, the advantage of the granulation curve is that it can be deﬁned to replicate all the separations in a speciﬁc sifter. To construct a granulation curve, ﬁrst sift the product sample using a test sifter with screens similar in micron size to the sieves in the corresponding sifter ﬂow. As the rolls wear, the rolls are adjusted to maintain the correct break release, but the distribution of the ground product will change. A larger amount of ﬁne product and less high quality semolina will indicate

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World Grain - September 2011

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