ight B Mth to th position of Article No and Ar B3-DV-9B Bevel-helical speed reduction gearbox B3

Flender/Flender Gear Units/Bevel-helical speed reduction gearbox B3

remove the bran layers, in the most cost-effective manner,without damage to the endosperm. Several mechanisms can be employed in the mechanical action. These include tearing by friction, cutting, grinding, and impact. Although all of these may be present in varying degrees in an actual milling system, modern rice-millingsystems can be classied into two categories of milling equipment. Friction-type machinesuse primarily friction and cutting actions. These machines use relatively high pressurewith low peripheral speed. Grinding-type machines employ mainly grinding and impactactions. They use low pressure with high peripheral speed. 2.4.1 Milling at Low Pressure with High Peripheral Speed In some milling systems the bran layers of the rice grains are removed by grinding action and an impact force, as grains come in contact with an abrasive roll. An abrasiveroll rotates on central shaft in perforated metal cylinder. Such systems are termedabrasive-type rice milling. typical high-speed abrasivetype-milling machine is shown in Fig. 9. Abrasive-type milling requires peripheral speed of over 6 /min, and an average milling pressure of less than 5 gf/cm 2(5 /m. 2.4.2 Milling at High Pressure with Low Peripheral Speed In other milling systems, frictional force and cutting force remove the bran layers. The grains are rubbed vigorously against each other and against the metallic surfaces of the milling chamber. The rice grains are enclosed in polygonal perforated metal enclosure in which rotating eccentric-milling roll agitates the grains and provides the pressure tobring about the frictional forces. Fig. 9 High-speed, abrasive-type rice-milling machine: grinding against an abrasive medium pro- vides the milling action. Rice Milling and Processing 3 Fig. 1 Typical low-speed, friction-type rice-milling machine: here milling takes place as result of frictional forces applied to the rice grains. Because friction is the major force of milling, this is termed friction-type