Miller Magazine Issue: 116 August 2019

61 COVER STORY MILLER / AUGUST 2019 In flour mills; milling, grinding and crushing pro- cesses occur in roller mills. There are two roll systems within those machines: feeding rolls and grinding rolls. Those systems are integrated into a single machine body. Those machines may have various features depending on models and cus- tomer demands. They are controlled either manu- ally or by PLC or electronic card systems. Density of the raw material is checked through sensors, load cells etc. Speed control device checks the motor and adjust the speed of feeding rolls in or- der to spread incoming raw material on the grind- ing surface better. Grinding rolls are rapidly moved against each other by the help of the pneumatic system when the raw material comes from the feeding system. When the amount of the raw material decreas- es, grinding rolls move away from each other and feeding system stops. There is also a sensor un- der the grinding roll to stop the system in order to prevent stuck of the rolls in case of a full load. Feeding and grinding rolls are monitored through a rotation monitor. The automation system halts the process when an uncontrolled slowdown oc- curs with pulley speeds and protects belts and other components of the machine from break- ing down. Roller bearing temperatures are also tracked and if a value above the threshold level is noticed, the system is stopped and an alert is given. Central automatic lubrication system per- forms the adequate level of lubricating in order to prevent human error. Features described above are implemented in a similar or different way by manufacturers. Roll- er mills can be sold within complete and turnkey projects or as individual machines. They are con- trolled via MCC panels (see Image 2 and Image 3) on the control units. As the number of rolls and KW values of motors increase, the importance of control systems for electrical circuit and automa- tion also increases. Earthing is vital in order to protect electronic components of the machine. Feeding and grind- ing roll motors and roller bodies must be earthed. Inexperienced and untrained individuals should not be let to get close to the machine. Emer- gency stop button on the control panel is also vital for safety of people. When trying to solve the problems with rolls, people often intervene man- ually to rolls and belts. Therefore, the master and the machine operator should have a clear com- munication. After the operation is completed and roller coverings are closed, the machine should be cranked. The emergency stop button is the key for all those processes. It prevents from un- controlled operations. (Image 1) There are some features to be present on MCC panel for machines to be run better and for an extended period of time: • Earthing of the panel and earthing connec- tions for motor cables. • Discharge fans for decreasing the tempera- ture within the panel. • Voltage tracking, halting the system when phase loss or extreme voltage values are spotted. • Choosing the copper bars within the panel according to specific needs. • Stopping feeding motors when machines without by-pass feature within the grinding part of the mill stops. • Stopping only feeding motors for grinding part stopovers and preventing unnecessary halt- ing and running actions for grinding motors and preventing overcurrent. • Connection between start and emergency stop buttons on the roller control system with MCC panel. • Condensation system. (See Image 4) Capaci- tors balance phase shifting of the current (COSØ) and voltage that stems from the structure of the motor and enables using the energy with the most efficient and effective way. Motors can gain more power with less current. The electricity al- ways chooses the easiest way. Capacitors help protecting motors and other systems from possi- ble harmonic and peaks from electricity network and increase energy efficiency. Image 1