Flour mills are the most important flour-making equipment. Manual and fully automatic flour mills are the products of development in the mid-20th century. In China, in the 1970s, manual and automatic flour mills began to be widely used. A flour mill consists of two parts: feeding and milling (roller). The so-called manual flour mill refers to a mill where the feeding part cannot control the automatic clutch of the milling part, and it is necessary to manually clutch the milling part (roller). Manual flour mills are limited to mills with a roller length of 600mm and an outer diameter of 250mm or less, such as FM2235, 2240, 2250, 2560, etc. Fully automatic flour mills refer to mills with a roller length of 400mm and an outer diameter of more than 250mm. Fully automatic flour mills have gone through the process of hydraulic, pneumatic, to electrical control, that is, the mill has achieved automatic control from feeding to grinding.
In the 1980s in China, MY-type hydraulic flour mills were mass-produced, which use gravity sensors (branch valves) in the feed bucket to obtain material signals. Mechanical levers transfer the mechanical signals to the hydraulic part, and the hydraulic mechanism performs the opening and closing of the feed hooper size and the action of feeding through levers, while controlling the clutch of the roller. This type of feeding system can alleviate the imbalance between the feeding amount and the material entering the mill, but it requires high manufacturing precision, hence the cost is relatively high. The actuating mechanism of the flour mill is a hydraulic system, which has a complex structure and is not easy to maintain. The material level signal is transmitted by the branch valve through a lever, and these parts have a lot of dust, so they have become invalid.
Entering the 1990s, the hydraulic control system was gradually replaced by the pneumatic control form. The feeding control system of the pneumatic flour mill is composed of a gravity-type sensor to detect the material level signal, and the feeding amount is adjusted by the pneumatic servo mechanism to control the gap of the feed door. The principle of pneumatic control is basically the same as that of hydraulic control, but the former's feeding control system has better performance in adjusting the feeding amount than the latter, with the advantages of being clean, oil-free, and having a higher degree of automation. However ，its sensitivity is still not enough to ensure the dynamic balance between the feeding amount and the material entering the mill, and it is difficult to avoid the instability of the process and quality caused by automatic disconnection and running empty due to material interruption. In the mid-to-late 1990s, the feeding control method of flour mills gradually shifted towards electrical control. The material level detection and feeding amount adjustment devices of the electrically controlled feeding automatic control system are both of an electrical nature. This type of feeding automatic control system consists of a material level sensor, a feed roller speed adjustment mechanism, and a control device. Based on the signal detected by the electronic material level sensor, the feeding amount is finely adjusted by regulating the speed of the feed roller through a frequency converter. This control method has a high degree of automation, is easy to centrally control, and has intelligence, making it a more ideal control method.
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