Roller mills are an important part of the brewing process. So, what is the core component of a roller mill? How does the roller mill affect the finished beer? Let’s take a look!
(1) Material of grinding rollers
The grinding roll of a grain mill is a chilled hard cast iron, made by a centrifugal casting process. The surface of the rollers has an extremely high degree of hardness. The diameter of the rollers is about 250 mm. The diameter should not be too small, otherwise the grain-containing angle (the grain-containing angle formed on the surface of the rollers) is too small and the crushing capacity is reduced.
(2) Surface treatment of the grinding roller
The surface of the roller is divided into two kinds, one is flat roller and the other is brushed roller. For the multi-roller mill with vibrating screen, the first and second pair of grinding rollers are mostly flat rollers, and the others are brushed rollers.
The grooved rolls are not parallel to the axis of the rolls. They have a certain edge tilt angle (beveled groove), which enhances the rolling effect until shearing occurs. The taper of both rolls is always the same, between 4% and 14%.
(3) Speed of the rollers
The speed of smashing rollers is different, the speed of driving wheel is high, and the speed of driven wheel is low. The speed ratio of stretching roller is about 2.5:1; the speed ratio of flat roller is about 1.25:1.
The speed of the rolls is: pre-roll, 400-420r/min; wheat roll, 400r/min; coarse roll, 380-440r/min. The length of the rolls is usually 0.8-1 m; especially 0.4 m for small crushers; extra large crushers can reach 1.5 m.
(4) Roller clearance
The roller gap is steplessly adjusted between 0-2.5mm. The clearance of the four-roller mill is generally 1.5-1.5mm for the pre-roller clearance and 0.3-0.6mm for the coarse grain roller clearance.
Roller parallelism adjustment. The parallelism of the rolls is a prerequisite for uniform shredding. When adjusting the shredder, check the roll parallelism by inserting a feeler or a card that must be inserted vertically into the shredder.
(5) Roll drive
One roller is fixedly mounted to run on a conveyor belt, and the other roller is fixed to a spring that runs together. If a hard object is present, it will not seriously damage the rollers. In modern shredding systems, some shredders are equipped with separately driven rollers.
Modern shredders can have a capacity of up to 14t/h and can finish a pot in one hour. The power requirements for fine shredders are. 2.3-2.5 kW for hearth crushers and 3.3-3.8 kW for filter crushers.