Roller mills play a crucial role in the beer brewing process. So, what is the main component of a roller mill? How does it impact the final beer product? Let’s find out!
Material of Grinding Rollers
The grinding rolls of a grain mill are made of chilled hard cast iron using a centrifugal casting process. The roller surfaces have an extremely high degree of hardness. The diameter of the rollers is approximately 250 mm. It shouldn’t be too small, as a smaller diameter reduces the grain-containing angle on the roller surface and diminishes the crushing capacity.
Surface Treatment of the Grinding Rollers
The roller surface can be categorized into two types: flat rollers and brushed rollers. In multi-roller mills with vibrating screens, the first and second pairs of grinding rollers are typically flat, while the remaining ones are brushed.
The grooved rolls are not parallel to the roll axis. They have an inclined angle (beveled groove), which enhances the rolling effect until shearing occurs. The taper of both rolls is always the same, ranging from 4% to 14%.
Roller Speed
The smashing rollers rotate at different speeds, with the driving wheel having a higher speed and the driven wheel a lower speed. The stretching roller has a speed ratio of approximately 2.5:1, while the flat roller has a speed ratio of about 1.25:1.
The roll speeds are as follows: pre-roll – 400-420r/min, wheat roll – 400r/min, coarse roll – 380-440r/min. The length of the rolls usually ranges from 0.8-1 m, with small crushers having a length of 0.4 m and large crushers reaching up to 1.5 m.
Roller Clearance
The roller gap can be continuously adjusted between 0-2.5mm. For four-roller mills, the pre-roller clearance is typically 1.5-1.5mm, while the coarse grain roller clearance is 0.3-0.6mm.
Adjusting Roller Parallelism: Ensuring parallelism of the rolls is essential for uniform shredding. When adjusting the shredder, the roll parallelism is checked by inserting a vertically positioned feeler or card into the shredder.
Roller Drive
One roller is fixed and operates on a conveyor belt, while the other roller is fixed to a spring and runs alongside it. In the presence of a hard object, the rollers are not significantly damaged. In modern shredding systems, some shredders have independently driven rollers.
Modern shredders can have a capacity of up to 14t/h and can complete a batch 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.
