What does SPB-5 mean?
SPB is a widely used narrow-section V-belt (wedge belt) standard, with a belt top width of about 16 mm. 5 is the number of grooves: the pulley runs five SPB belts side by side. Five belts reliably transfer the main drive power of the roller mill from the motor to the roll pulley.
Why four diameters?
The diameter ratio between the motor pulley and the roll pulley sets the roll’s rpm. With the motor speed fixed, changing the motor pulley diameter is the most practical way to adjust roll speed. For example, on a mill with a 355 mm roll pulley:
- a 200 mm motor pulley gives the highest roll speed,
- 190 mm and 180 mm give intermediate values,
- 170 mm gives the lowest roll speed.
Roll peripheral speed is set by the milling engineer according to passage type, roll diameter and capacity target, so the pulley diameter should match the mill flow sheet.
What we need to choose correctly
- Motor speed and shaft diameter,
- Roll pulley diameter (e.g. SPB-5 355),
- Target roll speed or the diameter of the current pulley.
Installation and maintenance
All five belts should be replaced together and be matched (from the same set); belts of different lengths do not share the load evenly. Align the motor and roll pulleys in one plane and set tension with the motor slide rails. Polished grooves or belts bottoming in the grooves mean the pulley is due for replacement.
