Application Guide

63-7062 46
VFD Features Used
— Digital or analog speed control.
— Stall prevention.
— Forward - reverse.
— Variable torque.
— Overtorque trip.
IMPORTANT
Existing safety limits must not be altered.
Screw Press (See Fig. 55)
To Process
Dry Product
Wet Product
Screw Press
Variable
Pitch Pullies
Motor
37kW
Manual
Adjustment
Mechanism
Fig. 55. Screw press application.
Application Description
A screw press is used to reduce the moisture content of a wet product. This application was used on a whisky distillery in
Scotland. The product was the left over malted barley, after having the moisture removed by the screw press, it is then dried
and used in cattle feed. Conventional control uses a set of mechanically variable pitch pulleys. The operator fixes the speed of
the screw in order to meet the process requirements. However, differences in the wetness of the mixture means that the end
product suffers from inconsistency. The mechanical speed variation is also unreliable and wear can take place thus changing
the speed with respect to the adjuster position.
Modification
Replace the variable pitch pulleys with fixed pulleys (selected for the correct ratios), install VFD and vary speed electronically.
Benefits
— No mechanical speed variation to wear or brake-increased reliability and consistent control.
— Speed control can be automated since the VFD can be easily connected to a product sensor measuring wetness, thus
providing closed loop control.
— Reduced possibility of damage to the screw press since the VFD can be programmed to maintain a fixed torque or to trip if
overtorque conditions occur.