The V - flat drive comprises of one grooved pulley & one flat pulley. V - Flat drives are generally used where; under certain conditions intermittent loading & large moment of inertia have to be considered. The conversion from a flat drive to a V - flat drive is a relatively low cost exercise because of the presence of the existing flat pulley.
Prerequisites for a V - flat drive:
1) The smaller pulley should always be V - grooved pulley.
2) When using single belts, only classical belts are to be used because of higher top width to height ratio (1 : 6 : 1 )
3) Wedge belts should never be used on these drives because of their lower top width to height ratio (1 : 2 : 1 ), which makes these belts more vulnerable to turning on their sides.
4) Darwin Plus banded belts are more justifiable on these drives. The reinforced band over the belts provides the required lateral rigidity preventing the belt from turning over even under the extreme adverse conditions.
5) V- flat drives are economical when ? lies between 0.5 & 1.15
D a = outside diameter of flat pulley (mm)
d d = pitch diameter of grooved pulley (mm)
d a = outside diameter of grooved pulley (mm)
a = centre distance (mm)
The ideal drive is achieved when ? = 0.85
The design procedure for V - flat drive is similar to that of normal V belt drives, except that the arc of contact correction factor has to be modified.