The Delft Sand, Clay & Rock Cutting Model, 2019a

Rock Cutting: Atmospheric Conditions.
In the case of wear calculations the normal and friction forces on the front side and the wear flat can be interesting.
According to Evans the normal and friction forces are the same on both sides, since this was the starting point of
the derivation, this gives for the normal force Rn:
1
Rn
T h w cos
1
sin 2
(8-69)
The friction force Rf is now:
1
Rf
T h w sin
1
sin 2
(8-70)
8.3.4. Summary of the Evans Theory.
Figure 8-23: The model of Evans used for a pick point.
The Evans theory has been derived for 3 cases:
1. The basic case with a horizontal moving chisel and the centerline of the chisel horizontal.
2. A horizontal moving chisel with the centerline under an angle ε.
3. A pick point with the centerline angle ε equal to half the top angle α, horizontally moving.
Once again it should be noted that the angle α as used by Evans is half the top angle of the chisel and not the blade
angle as α is used for in most equations in this book. In case 1 the blade angle would be α as used by Evans, in
case 2 the blade angle is α+ε and in case 3 the blade angle is 2·α. In all cases it is assumed that the cutting velocity
vc is horizontal.
Copyright © Dr.ir. S.A. Miedema TOC Page 267 of 454