Design Theories on Scoop-Surfaces of Rotary Blades for Tractors
1977 Volume 39 Issue 1 Pages 11-20
Details
1977 Volume 39 Issue 1 Pages 11-20
The scoop-surface of the sidelong blade (Fig. 1), which is equivalent to the share and moldboard of the plow, is one of the most important portions of the rotary blade. However, scoop-surface designing has a tendency to be done by only experience. In this paper the authors propose systematic design theories of the scoop-surface of the rotary blade tip, with the analysis of soil clod motion and blade cutting characteristics. Main results are listed as follows.
1. Avoiding the friction between the back surface of the scoop-surface and untilled, soil, the lower part of the scoop-surface has to have a small cutting angle to minimize the cutting resistance. The upper part of it has to have efficient throwing performance for soil clods that are already cut and possibly sheared by the lower part of it.
2. The necessary distance of the clod throw should be reasonable under the condition that the clods have no repetition of being beaten by the blades.
3. The scoop-surface is determined by the following equations in polar coordinate:
r=√(R-H)2+{√RA2-(R-H)2-(v+v0)t/-1/2αt2}2
θ=6nt+tan-1√RA2-(R-H)2-(v+v0)t-1/2αt2/R-H-tan-1√RA2-(R-H)2/R-H
where, R=radius of rotor, cm
RA=radius of the cutting edge point A (refer to Fig. 10), cm
H=depth of tillage, cm
v=forward velocity, cm/sec
v0-initial horizontal velocity of clods, cm/sec
α=horizontal acceleration of clods, cm/sec2
n=angular velocity of rotor, rpm
t=time, sec
4. The back-surface of the scoop-surface is determined by the equations (35) and (36). The scoop-surface is designed by adding the reasonably shaped edge of uniform thickness to the back-surface.
5. As it is generally the case that the vertical section of the scoop-surface can be simply circular, the radius of it is determined by the following equation:
Rs′=√(R-r1cos θ1)2+(r1sin θ1)2/2cos(ζ+tan-1r1sin θ1/R-r1cos θ1) (39)
where, r1, θ1=polar coodinate of a point on the back-surface
ζ=90°-β1(see Fig. 16)
β1=the angle between the back-surface and the radial direction at the edge point A0 (see Fig. 1)
