GB2081062A

GB2081062A - Serrated blade for a mowing machine

Info

Publication number: GB2081062A
Application number: GB8025049A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1980-07-31
Filing date: 1980-07-31
Publication date: 1982-02-17
Also published as: GB2081062B; FR2488484A1; FR2488484B1; DE3029647A1; DE3029647C2

Abstract

A serrated blade for a mowing machine has a plurality of fingers 4 arranged at regular intervals around the circumference of an imaginary circle 5, and a plurality of sawteeth 2 provided between each pair of adjacent fingers 4. The sharp-pointed ends of the sawteeth 2 lie on a substantially circular arc which has a smaller radius of curvature than the imaginary circle, and is eccentric thereto, so that on one side of each of the fingers the circular arc defined by the ends of the sawteeth is radially recessed relative to the associated finger. <IMAGE>

Description

SPCIFICATION Serrated blade for a mowing machine The present invention relates to a serrated blade for a mowing machine.

So far, buzz saws for cutting lumber have been used for mowing. The trouble is that the sawteeth become blunt or break off as soon as they touch hard objects, such as pebbles, during the mowing operation. Those who mow the grass with buzz saws, therefore, are compelled to take utmost care not to have the sawteeth touch hard objects. Because of this worry, sufficient efficiency is not obtained.

It is an object of the present invention to provide a serrated blade which obviates the above-described drawback.

According to the present invention, there is provided a serrated blade to be mounted on a mowing machine, having a plurality of fingers arranged at regular intervals along the circumference of an imaginary circle and a plurality of sawteeth provided between the adjacent fingers. The sharp-pointed ends of the sawteeth form a substantially circular arc which has a smaller radius of curvature than the imaginary circle and is eccentric thereto so that each of the fingers has a beveled shoulder on one side.

In order that the present invention may be more clearly understood, reference will now be made to the accompanying drawings, in which: Fig. 1 is a top view of a first embodiment of the present invention; Fig. 2 is an enlarged top view of a part thereof; Fig. 3 is a top view of a second embodiment of the present invention; and Figs. 4 to 8 are top views of third to seventh embodiments of the present invention, respectively.

Referring now to Fig. 1, a serrated blade 1 in accordance with a first embodiment of the present invention is made of a plain sheet steel and provided with a plurality of fingers 4, which are arranged at regular intervals around the circumference of an imaginary circle 5. Each finger 4 has a circumferential edge 6 which lies upon the circumference of the circle 5.

Apluralityofsawteeth 2 are provided between adjacent fingers 4 in such a manner that the sharppointed ends of the sawteeth 2 lie on a substantially circular arc. Each circular arc formed by the sharppointed ends of the sawteeth is eccentric to the cir cle 5 by an angle of &commat;, 8. that each circular arc extends from a cusp 7 of one finger to the beveled opposite edge 8 of an adjacent finger 4.

Each sawtooth 2 is provided with a cutting edge 3, which faces an opposed cutting edge 9 provided on the beveled edge 8 of the finger 4. Each cutting edge 3 is substantially perpendicular to a line drawn tangentially to the circular arc at the sharp-pointed end of the sawtooth 2. Consequently, each cutting edge 3 sweeps forward by an angle of 8 relative to the radius 10 of the circle 5 which passes or is coincident with the sharp-pointed end of the cutting edge 3.

Referring now to Fig. 3, showing a second embodiment, a serrated blade 1 is provided with a plurality of sawteeth 2a and 2b between adjacent fingers 4 in such a manner that the sharp-pointed ends of the sawteeth 2a and 2b form two circular arcs, respectively, which have smaller radii of curvature than the circle 5 and are eccentric thereto so that both of the two circular arcs fall within the circle 5. Each sawtooth 2a or 2b is provided with a cutting edge 3a or 3b in such a manner that the cutting edges 3a provided on the sawteeth 2a forming one circular arc face the cutting edges 3b provided on the sawteeth 2b forming the other circular arc. Each cutting edge 3a or 3b is substantially perpendicular to a line drawn tangentially to the circular arc at the sharppointed end of the sawtooth 2a or 2b.Consequently, each cutting edge 3a sweeps forward by an angle of 81 relative to the radius 10a of the circle 5 which passes the sharp-pointed end of the cutting edge 3a, and each cutting edge 3b sweeps forward by an angle of 02 against the radius 10b of the circle5 which passes or is coincident with the sharppointed end of the cutting edge 3b.

While the serrated blades shown in Figs. 1, 2, 4, 5, 6,7 and 8 are intended to be rotated in a clockwise direction in a mowing operation, the serrated blade shown in Fig. 3 can be rotated in either direction.

In operation, the serrated blade 1 is fixed to the tip of the rotary shaft of a mowing machine. The serrated blade 1 begins to rotate when the mowing machine is switched on. During the mowing operation, most of the hard objects such as pebbles are knocked away by the circumferential edges 6 and hardly come in contact with the sawteeth 2. When the serrated blade 1 touches a hard object sticking fast to the ground, it produces a high-pitched sound or emits sparks, at which signal the mowing operation has only to be suspended so that the sawteeth 2 may be protected from becoming blunted or damaged.

Mowing machines which are in general use at pre sent have a rotational speed of 80 to 150 r.p.s., which is equivalent to 60 to 110 m/s in terms of the peripheral velocity of the serrated blade 1. On the other hand, the serrated blade 1 is usually moved from side to side or back and forth at a speed of 2 to 4 m/s. A hard object, such as a pebble, comes into the circle 5 in a direction reverse to the direction of the resultant velocity which is the sum of the above-mentioned two velocities.Because of the fact that the diametrical component of this resultant velocity is incomparably smaller than the tangential component the diametrical distance by which a hard object can come into the circle 5 is generally as short as 1.5 to 4 mm, depending upon the diameter of the circle 5, the number of fingers 4, and the length of the circumferential edge 6. The diametrical distance by which a hard object can come into the circle 5, which is designated by the letter a in Fig. 2, is equivalent to the depth of damage which may be sustained by each finger 4 during the mowing opera The drawing(s) originally filed was/were informal and the print here reproduced is taken from a later filed formal copy.

tion. The depth a is in inverse proportion to the number of fingers 4.

Damage sustained by each finger 4 was investi gated in mowing experiments made with the serrated blade 1 having six fingers 4 and six sawteeth 2 between each of the adjacent fingers 4. The damage took the form of a rounding of the corner or cusp 7 of each finger 4 as shown by a dotted line 11 in Fig. 2. The depth a amounted to approximately 2 mm, 3.5 mm and4to5mm after, 1-, 3-, and 6-hour continuous operation, respectively. Thereafter, the depth a hardly increased, while the sawteeth 2 began to be slightly worn away probably by the sand sticking to the parts nearthe roots of grass.

The serrated blade embodying the present invert tion remains sharp even after use for a long period of time. Its life is more than 20 times as long as that of the conventional serrated blades. This is because the sawteeth 2 are provided in the recessed positions.

The grass is securely caught and cut by the cutting edges 3 because each cutting edge 3 substantially forms an angle of advance of 8 with respect to a radius 10 which passes or is coincident with the sharp-pointed end of the cutting edge 3.

While several embodiments of the present invention have been disclosed, it is to be understood that they have been described by way of example only, and that various modifications may be made.

Claims

1. A serrated blade for a mowing machine, having a plurality of fingers arranged at regular intervals along the circumference of an imaginary circle and a plurality of sawteeth provided between each of the adjacent two of said fingers in such a mannerthat the sharppointed ends of said sawteeth form a substantially circular arc, characterized in that each of said fingers has a circumferential edge which lies upon the circumference of said imaginary circle, that said circular arc formed by the sharp-pointed ends of said sawteeth between each adjacent two of said fingers has a smaller radius of curvature than said imaginary circle and is eccentric to said imaginary circle so that each of said fingers has a recess on one side, that each of said sawteeth is provided with a cutting edge on the opposite side of each of said fingers, and that said cutting edge is substantially perpendicular to a tangent to said circular arc at the sharp-pointed end of each of said sawteeth.

2. A serrated blade to be mounted on a mowing machine, having a plurality of fingers arranged at regular intervals along the circumference of an imaginary circle and a plurality of sawteeth provided between adjacent two of said fingers in such a marr ner that the sha rppointed ends of said sawteeth form two circular arcs, characterized in that each of said fingers has a circumferential edge which lies upon the circumference of said imaginary circle, that said two circular arcs formed by the sharp-pointed ends of said sawteeth between adjacent two of said fingers have smaller radii of curvature than said imaginary circle and are eccentric to said imaginary circle so that both of said two circular arcs fall within said imaginary circle, that each of said sawteeth is provided with a cutting edge in such a manner that the cutting edges provided on the sawteeth forming one circular arc face the cutting edges provided on the sawteeth forming the other circular arc, and that said cutting edge is substantially perpendicular to a tangent to said circular arc at the sharp-pointed end of said each of said sawteeth.

3. A serrated blade for a rotary mowing machine, substantially as hereinbefore described with reference to Figures 1 and 2, or with reference to any one of Figures 3 to 8, of the accompanying drawings.

4. A mowing machine having 2 serrated blade as claimed in claim 1,2 cur3.