Trimmer line for string trimmers
A novel monofilament trimmer line is provided for reducing noise, reducing air drag and increasing durability by having a non-round cross-sectional shape defined as a polygon with three to six sides wherein the vertices between adjacent sides have been replaced with generous circular arcs, the arcs of a parabola, or even other arc shapes so long as the arc is convex and contains no sharp edges and wherein each arc is tangent to the two adjacent sides with a smooth and continuous transition, and the sides of the polygon are either straight or slightly convex, but not concave.
1. A twist trimmer line for use with a powered rotary trimmer device comprising:
a filament body having a non-circular cross-sectional shape comprising at least three distinct sides wherein each of the sides is convex, the filament body having a longitudinal axis,
wherein the filament body further comprises vertices equal in number to the number of distinct sides, the vertices being located where adjacent distinct sides converge and comprising a convex arc contour, each convex arc contour forming a smooth and continuous convex transition with the sides adjacent thereto,
wherein the cross-sectional shape has an area of from 2.92 to 4.34 mm 2 and a diameter of a circle circumscribing the cross-sectional shape is from 1.2 mm to 4.5 mm,
wherein the filament body is fixedly twisted about its longitudinal axis, such that each of the vertices follows a helical path along a length of the filament body, and
wherein the filament body forms the twist trimmer line and is configured to cut vegetation when rotated in a powered rotary trimmer device.
2. The trimmer line as claimed in claim 1 , wherein the non-circular cross-sectional shape further comprises a polygon having three to six vertices.
3. The trimmer line as claimed in claim 1 , wherein the convex arc contours of the vertices comprise circular arcs or the arcs of a parabola.
4. The trimmer line as claimed in claim 1 , wherein each convex arc contour has a radius R, and the ratio of the radius (R) to the diameter of a circle capable of circumscribing the cross-sectional shape of the filament body (D) falls within the range of 0.05 to 0.30.
5. The trimmer line as claimed in claim 4 , wherein the ratio of an arc radius (R) to the diameter of a circle circumscribing the cross-sectional shape of the filament body (D) is about 0.20.
6. The trimmer line as claimed in claim 4 , wherein the filament body is fixedly twisted rotated about its longitudinal axis at a rate of between about 0.75 inches to about 3.00 inches of trimmer line per full 360 degree revolution of the filament body.
7. The trimmer line as claimed in claim 1 , wherein the filament body is fixedly twisted rotated about its longitudinal axis at a rate of between about 0.75 inches to about 3.00 inches of trimmer line per full 360 degree revolution of the filament body.
8. The trimmer line as claimed in claim 1 , wherein the filament body is fixedly twisted about its longitudinal axis at a rate of not more than one full 360 degree revolution of the filament body per 0.75 inches of trimmer line.
9. The trimmer line as claimed in claim 7 or 6 , wherein the filament body is fixedly twisted about its longitudinal axis at a rate of between about 1.6 and 1.7 inches of trimmer line per full 360 degree revolution of the filament body.
10. The trimmer line as claimed in claim 1 , wherein each convex arc contour does not exceed 50 % of the distance between the side and a circle circumscribing the cross-sectional shape of the filament body when measured at a mid-point of the side.
11. The trimmer line as claimed in claim 10 , wherein each convex arc contour is 33% of the distance between the side and a circle circumscribing the cross-sectional shape of the filament body when measured at a mid-point of the side.
12. The trimmer line as claimed in claim 10 , wherein the sides of the cross-sectional shape are free of convex grooves.