GB2176683A

GB2176683A - Rotary lawn mower blade

Info

Publication number: GB2176683A
Application number: GB08515833A
Authority: GB
Inventors: George Lucas
Original assignee: Individual
Current assignee: Individual
Priority date: 1985-06-21
Filing date: 1985-06-21
Publication date: 1987-01-07
Also published as: GB8515833D0

Abstract

A blade for a rotary lawn mower has a cutting edge which is sinusoidal in plan and tapers in traverse section, and one face of the blade is spray coated with tungsten carbide at the cutting edge. <IMAGE>

Description

SPECIFICATION Rotarylawn mower blade The invention relates to blades for so-called rotary lawn mowers, that is to say those mowers in which the blade rotates in a plane parallel orsubstantially parallel to the surface to becut.

Blades as known hitherto are reasonably satisfac tory for the trimming ofshort grass but experience shows that they are less effective when thegrass is long and particularly when it is also wet oF includes moss. In such conditions the torque experienced by the blade drive tends to be excessive resulting in overloading of the source of rotary motion, conven tionally an electric motor or petrol engine, as well as resulting in an unevenly cut lawn. Conventional blades tend rapidly to become blunt, and this also increases the load on the drive.

Morever, blades as used hitherto are found to be very susceptible to damage by impact with stones, and one object of the presentinventionin oneof its aspects is to avoid this problem.

According to one aspect of my invention there is provided a blade for a rotary lawn mowerwherein the cutting edges, beingthe leading edges in relation to the rotary motion of the blade, are provided with a plurality of indentations. Preferably the indentations are rectilinear and each maycomprisetwo edges inclined inwardly each at about 60" to the leading edge and a third edge parallel to and set back from the leading edge. Each of the edges comprising the cutting edge is sharpened by tapering the thicknessof the blade from one face, and the other face of the blade may be provided with a layer of material ha harder than the blade itself. Preferably-the layer is provided by spray coating with tungsten carbide. The coating may have a thickness of about 5,000 of an inch.

According to a further aspect of the invention there is provided a blade for a rotary lawn mower in which the tips of the leading edges are notsharpened but are rounded in plan to withstand impact with stones.

Embodiments ofthe invention willnow be be de- scribed, by way of example, with reference to the accompanying drawings of which: Figure 1 shows respectively at A, B, and C a plan view, a side elevation and an end elevation of one end of a conventional blade for a rotary lawn mower; Figure 2 shows respectively atA, B, and C a plan view, side view and end elevation of one end of a blade according to the invention in one embodiment; and Figure 3 shows at A, B, and C in planview, side elevation and end elevation a blade according to a further embodiment ofthe invention.

As shown in Figure 1 the conventional blade has straight parallel edges, a leading edge 1 and a trailing blade to a cutti ng edge 6 as shown more pa rticularly ir Figure 1 C.

In contrast to the conventional blade as shown in Figurei,thebladesshownin Figures 2and 3 have cutting edges which are provided with multiple indentations. The blade shown in Figure 2 is formed o a flat-plate of steel having a straighttrailing edge 92 and a generally parallel leading edge 19, but the leading edge 19 eomprises a cutting edge portion 11 through plurality of indentationsl3.

Each indentation comprises edge portions 14 inclined towards one another and each at an angle of 60 to the general line of the leading edge, theedge portions 14 leadingto a further edge portion 15 parallel to and set backfrom the generality of the leading edge 19.

Each ofthe edge portions 14 and 15 istaperedfrom one facet a chisel edge 16 as shown more particularly in Figure 2C and the face 17 oftheblade, a at leastthat portion of the face 17 adjacentthechisel edges 16 is faced with a layer of tungstencarbide, about 5,000 of an inch thick, applied by spraying. The purpose ofthe layer oftungsten carbide is to reduce the wearonthe cutting edge.

Swill be seen from Figure 2 the indentations 13 stop short oftheend ofthe blade, and the terminal portion 18 ofthe leading edge 19 is nottapered in section but is rounded in plan view. This construction provides that any stones encountered inthe approacl of the rotating blade will tend to contact the portion ii which is less susceptible of damagethan if it, like the edge portions 14 and 15, were sharpened.

In the embodiment shown in Figures 3, the indentations 23 in the leading edge 21 are curvilinear rather than angular, but in other respects the construction ol the blade is similar to that shown in Figures 2. Thusth blade has an unsharpened tip to the leading edge 21.

Moreover, asisthe case with the embodiment shown in Figure 2, the portion ofthe leading edge which is sharpened is longerthan is generally found in conventional blades.

1. A blade for a rotary lawn mower of which the cutting edges, being the leading edges in relation to the intended rotary motion of the blade, are generally sinusoidal in plan.

2. A blade according to Claim 1 wherein at least the major portion of each cutting edge is sharpened b tapering from one face of the blade, the other face being provided with a surface layer of materiai harden than the material underthe surface.

3. A blade according to Claim 2 wherein the surface layer is provided by spray coating with tungsten carbide.

4. A blade according to any of the preceding claims wherein the tip of each leading edge is not

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Rotarylawn mower blade The invention relates to blades for so-called rotary lawn mowers, that is to say those mowers in which the blade rotates in a plane parallel orsubstantially parallel to the surface to becut. Blades as known hitherto are reasonably satisfac tory for the trimming ofshort grass but experience shows that they are less effective when thegrass is long and particularly when it is also wet oF includes moss. In such conditions the torque experienced by the blade drive tends to be excessive resulting in overloading of the source of rotary motion, conven tionally an electric motor or petrol engine, as well as resulting in an unevenly cut lawn. Conventional blades tend rapidly to become blunt, and this also increases the load on the drive. Morever, blades as used hitherto are found to be very susceptible to damage by impact with stones, and one object of the presentinventionin oneof its aspects is to avoid this problem. According to one aspect of my invention there is provided a blade for a rotary lawn mowerwherein the cutting edges, beingthe leading edges in relation to the rotary motion of the blade, are provided with a plurality of indentations. Preferably the indentations are rectilinear and each maycomprisetwo edges inclined inwardly each at about 60" to the leading edge and a third edge parallel to and set back from the leading edge. Each of the edges comprising the cutting edge is sharpened by tapering the thicknessof the blade from one face, and the other face of the blade may be provided with a layer of material ha harder than the blade itself. Preferably-the layer is provided by spray coating with tungsten carbide. The coating may have a thickness of about 5,000 of an inch. According to a further aspect of the invention there is provided a blade for a rotary lawn mower in which the tips of the leading edges are notsharpened but are rounded in plan to withstand impact with stones. Embodiments ofthe invention willnow be be de- scribed, by way of example, with reference to the accompanying drawings of which: Figure 1 shows respectively at A, B, and C a plan view, a side elevation and an end elevation of one end of a conventional blade for a rotary lawn mower; Figure 2 shows respectively atA, B, and C a plan view, side view and end elevation of one end of a blade according to the invention in one embodiment; and Figure 3 shows at A, B, and C in planview, side elevation and end elevation a blade according to a further embodiment ofthe invention. As shown in Figure 1 the conventional blade has straight parallel edges, a leading edge 1 and a trailing blade to a cutti ng edge 6 as shown more pa rticularly ir Figure 1 C. In contrast to the conventional blade as shown in Figurei,thebladesshownin Figures 2and 3 have cutting edges which are provided with multiple indentations. The blade shown in Figure 2 is formed o a flat-plate of steel having a straighttrailing edge 92 and a generally parallel leading edge 19, but the leading edge 19 eomprises a cutting edge portion 11 through plurality of indentationsl3. Each indentation comprises edge portions 14 inclined towards one another and each at an angle of 60 to the general line of the leading edge, theedge portions 14 leadingto a further edge portion 15 parallel to and set backfrom the generality of the leading edge 19. Each ofthe edge portions 14 and 15 istaperedfrom one facet a chisel edge 16 as shown more particularly in Figure 2C and the face 17 oftheblade, a at leastthat portion of the face 17 adjacentthechisel edges 16 is faced with a layer of tungstencarbide, about 5,000 of an inch thick, applied by spraying. The purpose ofthe layer oftungsten carbide is to reduce the wearonthe cutting edge. Swill be seen from Figure 2 the indentations 13 stop short oftheend ofthe blade, and the terminal portion 18 ofthe leading edge 19 is nottapered in section but is rounded in plan view. This construction provides that any stones encountered inthe approacl of the rotating blade will tend to contact the portion ii which is less susceptible of damagethan if it, like the edge portions 14 and 15, were sharpened. In the embodiment shown in Figures 3, the indentations 23 in the leading edge 21 are curvilinear rather than angular, but in other respects the construction ol the blade is similar to that shown in Figures 2. Thusth blade has an unsharpened tip to the leading edge 21. Moreover, asisthe case with the embodiment shown in Figure 2, the portion ofthe leading edge which is sharpened is longerthan is generally found in conventional blades. CLAIMS