GB2036524A - Rotary mower safety blade - Google Patents

Abstract

A safety blade for a rotary lawn mower comprises a homogeneous body of comminuted waste rubber and plastics fibres vulcanized about a central metallic bar 13 with end portions extending beyond the bar with each end portion having a cutting edge 20 and a lift 22 on the opposite edge. The central section including the metallic bar is formed with apertures 25, 27 for mounting the blade on the vertical drive shaft of a rotary mower. Also disclosed is a method of making the blade. Cross lines at the ends of blade indicate where the blade may be cut to suit it to particular mowers. <IMAGE>

Description

SPECIFICATION Rotary mower safety blade The present invention relates to mower safety blades and is concerned primarily with a blade having a homogeneous body of waste rubber and plastic fibres which is mounted about a central bar and has end portions in which the metallic bar is omitted and which are formed with cutting edges.

In United States Patent No. 3,911,653, there is disclosed a safety blade for rotary lawn mowers which is believed to be the closest approach to the instant invention. This patented blade comprises a central section and end portions. A pair of metallic bars are included in the central section and a body of rubberlike bonding material and layers of fabric are bonded about the metallic bars and extend through the end portions. Each of the end portions is formed with a cutting edge.

While this patented blade has proven to be highly satisfactory as compared to any prior art devices known at the time at which the application on which the patent issued was filed, it is believed that it pres ends two aspects which are subject to improvement.

Thus, the body of rubber-like material and fabric does not have as long a service life as it is believed to be possible to attain and it is also believed that the cutting edges, being of the rubber-like material alone, do not have the best cutting effects which it is possible to achieve. They are also subject to deterioration after long periods of use.

With the foregoing conditions in mind, the present invention has in view the following objectives; 1. To provide a safety blade for a rotary lawn mower which includes a rubber-like body which is susceptible of a long service life and presents cutting edges of improved quality.

2. To provide in a safety blade of the type noted a homogeneous body comprising finely ground and comminuted waste rubbertogether with cut plastic fibres.

3. To provide a safety mower blade of the character aforesaid comprising a central section and two end sections with the body being moulded and vulcanized about a rigid metallic bar, with the end sections extending beyond the ends of the bar and consisting only of the homogeneous body.

4. To provide in a rotary safety blade of the kind described end portions which have a cutting edge on one side and a lift on the opposite edge.

5. To provide in a rotary safety blade of the type noted a central section which is formed with means for connecting itto the vertical drive shaft of a rotary mower.

6. To provide a method of making a safety mower blade which fulfills the above objectives.

Various other more detailed objects and advantages of the invention such as arise in connection with carrying out the above-noted ideas and a practical embodiment will in part become apparent and in part be hereinafter stated as the description of the invention proceeds.

The foregoing objects are achieved by providing a lawn mower blade comprising a central section and end portions extending from each end of the central section. A single rigid metallic bar is positioned longitudinally of the central section and spaced from its side edges. A homogeneous body comprising finely comminuted waste rubber and plastic fibres is moulded about and vulcanized to the metallic bar, leaving the end portions consisting only of th is homogeneous body. Each end portion has a cutting edge on one side and a lift on the other side. Each end section is also marked with indicia that is used in cutting off portions of the end sections to fit the blade to a particular mower. The central section is formed with means for drivably mounting the blade on the end of the vertical drive shaft of a rotary lawn mower.

The above-described safety mower blade may be formed by the steps of first cutting and grinding reclaimed scrap or waste rubber into a finely comminuted state and then cleaning this rubber. A hydrocarbon solvent agent is then added to the comminuted rubber. At this stage in the process, cut plastic fibres of the copolymer family are added and the mixture agitated to achieve a thorough intermixture of the ingredients. The next step is to add a vulcanizing agent such as sulphur and magnesium oxide and carbonblack. A plasticizer is then added. While castor oil and glycerin are satisfactory, used motor oil is considered the preferred plasticizer. At this stage in the process, a reaction accelerator such as zinc and stearic acid is added. While it is not absolutely essential a stabilizer agent such as ethylene thiourea is added.The mixture is then placed in a mould with a rigid metallic bar of the proper size and shape and is heated under pressure in the mould to vulcanize the homogeneous body about the bar to bond it thereto and to form the end portions with the cutting edges and lips.

For a full and more complete understanding of the invention, reference may be had to the following drawings; in which; Figure 1 is a perspective of a safety blade for rotary lawn mower made in accordance with the precepts of this invention; Figure 2 is a top plan view of the blade with the body of the central section broken away above the metallic bar; Figure 3 is a detail in end elevation of each end of the blade; Figure 4 is a detail cross-section through the blade taken about on the plane represented by the line 4-4 of Figure 1; Figure 5 is a detail top plan of one end portion of the blade; and Figure 6 is a flow chart which diagrammatically illustrates the method.

Referring now to the drawing, wherein like reference characters denote corresponding elements throughout the several views, and first more particu marly to Figures 1-5, inclusive, the safety mower blade of this invention will be described.

The blade is designated in its entirety at 10. It comprises a central section 11 and end portions 12.

Central section 11 includes a rigid metallic bar 13 with steel being a good example of the material from which bar 13 is made. Bar 13 is of elongated rectan gularshape, presenting side edges 14, end edges 15, an upperface 16, and a lower face 17. As shown in Figure 2, side edges 14 are spaced inwardly from side edges of the blade, and as depicted in Figure 4, upper face 16 is spaced from the upper surface of the blade and lower face 17 is spaced from the bottom surface of the blade. As is more clearly brought out in Figure 2, end portions 12 extend beyond the ends 15 of bar 13. As illustrated in Figure 3, each end portion 12 has an upper face 18 and a lowerface 19. A cutting edge 20 is formed by an inclined surface 21 intersecting bottom face 19.A lift 22 extends at an angle upwardly from the surfaces 18 and 19 on the side of end portion 12 opposite to cutting edge 20.

Blade 10 includes a homogeneous body made of cut and finely ground waste rubber which is thoroughly intermixed with cut fibres of a plastic of the copolymer family, of which nylon is an example.

In this body, the cut plastic fibres are present in a proportion ranging from 30% to 60% of the body.

This homogeneous body completely encases the bar 13 in the central section 11 and forms the end portions 12. The cut plastic fibres impart abrasive characteristics to the cutting edges 20 to increase their cutting effects, and the homogeneous body of these materials imparts a long service life to the blade.

As shown more clearly in Figures 1,2 and 5, each end portion 12 is formed with indicia in the form of cross lines on the end portion. These cross lines are marked to indicate the particular length of a blade required for a specific mower. The blade is manufactured in standard maximum lengths and portions may be cut off along one of these cross lines to adapt the blade to a mower of a particular size.

As illustrated in Figure 1,the rubber-like composition body is formed on both its upper and lower faces with a stepped circular recess 23 which terminates in a membrane 24 which overlies a circular aperture 25 formed in bar 13. Each of the upper and lower faces of the body is also formed with a pair of keyhole-shaped recesses 26, the bottoms of which take the form of webs between the upper and lower surfaces of bar 13 and which are located at keyhole slots 27 in bar 13. The stepped recesses 23, aperture 25 and keyhole-shaped recesses 26 constitute means for drivably mounting the blade 10 on the vertical drive shaft of a rotary lawn mower.

In accordance with the method of making the above described safety blade, scrap rubber, chiefly including vehicle tyre carcasses, is cut, ground or crushed into a finely divided comminuted state. The particulate rubber is mixed with a detergent solution to remove unwanted residue. Typically, two parts of a synthetic commercial detergent is mixed with 100 parts of water in a tumbling drum to which 50 parts of comminuted rubber scrap is added. The mixture is tumbled at the rate of 8-15 revolutions per minute for approximately 1 hour and the water solution is removed.

A conventional hydrocarbon solvent is then added to the clean rubber in the proportion of 2 parts sol vent to 1 part rubber in the tumbling drum. The mixture is agitated in similar fashion for 30-35 minutes and the solvent is removed. At this point, cut plastic fibres of the copolymerfamily, of which nylon is an example, is added in the proportion ranging from 30% to 60% of the complete body. The remaining rubber and the cut plastic fibres are then agitated for an additional 30 minutes. The solvent acts to open the pores of the rubber particles, thus increasing the reacting surface area of the rubber mass and its ability to react to chemical additives. Also, the solvent decomposes a great amount of the fibres within the rubber-like mass, making the rubber more susceptible to subsequent moulding operations.

The rubber-like mass is then mixed with a vulcanizing agent such as sulphur or magnesium oxide and with carbon black, the latter increasing the ultimate strength of the finished product by promoting molecular cross-linking. Approximately, 10% to 25% carbon black is added to the rubber-like mass.

A plasticizer is also added to the mixture to soften the rubber and permit successful moulding.

Although castor oil, glycerin and the like may be used as conventionally known, other petroleumbased agents may be employed. A unique feature of the present invention is the use of used motor oil in the amount of 3% to 10% of the rubber-like mass as a plasticizer.

At least one accelerating agent is also added to the mixture. The accelerator acts to increase the heat due to the chemical reaction during the moulding process, thus hastening the overall reaction and re-vulcanization. Generally speaking, a plurality of accelerating agents may be added, each active within a separate temperature range. Thus, the revulcanization process is hastened while the mass is heating in the mould as well as when the mass attains a steady state vulcanization temperature.

Stearic acid in the amount of 1%-5% of the rubberlike mass by weight is added to accelerate the reaction at low temperatures. Zinc oxidein the amount of 2%-5% by weight of the rubber-like mass acts to accelerate the reaction when the mass reaches a higher temperature range. Diphenyl in the amount of 1%-2% by weight of the rubber-like mass may be added as an accelerator.

A stabilizer may also be added to the mixture.

Ethylene thiourea in the amount of 1%-3% of the rubber-like mass by weight is used for stabilizing purposes. As the addition of the stabilizer is a somewhat optical step, the final step of the process isto position a bar 13 in a mould, and pourthe mixture into the mould where it is subject to heat under pressure. This final step may be taken either after the stabilizer is added or, if that step is omitted, after the addition of the plasticizer and accelerator.

While a preferred specific embodiment of the invention is hereinbefore set forth, it isto be clearly understood that the invention is not to be limited to the exact construction materials and steps illustrated and described because various modifications of these details may be provided in putting the invention into practice.

Claims (13)

CLAIMS:

1. A safety blade for a rotary lawn mower which blade includes a central section and end portions, consisting of; (a) a rigid elongate metallic bar in said central sec tion; (b) a homogeneous body of finely ground comminuted rubber intermixed with cut plastic fibres of the copolymer family in a proportion ranging from 30%-60% of the body, said body being moulded about and vulcanized to said metallic bar; (c) each of said end portions extending beyond an end of said bar and formed with cutting edge; and (d) means on said central section of drivably mounting the blade on the drive shaft of a rotary lawn mower.

2. A safety mower blade according to Claim 1 in which the cut plastic fibres are nylon.

3. A safety mower blade according to Claims 1 or 2 having a lift on each end portion at the side opposite to that formed with the cutting edge.

4. A safety mower blade according to any of the preceding claims having indicia on each end portion indicating portions which are to be removed therefrom to achieve a desired length in the blade.

5. A safety mower blade according to any of the preceding claims in which the means for drivably mounting the blade on the drive shaft of a rotary mower comprises a circular aperture at the centre of said bar and a pair of keyhole slots on opposite sides of said aperture, said body in said central section being formed with a stepped recess on each side of the central bar with each recess terminating in a membrane at said aperture, and keyhole recesses in said body on opposite faces of the bar terminating in webs at the keyhole slots in the bar.

6. A method for the manufacture of a safety blade for rotary lawn mowers, said blade including a central section and end portions with a rigid metallic bar embedded in said central section, comprising the steps of; (a) cutting and grinding scrap and waste rubber into a finely comminuted state and cleaning the rubber; (b) adding a solvent to the comminuted rubber and at the same time adding cut plastic fibres of the copolymer family to the rubber; (c) mixing the comminuted rubber, plastic fibres and solvent; (d) adding a vulcanizing agent to the rubber-like mixture; (e) adding a plasticizer and a reaction accelerator to the mixture; (f) mixing the materials in the mixture; (g) pouring the mixture into a mould about a metallic bar which has been placed therein; and (h) Heating under pressure to vulcanize the body about said bar and provide said end portions, consisting solely of said rubber-like mixture.

7. The method of Claim 6 together with the step of adding a stabilizer to the mixture before it is poured into the mould.

8. The method of Claim 6 or 7 in which the solvent agent is a hydrocarbon.

9. The method of Claims 6,7 or 8 in which the cut plastic fibres are nylon.

10. The method of Claims 6, 7, 8, or 9 in which the vulcanizing agent is sulphur, magnesium oxide and carbon black.

11. The method of Claims 6 to 10 in which the plasticizer is used motor oil in a proportion of 3%-10% by weight of the total mixture.

12. The method of Claims 6 to 11 in which the reaction accelerator comprises zinc in a proportion ranging from 2%-5% of the body and stearic acid in a proportion ranging from 1%-5% of the body.

13. The method of Claim 7 in which the stabilizer is ethylene thiourea in a proportion ranging from 1%-3%.