CA1095269A - Rotary mower safety blade and method of making same - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A safety blade for a rotary lawn mower is provided herein. The blade comprises a homogeneous molded, vulcanized body of comminuted waste rubber and plastic fibers which is vulcanized about a central metallic bar with end portions extending beyond the bar. The central section including the metallic bar is formed with means for mounting the blade on the verti-cal drive shaft of a rotary mower. Each end portion extends beyond the metallic bar, and has a cutting edge and a lift on the opposite edge. Each end portion consists solely of the molded homogeneous body. Also disclosed is a method of making the blade. The molded vulcanized body of the blade so provided has a longer service life than such blades provided heretofore.
Moreover, the cutting edges provide a better cutting effect than ?n blades heretofore provided.

Description

The present invention relates to safety blades for rotary lawn mowers.
In United States Patent NO. 3,~11,653, a safety b]ade for rotary lawn mowers is disclosed. This patented blade comprises a central section and end portions. A pair of metallic bars are included in the central sec-tion and a body of rubber-like 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 other piror art devices~ it is believed that it presents two aspects which are sub;ect 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 posslble to attain. It is also believed that the cutting edges, being of the rubber-like materlal alone, do not have the best cutting effects which it is possible to achieve. They also are subJect to deterioration after long periods of use.
An ob~ect of an aspect o this invention is to provide a safety blade for a rotary lawn mower which includes a rubber-like body which is susceptible of a long servlce life and presents cutting edges of improved quality.
An object of another aspect of this invention is to provide in a safety blade of the type noted a homogeneous body comprising finely gr~und and c~mminuted waste rubber together with cut plastic fibers.
An ob~ect of yet another aspect of thls invention is to provide a safety mower blade of the character aforesaid comprising a central sec-tion and two end sections with the body being molded and vulcanized about a rigld metallLc bar, with the end sections extending beyond the ends of the bar and consisting only of the homogeneous body.

: .. .: ::: . ., . ;. . ;

,, '`' " ` '; '' `' .:
:` :: ,'` : :, . . .. : ~ , ' ' : :

s~"~

An object of a still further aspect of this invention is to provide in a rotary blade of the kind described end portions which have a cutting edge on one side and a lift on the opposite edge.
An ob~ect of another aspect of this invention is to provide in a rotary safety blade of the type noted a central section which is formed with means for connecting it to the vertical drive shaft of a rotary mower.
An object of a still further aspect of this inventon is to provide a novel method of making such a safety mower blade.
By a broad aspect of thls invention, an impsovemen~ is provided in a safety blade for rotary lawn mower, the blade comprising a central section having a rigid metallic bar embedded in the central section, and end por-tions, the improvement comprlsing ~a~ a homogeneous body of finely ground co~minuted, cleaned rubber intermi~ed with cut fibers of a syntlletic plas-tics copolymer in a proportion of 30% to 60~ of the rubber, the body being molded about, and vulcanized to, the metallic bar; (b) means on the central section for drivably mountihg the blade on the drive shaft of a rotary lawn mower; and (c~ each of the end portions extending beyond an end of the bar and formed with a cutting edge, each end por~ion consisting solely of the molded homogeneous body of the finely ground comminuted cleaned rubber and the cut fibers of the synthetic plastics copolymer.
i By one variant thereof, the cut fibers of a synthetic plastic co-; polymer are nylon.
By another variant, the blade is provided with a lift on each end portion at the side opposite to that formed with the cutting edge.
By another variant, the blade is provided with indicia on each end portion indicating portions which are to be removed therefrom to achieve a desired length in the blade; and including an inscription associated with the indicia indicating the maximum portion which can be removed.
By yet another variant, the means for drivably mounting the blade , .~,, z~ :

on thP drive shaft of a rotary mower comprises: a circular aperture at the center of the bar and a pair o~ keyho]e slots on opposite sides of the aper-ture; in which the body, in the central section, is formed with a stepped recess on each side of the central bar with each recess terminating in a membrane at the aperture; and in which keyhole recesses are provided in the body on opposite faces of the bar terminating in webs at the keyhole slots in the bar.
In more general terms, a lawn mower blade is provided comprising a central section and end portions extending from each end of the central section. A single rigid metallic bar is positioned longitudinally oi the central section and spaced from its side edges. A homogeneous molded vulcanized body derived from finely comminuted waste rubber and plastic fibers is molded about, and vulcanized to, the metallic bar, leaving the end portions consisting only of this homogeneous molded, vulcanized body.
Each such end portion hss a cutting edge on one side and may have a lift on the other side. Each end section may aslo be marked with indicia that is used in cutting off portions of the end sections to Eit the blade to a particular mower. The central section is formed with means ior drivably mounting the blade on the end of the vertical drive shaft of a rotary lawn mower.
By another aspect of this invention, an improved method is pro-vided in the manufacture of a safety blade for rotary lawn mowers, the blade includlng a central section and end portions with a rigid metallic bar em-bedded in the central section, the method comprising the steps of: (a) cut-ting and grindlng 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 fibers of synthetic plastic copolymer in a propor-; tion of 30% to 60% of the rubber-like mixture to the rubber; (c) mixing the comminuted rubber, the fibers of synthetic plastics copolymer and the solvent to provide a rubber-like mixture; (d) adding a vulcani~ing agent to .. . . . . . , . ~ , .

. , , , . .. , ~ . . .. . ~ .
" . .: . :.
,~
. . . . . ~.~
- ,. .: ~ ,. :

the rubber-like mixture to provide a further mixture; (e) add:Lng a plasti-cizer and a reaction accelerator to the further mixture; (f) mixing the materials in the further mixture; (g) pouring the further mixture into a mold a~out a metallic bar which has been placed therein; and (h) heat-ing under pressure to vulcanize the molded body so formed abou~ the bar and to provide the end protions which consist solely of the rubber-like mixtura.
By one variant, the method includes the step of adding a stabili-zer to the further mixture before it is-poured into the mold.
By another variant, the solvent is a hydrocarbonO
By a further variant, the cut fibers of synthetic plastic copoly-mer are nylon.
By another variant, the vulcanizing agent comprises sulphur, mag-nesium oxide and carbon black.
By still another variant, the plasticizer comprises used motor oil, in a proportion of 370-10% by weight of the total further mixture.
By yet another variant the reaction accelerator comprises zinc, in a proportion ranglng ~rom 2~-5% of the molded body, and stearic acid, in a proportiorl ranging from 1~-5% of the molded body.
By a further variantl the stabilizer comprises ethylene thiourea, ln a proportion ranging from 150-3%.
In more genera] terms, the 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 sol-vent agent is then added to the comminuted rubber. At this stage in the method, cut plastic fibers of the copolymer family are added and the mix-ture agitated to achieve a thorough intermixture. of the ingredients. The next step is to add a vulcani~ing agent e.g. sulphur or magnesium oxide to-gether with carbon black. A plasticizer is then added. While castor oil and glycerin are satisfactory, used motor oil is consldered the preferred plasti.izer. At this stage in the method, a reaction accelerator e.g. zinc and stearic acld is added. While it is not absolutely essential, a stabili-zer agent e.g. ethylene thiourea may be added. The mixture is then placed in a mold with a rigid metallic bar of the proper size and shape and is heated under pressure in the mold to bulcanize the homogeneous body about the bar to bond it thereto and to form the end protions with the cutting edges and lips.
In the accompanying drawings, Figure 1 is a perspective of a safety blade for rotary lawn mower made in accordance with the precepts of aspects 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;

- 5 a -L~

2~
Figure 4 is a detail cross-section through the blade taken about on the plane represen~ed by the line 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 of an aspect of this invention.
Referring now to the drawing~ wherein like reference characters denote corresponding elements throughout the several views7 and first more particularly to Figures 1-5, inclusive, the safety mower blade of an aspect 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 inc:Ludes a rigid metallic bàr 13~ with steel being a good example of the material from which bar 13 is made. Bar 13 is of elongated rectangular shape, presenting side edges 14, an~ edges 15, an upper face 16, and a lower face 17. As shown in Figure 2, side edges l4 are spaced inwardly from side edges of the blade, and as depicted in Fi~ure 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 the bar 13. As illustrated in ~igure 3, each end portion 12 has an upper face 18 and a lower face 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 cuttlng edge 20.
Blade 10 includes a homogeneous body made o cut and finely ground waste rubber ~hich is thoroughly lntermixed with cut fibers of a plastic of the copolymer famlly, of which nylon is an example. In this body, the cut plastic fibers are present in a proportion ranging from 30% to 60% of the body. This homogeneous body completely encases the bar 13 in the cen-tral sectlon 11 and forms the end portions 12. Thc cut plastic -. .

~ ' ' ::::,i :: :

z~

fiber~ impart abrasivP charac~eris~ics to the cutting edges 20 to increase their cutting effect6, and the homogeneous body of these materials imparts a long service life to the blade.
As shown more clearly in Figures 19 2, and 5~ each end portion 1~
i5 formed with indicia in the form of crosslines on the end portions. These cross lines are marked to indicate the particular length of a blade re-quired for a specific mower. ~le 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. The inner terminal line has an inscription associated therewith to indicate the maximum which may be severed from either end and still retain the origi~al function of the blade.
As particularly noted in Fig. 5, a preferred inscription is in the form of the words "safeline".--As Lllustrated in Figure 1, the rubber-like composition body is formed on both its upper and ~ower faces with a stepped circular recess 23 which terminates in a membrane 21 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 2~, 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, aper-ture 25, and keyhole-shaped recesses 26 constitute means for drivably mounting the blade 10 on the vertical drlve shaft of a rotary lawn mower.
In accordance with the method according to another aspect of this invention of making the above described safety blade, scrap rubber, chiefly including vehicle tire carcasses, is cut, ground or crushed into a finely divided commirluted state. This particular rubber is mixed with a detergent solution to remove mwanted 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 ' ~

; .
:,, : i ~. . . . -. :

tumbled at the rate of 8 :L5 revolutLons per minute for approxi~ately 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 solvent to 1 part rubber in the tumbling ~, ZO

:

,~

7 a -r~,P
V~6''~` `

~5~
drum The mixture is agita~ed in similar fashion for 30-35 minutes and the solvent i5 removed. At ~his point, cut plastic fibers of the ropolymer familyg of which nylon is an e~ample, is added in the proportion ranging from 30% to 60% of the complete body. The remaining rubber and the cut plastic fibers are then agitated for an additional 30 minutes. The solvent acts ~o 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. Also9 the solvent decomposes a great amount of the fibers with-in the rubber-like mass, making the rubber more susceptible to subsequent molding operations.
The rubber-like mass is then mixed with a vulcaniæing agent e.g.
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 molding. Although castor oil, glycerin and the like may be used as conventionally known, other petroleum-based agents may be employed. A unique feature of thls aspect of the present invent~on is the use of used motor oil in the amount of 3% to 10% of the rubber-like mass as a plasticizer.
At ]east one accelerating agent is also added to the mixture.
The accelerator acts to increase the heat due the chemical reaction during the molding process, thus hastening the overall reaction and re-vulcanizing.
Generally speaking, a pluralit~ of accelerating agents may be added, each active wlthin a separate temperature range~ Thus, the re-vulcanizing pro-cedure is hastened while the mass is heating in the mold as well as when the mass attains a steady state vulcanization temperature. Stearic acid in the amount of 1%-5% of the rubber-like mass by weigh~ is added to accelerate , :

~3 the reaction at low temperatures. Zinc oxide in the clmount 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 am~unt of 1%-2 by weight of the rubber-like mass may be added as an accelerator.
A stabilizer may also be added to the mixtu~e. Ethylene thiour~a in the clmount of 1%-3~ of the rubber-like mass by wei~ht is used for stabilizing pur~oses. As the addition of the stabilizer is a scm~lhat optional step, the final step of the method is to position a bar 13 in a ~Ola, and pour the muxture intD the m~ld where it is sub~ect to heat under pressure. This final step ~ay be taken either atter the stabilizer is added or, iE that step is omitted, a~ter the addition of the plasticizer and accelerator.

_ g _ :, ' ` '`. : `

Claims (13)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a safety blade for rotary lawn Mower, said blade compris-ing a central section having a rigid metallic bar embedded in said central section, and end portions, the improvement comprising (a) a homogeneous body of finely ground comminuted, cleaned rubber intermixed with cut fibers of a synthetic plastics copolymer in a proportion of 30% to 60% of said rubber, said body being molded about, and vulcanized to, said metallic bar;
(b) means on said central section for drivably mounting said blade on the drive shaft of a rotary lawn mower; and (c) each of said end portions extending beyond an end of said bar and formed with a cutting edge, each said end portion consisting solely of said molded homogeneous body of said finely ground comminuted cleaned rubber and said cut fibers of said synthetic plastics copolymer.

2. The safety mower blade of Claim 1 in which the cut fibers of a synthetic plastic copolymer are nylon.

3. The safety mower blade of Claim 1 together with a lift on each end portion at the side opposite to that formed with the cutting edge.

4. The safety mower blade of Claim 1 together with indicia on each end portion indicating portions which are to be removed therefrom to achieve a desired length in the blade, and including an inscription associ-ated with said indicia indicating the maximum portion which can be removed.

5. The safety mower blade of Claims 3 or 4 in which said means for drivably mounting said blade on said drive shaft of a rotary mower com-prises: a circular aperture at the center of said bar and a pair of keyhole slots on opposite sides of said aperture; in which said body, in said cen-tral section is formed with a stepped recess on each side of said central bar with each recess terminating in a membrane at said aperture; and in which keyhole recesses are provided in said body on opposite faces of the bar terminating in webs at said keyhole slots in the bar.

6. In the manufacture of a safety blade for rotary lawn mowers, said blade including a central section and end portions with a rigid metal-lic bar embedded in said central section, the method comprising the steps of:
(a) cutting and grinding scrap and waste rubber into a finely com-minuted state and cleaning the rubber;
(b) adding a solvent to said comminuted rubber and at the same time adding cut fibers of a synthetic plastic copolymer in a proportion of 30% to 60% of the said rubber-like mixture to said rubber;
(c) mixing said comminuted rubber, said fibers of synthetic plastics copolymer and said solvent;to provide a rubber-like mixture;
(d) adding a vulcanizing agent to said rubber-like mixture to provide a further mixture;
(e) adding a plasticizer and a reaction accelerator to said fur-ther mixture;
(f) mixing said materials in said further mixture;
(g) pouring said further mixture into a mold about a metallic bar which has been placed therein; and (h) heating under pressure to vulcanize the molded body so formed about said bar and to provide said end portions which consist solely of said rubber-like mixture.

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

8. The method of Claims 6 or 7 in which said solvent is a hy-drocarbon.

9. The method of Claims 6 or 7 in which said cut fibers of syn-thetic plastic copolymer are nylon.

10. The method of Claims 6 or 7 in which said vulcanizing agent comprises sulphur, magnesium oxide and carbon black.

11. The method of Claims 6 or 7 in which said plasticizer com-prises used motor oil, in a proportion of 3%-10% by weight of said total further mixture.

12. The method of Claims 6 or 7 in which said reaction accelera-tor comprises zinc, in a proprotion ranging from 2%-5% of said molded body, and stearic acid, in a proportion ranging from 1%-5% of said molded body.

13. The method of Claim 7 in which said stabilizer comprises ethylene thiourea, in a proportion ranging form 1%-3%.