Note: Descriptions are shown in the official language in which they were submitted.
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.
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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
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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
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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
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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;
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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
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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
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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
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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
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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.
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