Note: Descriptions are shown in the official language in which they were submitted.
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RAZOR BLADE AND CARTRIDGE INCLUDING SAME
AND METHOD OF MAKING SAME
Background of the Invention
The invention relates to a razor blade, a cartridge including the razor
blade, and a method of making the razor blade.
Razor blade cartridges typically include plastic housings that are attached
to or made integral with a handle and have one or more fixed or movable razor
blades
mounted on the housing. The housing typically includes a guard structure in
front of
the blades that engages and stretches the skin in front of the blades and a
cap structure
behind the blades that slides over the skin. On razors, the blade tangent
angle for a
blade is defined as the angle made by a line drawn through the central
longitudinal axis
of the blade cross section and extending from the cutting edge of the blade,
and a
tangent line drawn between the top surfaces of the structures contacted by the
skin
immediately in front of the cutting edge and the tip of the cutting edge.
Blade
exposure is defined as the distance of the cutting edge above or below a
tangent Line
drawn between the top surfaces of the structures in front of and behind the
cutting
edge; the distance is measured normal to the tangent line.
Razor blades are typically sharpened and processed to provide the
desired shape and hardness prior to mounting on the housing. In one type of
razor
design, flat razor blade members having straight cutting edges are supported
on
L-shaped supports that are resiliently mounted on the housing.
In designing razor blade cartridges, it is desirable to provide a close
shave while avoiding nicks and cuts by adjusting such parameters as blade
sharpness,
blade tangent angle, and exposure. Slicing cuts typically occur when a
straight cutting
edge is inadvertently moved sideways (i.e., transverse to the usual upward or
downward
motion of the razor) on the skin such that the straight razor edge slices into
the skin.
This sideways movement can cause the blade edge to act as a knife cutting
cleanly
through the skin.
It is also desirable to provide general shaving comfort and overall
performance. It is also desirable to have a blade edge that has sufficient
strength to
survive the rigors of shaving and to provide confidence to the razor blade
designer that
the blade edge will not distort or deflect owing to the shaving forces applied
to the
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blade edge.
Summary of the Invention
In one aspect, the invention features, in general, a blade for a shaving
razor that has a nonlinear front cutting edge that is defined by a plurality
of waves
having crests and valleys extending above and below a transverse length axis.
The
nonlinear cutting edge is provided on a blade member that is generally flat
and has a
width along a width axis, a length along a transverse length axis, and smaller
dimensions along a thickness axis defined normal to both the length and width
axes.
The non-linear front cutting edge generally extends along the length axis, and
the
waves extend above and below the length axis in a direction that is parallel
to the
thickness axis.
Certain implementations of the invention may include one or more of the
following features. In certain implementations, the blade includes an "L-
shaped"
support under the blade member; the support is thicker than the blade member,
and
includes an upper portion to which the blade member is attached and an
extension
extending downward therefrom; the upper portion has a plurality of waves that
are
aligned with the waves of the blade member. The blade member has a length of
between 1 and 2 inches, and has between 2 and 24 waves (most preferably
between 6
and 18 waves). The waves have an amplitude between crests and valleys of less
than
0.012", preferably between 0.002" and 0.004", and most preferably about
0.003". The
blade member is made of metal between about 0.002" and about 0.010" thick,
preferably between about 0.003" and about 0.004" thick. The waves have an
amplitude
of distance between the crests and valleys that is between 50% and 150% of the
thickness of the metal, most preferably between 75% and 125% of the thickness.
The
waves preferably extend throughout the width of the blade member.
In another aspect, the invention features, in general, a blade with a wavy
blade member as has already been generally described, the waves having an
amplitude
of distance between crests and valleys selected to be greater than an
amplitude that
causes unnecessary cuts in the skin if the cutting edge is slid sideways on
the skin and
to be less than an amplitude that causes a decrease in shaving comfort when
compared
to a linear front cutting edge. Preferably the waves have an amplitude between
crests
and valleys of greater than 0.001 " and less than 0.012", most preferably
between 0.002"
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and 0.004".
In another aspect, the invention features, in general, a blade with a
strengthened wavy blade member as has already been generally described, the
strengthened blade member having a moment of inertia that is at least 20%
greater
(preferably at least 35% greater) than a moment of inertia for a flat, linear
edged, blade
member made of material having the same thickness as the strengthened blade
member
with waves.
In another aspect, the invention features, in general, a razor blade
cartridge including a housing and a blade with a nonlinear, wavy front cutting
edge as
has already been generally described.
Certain implementations of the invention may include one or more of the
following features. In certain implementations, the cartridge has a plurality
of blades,
and the waves in one blade member preferably are aligned with the waves in
another
blade member. The housing has connecting structure for connection to a handle
and
pivoting structure providing pivoting of the housing with respect to the
handle. The
connecting structure and the pivoting structure are provided by a structure
that provides
a pivotal connection between the cartridge and the handle. In some
implementations
the blade members are mounted on an upper portion of an "L-shaped" support
that also
has a downward extension that is slidably mounted within a slot in the
housing, the
upper portion having waves aligned with the waves in the blade member. In some
other implementations blades) may be fixedly mounted on a platform portion of
the
housing, and may be separated by a spacer.
In another aspect, the invention features, in general, a method of making
a blade that includes sharpening a generally flat blade member to form a
linear cutting
edge that extends along a length axis, and thereafter deforming the blade
member to
cause a nonlinear, wavy front cutting edge as has already been generally
described.
Certain implementations of the invention may include one or more of the
following features. In certain implementations, the blade member is mounted on
a
portion of a support prior to the deforming step, and both the blade member
and the
portion of the support underneath the blade member are deformed. The blade
member
is preferably mounted on the support by spot welds located at valleys or
crests
(preferably valleys) of the waves. The deforming includes bending between
opposed
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dies that preferably have nonmatching surfaces so as to provide regions for
material
flow of the blade member and the support portion thereunder during deforming.
The
dies have surfaces that cause three-point or four-point bending of the blade
member and
the support portion-thereunder.
$ Embodiments of the invention may include one or more of the following
advantages.
The provision of waves in the cutting edge of the blade can avoid "slash"
cuts that occur when a blade is accidentally side-slipped along the cutting
edge (length)
axis. Since the non-linear blade edge has an undulating edge, the edge, when
it side
slips, merely "scrapes" across the skin without slicing into the skin.
In addition, hairs being cut can be subjected, in successive strokes, to
different portions of the blade having different blade tangent angles,
potentially
providing for a closer cutting of hairs with varying orientation. The wavy
nature of the
blade may provide for better skin engagement and skin-stretching, and, in the
case of a
two or three blade system, the first blade functions as a front guard for a
blade behind
it.
The wavy nature of the blade and/or its support additionally strengthens
the blade structure and promotes blade stiffness, reducing uncontrolled blade
edge
flexure which may cause unpredictable or variable blade contact angles and/or
exposure
with the surface of the skin.
Other advantages and features of the invention will be apparent from the
following description of the preferred embodiments thereof and from the
claims.
Brief Description of the Drawings
Fig. 1 is a perspective view of a razor blade.
Fig. 2 is a plan view of the Fig. 1 blade.
Fig. 3 is a partial elevation of the Fig. 1 blade.
Fig. 4 is a vertical, sectional view of the Fig. 1 blade prior to bending.
Fig. 5 is a vertical, sectional view of a razor blade cartridge including
two blades as shown in Fig. 1.
Fig. 6 is a vertical, sectional view of an alternative razor blade cartridge
including an alternative razor blade.
Fig. 7 is a diagram showing a press and fixturing system used to provide
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waves in the Fig. 1 blade.
Fig. 8 is a partial elevation showing the die portions for providing
three-point bending in the Fig. 7 system.
Fig. -9 is a partial elevation showing the die portions for providing
four-point bending in the Fig. 7 system.
Fig. 10 is a graph (not drawn to scale) showing the height of a blade
member versus length for a single wave of a hypothetical blade member having
waves
that follow a sine curve.
Fig. 11 is a front view showing the alignment of valleys and crests of
waves of cutting edges in front and back blades of the Fig. 5 cartridge.
Fig. 12 is an front elevation of the blade member of the
Fig. 1 blade.
Description of the Preferred Embodiments
Referring to Figs. 1-3, there is shown razor blade 10 including blade
member 12 and angled support 14. Blade member 12 is generally flat and has a
width
along width axis W, a length along transverse length axis L, and smaller
dimensions
along thickness axis T that is normal to width axis W and length axis L.
Support 14
has upper portion 16 to which blade member 12 is preferably attached by
thirteen spot
welds 18. Support 14 also has elongated extension 20 thereunder.
Blade member 12 has a nonlinear front cutting edge 13 that generally
extends along length axis L and preferably is defined by twelve waves 15
having crests
and valleys extending above and below length axis L in a direction that is
parallel to
thickness axis T. Waves 15 extend rearward from front cutting edge 13 parallel
to each
other preferably over the entire width of blade member 12. Upper portion 16
has
twelve waves 17 corresponding to and aligned with waves 15. The valleys of the
waves occur at spot welds 18. Waves 15, 17 are smooth and have crest to valley
amplitudes below 0.012", preferably between 0.002" and 0.004", and most
preferably
about 0.003". The amplitude of 0.003" is believed to be sufficiently high to
provide
good protection against "slash" sideways cuts but not so high as to cause
undue
discomfort or irritation and propensity to cause nicks and cuts during normal
up and
down shaving strokes. The amplitude also yields acceptable overall shaving
comfort
values as compared to flat blades based upon shave tests and accepted
statistical
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analysis. It is believed that a value of crest to valley amplitude greater
than 0.001 " provides a
minimum level of protection against sideways slash cuts and that values about
0.012" will
result in undue irritation. As shown in Fig. 3, there is a slight gap 19
between blade member 12
and upper portion 16 owing to spot welds 18 therebetween.
Fig. 4 shows undeformed blade 10' including flat blade member 12' and support
14' prior to forming. Blade member 12' is preferably made of 0.003 " or 0.004"
thick razor
blade quality stainless steel which is martensitic and has a uniform thickness
section with a
width "d" of about 0.033 " and a sharpened portion extending in front for a
dimension "c" of
about 0.012". Upper portion 16' preferably has a dimension "b" of 0.0325 ".
Support 14' is
made of 0.011 " thick stainless steel. Extension 20' of support 14' extends
downward from
upper platform 16 a distance of 0.0596".
Referring to Fig. 5, razor blade cartridge 22 has housing 24 with arcuate
surface
26 for providing a pivotal shell type bearing connection to a razor handle
(not shown). Housing
24 supports two movable blades 10 in respective slots 25 in the side walls of
the housing.
Blades 10 are biased upward to the positions shown in Fig. 5 by spring members
28. The crests
80 and valleys 82 of cutting edge 13 of the first blade 10 are preferably
aligned with the crests
80 and valleys 82 of the cutting edge of the second blade 10 in order to avoid
regions of
excessive exposure that could cause undue nicking (see Fig. 11). Cartridge 22
also has flexible
fin guard member 30 in front of the blades and lubricating strip 32 at cap
section 34. U. S.
Patent No. 4,498,357 describes such a moving-blade cartridge design.
Referring to Fig. 6, alternative razor blade cartridge 40 includes two fixed
blades
42 on sandwiched platform support 44. Cartridge 40 also has guard member 46
and cap
member 48. Blades 42 have waves of the same shape and amplitude as blade
member 12, and
the crests and valleys of the two blades are aligned. U. S. Patent No.
4,026,016 describes such a
fixed blade, cartridge design.
In manufacture, blade member 12' is preferably sharpened, coated, and sintered
according to techniques well-known in the industry to obtain undeformed blade
10' as shown in
Fig. 4. U.S. Patents Nos. 3,652,443; 3,761,374; and 3,829,969, for example,
describe such
techniques. The blade member 12' is preferably secured to support upper
portion 16' by laser
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spot welding, as described in U.S. Patent No. 4,379,219.
Refernng to Figs. 7-9, an undeformed blade 10' is formed in apparatus 49
between upper die 52 and lower die 50 to provide waves 15 and 17 (Fig. 3).
Portion 16' of
support 14' (Fig. 4) is supported on lower die 50. Upper die 52 is moved
downward toward
and contacts blade member 12'. With continued downward movement of upper die
52 toward
lower die 50, blade member 12' and upper portionl6' are deformed, resulting in
waves 1 S and
17 extending throughout the width of blade member 12' and the underlying area
of upper
portion 16', respectively. Upper die 52 continues downward until it reaches
stop 54, which
determines the amount of maximum deflection of blade member 12' and upper
portion 16' .
Upper die 52 is then raised, and blade 10' elastically returns to
approximately 50% of the
maximum deflected value. Thus, a maximum die deflection of amplitude of about
X0.003",
which corresponds to a crest to valley amplitude of about 0.006 ", results in
a preferable final
crest to valley wave amplitude of about 0.003 ".
Opposed dies 50 and 52 have nonmatching surfaces so as to provide regions for
1 S material flow during forming of undeformed blade member 12' and undeformed
upper support
portion 16' into formed blade member 12 and formed upper support portion 16.
In particular,
referring to Figs. 8 and 9, upper die 52 is used with lower die 50 (Fig. 8)
for three-point
bending, and upper die 52 is used with lower die 50' (Fig. 9) for four-point
bending. Three-
point or four-point bending is used to permit material flow during the
deflection and
deformation process and to permit forming of upper portion 16' while extension
20' remains
flat. In both cases, upper die 52 has thirteen semi-circular ridges 56 with
center-to-center
spacing of 0.119 ", a depth "e" of 0.0453 ", a radius 72 of 0.0315 ", and a
small flatter central
portion 85 of radius 73 of 0.069" having an arc segment length of about 0.001
". Lower die SO
(Fig. 8) has twelve circular ridges 60 with center-to-center spacing of 0.119
", a depth "~" of
0.0358", a radius 74 of 0.0596", and a flat space "g" between ridges of
0.0096". Lower die 50'
(Fig. 9) has 24 ridges 62 having center-to-center spacing of 0.595 ", a depth
75 of 0.0178 ", a
radius 76 of 0.0298", a small flatter area 64 with a radius 77 of 0.0535"
having an arc segment
length of about 0.001 ", a flat spacing between ridges "h" of
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0.0048", and a base dimension "i" of 0.0547". Ridges 56, 60, and 62 extend
parallel to
each other over a distance at least as long as the width of blade member 12'.
In the
three-point bending of Fig. 8, the three contact points for bending the waves
in the
blade edge for each wave are provided by an upper ridge 56 and the two lower
ridges
60 on both sides. In the four-point bending of Fig. 8, the four points of
contact for
forming each wave are provided by two upper ridges 56 and the two lower ridges
62
between them. In both types of bending, spot welds 18 are located in the
valleys under
semicircular ridges 56 in order to provide better control of the amplitude of
deflection
and to provide for a stiffer structure.
Referring to Fig. 12, in the current preferred system, the distance 78
between successive wave crests is set at 0.1 I9", and the preferred crest to
valley wave
amplitude is about 0.003". With three point bending (Fig. 8). the resulting
non-linear
wave edge has a wave crest radius RI of slightly more than the 0.0596" radius
74 of
ridge 60 and a wave valley radius R2 of slightly more than the 0.0315" radius
72 of
ridge 56, owing to the release of the deflected blade member after the maximum
die
deflection. Because the radius of ridge 60 is about twice the radius of ridge
56, the
resulting crests and valleys have a ratio RI/R2 of about 2:1. With the four
point
bending of Fig. 9, the formation of a single wave crest around two ridges 62
results in
approximately the same crest radius R1; approximately the same valley radius
R2 is
caused by ridges 56. Thus, four-point bending with the apparatus of Fig. 9
also results
in a ratio R1/R2 of about 2:I. The crests and valleys could also have a ratio
RI/R2 of
about I:1 (this can be described by a sine wave) or of about 1:2. Preferably
the ratio
R1/R2 is between 0.5 and 2. Four-point bending is preferred over three-point
bending.
Blades 10 (Fig. 5) and blades 42 (Fig. 6) are formed using similar dies.
When the resulting blades are mounted on a housing, they have varying
blade tangent angles along their lengths. During shaving, with successive
strokes over
the same skin area, different portions along the length of blade 10 or 42 will
engage
the same hair. By subjecting the hair to blade portions having different blade
tangent
angles, closer shaving can result.
The use of waves in the blade can avoid "slash" cuts that occur when a
blade is accidentally side-slipped along the cutting edge axis; slash cuts can
be
problems with women shavers in particular. The wavy nature of a blade can also
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provide for better skin flow management, and the first blade can act as a
better guard
for the second blade behind it in two or three blade systems. This is because
the
effective contact length with a wavy cutting edge on the skin is substantially
longer
than with a flat blade, thus providing more points of contact in stretching
the skin.
The waves also make the blade member a stiffer structure which is
subject to less bending during shaving, tending to better maintain designed
exposures
and blade tangent angles during shaving than flat blade counterparts (i.e.,
made of the
same thickness material). The increased strength provided to blade member 12
by the
wavy structure can be estimated by assuming that the wave follows a sine curve
and
calculating and comparing moments of inertia (which determine the blade
stiffness and
resistance to deflection) for the wavy blades and the weaker undeformed flat
blades.
Referring to Fig. 10, the following formula can be used to describe the
location of a
midline through the blade member 12, Y~, as a function of length, x, and the
upper
surface Y~ + h/2, and the lower surface, Y~ - h/2:
Y" _ ~ sin 2'~~ x ; Yn + (hl2); Yn - (hl2
)
where: ~ = 1 /2 the crest to valley wave amplitude,
1 = wavelength, and
h = blade thickness.
The moment of inertia, Ix~, for the wavy blade can be calculated as follows:
(yn + hl2)
1~= f~y'dA= fx f y'dydx=h31+h~21
(y" - hl2) 12 2
The moment of inertia for a flat sheet (without waves) can be calculated as
follows:
Flat Blade (~=O): Ixx - h'1
12
The change in moment of inertia, and thus the additional blade stiffness,
caused by
forming the waves in an initially flat blade is given by the following
formula:
OBlade Stiffness (per unit length):
Olz, = I,~(wavy) - I~(flat) = h~2
2
The ratio of the moment of inertia for a wavy blade to the moment of inertia
for a flat
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blade is given by the following formula:
ABlade Stiffness Ratio: R = Ixz(wavy) = I + 6 (~)~ -
I lflat) h
These formulas were used to calculate the moments of inertia for a wavy blade
member
(having a crest to valley amplitude of 0.003") and a flat blade member (used
as a
control) for two thicknesses, 0.003" and 0.004". The results of the moment of
inertia
calculations, the ratio of the moment of inertia for a wavy blade member to
that for the
flat blade member, and the % increase of moment of inertia of the wavy blade
member
over that of the flat blade member are presented below in Table 1.
TABLE 1
Calculations
of Blade
Stiffness
(Moment
of Inertia
per Unit
Length):
Wavy
vs. Control
Blades
Flat Edges
h I
Thickness
0.004 5 . 3 3
3 x 10-9
0.003 2.25 x 10-9
Wavy Blade
h I Ratio o I %Increase
thickness1/2 wave (I(wavy)/ I wavy
amplitude I (flat) over
I flat
0.004 0.0015 9.833 x 1.844 4.5 x 10-9 84.4%
10-9
0.003 0.0015 5.625 x 2.500 3.375 x 150.%
109 10-''
From the above table it is seen that the moment of inertia for a wavy
blade of 0.004" thickness increases 84.4% over that of a flat blade of the
same
thickness, and for a wavy blade of 0.003" thickness the moment of inertia
increase is
150%. It thus appears that the added stiffness provided by the wave shape can
be
particularly significant for blade members made of the thinner 0.003" thick
metal.
In multiple blade systems (such as shown in Fig. 5 or Fig. 6), it is
preferable to align the crests 80 and valleys 82 of the f rst blade with the
crests 83 and
valleys 84 of the second blade, respectively, as shown in Fig. 11.
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Other embodiments of the invention are within the scope of the
appended claims. E.g.; the waves could be provided at only the front portion
of blade
member 12, and, instead of extending parallel to each other perpendicular to
the front
cutting edge, the waves could alternately converge and diverge as they extend
rearward
from the front edge. Also, in multiple blade systems, the crests and valleys
can be
unaligned with one another.
