U.S. patent application number 11/636868 was filed with the patent office on 2007-06-14 for automated control of razor blade colorization.
This patent application is currently assigned to The Gillette Company. Invention is credited to Joseph A. DePuydt, Adam Kelsey, Alfred Porcaro, Kenneth J. Skrobis.
Application Number | 20070131060 11/636868 |
Document ID | / |
Family ID | 37951801 |
Filed Date | 2007-06-14 |
United States Patent
Application |
20070131060 |
Kind Code |
A1 |
Kelsey; Adam ; et
al. |
June 14, 2007 |
Automated control of razor blade colorization
Abstract
Methods of and systems for automated color control are provided.
These methods and systems are suitable for use in various oxidation
processes for the coloration of heat treated steel, for example
razor blade steel. A feedback loop (closed loop control) is
established, including the steps of measuring color, comparing the
measured color to a target color and quantifying the difference
there-between, and, if the difference exceeds a predetermined
threshold, adjusting a color adjustment parameter, e.g., the
airflow to the oxidation zone, so that the measured and target
colors are equivalent or within a predetermined variance.
Inventors: |
Kelsey; Adam; (Newton,
MA) ; Skrobis; Kenneth J.; (Maynard, MA) ;
Porcaro; Alfred; (Everett, MA) ; DePuydt; Joseph
A.; (Quincy, MA) |
Correspondence
Address: |
THE PROCTER & GAMBLE COMPANY;INTELLECTUAL PROPERTY DIVISION - WEST BLDG.
WINTON HILL BUSINESS CENTER - BOX 412
6250 CENTER HILL AVENUE
CINCINNATI
OH
45224
US
|
Assignee: |
The Gillette Company
|
Family ID: |
37951801 |
Appl. No.: |
11/636868 |
Filed: |
December 11, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60750962 |
Dec 14, 2005 |
|
|
|
Current U.S.
Class: |
76/104.1 |
Current CPC
Class: |
G01N 21/31 20130101;
B26B 21/60 20130101; C21D 1/76 20130101; C23C 8/02 20130101; C23C
8/10 20130101; C21D 9/561 20130101; C21D 11/00 20130101; C23C 8/80
20130101 |
Class at
Publication: |
076/104.1 |
International
Class: |
B21K 11/00 20060101
B21K011/00 |
Claims
1. A process for manufacturing a razor blade comprising: an
automated feedback loop, measuring a color parameter of a blade
steel strip exiting a coloration process, comparing the measured
color to a target color and quantifying the difference
there-between, and, if the difference exceeds a predetermined
threshold, adjusting a color adjustment parameter so that the
measured and target colors are equivalent or within a predetermined
variance.
2. The process of claim 1 wherein the coloration process includes
passing the steel strip through an oxidation zone, and the color
adjustment parameter comprises air flow rate in the oxidation
zone.
3. The process of claim 1 wherein the measuring step comprises
measuring the reflection spectrum of the blade steel.
4. The process of claim 3 wherein the color parameter is the
maximum or minimum value of the reflection spectrum.
5. The process of claim 3 wherein the measuring step is performed
using a spectrometer.
6. The process of claim 2 wherein the adjusting step comprises
using a mass flow controller to adjust the air flow.
7. The process of claim 1 wherein the coloration process comprises
a thermal oxidation process or a reduction/re-oxidation
process.
8. The process of claim 7 wherein the thermal oxidation process or
reduction/re-oxidation process are part of the steel hardening
process.
9. The process of claim 1 wherein the quantification of the
difference is performed by a processor.
10. A system for automated control of razor blade color comprising:
a spectrometer configured to measure the reflection spectrum from
the blade steel as it exits the colorization process, a controller
configured to adjust a parameter of the colorization process, a
processor configured to determine a parameter associated with the
measured reflection spectrum, calculate the difference between the
measured parameter and a predetermined target value, and, if the
difference is above a predetermined threshold, send a voltage to
the mass flow controller, and a hardening furnace equipped with an
oxidation zone.
11. The system of claim 10 wherein the parameter is the wavelength
of the minimum reflected light (.lamda.hd min) or maximum reflected
light .lamda..sub.max) of the reflection spectrum or higher order
minimums or maximums.
12. The system of claim 10 wherein the controller includes a mass
flow controller configured to either increase or decrease the flow
of oxidizing gas to the oxidation zone, such that the target value
is approached.
13. The system of claim 11 wherein the oxidizing gas comprises
clean, dry air.
14. The system of claim 11 wherein the oxidizing gas is mixed with
an inert carrier gas to decrease system response time.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional
Application No. 60/750,962, filed Dec. 14, 2005.
FIELD OF THE INVENTION
[0002] This invention relates to the field of razor blades and
processes for manufacturing razor blades and more particularly to
automated control of razor blade color in such processes.
BACKGROUND OF THE INVENTION
[0003] Razor blades are typically formed of a suitable metallic
sheet material such as stainless steel, which is slit to a desired
width and heat-treated to harden the metal. The hardening operation
utilizes a high temperature furnace, where the metal may be exposed
to temperatures greater than 1100.degree. C. for up to 10 seconds,
followed by quenching. After hardening, a cutting edge is formed on
the blade. The cutting edge typically has a wedge-shaped
configuration with an ultimate tip having a radius less than about
1000 angstroms, e.g., about 200-300 angstroms. Various coatings may
be applied to the cutting edge. For example, hard coatings such as
diamond, amorphous diamond, diamond-like carbon (DLC) material,
nitrides, carbides, oxides or ceramics are often applied to the
cutting edge or the ultimate tip to improve strength, corrosion
resistance and shaving ability. Interlayers of niobium or chromium
containing materials can aid in improving the binding between the
substrate, typically stainless steel, and the hard coatings. A
polytetrafluoroethylene (PTFE) outer layer can be used to provide
friction reduction.
[0004] It is important that these coatings be applied, and any
other post-hardening processing steps be performed, under
sufficiently low temperature conditions so that the hardened,
sharpened steel is not significantly tempered. If the steel is over
tempered it will lose its hardness and may not perform properly
during use.
[0005] Examples of razor blade cutting edge structures and
processes of manufacture are described in U.S. Pat. Nos. 5,295,305;
5,232,568; 4,933,058; 5,032,243; 5,497,550; 5,940,975; 5,669,144;
EP 0591334; and PCT 92/03330, which are hereby incorporated by
reference.
[0006] Razor blades may include a colored coating, i.e., a coating
having a color different from the color of the underlying blade
material. The term "colored" as used herein, includes all colors,
including black and white. The colored coating provides a desirable
aesthetic effect, without deleteriously affecting the performance
or physical properties of the blade. The color of the razor blades
can be color-coordinated with the color of the housing of a razor
cartridge or the handle or other components of a shaving system. In
some preferred implementations, the coating covers substantially
the entire blade surface, enhancing the aesthetic effect and
simplifying manufacturing. The coatings are durable, exhibit
excellent adhesion to the blade material, and can be produced
consistently and relatively inexpensively.
[0007] Razor blades can be colored during a steel hardening process
by using techniques such as (a) thermal oxidation of the blade
steel, or (b) reduction and controlled re-oxidation of a hard metal
oxide surface coating, e.g., titanium dioxide, provided on the
blade steel. To reduce costs, decrease scrap, and achieve color
quality and control, these two techniques require an automatic
color control process and tooling.
[0008] The thermal oxidation technique includes subjecting a blade
material to a hardening process; and, during the hardening process,
exposing the blade material to clean dry air in order to form an
oxide layer on its surface. The method also includes quenching the
blade material, after the oxidizing step, to initiate martensitic
transformation of the blade material, and forming the hardened
blade material into a razor blade, the oxide layer providing the
razor blade with a colored surface. Preferred methods do not
deleteriously affect the final properties of the blade.
[0009] The reduction and controlled re-oxidation of a hard metal
oxide surface coating blade coloration process involves applying a
layer of hard metal oxide and/or metal oxynitride, e.g., titanium
oxide, and/or other transition metal oxides including zirconium,
aluminum, silicon, tungsten, tantalum, niobium, iron, and mixtures
thereof to a sheet of soft blade steel, e.g., by physical vapor
deposition (PVD), plasma enhanced chemical vapor deposition
(PECVD), or other deposition technique, in a layer of uniform
thickness. For this coloration process, the hardening operation
includes subjecting the metal oxide coated blade material to a
hardening process; and, during the hardening process, reducing the
oxygen content in the existing metal oxide or oxynitride coating
and then re-oxidizing the oxide through exposure of the coating to
a controlled amount of clean dry air in proportion to the targeted
final coating color. This method also includes quenching the blade
material, after the re-oxidation step, to initiate martensitic
transformation of the blade material, and forming the hardened
blade material into a razor blade. Preferred methods do not
deleteriously affect the final properties of the blade.
[0010] The thermal oxidation technique includes passing the blade
material through a tunnel oven consisting of two zones. The first
zone is used to austenize the blade steel and to remove any native
oxide coating. This first zone contains mainly hydrogen and
nitrogen. A second zone of the tunnel oven, referred to as the
oxidation zone, which follows directly after the first zone, is
used to oxidize the stainless steel strip surface. The first zone
has temperatures near 1100.degree. C. throughout most of its
length. Temperatures near the exit of the first zone, just prior to
the oxidation zone, reduce the temperature of the blade material
from over 1100.degree. C. during austenization to less that about
800.degree. C. as it enters the second zone. The available oxygen
in the oxidation zone of the tunnel oven can be controlled by
controlling the amount of dry air and nitrogen fed to this zone. By
controlling the available oxygen to the oxidation zone, the color
of the oxide film formed may be targeted and controlled. After the
oxidized steel passes through the oxidation zone of the tunnel
oven, by means of water cooled quench blocks, the martensitic
quenching is initiated. The hardening process results in
martenization of the blade material.
[0011] The thermal oxide blade coloration processes described above
allow a decorative oxide film to be grown on blade steel during the
hardening process, after austenization and prior to the martensitic
transformation. If, instead, the blade steel were colorized using a
thermal oxide coloration process prior to the hardening process,
the color would generally be degraded during the standard hardening
process. If a thermal oxide coloration process were employed after
the martensitic transformation, it would generally destroy the
martensitic properties of the stainless steel strip. The processes
described above generally provide highly adherent, protective
oxides, while allowing excellent color control and without
detrimentally impacting the metallurgic properties of the hardened
stainless steel blade strips.
[0012] The reduction and controlled re-oxidation of a hard metal
oxide surface coating blade coloration and hardening technique
includes passing the blade material through a tunnel oven
consisting of two zones. The first zone is used to austenize the
blade steel and to reduce the oxide coating. This first zone
contains mainly hydrogen and nitrogen. A second zone of the tunnel
oven, which follows directly after the first zone, is used to
re-oxidize the coating. The oxygen partial pressure in the second
zone of the tunnel oven can be controlled independently of the
ambient conditions in the first zone ofthe tunnel oven. By
controlling the oxygen partial pressure in the second zone of the
tunnel oven, the desired color of the oxide film may be further
targeted and controlled. After the coated steel passes through the
second zone of the tunnel oven, by means of water cooled quench
blocks, the martensitic quenching is initiated. The hardening
process results in martenization of the blade material.
[0013] The reduction and re-oxidation blade coloration processes
described above allow a decorative transition metal oxide film to
be specially modified (colorized) during the hardening process of a
martensitic stainless steel. If a decorative transition metal oxide
film is colorized prior to the hardening process, it would
generally be degraded during the standard hardening process. If a
coloration process were employed after the martensitic
transformation, it would either destroy the martensitic properties
of the stainless steel strip, or would require extensive
temperature control and special material handling. The processes
described above generally provide highly adherent, protective
oxides, while allowing excellent color control and without
detrimentally impacting the metallurgic properties of the hardened
stainless steel blade strips.
[0014] In both methods of producing colored blades described above,
thermal oxidation of the blade steel and reduction and controlled
re-oxidation of a hard metal oxide surface coating, the color
arises from thin film interference between the partial reflectance
of light from the air/oxide interface and the reflectance of light
from the oxide/steel interface. Constructive interference occurs
when the reflected light from one interface combines in phase with
the reflected light from the other interface, producing brightness.
Destructive interference occurs when the reflected light from the
interfaces combines out of phase, producing darkness. The optical
phase difference between reflected light from each interface
depends on the optical path length, OPL, through the oxide thin
film. The OPL is given by OPL=2n.sub.fd cos.theta., (1) where
[0015] n.sub.f=refractive index of the thin film
[0016] d=thickness of thin film
[0017] .theta.=angle the incident light makes to the normal of the
thin film surface.
The factor of 2 takes into account the double pass through the film
due to reflection.
[0018] In the case of thermal oxidation of bare blade steel, the
oxide refractive index is assumed nearly constant and the color is
primarily due to the final oxide thickness, d. When re-oxidizing a
hard metal oxide film on blade steel, the hard metal oxide
thickness is assumed nearly constant and the color is primarily a
function of the degree of re-oxidation, which correlates with an
associated increase in refractive index.
[0019] Variation in the parameters associated with the hardening
process, including temperature, gas flow rates, and gas leaks,
result in color drift for the thermal oxidation color process.
Variation in the hardening process parameters as well as in the
thickness or refractive index of the pre-hardened metal
oxide/oxynitride film, if left uncompensated, will also lead to
associated color drift in the hardened blade steel for the
reduction/re-oxidation process. In addition, abrupt changes in
pre-deposited metal oxide film thickness can occur when slitted
strips are welded together for continuous processing, thereby
causing abrupt color changes in the final product.
[0020] For the blade coloration processes discussed, variations can
be compensated for, and thus a target color can be reached, through
observation of the hardened blade steel color followed by an
adjustment to the flow of clean dry air during the oxidation or
re-oxidation processes. However, manual adjustment increases
production costs and does not allow sufficiently responsive
compensation for color drift, increasing the amount of unacceptable
blade material that is produced.
[0021] The present invention steps in to provide an improvement in
automating color control. Such methods and systems are described
below. These methods and systems are suitable for use in various
oxidation processes for the coloration of razor blade steel. A
feedback loop (closed loop control) is established, including the
steps of measuring color, comparing the measured color to a target
color value, and quantifying the difference there-between, and, if
the difference exceeds a predetermined threshold, adjusting a color
adjustment parameter, e.g., the airflow to the oxidation zone, so
that the measured and target colors are equivalent or within a
predetermined variance.
SUMMARY OF THE INVENTION
[0022] The present invention relates to a process for manufacturing
a razor blade comprising: an automated feedback loop, measuring a
color parameter of a blade steel strip exiting a coloration
process, comparing the measured color to a target color and
quantifying the difference there-between, and, if the difference
exceeds a predetermined threshold, adjusting a color adjustment
parameter so that the measured and target colors are equivalent or
within a predetermined variance.
[0023] In another embodiment, the invention relates to a system for
automated control of razor blade color comprising: [0024] a
spectrometer configured to measure the reflection spectrum from the
blade steel as it exits the colorization process, [0025] a
controller configured to adjust a parameter of the colorization
process, [0026] a processor configured to determine a parameter
associated with the measured reflection spectrum, calculate the
difference between the measured parameter and a predetermined
target value, and, if the difference is above a predetermined
threshold, send a voltage to the mass flow controller, and [0027] a
hardening furnace equipped with an oxidation zone.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] FIG. 1 is a flow diagram showing steps in a razor blade
manufacturing process, including blade coloration through thermal
oxidation, according to one embodiment of the invention.
[0029] FIG. 2 is a temperature profile for a hardening furnace.
[0030] FIG. 3A is a diagrammatic side view of an oxidation
zone.
[0031] FIG. 3B is a diagrammatic cross-sectional view of a sparger,
taken along line A-A in FIG. 3A.
[0032] FIG. 3C is a front view of an exit gate used with oxidation
zone shown in FIG. 3A.
[0033] FIG. 4 is a flow diagram showing steps in a razor blade
manufacturing process, including blade coloration through reduction
and controlled re-oxidation, according to one embodiment of the
invention.
[0034] FIG. 5 is a graph of the reflection spectra for hard metal
oxide blade steel in its pre-hardening condition and in various
post-hardening conditions (hardening having been conducted with
different air flow rates in the oxidation zone). The graph also
shows the correlation between the spectrum minimum value,
.lamda..sub.min, and the approximate blade color.
[0035] FIG. 6 is a diagram showing an automated color control
feedback loop, consisting of a spectrometer, a processor, a mass
flow controller, and a hardening furnace equipped with an oxidation
zone.
[0036] FIG. 7 is a flow chart describing the color control feedback
process.
[0037] FIG. 8 is a graph showing the .lamda..sub.min of a hard
metal oxide film on pre-hardened blade steel, .lamda..sub.min of a
hard metal oxide film on post-hardened blade steel under feedback
control, as well as the target minimum wavelength
.lamda..sub.T.
[0038] Like reference symbols in the various drawings indicate like
elements.
DETAILED DESCRIPTION OF THE INVENTION
[0039] A suitable thermal oxide process for forming the colored
oxide layer and manufacturing the razor blade is shown
diagrammatically in FIG. 1. First, a sheet of blade steel is slit
into strips. The strips are then welded together and then
perforated for ease of handling during subsequent processing.
[0040] When the desired sequence of pre-hardening steps has been
completed, the blade material is subjected to a hardening process,
which includes austenization of the stainless steel. A typical
temperature profile for the hardening process, which is conducted
in a tunnel oven, is shown in FIG. 2. The material is quickly
ramped up to a high temperature, e.g., approximately 1160.degree.
C., maintained at this temperature for a period of time, during
which austenization of the stainless steel occurs, and then allowed
to cool. A forming gas (e.g., including hydrogen and nitrogen)
flows through the high temperature zone of the oven during
austenization. The composition and flow rate of the forming gas are
controlled so that no oxidation occurs, and any native oxide is
reduced. In an embodiment, the forming gas includes hydrogen, to
prevent oxidation and reduce any native oxide, and nitrogen, as an
inert gas used to dilute the over-all hydrogen concentration. For
example, in some implementations the forming gas may include about
75% hydrogen and about 25% nitrogen, and may be delivered at a flow
rate of from about 7 to 38 L/min.
[0041] After austenization, the strips pass through an oxidation
zone, in which the colored oxide layer is grown on the surface of
the blade steel. The forming gas flows from the hardening furnace
into the oxidation zone. An oxidation gas (e.g., including oxygen)
is introduced to the forming gas at a desired point in the
oxidation zone (a point at which the strips have reached a
temperature suitable for oxidation), and drives the oxidation
process. The oxygen may be provided in the form of clean dry air.
The oxidation zone and oxidation conditions (e.g., hydrogen to
oxygen ratio) will be discussed in detail below. After the material
exits the oxidation zone, it is rapidly quenched, resulting in a
martensitic transformation ofthe stainless steel. Quenching does
not deleteriously affect the color of the oxide layer.
[0042] The processes described herein may be added to existing
blade steel hardening processes, often with minimal changes to the
existing process. For example, one existing blade steel hardening
process utilizes a high temperature furnace (greater than about
1100.degree.C.) containing a flowing forming gas. Two parallel
continuous stainless steel blade strips are pulled through this
high temperature furnace at 36.6 m/min (120 ft/min) each. This high
temperature treatment is used to austenitize the stainless steel
strips. Near the exit of the high temperature furnace is a
water-cooled jacketed tube (also referred to as the water-cooled
muffle tube). This section is used to start the cooling process of
the stainless steel blade strips. Just after the water-cooled zone,
the stainless steel blade strips are pulled through a set of
water-cooled quench blocks. The quench blocks initiate the
martensitic transformation of the steel. This existing process may
be modified to form a colored oxide layer by replacing the
water-cooled muffle tube, between the high temperature furnace and
the quench blocks, with the oxidization zone referred to above. In
certain instances the temperature profile of the furnace may be
modified so that the strips exit the furnace at a temperature less
than about 800.degree. C., or from about 400 to 750.degree. C., or
even from about 600-700.degree. C.
[0043] A suitable oxidization zone is shown diagrammatically in
FIG. 3A. The oxidation zone may be, for example, an Inconel tube
attached to the tubing used in the high temperature furnace of the
hardening line. In one embodiment, a gas sparger system 200 is
installed about 2.9 cm from the entrance of the tube 202 and
dimensioned to extend about 5.1 cm down the tube. In this case, the
sparger has a total of 16 inlet gas ports (not shown), and is
designed so that gas injected through the sparger (arrows, FIG. 3A)
will uniformly impinge upon the stainless steel strips. Gas is
introduced to the sparger through a pair of inlet tubes 201, 203. A
gas baffle 204 may be included so that the two stainless steel
strips of blade material are separated from each other so that the
gas composition on each side of the baffle may be controlled
partially independent from the other side. The baffle 204 may
define two chambers 210, 212, as shown in FIG. 3B. In this case,
the gas baffle may, for example, begin about 0.3 cm from the
entrance of the oxidation zone and extend down the tube about 10.2
cm. If desired, the gas baffle 204 may extend along the entire
length of the oxidation zone so that there is no mixing of gas
flows from inlet tubes 201 and 203, allowing for independent
control to the two sides of the baffle within the tube (210 and
212). The gas sparger is designed so that dual gas flow control is
possible, allowing two strips to be processed at the same time,
using the same furnace. Gas flow rates may be controlled using gas
flow meters. The exit of each chamber of the oxidation zone may be
equipped with a flange and two pieces of steel 218 which define a
slit 219 and thereby act as an exit gate 220 (FIG. 3C). The slit
may be, for example, from about 0.1 to about 0.2 cm wide. This exit
gate prevents any back-flow of ambient air into the oxidation zone
and also encourages better mixing of the gases within the oxidation
zone. As discussed above, just after the oxidation zone, the
stainless steel blade strips are pulled through a set of
water-cooled quench blocks 206. The quench blocks initiate the
martensitic transformation of the steel.
[0044] The desired color is generally obtained by controlling the
thickness and composition of the oxide layer. The thickness and
composition of the colored oxide layer will depend on several
variables. For example, the thickness of the oxide layer will
depend on the temperature of the stainless steel strip when the
oxidation gas is introduced, and by the hydrogen-to-oxygen ratio of
the mixture of forming gas and oxidation gas in the oxidation zone.
The composition, or stoichiometry, of the oxide layer will depend
on these same factors, and also on the morphology and surface
composition of the strips. Generally, lower temperatures and flow
rates will produce gold colors, and higher temperatures and flow
rates will produce violet to blue colors. In some implementations,
the hydrogen to oxygen ratio is from about 100:1 to 500:1. For a
given type of blade material, with the hydrogen to oxygen ratio
around the midpoint of this range, an aesthetic deep blue colored
oxide will be obtained. Increasing the relative amount of oxygen
will tend to result in light blue and light blue-green colors,
while decreasing the relative amount of oxygen will tend to result
in violet and then gold colors.
[0045] The speed at which the material travels through the
oxidation zone and the length of the oxidation zone will also
affect colorization. Suitable speeds may be, for example, in the
range of from about 15 to about 40 m/min.
[0046] In some cases, it may be necessary to adjust the process
parameters of the hardening and/or oxidation process in order to
obtain a consistent end product. The temperature of the strip as it
enters the oxidation zone may be controlled by adjusting the
temperature of the last zones in the hardening furnace, and/or by
the use of heating elements in the oxidation zone. Increasing the
temperature of the strip as it enters the oxidation zone will
increase the oxide thickness produced in the oxidation zone. When
the process is performed using most conventional furnaces, the
temperature of the strip as it enters the oxidation zone can be
adjusted only when first setting up the process. Since the gas
composition of the oxidizing gas to the oxidation zone can be
quickly adjusted, it is this parameter which is generally used to
compensate for variations in the strip material and to fine-tune
the oxide color. The exact temperature setting of the last zones of
the hardening furnace and the exact composition of the oxidizing
gas are selected based on, among other factors, the desired color,
the size, shape, composition, and speed of the steel strip.
[0047] A suitable process for applying the colored coating through
the reduction/re-oxidation process and manufacturing the razor
blade is shown diagrammatically in FIG. 4. As shown in FIG. 4,
preferably, the oxide or oxynitride layer is applied to the sheet
material from which the blade is formed, prior to the slitting of
the sheet material to a desired width that is typically
significantly wider than the final blade width. Performing the
coating step at this stage simplifies manufacturing, because a
large surface area can be coated at once. The oxide coating is
applied to a sheet of soft blade steel, e.g., by physical vapor
deposition (PVD), plasma enhanced chemical vapor deposition
(PECVD), or other deposition technique, in a layer of uniform
thickness. The layer is typically about 400 to about 10,000
Angstroms, for example about 500 to about 800 Angstroms.
[0048] When the desired sequence of pre-hardening steps has been
completed, the blade material is subjected to a hardening process,
which results in martensitic transformation of the stainless steel.
A typical temperature profile for the hardening process, which is
conducted in a tunnel oven, is shown in FIG. 2. This temperature
profile within the oven involves quickly ramping the temperature of
the material up to a high temperature, e.g., approximately
1160.degree. C., maintaining the material at this temperature for a
period of time, during which austenization of the stainless steel
occurs. After the material exits the oven, it is rapidly quenched,
causing martenization of the stainless steel.
[0049] During the hardening process, the oxide coating is
"colorized," i.e., the coloration of the oxide coating is enhanced
and/or changed. Colorization may result in an enhancement of the
color, for example to a brighter shade or more brilliant
appearance, and/or may result in a change of the color of the
coating to a different color, e.g., from blue-gray to violet, gold,
or blue, or from dull-green to bright green-yellow, dark green, or
blue-green. This colorization results from a change in the
refractive index of the coating, which in turn results from a
change in the composition, stoichiometric composition, and/or the
crystalline structure of the oxide coating. The degree of change in
the apparent film index of refraction will control the color of the
colorized film.
[0050] The composition and crystalline structure of the coating
after colorization, and thus the final color of the coating, will
depend on several variables. For example, the composition, or
stoichiometry, of the coating will depend on the gases that are
present in the furnace during the hardening procedure. Introducing
only nitrogen into the furnace will generally change an initially
gray-blue colored titanium oxide coating to bright blue or
blue-violet. This color change is due to a reduction in the oxygen
content of the titanium oxide coating. If air and/or moisture are
introduced to the furnace, the reduction in the oxygen content of
the titanium oxide coating is much less, and the resulting index of
refraction is higher.
[0051] Other variables that affect colorization are the initial
thickness and composition of the oxide coating, the temperature
profile of the hardening furnace, and the speed at which the
material travels through the furnace. If the thickness and/or
composition of the coating vary over the length of the material, it
may be necessary to adjust the process parameters of the hardening
process in order to obtain a consistent end product. Because it is
difficult to rapidly adjust the temperature and ambient conditions
in the large tunnel ovens that are typically used for hardening, it
may be desirable to provide a separate, shorter oven that is more
rapidly adjustable (referred to below as "the oxidation zone").
Thus, the conventional, large tunnel oven may be used for the high
temperature step of the hardening operation and to slightly reduce
the oxide coating (which may also increase the uniformity of its
composition), and the additional, shorter oven may be used for
oxidation/colorization, providing an oxidation zone in which the
gas composition can be relatively quickly adjusted to compensate
for variations in the material. The strip temperature in this
oxidation zone, and hence the coloration ambient responsiveness,
can be adjusted up or down, by adjusting the set point of the last
zones of the high temperature furnace. The composition and/or flow
rate of the gas(es) introduced to the oxidation zone can then be
altered, based on the appearance of the material as it exits the
oxidation zone and quenching area.
[0052] The oxidation zone may be similar to that described for the
thermal oxide blade coloration above, and as previously shown in
FIG. 3A. The oxidation zone, when utilized, is located between the
high temperature furnace and the first set of water-cooled quench
blocks, and replaces the water-cooled muffle tube used on a
standard hardening line. The furnace temperature profile may be
modified so that the coated stainless steel blade strips emerge
from the hardening furnace and enter the oxidation zone at a
temperature near or below about 1160.degree. C. Addition of heating
elements to the oxidation zone may also be employed to improve the
stability of the process, such as during start-up. The oxidation
gas, for example a mixture of oxygen and nitrogen introduced as dry
air and nitrogen, may be used to control the coloration process, in
which case it is added directly to the flow of gases from the high
temperature furnace. The inventors have developed methods of, and
systems for, automated color control that are suitable but not
limited to use in either of the coloration processes described
above. A feedback loop (closed loop control) is established,
including the steps of measuring color, comparing the measured
color to a target color and quantifying the difference there
between, and, if the difference exceeds a predetermined threshold,
adjusting a color adjustment parameter, e.g., the airflow to the
oxidation zone, so that the measured and target colors are
equivalent or within a predetermined variance. Preferred systems
and methods substantially reduce detectable long-term color
variation or drift.
[0053] In one aspect, the invention features systems for automated
control of razor blade color that include a spectrometer, a
processor, a mass flow controller (MFC), and a hardening furnace
equipped with an oxidation zone. The spectrometer measures the
reflection spectrum from the blade steel as it exits the
colorization process (e.g., the hardened and re-oxidized metal
oxide coated blade steel or the thermally oxidized blade steel).
The reflection spectrum is the percent of reflected light that
returns to the spectrometer versus the wavelength of the reflected
light. The processor determines a parameter associated with the
measured reflection spectrum, e.g., the wavelength of the minimum
reflected light (.lamda..sub.min), and calculates the difference
between the measured parameter and a predetermined target value. If
the difference is above a predetermined threshold, the processor
then sends a voltage to the mass flow controller to either increase
or decrease the flow of clean dry air to the oxidation zone, such
that the target value is approached. In some implementations, the
parameter is the wavelength of the maximum reflected light,
.lamda..sub.max. The measurement of color can be rather subjective
and complicated due to the variety of measurement configurations,
standards, and methods and the degrees of freedom that comprise
"color space." The International Commission on Illumination (CIE)
has developed standards by which defined numbers are used to
represent a color. According to CIE's standards, color is typically
defined by 3 parameters. Advantageously, by using a single
parameter, e.g., .lamda..sub.min or .lamda..sub.max, as a
designation for color, 3-dimensional color space is represented by
a single number. This single number can then be easily used as the
color control parameter to adjust a single color adjustment
parameter (e.g., airflow) in a real-time feedback loop.
[0054] With respect to the present invention, the first step toward
achieving automated color control is to measure and define color.
The reflection spectra of a hard metal oxide or oxide film on blade
steel follows the relationship for thin filn interference given by
the following equation which can be derived from equation (1)
above. 2n.sub.fd=(m-1/2).lamda..sub.min (2) where
[0055] n.sub.f=refractive index of the metal oxide film
[0056] d=metal oxide film thickness
[0057] m=an integer, representing the interference order
[0058] .lamda..sub.min =wavelength of reflectance minimum, and
[0059] .theta.=0 for light normally incident on the oxide film.
In equation (2), n.sub.f >n.sub.s, where n.sub.s, is the
refractive index of the substrate (blade steel). When
n.sub.f<n.sub.s, the relationship for thin film interference is
modified as shown below: 2n.sub.fd=m.lamda..sub.min (3).
[0060] Each spectra has a minimum value, .lamda..sub.min, which is
proportional to the film thickness, d, and refractive index,
n.sub.f.
[0061] FIG. 5 is a graph of the pre- and post-hardened reflection
spectra (reflected light vs wavelength) from titanium dioxide
coated blade steel, measured with a fiber optic spectrometer. Each
curve corresponds to the same film thickness but different
refractive indices. The pre-hardened film is represented by
spectral curve 1 with a .lamda..sub.min 2 of about 720 nm.
Undergoing the hardening process, the oxide in the film is reduced,
which also decreases n.sub.f and shifts the spectrum and associated
.lamda..sub.min to shorter wavelengths. The remaining spectral
curves represent post-hardened titanium dioxide films that have
experienced different amounts of airflow in the oxidation zone. For
example, post-hardened reflectance curve 3 exhibits a
.lamda..sub.min 4 of about 480 nm. This material was produced with
no air flow to the oxidation zone. Adjacent curves, with increasing
.lamda..sub.min, represent post-hardened titanium dioxide films
with increasing airflow to the oxidation zone. Since the amount of
re-oxidation increases with airflow, the refractive index increases
as well. This shifts the spectra and associated k min to longer
wavelengths. The airflow rates used for the post-hardened titanium
dioxide films in FIG. 5 were in the range (but not limited to)
0-200 mL/min for the associated set of conditions. Each spectrum
and associated .lamda..sub.min correlates to a distinct color as
seen by the color scale at the top of the graph (the color scale is
reproduced in black and white--the original scale started with pink
on the far left, darkening to violet, blue-violet, and deep blue in
the center, and then fading to light blue on the far right).
Following the cursor 5 from the minimum wavelength 2 of the
hardened material spectral curve 1 to the color scale at the top of
the graph indicates that a .lamda..sub.min of 720 nm would have the
visual appearance of light blue 6. Following the cursor 7 from the
minimum wavelength 4 of the post-hardened material spectral curve 3
to the color scale at the top of the graph indicates that a
.lamda..sub.min of 480 nm would have the visual appearance of
violet 8. Therefore, using .lamda..sub.min as a designation for
film color allows the representation of 3-dimensional color space
by a single parameter.
[0062] The second step in achieving color control is to develop a
feedback loop which enables a targeted color to be maintained
despite drifts in the hard metal oxide film thickness and
refractive index, or drifts in the parameters associated with the
thermal oxide coloration process (e.g., temperature, gas
concentration, etc). FIG. 6 depicts an automated color control
feedback loop consisting of a spectrometer system 9, a processor
13, a mass flow controller 14, and a hardening furnace equipped
with an oxidation zone 15. A software program, residing on the
processor, communicates with and controls the spectrometer,
analyzes the reflection spectra, and communicates with and controls
the mass flow controller. The spectrometer system 9 consists of a
light source 10, e.g., a tungsten light source, a spectrometer 11,
and a fiber optic reflection/backscatter probe 12. Light from the
light source 10 is coupled into a bundle of six illuminating fibers
17. These six illuminating fibers surround a centrally located read
fiber 18, which is coupled to the spectrometer 11. Light emitted
from the illuminating fibers 17 is directed onto the sample 16. The
light reflected from the sample is then collected by the central
read fiber 18, and coupled into the spectrometer 11. Within the
spectrometer 11, the light is collimated and dispersed from a
diffraction grating onto a detector array whose pixels are
spatially calibrated so as to correlate linear position along the
array to a particular wavelength. A processor 13 displays the
intensity of the reflected light at each wavelength. The fiber core
diameters are typically (but not limited to) in the range of
100-400 microns. A smaller fiber core diameter allows a smaller
sampling spot diameter at the expense of a lower optical coupling
efficiency into the fiber, resulting in less available light for
the measurement. The processor determines the wavelength with the
minimum reflected light, then sends a calculated control voltage
V.sub.N+1 19 to a mass flow controller 14 that controls the amount
of air flow to the oxidation zone 15, thus completing the feedback
loop. The calculated control voltage is related to the difference
between the target wavelength of minimum reflectance, .lamda.hd T,
and the measured wavelength of minimum reflectance,
.lamda..sub.min. The calculation of the control voltage can utilize
traditional proportional, integral, derivative (PID) type feedback
based on the color difference and/or incorporate a variety of
feed-forward and adaptive modeling techniques to reduce color
variation due to noise as well. An example of an algorithm used to
determine the mass flow controller (MFC) control voltage required
to achieve (.lamda..sub.T-.lamda..sub.min)<threshold would be as
follows:
V.sub.n+1=V.sub.n+.DELTA.V=V.sub.n+[(.lamda..sub.T-.lamda..sub.min)G]/[M.-
sub.colorM.sub.MFC] (4) where [0063] V.sub.n+1: new MFC control
voltage in units of volts [0064] V.sub.n: old MFC control voltage
in units of volts [0065] .DELTA.V: required change in control
voltage for (.lamda..sub.T-.lamda.min)< threshold in volts
[0066] .lamda..sub.T: target minimum wavelength in units of nm
[0067] .lamda..sub.min: measured minimum wavelength in units of nm
[0068] G: feedback loop gain setting, unitless [0069] M.sub.color:
color slope in units of (nm-min)/mL [0070] M.sub.MFC: mass flow
controller slope in units of mL/(min-volt) In equation 4 above, the
new MFC voltage setting, V.sub.n+1, required to make
(.lamda..sub.T-.lamda..sub.min) less than some predetermined
threshold, T, is equal to the existing voltage setting, V.sub.n,
plus some adjustment voltage, .DELTA.V. The color slope,
M.sub.color, determined experimentally, is the slope of the
.lamda..sub.min versus airflow rate curve for a specific metal
oxide coated material on blade steel and hardening furnace
parameters. The MFC slope, M.sub.MFC, is the equation describing
the relationship between voltage applied to the MFC and associated
flow rate. For example, if the MFC flow range is 0-200 mL/min for a
corresponding control voltage of 0-5 volts, the slope would be 40
mL/(min-volt). The threshold, T, can be set very small for tight
color control, or even set to zero. A flow chart depicting the
color control feedback process is shown in FIG. 7.
[0071] A graph displaying the performance of the feedback loop is
shown in FIG. 8. The triangular data points 100 at the top of the
graph represent the as-received (pre-hardened) minimum wavelength
(AR .lamda..sub.min), measured from the reflection spectrum of
titanium dioxide film on blade steel. The mean value is 760.4 nm
with a standard deviation of 2.8 nm. To simulate a large
differential between the .lamda..sub.min of a hard metal oxide film
on pre-hardened blade steel and the target minimum wavelength
.lamda..sub.T, and to demonstrate a range of color control, the
setpoint, or target color, .lamda..sub.T, was incrementally changed
as seen by the staircase of dashed lines 101, 102, . . . , 108. The
diamonds, 109, 110 . . . , 116, surrounding the dashed lines,
represent the post-hardened measured minimum wavelength, AH
.lamda..sub.min, under feedback control. The measured
.lamda..sub.min follows the setpoint .lamda..sub.T with a standard
deviation of about 3.3 nm. Averaging of the spectral scans can be
used to improve the signal to noise ratio and reduce measurement
error at the expense of a longer time delay between updates.
[0072] To improve the responsiveness of the feedback loop, the
response time of the mass flow controller should be as fast as
possible and the volume of space comprising the oxidation zone and
associated tubing which carries the clean dry air to the oxidation
zone should be minimized. Also, since the blade steel is traveling
through the hardening furnace and oxidation zone at relatively high
speeds, (e.g., 24 in/sec), it is important to place the
spectrometer's fiber optic probe (or other measurement instrument)
as close to the oxidation exit port as possible.
[0073] As the film thickness increases, the reflectance spectra may
exhibit multiple maxima and minima corresponding to successive
interference orders, m. If multiple reflectance minima exist within
the spectrometer wavelength range, the processor software program
can use a windowing function to limit its search for
.lamda..sub.min to a specific portion of that wavelength range in
order to isolate the spectral minima corresponding to a specific
interference order. More complex software can utilize the number
and location of multiple reflection maximum and minimum to monitor
and control the strip color.
[0074] A number of embodiments of the invention have been
described. Nevertheless, it will be understood that various
modifications may be made without departing from the spirit and
scope of the invention.
[0075] For example, in addition to using a characteristic of the
reflection spectrum measured with a spectrometer as the feedback
control parameter, other types of measurement systems with their
own characteristic can be used to specify a control parameter for
the feedback loop. For example, an "RGB," three light source color
differentiating sensor can represent color using the ratios of
reflected red, green and blue light from a sample material compared
to the ratios of these colors from a material of a specific target
color. The sensor output is a percentage representing how close the
sample material color is to the target material color. The sensor
output can be used as the feedback loop control parameter.
[0076] Moreover, as noted above, the reflectance maxima,
.lamda..sub.max, can be used as a designation for color rather than
.lamda..sub.min, and follows a similar relationship for thin film
interference. Accordingly, other embodiments are within the scope
of the following claims.
[0077] The dimensions and values disclosed herein are not to be
understood as being strictly limited to the exact numerical values
recited. Instead, unless otherwise specified, each such dimension
is intended to mean both the recited value and a functionally
equivalent range surrounding that value. For example, a dimension
disclosed as "40 mm" is intended to mean "about 40 mm".
[0078] All documents cited in the Detailed Description of the
Invention are, in relevant part, incorporated herein by reference;
the citation of any document is not to be construed as an admission
that it is prior art with respect to the present invention. To the
extent that any meaning or definition of a term in this document
conflicts with any meaning or definition of the same term in a
document incorporated by reference, the meaning or definition
assigned to that term in this document shall govern.
[0079] While particular embodiments of the present invention have
been illustrated and described, it would be obvious to those
skilled in the art that various other changes and modifications can
be made without departing from the spirit and scope of the
invention. It is therefore intended to cover in the appended claims
all such changes and modifications that are within the scope of
this invention.
* * * * *