U.S. patent number 3,801,349 [Application Number 05/062,019] was granted by the patent office on 1974-04-02 for coating a continuous metallic strip with pulverant material with a non-destructive measuring method.
This patent grant is currently assigned to Caterpillar Tractor Co.. Invention is credited to Glenn W. Bush, Walter A. Wilson.
United States Patent |
3,801,349 |
Wilson , et al. |
April 2, 1974 |
**Please see images for:
( Certificate of Correction ) ** |
COATING A CONTINUOUS METALLIC STRIP WITH PULVERANT MATERIAL WITH A
NON-DESTRUCTIVE MEASURING METHOD
Abstract
Characteristics of a pulverant material coating or its
supporting surface can be determined by measurement of diffused
energy return after impingement with beam of light, ultraviolet,
infra-red, monochromatic light, or the like. Methods and apparatus
for non-destructive measurement of characteristics such as coating
thickness during electrostatic coating process for metallic powder
on a continuous metallic strip are provided.
Inventors: |
Wilson; Walter A. (Pittsburgh,
PA), Bush; Glenn W. (Coraopolis, PA) |
Assignee: |
Caterpillar Tractor Co.
(Peoria, IL)
|
Family
ID: |
22039692 |
Appl.
No.: |
05/062,019 |
Filed: |
August 7, 1970 |
Current U.S.
Class: |
427/10; 73/150R;
118/664; 118/665; 222/55; 250/216; 427/209 |
Current CPC
Class: |
G01B
11/0616 (20130101); G05D 5/03 (20130101); B05B
12/126 (20130101); G01B 11/0625 (20130101) |
Current International
Class: |
B05B
12/08 (20060101); B05B 12/12 (20060101); G01B
11/06 (20060101); G05D 5/00 (20060101); G05D
5/03 (20060101); B44d 001/34 (); C23c 017/00 ();
B23p 003/06 () |
Field of
Search: |
;117/31,33,DIG.2,131
;222/55 ;73/150 ;118/9,2 ;250/216,220 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
Reflectance Spectroscopy by Wendlandt et al., Chapter 111-Theory
11, Diffuse Reflectance, pgs. 46-89. .
Journal of Research of the Nat. Bureau of Standards, Vol. 25, July
to Dec. 1940, Research Paper 1345, pp. 581-618..
|
Primary Examiner: Martin; William D.
Assistant Examiner: Trenor; William R.
Attorney, Agent or Firm: Shanley and O'Neil
Claims
What is claimed is:
1. Coating method using non-penetrative radiant energy for
non-destructive quantitative measurement of pulverant material
coating within coating ranges below deposition of pulverant
material which is fully opaque to such non-penetrative radiant
energy, the pulverant material being distributed on a continuous
metallic strip for purposes of obtaining a uniform thin coating,
consisting essentially of the steps of
depositing metallic pulverant material of particle sizes between
about 30 mesh and about 200 mesh on a continuous metallic strip of
extended surface area, said pulverant material having scattering
characteristics for non-penetrative type radiant energy differing
from those of the continuous metallic strip and being deposited in
a coating weight range between about 10 gr/ft.sup.3 to about 90
gr/ft.sup.3,
directing non-penetrative type radiant energy in angled
relationship onto such coated continuous metallic strip subsequent
to deposition of pulverant material,
detecting and quantitatively measuring non-penetrative type radiant
energy diffusion-scattered by the deposited pulverant material, at
a location bearing an angled relationship which is less than about
45.degree. to the direction of impingement of such radiant energy,
as an indication of a quantitative characteristic such as
uniformity of particle distribution and coating weight per unit
area of the pulverant material, and treating such pulverant
material coating by heating or mechanical compaction.
2. The method of claim 1 in which impingement of the
non-penetrative type radiant energy is substantially normal to such
strip.
3. The method of claim 1 including the step of
controlling deposition of such pulverant material responsive to
measurement of such scattered non-penetrative type radiant
energy.
4. The method of claim 1 in which coating weight of the pulverant
material per unit area of the continuous metallic strip is
controlled responsively to such measurement of such scattered
radiation.
5. The method of claim 1 further including the step of
wetting the surface of the continuous strip with a binding agent
prior to deposition of pulverant material to coat the continuous
metallic strip with a slurry of the pulverant material and the
binding agent.
6. The method of claim 1 further including the steps of
measuring the speed of longitudinal strip movement, and
combining the strip speed measurement with the scattered radiant
energy measurement to determine the rate of pulverant material
deposition.
7. The method of claim 1 wherein the pulverant material comprises
powdered metal includes chromium.
8. The method of claim 5 wherein the binding agent includes a
halogen containing solution.
Description
This invention is concerned with measuring methods and apparatus
applicable to pulverant material on a supporting surface for
determining characteristics of the pulverant material or the
support surface. In its more specific aspects the invention is
concerned with non-destructive measurement of pulverant material
distribution on a supporting surface and with providing methods and
apparatus for control of processes involving pulverant material
deposition including automated control for such processes. One
embodiment of the invention is concerned with distribution of
pulverant material on a solid substrate, for example, uniform
distribution of a metallic, corrosion-protective, powdered metal on
flat rolled steel.
Significant opportunity exists for wider commercial application of
powder coating methods but no satisfactory method has existed for
making non-destructive coating weight determinations. The problem
is compounded by the need for a satisfactory gage to be able to
function with differing powders, wet or dry application methods,
and substrates of varying thicknesses and compositions. Such
factors eliminate x-ray gages, beta ray gages, and the like,
because the penetrative character of the radiation in such gages
does not permit the adaptability required for coating lines in
which the coating material, thickness of the substrate, and the
like, are subject to change. As a result no practical method of
making a non-destructive determination of coating distribution,
coating weight, or coating thickness of pulverant materials for
commercial coating processes, such as continuous steel strip
coating processes, has existed, notwithstanding the obvious and
pressing need in the powder coating field.
The present invention provides commercially acceptable and reliable
non-destructive methods and apparatus for measurement of pulverant
material deposition on multipurpose lines suitable for differing
powders, wet or dry application methods, varying substrates, and
the like. The invention teaches use of what is described as a
non-penetrative (sometimes referred to as non-ionizing) type of
wave energy, such as ultraviolet, regular light, monochromatic
light, infra-red, and the like, extending into the quasi-optical
region of the electromagnetic wave spectrum. Selective measurement
of returned wave energy without mechanical contact of the work
product is made. Such selective, non-destructive measurements
provide the accuracy required for commercial processing and rapid
results for substantially any process, including high speed
continuous strip processing. The pulverant material can be metallic
or non-metallic finely divided particles of spherical or other
shape, such as flake particles. The thickness of a substrate, such
as continuous strip flat rolled steel can vary without affecting
the measurement.
A typical commercial application for the invention exists in the
coating of flat rolled steel product with a metallic powder, such
as chromium powder. The invention will be disclosed in that
environment. It will be apparent that other substrates, other
coating materials, and other processes fall within the scope of the
invention. In making a detailed disclosure, the accompanying
drawings, briefly described below, will be referred to:
FIG. 1 is a schematic elevational view of a coating line, for
coating a single surface of a substrate, embodying the
invention,
FIG. 2 is a schematic elevational representation of a coating line,
for coating both surfaces of a substrate, embodying the
invention,
FIG. 3 is a schematic elevational view of measuring apparatus
embodying the invention, and
FIG. 4 is a schematic elevational view of pulverant material on a
supporting surface used for disclosing a concept of the
invention,
FIGS. 5 through 8 are graphical representations of data
illustrative of the invention,
FIG. 9 is a schematic plan view of a portion of a coating line
embodying the invention, and
FIG. 10 is a schematic circuit diagram embodying the invention.
In FIG. 1 continuous strip material 12 is fed from coil 14 in the
direction indicated by arrow 15 around coating drum 16. Pulverant
material from hopper 20 is fed in the direction indicated by arrow
22 into a deposition chamber 24. The pulverant material is directed
as indicated at 26 and deposited on strip 12 during its travel
around the coating drum 16. The strip is then directed for further
treatment of the coating, usually involving compaction by passage
through a sintering furnace 28 and a compaction roll stand 30. The
strip is then coiled on take-up reel 32. Line speed can be measured
at coating drum 16 or other locations along the line and indicated
as required. Line speed and the rate of powder deposition are
controllable. Further details of an electrostatic powder coating
line can be obtained from the copending patent application entitled
"Electrostatic Coating of Metal Powder on Metal Strip," filed by
Edwin J. Smith et al, on Aug. 15, 1967, Ser. No. 660,787 refiled as
continuation application Ser. No. 63,896, now U.S. Pat. No.
3,745,034.
Apparatus 34 for making quantitative measurements of the surface
coating is located downstream of coating roll 16. Measuring
apparatus 34 (shown diagrammatically) is positioned between coating
applicator means and subsequent treatment means permitting viewing
of the strip as coated with pulverant material. Measuring apparatus
34 includes wave energy source 36 and detector apparatus 38.
Signals from detector apparatus are sent over line 40 to control
apparatus 42. A control signal from control apparatus 42 is
directed over line 44 to control processing line variables
affecting coating weight, particle distribution, and the like.
In the processing line shown in FIG. 2, continuous strip is fed
from coil 46 around guide roll 48 toward wetting station 50. A
binder solution is directed from tank 52 to wet one or both
surfaces of the strip material prior to coating. At coating station
54, hoppers 56 and 58 feed powder to be deposited on opposite sides
of the strip forming a slurry coating on the strip.
Coated strip 56 can be fed directly to compacting apparatus or, as
shown in FIG. 2, after passing measurement station 59, coated strip
can be fed through a tandem coating apparatus 60 where pulverant
coating material is added to one or both sides. The strip can then
be fed directly through compacting apparatus, not shown, and/or
through an additional measuring station 62. Further tandem
deposition and measuring apparatus can be included in the line.
After coating and compaction the strip is coiled at reel 64. Line
speed can be measured at roll 48 or otherwise along the line and
powder deposition rate at each station can be controlled.
Additional details of an electrostatic wet process powder coating
line can be obtained from the copending application, entitled
"Electrostatic Coating of Metal Powder on Metal Strip," filed by
Lowell W. Austin et al, on Jan. 5, 1968, Ser. No. 695,957 now U.S.
Pat. No. 3,575,138.
The coating measurement stations 59 and 62 each include top surface
and bottom surface gage means. One or both surface gages may be
used at each station dependent on whether coating is added on both
surfaces at each station. Signals from each detector means of these
measuring apparatus are fed separating over the signal line shown
into control station 66. Means are provided at control station 66
for accepting and storing information, read-out of information,
making comparisons and calculations for generating control signals
for controlling line variables, such as the rate of particle feed
at each station, application of wetting agent, line speed, and the
like.
The coating measuring apparatus shown diagrammatically in FIGS. 1
and 2 can be used to determine quantitative characteristics of
particle coatings, such as uniform distribution of the particles,
coating thickness, or coating weight per unit area, and other
characteristics. It has been discovered that diffusion of wave
energy, such as a collimated light beam, by pulverant material,
such as powdered metal, deposited on a solid substrate can be used
to measure coating deposition between a "coating-free" stage and a
complete coverage stage; also such determination can be utilized
for ascertaining rate of deposition which can be used to control
additional coating by proportioning. Detailed examples of these
operations will be presented later.
As shown schematically in FIG. 3, a collimated light beam 67 from
source 68 is directed downwardly in angled relationship toward
strip material 69 which is coated with pulverant material layer
70.
Returning light energy beam 71 is measured at detector 72
positioned at angle 73 with respect to perpendicular beam 67. The
signal from detector apparatus 72 is fed to control apparatus 74
which may include meter, or a separate indicator, e.g., voltmeter
75, may be used.
It has been discovered that light energy diffusion caused by a
granular coating on a supporting surface, which surface is a better
reflector than is the granular coating, can be used as a measure of
coating characteristics. In practice of the invention, incident
light energy can be directed at substantially any angle toward the
coated surface. For example in FIG. 3, light source 68 can be
changed from the perpendicular relationship to the position
indicated in dotted lines from source 76. For practical purposes
the angular relationship between the incident light and the coated
surface is selected within about 60.degree. on either side of
normal (beam 67). If required, larger angles could be used but the
light diffusion effect may be decreased due to greater reflection
of incident light by the outer surface of the coating at
substantially greater angles.
The angle of view for detector 72 is also selected for maximum
sensitivity and intensity of light return. Angle 73 can vary from
about 0.degree. immediately adjacent to or in circumscribing
relationship to source 68 as indicated in dotted lines to detector
77, to as high as 120.degree. from the direction of incident light
impingement. Generally the angle between the incident light and the
light is selected to be less than about 90.degree. and, preferably
significantly less, e.g., less than about 45.degree..
Either the light source or the detector can be positioned first in
making a set-up for measurement. The angular relationship,
providing suitable intensity of return light energy, can then be
selected empirically. Such angular relationships are then
maintained throughout the measuring period. The source and detector
can also be mounted in a structure in which the angular relation is
fixed and this is followed in practice with the light source being
along the angle of incidence and the detector along the angle of
reflection.
Referring to FIG. 4, light energy from beam 78 shown in dotted
lines strikes coating surface 79 as indicated. Because of the
granular nature of the material, diffusion of the light occurs as
the material builds up. In the embodiment described for disclosure
purposes electrostatically deposited chromium powder on flat rolled
steel is considered. Diffusion of the impinging light energy
results from the granular structure of the deposited metallic
powder. Diffusion also results from the refraction and reflection
of light rays at the interfaces of the particles and between the
particles and the surface of the flat rolled steel.
Conventional flat rolled steel, free of powder coating, if
principally a reflector. Light which is diffused through a particle
coating on the steel to the substrate surface returns to the outer
surface and leaves in all directions. A non-coated surface provides
maximum reflectivity and an optically opaque coating of pulverant
material provides maximum diffusion with the effect of decreasing
light return. It has been discovered that an area of substantially
linear response exists between these extremes. Such area is of
sufficient range to be readily useful for practically any
commercial coating operation. In this range of linear response,
reflection and diffusion, it is believed, can effect the light
return but, the diffusion effect is considered the basic mechanism
of measurement in accordance with the invention.
This linear response is shown in FIG. 5 wherein the gage response
(light return measurement) versus coating weight is graphed. The
linear relationship between the returned light detected and the
coating weight exists in the zone between dotted lines 78 and 79.
This figure sets forth typical gage responses versus the coating
weight in grams per square foot. The coating powder used for
collecting the data of FIG. 5 was 200 mesh chromium. The substrate
was cold rolled steel. The light return decreases with increase in
coating weight due to diffusing of the light by the pulverant
material. The detector can be conveniently connected to provide
readings in the direction shown, that is, increasing with
increasing coating thickness. The detector can be connected
otherwise with no effect on accuracy.
It will be noted in FIG. 5 that the response in the zone to the
left of dotted line 78 provides a reading from which coating weight
can be determined above about 2.5 grams per square foot. But a
purely linear relationship between the diffused light measured and
the coating weight does not exist throughout this zone. Also note
in the zone to the right of dotted line 79 that when the base metal
becomes opaquely coated with powdered chromium that the curve
flattens off.
As pointed out earlier, diffusion properties of the supporting
surface for the coating material should differ from those of the
granular material being coated in order to provide the desired
relationship for accurate measurement when graphed, a 45.degree.
slope linear relationship would be the ideal. This will be
considered in more detail in presenting data from various substrate
surfaces later.
In making measurements it has been found that a number of areas of
measurable sensitivity exist. These include the thickness of the
coating itself, the particle size, relative diffusion
characteristics of the powder and the supporting surface, and the
attenuating characteristics of the binding agent (if a wet process
is used). The effect of certain of these factors in making a
coating thickness measurement setup, for example, are determined
empirically and taken into consideration. Data relating to such
factors will be presented later.
Referring again to FIG. 3, a detector means 72, sensitive to the
wave energy used (visible light, infra-red, other monochromatic
light, etc.) is positioned in a predetermined location providing
strong light return over the measuring range of interest. The
angular relationship between the angle of incidence and the angle
of view for the light return means is determined empirically or can
be preset based on experience with the powdered metal being coated.
For practical purposes the angle can vary widely as discussed
previously but an angle of less than about 90.degree. is preferred
for higher intensity diffused light return. Readings can be
compared with previous calibration values determined with the same
subsurface and coating material, or, the meter can be calibrated
for the run based on a comparison of responses and weighed coating
samples.
Referring to FIG. 6, a family of curves is shown displaying the
detector responses as a function of the chromium powder coating
weight with measurements being made at various angles of incidence
for the impinging light. The angle of view for the detector was
fixed at 25.degree. from perpendicular to the base metal. The angle
of incidence for impinging light was changed for each curve. The
impinging light was directed perpendicularly against the strip
(0.degree. angle of incidence) in collecting the data for curve 80.
With curve 81 the angle of incidence of the impinging light was
30.degree. and with curve 82 the angle of incidence for the
impinging light energy was 40.degree.. This family of
closely-spaced curves, with near identical slopes, demonstrates
that the basic mechanism of the invention is measurement of the
effect of diffusion, or stated otherwise, the effect on
reflectivity, since the comparable measurement data is obtained
even though the angle of incidence of the impinging light energy is
varied widely.
FIG. 7 shows the effect on coating weight sensitivity of varying
the substrate surface. Detector response for differing substrates
coated with a chromium powder is plotted. Various surfaces of
differing reflectivity and diffusion characteristics were measured
first with no coating (indicated along the zero coating weight
line). Values are then recorded at an intermediate coating between
no coating and opaque, i.e. 12 grams per square foot. Finally, data
measured with coating covering the entire surface so that the
chromium powder made on opaque coating was recorded at
approximately 20 grams per square foot. Line 83 is merely a
45.degree. line for use as a reference.
Note first in FIG. 7, that at the opaque coating measurement
condition all the readings were grouped together as indicated at
84. Then to consider a surface which has diffusion characteristics
similar to the chromium powder, note the "JP" readings. "JP" is a
trademark covering a product, made by National Steel Corporation,
Pittsburgh, Pennsylvania, which is a special alloy of a zinc
galvanizing spelter coating with flat rolled mild steel base metal.
The zinc coating is alloyed with the base metal in such a manner
that the surface has a powdery appearance. The readings for JP
(shown by a dot in a circle), indicate that the material has
similar diffusion properties for visible light as chromium powder.
Note that a line interconnecting the JP marks would be practically
horizontal from zero to 20 grams per square foot.
The other products tested for example, minimized spangle, which has
reflection properties approaching that of regular spangle
galvanized material but is more uniform, cold rolled steel, and
tinplate all exhibit sufficient difference between the diffusion
characteristics of the surface before coating with powder and after
coating that a satisfactory sloped curve results providing for
accurate indications of coating weight by the method of the present
invention without special procedures.
The data of FIG. 8 brings out teachings of the invention relating
to the effect of and the sensitivity to particle size. Diffusion of
the light energy increases as the particle size diminishes;
therefore an opaque coating results with less coating weight. The
curves of FIG. 8 show the response versus the coating weight for
selected particle sizes of chromium powder applied to cold rolled
steel with a water binder. It will be noted that the 200 mesh
(finest powder) curve levels off earlier than the 50 mesh (coarser
powder). The 200 mesh curve levels off at about 22 grams per square
foot. The 50 mesh powder provides accurate indications up to about
45 grams per square foot before leveling off. Whereas, at 60 plus
grams per square foot, accurate measurements continue with this
coarsest of the three powders represented, 30 mesh.
The present invention finds greatest use in making coating weight,
and the like, determinations. However, it is clear from the data
presented that other areas of sensitivity can be used to make
determinations such as average particle size of a pulverant
material and roughness or other surface characteristic of the
supporting surface. The average particle size can be determined
when the powder becomes optically opaque to the non-penetrating
type of radiation, i.e., when the curve levels off by comparison to
previously collected data.
The "JP" is an example of a determination of a surface
characteristic. The level response curve indicates its surface has
substantially the same diffusion characteristic of the chromium
powder. The invention provides a simple method of determining
whether this desired powdery surface characteristic is being
maintained in production by a powder application test method.
FIG. 9 shows apparatus for making determinations of coating
distribution across the width of the strip. In FIG. 9 strip 85 is
moving toward the right from coating application chamber 86. Within
chamber 86, individual powder blowers 87, 88, 89 are spaced across
the width of the strip distributing powder on the left, center, and
right portions of the strip, respectively. Measuring gages 90, 91
and 92 are located across the width of the strip, left, center, and
right portions, respectively. Obviously a greater or lesser number
of blowers and measuring gages can be used without departing from
the teachings of the invention. Each measuring apparatus has a
signal-receiving and/or indicating station 93, 94, and 95,
respectively. These are connected to a control apparatus, such as
set point comparator 98 for comparing measured values to target
values for coating weight across the strip. Deviations from the
target value cause signals to be sent to control the feed rate of
powder to one or more of the blowers 87, 88, and 89.
FIG. 10 shows a simplified schematic circuit diagram of apparatus
used in accumulating the data discussed above. Light source 96 is a
conventional instrument light, G.E. No. 1630, rated 6.5 V at 2.75
A, 18 watts. Detector 97 is a semiconductor photocell RCA No. 7163,
100 DC, regulated supply. The signal from the detector 97 is fed
through switch 98 to buffer amplifier 99. The amplified signal from
buffer amplifier 99 is fed to the signal conditioner amplifier 100
and continues on to digital read-out apparatus 102. Buffer
amplifier 99 can be Model No. P85AU and the signal conditioner
amplifier 100 can be Model No. P25AU, both manufactured by and
available from Philbrick Researches, Inc., Dedham, Massachusetts.
Signal read-out apparatus 102 can be a volt-meter calibrated in
grams per square foot. Other sources and detectors and equivalent
circuit apparatus will be readily available to those skilled in the
art.
In practice of the invention the measuring apparatus can be set up
from data obtained on the line at the start of a run, that is by
comparison of electrical response to coating characteristics
physically determined, e.g., by weighing powder from a unit area.
Also, the measuring apparatus can be set up using precoated samples
or known calibration data by comparison of responsive readings.
When the wet process of powder application is used possible
attenuating characteristics of the wet binder are considered.
Readings are taken while the binder is wet, that is while the
powder is in the slurry form, before drying becomes apparent in
order to avoid the different effects between the wet and the dry
binder.
In practice the binder may be selected to be a clear liquid without
attenuating characteristics or if a liquid having a tint is called
for filters can be used on the light impingement and/or the angle
of view sides to avoid any attenuating effect. For example, in wet
process coating of chromium powder a halogen solution binding agent
is utilized and compensation is made for the greenish tint of this
material. Under certain circumstances, depending on the binding
agent, it may be necessary to select a differing type of wave
energy which is not attenuated by the binder.
For purposes of disclosing the invention specific steps,
components, and various materials have been described; it is
understood that other steps, materials, and components can be used
without departing from the spirit of the invention. Therefore, in
determining the scope of the invention reference will be had to the
appended claims.
* * * * *