Information
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Patent Grant
-
6409104
-
Patent Number
6,409,104
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Date Filed
Wednesday, April 19, 200024 years ago
-
Date Issued
Tuesday, June 25, 200222 years ago
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Inventors
-
Original Assignees
-
Examiners
Agents
-
CPC
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US Classifications
Field of Search
US
- 239 703
- 239 223
- 239 224
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International Classifications
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Abstract
A wear resistance coated bell atomizer (32) and method for making same. The coating applied to the outer surface of a bell cup (36) of the bell atomizer (32) is preferably a silicon-doped amorphous carbon coating. This silicon-doped amorphous carbon coating significantly increases the usable life of a bell cup (36) in a bell atomizer paint system (10) by limiting the effects of abrasive materials on the wearable surfaces of the bell cup (26), including the top serrated edges (46), which may negatively affect the performance of uncoated bell atomizer spray equipment.
Description
TECHNICAL FIELD
The present invention relates to polymer coating application equipment and more particularly to components having a wear resistant coating formed thereupon.
BACKGROUND
Rotary paint atomizers (commonly referred to as “bells” or “paint bell atomizers”) are typically used for electrostatically applying fluids, such as polymer coatings, to many kinds of surfaces. Current technology uses paint bell atomizers composed of materials such as aluminum and high cost titanium. One problem with current paint bell atomizers is that they tend to wear out quickly (typically 5-7 weeks for paint bells used in automotive applications). When metallic, mica-based, or heavily pigmented coatings are used, the metal flakes, mica flakes, or abrasive pigments within the coatings tend to wear grooves into the surface of the bells. Such degraded paint bell atomizers may then apply coatings having an uneven or globbed appearance, which in turn require expensive and time-consuming defect removal and refinishing. In addition, it is relatively expensive to replace paint bells or paint bell components such as bell cups.
One possible solution to the wearing problem is to use harder metals, such as pure titanium, in the bells. Titanium paint bells typically last longer than bells. Titanium paint bells typically last longer than standard aluminum paint bells, but cost two or three times as much.
SUMMARY OF THE INVENTION
It is an object of the present invention to improve the durability of paint bells without significantly affecting the cost or performance of the equipment.
In accordance with the present invention, a silicon-doped (sometimes referred to as silicon-stabilized) amorphous carbon coating is applied to the wear surfaces, and specifically to the metallic bell cups, of metallic paint bell atomizers. Coated metallic bells have a significantly longer life than standard uncoated aluminum bells and have superior wear characteristics than standard uncoated titanium bells. In this regard, both aluminum and titanium bells have exhibited similar results with coatings applied.
The silicon-doped amorphous carbon coating has the further advantage of being relatively inexpensive to make and apply, especially when compared with the costs associated with replacing aluminum and titanium bell cups or with the cost of replacing an entire bell atomizer.
Other objects and advantages of the present invention will become apparent upon considering the following detailed description and appended claims, and upon reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1
is a perspective view of a paint spray system according to the present invention;
FIG. 2
is a cross-sectional view of a paint atomizer head formed according to the present invention;
FIG. 3
a
is a perspective view of an uncoated bell cup prior to use on a paint system;
FIG. 3
b
is a perspective view of an uncoated bell cup after use on a paint system;
FIG. 3
c
is an enlarged view of circle A on
FIG. 3
b;
FIG. 3
d
is an enlarged vied of circle B on
FIG. 3
b;
FIG. 4
is a logic flow diagram for the preparation and coating of the bell cups;
FIG. 5
is a more detailed logic flow diagram of
FIG. 4
for coating an aluminum bell cup; and
FIG. 6
is a more detailed logic flow diagram of
FIG. 4
for coating a titanium bell cup.
DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
In the following figures, the same reference numerals will be used to identify identical components in the various views. The present invention is illustrated with respect to automated spray application equipment particularly suited for the automotive field. However, the present invention is applicable to various uses such as consumer appliances, industrial machinery, and other paint processes.
Referring now to
FIG. 1
, a paint spray system
10
for painting a part or surface is illustrated having a plurality of robotic arms that may include an overhead arm
14
and side arms
16
. Each arm
14
,
16
is coupled to a rack
18
. In such systems, arms
14
,
16
move according to XYZ coordinates with respect to rack
18
. Commonly, the XYZ coordinates of arms
14
,
16
vary depending upon the part
12
to be painted. It is common, for example, to maintain a predetermined distance from the surface to be painted. Each arm
14
,
16
has a plurality of motors (not shown) that permit movement of the arms
14
,
16
into desired positions with respect to part
12
. A power source
20
is coupled to paint spray system
10
to power arms
14
,
16
. Each arm
14
,
16
has a paint atomizer head
22
positioned thereon. As will be further described below, each paint atomizer head
22
generates a desired paint spray with respect to part
12
. Each paint atomizer head
22
is fluidically coupled to a paint source
24
that supplies paint thereto.
Referring now to
FIG. 2
, an atomizer head
22
is illustrated in further detail. Atomizer head
22
has a support housing
26
with a front surface
28
that faces the parts
12
to be painted. Support housing
26
also has a plurality of other surfaces such as side surfaces. As would be evident to those skilled in the art, various shapes of heads
22
may be used. For example, side arms
16
may use different heads than overhead heads. The teachings set forth herein are applicable to all types of heads
22
.
Front surface
28
has a bell-atomizer
32
extending therefrom. Bell-atomizer
32
has a bell housing
34
and a bell cup
36
. Bell cups
36
are typically composed of aluminum or titanium. A paint channel
38
extends through the bell-atomizer
32
and support housing
26
and eventually couples to the paint source
24
. Bell-atomizers
32
in their operation are well known in the art. Bell cups
36
receive paint from paint channel
38
. Bell cups
36
rotate to generate stream lines (atomization) directing paint particles
40
to part
12
. In addition to the stream lines directing paint particles
40
to part
12
, the bell-atomizer
32
is coupled to power source
20
to impart a potential difference on paint particles
40
relative to the part
12
so that they are directed electrically to part
12
. Thus, a potential difference exists between particles
40
and part
12
.
FIGS. 3
a-d
refer to the bell cups
36
both prior to and after use on a paint system
10
.
Referring to
FIG. 3
a
, a pristine uncoated bell cup
36
is shown having a paint channel
38
and a distribution disk
42
prior to installation on a paint system
10
. The bell cup
36
also has an inner cavity wall (shown as
44
on
FIG. 3
b
) and a serrated edge
46
.
FIGS. 3
b-d
shows the same bell cup
36
as
FIG. 3
a
after use in a paint system
10
for a period of time. The atomization rates (typically around 40-60,000 rpm) and fluid flow rates (typically around 100-400 cc's per minute) of coatings through a bell-atomizer
32
have a tendency to wear grooves
44
A on the inner cavity wall
44
, as shown best in
FIG. 3
c
, and wear grooves
46
A on the serrated edges
46
, as shown best in
FIG. 3
d
, of bell-atomizers
32
. Metallic or mica-content in coatings, such as automotive basecoats, increases this wear rate dramatically. Heavily pigmented coatings, such as primers, have a similar effect.
As shown in
FIGS. 3
b
and
3
c
, the wear on either side of the distribution disk
42
forms grooves
44
A on the inner cavity wall
44
over the course of time. These grooves
44
a can cause bell fluid flow deviation, plugging, and spitting. The grooves
46
A formed on the serrated edge
46
, as shown in
FIG. 3
d
, may cause irregular atomization and spitting.
The present invention addresses these wearing problems by adding a silicon-doped amorphous carbon coating to the surfaces of the bell cup
36
. The silicon-doped amorphous carbon coating increases the wear performance of both aluminum and titanium bell-atomizers
32
without adding significant cost.
FIG. 4
illustrates a general logic flow diagram for preparing and coating the surface of the metallic bell cups
36
. To prepare the bell cups
36
for the silicon-doped amorphous carbon coating, the bell cups
36
are first cleaned with a combination of water, soap, and solvent in Step
100
. Next, the bell cups
36
are etched, rinsed, and etched again for a predetermined time. The bell cups
36
are then rinsed with water, air dried and then vacuum dried for a predetermined time in Step
120
.
Next, the bell cups
36
are atomically cleaned in Step
130
by argon bombardment at 200V, 500V, and 200V again. The bell cups
36
are then coated in Step
140
with a silicon-doped amorphous carbon coating. A more detailed logic flow diagram of the preparation and coating of aluminum bell cups
36
according to a preferred embodiment is shown below in
FIG. 5
, while a more detailed logic flow diagram of the preparation of titanium bell cups
36
according to another preferred embodiment is shown below in FIG.
6
.
Referring now to
FIG. 5
, the surfaces of the aluminum bell cups
36
are first cleaned with soap, water, and solvent in Step
200
. Next, in Step
210
, the aluminum bell cups
36
are etched with a 5% solution of sodium hydroxide for
20
seconds, often under ultrasonic agitation. In Step
220
, the aluminum bell cups
36
are rinsed in water, and in Step
230
the aluminum bell cups
36
are etched in a 1% nitric acid solution for 5 minutes under ultrasonic agitation. The aluminum bell cup
36
is then rinsed with water in Step
230
and blown dry in Step
240
. The bell cups
36
are then placed in a vacuum pressure chamber pressurized to 10
−7
torr in Step
260
. While Steps
200
through
260
are the preferred method for preparing the surface of the aluminum bell cups
36
for applying a coating, it is contemplated that some of these steps may be unnecessary or may be altered to achieve the same desired result.
In Step
270
, the aluminum bell cups
36
are atomically cleaned by argon bombardment at 200V, 500V, and 200V again. The aluminum bell cups are now ready to have the silicon-doped amorphous carbon coating applied.
In Step
280
, a layer of silicon-doped amorphous carbon coating is applied to the bell cups
36
by placing the bell cups
36
in a chamber containing a gaseous mixture of methane and tetramethylsilane. A 13.56 MHz radio frequency power source is turned on until a 500V bias is achieved. A 10-15% silicon film is deposited on the surface of the aluminum bell cups
36
after approximately 3 hours. The coated bell cups
36
are ready for use in an atomizer
32
system.
While Step
280
represents the preferred method for coating an aluminum bell cup
36
, it is contemplated that other dopants may be used. For example, tungsten-doped or titanium-doped amorphous carbon may be used. In addition, other hydrocarbons may replace methane. These hydrocarbons include acetylene, ethene, butane, pentyne, and benzene. Also, other sources of silicon will work as well, such as diethylsilane. Finally, other frequencies or voltage biases may be used. For example, frequencies other than 13.56 MHz may be used, including pulsed direct current. A range of voltage biases varying from 200V to 1000V may be used as well, with 200V biases giving the hardest film and 1000V biases having the fastest deposition rate.
Referring now to
FIG. 6
, the surfaces of the titanium bell cups
36
are cleaned with soap, water, and solvent in Step
300
. Next, in Step
310
, the titanium bells
36
are etched for
60
seconds in a 3% nitric acid in ethanol solution under ultrasonic agitation. The titanium bell cup
36
is rinsed with water in Step
320
, and then placed in ethanol for 5 minutes under agitation in Step
330
.
The titanium bell cups
36
are then rinsed with water in Step
340
and blown dry in Step
350
. The titanium bell cups
36
are then placed in a vacuum chamber a pressurized to 10
−7
torr in Step
360
. While Steps
300
through
360
are the preferred method for preparing the surface of the titanium bell cups
36
for applying a coating, it is contemplated that some of these steps may be unnecessary or may be altered to achieve the desired result.
In Step
370
, the aluminum bell cups
36
are atomically cleaned by argon bombardment at 200V, 500V, and 200V again. A sputtered layer of chrome is then applied to the surface of the titanium bells
36
in Step
380
. The chrome layer serves as an adhesion promoter for the silicon-doped amorphous carbon coating.
A layer of silicon-doped amorphous carbon coating is applied to the chrome surface of the titanium bell cup
36
in Step
380
. This is accomplished by placing the bell cups
36
in a chamber containing a gaseous mixture of methane and tetramethylsilane. A 13.56 MHz radio frequency power source is turned on until a 500V bias is achieved. A 10-15% silicon film is deposited on the surface of the bells
36
after approximately 3 hours. The coated bell cups
36
are ready for use in an atomizer
32
system.
While Step
380
represents the preferred method for coating a titanium bell cup
36
, it is contemplated that other silicon dopants may be used. For example, tungsten-doped or titanium-doped amorphous carbon may be used. In addition, other hydrocarbons may replace methane. These hydrocarbons include acetylene, ethene, butane, pentyne, and benzene. Also, other sources of silicon will work as well, such as diethylsilane. Finally, other frequencies or voltage biases may be used. For example, frequencies other than 13.56 MHz may be used, including pulsed direct current. A range of voltage biases varying from 200V to 1000V may be used as well, with 200V biases giving the hardest film and 1000V biases having the fastest deposition rate.
While the preferred method for applying an amorphous carbon coating is described above, it is understood that there are many other methods for applying doped amorphous carbon coatings to aluminum and titanium surfaces that are well known in the art, such as laser ablation, ion beam assisted bombardment and ion beam bombardment.
Validation studies were performed to show that the silicon-doped amorphous carbon coatings improved the wear resistance of the aluminum and titanium bell cups
36
.
In one validation study, four bell cups
36
were used. Two aluminum Behr Eco-bell cups
36
were coated with silicon-doped amorphous coating according to the preferred embodiment of the present invention, as detailed above. One uncoated aluminum Behr Eco-bell cup
36
and one uncoated titanium Behr Eco-bell cup
36
were also used.
The four cups
32
were placed on a main enamel basecoat line, with coated and non-coated bells
32
placed on opposite sides of a paint booth on two pairs of Behr SF3 side machines. The opposing pairs of side machines were set up with identical spray programs. The machines were run continuously for 10 weeks, 20 hours per day. The bells
36
were taken off line only for cleaning and photographing.
Photomicrographs were taken of each bell cup
36
once per week. Digital images were taken of the inside cavity wall
44
and the serrated edge
46
of each cup
36
at approximately 10X magnification. All photographs were labeled and mounted in an album. Time of failure was determined by comparison of the photomicrographs to photomicrographs of other failed bell cups
36
. In addition, time to failure was determined by evaluating sprayed surfaces for defects associated with worn bell cups
36
.
During the course of the experiment, each bell cup
36
exhibited a progressive wear pattern as the time of service increased. The uncoated aluminum bell
36
, showed significant abrasive wear starting from the first exposure to the abrasive painting environment, and by six weeks was taken off line due to severe wear. The titanium bell cup
36
held up for the entire test period, but showed increase in surface wear with respect to time in service. The coated aluminum bell cups
36
showed no significant abrasive wear on the inner cavity wall
44
of the bell cups
36
.
The serrated top edges
46
of the aluminum and titanium uncoated bell cups
36
both displayed signs of abrasive wear on the serrated teeth of the inner surface, conditions that can cause spitting and other related surface irregularities. No significant wear was evident on either the coated aluminum or titanium bell cups
36
during the 10-week study.
The test conclusions indicated that the bell-cups
36
that had silicon-doped amorphous coatings lasted at least twice as long as the standard uncoated aluminum bell cups
36
. The tests also indicated that titanium bell cups
36
, while superior to standard aluminum cups
36
, were inferior to the coated bell cups
36
of the present invention for the bell application of an enamel basecoat.
While the invention has been described in terms of preferred embodiments, it will be understood, of course, that the invention is not limited thereto since modifications may be made by those skilled in the art, particularly in light of the foregoing teachings.
Claims
- 1. An improved bell atomizer for use in electrostatic applications having a bell housing and an aluminum bell cup, the improvement comprising:a wear resistant coating formed on a surface of the aluminum bell cup, wherein said wear resistant coating comprises a silicon-doped amorphous carbon coating.
- 2. An improved bell atomizer for use in electrostatic applications having a bell housing and a titanium bell cup, the improvement comprising:an adhesion promoter applied to a surface of the titanium bell cup; and a wear resistant coating formed on said adhesion promoter, wherein said wear resistant coating comprises a silicon-doped amorphous carbon coating.
- 3. The bell atomizer of claim 2, wherein said adhesion promoter comprises a layer of sputtered chrome.
- 4. A spray applicator for use in dispensing liquids having improved wearability comprising:a silicon-doped amorphous carbon coating formed on an aluminum surface of the spray applicator.
- 5. A spray applicator for use in dispensing liquids having improved wearability comprising:an adhesion promoter applied to a titanium surface of the spray applicator; and a wear resistant coating formed on said adhesion promoter, wherein said wear resistant coating comprises a silicon-doped amorphous carbon coating.
- 6. The spray applicator of claim 5, wherein said adhesion promoter comprises a layer of sputtered chrome.
US Referenced Citations (13)