EP0850108A1

EP0850108A1 - Method and apparatus for overcoating by autodeposition

Info

Publication number: EP0850108A1
Application number: EP96935807A
Authority: EP
Inventors: George P. Derderian; Oscar E. Roberto; Kevin L. Woock
Original assignee: Henkel Corp
Current assignee: Henkel Corp
Priority date: 1995-09-27
Filing date: 1996-09-18
Publication date: 1998-07-01
Also published as: ZA967941B; WO1997011786A1; AU7360196A; BR9610952A; EP0850108A4; JPH11514914A; AR003704A1; CA2233000A1

Abstract

Articles coated with a non-metallic continuous phase matrix containing fine metal particles are overcoated with a polymer by continuously moving the articles through a first station in which the articles are immersed in a coating chemical bath (7), a second station for rinsing the articles with a rinse fluid from risers (15 and 19) to remove excess coating chemicals therefrom, and a third station for curing the polymer coating on each article at an elevated temperature in an oven (25).

Description

Description Method and Apparatus For Overcoating By Autodeposition.

REFERENCE TO RELATED INVENTIONS The invention of the present application is related to the commonly as¬ signed inventions of U.S. Patent No. 5,409,737, issued from Serial No. 08/102.662 filed August 5, 1993, a CIP from Serial No. 07/847,543, issued on April 25, 1995, for "PROCESS FOR SEPARATING MULTIVALENT METAL IONS FROM AUTO¬

DEPOSITION COMPOSITIONS AND PROCESS FOR REGENERATING CHELAT¬ ING TYPE ION EXCHANGE RESINS USEFUL THEREWITH"; U.S. Serial No. 08/427/480, a CLP. of the above Serial No. 08/102,662; U.S. Patent No. 5,393,416, issued from Serial No. 08/008.956 on February 28, 1995, for "APPARATUS FOR MAJNTAΓNΓNG A STABLE BATH FOR AN AUTODEPOSITION COMPOSITION

BY PERIODICALLY SEPARATING PARTICULAR METAL IONS FROM THE COMPOSITION"; and divisional application Serial No. 08/231 ,075 filed November 7, 1994 from the latter 08/008,956; and divisional applications from the latter 08/231 ,075 including Serial Nos. 08/452,926 filed May 30, 1995, and 08/453,618 filed May 30, 1995; and lastly Serial No. 08/276,284 filed on July 18, 1994, for "DUAL

COATED METAL SUBSTRATES AND METHODS OF MAKING THE SAME". The teachings of these co-pending applications are incorporated into this present appli¬ cation in their entirety by reference, provided any such teachings are not inconsistent with any explicit teaching herein. BACKGROUND

1.0 Field Of The Invention:

The field of the present invention relates generally to systems providing for coating materials, such as metals including steel, with a paint coating via a chemical reaction through use of an autodeposition composition bath. The present invention is particularly related to apparatus for an autodeposition system for coating metal substrates, which were previously coated with an undercoat of a metal rich organic layer, i.e. a non-metallic continuous phase matrix to which par¬ ticles of metal have been added, with an overcoat of an autodeposited material, such as poly {vinylidene chloride} (hereinafter usually abbreviated as "PVDC") or acrylic material.

2.0 Discussion Of Related Art:

Autophoresis and electrophoresis are two known processes for coating objects, particularly those fabricated from metallic material, with a coating composition. The electrophoresis effect provides for electrodeposition through the use of an electric field to control the movement of charged organic molecules to a workpiece serving as one electrode of a typically two-electrode system. The magnitude of electrical current and time of application is controlled for coating the workpiece to a desired thickness. The autophoresis effect permits an autodeposition coating process to be carried out via con¬ trol of the de-stabilization and deposition of high-molecular-weight negative or neutral¬ ly-charged latex polymer particles, for example, onto a workpiece having a metallic surface that is chemically treated to produce positively charged ions at the surface of the workpiece which attract the oppositely or neutrally charged particles of coating composition. The chemical baths may also include acrylic material or PVDC, for ex¬ ample. The parts to be coated are typically dipped into a coating bath containing the desired coating composition or are flow coated. Workpieces of iron, steel, galvanized metal coated with zinc, and so forth, at least about the outer surfaces of the workpiece, can typically be coated via an autodeposition coating process. Metal substrates including unthreaded parts such as panels and fasteners and threaded parts in the form of nuts, bolts and other parts useful for the automotive and other industries are coated to improve resistance to corrosion and to provide other de¬ sirable properties.

It is known to coat metal substrates with an aqueous coating composition which provides an adherent, water insoluble, alkali and corrosion resistant coating. For ex¬ ample Irving Malkin et al., U.S. Patent No. 3,671 ,331 and Leo D. Barrett et al., U.S. Patent No. 3,907,608 and patents cited therein disclose a coating composition which is made from an intimate mixture in an aqueous liquid medium of a hexavalent-chrom- ium-providing substance and a pulverulent metal and may further contain a water solu- ble organic liquid substance. Such compositions provide corrosion resistance on such metal substrates as aluminum, zinc, cadmium, titanium, mixtures and alloys thereof, and the like. Modifications have been made to such compositions to improve corrosion re¬ sistance and other properties of the coating. For example, Bert E. Palm et al., U.S. Patent No. 3,849,141 employs zinc as the pulverulent metal in finally divided form so as to improve adhesion. Jon A. deRidder, U.S. Patent No. 3,940,280 discloses the ad- dition of a minor amount of water soluble cellulose ether to improve the foam suppres¬ sion properties of the coating liquid.

Walter H. Gunn et al., U.S. Patent No. 3,954,510 disclose an improvement in the stability of the coating composition through the pH control of the components of the composition. Takao Higashiyama et al., U.S. Patent No. 4,266.975 disclose an anti-corrosive coating composition using an optional pH modifier and the substitution of a boric acid component for a portion of the chromic acid component. Each compo¬ sition is stated to provide improved corrosion-resistant properties in both fresh and salt water environments.

Michael Fourez et al., U.S. Patent No. 4,891,268 disclose the addition of a sol- id lubricant to the coating composition, particularly for the coating of threaded devices such as nuts, bolts and the like. Arthur A. Luecke et al., U.S. Patent No. 5,006,597 disclose a two layer coating system in which the underlying layer contains chromium in non-elemental form and the top coating is comprised of an aqueous colloidal disper¬ sion of carbon black. Such coatings are stated to be particularly useful in the automot- ive industry for treating small metal parts such as metal fasteners, nuts, bolts and inter¬ ior body panels. The coating composition is further stated to provide a uniform black color which is particularly desirable in the automotive industry although commercial acceptance has not been forthcoming. All of the above-mentioned United States patents are incorporated herein by reference. Autodepositing compositions are also known for coating metal substrates to im¬ prove corrosion resistance. Such compositions are generally comprised of aqueous so¬ lutions of acid and an oxidizing agent, and aqueous dispersed resin. Autodeposition is similar to electrodeposition, but does not require the aid of external electrical current to deposit the resin particles on the metal surface. Such coatings have a relatively high degree of corrosion resistance and, when the autodepositing composition contains a suitable pigment, are particularly suited for providing a uniform colored (e.g. black) appearance, highly desirable in many industries including the automotive industry. Examples of autodepositing compositions are disclosed, for example, in Euro¬ pean Patent Publication 0132828, Bashir M. Ahmed, U.S. Patent No. 4,647,480 and Wilbur S. Hall, U.S. Patent No. 4,186,219 and patents cited therein each of which is incoφorated herein by reference. Such compositions are particularly effective when the resin material is provided in the form of a latex made from the emulsion polymer¬ ized product of at least two polymerizable ethylenically unsaturated monomers.

Despite these efforts there remains the need for developing coatings for metal substrates with improved properties, especially corrosion resistance. In addition it is highly desirable to provide corrosion resistant metal parts having a uniform black col- or.

Applicants discovered that an autodeposited coating, heretofore applied directly to the metal part itself, can be effectively applied and bonded to an adherent coating of the type described in, for example, Irving Malkin et al., U.S. Patent No. 3,671 ,331 and Leo D. Barrett et al., U.S. Patent No. 3,907,608, and other related patents includ- ing those cited herein. The resulting coated product exhibits excellent corrosion resist¬ ance and may be produced with a commercially acceptable uniform black color. Ap¬ plicants, to satisfy a need in the field of the present invention, conceived and devel¬ oped a substantially automated autodeposition system for overcoating articles as indi¬ cated above. 3.0 Summary of the Invention:

An object of the invention is to provide an improved system for autodeposition processes for coating over a non-metallic continuous phase matrix to which particles of metal have been added.

Another object of the invention is to provide an improved system for sub- stantially automating autodeposition processes for overcoating various parts and articles that have been previously coated with corrosion resistant materials of a non-metallic continuous phase matrix to which metal particles have been added, for improving the appearance of the articles, enhancing corrosion resistance, and providing other desira¬ ble properties such as a low friction coating in a rinse process subsequent to autodepo- sition coating.

With these and other objects of the invention in mind, the present invention provides for a substantially integrated and continuous line processing system for the coating via autodeposition of various articles, particularly metal articles that have been previously coated with an anticorrosion coating of metal rich organic material. In one embodiment of the invention, the autodeposition system includes four stations. A first station is for loading parts to be autodeposition coated from a hopper onto a continu- ous conveyor belt. The parts are then transported via the belt at a predetermined speed to a chemical bath. The belt is immersed into the chemical bath for moving the parts through the chemical bath for a predetermined time to autodeposition coat the parts with the chemical material. After immersion, the parts are moved by the belt from the chemical bath to a third station for first prerinsing the autodeposition coated parts to remove excess coating material therefrom, and discharge the contaminated rinse water into a wasteline.

After prerinsing, the parts are further processed at Station III by passing them under a plurality of risers for further water rinsing via recirculated water, and there¬ from under a misting riser for final rinsing with virgin dionized water. Note that at Station III the main rinse water is recirculated, and a portion is provided for the pre- rinse water, which portion is as indicated discharged into a waste line. A main tank is used for holding the recirculated water, which is kept at a predetermined level via the periodic addition of clean water and run off from the misting riser.

The parts or articles are then moved on the belt into a fourth station including an oven for curing the parts at a predetermined temperature for a predetermined time.

The continuously moving conveyor belt is arranged in a seφentine configured path through the oven, whereby the parts after curing are automatically discharged by grav¬ ity from the conveyor belt into a pans cart.

The above-described first embodiment of the invention is prefened for autode- positing chemicals such as PVDC, for example. In a second embodiment of the inven¬ tion, for autodepositing coating materials such as acrylics, a second embodiment of the invention is prefened in which a fifth station is added for providing a second oven. The first oven at Station IV is configured to discharge the semicured parts or articles therefrom onto a second conveyor for transport into the second oven at Station V. in which the acrylic coated parts or articles are finally cured at a substantially higher temperature than the temperature maintained in the first oven. The belt in the second oven is arranged in a manner for continuously moving the parts or articles to be cured through the oven, and discharging the same from the oven into a parts cart.

In the second embodiment of the invention, in view of the greater sensitivity of acrylic coatings to deterioration during rinse operations prior to curing, the rinse apparatus at Station III must be adjusted to account for this sensitivity. For example, instead of using spray nozzles in the risers as in the first embodiment of the invention for coating PVDC, the risers are configured for recirculating water with overflow over the acrylic coated parts in order to insure gentle rinsing thereof.

Note further that at Station II, means are provided for adjusting the sag of the belt into the chemical bath, for providing a range of adjustment for timing the duration of immersion of the parts or articles in the chemical bath. The belt itself is continu¬ ously moving at a predetermined speed.

BRIEF DESCRIPTION OF THE DRAWINGS Various embodiments of the present invention are described below with refer- ence to the drawings, in which like items are identified by the same reference designa¬ tion, and in which:

Fig. 1 is a cutaway side elevational view of the continuous processing autodep¬ osition coating line of one embodiment of the invention;

Fig. 2 is a sectional view taken along section line 2-2 of Fig. 1 , but looking through from the front of the conveyor belt where it wraps around the side of the tank holding the chemical bath, as shown in Fig. 1 ;

Fig. 3 is a sectional view taken along section line 3-3 of Fig. 1 of the spray or rinse station, and also shows diagramatically various components associated with the rinse station; Fig. 4 shows a cross sectional view along section line 4-4 of Fig. 1 ;

Fig. 5 shows a second embodiment of the invention for the curing oven; and Fig. 6 shows a third embodiment of the invention for a two zone curing oven.

DETAILED DESCRIPTION OF THE INVENTION

With reference to Fig. 1, a system for one embodiment of the invention where coating parts or articles via autodeposition is shown to include four stages or stations

(I through IV). The first station is an entry station "I" where parts or articles from a hopper 1 are dropped onto a closed loop conveyor belt 3 that is continuously moving. The next station is an autodeposition coating station "II" that in this embodiment in¬ cludes a tank 5 for containing the autodeposition chemical 7 for permitting the convey¬ or belt 3 to be moved through the chemical bath 7, thereby providing an immersion coating process, in this example. In an alternative embodiment of the invention, the coating station II can be re¬ configured to provide a flowcoat coating of the articles (not shown) through use of ris¬ ers suspended over the tank 5, and a pumping means (not shown) for pumping the aut¬ odeposition chemical bath into the risers configured for permitting the chemical bath to flow from slotways in the risers onto the parts or articles to be coated. This altern- ative configuration is not shown in Fig. 1.

With further reference to Fig. 1 , a third station is a rinse station "III" for receiving coated parts or articles from the coating station II to rinse the same wim water, in this example. Note that in another embodiment of the invention the rinse station can be provided with chemicals added to the water for both rinsing the parts or articles and applying thereto a low friction coating. The rinse station III includes a tank 9 for containing the rinse solution 1 1. A housing 13 is provided over the tank 9 for enclosing a rinse-off riser 15 mounted above the belt near the point of entry of the articles moving on the belt 3. The point of entry is provided by an entrance opening slot 17 in the side of the housing 13, as shown. Also enclosed by housing 13 are a plurality of water rinse risers 19 mounted over the belt 3 above tank 9, as shown. Lastly, at the opposite side interior to the enclosure 13 and above the belt 3 is a misting riser 21, as shown. The opposite side of housing 13 includes an open exit slot 23 through which the belt 3 moves to cany articles from the rinse station III to the curing or oven station IV. The curing station IV consists of an oven 25 that in- eludes a housing 27 fabricated from mild steel, in this example.

The belt 3, in this example, has a width of about 1 ' (one foot), as shown in Fig. 2, and consists of a 316 stainless steel mesh belt with horizontal crossbars 29 on 6" (six inch) centers, in this example (only a portion of the crossbars 29 are shown for the sake of simplicity). The horizontal side guards 29, which are part of belt 3, pre- vent the articles or parts being carried on the belt from falling off the sides of the belt

3. The belt 3 is driven by motor driven sprocket wheels 31 through 38, as shown. A vertically adjusted support roller 39 may be provided within tank 5 for supporting the central portion of belt 3 between sprocket wheels 32 and 33. Sprocket wheels 32 and 33 are adjustable for increasing or decreasing the distance between them, for ef¬ fectively increasing or decreasing the length of belt 3 that is immersed in the coating chemical 7 in tank 5, thereby providing control of the length of time that the parts or articles to be coated are immersed in the coating bath. If the support roller 39 is used, any adjustment of sprocket wheels 32 and 33 for increasing or decreasing the length of belt 3 immersed in tank 5 must also include adjustment of the vertical height of support roller 39 within tank 5, as appropriate. The belt 3 is supported on its bottom outer edges by a pair of opposing and parallel edge support members 40 (only one is shown) between sprocket wheels 31 and 32. The edge supports 40 can be provided by longitudinal angle iron or flat bars, for example. Similar belt edge supports 42 are also included on the underside opposing edges of belt 3 between sprocket wheels 33 and 34, and belt edge supports 44 between sprocket wheels 34 and 35. In Fig. 4, a sectional view along 4-4 shows the horizontal crossbars 29, and an example of the use of angle iron for belt edge supports 44. Similar belt edge supports are used for other of the conveyor belts in this and other embodiments of the invention.

Within oven 25 a second or intermediate movable belt 45 is mounted and dri¬ ven by a pair of sprocket drive wheels 47 and 49 at opposite ends of the belt, as shown. A pair of parallel edge supports 51 are provided for supporting the opposing bottom edges of belt 45 between sprockets 47 and 49, as shown. A third and bottom¬ most conveyor belt 53 is mounted within oven 25 under belt 45, and is supported and driven by a pair of sprocket drive wheels 55, 57 at opposite ends of belt 53. A pair of opposing belt edge supports 59 are located along the opposing bottom edges of the first segment of belt 53, as shown. In this example, the conveyor belts 45 and 53 consist of mild steel material, or high temperature PVC (polyvinyl chloride), or stain¬ less steel, depending upon the particular application. An opening 61 is provided in the bottom section of oven enclosure or housing 27 for permitting parts or articles cured in the oven to be dropped from one end of belt 53 into a parts cart 63 positioned be¬ neath the article discharge slot 61. In an alternative embodiment of the invention for a single zone curing oven, oven 25 is reconfigured to the configuration shown in Fig. 5 for curing oven 26. As shown, another conveyor belt 54 has been added to the configuration of oven 25. Sprocket drive wheels 56 and 58 are also included for driving belt 54, located beneath and parallel with conveyor belt 53, as shown. In this alternative configuration, parts travelling on belt 53 rotating in a clockwise direction, in this example, will fall off the end of belt 53 and onto belt 54 rotating in a counterclockwise position, for keeping the parts within oven 26 for a longer period of time than would otherwise be obtained with the configuration of oven 25. The cured parts fall from belt 54 at the opposite end thereof from entry, down through a discharge slot 62 into parts cart 63, as shown. By adding the additional conveyor belt 54, the range of curing times can be extended. The tank 5 for the chemical bath 7 is provided with an overflow trough 65 mounted along the top leading edge of the tank, as shown. Any chemical bath that overflows during operation of the system into trough 65 is discharged therefrom via a wasteline, not shown. Note also that the opposing side edge of tank 5 is joined via a splash panel 67 to the bottom of the entry slot 17 of housing 13 of the rinse station III. A rinse-riser V-shaped trough 69 is provided at the bottom of housing 13 under the rinse-off riser 15 and belt 3, as shown. A waste line 71 is provided at the bottom of the trough 69 for discharging waste water therefrom. A splash panel 73 is formed in housing 13 between trough 69 and tank 9, as shown. Also, a V-shaped trough 75 is included between the opposite end of housing 13 and a side portion of oven housing 27 beneath the entry slot 77. A waste line 79 is connected to an outlet at the bottom of the trough 75 for discharging liquids therefrom.

In Fig. 2, a sectional view taken along 2-2 of Fig. 1 through chemical bath tank 5, looking past the front end of the conveyor belt 3, shows coils 81 of a heater/chiller package located in tank 5. As shown, the coils 81 are immersed in the chemical bath 7. Also, two mixers 83 (only one is shown) have their motors 85 clamped or rigidly mounted upon steel tubing 87, in this example, at opposing front and rear portions of the tank 5. Each of the mixers 83 include a shaft 89 with a mixer blade 91 secured to the free end thereof, and immersed well within the chemical bath, respectively, as shown. Note also that the tank 5 includes fillets 93 rigidly secured between bottom, side, front, and rear wall portions of the tank 5, to eliminate solution vortexing at the corners of the tank 5. In this example, the tank consists of a mild steel material with a B.F. Goodrich Tri-Flex 1000_TM rubber lining PVC or polypropylene. Also, in this example, the heater-chiller coils 81 are part of a heater-chiller system manufactured by Koolant Koolers, Inc., of Kalamazoo, Michigan. The system is used for maintain¬ ing the chemical bath 7 at a temperature between 68°F to 72°F, with the prefened temperature being 70°F, in this example. Also, the two mixers 83 consist of XJ30 mixers manufactured by Lightnin, a unit of General Signal, Avon, NY, in this examp- le.

In Fig. 3, a partial sectional view and partial cutaway view taken along section line 3-3 of Fig. 1 shows a portion of the interior layout of rinse tank 9 and the associ¬ ated riser housing 13 and interior assembly thereof. The tank 9 includes an overflow trough 95 with a waste line 97 for discharging water therefrom to a waste disposal line (not shown). In this example, the risers 19 each include a pair of spaced apart nozzles

99, for spraying recirculated water from tank 9 onto coated parts or articles moving past the nozzles 99 on belt 3. The rinsing fluid 1 1 in tank 9 is pumped therefrom via the components connected in series and shown schematically to include a valve 101 , a PVC basket strainer 103, a PVC pump 105, a flow regulating valve 107, a pressure gage 109, all connected in series via PVC piping 1 1 1 between the risers 19 and tank

9, in this example. As would be known to one of skill in the art, other conventional pumping systems and control and regulating means can be used, and the combinations shown herein are not meant to be limiting. Note also that the recirculating pump sys¬ tem is used to drive rinse water 1 1, in this example, into riser 15 for spraying from an associated nozzle (not shown) in providing the prerinse or first rinse operation.

Virgin deionized (hereinafter usually abbreviated as "DI") water is supplied under pres¬ sure from an associated storage tank or DI supply (not shown) through use of a con¬ ventional pumping system (not shown). In this example, each of the risers 19 include a pair of spray heads 99 consisting of model GG15 S.S. nozzles for spraying 1.5 gal- Ions per minute at 10 psi (ten pounds per square inch) each; rinse-off riser 15 includes a single nozzle (not shown) Model No. GG15 S.S. for spraying at 1.5 GPM at 10 psi; and misting riser 21 includes a single nozzle model no. 1/4 LNN 1.5 S.S.; with all of the nozzles in this example being manufactured by Spraying Systems Co., Illinois. Depending upon the application, as would be known to one of skill in the art,, different nozzles with different spray rates may be incoφorated in the system for optimum operation. The use of nozzles as indicated herein is not meant to be limiting. In a third embodiment of the invention, as shown in Fig. 6, a two zone curing oven is provided particularly for the curing of parts autodeposition coated with an acrylic material. As shown, the only difference between the two zone oven 1 18 and the altemative single zone oven configuration 26 shown in Fig. 5, is that a partition 120 is added in the center of the oven for dividing the oven into a first oven zone 66 heated to one temperature, and a second zone 122 for heating the oven to a second temperature different from the first. Parts are cured in the first zone 66 by traveling therein on conveyor belt 3, falling from conveyor belt 3 at an extreme end from entry onto the oppositely directed or moving conveyor belt 45, and dropping from the latter through an opening 121 in the oven partition 120, and onto the clockwise rotating belt

53. The parts then travel on belt 53 in the second zone 122, and drop from belt 53 at the opposite end onto belt 54 rotating counterclockwise. The parts then travel to the opposite end of belt 54, and are dropped therefrom through an opening 62 in the bottom of housing 27 into the parts cart 63, as previously described. The general operation of the inventive system will now be described, followed by specific examples. The belt 3 is driven at a predetermined substantially constant speed for the continuous autodeposition coating of parts and articles in the system. The speed of belt 3 in association with the dimensional parameters of various elements of the system is determinative of the length of time a particular piece, part or article is processed at each of the four stages or Stations I through IV, respectively, in this example. Initially, parts or articles to be coated are loaded into a hopper 1 , and through control mechanisms of a conventional nature (not shown) are automatically or manually permitted to drop individually from hopper 1 onto belt 3 moving beneath a discharge outlet 1 13 of hopper 1. As indicated, the parts or articles (not shown) are then continuously moved on belt 3 as follows.

First, the parts move to Station II where the belt 3 dips into the tank 5, in this example, for immersing the parts in the chemical bath 7 for a predetermined and suffi¬ cient period of time to autodeposition coat the parts with a desired thickness of the chemical or coating being applied. Belt 3 then proceeds to move the coated parts out of the chemical solution to Station III, where rinse-off riser 15 is activated for spray¬ ing recirculated rinse solution onto the parts for removing any excess coating material therefrom. The contaminated rinse solution is discharged from trough 69 into a waste line 71, as previously described. The parts then continue to move on belt 3 and pass beneath water rinse risers 19 where rinse solution is sprayed on the parts for a prede¬ termined time to complete the primary rinsing operation. Most of the rinse fluid sprayed on the parts from nozzles 99 of risers 19, respectively, is returned to tank 9, and recirculated, as previously described. The parts then pass beneath misting riser

21 which sprays them with virgin rinse solution for insuring all contaminants are rinsed away from the parts. The parts then move into oven 25 for curing at a prede¬ termined temperature.

In this example, the parts move on belt 3 from entry slot 77 of oven 25 to near the opposite end thereof, where the parts are dropped from belt 3 onto belt 45 moving in the opposite direction or counter-clockwise. The parts then move on belt 45 toward the entry end of oven 25, and at the end of belt 45 are dropped therefrom onto the un¬ derlying conveyor belt 53 moving clockwise, for moving the parts back towards the opposite end of the oven. The parts are then dropped off of the opposite end of belt 53, and fall through a discharge opening 61 at the bottom of oven 25, in this example, into a parts cart 63. The speed of belts 3, 45, and 53, determine the curing time for the parts in oven 25. Note that the particular belt configuration shown in this example is not meant to be limiting, and other configurations can be utilized for moving the parts through the oven during the curing process.

® Specific examples of processing M-10 bolts coated with Dacromet 320 will now be given. In the examples, belt 3 is being driven at 5 fpm (five feet per minute).

Belt 45 is being driven at 5 fpm (five feet per minute), and belt 53 is being driven at

5 fpm (five feet per minute). Please refer to Table 1 below.

Table 1 shows the process parameters for coating the bolts with PVDC. In this example, the PVDC is provided by Autophoretic 800 coating chemicals manufactured by Henkel Coφoration, Madison Heights, Michigan. As shown, the concentration used is 6.8% weight per unit volume. The immersion time in chemical bath 7 for the parts ranges from 30 seconds to 1 minute and 45 seconds, depending upon the thick¬ ness of coating desired. The chemical bath 7 is kept at ambient temperature, preferab- ly at 70°F, but at least within a range of 68° to 72°F. The "ORP" refers to an oxi¬ dation reduction potential meter known in the art for measuring the oxidation potential in millivolts of the chemical solution, and is indicative of the amount of complexed TABLE 1

DATA PROCESS PARAMETERS

STATION II III IV

OPERATION COAT RINSE CURE

CHEMICAL PVDC TAP WATER

APPLICATION DIP DIP OR SPRAY

CONC. 6.8% W/V

TIME 30" TO 60" 30' "-sees; '-mins 1 '45"

TEMPERATURE AMBIENT AMBIENT 230°F

ORP 355 mv

101 150 μmhos

fluoride in the chemical bath 7. As shown, the oxidation potential is maintained at 350 millivolts for assisting in adjusting the bath to stabilize it in order to keep iron fluoride in solution. When the measured millivolts drops below the desired level, ad¬ ditional hydrogen peroxide is added to the bath in order to keep the measured value at 350 millivolts, as indicated. The "101" shown in the Table 1 refers to a meter man¬ ufactured by Henkel Corporation, Madison Heights, Michigan, for measuring the free fluoride activity in the chemical bath 7 (the meter uses the rate of dissolution of a plat¬ inum electrode to make this measurement), and provides the measurement in micro- mhos. As shown in Table 1, it is prefened that the free fluoride activity be kept at 140 micromhos, in this example. In order to increase the free fluoride activity, more acid is added to the chemical bath 7.

After coating, the bolts (not shown) proceed to Station III for rinsing with tap water kept at ambient temperature. The total rinse time takes about 60 seconds. After rinsing with tap water as previously indicated, the bolts are conveyed to Station IV for curing in the oven 25 at 230°F, in this example, for 30 minutes. After curing, the bolts are dropped into cart 63, as previously described.

If the chemical bath consists of an acrylic material, the processing parameters are different. One material proposed for providing an acrylic coating is Autophoretic 700 coating material manufactured by Henkel Coφoration, Madison Heights, Michi¬ gan. Table 2 shows the process parameters for one embodiment of the invention for acrylic coating using one oven 25. Table 3 shows the process parameters for a pre¬ fened embodiment of the invention using a two stage or dual oven 118 for applying an acrylic coating to the previously indicated bolts, and curing the coating first for fif¬ teen minutes at 230°F in zone 66, and then for fifteen minutes at 350°F in zone 122. For processing other parts with different undercoatings on them, or with overcoating using other autodeposition materials, the process parameters are expected to be ad¬ justed from those indicated in Tables 1 through 3 in order to obtain an optimum auto¬ deposition coating on such other parts or articles. Note also that in each one of Tables 1 through 3, a dwell time of 30 seconds is prefened in transferring parts from coating station II to rinse station III.

TABLE 2

DATA PROCESS PARAMETERS

STATION II III IV

OPERATION COAT RINSE CURE

CHEMICAL ACRYLIC TAP WATER

APPLICATION DIP DIP

CONC. 6.6% W/V

TIME 45" TO 60" 30' "-sees; '-mins 1 '30"

TEMPERATURE AMBIENT AMBIENT 350°F

ORP 360 mv

101 160 μmhos TABLE 3

DATA PROCESS PARAMETERS

STATION II III IV- 1 IV-2

OPERATION COAT RINSE CURE CURE

CHEMICAL ACRYLIC TAP WATER

APPLICATION DIP DIP

CONC. 6.6% W/V

TIME 30" TO 60" 14' 14' "-sees '-mins 1^*30"

TEMPERATURE AMBIENT AMBIENT 230°F 350°F

ORP 360 mv

101 160 μmhos

Although various embodiments of the invention have been shown and described ■•herein, they are not meant to be limiting. Those of skill in the art may recognize vari¬ ous modifications to these embodiments, which modifications are meant to be covered by the spirit and scope of the appended claims.

Claims

1. An autodeposition system for applying a polymer coating over an or¬ ganic coating of a non-metallic continuous phase matrix containing fine metal partic¬ les, the latter coating being on each one of a plurality of articles to be processed, said system comprising: transport means for continuously moving said articles through said system during processing; a first tank containing a chemical bath of autodeposition material; immersion means for immersing said articles in said chemical bath for a predeterrnined period of time to apply said polymer upon said articles as they move through said chemical bath; rinsing means for applying rinse fluid upon overcoated ones of said articles to remove excess polymer and chemical bath therefrom; and curing oven means for receiving articles from said rinsing means for curing the polymer coating upon said articles by applying sufficient heat thereto for a predetermined period of time.

2. An autodeposition system as set forth in claim 1 , wherein: said transport means is a closed loop conveyor belt; and wherein said immersion means includes sets of sprocket wheels at opposite ends of said first tank that engage said conveyor belt so as to allow a portion of said conveyor belt to dip down into said first tank, the amount by which said conveyor belt dips determining said predetermined period of time for any given speed of movement of said conveyor belt.

3. An autodeposition system as set forth in claim 2 further comprising: means for adjusting the distance between said sets of sprocket wheels so as to permit the adjustment of said predetermined period of time.

4. An autodeposition system as set forth in claim 2 further comprising: a vertically adjustable support roller for contacting the lowest point of said portion of said conveyor belt in said first tank.

5. An autodeposition system as set forth in claim 1, wherein said rinsing means includes: a second tank having walls and an entrant end and an exit end; a first splash panel sloping upwardly from the entrant end of said tank; a second splash panel sloping upwardly from the exit end of said second tank; a first drain trough adjoining said first splash panel; a second drain trough adjoining said second splash panel; a riser coupled between said second tank and a point above said first trough; a plurality of risers coupled between said second tank and points above it; and means for pumping fluid when present in said second tank from said second tank and through said risers.

6. An autodeposition system as set forth in claim 5, further comprising: a misting riser coupled between said second tank and a point above said second splash panel; and means for coupling said misting riser to said means for pumping fluid.

7. An autodeposition system as set forth in claim 5, further comprising: an overflow trough mounted adjacent said first tank so as to maintain a maximum level of fluid therein.

8. An autodeposition system as set forth in claim 1 , wherein: said transport means is a first endless conveyor belt that passes through said first tank and said rinsing means and into said curing oven; and which further comprises a second endless conveyor belt mounted in said curing oven so as to receive coated articles falling off an end of said first conveyor belt, whereby the time the coated articles spend in said curing oven can be increased.

9. An autodeposition system as set forth in claim 8, further comprising: a discharge slot in the bottom of said oven; and at least a third endless conveyor belt mounted in said curing oven so as to receive coated articles falling from said second endless conveyor belt and delivering them to a point above said discharge slot.

10. An autodeposition system as set forth in claim 9, wherein said first and third endless conveyor belts rotate in a direction to move articles on them away from said rinsing means, and said second endless conveyor belt rotates in the opposite direction.

1 1. An autodeposition system as set forth in claim 5, further comprising fillets rigidly secured between the bottom and the walls of said second tank so as to eliminate vortexing at its comers.

12. An autodeposition system as set forth in claim 1 , further including: means for mamtaining the oxidation reduction potential of said chemical bath at a level for keeping complexed fluoride compounds in solution; and means for measuring and maintaining free fluoride activity of said chemical bath at a desired level.

13. A method for coating articles with a given chemical comprising the steps of: dipping an article in a solution of the chemical having a given w/v and a first temperature for a first period of time; rinsing the article after it has been dipped with tap water at a second temperature for a second period of time; and curing said article after it has been rinsed at a third temperature for a third period of time.

14. A method for coating an article as set forth in claim 13, wherein: said given chemical is PVDC having a w/v of 6.8%; said first temperature is the ambient temperature; said first period of time is between 30 minutes and one hour and 45 minutes; said second temperature is the ambient temperature; said second period of time is 60 minutes; said third temperature is 230°F; and said third period of time is 30 minutes.

15. A method for coating an article as set forth in claim 13, wherein: said given chemical is acrylic having a w/v of 6.6%; said first temperature is the ambient temperature; said first period of time is between 45 minutes and one hour and thirty minutes; said second temperature is the ambient temperature; said second period of time is 60 minutes; said third temperature is 350°F; and said third period time is 30 minutes.

16. A method for coating an article as set forth in claim 13, wherein: said given chemical is acrylic having a w/v of 6.6%; said first temperature is the ambient temperature; said first period of time is between 45 minutes and one hour and thirty mmutes; said second temperature is the ambient temperature; said second period of time is 60 minutes; said third temperature is 230°F; said third period time is 14 minutes; and wherein said article is further cured at a temperature of 350° for a period of 14 minutes.

17. The method of claim 13, wherein said chemical solution includes free fluoride, and complexed fluoride due to metal particles from said articles going into solution and combining with free fluoride ions, said method further including the steps of: maintaining the oxidation reduction potential of said chemical solution at a level for keeping complexed fluoride compounds in solution; and maintaining the free fluoride activity of said chemical solution at a desired level.

18. A method for applying a polymer coating via autodeposition over an organic coating of a non-metallic continuous phase matrix containing fine metal partic¬ les, the latter coating being on each one of a plurality of articles to be overcoated with said polymer, said method comprising the steps of: continuously moving said articles through each step of said method; immersing said articles in a bath of autophoretic coating chemicals for a predetermined period of time, for applying a polymer coating upon said articles; and curing the polymer coating on said articles by moving the articles through an oven at elevated temperatures relative to the ambient for a predetermined period of time.