CA2099094A1 - Adjustable rack for electrostatic painting and the like - Google Patents
Adjustable rack for electrostatic painting and the likeInfo
- Publication number
- CA2099094A1 CA2099094A1 CA 2099094 CA2099094A CA2099094A1 CA 2099094 A1 CA2099094 A1 CA 2099094A1 CA 2099094 CA2099094 CA 2099094 CA 2099094 A CA2099094 A CA 2099094A CA 2099094 A1 CA2099094 A1 CA 2099094A1
- Authority
- CA
- Canada
- Prior art keywords
- rack
- elements
- frame
- cross bar
- supporting
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Landscapes
- Spray Control Apparatus (AREA)
- Electrostatic Spraying Apparatus (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A rack, for supporting workpieces during an electrostatic paint spray operation, is comprised of a rack frame arranged to be suspended from a conveyor system and having means for selective mounting and removal of individual cross bars. Stainless steel hooks are permanently welded to the cross bars and provide means for supporting of the workpieces. When the cross bars become heavily layered with coating material, they may be removed from he frame and burned off in a high temperature oven without deterioration of the hooks or loss of electrical conductivity. Necessary burn-off operations are facilitated by easy removability of the cross bar elements, which enable the cross bars to be burned off separately from the rack frames, which need to be burned off less frequently. This also permits the oven to be loaded more compactly and with less tangling of parts. Highly efficient electrical contact is assured by using permanently welded stainless steel elements for the workpiece-supporting hooks, and by using a stainless steel hook element for supporting the rack on the system conveyor.
A rack, for supporting workpieces during an electrostatic paint spray operation, is comprised of a rack frame arranged to be suspended from a conveyor system and having means for selective mounting and removal of individual cross bars. Stainless steel hooks are permanently welded to the cross bars and provide means for supporting of the workpieces. When the cross bars become heavily layered with coating material, they may be removed from he frame and burned off in a high temperature oven without deterioration of the hooks or loss of electrical conductivity. Necessary burn-off operations are facilitated by easy removability of the cross bar elements, which enable the cross bars to be burned off separately from the rack frames, which need to be burned off less frequently. This also permits the oven to be loaded more compactly and with less tangling of parts. Highly efficient electrical contact is assured by using permanently welded stainless steel elements for the workpiece-supporting hooks, and by using a stainless steel hook element for supporting the rack on the system conveyor.
Description
2~9~0~
ADJUSTABLE RACR FOR ELECTROSTATIC PAINTING AND THE LIKE
Background and Summary of the Invention In a typical electrostatic paint spraying operation, workpieces to be painted are suspended on a conveyor which advances through a spray painting booth. The spray device and the workpiece are oppositely charged at a high voltage, so that charged paint particles issued from the spray device are electrostatically attracted to the workpiece to be painted, enabling the workpiece to be coated on surfaces that are not directly visible to the spray device. In most cases, special hangers or adaptors are provided for suspending the workpiece from the conveyor at a suitable location. Additionally, where the workpieces are relatively small, it is common to employ special rack devices, which are suspended from the conveyor and which in turn support a plurality of workpieces.
For efficient production operations, it is beneficial to provide for optimum density of the workpieces being carried by the conveyor. Typically, this is provided for by utilizing adjustable rack devices, which can be manually configured to suspend a plurality of workpieces in a desired arrangement, depending upon the size and shape of the workpieces. For this purpose, the racks are provided with a plurality of metal hooks upon which the workpieces can be suspended in an arrangement and configuration providing optimal density.
When workpieces are being conveyed through the spray painting booth, the supporting rack is maintained at ground potential by reason of its contact with the conveyor mechanisms, and the workpieces themselves are maintained at ground potential by reason of their contact with the hooks 209903~
by which they are suspended on the rack. Because both the rack and the workpieces are at ground potential, the highly charged paint particles are attracted to the rack as well as to the workpieces supported thereon. After a few cycles S of use, there is a continuing buildup of paint on the rack, which begins to present a progressively larger surface area to the spray devices. Eventually, the efficiency of the spray coating operation deteriorates. Accordingly, after a certain number of cycles of use, the racks are placed in a burn-off oven and subjected to high temperature for a period of time sufficient to incinerate the layers of coating accumulated thereon.
In order to minimize the inventory of racks required in a typical operation, it has been proposed previously to construct the racks to accommodate the use of workpiece-supporting hooks in various configurations and of various types. One example as such is represented by the Hines U.S. Patent No. 4,628,859, wherein hook devices are formed with spring clip means for mounting of the hooks on cross bars of a rack. Previously known designs for such racks have, however, suffered from significant shortcomings, which are addressed by the present invention. Among those, when the rack, or parts thereof, are subjected to extended high temperature baking in the burn-off ovens, the temper of the spring steel is lost, resulting, in some cases, in the hooks being unsuitable for further use and, in other cases, in an inefficient electrical contact. Where electrical contact between the hook and the rack is inefficient, the workpiece supported by the hook receives a reduced amount of paint, and the rack itself tends to become a primary target.
Pursuant to the present invention, a novel and improved electrostatic paint spray rack is provided, in 209909~1 which a skeletal rack frame is arranged for removable mounting thereon of a plurality of cross bar supports at various horizontal levels over the vertical length of the rack frame. To advantage, the mounting means for the cross bar supports can be a plurality of threaded sockets for receiving thumb screws or the like for securing of the cross bars. When the rack is set up for a given operation, one or a plurality of the cross bars is assembled to the rack frame, depending upon the size and shape of the workpieces to be painted.
Each of the cross bar supports is provided with a plurality of workpiece-supporting hooks. In accordance with the invention, the hooks are formed of stainless steel wire, and are permanently secured to the cross bar supports by welding. The stainless steel hooks are highly resistant to the extended baking required in the burn-off ovens.
Additionally, unlike spring steel or cold rolled steel, the stainless steel does not acquire an oxide coating during the course of the burn-off operations and is thus better able to maintain good electrical contact with workpieces to be painted. In this respect, the welding of the stainless steel hooks to the cross bar support provides for excellent electrical contact between the hooks and the support, far superior to that achieved by spring clip devices or the like, especially after being subjected to burn-off cycles.
The necessary burn-off operations are greatly facilitated by the rack design of the present invention, because the individual cross bar supports may be quickly removed from the skeletal frame struc'.ure and placed in the oven separately from the frame structures. This enables far greater efficiency in the loading of the burn-off oven, and minimizes tangling of the parts etc.
209~09~
In general, the frame structure of the invention provides for significantly greater efficiencies in the painting operations, while at the same time providing for low cost inventory of the workpiece-supporting racks.
For a more complete understandlng of the above and other features and advantages of the invention, reference should be made to the following detailed description of preferred embodiments of the invention and to the accompanying drawings.
Description of the Drawin~s Fig. 1 is a partially exploded perspective view of a typical form of electrostatic paint spray rack constructed in accordance with the principles of the invention.
Fig. 2 is an enlarged, fragmentary view illustrating details of the mounting of cross bar supports on the skeletal frame structure.
Fig. 3 is an enlarged, cross sectional view as taken generally on line 3-3 of Fig. 2.
Fig. 4 is a cross sectional view as taken generally along line 4-4 of Fig. 1.
Figs. 5-7 are fragmentary perspective illustrations of various representative forms of workpiece-supporting hooks utilized in the rack structure of Fig. 1.
Description of Preferred Embodiments Referring now to the drawing, and initially to Fig.
1, the reference numeral 10 designates generally a skeletal frame structure of an adjustable rack. The frame includes a pair of spaced-apart vertically extending rod-like frame ~99~
elements 11, 12, which are rigidly fixed in spaced-apart relation to a pair of horizontally extending frame elements 13, 14. Additional frame elements 15, 16 are secured to the respective vertical elements 11, 12 and extend convergently upward, joining at the center. The several frame elements 11-16 are welded together to form a rigid structure. In a typical construction, the frame elements 11-16 may be of cold rolled steel rod of, for example, 3/16 - 1/4 quarter inch diameter.
At the region where the upwardly convergent frame elements 15, 16 join, a washer 17 is secured by welding.
Directly below the washer 17, a similar washer 18 is welded to the horizontal rods 13, 14.
A removable hanger element 19, preferably formed of stainless steel rod, is provided at spaced-apart points, corresponding to openings in the respective washers 17, 18, with threaded nuts 20, 21. Advantageously, the nuts 20, 21 have a somewhat greater than normal axial length. By way of example, they may be one quarter - 20 SAE standard high nuts. These are secured to the hanger element 19 by welding.
As shown in Fig. 4, the hanger element 19 is removably secured to the rack frame by means such as thumb screws 22, threaded portions 23 of which extend through the respective washers 17, 18 and into the nuts 20, 21.
The hanger element 19 may be as long as desired, and is formed with a hook portion 24 at its upper end, for engagement with a paint system conveyor ~not shown). To advantage, the hanger element 19 may be easily replaced with one longer or shorter, by merely removing and replacing the thumb screws 22, so that the rack frame 10, 20~9~9~
and any workpieces carried thereby, may be optimally positioned, heightwise, within the spray booth.
In accordance with the invention, each of the vertical rods 11, 12 has secured thereto by welding, at S spaced points, nuts 25, which are similar to the nuts 20, 21 previously described. In a preferred construction, the nuts may be spaced apart vertically approximately two inches, and are arranged in cooperating pairs along the spaced apart vertical rods 11, 12.
In accordance with the invention, the rack is provided with removable cross bar elements 26, typically comprising straight, horizontal rods of cold rolled steel formed into a mounting eye 27 (Fig. 2) at each end, of a diameter suitable for receiving the threaded portion 23 of a thumb screw 22. Typically, the thumb screw 22 is provided with a circular flange 28 adjacent the end of the threaded portion 23. A cross bar 26 is rigidly mounted to the rack frame structure by securing the mounting eyes 27 at each end to an appropriate pair of the welded-on nuts 25 using thumb screws at each end. The thumb screws are tightened firmly, so that excellent electrical contact is established between the cross bar 26 and the vertical frame rods 11, 12.
The number of cross bars 26 employed in a completed rack assembly is of course a function of the size and character of the workpieces to be painted. It is to be understood, of course, that the specific structure of a frame may assume a rather wide variety of sizes and configurations. By way of example only, a typical rack may utilize vertical rods 11, 12 of sufficient length to provide for 12-14 pairs of nuts 25 spaced about two inches apart. Normally, only a few of these pairs, chosen to provide appropriate spacing, would be employed in a given 2~9~0~
rack configuration.
Pursuant to the invention, each of the cross bars 26 is provided with a plurality of workpiece suspending hook elements 29 (Fig. l). The individual hook elements are formed of a stainless steel wire, for example, thirteen to sixteen gauge wire, and may take a wide variety of specific configurations, depending upon the workpieces to be handled. Importantly, each of the hooks is permanently secured by welding to the cross bar 26 to provide and maintain optimum electrical conductivity between the cross bar and the workpiece hook.
While it will be understood that the workpiece-supporting hooks 29 may be of a wide variety of shapes and sizes, representative examples are shown in Figs. 5, 6 and 7. In the modification shown in Fig. 5, which is the same as in Fig. l, the hooks 29 are formed with vertically extending shank portions 30, welded to the cross bar 26 and terminating in a sharp "V" 31 at the lower end. In the version of Fig. 6, the hook members 29' are provided with horizontal shank portions 32, rigidly welded to the cross bar 26 and terminating at their outer ends with a relatively shallow, generally U-shaped portion 33 for receiving the workpiece. In the modification of Fig. 7, the hook elements 29'' have horizontally extending shank portions 33 welded to the cross bar 26 and terminating at their outer ends in a sharply defined V-shaped sections 34.
In the versions shown in both Figs. 6 and 7, the hook members 29', 29 " extend alternately in opposite directions from the cross bar 26 to assist in spacing of the workpieces. The particular type and design and arrangements of the hooks is relatively limitless, and does not form a part of the present invention, apart from the consideration that the hooks are to be of stainless steel ~099~9~
permanently welded to the cross bar elements 26.
As reflected in Fig. 1, a typical rack configuration may include, for example, two or three cross bars 26 carrying a plurality of hooks 29 of the desired configuration. Desirably, the unused nuts 25 of the frame are covered with masking caps 35 (Fig. 3). To advantage, these may be of a style manufactured by Mocap, St. Louis, MO. Particularly where the frames are to be used for electrostatic powder coating, the masking caps should be resistant to relatively high temperature, because the rack will be exposed to a curing oven, immediately following electrostatic powder coating, in order to fuse the powder particles to the coated workpiece. The masking caps 35 keep the outer surfaces, and also the internal, threaded portions of the nuts 25 free of any of the coating material. This not only simplifies cleanup of the frame portions of the rack, when that becomes necessary, but also enables the rack to be reconfigured at any time without baking of the frame, where that is appropriate.
In the normal use of a rack of the type shown in Fig.
1, the rack is initially configured according to the nature of the workpieces to be painted, in order to achieve an optimum workpiece density. Electrically conductive workpieces are suspended from the hooks 29, and the entire rack is suspended by its own hook 24 from the paint system conveyor. The rack and its parts are then conveyed through a spray booth containing one or more electrostatic spray nozzles for applying a desired coating material to the workpieces. The spray nozzles are typically charged to a relatively high voltage in relation to the paint system conveyor, which is at ground potential. The rack 10 is also at ground potential, by reason of its contact with the conveyor through the hook 24, as are the conductive 2099~9~
workpieces (not shown) by reason of their contact with the hooks 29. After the parts are spray coated, they are typically passed through an oven, to drive off any liquid vehicle, in the case of liquid coating materials, or to fuse the powder particles, in the case of electrostatic powder coating.
As will be understood, during the spray coating procedure, the elements of the rack itself become coated, as well as the workpieces. Accordingly, after a few round trips through the painting system, a given rack accumulates a heavy coating of the sprayed-on material, as successive layers build up over previously applied layers. Moreover, as the layers build up, an increasingly larger surface area of the rack is presented to receive coating material from further coating operations. As a result, the operation becomes progressively less efficient, and at some point the rack must be taken out of service and cleaned. Typically this is done by placing the rack in a high temperature oven for a sufficient period of time to burn off the accumulated paint products.
One of the significantly advantageous features of the present invention resides in the fact that the cross bar elements 26 can be quickly separated from the rack frame, by removal of the thumb screws 22, and placed separately in the burn-off oven. Several advantages are derived from this: For one, the rack frame may not require burn-off as frequently as the hook-supporting cross bars 26. With the structure of the present invention, the rack frame can be reconfigured with ne~ cross bar elements and used again.
In this respect, the masking caps 35 keep the unused nuts clean and free of coating material, so that a coated rack frame may nevertheless be utilized with "new" cross bar elements either in the same locations or in different 209~(39'~
locations, as may be desired.
Because the burn-off operations involve principally the cross bar elements, smaller oven facilitates may be employed, as a group of cross bar elements will nest together in a highly compact manner. If rack frames are also being burned off, it is also possible to place them in the oven in flat, compact relation, after the cross bar elements have been detached. In all cases, the burn-off operation is simplified and expedited in comparison to previous experience.
The structure of the applicant's rack, comprising permanently mounted stainless steel hooks for suspending the workpieces, and where desired a stainless steel hook for suspending the rack itself from the system conveyor, has very significant advantages over conventional racks.
With racks of conventional design, for example, using hooks of spring steel material, the hooks generally loose their temper after about two burn~off operations, after which they must be discarded. Additionally, parts made of cold rolled steel form a black oxide coating during the burn-off operation, which substantially reduces the conductivity at critical points, where the hooks are attached to the rack frame, where the hooks engage the workpiece, and where the rack engages the electrically grounded system conveyor.
Reduction of conductivity in any or all these areas leads to serious inefficiencies, as the workpieces become less attractive to the particles of coating material, and a higher proportion of the coating material may be attracted to the rack itself. With the structure of the invention, on the other hand, the individual work-supporting hooks are permanently welded to the cross bar, so that conductivity between the hooks and the cross bar is totally unaffected by burn-off or other activity. Additionally, the ~ o 9 ~
workpiece-supporting hooks do not acquire an oxide coating during burn-off, so that there is no diminution of the conductivity between workpiece and supporting hook.
Likewise, the hanger element by which the rack is supported from the conveyor, if fcrm~d of stainless steel, will maintain optimum electrical contact at that point as well.
In the rack design of the present invention, although the cross bar elements 26 are formed of cold rolled steel and will themselves acquire an oxide coating during burn-off, good electrical contact is easily established betweenthe rack frame and the cross bars, by tightening of the thumb screws 22, which clamp the mounting eyes 27 of the support member tightly, and with some relative movement between the circular flanges 28 and the surface of the mounting eye 27 to provide a cleaner metal-to-metal contact.
The rack structure of the invention, among other advantages, has a greatly extended operating life as compared to conventional rack designs. Because there is essentially no deterioration of the hooks and/or of the conductive association of the hooks with the cross bar 26, the cross bar elements may be exposed to extensive burn-off operations without significant degrading of performance.
It should be understood, of course, that the specific forms of the invention herein illustrated and described are intended to be representative only, as certain changes may be made therein without departing from the clear teachings of the disclosure. Accordingly, reference should be made to the following appended claims in determining the full scope of the invention.
ADJUSTABLE RACR FOR ELECTROSTATIC PAINTING AND THE LIKE
Background and Summary of the Invention In a typical electrostatic paint spraying operation, workpieces to be painted are suspended on a conveyor which advances through a spray painting booth. The spray device and the workpiece are oppositely charged at a high voltage, so that charged paint particles issued from the spray device are electrostatically attracted to the workpiece to be painted, enabling the workpiece to be coated on surfaces that are not directly visible to the spray device. In most cases, special hangers or adaptors are provided for suspending the workpiece from the conveyor at a suitable location. Additionally, where the workpieces are relatively small, it is common to employ special rack devices, which are suspended from the conveyor and which in turn support a plurality of workpieces.
For efficient production operations, it is beneficial to provide for optimum density of the workpieces being carried by the conveyor. Typically, this is provided for by utilizing adjustable rack devices, which can be manually configured to suspend a plurality of workpieces in a desired arrangement, depending upon the size and shape of the workpieces. For this purpose, the racks are provided with a plurality of metal hooks upon which the workpieces can be suspended in an arrangement and configuration providing optimal density.
When workpieces are being conveyed through the spray painting booth, the supporting rack is maintained at ground potential by reason of its contact with the conveyor mechanisms, and the workpieces themselves are maintained at ground potential by reason of their contact with the hooks 209903~
by which they are suspended on the rack. Because both the rack and the workpieces are at ground potential, the highly charged paint particles are attracted to the rack as well as to the workpieces supported thereon. After a few cycles S of use, there is a continuing buildup of paint on the rack, which begins to present a progressively larger surface area to the spray devices. Eventually, the efficiency of the spray coating operation deteriorates. Accordingly, after a certain number of cycles of use, the racks are placed in a burn-off oven and subjected to high temperature for a period of time sufficient to incinerate the layers of coating accumulated thereon.
In order to minimize the inventory of racks required in a typical operation, it has been proposed previously to construct the racks to accommodate the use of workpiece-supporting hooks in various configurations and of various types. One example as such is represented by the Hines U.S. Patent No. 4,628,859, wherein hook devices are formed with spring clip means for mounting of the hooks on cross bars of a rack. Previously known designs for such racks have, however, suffered from significant shortcomings, which are addressed by the present invention. Among those, when the rack, or parts thereof, are subjected to extended high temperature baking in the burn-off ovens, the temper of the spring steel is lost, resulting, in some cases, in the hooks being unsuitable for further use and, in other cases, in an inefficient electrical contact. Where electrical contact between the hook and the rack is inefficient, the workpiece supported by the hook receives a reduced amount of paint, and the rack itself tends to become a primary target.
Pursuant to the present invention, a novel and improved electrostatic paint spray rack is provided, in 209909~1 which a skeletal rack frame is arranged for removable mounting thereon of a plurality of cross bar supports at various horizontal levels over the vertical length of the rack frame. To advantage, the mounting means for the cross bar supports can be a plurality of threaded sockets for receiving thumb screws or the like for securing of the cross bars. When the rack is set up for a given operation, one or a plurality of the cross bars is assembled to the rack frame, depending upon the size and shape of the workpieces to be painted.
Each of the cross bar supports is provided with a plurality of workpiece-supporting hooks. In accordance with the invention, the hooks are formed of stainless steel wire, and are permanently secured to the cross bar supports by welding. The stainless steel hooks are highly resistant to the extended baking required in the burn-off ovens.
Additionally, unlike spring steel or cold rolled steel, the stainless steel does not acquire an oxide coating during the course of the burn-off operations and is thus better able to maintain good electrical contact with workpieces to be painted. In this respect, the welding of the stainless steel hooks to the cross bar support provides for excellent electrical contact between the hooks and the support, far superior to that achieved by spring clip devices or the like, especially after being subjected to burn-off cycles.
The necessary burn-off operations are greatly facilitated by the rack design of the present invention, because the individual cross bar supports may be quickly removed from the skeletal frame struc'.ure and placed in the oven separately from the frame structures. This enables far greater efficiency in the loading of the burn-off oven, and minimizes tangling of the parts etc.
209~09~
In general, the frame structure of the invention provides for significantly greater efficiencies in the painting operations, while at the same time providing for low cost inventory of the workpiece-supporting racks.
For a more complete understandlng of the above and other features and advantages of the invention, reference should be made to the following detailed description of preferred embodiments of the invention and to the accompanying drawings.
Description of the Drawin~s Fig. 1 is a partially exploded perspective view of a typical form of electrostatic paint spray rack constructed in accordance with the principles of the invention.
Fig. 2 is an enlarged, fragmentary view illustrating details of the mounting of cross bar supports on the skeletal frame structure.
Fig. 3 is an enlarged, cross sectional view as taken generally on line 3-3 of Fig. 2.
Fig. 4 is a cross sectional view as taken generally along line 4-4 of Fig. 1.
Figs. 5-7 are fragmentary perspective illustrations of various representative forms of workpiece-supporting hooks utilized in the rack structure of Fig. 1.
Description of Preferred Embodiments Referring now to the drawing, and initially to Fig.
1, the reference numeral 10 designates generally a skeletal frame structure of an adjustable rack. The frame includes a pair of spaced-apart vertically extending rod-like frame ~99~
elements 11, 12, which are rigidly fixed in spaced-apart relation to a pair of horizontally extending frame elements 13, 14. Additional frame elements 15, 16 are secured to the respective vertical elements 11, 12 and extend convergently upward, joining at the center. The several frame elements 11-16 are welded together to form a rigid structure. In a typical construction, the frame elements 11-16 may be of cold rolled steel rod of, for example, 3/16 - 1/4 quarter inch diameter.
At the region where the upwardly convergent frame elements 15, 16 join, a washer 17 is secured by welding.
Directly below the washer 17, a similar washer 18 is welded to the horizontal rods 13, 14.
A removable hanger element 19, preferably formed of stainless steel rod, is provided at spaced-apart points, corresponding to openings in the respective washers 17, 18, with threaded nuts 20, 21. Advantageously, the nuts 20, 21 have a somewhat greater than normal axial length. By way of example, they may be one quarter - 20 SAE standard high nuts. These are secured to the hanger element 19 by welding.
As shown in Fig. 4, the hanger element 19 is removably secured to the rack frame by means such as thumb screws 22, threaded portions 23 of which extend through the respective washers 17, 18 and into the nuts 20, 21.
The hanger element 19 may be as long as desired, and is formed with a hook portion 24 at its upper end, for engagement with a paint system conveyor ~not shown). To advantage, the hanger element 19 may be easily replaced with one longer or shorter, by merely removing and replacing the thumb screws 22, so that the rack frame 10, 20~9~9~
and any workpieces carried thereby, may be optimally positioned, heightwise, within the spray booth.
In accordance with the invention, each of the vertical rods 11, 12 has secured thereto by welding, at S spaced points, nuts 25, which are similar to the nuts 20, 21 previously described. In a preferred construction, the nuts may be spaced apart vertically approximately two inches, and are arranged in cooperating pairs along the spaced apart vertical rods 11, 12.
In accordance with the invention, the rack is provided with removable cross bar elements 26, typically comprising straight, horizontal rods of cold rolled steel formed into a mounting eye 27 (Fig. 2) at each end, of a diameter suitable for receiving the threaded portion 23 of a thumb screw 22. Typically, the thumb screw 22 is provided with a circular flange 28 adjacent the end of the threaded portion 23. A cross bar 26 is rigidly mounted to the rack frame structure by securing the mounting eyes 27 at each end to an appropriate pair of the welded-on nuts 25 using thumb screws at each end. The thumb screws are tightened firmly, so that excellent electrical contact is established between the cross bar 26 and the vertical frame rods 11, 12.
The number of cross bars 26 employed in a completed rack assembly is of course a function of the size and character of the workpieces to be painted. It is to be understood, of course, that the specific structure of a frame may assume a rather wide variety of sizes and configurations. By way of example only, a typical rack may utilize vertical rods 11, 12 of sufficient length to provide for 12-14 pairs of nuts 25 spaced about two inches apart. Normally, only a few of these pairs, chosen to provide appropriate spacing, would be employed in a given 2~9~0~
rack configuration.
Pursuant to the invention, each of the cross bars 26 is provided with a plurality of workpiece suspending hook elements 29 (Fig. l). The individual hook elements are formed of a stainless steel wire, for example, thirteen to sixteen gauge wire, and may take a wide variety of specific configurations, depending upon the workpieces to be handled. Importantly, each of the hooks is permanently secured by welding to the cross bar 26 to provide and maintain optimum electrical conductivity between the cross bar and the workpiece hook.
While it will be understood that the workpiece-supporting hooks 29 may be of a wide variety of shapes and sizes, representative examples are shown in Figs. 5, 6 and 7. In the modification shown in Fig. 5, which is the same as in Fig. l, the hooks 29 are formed with vertically extending shank portions 30, welded to the cross bar 26 and terminating in a sharp "V" 31 at the lower end. In the version of Fig. 6, the hook members 29' are provided with horizontal shank portions 32, rigidly welded to the cross bar 26 and terminating at their outer ends with a relatively shallow, generally U-shaped portion 33 for receiving the workpiece. In the modification of Fig. 7, the hook elements 29'' have horizontally extending shank portions 33 welded to the cross bar 26 and terminating at their outer ends in a sharply defined V-shaped sections 34.
In the versions shown in both Figs. 6 and 7, the hook members 29', 29 " extend alternately in opposite directions from the cross bar 26 to assist in spacing of the workpieces. The particular type and design and arrangements of the hooks is relatively limitless, and does not form a part of the present invention, apart from the consideration that the hooks are to be of stainless steel ~099~9~
permanently welded to the cross bar elements 26.
As reflected in Fig. 1, a typical rack configuration may include, for example, two or three cross bars 26 carrying a plurality of hooks 29 of the desired configuration. Desirably, the unused nuts 25 of the frame are covered with masking caps 35 (Fig. 3). To advantage, these may be of a style manufactured by Mocap, St. Louis, MO. Particularly where the frames are to be used for electrostatic powder coating, the masking caps should be resistant to relatively high temperature, because the rack will be exposed to a curing oven, immediately following electrostatic powder coating, in order to fuse the powder particles to the coated workpiece. The masking caps 35 keep the outer surfaces, and also the internal, threaded portions of the nuts 25 free of any of the coating material. This not only simplifies cleanup of the frame portions of the rack, when that becomes necessary, but also enables the rack to be reconfigured at any time without baking of the frame, where that is appropriate.
In the normal use of a rack of the type shown in Fig.
1, the rack is initially configured according to the nature of the workpieces to be painted, in order to achieve an optimum workpiece density. Electrically conductive workpieces are suspended from the hooks 29, and the entire rack is suspended by its own hook 24 from the paint system conveyor. The rack and its parts are then conveyed through a spray booth containing one or more electrostatic spray nozzles for applying a desired coating material to the workpieces. The spray nozzles are typically charged to a relatively high voltage in relation to the paint system conveyor, which is at ground potential. The rack 10 is also at ground potential, by reason of its contact with the conveyor through the hook 24, as are the conductive 2099~9~
workpieces (not shown) by reason of their contact with the hooks 29. After the parts are spray coated, they are typically passed through an oven, to drive off any liquid vehicle, in the case of liquid coating materials, or to fuse the powder particles, in the case of electrostatic powder coating.
As will be understood, during the spray coating procedure, the elements of the rack itself become coated, as well as the workpieces. Accordingly, after a few round trips through the painting system, a given rack accumulates a heavy coating of the sprayed-on material, as successive layers build up over previously applied layers. Moreover, as the layers build up, an increasingly larger surface area of the rack is presented to receive coating material from further coating operations. As a result, the operation becomes progressively less efficient, and at some point the rack must be taken out of service and cleaned. Typically this is done by placing the rack in a high temperature oven for a sufficient period of time to burn off the accumulated paint products.
One of the significantly advantageous features of the present invention resides in the fact that the cross bar elements 26 can be quickly separated from the rack frame, by removal of the thumb screws 22, and placed separately in the burn-off oven. Several advantages are derived from this: For one, the rack frame may not require burn-off as frequently as the hook-supporting cross bars 26. With the structure of the present invention, the rack frame can be reconfigured with ne~ cross bar elements and used again.
In this respect, the masking caps 35 keep the unused nuts clean and free of coating material, so that a coated rack frame may nevertheless be utilized with "new" cross bar elements either in the same locations or in different 209~(39'~
locations, as may be desired.
Because the burn-off operations involve principally the cross bar elements, smaller oven facilitates may be employed, as a group of cross bar elements will nest together in a highly compact manner. If rack frames are also being burned off, it is also possible to place them in the oven in flat, compact relation, after the cross bar elements have been detached. In all cases, the burn-off operation is simplified and expedited in comparison to previous experience.
The structure of the applicant's rack, comprising permanently mounted stainless steel hooks for suspending the workpieces, and where desired a stainless steel hook for suspending the rack itself from the system conveyor, has very significant advantages over conventional racks.
With racks of conventional design, for example, using hooks of spring steel material, the hooks generally loose their temper after about two burn~off operations, after which they must be discarded. Additionally, parts made of cold rolled steel form a black oxide coating during the burn-off operation, which substantially reduces the conductivity at critical points, where the hooks are attached to the rack frame, where the hooks engage the workpiece, and where the rack engages the electrically grounded system conveyor.
Reduction of conductivity in any or all these areas leads to serious inefficiencies, as the workpieces become less attractive to the particles of coating material, and a higher proportion of the coating material may be attracted to the rack itself. With the structure of the invention, on the other hand, the individual work-supporting hooks are permanently welded to the cross bar, so that conductivity between the hooks and the cross bar is totally unaffected by burn-off or other activity. Additionally, the ~ o 9 ~
workpiece-supporting hooks do not acquire an oxide coating during burn-off, so that there is no diminution of the conductivity between workpiece and supporting hook.
Likewise, the hanger element by which the rack is supported from the conveyor, if fcrm~d of stainless steel, will maintain optimum electrical contact at that point as well.
In the rack design of the present invention, although the cross bar elements 26 are formed of cold rolled steel and will themselves acquire an oxide coating during burn-off, good electrical contact is easily established betweenthe rack frame and the cross bars, by tightening of the thumb screws 22, which clamp the mounting eyes 27 of the support member tightly, and with some relative movement between the circular flanges 28 and the surface of the mounting eye 27 to provide a cleaner metal-to-metal contact.
The rack structure of the invention, among other advantages, has a greatly extended operating life as compared to conventional rack designs. Because there is essentially no deterioration of the hooks and/or of the conductive association of the hooks with the cross bar 26, the cross bar elements may be exposed to extensive burn-off operations without significant degrading of performance.
It should be understood, of course, that the specific forms of the invention herein illustrated and described are intended to be representative only, as certain changes may be made therein without departing from the clear teachings of the disclosure. Accordingly, reference should be made to the following appended claims in determining the full scope of the invention.
Claims (11)
1. A rack structure for supporting workpieces during electrostatic spray coating, which comprises (a) a rack frame comprising a pair of generally vertically extending, spaced-apart metal frame elements, (b) one or more metal cross bar elements extending between and removably secured to said vertically extending frame elements in electrically conducting relation therewith, and (c) one of more workpiece-supporting hooks, formed of stainless steel and permanently welded to said cross bar elements for supporting electrically conductive workpieces.
2. A rack structure according to claim 1, further characterized by (a) said metal cross bar elements being of rod-like form and being formed of cold rolled steel, and (b) cooperating means on said vertically extending frame elements and said cross bar elements for tightly securing said cross bar elements to said frame elements.
3. A rack structure according to claim 2, further characterized by said cooperating means comprising (a) a mounting eye on each end of each cross bar element, (b) opposed pairs of threaded sockets on said vertically extending frame members, and (c) screw devices for securing said mounting eyes to said threaded sockets.
4. A rack structure according to claim 1, further characterized by (a) a vertically disposed hanger element for said rack, (b) said rack frame being formed of cold rolled steel, and (c) said hanger element being formed of stainless steel.
5. A rack structure according to claim 4, further characterized by (a) said one of said rack frame and said hanger element being provided with one or more threaded socket means, and (b) screw means engageable with said threaded socket means for tightly but removably securing said hanger element to said rack frame.
6. A rack structure according to claim 1, further characterized by (a) a plurality of pairs of threaded nuts welded to said vertically extending frame elements at vertically spaced intervals, (b) cross bar elements being secured to selected pairs of said threaded nuts by screw elements extending through said cross bar elements and threadedly engaging said nuts.
7. A rack structure according to claim 6, further characterized by (a) masking caps of insulating plastic material received over each of said nuts not engaged by said screw elements.
8. A rack structure according to claim 6, further characterized by (a) said screw elements include a projecting portion adapted to be mannually engageable for manual installation and removal of said screw elements.
9. A rack structure for supporting workpieces during electrostatic spray coating, which comprises (a) a rack frame comprising a pair of generally vertically extending, spaced-apart frame elements, (b) one or more cross bar elements of conductive metal extending between and removably secured to said vertically extending frame elements in electrically conducting relation with at least one of them, and (c) one of more workpiece-supporting hooks, formed of stainless steel and permanently welded to said cross bar elements for supporting electrically conductive workpieces.
10. A rack structure according to claim 9, further characterized by (a) said cross bar elements being formed of cold rolled steel rod.
11. A rack structure according to claim 9, further characterized by (a) said rack frame being formed at least in part of cold rolled steel rod, and (b) a hanger for suspending said rack frame from an electrically conductive conveyor or the like, (c) said hanger being formed of stainless steel and being secured in electrically conductive relation to said rack frame.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US90389192A | 1992-06-25 | 1992-06-25 | |
| US07/903,891 | 1992-06-25 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2099094A1 true CA2099094A1 (en) | 1993-12-26 |
Family
ID=25418213
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2099094 Abandoned CA2099094A1 (en) | 1992-06-25 | 1993-06-23 | Adjustable rack for electrostatic painting and the like |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2099094A1 (en) |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6790484B2 (en) * | 2001-12-14 | 2004-09-14 | Carlton Mann | Method and apparatus for cleaning electrostatic painting hooks |
| CN107309117A (en) * | 2017-06-13 | 2017-11-03 | 江西广迪智能钢艺集团有限公司 | Spraying hanging tool |
| CN107626491A (en) * | 2017-09-28 | 2018-01-26 | 芜湖三花制冷配件有限公司 | A kind of silencer for air conditioner electrostatic spraying support and spraying method |
| CN116273536A (en) * | 2022-12-30 | 2023-06-23 | 浙江国达智能机电装备科技有限公司 | Energy-saving electrostatic spraying device |
-
1993
- 1993-06-23 CA CA 2099094 patent/CA2099094A1/en not_active Abandoned
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6790484B2 (en) * | 2001-12-14 | 2004-09-14 | Carlton Mann | Method and apparatus for cleaning electrostatic painting hooks |
| CN107309117A (en) * | 2017-06-13 | 2017-11-03 | 江西广迪智能钢艺集团有限公司 | Spraying hanging tool |
| CN107626491A (en) * | 2017-09-28 | 2018-01-26 | 芜湖三花制冷配件有限公司 | A kind of silencer for air conditioner electrostatic spraying support and spraying method |
| CN116273536A (en) * | 2022-12-30 | 2023-06-23 | 浙江国达智能机电装备科技有限公司 | Energy-saving electrostatic spraying device |
| CN116273536B (en) * | 2022-12-30 | 2024-01-30 | 浙江国达智能机电装备科技有限公司 | Energy-saving electrostatic spraying device |
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| Date | Code | Title | Description |
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