Patent Publication Number: US-2015069150-A1

Title: System for applying a coating to a workpiece

Description:
FIELD OF THE INVENTION 
     The field of the present invention relates to systems for applying a coating to a workpiece with a sprayed liquid. 
     BACKGROUND OF THE INVENTION 
     Edge-coating a workpiece as it moves along in a direction generally parallel to its edge is generally known. Systems have been developed that spray the passing edge with a liquid and then vacuum the excess liquid off the edge in order to obtain a very smooth and uniform coating of the liquid on edge of the workpiece. 
     U.S. Pat. No. 5,298,072 describes a system for coating the edges of panels (and other types and forms of workpieces) in which the panel is moved along a conveyor past a painting station, so that the edge of the panel moves longitudinally past the applicator head, which serves as both a spray head to apply the paint and a vacuum head to remove excess paint. The applicator head is shaped to have a complementary shape to the shape of the edge of the panel, and as the panel moves past the applicator head, paint is applied and excess paint is removed to leave the smooth finish. 
     Problems with this prior art system are found in uneven coating of the applied liquid on the workpiece, undesired buildup of the liquid on pans of the system itself, downtime for maintenance, and cost of maintenance itself. All of these issues may be addressed by one or more improvements in such systems. 
     SUMMARY OF THE INVENTION 
     The present invention is directed toward a system for applying a coating to a workpiece. The workpiece is conveyed past the applicator head so that the edge of the workpiece is positioned adjacent and exposed to the applicator bead. The applicator head dispenses a liquid onto the edge of the workpiece and establishes a vacuum to remove excess liquid from the edge, thereby coating the edge with the liquid. The applicator head includes an applicator manifold, which includes two manifold plates and an applicator channel formed therebetween. The applicator channel opens up to an applicator port at a leading edge of the applicator manifold, and liquid is dispensed through the applicator port. At the leading edge of the applicator manifold, the manifold plates are configured to be complementary in shape to the edge of the workpiece on which liquid is being coated. Face plates are disposed over the leading edges of the applicator manifold to cover a portion of the applicator port. 
     In a first separate aspect of the present invention, the applicator head includes a manifold shell having opposing shell plates, and each shell plate includes a shell aperture and a conduit attachment coupled to the shell aperture. An applicator manifold is affixed to at least one of the shell plates. One of the manifold plates of the applicator manifold includes a manifold aperture which aligns with the shell aperture, so that the applicator channel is fluidically coupled to the manifold aperture and to the shell aperture, thereby enabling a liquid to flow from the conduit attachment to the applicator channel. 
     In a second separate aspect of the present invention, one of the two manifold plates has a greater width than the other manifold plate at the leading edge of the applicator manifold. The one manifold plate may have a width that is twice as wide, or even more, as the other manifold plate. 
     In a third separate aspect of the present invention, the face plates may include a beveled edge over the applicator port. These beveled edges may face the applicator port, and they may form a point. 
     In a fourth separate aspect of the present invention, the applicator channel includes a surface in which a flow channel is formed. Such a flow channel may be configured to direct more of the liquid being applied to the edge of a workpiece toward a portion of the applicator port. 
     In a fifth separate aspect of the present invention, the leading edge of the applicator manifold is configured with a first portion which is complementary in shape to the edge of the workpiece to form a first application gap, and a second portion which is complementary in shape to the edge of the workpiece to form a second application gap, with the second application gap being different than the first application gap. 
     In a sixth separate aspect of the present invention, any of the foregoing aspects may be employed singly or in any desired combination. 
     Accordingly, an improved system for applying a coating to a workpiece is disclosed. Advantages of the improvements will be apparent from the drawings and the description of the preferred embodiment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing summary, as well as the following detailed description of the exemplary embodiments, will be better understood when read in conjunction with the appended drawings. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown in the following figures: 
         FIG. 1  is a perspective view of an edge coating apparatus; 
         FIG. 2  is a perspective view of an applicator head for an edge coating apparatus; 
         FIG. 3  is a perspective view of a manifold shell for the applicator head of  FIG. 2 . 
         FIG. 4  is a front elevation view of the applicator head of  FIG. 1 ; 
         FIG. 5  is an exploded view of an applicator manifold for the applicator head of  FIG. 2 ; 
         FIG. 6  is a multiview orthographic projection showing three sides of the applicator manifold of  FIG. 5 ; 
         FIG. 7  is a side elevation view of a manifold plate showing the applicator channel; and 
         FIG. 8  is detail view of the edge of a workpiece passing by an applicator head. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The description of illustrative embodiments according to principles of the present invention is intended to be read in connection with the accompanying drawings, which are to be considered part of the entire written description. In the description of embodiments of the invention disclosed herein, any reference to direction or orientation is merely intended for convenience of description and is not intended in any way to limit the scope of the present invention. Relative terms such as “lower,” “upper,” “horizontal,” “vertical,” “above,” “below,” “up,” “down,” “left,” “right,” “top” and “bottom” as well as derivatives thereof (e.g., “horizontally,” “downwardly,” “upwardly,” etc.) should be construed to refer to the orientation as then described or as shown in the drawing under discussion. These relative terms are for convenience of description only and do not require that the apparatus be constructed or operated in a particular orientation unless explicitly indicated as such. Terms such as “attached,” “affixed,” “connected,” “coupled,” “interconnected,” and similar refer to a relationship wherein structures are secured or attached to one another either directly or indirectly through intervening structures, as well as both movable or rigid attachments or relationships, unless expressly described otherwise. Moreover, the features and benefits of the invention are illustrated by reference to the preferred embodiments. Accordingly, the invention expressly should not be limited to such preferred embodiments illustrating some possible non-limiting combinations of features that may exist alone or in other combinations of features; the scope of the invention being defined by the claims appended hereto. 
     In the context of the description below, the liquid is discussed in terms of a water-based paint. However, as is known to those of skill in the art, the liquid can also be a primer, a lacquer, a preservative, or any other desired treatment liquid that is appropriate as a coating for a particular workpiece and the intended utilization of that workpiece. In addition, the liquid may serve as a carrier for solid or filler particles. For example, the filler particles may have an average particle size ranging from about 100 microns to 600 microns, and the liquid carrier may have a composition of up to 90% of filler particles by dry solids weight. Examples of filler particles includes calcium carbonate, dolomite, dolomitic limestone or combinations thereof. In addition to the solid or filler particles, the liquid may also include as part of its composition a binder and/or a pigment, as desired by design choice for a particular coating application. Examples of binders that may be included in the liquid include natural polymers, modified natural polymers, synthetic polymers and combinations thereof. The synthetic polymers are formed from the following monomers: vinyl acetate, vinyl propionate, vinyl butyrate, ethylene, vinyl chloride, vinylidine chloride, vinyl fluoride, vinylidine fluoride, ethyl acrylate, methyl acrylate, propyl acrylate, butyl acrylate, ethyl methacrylate, methyl methacrylate, butyl methacrylate, hydroxyethyl methacrylate, styrene, butadiene, urethane, epoxy, melamine, ester, and combinations thereof. U.S. Pat. No. 7,033,963, the disclosure of which is incorporated herein by reference in its entirety, describes other examples of liquids that may be used with the coating system described below. The coating system may also be used with other types of liquids and liquid compositions), other than those referenced herein. 
     Turning in detail to  FIG. 1 , a vacuum coating system  11  includes a vacuum tank  13  and a paint feed apparatus  15 , and both are coupled to an edge-coating applicator head  17 . The applicator head  17  is arranged adjacent a conveyor  21  which transports workpieces  23  past the applicator head  17 , in a transport direction, TD, so that the edges  25  of the workpieces  23  can be coated. The paint feed apparatus  15  feeds paint through conduits  27  into the applicator head  17 , and the vacuum tank  13  establishes a vacuum through a vacuum line  29  coupled to the back side of the applicator head  17 . The operation of such a vacuum coating system  11  is known in the art, and background details may be found in U.S. Pat. No. 5,298,072, the disclosure of which is incorporated herein by reference in its entirety. A steam manifold  31  may be affixed to the applicator head  17 . The steam manifold  31  is coupled to a steam source  33  by steam supply conduits  35 . The steam manifold  31  may be included to maintain a moist environment in and around the applicator head  17  in order to help avoid a build-up of dried paint during operation. 
       FIG. 2  shows a detailed view of the applicator head  17 , which includes a manifold shell  41  around which is disposed the steam manifold  31 . Steam may be directed into the steam manifold  31  by connecting a steam conduit to inlet ports  37 . The manifold shell  41  supports two applicator manifolds  43 ,  45 , each of which is affixed to one of two opposing side shell plates  47 . Both applicator manifolds  43 ,  45  are removably affixed to the side shell plates  47  by bolts passing through the shell plates  47  and into threaded holes provided in each applicator manifold  43 ,  45 , thereby facilitating maintenance and replacement of the applicator manifolds as needed. Each shell plate  47  includes a shell aperture  49  which is positioned to align with a corresponding manifold aperture in each of the applicator manifolds  43 ,  45 . Top and bottom covers  51 ,  53  are secured, respectively, to the top and bottom shell plates  55 ,  57  of the manifold shell  41 . Each top and bottom cover  51 ,  53  includes a face plate  59 ,  61  which extends over both of the applicator manifolds  43 ,  45 , and each may include an additional steam port  63  through which steam may be directed between the two applicator manifolds  43 ,  45 . 
     The manifold shell  41  with conduit attachments  71  coupled to the each of the shell apertures  49  is shown in  FIG. 3 . Each conduit attachment  71  is affixed to the manifold shell  41  over the shell aperture  49  so that paint may pass from the conduits and into each of the applicator manifolds during operation. Paint supply conduit (not shown) is connected to each conduit attachment  71  during operation. The top and bottom shell plates  55 ,  57  include attachment holes for the top and bottom covers, respectively. The side, top, and bottom shell plates  47 ,  55 ,  57  are all affixed to the backing plate  73 , which also serves as a cover plate for a vacuum chamber (not shown), so that a vacuum may be established during operation within the interior space defined by the side, top, and bottom shell plates  47 ,  55 ,  57 . 
       FIG. 4  shows the assembled applicator head  17  with the applicator manifolds  43 ,  45  and the top and bottom covers  51 ,  53  in place; no fasteners, i.e., bolts, screws, etc., are shown in order to simplify the illustration. The exposed part of the leading edges  75  of the applicator manifolds  43 ,  45  are configured to have a shape which is complementary to the edge of a workpiece conveyed past the applicator head  17  (see the discussion of  FIGS. 5-9  below for more about the applicator manifolds). Applicator ports  77 ,  79 , through which paint is dispensed during operation, are formed at the leading edges  75  of each applicator manifold  43 ,  45 . The top and bottom covers  51 ,  53 , each include a face plate  59 ,  61  which extends over the leading edges  75  of the applicator manifolds  43 ,  45 . The face plates  59 ,  61  each cover a portion of the applicator ports  77 ,  79 , so that the exposed portion of the applicator ports  77 ,  79  closely match, but are not smaller than, the dimension of the edge of the workpieces being conveyed past the applicator head. 
     The embodiment shown facilitates maintenance and replacement of the applicator manifolds. Whereas with applicator heads of the prior art, when the leading edge began to wear, or a different tooling is needed to coat the edges of a workpiece having a different profile, the entire applicator head would need to be replaced. With the applicator head disclosed herein, the applicator manifolds themselves are replaceable, and the manifold shell and the steam conduit may remain in place with the rest of the system. 
     The applicator manifolds of the embodiment shown in  FIG. 4  are easily removed by first detaching the top and bottom covers from the manifold shell, then removing the bolts that secure each applicator manifold to the manifold shell. This allows the applicator manifolds to be removed, and when appropriate, a new applicator manifold inserted in place of the old one. Once the top and bottom covers are secured in place once more, then the coating system may be up and running again. The ease of changing out the applicator manifolds facilitates replacing a worn out part, and it facilitates “retooling” the applicator head to coat a workpiece having a different edge profile by inserting applicator manifolds configured with a shape to match the profile of the new workpiece. 
     During operation, as the edge of a workpiece is conveyed past the applicator head  17  to coat the workpiece, an application gap between the leading edge of the applicator manifold and the edge of the workpiece is maintained within a predetermined range. As used herein, “application gap” is the horizontal spacing between complementary points on the leading edge of the applicator manifold and the surface profile of the edge of the workpiece being conveyed past the applicator head. In the embodiment shown in  FIG. 4 , the applicator manifolds are configured to have a constant application gap between the leading edge of the applicator manifold and the edge of the workpiece. As is discussed below, depending upon the workpiece, advantages may be obtained by having the leading edge of one or more of the applicator manifolds configured to have different application gaps with different portions of the edge of a workpiece. 
     When a selected liquid, such as paint, is being applied to a particular workpiece, the application gap is one of the variables that may be adjusted to help control the thickness and consistency of the coating being applied to the edge of the workpiece. Generally, the application gap may be within the range of what is referred to as an “operational window” in order to obtain satisfactory results. For an application of paint, the satisfactory results may be based upon the amount of paint applied and the application resulting in a substantially uniform appearance. Other variables which may be taken into consideration for determining the operational window of a particular configuration, in addition to the application gap, include the viscosity of the paint, the pressure at which the paint is pumped into the applicator manifolds, and the rate at which the workpiece is moved past the applicator head. 
     By way of example, a test was performed using an applicator head of the prior art (i.e., the applicator ports were integrally formed as part of the applicator head and there was no steam manifold) to apply paint to a workpiece, with the workpiece conveyance rate set to 50 feet per minute and the vacuum established at the applicator head, the following acceptable operational ranges were empirically identified:
         Pump Pressure Range: 5.3 bar-7.3 bar   Relative Head Position: −0.007 in.-0.008 in.       

     The zero point, or center position, for the applicator head was empirically determined in advance as the relative position between the edge of the workpiece and the applicator head that provided the most visually acceptable and color accurate results. When these test results using a prior an applicator head are compared to other test results presented below, it can be seen how improvements to a coating system may be realized by making one or more changes in the configuration of the applicator head. 
     Returning to  FIG. 4 , the direction of workpiece conveyance is indicated by the arrow. The edge of a workpiece is conveyed initially past the first applicator manifold  43 , and then next past the second applicator manifold  45 . The first applicator manifold  43  is formed by two manifold plates  91 ,  93 , both of which have the same width at the leading edge of the applicator manifold  43 . The applicator port  77  is formed between the two manifold plates  91 ,  93 , and this applicator port  77  has the same width as the two manifold plates  91 ,  93 . The second applicator manifold  45  is also formed by two manifold plates  97 ,  99 , which do not have the same width. The applicator port  79  is formed between the two manifold plates  97 ,  99 , and the applicator port  79  and the second manifold plate  99  have the same width. The first manifold plate  97  has a greater width than the second manifold plate  99 . The width of the first manifold plate  97  may be 50% or more greater than the width of the first manifold plate  99 . Although limited testing was run, it is expected that the difference in widths between these two manifold plates of the exit-side applicator manifold may have a broad range of adjustment, depending upon the other variables, such as those discussed herein, with which the applicator head is configured and used with. 
     By way of a another example, a second test was performed using an applicator head with replaceable applicator manifolds and a steam manifold providing steam around the applicator head during testing. The applicator plates of each applicator manifold had a thickness of 0.100 in., and the widths of the applicator ports were the same, at 0.100 in. The paint used to coat the edge of the workpiece was more viscous than the paint used in the first test, the workpiece conveyance rate was set to 50 feet per minute, and the vacuum was established at the applicator head. With these settings, the following acceptable operational ranges were empirically identified:
         Pump Pressure Range: 5.5 bar-6.8 bar   Relative Head Position: −0.007 in.-0.007 in.       

     As is not surprising, most of the ranges for this second test are about the same as the ranges for the first test, which was performed using an applicator head of the prior art. 
     By way of another example, a third test was performed using an applicator head with replaceable applicator manifolds and a steam manifold providing steam around the applicator head during testing. The applicator plates of the first applicator manifold (the edge of the workpiece passes by the first applicator manifold first for purposes of this test) had a thickness of 0.100 in., as did the thickness of the applicator port of the first applicator manifold. The first applicator plate of the second applicator manifold had a thickness of 0.100 in., as did the thickness of the applicator port of the second applicator manifold. The second applicator plate (the lead-in plate to the second applicator manifold, based on the travel direction of the workpiece) of the second applicator manifold had a thickness of 0.200 in. The paint used to coat the edge of the workpiece was more viscous than the paint used in the first test, the workpiece conveyance rate was set to 50 feet per minute, and the vacuum was established at the applicator head. With these settings, the following acceptable operational ranges were empirically identified:
         Pump Pressure Range: 4.0 bar-6.0 bar   Relative Head Position: −0.016 in.-0.016 in.       

     By way of another example, a fourth test was performed using an applicator head with replaceable applicator manifolds and a steam manifold providing steam around the applicator head daring testing. The applicator plates of the first applicator manifold (the edge of the workpiece passes by the first applicator manifold first for purposes of this test) had a thickness of 0.100 in., as did the thickness of the applicator port of the first applicator manifold. The second applicator plate of the second applicator manifold had a thickness of 0.100 in., as did the thickness of the applicator port of the second applicator manifold. The first applicator plate (the lead-in plate to the second applicator manifold, based on the travel direction of the workpiece) of the second applicator manifold had a thickness of 0.275 in. The paint used to coat the edge of the workpiece was more viscous than the paint used in the first test, the workpiece conveyance rate was set to 50 feet per minute, and the vacuum was established at the applicator head. With these settings, the following acceptable operational ranges were empirically identified:
         Pump Pressure Range: 3.7 bar-6.0 bar   Relative Head Position: −0.010 in.-0.014 in.       

     As can be seen from the third and fourth tests, the absolute pump pressure ranges remained about the same, while the lower and upper ends of the pump pressure ranges were reduced by 1.3 bar each. In addition, the absolute range for the relative head position was more than doubled in the third test, and the absolute range for the relative head position was increased by about 66% in the fourth test. This data shows that significant improvements in the operational efficiencies of an edge coating system may be realized merely by increasing the thickness of the one manifold plate. 
     Turning back to the figures,  FIG. 5  illustrates an applicator manifold  111  formed by two applicator plates  113 ,  115 . Both applicator plates  113 ,  115  include a first set of screw holes  117  for fastening the plates together, and a second set of screw holes  119  for securing the plates to the side shell plate of the manifold shell. Both applicator plates  113 ,  115  have leading edges  121 ,  123  that are configured to be complementary in shape to the edge of a workpiece to be coated using the applicator manifold  111 . When the applicator plates  113 ,  115  are secured together, as is shown in  FIG. 6 , the edges  121 ,  123  of the two applicator plates  113 ,  115  form the leading edge of the applicator manifold  111 . One applicator plate  113  includes an applicator channel  125 , while the other applicator plate  115  includes a manifold aperture  127 . When the applicator plates  113 ,  115  are secured together, the manifold aperture  127  is fluidically coupled to the applicator channel  125 . The applicator plate  115  with the manifold aperture  127  is disposed nearest the side shell plate when the applicator manifold  111  is secured within the manifold shell. This aligns the manifold aperture  127  with the shell aperture in the manifold shell, so that liquid, such as paint, can flow from the liquid conduit through to the applicator channel  125 , and out through the applicator port. 
     Multiple elevation views of the applicator manifold  111 , assembled, are shown in  FIG. 6 . Here, the fluidic coupling between the manifold aperture  127 , the applicator channel  125 , and the applicator port  129  is shown, which enables the liquid to flow from the liquid conduit out through the applicator port. Also highlighted in these views is the leading edge  131  of the applicator manifold  111 . This leading edge  131  is angled to account for the angle that the applicator manifold  111  is mounted within the manifold shell relative to the path of the workpieces as they are conveyed past the applicator head. 
       FIG. 7  shows another modification to an applicator plate  141  which may be used to create a better flow distribution of the liquid emerging from the applicator port. This modification introduces a flow channel  143  in a surface of the applicator channel  145 , which itself is formed in the applicator plate  141 . The flow channel  143  creates an enlarged space within the applicator channel  145 , and this enlarged space may take on any appropriate shape and be used to direct additional liquid toward part of the edge of the workpiece being coated. As shown, the flow channel  143  has an enlarged body portion  147  disposed away from the leading edge  149  of the applicator plate  141 , with a finger portion  151  extending in the direction of, but not extending to, the leading edge  149 . 
     It has been found that gravity may often cause the liquid being coated onto a workpiece to have a greater volume of flow at the bottom of an applicator port than it does at the top of an applicator port. The flow channel shown in  FIG. 7 , which is disposed near the top of the applicator channel and includes the finger portion extending toward the top of the applicator port, increases the flow of liquid to the top of the applicator port. This increased flow can help offset the effects of gravity during the application process. 
     Flow channels may be almost any shape and size within the applicator channel, and multiple flow channels may also be incorporated into the applicator channel. The shape, size, and number of flow channels are highly dependent upon the desired properties of the coating for the particular workpiece being coated. These factors may include the shape of the edge of the workpiece, the desired distribution of and/or finish qualities for the liquid on the edge, the type and qualities of the liquid being applied, the desired rate of application, among many other factors. 
     Two other modifications which may be made to an applicator head to improve the coating process are shown in the detailed view of an applicator head  17  illustrated in  FIG. 8 . These modifications may be made individually or in combination with any other modification discussed herein. The applicator head  17  is shown adjacent the edge  161  of a workpiece  163  being coated with a liquid. The applicator head  17  includes the applicator manifold  165  and the face plates  167 ,  169  extending down over the leading edge  171  of the applicator manifold  165 . Each face plate  167 ,  169  include a beveled edge  173 ,  175  which is disposed over the applicator port  177  formed at the leading edge  171  of the applicator manifold  165 . These beveled edges  173 ,  175  are positioned with the bevel facing the leading edge  171  of the applicator manifold  165 , and each beveled edge  173 ,  175  forms a point  179 . 
     It has been found that by including the beveled edges in the face plates, the air flow being drawn into the applicator head by the vacuum is improved around these edges of the face plates. This improved air flow leads to less liquid being deposited on the top and bottom surfaces of the workpiece, which in turn leads to a better visual appearance for the top and bottom surfaces of the workpiece. 
     The second improvement is in the application gap formed between the leading edge  161  of the applicator manifold  165  and the edge of the workpiece  163 . Typically, the applicator manifold is configured so that the application gap is a constant along the entire edge of the workpiece being coated. The applicator manifold  17  may instead include an applicator manifold which has a first part  181  of its leading edge  171  configured with a first application gap and a second part  183  of its leading edge configured with a second application gap with the two application gaps being different from each other. To accomplish this, when coating the edge of a particular workpiece, the applicator manifold is configured to have a first application gap which is at a constant, X, and it is configured to have a second application gap which is at the constant plus an additional factor. X+Y, where Y is a non-zero distance, measured in length, which may be positive or negative. For example, measured in inches, Y may be 0.010 in., which would enable use of this modification with the applicator head used in the second test above, since the absolute range of the operational window for that test was 0.014 in. By way of another example, Y may be 0.015 or greater, up to about 0.030, which would enable use of this modification with the applicator head used in the third test above, since the absolute range of the operational window for that test was 0.032 in. 
     By configuring the applicator manifold to have different application gaps with respect to the edge of a workpiece, the effects of gravity on the flow of a liquid in the applicator channel may be compensated. By way of example, as shown in  FIG. 8 , the bottom portion of the applicator manifold may be configured to have an application gap that is greater than the application gap formed at the top portion of the applicator manifold, so that the top portion of the edge of the workpiece has more liquid deposited thereon than does the bottom portion of the edge. In this way, the finish of the coating may be better balanced, and therefore have a more even appearance, across the entire edge of the workpiece. As a further option, for an applicator head which includes two or more applicator manifolds, each applicator manifold may be configured to have different application gaps with respect to the edge of the same workpiece. 
     While the invention has been described with respect to specific examples including presently preferred modes of carrying out the invention, those skilled in the art will appreciate that there are numerous variations and permutations of the above described systems and techniques. It is to be understood that other embodiments may be utilized and structural and functional modifications may be made without departing from the scope of the present invention. Thus, the spirit and scope of the invention should be construed broadly as set forth in the appended claims.