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CROSS-REFERENCE TO RELATED APPLICATIONS 
     This patent application claims the benefit of U.S. Provisional Patent Application No. 60/627,218, filed Nov. 12, 2004 
    
    
     FIELD OF THE INVENTION 
     This invention pertains generally to the manufacture and processing of products made from a moving web or other continuous sheet material, and more particularly, to an apparatus and method for applying markings onto the moving sheet material. 
     BACKGROUND OF THE INVENTION 
     Often it is necessary to provide markings on various web or sheet formed products. Preferably, the markings are applied to the web or sheet products as they are undergoing other processing. For example, roofing materials, such as asphalt shingles, commonly are produced in a process line in which a web of sheet material, made of organic or fiberglass material, is drawn from a supply roll through (1) a coating station in which the web is coated with a hot liquid tar or asphalt, (2) a surfacing station in which granular surfacing material is directed onto the hot liquid coating, (3) a cooling and press roll station in which the granular surface material is pressed into the hot liquid coating and sheet material and coating are cooled by spraying a cooling liquid onto the moving sheet material and (4) cutting and stacking stations in which the cooled sheet material is cut into predetermined-size shingles and stacked. 
     Roofing products include a variety of different shingles and rolls each of which is designed to be nailed down in a particular location. In order to help the roofers who install the products determine where a particular roofing product should be nailed, roofing material processing lines can include a nail marking system. A typical nail marking system uses one or more marking wheels to apply a rough line that runs the length of the roofing product identifying where the particular roofing product should be nailed. The marking wheels pick-up the marking fluid, which is a mixture of industrial latex paint and water, from a trough to which the marking fluid is pumped. Known water/paint mixtures used as marking fluids have water to paint mix ratios of 70/30 to 40/60. 
     Roofing material processing lines are now running at faster and faster speeds as compared to in the past with most roofing material lines running at close to 750 ft/min. Unfortunately, at higher speeds, the line produced by the marking wheel in conventional nail marking systems can include skips or become crooked, ragged and/or faint. Because improperly marked roofing products must be scrapped or rejected, failure of the marking system can be expensive and time consuming. 
     In addition, nail marking systems using applicator wheels are quite messy and relatively labor intensive and expensive to maintain. For example, because of paint build-up, the applicator wheels have to be cleaned and replaced on a regular basis. Moreover, the paint used in the marking fluid is relatively expensive. However, it is difficult to monitor and control paint utilization with wheel and trough marking systems leading to further inefficiencies. 
     BRIEF SUMMARY OF THE INVENTION 
     The invention provides an apparatus for applying a marking to an elongated sheet material. The apparatus includes a processing machine through which an elongated length of the sheet material is passed. A marking system is arranged to apply a marking to the elongated length of sheet material passing through the processing machine. The marking system comprises at least one spray gun and a pump for supplying marking fluid to the spray gun. The pump is operable at selectively variable speeds. A controller controls the speed of the pump based upon a speed at which the sheet material is passed through the processing machine. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A and 1B  are a diagrammatic depiction of an illustrative asphalt shingle processing line having a marking system in accordance with the invention. 
         FIG. 2  is a perspective diagrammatic depiction of a portion of the shingle processing line of  FIGS. 1A and 1B  showing the marking system of the invention situated before the finish product accumulator or looper. 
         FIG. 3  is a perspective diagrammatic depiction of a portion of the shingle processing line of  FIGS. 1A and 1B  showing the marking system of the invention situated before the shingle cutter. 
         FIG. 4  is a schematic diagram of an exemplary marking fluid circulation system for the marking system of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now more particularly to  FIGS. 1A and 1B  of the drawings, there is shown an illustrative roofing material processing line  10 , in this case a shingle processing line, including a marking system in accordance with the present invention. While the present invention is described in connection with producing a generally continuous nail marking line on a web of roofing material, and in particular a web of roofing shingles, it will be understood by those skilled in the art that the present invention is not limited to roofing material processing lines or applications in which a continuous marking line is applied to a material. To the contrary, the present invention can be used in any application in which it may be desirable to place some sort of mark on a web or sheet material. 
     The illustrated asphalt shingle processing line  10  basically is of a conventional type. In this case, the processing line  10  includes an unwind stand  11  in which a spool of a continuous web or sheet material  12 , such as fiberglass or felt, is drawn from a takeout roll  14  over a splicing table  15  and through an accumulator  16  by means of pull rolls  18 . The web  12 , as shown in  FIG. 1A , is directed in serpentine fashion through the accumulator  16 , in which upper rolls thereof can be raised and lowered in a known manner for providing a continuous supply of sheet material to the processing line  10  notwithstanding any breakage or an interruption in the supply of material from the takeout roll  14 . The web  12  is then drawn through a saturator  19  which coats both sides of the web with hot asphalt or tar. The coated web is then directed via a feed station  20  to a further accumulator  21  then directed via a stride-in section  22  to a surfacing section  24  where granular material is released onto the hot-coated web. The surfaced web  12  is thereupon directed to a cooling and press roll station  25  ( FIG. 1B ) that initially cools the coating and sheet material prior to direction through a press roll  26 . The web is then cooled in the cooling section  25  and dried by a blower  28 , prior to direction to a shingle cutting and shingle stacking stations  29 ,  30  via a finished product accumulator  31 . Additional details regarding the construction and operation of the shingle processing line can be found in commonly owned U.S. application Ser. No. 10/910,842, the disclosure of which is incorporated herein by reference. 
     In accordance with the present invention, for producing a mark on the roofing material, in this case a line that runs the length of the roofing product identifying where the shingles should be nailed, the illustrated shingle processing line  10  includes a marking system  32  in which the application rate of the marking fluid can be controlled on the basis of the speed of the processing line  10 . As described in greater detail below, unlike conventional wheel and trough marking systems that produce ragged edged, uneven lines at higher line speeds, the marking system  32  of the present invention is able to provide a clean, distinct line of consistent width across a wide range of processing line speeds. Moreover, the marking system  32  of the present invention can be operated at relatively low paint to water ratios leading to significant cost savings (because of the use of less paint) as compared to conventional wheel and trough marking systems. 
     To this end, the marking system  32  includes a plurality of spray guns  34  that are supplied with marking fluid via a pump  36 , in this case a positive displacement gear pump, as shown in  FIG. 2 . Advantageously, the positive displacement gear pump  36  can quickly change speeds, thus allowing the flow rate out of the spray guns  34  to be adjusted quickly based on the speed of the shingle processing line  10 . For example, the pump  36  can be operated at a higher speed so as to provide a higher flow rate through the spray guns  34  when the processing line  10  is operating at higher line speeds to ensure that the nail marking line is clear and distinct. Conversely, at slower line speeds, such as during start-up or shut-down, the pump  36  can be operated more slowly so that only the amount of marking fluid necessary to produce a clear distinct line is directed through the spray guns  34 . Accordingly, the use of the positive displacement pump  36  allows the marking system  32  to accurately meter the marking liquid onto the shingles across a relatively wide range of line speeds. This not only results in a clear visible marking line even at high processing line speeds, but also optimizes usage of the marking fluid by ensuring that excess marking fluid is not applied at slower line speeds. 
     The illustrated spray guns  34  are supported on a header  38  arranged, in this case, above the moving web  12  of roofing shingles. As will be appreciated by those skilled in the art, the spray guns  34  are arranged on the header  38  so that the marking fluid discharged by each of the spray guns  34  hits the moving web  12  in a desired location so as to produce a continuous marking line along the web identifying where the finished shingles should be nailed. In the embodiment illustrated in  FIG. 2 , the spray gun header  38  is arranged so as to situate the spray guns  34  above the shingle web  12  just downstream of the cooling section  25  and upstream of where the shingle web enters the finished product accumulator  31 . Alternatively, as shown in  FIG. 3 , the spray gun header(s)  38  for the nail marking system  32  can be further downstream in the processing line  10  just before the shingle cutter  29 . Of course, the marking system  32  of the present invention is not limited to any particular location in the shingle processing line  10 . 
     Each spray gun  34 , in this case, is a pneumatic spray gun  34  equipped with a solid stream type spray nozzle. The spray nozzles can be selected so as to provide a marking line of the desired width, e.g. 0.125 in. One suitable type of spray nozzle is the ¼JAU automatic spray gun available from Spraying Systems, the assignee of the present invention. In the illustrated embodiment, each spray gun  34  has lines connecting to a common marking fluid supply line  40  and a common pressurized air line  42  (see  FIG. 2 ). The pressurized air line  42  controls operation, i.e. opening and closing, of the spray guns  34  in a known manner (in the embodiment illustrated in  FIG. 2 , the pneumatic system and the pump  36  are integrated into a single unit). The marking fluid supply line  40  provides the marking fluid to the spray guns  34 . As previously discussed, flow of the marking fluid through the fluid supply line  40  is controlled by the positive displacement pump  36 . 
     To control the pump  36  as well as monitor other operational parameters of the marking system  10 , a controller  44  can be provided. In order to monitor the speed of the processing line  10 , the controller  44  can be in communication with one or more line speed sensors associated with the shingle processing line. A shingle processing line typically includes one or more such sensors with which the controller can communicate. For example, the processing line  10  can include a speed sensor  46  arranged to detect the rotational speed of the one of the rollers that can be in communication with the controller  44  as diagrammatically depicted in  FIG. 2 . The controller  44  is also in communication with the pump  36  and programmed so as to adjust the speed of the pump based on the processing line speed as sensed by the one or more line speed sensors. One example of a controller suitable for use in the marking system of the present invention is the AutoJet Model 2250 spray controller available from Spraying Systems, the assignee of the present invention. 
     The controller  44  can also provide fault or warning signals or other information associated with the operation of the marking system  10 . For example, with the system of the present invention, the positive displacement pump  36  acts as a virtual flow meter allowing for much closer monitoring of the paint utilized by the system. In particular, the positive displacement pump  36  monitors the set point or reference flow rate through the spray guns  34  and reports that information to the controller  44 . The controller  44  can be adapted to display the flow rate and the line speed so that the shingle processing line operators are able to monitor the amount of marking fluid being consumed by the system. In addition, the controller  44  can compare the reference flow rate as measured by the positive displacement pump  36  to a theoretical or predetermined desired flow rate for the system. In such as case, the controller  44  can be programmed to provide a high or low flow alarm if the measured flow rate exceeds the theoretical or predetermined flow rate for a predetermined period of time. 
     To further ensure the application of a clear and distinct mark on the roofing materials, the marking system  32  can include flow sensors  48  arranged to monitor the discharge from the spray guns  34 . The flow sensors  48  can be used to detect whether the spray guns  34  are actually spraying or whether the discharging spray is wobbling or drooping (due, for example, to a partially clogged spray gun) in such a manner that the marking line is not being applied to the moving web correctly. The flow sensors  48  can communicate with the controller  44  or some other device capable of providing a warning signal when the flow from one or more of the spray guns  34  has stopped, is wobbling or drooping. This warning signal can allow the shingle processing line operators to take appropriate actions to minimize product loss due to plugged nozzles or spray wobble or droop by warning the operators so that they can take appropriate action. 
     To help clean-out the system when it is shut down, the marking system  32  of the present invention can be configured to execute a quick system flush. The system flush mode can be executed quickly (e.g., 5-7 seconds) by directing one or more bursts of a flushing liquid such as water through the system.  FIG. 4  is a schematic diagram of an exemplary piping system for the marking system of the present invention as equipped with such a system flush mode. The illustrated system includes a closed loop marking fluid supply system including an agitated marking fluid supply tank  52 , a marking fluid supply pump  54 , a backpressure regulator  56  and a marking fluid circulation line  58 . Branching off of the marking fluid supply system is the marking fluid supply line  40  to the spray guns  34 . In this case, a filter  60  is provided just upstream of where the marking fluid supply line  40  branches off of the marking fluid circulation line  58 . A flushing fluid supply line  62  also connects to the marking fluid supply line  40  via a three-way control valve  63 . The flushing fluid supply line  62  is part of a flushing fluid system including, in this case, a water supply  64 , a filter  66  and a flush valve  68 . 
     As shown in  FIG. 4 , the positive displacement pump  36  is arranged downstream from the three-way control valve  63 . A bypass line  70  having a bypass control valve  72  extends around the positive displacement pump  36 . A second three-way control valve  74  is arranged downstream of the positive displacement pump and the location where the bypass line  70  rejoins the marking fluid supply line  40 . The second control valve  74  can direct flow either to a dump tank  76  or to the spray guns  34 . In normal operation, the first three-way control valve  63  would be set to block fluid flow from the flushing fluid supply line  62 , the bypass control valve  72  would be closed and the second three-way control valve  74  would be set to block fluid flow to the dump tank  76 . In the system flush mode, the first three-way valve  63  would switch to block flow from the marking fluid supply system and allow fluid flow from the flushing fluid supply line  62 . Additionally, the bypass control valve  72  would open and the second three-way control valve  74  would switch to block flow to the spray guns  34  and open flow to the dump tank  76 . 
     Advantageously, the system flush will clean out most of the marking system piping upstream of the spray guns leaving only the spray guns themselves to be cleaned out manually. A flush mode is particularly useful in situations where the line between the pump and the spray guns is relatively long. According to one preferred embodiment, the switch to a system flush mode can be controlled by the controller and automated based on the occurrence of a triggering event associated with operation of the shingle processing line such as an interruption in the movement or breakage of the web. 
     All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein. 
     The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention. 
     Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.

Summary:
An apparatus for applying a marking to an elongated sheet material is provided. The apparatus includes a processing machine through which an elongated length of the sheet material is passed. A marking system is arranged to apply a marking to the elongated length of sheet material passing through the processing machine. The marking system comprises at least one spray gun and a pump for supplying marking fluid to the spray gun. The pump is operable at selectively variable speeds. A controller controls the speed of the pump based upon a speed at which the sheet material is passed through the processing machine.