Abstract:
A flame safety system for a thermoplastic applicator comprises a gas burner and a flame indicator. The gas burner expels a jet of pressurized combustible gas from an outlet nozzle, and includes an attachment groove near the nozzle. The flame indicator includes an attachment ring configured to fit into the groove, thereby securing the flame indicator to the gas burner, and a flame path portion extending from the attachment ring into the jet of pressurized combustible gas. The flame path portion is formed from a material which incandescently glows whenever the jet of combustible pressurized gas is lit.

Description:
BACKGROUND 
       [0001]    The present invention relates generally to fire safety, and more particularly to a flame indicator for a mobile applicator for marking pavement with thermoplastics. 
         [0002]    Alkyd and hydrocarbon thermoplastics are commonly used to mark pavement surfaces with visible lines and symbols such as lane dividers and guide lines. In particular, thermoplastics provide a durable alternative to pavement painting, and are commonly used to mark street intersections, parking lots, and other high-traffic pavement surfaces from which paint would quickly wear away. 
         [0003]    Thermoplastics are conventionally applied to pavement surfaces using a mobile applicator comprising a heated reservoir or kettle, and an application screed die. Melted thermoplastic is dispensed from the kettle at a controlled rate and applied in a thin layer atop pavement surfaces with the screed die. Some applicators further comprise secondary burners which heat secondary reservoirs or screed die. Many applicators burn pressurized gas, such as propane and butane, at secondary burners and to heat applicator kettles. Manually driven and self-powered applicators are both relatively common, and some applicators can be attached to and driven by vehicles. 
         [0004]    Burners for thermoplastic melters and applicators typically operate by releasing a jet of pressurized combustible gas. When lit, this gas acts as a torch which is directed at components to be heated, such as the applicator kettle or screed die. Unlit jets of pressurized gas can constitute a serious safety hazard, rapidly releasing dangerous quantities of combustible gas into the air. Flames on gas burners can be pale and difficult to see, particularly in bright light, making it difficult for mobile applicator operators to ascertain whether a gas jet is lit (and therefore safe) or unlit (and therefore potentially dangerous). 
       SUMMARY 
       [0005]    The present invention is directed toward a flame safety system for a thermoplastic applicator. The flame safety system comprises a gas burner and a flame indicator. The gas burner expels a jet of pressurized combustible gas from an outlet nozzle, and includes an attachment groove near the nozzle. The flame indicator includes an attachment ring configured to fit into the groove, thereby securing the flame indicator to the gas burner, and a flame path portion extending from the attachment ring into the jet of pressurized combustible gas. The flame path portion is formed from a material which incandescently glows whenever the jet of combustible pressurized gas is lit. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a first perspective view of a mobile applicator of the present invention. 
           [0007]      FIG. 2  is a second perspective view of the mobile applicator of  FIG. 1 . 
           [0008]      FIG. 3  is a perspective view of a screed die box of the mobile applicator of  FIG. 1  and surrounding components. 
           [0009]      FIG. 4  is a perspective view of several die box burners of the mobile applicator of  FIG. 1 . 
           [0010]      FIG. 5  is a perspective view of a flame indicator for the die box burners of  FIG. 10 . 
       
    
    
     DETAILED DESCRIPTION 
       [0011]    The present invention relates to a flame indicator described below with respect to  FIGS. 4 and 5 . This flame indicator is used in mobile thermoplastic applicators. To place the invention in perspective,  FIGS. 1 ,  2 , and  3  are included to provide an overview of such a mobile applicator. 
         [0012]      FIGS. 1 and 2  are perspective views of mobile applicator  10  that will be discussed simultaneously. Mobile applicator  10  comprises frame  12 , kettle  14 , gas tank cradle  16 , gas system  18  (with gas tank hookup  20  and gas safety valve  22 ), kettle lid  24  (with lid handles  26  and lid hinges  28 ), kettle supports  30 , agitator arm  32 , lifting eyes  34 , bead reservoir  36 , push bar  38  (with handbrake  40 ), agitator lever  42 , chute  44 , gate valve  46 , screed enclosure  48  (with screed enclosure top  50  and screed shroud door  52  connected at shroud door hinges  54 ), screed actuator link  56 , screed actuator lever  58 , gate valve lever  60 , screed box burners  62 , hand torch  64 , wheels  66 , shroud door latch  68 , and bead tube  70 . 
         [0013]    Mobile applicator  10  is a tool capable of marking pavement lines by melting and then applying thermoplastic a pavement surface. Mobile applicator  10  includes frame  12  which provides support for other components of mobile applicator  12 . Frame  12  may, for instance, be comprised of a framework of aluminum and/or steel beams, tubes, and struts. Gas tank cradle  16  is attached to frame  12  at the forward end of frame  12 . Gas tank cradle  16  is a holding structure sized to retain a tank of propane, butane, or other appropriate combustible gas. Wheels  66  are rotatably attached to the bottom of frame  12  and allow mobile applicator  10  to move along pavement. In the depicted embodiment, mobile applicator  10  includes three wheels  66 : a single front wheel which swivels and provides directional control, and two rear wheels which track behind the front wheel. Push bar  38  is attached at the aft of frame  12  and includes handbrake  40 . Push bar  38  allows a user to propel mobile applicator  10  and handbrake  40  allows the user to stop applicator  10 , such that the user can direct where the pavement lines are made. One skilled in the art can appreciate that although directional terms such as “forward”, “aft”, “bottom”, “top”, “right side”, and “left side” have been used in describing this invention, but such terms are merely relational descriptors of the illustrated embodiments shown herein. 
         [0014]    Mounted to the top of frame  12  is kettle  14 , which is a receptacle that is heated to melt granular thermoplastic for application to pavement surfaces. In the illustrated embodiment, kettle  14  is a substantially hemi-cylindrical receptacle heated from below by a plurality of gas burners. Kettle  14  may, for instance, be formed of aluminum. Kettle  14  is attached to frame  12  via kettle supports  30 , which are rigid struts or surfaces formed, for instance, of steel or aluminum. 
         [0015]    Kettle lid  24  covers the open top of kettle  14  and prevents molten thermoplastic, thermoplastic vapor, and heat from escaping from kettle  14  during operation. Kettle lid  24  can be opened and closed with lid handles  26 , which are attached to the left side of kettle lid  24 . In some embodiments, kettle  14  may include latches which allow kettle lid  24  to be locked shut. Kettle lid  24  is connected to kettle  14  via lid hinges  28  which are on the right side of kettle lid  24  (opposite of lid handles  26 ). Lid hinges  28  may be any sort of conventional hinge selected for heat resilience and resistance to fouling when exposed to melted thermoplastic. In addition, kettle  14  includes agitator arm  32  which is connected to a plurality of agitators inside kettle  14  used to stir the molten thermoplastic. 
         [0016]    Also attached to the top of kettle  14  are lifting eyes  34 . Lifting eyes  34  are attachment points that allow mobile applicator  10  to be hoisted into position or loaded onto or off of a transportation vehicle. In the illustrated embodiment, lifting eyes  34  are tabs with holes which extend from the top surface of kettle  14 , but a person skilled in the art will recognize that lifting eyes  34  may generally be any sort of load-bearing anchors for a hoist or crane, and could, for instance, be located on frame  12 , instead. 
         [0017]    At the bottom right side of kettle  14  is gate valve  46 . Gate valve  46  is positioned between the interior of kettle  14  to chute  44 . Chute  44  is a rigid, heat-resistant chute or trough which guides molten thermoplastic from kettle  14  to the screed die box. Chute  44  is comprised of a heat-resistant material including, but not limited to, aluminum or steel. 
         [0018]    As stated previously, gas tank cradle  16  holds a tank of combustible gas (not shown), and gas from this tank is utilized by gas system  18 . Gas system  18  is largely located beneath kettle  14  and kettle supports  30 , and is anchored to frame  12 . Gas system  18  includes gas hookup  20 , a fluid connection which receives gas from a tank at gas tank cradle  16 . Gas system  18  also includes gas safety valve  22 , and a plurality of other valves and gas distribution tubes. Gas safety valve  22  is an electrically actuated multi-path valve which controls gas flow to pilot burners and main burners heating kettle  14 . Gas system  18  provides combustible gas to burners which heat kettle  14 , and to screed box burners  62  and hand torch  64 . Hand torch  64  is a handheld burner which can be used by a human operator to touch up or remove thermoplastic applied using mobile applicator  10  and is therefore located at the aft of mobile applicator  10 . In addition, screed box burners  62  are connected to gas system  18 . 
         [0019]    Screed enclosure  48  is anchored to frame  12  at the bottom right side of frame  12 . Screed enclosure  48  includes screed enclosure top  50  and screed shroud door  52 . Screed enclosure  48  surrounds screed box burners  62  and the screed die box (see  FIG. 3 , below). Screed enclosure top  50  partially covers the screed die box, and screed shroud door  52  is connected to screed enclosure top  50  by shroud door hinges  54 , such that screed shroud door  52  can be pivoted upward from door hinges  54  to reach, remove, or insert the screed die box. Screed shroud door  52  is secured to frame  12  by shroud door latch  68 , which holds shroud door  52  in the depicted (closed) position during operation of mobile applicator  10 . Screed enclosure  48  shields the screed die box from wind and debris and conversely shields the operator from the molten thermoplastic therein. 
         [0020]    In order to operate mobile applicator  10 , a user ignites pilot burners and main burners under kettle  14 . Then the user opens kettle lid  24  and deposits a sack of granular thermoplastic atop heat exchanger plenums located inside kettle  14 . The sack itself is formed of a meltable thermoplastic material, so heat from main burners  116  melts the sack and the granules. The user can then rotate agitator arm  32  back and forth across a substantially 180° range, thereby sweeping the agitators through the interior of kettle  14  so as to mix the thermoplastic as it melts. Alternatively, the user can attach agitator arm  32  to agitator lever  42 , allowing the user to move agitator arm  32  from the aft of mobile applicator  10 . 
         [0021]    Once the thermoplastic is uniformly melted, the user can pull gate valve lever  60 , which opens gate valve  36 . Opening gate valve  36  allows thermoplastic from kettle  14  to flow down chute  44  into the screed die box (shown in  FIG. 3 ). Screed box burners  62  heat the screed die box, allowing the thermoplastic to remain molten as it is dispensed. In addition, light reflective beads are commonly used to provide increased visibility to thermoplastic stripes, for some applications. These beads, which are usually formed of glass, are deposited on freshly applied molten thermoplastic. Some embodiments of mobile applicator  10  include bead reservoir  36  (located at the top aft of mobile applicator  10 ), which is a receptacle for storing such glass beads. Bead tube  70  carries beads from bead reservoir  36  to screed enclosure  48 , allowing beads to be deposited as thermoplastic is applied. 
         [0022]    The components and configuration of mobile applicator  10  as shown in  FIGS. 1 and 2  allow for a bag of thermoplastic granules to be transformed into a pavement line. This occurs by mobile applicator  10  melting the thermoplastic in kettle  14 , transferring the melted thermoplastic into a screed die (shown in  FIG. 3 ) via gate valve  46  and chute  44 , and dispensing the molten thermoplastic onto the pavement. A pavement line is formed as the user propels mobile applicator  10 . 
         [0023]      FIGS. 1 and 2  depict one embodiment of the invention, to which there are alternatives. For example, mobile applicator  10  can include mounting points such that mobile applicator  10  can be attached to a motor vehicle. In such an embodiment, the motor vehicle pushes and/or pulls mobile applicator  10  in order to direct where the pavement lines are made. 
         [0024]      FIG. 3  provides a close-up view of die box  74  and surrounding components of mobile applicator  10 , with screed enclosure  48  removed for increased visibility.  FIG. 3  depicts frame  12 , chute  44 , screed actuator link  56 , screed burners  62  (including four aft screed burners  62   a  and three fore burners  62   b ), wheel  66 , bead tube  70 , bead dispenser  72 , screed die box  74 , and flame indicators  76 . Screed die box  74  comprises screed die box lever  78 , screed die box bucket  80 , screed die box gate  82 , screed die box anchor  84 , and retention pin  86 . 
         [0025]    As stated above with respect to  FIGS. 1 and 2 , screed die box  74  is positioned beneath chute  44  in order to receive molten thermoplastic from chute  44 . Screed die box  74  is primarily comprised of screed die bucket  80 , a five-sided container open on top to receive thermoplastic from chute  44 . Screed die bucket  80  is anchored relative to other components of mobile applicator  10  by screed die box anchor  84 , which is welded to or integrally formed on the forward side of bucket  80 . In the illustrated embodiment, screed die box anchor  84  is an elongate post which extends through and can be locked into place relative to frame  12 . Screed die box anchor  84  can be locked in place to frame  12  anywhere along the length of die screed die box anchor  84 , allowing the position of screed die box  74  to be adjusted for different applications. A person skilled in the art will recognize that screed die box  74  could alternatively be anchored to frame  12  by other flexible or inflexible means, and that screed die box anchor  84  could accordingly take other forms which equivalently allow screed die box  74  to be secured to frame  12 . Screed die box anchor  84  may double as a handle used by operators to install, remove, and transport screed die box  74 . 
         [0026]    Screed die box lever  78  attaches to screed die box gate  82 . The screed die box gate is a slidable plate along the bottom of screed die bucket  80 . Screed die box lever  78  is detachably attached to screed actuator link  56  by means of retention pin  86 , and is fastened to screed die box gate  82 . When screed actuator lever  58  (shown in  FIG. 2 ) is pulled or pushed, a torque is applied to screed die box lever  78  via screed actuator link  56 , which opens or closes screed die box gate  82 . Screed die box gate  82  opens and closes by shifting forward or aftward to create or remove an open space in the bottom of screed die box bucket  80 . Screed die box  74  may have a plurality of distinct embodiments with different dimensions and additional features for use in different applications, any of which may be freely swapped in and out of mobile applicator  10  by fastening screed die box  74  to frame  12  using screed die box anchor  84 , and attaching screed die box lever  78  to screed actuator link  56  with retention pin  86 . 
         [0027]    Also shown in  FIG. 3 , bead dispenser  72  is attached to frame  12  and supports aft screed burners  62   a.  Bead dispenser  72  receives and deposits visibility-enhancing beads from bead tube  70 , as understood in the art. In addition, fore burners  62   b  are supported by frame  12  and are located forward of screed die box  74 . 
         [0028]    Screed die box  74  is heated by screed burners  62 , to ensure that thermoplastic deposited in screed die box  74  from chute  44  remains molten during the application process. As stated previously, all screed burners  62  receive combustible gas from gas system  18 . Screed burners  62  include aft screed burners  62   a,  which are directed to an aft portion of screed die box  74 , and fore screed burners  62   b.  Although the embodiment of mobile applicator  10  depicted in  FIG. 3  includes four aft screed burners  62   b  and three fore screed burners, a person skilled in the art will understand that the number and placement of screed burners may be varied without departing from the spirit of the present invention. In particular, some embodiments of mobile applicator  10  may not include aft screed burners  76 . Alternatively, one or both of aft and fore screed burners  62   a  and  62   b,  respectively, may be modular components which may be connected to gas system  18  if and when desired. As shown in  FIG. 3 , two of fore screed burners  62   b  are directed to a fore portion of screed die box  74  near where screed die box anchor  84  attaches to screed die box bucket  80 , while a third screed burner  62   b  is directed at chute  44  to prevent thermoplastic from solidifying in chute  44 . As depicted, all screed burners are ignited manually, although a person skilled in the art will recognize that automatic ignition tools such as electrical sparkers may be utilized instead. 
         [0029]    The components and configuration of mobile applicator  10  as shown in  FIG. 3  allow for molten thermoplastic to be applied to pavement. Screed burners  62  heat die box  74  and chute  44 , allowing molten thermoplastic to flow smoothly from kettle  14  into screed die box  74  and maintaining thermoplastic in screed die box  74  in a molten state. By pulling screed actuator lever  58  (shown in  FIG. 2 ), an operator can deposit molten thermoplastic from screed die box  74  onto a pavement surface. 
         [0030]    As noted above in the Background of the present invention, flames from combustible gasses such as propane and butane can be hard to see, particularly in conditions of bright sunlight. Consequently, it can be difficult to visually ascertain whether screed burners  62  (or, potentially, hand torch  64 ) are lit. To reduce the risk of undetected gas leakage from an unlit burner, screed burners  62  are fitted with flame indicators, as described below with respect to  FIGS. 7 and 9 . 
         [0031]      FIG. 4  depicts a portion of gas system  18  including screed burners  62   a  with grooves  88 . Aft screed burners  62   a  are anchored to and receive gas from manifold  96 , which is attached to beat dispenser  72  (not shown; see  FIG. 3  above) via mounting brackets  98 . Each aft screed burner  62   a  is fitted with a flame indicators  76  having attachment ring  90  and flame path portion  92 . Attachment ring  90  snaps into groove  88 , securing flame indicator  76  to aft screed burner  62   a  such that flame path portion  92  extends into the path of the gas jet projected from aft screed burner  62   a.  When this gas is ignited, flame from aft screed burner  62   a  heats flame path portion  92  of flame indicator  76 , causing it to incandescently glow, This glow improves flame visibility. Although flame indicator  76  is described herein with reference to aft screed burners  62   a , a person skilled in the art will recognize that flame indicator  76  may also be used on other burners where flame visibility is normally limited, including on hand torch  64  and fore screed burners  62   b.    
         [0032]      FIG. 5  depicts flame indicator  76 , comprising attachment ring  90 , flame path portion  92 , and turn  94 . Attachment ring  90  is a snap ring which deforms to snap into groove  88 , anchoring flame indicator  76  to aft screed burner  62   a  (see  FIG. 4 ). Flame path portion  92  is formed of a metallic alloy such as inconel or stainless steel, which changes color or incandescently glows when heated to sufficient temperatures. In some embodiments, flame path portion  92  incandescently glows red. Attachment ring  90  deforms to snap into groove  88 , securing flame indicator  76  to screed burner  62   a.    
         [0033]    As depicted in  FIG. 5 , flame indicator  76  is comprised of a single piece of wire bent into attachment ring  90  and flame path portion  92 , with attachment ring  90  meeting flame path portion  92  at substantially a right angle at turn  94 . This embodiment is both inexpensive and easily manufactured. In alternative embodiments, however, flame path portion  92  and attachment ring  90  may be separate pieces, potentially of different materials, which are welded or otherwise joined together. 
         [0034]    Flame indicators  76  improve visibility of flames from screed die burners  62 , reducing the risk that gas will escape undetected from unlit burners, and accumulate in hazardous quantity. Flame indicators  76  accordingly improve fire safety, and are both easily manufactured and inexpensive to produce. 
         [0035]    While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.