Device for melting and applying thermoplastic material to surface

#This invention relates generally to the field of a road surface marking apparatus, and in particular to a device for heating and applying thermoplastic material to a road surface.

#In the United States, the first documented use of a painted center line was along Trenton's River Road in Wayne County, Mich., in 1911, when Edward N. Hines watched a leaky milk wagon leave a white trail along a road. A road surface marking is any kind of device or material applied to a road surface in order to convey official information. Typically, road surface markings are used on paved roadways to provide guidance information to both drivers and pedestrians. Marking uniformity is an important factor in minimizing confusion and uncertainty about their meaning, and efforts exist to standardize such markings.

#Road surface markings vary in form: surface level permanently affixed, surface level temporarily but not permanently affixed, higher than road surface markers, and/or even mechanical devices. They are designed to inform motorist and pedestrians. Their designs range from merely a daytime or nighttime visual presentation to a raised pavement marker that advises motorist by light reflection or vehicle vibration resulting from contact between the vehicles tires and the raised marker. Efforts to improve road marking systems exist in the realm of the application of such markings, adding retro-reflectivity, increasing longevity, and lowering installation cost.

#FIG. 1 is a perspective view of the present device;

#FIG. 2 is a perspective view with portions of the present device illustrated in hidden lines;

#FIG. 3 is a top view of the present device;

#While the present invention is susceptible of embodiment in various forms, there is shown in the drawings and will hereinafter be described a presently preferred, albeit not limiting, embodiment with the understanding that the present disclosure is to be considered an exemplification of the present invention and is not intended to limit the invention to the specific embodiments illustrated.

#Now referring to FIGS. 1-14, a pavement striping device 10 for heating and applying thermoplastic material to a road surface is illustrated. The pavement striping device 10 is comprised of: a hopper 20 for holding a supply of particulate thermoplastic marking material 12 in a non-molten state, a screw conveyor 40 for transporting the thermoplastic particulate 12 from the hopper 20 to a single conduit or a series of coaxial conduits 66 within the melting kettle 60 which may be air or oil-heat transfer medium; the melting kettle 60 having at least one and more preferably a series of coaxial conduits 66 therein, a heating mechanism 30 for heating the melting kettle 60 air or oil jacket 61. In at least one embodiment, the screw conveyor 40 may also be heated to a temperature suitable for pre-heating or melting thermoplastic. At least one embodiment includes a drive motor 70 for scraping the sides of the conduits and/or driving the stream of molten thermoplastic 14 through the series of coaxial conduits 66 to a nozzle 80 that directs the molten thermoplastic 14 through an extrusion die (not shown) for sizing and controlling the flow of the molten thermoplastic prior to application on the pavement surface. The pavement striping device 10 may be mounted on a walk behind system, pulled on a trailer, or built on a vehicle chassis without departing from the scope of the invention.

#The hopper 20 is a storage container 22 for thermoplastic particulate that is used to dispense particulate through a chute 24 into the screw conveyor 40. The hopper includes an open top suitable for easily pouring pelletized or ground thermoplastic therein. The hopper also preferably includes tapered sidewalls, which direct the granulated or pelletized thermoplastic to the inlet of the screw conveyor. The screw conveyor 40 is comprised of a hollow barrel 46 having a rear end 42 and front end 44, a rotating screw 48, and a screw drive motor 50. The rotating screw 48 is positioned within the barrel 46 of the screw conveyor 40 and driven by the screw drive motor 50. The screw conveyor 40 runs from the chute 24 to the melting kettle 60. In the preferred embodiment, the rear end 42 of the screw conveyor 40 is placed within the hopper 20. Gravity forces the particulate 12 in the hopper 20 downwards into the barrel 46 of the screw conveyor 40 and in contact with the rotating screw 48. Preferably, the amount of particulate 12 that is demanded at the nozzle 80 in real-time is transferred from the hopper 20. In that manner, the screw conveyor may include any number of devices for monitoring the volume of thermoplastic within the melting kettle. These devices would cause the screw conveyor to alternate between feeding material and not feeding material to the melting kettle. The thermoplastic particulate 12 is dispensed from the chute 24 of the hopper 20 and enters the rear end 42 of the screw conveyor 40, therein the particulate 12 comes into contact with the screw 48. The screw 48 forces the particulate 12 forward through the barrel 46, which in at least one embodiment is heated or pre-heated before being deposited in the melting kettle. The thermoplastic exits the front end 44 of the screw conveyor 40 and is fed into the single or series of coaxial conveyor conduits 66 within the air or oil-heat transfer medium melting kettle 60. In some embodiments, rotating screw 48 further acts to scrape the molten plastic from the sidewalls of the conduit(s) and agitate the thermoplastic material as it is forced toward the nozzle 80. Within the embodiments, where the screw conveyor is heated, the screw conveyor 40 is coupled to the heating mechanism 30, which provides hot air or oil to provide the necessary pre-heating to the thermoplastic. The heating mechanism 30 may provide heating zones within the screw conveyor 40 that gradually increase the temperature of the barrel 46 from the rear end 42 to the front end 44. In at least one embodiment, the screw conveyor utilizes a screw such as those utilized in plastic extrusion machines. This screw is constructed and arranged to create heat via friction within the thermoplastic as it is conveyed through the screw conveyor. In this manner, the screw may be constructed to pre-heat or melt the thermoplastic as it is transferred along the conveyor, reducing the heat that would need to be transferred to the thermoplastic for application to a road surface.