Asphalt Pothole Patcher with Electrically Heated Riser Tubes

Abstract

A portable device is shown for transporting asphalt repair materials for use in repairing potholes in asphalt pavements. The device has a body with a hopper compartment for transporting and dispensing asphalt mix materials. A heat transfer oil chamber is located below the hopper compartment and is heated by a primary heat source during normal working hours of the device. A pair of electrically powered electric heat riser tubes extend in a longitudinal direction in a horizontal plane in the hopper compartment above the bottom wall of the compartment for heating the asphalt materials in the hopper compartment during non-working hours.

Claims

1. A portable device for transporting asphalt repair materials for use in repairing potholes in asphalt pavements, the device comprising: a body adapted to he mounted on a portable base tier transporting the body to a repair site, the body having a hopper compartment with a V-shaped bottom wall for transporting asphalt mix materials and a generally V-shaped heating chamber located below the hopper compartment, the V-shaped bottom wall of the hopper compartment defining an upper extent of the heating chamber; an auger mounted in the bottom of the hopper compartment for dispensing asphalt mix materials therefrom; an agitator shaft located above the auger in the hopper compartment for agitating the hopper materials; a primary heat source associated with the heating chamber for heating the chamber and for transferring heat to the hopper compartment through the hopper bottom wall for heating the hopper compartment during normal working hours; a supplemental heat source located within the hopper compartment for heating the hopper compartment during non-working hours, the supplement heat source comprising one or more electric electric heat riser tubes which extend longitudinally within an interior of the hopper compartment and which are selected to provide low density heat to prevent asphalt materials within the hopper compartment from overheating and burning or deteriorating during periods of supplemental heating.

2. The device of claim 1, wherein the primary heat source is selected from the group consisting of an LP gas heating source, a CNG gas heating source, an electric heating source and a diesel tired heating source.

3. The device of claim 2, wherein the hopper compartment has a from wall, a rear wall and opposing side walls, the front and rear walls defining a chamber length therebetween, and wherein a pair of electric electric heat riser tubes are located in a generally horizontal plane which extends between the front and rear walls above the plane of the agitator shaft, the electric electric heat riser tubes extending generally parallel to one another on either side of the agitator shaft for a majority of the chamber length.

4. The device of claim 3, wherein the electric heat riser tubes are tear drop shaped in cross section and are used to contain electric heating rods which are plugged into a 220 volt electric supply outlet during non-working hours.

5. The device of claim 4, wherein the heating rods are 800 watt electric rods which are selected to supply low density slow heat to the electric heat riser tubes in the range from 250 F. to 275 F. to prevent asphalt materials in the hopper compartment from being overheated.

6. The device of claim 5, wherein the heating rods within the riser tubes are approximately 96 inches long and the riser tubes themselves are approximately 108 inches long.

7. The device of claim 6, wherein the electric heat riser tubes comprise an external plate-like structure with opposing longitudinal sides which diverge from an upper apex downwardly toward a curved bottom region of the heat tubes.

8. The device of claim 7, wherein the electric heat riser tubes are installed approximately two thirds of the way up an internal height of the hopper compartment and are effective to keep asphalt materials in the hopper compartment hot during non-working hours of the device when plugged into a 220 volt electric supply outlet.

9. The device of claim 8, wherein the electric heating rods in the electric heat riser tubes have a built-in thermocouple.

10. The device of claim 1, wherein the V-shaped bottom wall of the hopper compartment forms an upper, uninsulated common wall of the heating chamber, the heating chamber having an insulated bottom wall and insulated side walls.

11. The device of claim 10, wherein the heating chamber is a sealed heat transfer oil chamber and the heat transfer oil chamber is heated by one of the primary heat sources of the device.

12. A method of repairing a pothole in an asphalt pavement, comprising the steps of: providing a body on a portable base for transporting the body to a repair site, the body being equipped with a hopper compartment with a V-shaped bottom wall for transporting asphalt mix materials and a generally V-shaped heating chamber located below the hopper compartment, the V-shaped bottom wall of the hopper compartment defining an upper extent of the heating chamber; providing a screw conveyor mounted in the bottom of the hopper compartment for dispensing asphalt mix materials therefrom; providing a paddle shaft located above the screw conveyor in the hopper compartment for agitating the hopper materials; providing a primary heat source associated with the heating chamber for heating the chamber and for transferring heat to the hopper compartment through the hopper bottom wall to maintain the asphalt mix materials in a workable state during normal working hours of the machine; providing a supplemental heat source located within the hopper compartment for heating the hopper compartment during non-working hours, the supplement heat source comprising one or more electric heat riser tubes which extend longitudinally within an interior of the hopper compartment and which are selected to provide low density heat to prevent asphalt materials within the hopper compartment from overheating and burning or deteriorating during periods of supplemental heating, dispensing asphalt mix materials from the hopper compartment to fill and repair a pothole during normal working hours of the device; and turning off the primary heat source for the hopper compartment during non-working hours and turning on the supplemental heat source to heat asphalt materials in the hopper compartment during the non-working hours.

13. The method of claim 12, wherein the primary heat source is selected from the group consisting of an LP gas heating source, a CNG gas heating source, an all-electric heating source and a diesel fired heating source.

14. The method of claim 13, wherein the hopper compartment is provided with a front wall, a rear wall and opposing side walls, the front and rear walls defining a chamber length therebetween, and wherein a pair of electric heat riser tubes are installed in a generally horizontal plane which extends between the front and rear walls above the plane of the paddle shaft, whereby the electric heat riser tubes extend generally parallel to one another on either side of the paddle shaft for a majority of the chamber length.

15. The method of claim 14, wherein the electric heat riser tubes are tear drop shaped in cross section and are used to contain electric heating rods which are plugged into a 220 volt electric supply outlet during non-working hours.

16. The method of claim 15, wherein the heating rods are 800 watt electric rods which are selected to supply low density slow heat to the electric heat riser tubes in the range from 250 F. to 275 F. to prevent asphalt materials in the hopper compartment from being overheated.

17. The method of claim 16, wherein the electric heat riser tubes are installed approximately two thirds of the way up an internal height of the hopper compartment and are effective to keep asphalt materials in the hopper compartment hot during non-working hours of the device when plugged into a 220 volt electric supply outlet.

18. The method of claim 17, wherein the heating chamber is a sealed heat transfer oil chamber and the heat transfer oil chamber is heated by one of the primary heat sources of the device.

19. The method of claim 18, wherein heat is supplied to the heating chamber by means of a pair of oppositely arranged electric heaters located within the heating chamber on either side of the V-shaped bottom wall of the hopper, the electric heaters being heated by an electric generator also mounted on the body of the device, whereby the electric heaters can be used to supply heat to the bottom wall of the hopper to maintain the asphalt mix materials in a workable state.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] FIG. 1 is a perspective view, partly broken away, of the improved asphalt dispensing body of the invention.

[0021] FIG. 2 is an end, partial cross-sectional view of the improved device of FIG. 1.

[0022] FIG. 3 is an end, sectional view of one of the electric heat riser tubes which is used to house an electric heating rod and which makes up a supplemental heat source for the device of the invention.

[0023] FIG. 4A is a side view, partly in section, of one of tale electric heat riser tubes of the invention, showing the internal components thereof.

[0024] FIG. 4B is an end view of the heat riser tube of FIG. 4A.

[0025] FIG. 5 is simplified view of the side control panel used with the device of the invention, showing the electric power plug for supplying electric power to the electric heating rods of the electric heat riser tubes which make up the supplemental heat source.

[0026] FIG. 6 is perspective view, similar to FIG. 1, of a prior art asphalt dispending body, showing an alternative primary heat source for the hopper compartment.

[0027] FIG. 7 is an end view, partly in section, of the prior art device of FIG. 6.

DETAILED DESCRIPTION OF THE INVENTION

[0028] The present invention provides an improved pothole patcher design which meets the foregoing objectives. The invention described herein and the various features and advantageous details thereof are explained more fully with reference to the non-limiting examples which are illustrated in the accompanying drawing and detailed in the following description. Descriptions of well-known components and processes and manufacturing techniques are omitted so as to not unnecessarily obscure the workings of the invention. The examples used herein are intended merely to facilitate an understanding of ways in which the invention herein may be practiced and to further enable those of skill in the art to practice the invention. Accordingly, the examples should not be construed as limiting the scope of the claimed invention.

[0029] The advantages of present invention can perhaps best be understood with reference to Applicant's prior art device which utilized a propane retort heater system as a primary heat source for the asphalt materials which were to be dispensed. By primary heat source is meant the heat source that is normally used to heat the asphalt materials in the hopper compartment during normal working hours that the device is in service repairing potholes on a roadway, for example. Accordingly, turning to FIG. 6, the prior art asphalt dispensing apparatus 101 includes a body 103 which is adapted to be mounted on a portable base, such as a truck or trailer. The body has a hopper compartment 105 (FIG.'s 6 and 7) with a V-shaped bottom wall 107 for transporting asphalt mix materials. In this discussion, asphalt mix materials will be taken to mean pre-mix or aggregate hot or cold mix asphalt and asphalt aggregate. The term liquid asphalt emulsion or tack oil will he taken to mean asphaltic cements, liquid asphalts, and asphalt emulsions of the type carried in a separate tack oil tank.

[0030] As best seen in FIG. 7, the V-shaped bottom wall of the hopper compartment forms an upper, uninsulated common wall 119 of a V-shaped heating chamber 121. The V-shaped heating chamber 121 is thus located below the hopper compartment 105 with the V-shaped bottom wall of the hopper compartment defining an upper extent of the heating chamber 121. The heating chamber also has oppositely extending, insulated bottom wall portions 123, 125, as shown in FIG. 7.

[0031] As shown in FIGS. 6 and 7, the body 103 of the portable device is also equipped with an auger or screw conveyor 127 which is mounted in the bottom region 129 of the hopper which forms a trough-like opening extending longitudinally along the bottom wall thereof. The screw conveyor 127 is used to dispense asphalt mix materials contained within the hopper. An agitator means, such as paddle shaft 131 is located above the screw conveyor 127 in the hopper compartment 105 for agitating the hopper materials contained therein.

[0032] In the case of the prior art device shown in FIG.'s 6 and 7, the primary heat source comprises a dry heat means which is associated with the heating chamber 121 for heating the chamber and for transferring heat to the hopper compartment 105 through the hopper bottom wall 119 to maintain the asphalt mix materials contained therein in a workable state. In the prior art device, the dry heat means comprised a pair of oppositely arranged retort tubes 133, 135 which are located within the heating chamber 121 on either side of the V-shaped bottom wall of the hopper. The retort tubes are each heated by a 150,000 btu retort tube propane burner. The burners are thermostatically controlled and regulated at 10 psi. The burners utilized commercially available ignition systems, such as a 12 volt DC electronic igniter. The gas burner is preferably provided with a safety shut-off on loss of flame or excessive temperature. The commercially available burner, ignition and safety shut-off system for the retort tubes can be obtained from H. D. Industries, Inc., of Jacksonville, Tex. The commercially available burner has two stages, ignites on 10 ounces of pressure and operates at 10 psi. The retort tubes are used to supply dry, radiant heat to the bottom wall of the hopper compartment.

[0033] As shown in FIGS. 6 and 7, each retort tube 133, 135 forms a single pass loop which has a burner 137, 139 installed at one extent thereof and which communicates with an exhaust conduit such as exhaust stacks 141, 143 at an opposite extent thereof (FIG. 6). As best seen in FIG. 6, each retort tube 133, 135 is provided in the shape of an inclined U which is arranged in a plane which is generally parallel to a selected one of the oppositely extending, insulated bottom wall portions (123, 125 in FIG. 7) of the heating chamber 121. Each retort tube 133, 135 thus has a pair of outlets to the exterior of the tank. One of the outlets has the burner mounted therein while the other of the outlets communicates with the exhaust stacks 141, 143 as an exhaust conduit.

[0034] Each U-shaped retort tube includes a first leg 145 (FIG. 6) which contains the burner 139 and an oppositely extending second leg 147 which leads to the exhaust stack 143. The two legs 145, 147 are connected by a curved, loop portion 149. As shown in FIG. 7, the heating chamber 121 can also be provided with an electric emersion type heater 151. As best seen in FIG. 7, the heating chamber 121 further includes a pair a heat deflectors 153, 155 which are mounted in proximity to the screw conveyor 127 of the hopper. Each heat deflector is arranged to extend along a first leg of a respective retort tube to partially shield the region of the screw conveyor from the dry heat source.

[0035] As briefly mentioned, the asphalt dispensing apparatus shown in FIG.'s 6 and 74, as well as the is device of the invention, is most preferably intended to be truck mounted on the bed of a suitable road worthy vehicle. The device could also be a trailer mounted portable device with the device being mounted on the bed of a trailer which would be hauled by a suitable vehicle. The truck or trailer would serve as a portable base for transporting the body 101 to a repair site for repairing a pothole in an asphalt pavement.

[0036] While the device shown in FIG.'s 6 and 7 works well for its intended purpose, there are some situations in which it is desirable to have a supplemental heating source for providing heat during non-working hours of the machine. As has been explained, the previously described primary heat source is the heat source that is normally used to heat the asphalt materials in the hopper compartment during normal working hours that the device is in service repairing potholes on a roadway, for example. During non-working hours, for example at night, the primary heat source is shut off and is inactive. In some situations, for example, colder climates or in wintertime use, it may be desirable to provide supplemental heat to the hopper compartment in order to keep the asphalt materials hot and to keep them from seizing up. The present invention is directed to improvements in the heating system used to heat the hopper compartment for maintaining the asphalt repair materials contained therein in a workable state during non-working hours.

[0037] Turning now to FIG's 1 and 2, there is shown the improved asphalt dispensing apparatus of the invention, designated generally as 201. The device shown in FIG.'s 1 and 2 has many of the same general components as the previously described prior art device of FIG.'s 3 and 4, and the corresponding parts will be numbered similarly, generally incremented by 100 in each case. Thus, the improved device includes a body 203 which is adapted to be mounted on a portable base. The body has a hopper compartment 205 (FIG. 1) with a V-shaped bottom wall 207 for transporting asphalt mix materials. As best seen in FIG. 2, the V-shaped bottom wall of the hopper compartment forms an upper, uninsulated common wall 219 of a V-shaped heating chamber 221. The V-shaped heating chamber 221 is thus located below the hopper compartment 205 with the V-shaped bottom wall of the hopper compartment defining an upper extent of the heating chamber 221. The heating chamber also has oppositely extending, insulated bottom wall portions 223, 225, as shown in FIG. 2. The hopper is fully insulated with 2 industrial, high temperature 12R factor insulation encased in a double steel jacket. The V-shaped bottom wall of the hopper compartment thus forms an upper, uninsulated common wall of the heating chamber, the heating chamber having an insulated bottom wall and insulated side walls, as described.

[0038] As shown in FIG.'s 1 and 2, the body 203 of the portable device is also equipped with an auger or screw conveyor 227 which is mounted in the bottom region 229 of the hopper which forms a trough-like opening extending longitudinally along the bottom wall thereof. As previously described, the screw conveyor 227 is used to dispense asphalt mix materials contained within the hopper. An agitator means, such as paddle shaft 231 is located above the screw conveyor 227 in the hopper compartment 215 for agitating the hopper materials contained therein. The screw conveyor can be, for example, 10 feet long by 6 inches diameter progressive screw conveyor with hard surfaced flights welded continuously on 2 inch scheduled 80 steel pipe and is ball bearing mounted. The conveyor is driven by a 9200 in.lb. torque variable speed hydraulic motor with forward and reverse. It is used to feed a delivery chute (not shown) with 120 of pivot. The paddle shaft 231 is used to break up asphalt due to vibratory compaction. In one embodiment, it is a schedule 160 shaft with 12 spikes and is ball bearing mounted and driven by a 9,200 in.lb. torque variable speed hydraulic motor with forward and reverse.

[0039] The apparatus of the invention may include a separate emulsion or liquid asphalt tank (not shown) mounted on the portable base for transporting and dispensing liquid asphalt type materials used to dress a pothole prior to dispensing the asphalt mix materials from the hopper. The separate liquid asphalt tank could take the form of, for example, the tank described in issued U.S. Pat. No. 4,944,632, supra, assigned to the assignee of the present invention. That tank is provided with an internal circulation system for maintaining liquid tack oils in an emulsified state.

[0040] While the primary heat source used with the version of the asphalt dispensing machine shown in FIG's 6 and 7 was propane heated retort tubes, the primary heat source shown in the device of FIG.'s 1 and 2 is an ails-electric heat source associated with the liquid filled heating chamber 221 for heating the chamber and for transferring heat to the hopper compartment 205 through the hopper bottom wall 207. As shown in FIG.'s 1 and 2, the all-electric heat source preferably comprises a pair of oppositely arranged electric heaters 240, 242, located within the heating chamber 221 on either side of the V-shaped bottom wall of the hopper. The electric heaters are powered by an electric generator (246 in FIG. 1) also mounted on the body of the device, whereby the electric heaters can be used to supply heat to the bottom wall of the hopper to maintain the asphalt mix materials in a workable state. In this design of the asphalt dispensing device, there are no retort tubes. Instead, the electric heaters are enclosed within the 130 gallon heating chamber once the chamber is filled with heat transfer oil. The heating chamber 221 is then sealed up.

[0041] During working hours, the 130 gallon heat transfer oil heating chamber is heated by the two 208 to 240 volt AC single phase electric resistance heaters powered by a 50 amp, 12,000 watt, PTO hydraulic driven on-board electric generator. This exemplary system is capable of heating asphalt materials from 0 to 300 F. The electric generator could also be run off an auxiliary pony motor, or the like.

[0042] The improved supplementary heat source which is used to heat the asphalt materials in the hopper compartment during non-working hours will now be described. With reference to FIG.'s 1-5, the supplement heat source comprises one or more electric electric heat riser tubes. In the preferred design, there are two electric electric heat riser tubes 248, 250 which extend longitudinally within the interior of the hopper compartment 205 and which are selected to provide low density heat to prevent asphalt materials within the hopper compartment from overheating and burning or deteriorating during periods of supplemental heating,

[0043] The term low density heat is used in the general sense that this ten n is used, for example, in the water heater industry. In other words, electric storage water heaters use electrical resistance to raise the temperature of one or more heating elements mounted inside the water tank. These elements are categorized as low-density or high-density, based on their design. The density refers to the amount of wattage per square inch of surface area. As an example, a heater element with 10 square inches of surface area, rated for 1,500 watts, would conduct 150 watts per square inch when in use. By comparison, a 1,500 watt element with only 7.5 square inches of surface area would be a higher density element, conducting 200 watts per square inch. Low-density elements have more surface area than high-density elements, with comparable wattage.

[0044] The terms high-density and low-density as applied to electric heating elements of the type under consideration thus simply refers to how much wattage the element uses in comparison to its surface area or its size. An element with low density uses a lower temperature to operate. A unit with higher density uses a higher temperature to operate. In the preferred embodiment to be more fully described, the electric heating rods which are inserted within the electric heat riser tubes are 220 volt electric heating rods. They each have an 800 watt rating to provide low density, slow heat to prevent the asphalt materials in the hopper compartment for cooking on the exterior surfaces of the electric heat riser tubes in use. In the example shown, the electric heat riser tubes are approximately 108 inches long and the electric heating rods are approximately 96 inches long. With this particular configuration, the 220volt electric heat riser tubes can supply low density, slow heat to the electric heat riser tubes in the range from 250 F. to 275 F. to keep the asphalt in the hopper compartment hot but without overheating the asphalt.

[0045] With reference again to FIG. 1, it can he seen that the hopper compartment 205 has a front wall 251, a rear wall 253 and opposing side walls 255, 257, the front and rear walls defining a chamber length (1 in FIG. 1) therebetween. The pair of electric heat riser tubes 248, 250, are located in a generally horizontal plane which extends between the front and rear walls 251, 253, above the plane of the agitator shalt 231, the electric heat riser tubes extending generally parallel to one another on either side of the agitator shaft 231 for a majority of the chamber length. The electric heat riser tubes are installed approximately two thirds of the way up the internal height of the hopper compartment and are effective to keep asphalt materials in the hopper compartment hot during non-working hours of the device when plugged into a 220 volt electric supply outlet.

[0046] With reference now to FIG. 3, it will he seen that the individual electric heat riser tubes, such tube 248, are generally tear drop shaped in cross section. As will be appreciated from FIG.'s 1 and 3, the electric heat riser tubes comprise an external plate-like structure with opposing longitudinal sides 259, 261, which diverge from an upper apex 263 downwardly toward a curved bottom region 265 of the heat tubes. The heat riser tube 248 shown in FIG. 3 is made of 3/16 inch steel plate. It is approximately 6.01 inches high (h in FIG. 3) and 2.09 inches wide (w in FIG. 3. As has been mentioned, the riser tube of FIG. 3 is approximately 108 inches in length.

[0047] As perhaps best seen in FIG. 4, the electric heat riser tubes 248, 250, and are used to contain electric heating elements, such as the electric resistance heating rod 267 in FIG. 4. The electric heating rod 267 in FIG. 4 is U-shaped with two parallel legs which run the substantial length of the particular heat riser tube. The rod can be mounted in any suitable fashion within the heat riser tube, such as by mounting clamps 269, the clamps being situated at spaced locations along the length of the U-shaped rod 267. The interior of the heat riser tube 248 is sealed at one end and closed off at the opposite end by a mounting flange 271 to allow access to the interior of the riser tube for maintenance of the heating rods. Preferably, the electric heating rod 267 is also provided with a built-in thermocouple which runs to the same thermostat that controls the 220 volt electric heaters 240, 242 that constitute the primary heat source for the hopper compartment. FIG. 2 shows the electrical control lines 275, 277, that supply electric power to the heating rods and which convey control information form the heating rod thermocouples to the device thermostat 279.

[0048] As shown in simplified fashion in FIG. 5, the electric heating rods 267 are powered by plugging them into a 220 volt electric supply outlet 281 during non-working hours. In this case, the outlet is on the control panel of the truck mounted dispensing body.

[0049] One preferred version of the asphalt dispensing machine of the invention has been described in FIG.'s 1 and 2 as having the previously described all-electric primary heating source comprised of the 220 volt electric heaters 240, 242. However, it should be apparent that the heat riser tube features of the invention could also be used in dispensing machines heated by other primary heat sources commonly used in the industry. For example, the primary heat source could be selected from the group consisting of an LP gas heating source, a CNG gas heating source, an electric heating source and a diesel fired heating source, to name several conventional sources.

[0050] The operation of the version of the asphalt dispensing apparatus of FIG.'s 1 and 2 will now be briefly described. The heat transfer oil in the heating chamber 221 is heated by the two electric 220 volt resistance heaters 240, 242, which, in turn, heat the asphalt mix in the hopper compartment 205. The heat transfer oil in the heating chamber 221 is sealed off and does not intermix with the emulsion or tack oil contained in its separate tank. At the job site, suitable hydraulic tools are connected to outputs from the hopper compartment and the emulsion tank so that repairs can be quickly accomplished. Spray equipment such as a conventional wand can be connected to a discharge valve for dispensing liquid asphalts or emulsions to seal and tack the dressed cavity. The screw conveyor 227 is then actuated to dispense asphalt mix materials from the hopper compartment 205 through the discharge chute into the cavity as required. The filled cavity can then be compacted with a hydraulic tamper to complete the job.

[0051] In addition to the previously described apparatus used in the practice of the invention, there is also provided an improved method for repairing a pothole in an asphalt pavement, comprising the steps of:

[0052] providing a body on a portable base for transporting the body to a repair site, the body being equipped with a hopper compartment with a V-shaped bottom wall for transporting asphalt mix materials and a generally V-shaped heating chamber located below the hopper compartment, the V-shaped bottom wall of the hopper compartment defining an upper extent of the heating chamber; providing a screw conveyor mounted in the bottom of the hopper compartment for dispensing asphalt mix materials therefrom;

[0053] providing a paddle shaft located above the screw conveyor in the hopper compartment for agitating the hopper materials;

[0054] providing a primary heat source associated with the heating chamber for heating the chamber and for transferring heat to the hopper compartment through the hopper bottom wall to maintain the asphalt mix materials in a workable state during normal working hours of the machine;

[0055] providing a supplemental heat source located within the hopper compartment for heating the hopper compartment during non-working hours, the supplement heat source comprising one or more electric electric heat riser tubes which extend longitudinally within an interior of the hopper compartment and which are selected to provide low density heat to prevent asphalt materials within the hopper compartment from overheating and burning or deteriorating during periods of supplemental heating;

[0056] dispensing asphalt mix materials from the hopper compartment to fill and repair a pothole during normal working hours of the device; and

[0057] turning off the primary heat source for the hopper compartment during non-working hours and turning on the supplemental heat source to heat asphalt materials in the hopper compartment during the non-working hours.

[0058] An invention has been provided with several advantages. The device is simpler in design and more economical to manufacture than some of the prior art devices of the same general type. In the case of the all-electric version of the device, the heat system utilized heats more efficiently in some outside environments. Once the electric heaters get the hopper compartment hot, it stays hot for an extended period of time. The use of the submerged electric heaters in the sealed heating chamber has been found to increase the life expectancy of an associated electric generator by 50% over prior art systems. Since the heating chamber is sealed, it is only infrequently necessary to replenish the heat transfer medium or maintain such medium. In both the all-electric machine and in other machines having alternate primary heat sources, such as LP gas, and the like, the supplemental heating system provides heat to the hopper compartment during non-working hours when the primary heat source is turned off. The described electric heating rods and heat riser tube arrangement can effectively supply low density, slow heat to the electric heat riser tubes in the range from 250 F. to 275 F. to prevent asphalt materials in the hopper compartment from being overheated during the period of time that the electric heat riser tubes are employed.

[0059] While the invention has been shown in several of its forms, it is not thus limited but is susceptible to various changes and modifications without departing from the spirit thereof, as described in the claims which follow.