BACKGROUND
The present invention relates to equipment for smoothing the surface of ice, particularly the surfaces of indoor and outdoor skating rinks. The industry standard for ice rink resurfacing is a machine called a Zamboni, which was patented in the 1950s (U.S. Pat. Nos. 2,642,679 and 2,763,939). Zambonis operate by conditioning the roughened ice surface before it is flooded with clean water which is then allowed to freeze. Resurfacing is done in a single pass; but the machines are very costly, and a need exists for less expensive equipment. In the northern United States and Canada there are a great many seasonal outdoor ice rinks, very few of which are resurfaced using a Zamboni for a variety of reasons including cost, the need to store a Zamboni inside at a temperature above freezing, and the substantial weight of the machine which makes it impractical to use on the surface of a pond or lake where the ice may vary in thickness. There are other ice resurfacers that are smaller in size but, again, operate by spreading a thin layer of water onto a surface and allowing it to freeze (see U.S. Pat. No. 6,138,387, for example). Many ice rinks, however, do not have convenient access to water. In addition, the concept of resurfacing ice by melting it and allowing it to refreeze is known as shown in Canadian Patent No. 692,617; U.S. Pat. No. 6,644,301; and U.S. Patent Application Publication No. 2007/0187119 A1. For various reasons, none of these devices have proven to be a practical solution to the described problem.
SUMMARY
This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This summary is not intended to identify key features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.
An ice resurfacer is disclosed capable of applying heated gas directly to the surface of ice beneath the machine to cause it to melt. The ice resurfacer includes a sled-like structure mounting a fuel source such as a propane tank and means for directing the fuel to a plurality of burners mounted adjacent the front portion of the sled and adapted to direct heated gas through expansion chambers to a melting chamber positioned beneath the sled. The expansion chambers and the melting chamber are uniquely shaped to control gas flow to optimize fuel consumption and ice melting.
A pivoting windscreen and melt water spreader is positioned on the rear of the sled.
DESCRIPTION OF THE DRAWINGS
The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying photographs and drawings, wherein:
FIG. 1 is a perspective view of an ice resurfacer made according to the present invention;
FIG. 2 is a perspective view of the ice resurfacer of FIG. 1 showing an operator guiding the ice resurfacer by means of steering cords;
FIG. 3 is a top perspective view of the ice resurfacer of FIG. 1 with the propane tanks removed;
FIGS. 4A-4D show schematic views of an alternate form of propane tank mounting bracket capable of mounting one, two, or three tanks.
FIG. 5 is a bottom front perspective view of the ice resurfacer of FIG. 1;
FIG. 6 is a fragmentary perspective view of a front portion of the ice resurfacer of FIG. 5 showing the gas manifold and nozzles;
FIG. 7 is a fragmentary perspective view of a front portion of the gas manifold and nozzles of FIG. 5;
FIG. 8 is a bottom perspective view of a rear portion of the expansion chamber outlets of the ice resurfacer of FIG. 1;
FIG. 9 is a right side perspective view of the ice resurfacer of FIG. 1 showing the rear windscreen rotated upwardly;
FIG. 10 is a bottom rear perspective view of the melting chamber of the ice resurfacer of FIG. 1;
FIG. 11 is a side perspective view of the bottom of the ice resurfacer of FIG. 1; and
FIG. 12 is a schematic side elevation view of a section of the melting chamber of FIG. 11 showing the rearward, downward taper of the top surface of the melting chamber.
DETAILED DESCRIPTION
Referring initially to FIGS. 1 and 2, ice resurfacer 10 is disclosed to comprise a sled 12 having a top plate 14 and a pair of parallel spaced runners 16 (one visible) positioned to extend downwardly from the lateral sides of top plate 14. Guide ropes 17 are shown connected to opposite sides of top plate 14 to allow the operator to both pull the sled 12 across the ice and guide its path of travel. Alternatively, a rigid handle may be substituted for the guide ropes, but the ropes have the advantage of compactness when storing or transporting the device.
Turning additionally to FIG. 3, fuel source mounting bracket 18 is shown bolted to top plate 14 of sled 12, although it will be understood that any other suitable method for attaching the bracket, such as by welding, may also be used. In FIG. 3, mounting bracket 18 is shaped to hold either one centered propane tank or two laterally spaced propane tanks 20, but it will be understood that mounting bracket 18 could be formed to hold a greater or lesser number of propane tanks or containers for other types of gas or liquid fuel. For example, FIG. 4A discloses a form of mounting bracket 19 capable of mounting one, two, or three tanks 20. As shown, FIG. 4 illustrate bracket 19 when empty (FIG. 4A) and when holding one (FIG. 4B), two (FIG. 4C), and three (FIG. 4D) tanks 20, respectively. While a propane fuel source is shown with appropriate modification of the device, fuel sources such as natural gas or liquid fuels may alternatively be used to generate ice melting heated gas.
As illustrated in FIGS. 1 and 2, two 20-pound propane tanks 20 are shown mounted in mounting bracket 18. For reasons discussed hereafter, this has been found to be a suitable arrangement for use in connection with outdoor ice rinks. For indoor rinks, the mounting bracket is formed to hold a single 20-pound propane tank, for example, or a single 30-pound tank.
A propane storage tank contains liquid propane in its bottom portion and propane gas there above. At equilibrium, when a propane tank valve is closed, the pressure of the propane gas depends only on temperature and is independent of the amount of propane in the tank as long as there is at least some liquid present. At equilibrium, a full tank has exactly the same inside pressure as a nearly empty tank when both are at the same temperature. Thus, the amount of gas available to be removed from a tank is also dependent on the temperature of the tank. The warmer the tank, the more propane molecules pass from the liquid to gas state. When gas is vented out of the tank, the liquid propane will tend to evaporate as the gas pressure drops. More propane molecules leave the liquid phase than enter the liquid phase, thus causing the temperature of the liquid propane to cool. As the liquid cools, the rate that liquid propane molecules evaporate drops, the net result being that there is less propane gas available to be withdrawn.
The physics of propane has, in the past, made it difficult to melt ice with a propane flame for an extended period of time since, as gas is withdrawn from the tank, the liquid propane cools, reducing the rate of evaporation and, consequently, producing insufficient gas to efficiently melt ice in a reasonable time period. Partially countering this problem is the fact that as the propane tank cools below ambient air temperature, heat from the warmer ambient air begins to warm the propane tank and the liquid therein. Balancing liquid evaporation, gas withdrawal, gas burn rate and consequent heat flow to efficiently melt ice is thus critical to successful operation of the present invention.
In an ice resurfacer such as that shown in FIGS. 1 and 2, it will be understood that the addition of a second propane tank increases the surface area of the liquid propane and reduces by 50% the volume of gas that each tank must produce to melt a given amount of ice, thus slowing the rate of tank cooling. Likewise, three tanks mounted in the three-tank bracket of FIG. 4 reduces the volume needed to be produced by each tank to 33⅓%. Notwithstanding such reductions in the amount of gas needed to be produced by each tank, effective ice melting over the period of time needed to resurface an ice rink requires the use of additional novel design features in the ice resurfacer.
Turning to FIGS. 5 an 6, melting chamber 22 is shown to be defined by top surface 24 and portions of the inside walls of opposed runners 16. Runners 16 are hollow and formed with a relatively wide base to spread the weight of the sled to avoid digging into the ice. The edges of the base are also tapered and rounded to prevent the runners from catching the ice. The runners may be air cooled by providing openings in their outside walls to allow heat to escape so that the runners do not leave grooves in the ice.
Referring, additionally, to FIG. 7, gas manifold 26 is shown to comprise a laterally extending tube having a plurality of nozzles 28 adapted to direct burning gas into the tops of expansion chambers 30. Manifold 26 is designed to have an inside diameter greater than the diameter of the connected propane delivery hose inlet. This reduces or prevents a gas pressure drop at each fuel nozzle so that gas is distributed evenly to all of the nozzles spaced along the manifold tube. Nozzles 28 may be formed by internally threading cylindrical tubes and then threading therein a plug having a square head, an Allen head, or some other head configuration, with a hole drilled therethrough, into the tube. When valve 48 (FIG. 3) is opened, gas flows into manifold 26 and through the holes in nozzles 28. The flowing gas may be ignited using a torch or match held near any nozzle, access to which may be had through openings 36. Alternatively, a conventional electric spark igniter may be used. The flame then migrates to all of the nozzles.
The outlets 32 of expansion chambers 30 as shown in FIG. 8 are substantially larger than the upper inlets of the expansion chambers into which the ignited gas flows from the nozzles. The nozzles are centered in the upper inlets of expansion chambers 30 so that ample air is provided to ensure full and rapid gas combustion. As the burning gas flows out of the orifices and into the expansion chambers, its volume increases as the burning gas fills the expansion chambers. Combustion of the gas is substantially completed before the hot combustion gases exit the expansion chamber 30. The hot combustion gases then flow into the front end of the melting chamber 22 where it flows toward the rear of the chamber and exit 34. Expansion chambers 30 are oriented to push the heat of the flame into the ice and evenly across the length of the melting chamber 22.
As seen in the inverted view of melting chamber 22 in FIG. 10, top surface 24 of the melting chamber is sloped with respect to runners 16 such that the cross-sectional area of the melting chamber defined by top surface 24, lateral runners 16 and the ice surface, decreases as the hot gas moves away from expansion chamber outlets 32 toward chamber exit 34. The downwardly sloping top surface 24 may be a smooth curve or a series of bends. It has been found that the use of heavy 310-gauge stainless steel for the top surface of the melting chamber and for the expansion chambers 30 allows them to better withstand the extreme heat of the burn process. The reducing cross-sectional area of the melting chamber helps maintain the speed of the flow of hot gas rearwardly across the ice. Maintaining the velocity of the hot gas helps prevent the speed of the gas from stalling out as it cools or encounters a tail wind. The shape of the melting chamber thus allows optimum heat to be applied to the ice for melting throughout the passage of gas through the melting chamber.
Referring again to FIG. 5 and to FIG. 9, openings 36 are shown positioned along the upwardly turned front wall 38 of the sled 12 to supply air to the area adjacent the orifices to promote complete combustion of the gas thus ensuring that the temperature of the combustion gas is as hot as possible when it first encounters ice under the melting chamber 22. The propane is fully burned near the front end of the sled such that the resultant heated combustion gas flows across the ice through the melting chamber 22 and out exit 34. The hot gas is in thermal contact with the ice as it travels rearwardly, thus causing the ice surface to melt and the gas to cool.
It will be understood that if too small an amount of propane is provided to the nozzles 28 to be burned, the combustion gas will cool quickly to the ice temperature thus reducing the melting ability of the device. As the amount of fuel burned is increased, more heat is produced and the combustion gas maintains its melting capability for a longer time so that the gas exhaust temperature at exit 34 of the sled rises. If excess fuel is burned, the exhaust gas is overly hot when it exits the melting chamber 22, thus increasing the speed of ice melting but losing fuel efficiency. Since gas economy and melting efficiency depend on the temperature of the gas in contact with the ice, the gas outflow from the propane tanks 20 is monitored so that the amount of fuel burned keeps the gas hot as it passes through the melting chamber 22, but is relatively cool as it exits the chamber 22. This allows melting to be carried out both economically and at a reasonable speed.
Turning, again, to FIG. 3, pressure regulator 40 is shown positioned in the path of flow of the propane gas from a pair of tanks 20 (FIG. 1), through fittings or connectors 42 and short hoses 44. The hand-tightened connectors 42 are selected to produce the flow of gas needed to provide the appropriate melting temperature. Connectors capable of producing a gas flow designed for a maximum output of 500 BTUs works well. It has been found that a 5 psi pressure regulator produces an efficient gas flow from a pair of 20-pound propane tanks, although it will be understood that pressure regulators of greater or lesser size may be effectively used with appropriate modification of other elements in the gas delivery system such as the size of the nozzles 28.
Referring additionally to FIG. 1, after leaving pressure regulator 40, the gas flows through long hose 46 to one end of manifold 26. Valve 48 is shown mounted at the gas entrance point to the manifold 26 to control the flow of gas to be burned. Pressure meter 49 is provided to monitor the gas pressure at the distal end of manifold 26 to ensure that adequate amounts of gas are provided to all of the nozzles 28.
Turning to FIG. 9, windscreen 50 is shown mounted on the rearward end of sled 12 for rotation between the upward position shown in FIG. 9 and the lowered position shown in FIG. 1. Windscreen 50 helps stabilize the flow of hot combustion gas from its entrance into the melting chamber 22 at the front of sled 12 to its discharge at the rear exit 34 of the melting chamber. Windscreen 50 helps prevent tail winds from disrupting the flow of gas out the rear exit 34 of the melting chamber 22, which would reduce melting efficiency or even create fire hazards if the exiting gases are pushed back into the melting chamber. When lowered into contact with the ice, windscreen 50 also spreads the melt water into a thin layer, allowing it to refreeze quickly and levelly. When operated along the curved corner boards of a rink, windscreen 50 is rotated upwardly, thus shortening the length of the ice resurfacer to allow it to better conform to the curved edge of the rink so that the ice surface is melted all the way to the sideboards of the rink. The windscreen also acts as a lifting handle when the unit cools.
Referring to FIG. 12, a longitudinal cross section of melting chamber 22 illustrates one embodiment of the slope of top surface 24 of the melting chamber showing its downward slope toward outlet exit 34. Insulation such as a ceramic fiber blanket may be provided in the space 52 between the top plate 14 of the sled and the top surface 24 of the melting chamber to limit the amount of heat transmitted upwardly to the bottoms of the propane tanks 20 to prevent overheating of the tanks, and also to prevent heat damage to the top plate and reduce the possibility of operator contact burns.
While the preferred embodiment of the invention has been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the invention.
Patent Application
20110146111
