the present invention will now be described in detail hereinafter by reference to the accompanying drawings . the invention is not intended to be limited to the embodiments described ; rather , this detailed description is provided to enable any person skilled in the art to make and practice . on any given day , 2 . 25 billion cups of coffee are served . of this , americans represent 150 million daily consumers . with such popularity , much interest avails regarding the optimum coffee tasting experience . as a generality , five factors affect the coffee consumer &# 39 ; s tasting experience : the coffee beans , the brewing process , the water purity , the tasting temperature , and the drinking cup material . coffee is actually a more complex substance than wine . its organic structure actually changes as its temperature cools , adversely impacting its taste . the ideal consumable temperature range for preferred taste is between 130 ° f .- 175 ° f . if you allow the tasting temperature to cool too quickly , you miss out on the sophisticated nature of this complex substance . taste is a function of smell ; and smell is a function of temperature . if the temperature cools too quickly , the entire tasting experience is adversely impacted . moreover , the flavor may be tainted by the cup material . the presently described invention , therefore , addresses the two post - brew factors : tasting temperature and cup material . the novel structure of the mug according to the present invention enhances the aromatics and elongates the tasting experience by providing temperature control in the 130 ° f .- 170 ° f . range . the components are made from pure , bpa free , stainless steel ; thereby keeping the taste neutral . it is organic , easy to use , and easy to clean . according to the presently disclosed invention , coffee is quickly cooled to an ideal consumption temperature and the consumable temperature range is maintained for at least three times longer than a conventional coffee mug , such as a ceramic mug . more specifically , the present invention is directed to a thermal mug 10 for receiving a liquid - based food item , such as a hot beverage . for example , coffee may be served in the mug 10 according to the present invention . it should be obvious , however , that any food item , particularly a liquid - based food item ( e . g . soup ) may be received within the mug 10 . for the sake of discussion only , the mug 10 will be herein described for receiving any hot beverage and the discussion will specifically describe use with coffee . a drinking lid 12 is also provided to close the mug 10 and to provide means for drinking the coffee . as shown , the drinking lid 12 includes a drinking lip 13 and closeable drinking port 14 . as best shown in fig2 , the thermal mug 10 comprises a plurality of wall members forming concentric walls ( fig4 ) including the exterior wall 15 member , medial wall member 16 , and interior wall member 18 . each of these wall members 15 , 16 , 18 is preferably formed of stainless steel as explained in more detail below . the interior wall member 18 is tubular and is configured to receive an interior base member 19 . preferably , the interior base member is not integrally formed with the interior wall member , but such variation is not a departure from the present disclosure . the medial wall member 16 is formed as a tubular member having an open upper and lower end . a medial base member 20 is secured to the tubular medial wall member 16 to contain the phase change material 30 ( explained more fully below ). the exterior wall member 15 is formed as a tubular member and exterior base member 22 is joined to the exterior wall . base member 22 , as shown in fig7 , is generally circular and includes a bottom portion 32 with a convex center 33 defining a vacuum port 34 described in more detail below . the bottom portion 32 includes an upwardly extending flange 35 which is configured to cooperate with the exterior wall 15 . a bottom cap 36 is also provided and includes an upwardly extending flange 37 for cooperating with the exterior wall 15 . according to preferred embodiments of the present invention , the base member 22 and bottom cap 36 are formed of stainless steel . alternatively , the bottom cap 36 may be formed of a different material than base member 22 , such as a slip resistant formed material , e . g . a thermoplastic material . interstitial chambers are defined by the various wall members . the interior wall member 18 and interior base member 19 define a liquid receiving receptacle 24 . the circumference of the medial wall member 16 is greater than the circumference of the interior wall member 18 so as to define a first interstitial chamber 25 there between . the circumference of the exterior wall member 15 is greater than the circumference of the medial wall member 16 so as to define a second interstitial chamber 26 there between . while the width of each interstitial chamber ( defined between adjacent wall members ) may be any desired width to achieve respective heat transfer and insulating properties , preferably the interstitial chambers are substantially the same width . as shown in fig2 , 3 and 4 , the interior wall member 18 is greater in length than the medial wall member 16 and exterior wall member 15 . accordingly , the portion of interior wall member 18 extending longitudinally beyond the other wall members defines a mating rim 28 for cooperating with threading 38 of the drinking lid 12 . while any mating means may be employed , preferably the mating rim 28 of the interior wall is threaded as best shown in fig2 and 3 and the flange 37 of the drinking lid 12 is correspondingly threaded as best shown in fig8 . other mating means , such as a snap fit , may also be employed without departing from the scope of the invention . moreover , it is within the scope of the present invention to also provide a thermal mug without a drinking lid whereby the mating rim 28 may be free of threading or other mating means . the operation of the thermal mug 10 will now be described in detail . the first interstitial chamber 25 houses a phase change material 30 . it has been determined that the preferred phase change material be one which meets two criteria : a predetermined enthalpy of fusion and a selected melting point within the predetermined range . according to the present invention , it has been determined that the predetermined enthalpy of fusion be greater than 145 kj / kg , and preferably greater than 190 kj / kg . it has further been determined that the predetermined melting temperature range is between 45 ° c . and 70 ° c . ( approximately 110 ° f . to 160 ° f . ), and preferably around 60 ° c . ( approximately 140 ° f .). a phase change material , according to the present invention , acts as a constant temperature heat source in that can gain and release heat while remaining in its phase change state . for this reason , a phase change material can experiences little degradation over time . materials that are usually used as phase change materials include organic paraffins and non - paraffins and inorganic salts and metals . popular phase change materials are organic paraffins , fatty acids , and hydrates . while any phase change material with these criteria may be selected , it has been determined that a selected paraffin wax meets these criteria . while not intending to be bound by any particular theory , it is believed that the enthalpy of fusion and melting point temperature according to the present invention enable the phase change material to rapidly cool the beverage to within the consumable temperature range and then , upon the beverage cooling , pass back thermal energy ( heat ) back to the beverage to maintain its temperature within the consumable range . as to a hot beverage , such as coffee , this range may be between 130 ° f . and 175 ° f . for an extended period of time , and preferably for at least 60 minutes . more specifically , the paraffin wax , in its cooled state , is substantially solid . when a hot beverage is received within the mug according to the present invention , heat energy provided by the beverage is supplied to the phase change material . the temperature of the paraffin wax increases until the melting point is reached and the first signs of liquid formation become evident . thereafter , even though heat is continuously being applied to the paraffin wax from the beverage , the temperature of the phase change material remains substantially constant as long as both liquid and solid are present . only when the last vestiges of solid have disappeared does the temperature start to climb again . on a microscopic level , melting involves separating molecules which attract one another . this requires an increase in the potential energy of the molecules , and the necessary energy is provided in the form of heat from the beverage . the kinetic energy of the molecules remains constant during phase changes because the temperature doesn &# 39 ; t change . as used herein , the enthalpy of fusion refers to the heat energy a solid absorbs when it melts . the preselected phase change material is paraffin wax because it possesses the particular intermolecular forces to achieve the desired enthalpy of fusion . in the context of the coffee mug according to the present invention , the paraffin wax initially is present in the first interstitial chamber 25 in solid form . when the hot beverage is present in the liquid receiving receptacle 24 , heat transfers from the beverage , through the thermally conductive interior wall member 18 , and into the phase change material 30 . this initial transfer of thermal energy / heat rapidly cools the hot beverage . the cooling of the beverage , after the initial drop in temperature , significantly slows as the paraffin wax is in an interim phase wherein the melting point has not yet been achieved . the temperature of the paraffin wax continues to drop , but not continuously as described above , until the beverage and the paraffin wax are in thermal equilibrium meaning they are substantially the same temperature . the quantity of the paraffin wax is sufficient to absorb the desired amount of thermal energy for the initial beverage cooling . as the beverage loses heat to the surroundings , its temperature falls below the phase change temperature of the paraffin wax . under these system criteria , heats transfers back into the beverage sustaining the temperature of the beverage for an extended period of time . the temperature of the beverage will be similar to the temperature of the phase change temperature of the paraffin wax as it resolidifies . once the paraffin wax reverts to its solid phase or state , the beverage temperature will fall as heat is lost to the surroundings . it is believed that the phase change material , paraffin wax , remains at the phase change temperature during the phase change time period from liquid to solid and , therefore , the beverage sustains the phase change temperature for that extended time period . the second interstitial chamber 26 provides thermal insulation to the inner chambers and , hence , the coffee . preferably , the second interstitial chamber 26 is a vacuum chamber . the vacuum chamber 26 slows the loss of thermal energy from the phase change material 30 which , in turn , extends the amount of time the coffee &# 39 ; s temperature is maintained within the consumable range . a vacuum chamber is the preferred insulator because it does not contribute to the overall weight of the mug 10 and is cost efficient to manufacture . the thermal properties result because thermal conductivity requires molecular interaction and , obviously , a vacuum is substantially void of molecules . moreover , the lack of gas within the vacuum chamber prevents heat transfer by convection . referring to fig1 , the thermal characteristics of the thermal receptacle are shown . this graph illustrates the thermal characteristics of a ceramic coffee cup 42 , a paper coffee cup 43 , a thermos 40 and a thermal mug 41 according to preferred embodiments of the present invention . as shown , the paper mug and ceramic mug behave similarly wherein large amounts of heat are lost to the surroundings and the coffee temperature cools very rapidly . in such receptacles , the coffee must be consumed immediately and quickly as the beverage temperature is only within the preferred consumable range of between 130 ° f . and 175 ° f . for less than 30 minutes in the graph shown and its temperature falls to within the range within mere minutes . in contrast , hot coffee placed in a thermos maintains its high temperature for a very long period of time and cools relatively slowly . as shown , a consumer must wait for approximately 80 minutes to allow the coffee , with the initial temperature of 210 ° f ., to cool before the coffee &# 39 ; s temperature is within the consumable range of between 130 ° f . and 175 ° f . in significant contrast , when coffee having the same initial temperature of approximately 210 ° f . is placed within the thermal mug 10 according to the present invention , the temperature rapidly cools to 175 ° f . as shown , this occurs as quickly as within 5 - 10 minutes . as discussed above , during this time period , thermal energy from the coffee is absorbed by the phase change material 30 within the first interstitial chamber 25 . as the phase change material , that is , paraffin wax , melts and reaches its melting point , the cooling of the beverage is slowed . as such , the consumable range is achieved , that is 175 ° f ., and the thermal mug 10 maintains the temperature to within the consumable range for 200 % more time than a paper or ceramic mug . as illustrated , this range is maintained at least 60 minutes and preferably , at least 80 minutes . the thermal mug 10 of the present invention is manufactured according to a novel process . the process , generally , is represented in fig9 . the interior 18 , medial 16 , and exterior 15 tubular walls are cut to the appropriate lengths based upon the design criteria . utilizing a mold and a high pressure water stream , the walls are formed into tubes having a predetermined shape , preferably tubular . this occurs at the shaping station shown in fig1 . next , trimming occurs wherein excess metal , which may result from the inherent expansion and deformation of the stainless steel , is removed . at the threading station , the mating rim 28 of the exterior wall 15 is formed by the application of threading to its surface by an appropriate tooling process . the individual wall members are now properly formed and are ready to be assembled . the welding step includes the application of the base member 19 to the interior cylindrical wall member 18 . interior cylindrical wall member 18 and medial tubular wall member 16 are also welded together along top circumferential surfaces as represented by weld location a ( shown in fig5 ) and polished . leak detection is also preferably performed . the application of the phase change material 30 , paraffin wax , is applied as best shown in fig5 . the now welded interior wall member 18 and medial wall member 16 are inverted , thereby exposing the interior of the first interstitial chamber 25 . the paraffin wax , in a melted state , is injected , i . e . poured , into the first interstitial chamber 25 . thereafter , any excess wax may be removed , and the medial base member 20 may be applied to the medial wall member 16 and welded , such as at along its circumference represented by weld location b . leak detection is also preferably performed by known processes . after the first interstitial chamber 25 is filled with the phase change material 30 and sealed , the tubular exterior wall member 15 is positioned thereon . the exterior wall member 15 is welded to the previously sealed interior and medial wall members 18 , 16 along its circumference as represented by weld location c in fig5 . the surfaces are preferably tested for seam integrity using high intensity heat . if necessary , another polishing step occurs . once all three wall members 15 , 16 , 18 are welded , the exterior base member 22 is secured to the exterior wall 15 . preferably , the base member 22 is welded to the circumferential edge of the exterior wall 15 as represented by weld location d . next , the vacuum process is performed . utilizing the base cap port 34 , a small tube may be attached to the port 34 which serves as an evacuation port . the tube is connected to a vacuum source and the assembly is left to evacuate . when a sufficient vacuum is achieved within the second interstitial chamber 26 , the assembly is leak tested . a temperature test may be provided to ensure proper sealing of all members . if the vacuum suffices , the tube , still under active pumping , is crimped and removed . and finally , the bottom cap 36 is applied , such as by press fitting , onto the assembly . after assembly completion , restoration of metal qualities may be performed by and electrolysis procedure . external polishing and / or final grinding may also occur to complete the thermal mug 10 . while exemplary embodiments have been shown and described above for the purpose of disclosure , modifications to the disclosed embodiments may occur to those skilled in the art . the disclosure , therefore , is not limited to the above precise embodiments and that changes may be made without departing from its spirit and scope .
a reusable receptacle , and the method of producing the receptacle , for receiving liquid based substances , such as coffee , which rapidly cools the substance to obtain a consumable temperature and which substantially maintains a warm consumable temperature over a sufficient period of time . the receptacle includes a liquid receiving chamber , an interstitial chamber for receiving a phase change material and an interstitial chamber for providing a vacuum insulating chamber . the method of forming the receptacle includes the steps of welding the various wall members to form an integrated thermal mug in an efficient manufacturing process .