MXPA00005032A

MXPA00005032A - Method of manufacturing a water heater.

Info

Publication number: MXPA00005032A
Authority: MX
Inventors: Nield Jackson Barry
Original assignee: Water Heater Innovations Inc
Priority date: 1999-05-20
Filing date: 2000-05-22
Publication date: 2002-04-24
Also published as: CA2308882C; JP2001004221A; AU762874B2; JP3682204B2; CA2308882A1; AU3538700A

Abstract

A method of manufacturing a double walled vessel is herein disclosed. The method involves the steps of forming an outer vessel having at least one reassembly channel formed therearound and forming an inner vessel having at least one element fitting formed integral thereto. At least one control housing is secured to the outer surface of the inner shell in registration with the element fitting. Heating elements and other control apparatus are installed in the element fittings within the control boxes. The outer vessel is sectioned at the reassembly channel, thereby allowing the inner vessel to be inserted into the outer vessel. The outer vessel is reassembled to enclose the inner vessel therein and a curable foam material is injected into the space between the inner and outer vessels to maintain a constant spatial relationship therebetween and to ensure the structural integrity of the outer vessel. Finally, a portion of the wall of the outer vessel corresponding to an open face of the c ontrol housing is removed to permit access to the interior of the control housing through the wall of the outer vessel.

Description

METHOD TO MANUFACTURE A WATER HEATER BACKGROUND OF THE INVENTION The present invention relates to a method for manufacturing double-walled containers having control or other apparatus extending through the outer container and into the inner container. More specifically, the present invention relates to a novel method for manufacturing water heaters that consist of internal and external covers. Most water heaters currently used consist of double-walled containers that have an internal cover designed to hold heated water and an outer cover disposed above and around the inner cover to protect and support the inner cover. The outer cover also serves to retain an insulation layer around the inner cover and is a mounting point for several controls used to operate and monitor the water heater. Traditionally, both the internal and the external cover of a water heater are made of steel. However, water heaters made of steel are exposed to corrosion and impact damage that can adversely affect the appearance of the water heater and even make them inoperable. In addition, failure in a steel water heater often results in the escape of water contained within the inner casing of the water heater, thus causing unacceptable water damage to the structure where the water heater is installed. Normal metal water heaters traditionally use fiberglass-type insulation spun between the inner and outer covers of the vessel in order to insulate the inner shell and make the operation of the water heater more efficient. If the condensation in the pipes connecting the water heater to a water system of a structure, or a leak in those pipes, would cause the fiberglass insulation to be wetted, the efficiency of the water heater would be greatly reduced. In addition, wet insulation can also be converted into an incubator for organisms such as fungi or bacteria, which can cause the water heater in question to give off an unpleasant odor. Another disadvantage in using normal metal water heaters is that the manufacture of the water heater itself is relatively intense in terms of labor and material. What is more, the equipment required to manufacture a double-walled metal container such as the normal metallic water heater described above is expensive and occupies a large amount of space on a factory floor. Therefore, it can be seen that it would be convenient to provide an oxidation proof water heater, highly resistant to impact forces and which is well insulated within the insulation resistant to damage caused by moisture. In addition, it would be very convenient to provide a method for rapidly and efficiently manufacturing and assembling said water heater.

BRIEF DESCRIPTION OF THE INVENTION The present invention overcomes the problems of the prior art and fulfills the objectives set forth above by providing a novel method for manufacturing and assembling a double-walled container such as a water heater. A method for constructing a double walled container according to the present invention begins with the step of providing an inner cover having a predetermined size and shape. An outer cover having a predetermined size and shape sufficient to contain the inner cover is also provided. The outer cover has a size such that the walls of the respective covers can be spaced apart from one another when the inner cover is received inside the outer cover. The outer cover is then sectioned, that is, it has its base removed to allow the insertion of the inner cover into the interior of the outer cover. The inner cover can then be inserted into the outer cover and disposed in a predetermined relationship to the outer cover. Finally, the outer cover is closed, by replacing the base and ejecting expandable foam in the space between the inner and outer covers. The expandable foam expands to substantially fill the space between the inner and outer covers. During healing, the expandable foam becomes substantially rigid and permanently locates the inner cover within the outer cover in its predetermined relation to the outer cover. In providing an internal cover for use with a water heater, according to the present invention, it is preferable to include the step of installing at least one accessory of the integral element to the wall of the inner cover. Said integral accessory reduces the probability that the internal cover can be filtered. When it is convenient to locate the controls for the water heater between the inner and outer covers of the container, it is also necessary to include the step of securing a bottom surface of at least one control housing for the outer surface of the inner cover before inserting. the inner cover on the outer cover. A suitable control housing is sized to measure the space between the inner and outer covers and has a top surface comprising a flange adapted and constructed to contact the inner surface of the outer cover in a substantially flush manner. This ensures that when the foam is injected between the inner and outer covers, the rapidly expanding foam does not enter the control housing. In larger water heaters, more than one control housing can be secured to the outer surface of the inner cover. In this case, a conduit is preferably installed between the control housings to create a physical connection between them for the passage of cables and the like. In addition, it is preferred to register the control housing with integral element accessories to the wall of the inner cover. When more than one accessory of the element is formed integrally to the wall of the inner cover, each accessory of the element has a control housing secured to the inner cover. In order to facilitate the sectioning and reassembly of the outer cover around the inner cover, the outer cover is preferably provided with a channel structure comprising an internal surface that is radially offset inward from the surface of the cover external around the entire circumference of the outer cover. The inner surface of this channel structure is joined to its upper and lower ends through upper and lower circumferential transition areas that join the inner surface of the channel structure with the outer surface of the cover. Sectioning the outer shell according to the methods of the present invention involves removing the outer shell material comprising the upper transition area of the channel structure. The removal of the upper transition structure separates the upper portion of the outer cover from a base portion of the outer cover and allows the insertion of the inner cover into the interior of the outer cover. In order to have access to the interior of the control housing, a portion of the wall of the registered external cover must be removed on the open face of the control housing. Once the heating elements of the water heater and any control mechanism within the control housings have been installed, a housing cover is secured on the open face of the control housing. These and other objects and advantages of the invention will appear more fully from the following description, made together with the accompanying drawings in which the similar reference characters refer to the same or similar parts throughout the different views. YAlthough the description thereof is detailed and accurate to enable those skilled in the art to practice the invention, the physical embodiments described herein simply exemplify the invention which can be modalized into another specific structure. Although the preferred embodiment has been described, the details may be changed without departing from the invention, which is defined by the claims.

DESCRIPTION OF THE DRAWINGS Figure 1 is an elevated front view of a fully assembled water heater constructed in accordance with the present invention; Fig. 2 is a side elevational view of the water heater of Fig. 1 which is partially fragmented to show the details of the structure of the water heater; Figure 3 is a top view of the water heater of Figure 1; Figure 4 is a bottom view of the water heater of Figure 1; Figure 5 is a cross-sectional view of the upper part of the water heater taken along lines 5-5 in Figure 1; Fig. 6 is a partial cross-sectional view of the approach of the internal tank wall showing the fitting of the molded element in place; Figure 7A and 7B are schematic illustrations of the steps involved in the manufacture of a water heater according to the present invention; and Figure 8 is a front approach view of the water heater control box illustrating the manner in which the outer container is opened to expose the interior of the control box.

DETAILED DESCRIPTION OF THE INVENTION Figures 1 and 2 illustrate a water heater 1 manufactured according to the methods of the present invention. A water heater 1 consists of an inner cover 2 disposed within the outer cover 3. Between the inner and outer covers 2 and 3, there is an interstitial or annular space 4 and is normally filled with an insulating material 5 which is preferably an expandable and healing foam material. The insulating jet 5 used to fill the interstitial space 4 acts for ai? ' inner cover 2 of the environment in which the water heater is installed, and because in its cured state it is substantially rigid, it also acts to secure the inner cover 2 within the outer cover 3. Although the water heater 1 is a double-walled container, the use of an expandable and curable insulating foam material 5 in the interstitial space 4 between the inner and outer shells 2, 3 effectively creates a container having a solid, simple wall with highly insulating properties and a great resistance to impact damage. Both covers, internal and external 2, 3 are formed using known extrusion molding techniques. The inner cover 2 is preferably made of a polybutylene material and the outer cover 3 is preferably made of a polyethylene material. Although it is understood that other moldable materials can be used to form the inner and outer covers 2, 3, the polybutylene and polyethylene materials from which the inner and outer covers 2, 3 are made provide the required flexibility, resistance to wide swings of pressure and temperature and the low chemical reactivities needed to produce a water heater 1 that is resistant to physical damage, corrosion and durable enough to last almost indefinitely. The fact that the inner and outer covers 2, 3 can be formed through an extrusion molding process, further means that the inner and outer covers 2, 3 can be produced quickly and economically. Moreover, for the manufacturing process, only simple tools are needed, such as contorneadores, manual drills and a sharp knife to prepare the covers 2, 3. Referring to figures 2 and 5, you can see more clearly the structure of the inner cover 2. The inner cover 2 is provided at its upper end with three ports 6, 7 and 8. Port 6 acts as an inlet, which provides a conduit through which water can be introduced into the inner cover 2. Port 7 it is an outlet through which heated water can be removed from the inner cover 2. Port 8 acts as a suction cup having a pressure valve 10 secured thereto. When the pressure inside the inner cover 2 exceeds a predetermined level, the pressure valve 10 will open to allow air or pressurized water to escape from inside the inner cover 2, reducing the likelihood of damage to the inner cover 2 of the water heater 1. The inner cover 2 is also provided in its base with a drain port 9. A pipe 11, formed by the segments 11a and 11b, extends from the drain port 9 through the base wall of the outer cover 3 and has a tap 12 installed on the surface outer of the outer cover 3. The drain port 9 and tap 12 provide a means for draining the inner cover 2 of water as when it is necessary to perform maintenance to the water heater 1. The different ports 6-9 of the inner cover 2 are molded integrally to the inner cover 2. Ports 6-9 are constructed to allow standard compression fittings that consist of threaded universal joints 42 to be secured to them so that they are p can connect the different water lines and pressure valves to the inner cover 2. It is preferred to use compression fittings as the type of accessory that has a lower leak probability than the accessories stuck in place and that do not have the same potential for heat damage as well as agglutinated or welded accessories. In addition, it is preferable to use universal joint compression fittings 42 to avoid the need to twist the ports 6-9 integrally molded to the inner cover 2. To heat water contained in the inner cover 2, it is preferred to use electric heating elements 15, as illustrated in Figures 2 and 6. In the US patent No. 5,744,627 a suitable electric heating element 15 is disclosed. The U.S.A. No. 5,744,627 is commonly assigned and is incorporated herein by reference. In order to secure an electric heating element 15 through the wall of the inner cover 2 so as to be impermeable to water and to allow the replacement of the heating electric element 15, it is preferred to mold an accessory of the element 17 in a manner integral to the wall of the inner cover 2. See figure 6. The accessory of the element 17 traditionally comprises a bronze fitting 18 installed in a flange 18a. The accessory of the element 17 is placed in the mold used to form the inner cover 2 and during the manufacturing process, the flange 18a, and consequently the brass fitting 18, become integral parts of the wall of the inner cover 2. It is understood that the flange 18a may preferably be made of the same material from which the inner cover 21 is formed. In larger water heaters 1, it is preferable to install upper and lower accessories of the element 17 in the wall of the inner cover 2 for accommodating two heating elements 15. Once an accessory of the element 17 is in place, an electric heating element 15 or other control or heating device can be threaded or otherwise secured in the brass fitting 18. It is understood that the fitting 18 can be configured in any number of ways so long as a heating element 15 or other structure can be inserted and retained through the wall of the inner cover 2 in a water-impermeable manner. The brass fitting 18 may also be arranged to receive an accessory of the outer element 31 which in turn is arranged and constructed to install a heating element 15 therein. Moreover, the accessory 18 can be made of materials other than bronze that are suitable for this application. In addition, the accessory of the outer element 31 can be arranged to be installed thereon a thin plate 33. The plate 33 is traditionally attached to the accessory of the outer element 31 after a control box 19 is installed on the accessory of the outer element 31 The plate 33 is useful for installing control devices such as a thermostat or for printing warnings or instructions about the controls and components of the water heater 1.

Referring again to Figure 2, in order to prevent the insulating foam material 5 from covering the heating elements 15, a control box 19 such as that described in the patent application of E.U.A. Serial No. 09/211, 218, in the interstitial space 4 between the inner and outer covers 2, 3 of the water heater 1. The US patent. Serial No. 09/211, 218 is commonly assigned with the present application and is incorporated herein by reference. With reference to figure 2 of the patent of E.U.A. Serial No. 09/211, 218, it can be seen that a control box 19 useful in the manufacture of a water heater, consists of a substantially rectangular housing 21 having an open external surface, whose periphery is defined by a plurality of curvilinear segments which form a flange 22. The flange 22 is arranged to support the inner surface of the outer cover 3 in a flush manner. While the outer surface of the control box 18 is open, the curved bottom surface 25 of the control box 19 has a curvilinear shape that is complementary to the outer surface of the inner cover. As can be seen in Figure 2 of the present application, the control box 19 is arranged and constructed to measure the interstitial space 4 between the inner and outer covers 2, 3 and to contact the inner and outer cover 2, 3 in a flush way. Preferably, the lower surface of the control board 19 is adhered to the outer surface of the inner cover 2 on the accessory of the element 17 and accessories of the outer element 31. Through the lower surface of the control box 19, it is formed an opening 23 to allow access to the accessory of the element 17 and accessories of the outer element 31. The flange 22 of the control box 19 is not adhered to the inner surface of the outer cover 3. Rather, when the inner cover 2 is inserted in the outer cover 3, the flange 22 of the control box 19 is free to slide along the inner surface of the outer cover 3. In this way, the control box 19 helps maintain the preferred location of the cover internal 2 inside the outer cover 3, that is, it helps maintain a substantially interstitial space 4 around the entire surface of the inner cover 2. When water heaters are assembled 1 variable years, it is necessary to use control boxes 19 of the corresponding variable sizes. However, as described in the patent of E.U.A. Serial No. 09/21 1, 218, it is preferable to use a single size and style of control box 19 in the assembly of a water heater 1. Therefore, each external cover 3, no matter the size, has for at least one area of its wall that is complementary to the curvilinear flanges 22 of the standardized control box. Figures 3a-3d and 4 of the aforementioned patent application, illustrate that each outer cover or container 10 has at least one area of geometric discontinuity 32 formed integrally with the outer cover wall or container 10 that is disposed and constructed to be complementary with the flanges 22 of the standardized control boxes 19. In this way, the same control box 19 can be used with any of the series of external covers 3 of different sizes.

Since the control boxes 19 are traditionally adhered to the outer surface of the inner covers 2 on the accessories of the element 17, the lower surfaces of the control boxes 19 need not be adjusted flush with the curvature of the inner covers 2. However, it is also possible to provide the inner covers 2 of water heaters 1 of various sizes with at least one area that is complementary to the lower surface of the control box 19. The use of a single style of a control box 19 allows a large scale of sizes of water heaters 1 to be produced using molds, standardized parts and manufacturing equipment. This, in turn, reduces the cost to maintain large inventories of parts of different sizes and limits the amount of time that would otherwise be lost in modifying the molds used in the extrusion molding process to justify variations in the size of the water heater. As indicated above, when a water heater 1 is of sufficient size, more than one accessory of the element 17 will be molded integrally to the wall of the inner cover 2 thus allowing the installation of more than one electric heating element 15. Each accessory of the element 17 has associated therewith a simple control box 19. Although the element fittings 17 can be located almost anywhere on the surface of the inner cover 2, it is more convenient and preferable to align the accessories of element 17 of vertical mode on the external surface of the inner cover 2. In this way, the respective control boxes 19 secured on the corresponding element accessories 17 will also be vertically aligned on the outer surface of the inner cover 2. The electrical conduit ports 35 formed in the control boxes 19 allow the installation of a first length of conduit the 36a between the corresponding control boxes 19. The upper control box 19 will also have a second length of electrical conduit 36b which extends upwardly through the interstitial space 4 and through an opening 37 formed through the outer cover 3. The electrical conduit 36b passing through the opening 37 is positioned to extend into an electrical connection box 38 which is secured to the outer cover 3. The electrical conductors (not shown) are connected to the corresponding electric heating elements 15 and other control structures located in the corresponding control boxes 19 and are threaded through several electrical conduits 36a, 36b to the electrical connection box 38. The electrical conductors that are connected to the different heating elements 15 and other devices of control are connected to an external power source (not shown) in the box electrical connection 38. The outer cover 3 is generally cylindrical and has a height and an inner diameter sufficient to receive an inner cover 2 of predetermined size. The upper part of the outer cover is provided with a plurality of openings 13 which allow ports 6-8 to pass through the wall of outer cover 3 so that external connections to a hot water system can be made. . See figure 3. Figures 2 and 4 illustrate another opening 13 formed through the base of the outer cover 3 which allows the pipe 11 to connect the drain port 9 to the externally installed tap 12. The size, location and number of openings 13 formed in the outer cover 3 depends on the nature and number of ports formed in the inner cover 2 which requires external connections to be made through the outer cover 3. Referring generally to Figures 2 to 5, it is possible to see that an outer cover 3 or container 10 also consists of a channel structure 20 that is integrally formed to the outer cover 3. The channel structure 20 facilitates easy sectioning and reassembly of the outer cover 3. The structure of channel 20 comprises a circumferential channel 22 having an internal surface 24 substantially parallel to the wall of the outer cover 3 and which is radially offset inwardly from the wall the outer cover 3. An upper transition area 26 and a lower transition area 28 join the inner surface 24 of the channel 22 at its upper and lower ends. The upper and lower transition areas 26, 28 connect the inner surface 24 of the channel 22 to the wall of the outer cover 3. It is important to note that the diameter of the inner surface 24 of the channel 22 is smaller than the internal diameter of the external cover 3. Subsequently, after the outer cover 3 has been sectioned by removal of the material comprising the upper transition area 26, the outer cover 3 can be reassembled by inserting the cylindrical internal surface 24 of the channel 22 into the internal diameter of the upper portion of the outer cover 3 in a telescopic manner. In this way, the outer cover 3 and the inner cover 2 of the water heater 1 can be opened and the control structures associated with the inner cover 2 can be inserted into the outer cover 3. As indicated above, it is used a foam or expandable and curable insulation material 5 for filling the interstitial space 4 between the inner and outer covers 2, 3. One of the benefits of using an expandable and curable insulating foam 5 to fill the interstitial space 4 is that the foam 5 will measure the telescopic joint in the outer cover 3 created by the channel structure 20, thus mechanically retaining the cylindrical internal surface 24 of the channel structure 20 within the internal diameter of the upper portion of the outer cover 3. In order to improving the mechanical connection between the upper and lower portions of the outer cover 3, the outer cover 3 may further comprise a circumferential round ring Extending outwardly 32. Because the foam 5 will expand into the rounded ring 32, the shearing force of the foam 5 will prevent the lower portion of the outer cover from moving away from the upper portion of the outer shell . In order to create an airtight seal between the inner surface 24 of the channel 22 and the inner surface of the outer cover 3, a circumferential flange structure extending radially outwardly 30 can be formed on the inner surface 24 of the channel 22. The flange structure 30 creates a modest friction fit between the inner surface 24 of the channel 22 and the internal diameter of the upper portion of the outer cover 3 which serves to prevent the escape of the expandable and curable insulating foam 5 through the seam in the joint created by the structure of the channel 20. The method for manufacturing a water heater 1 in accordance with the present invention begins with the step of molding an inner cover 2 with ports 6-9 and accessories of the integral element 17. water heater 1 illustrated in figures 7a and 7b includes two accessories of the element 17 for two electric heating elements 15. Next, a membrane 40, which it is impermeable to undesirable volatile chemicals, is wound around the inner cover 2. The membrane 40 prevents volatile chemicals such as styrene from migrating through the polybutylene material from which the inner cover 2 is made and into the water contained therein. of the inner cover 2. To increase the pressing speed of the inner cover 2, a fiberglass tape or band impregnated with resin 41 is wound around the inner cover 2 on the membrane 40. The fiberglass ribbon 41 it is wound around the tape in a helical shape to a thickness of approximately 0.33 cm. The rolled-up inner cover 2 is then placed in an oven where the elevated temperatures quickly cure the fiber ribbon impregnated with resin 41. Once the fiberglass cover 41 has been cured, the threaded universal joint compression fittings 42 fold over ports 6-7. Threaded universal joints 42 allow water pipes to connect to water heater 1 without the need for a welding or welding operation, thus avoiding damage to ports 6-7. Similarly, a universal joint 42 is also compressed in the drain port 9. The pipe 11 consisting of an elbow 11a and a nipple 11b, is subsequently connected to the universal joint 42 attached to the outlet port 9. Also in this moment, a number of foam collars 43 are placed over ports 6-8. These foam collars 43 act as spacers between the inner cover 2 and the outer cover 3, helping to maintain a substantially constant interstitial space 4 between the inner and outer covers 2, 3 and also help to seal the openings 13 around the ports 6. -8, preventing leakage of the insulating foam material 5 and the ingress of moisture into the interstitial space 4. When forming the accessories of the element 17 together with the wall of the inner cover 2 of a water heater 1 using a process of extrusion molding, it is common for bronze fittings 18 to be blocked by a portion of the wall of the inner cover 2. Furthermore, the glass fiber layer impregnated with resin 41 also darkens the accessories 18. Therefore, it is necessary to use a device, such as a standard drilling saw 44 for exposing the bronze fitting 18, thereby allowing access to the accessory 18 and to the interior of the inner cover 2. It is preferable to expose the bronze fittings 18 in a two-step procedure. The first step involves using a large drilling saw 44 that typically has a larger diameter than that of the fixture 18, to cut through the fiberglass layer impregnated with resin 41 wound around the inner cover 2. In a second step, a drilling saw 44 having a diameter a little smaller than that of the fitting 18 is inserted through the fitting 18 to cut a hole in the wall of the inner cover 2 which can block access to the interior of the inner cover 2. It is preferred that the drill saws 44 used in these operations. Cutting are equipped with vacuum probes to remove the cut remains simultaneously with the cutting operation. In this way, no remainder of the cutting operations will fall on the inner cover 2. Next, an accessory of the outer element 31 is threaded or otherwise secured in the accessories 18 of the respective element accessories 17. It is preferable to print the accessories of the outer element 31 in the bronze accessories 18 so that they can not be removed. Once the accessories of the outer element 31 are secured within the respective brass fittings 18, all the ports 6-9 and the accessories of the outer element 31 are blocked so that the pressure test can be performed on the inner cover 2 The pressure test involves placing pressurized helium inside the inner cover 2 and using a helium sensitive probe to determine if there is a leak in some of the ports 6-9 or in the accessory of the outer element 31.

The water heater 1 illustrated in Figures 7a and 7b has been provided with means for mounting two electrical heating elements 15. It is to be understood that a water heater 1 constructed in accordance with the methods of the present invention may be provided with more than or less than 2 electrical heating elements 15 without exceeding the scope of the present invention. As indicated above, the control boxes 19 are adhered to the outer surface of the inner cover 2 on the accessories of the outer element 31. To allow electrical connections to be made between the respective control boxes 19, lengths of electrical conduits are secured 36 between the control boxes 19. As illustrated in Figure 7a, the control boxes 19 are connected by a first length of the conduit 36a. The conduit 36a is received at each of its ends at the respective conduit ports 35 formed in the respective control boxes 19 as shown in Fig. 2. The control box 19 located near the upper part of the inner cover 21 is provided with a second length of the electrical conduit 36b measured to extend from a port of the upper conduit 35 in the highest control box 19 through an opening 37 in the outer cover 3. The second length of the electrical conduit 36b attached to the The control box 19 is arranged to provide a connection between the control boxes 19 and the electrical connection box 31 in which the electrical conductors from an external power source are connected to the water heater 1.

It will be difficult to install a length of the conduit 36a between the respective control boxes 19 after the control boxes have been secured to the outer surface of the inner cover 2. Therefore, it is preferred to pre-assemble the control boxes 19 and the respective lengths of the electrical conduit 36a, 36b before the control boxes 19 are secured to the outer surface of the inner cover 2. A location template of the control box 45 is secured to the respective control boxes 19 to ensure that the assembly of the control box be placed on the outer surface of the inner cover 2 in such a way as to allow the openings 23 formed through the lower surface of the control boxes 19 to center on the fittings of the outer element 31. The location template of the control box 45 consists of a metal bar that has brackets attached to it at predetermined locations for the purpose of securing the respective control boxes 19 to the location template 45. The location template 45 also has means for extending into the accessories of the outer element 31 to center the openings 23 in the lower surface of the control boxes 19 on the accessories of the outer element 31. Prior to the placement of the control boxes 19 on the outer surface of the inner cover 2, a suitable adhesive, such as a hot melt glue, is applied to the surface of the outer cover 2 immediately surrounding the accessory of the outer element 31. Using the location template 45, the assembly of the control box is placed together with the outer surface of the inner cover 2 so that the openings 23 of the control boxes 19 are recorded on the accessories of the outer element 31. Once the adhesive has cooled or cured enough to secure the control boxes 19 to the outer surface of the cover In the interior 2, the location template 45 is removed. Once the location template 45 has been removed from the control boxes 19, the electric heating elements 15 and any other control apparatus such as thermostats and programmable logic controllers are they secure inside the respective control boxes 19. Wherever desired, the plates 33 can be attached to the accessories of the outer element. further, the conductors (not shown) are threaded through respective lengths of the electrical conduit 36a, 36b and are connected in a predetermined manner to the respective electric heating elements 15 and other control apparatuses. Referring now to Figure 7b, it can be seen that the outer cover 3 must be sectioned to allow insertion of the inner cover 2 into the outer cover 3. As shown in Figure 7b, the outer cover 3 is sectioned at removing the material forming the upper transition area 26 around the total circumference of the outer cover 3. This is achieved through the use of a tool such as a contour 46 that has a straight cutting tool 55. Once it is has removed the lower portion of the outer cover 3, the inner cover 2 can be inserted into the upper portion of the outer cover 3. The inner cover 2 is inserted in the upper portion of the outer cover 3 so that the ports 6-8 they extend through the openings 13 formed in the upper part of the outer cover 3. In addition, the curvilinear flanges 22 of the control boxes 19 will be in flush contact with the other. The interior surface of the outer cover 3. As described above, the foam collars 43 act to maintain a predetermined distance between the upper portions of the inner cover 2 and the outer cover 3. The control boxes 19 also act to maintain a predetermined distance between the side walls of the inner cover 2 and the outer cover 3. The lower portion of the outer cover 3 is subsequently placed on the lower portion of the lower cover 2 so that the water conduit 11 extends through the the opening 13 formed through the side wall of the lower portion of the outer cover 3. As can be clearly seen in Figure 4, a central opening 27 is formed in the center of the lower part of the outer cover 3. Once the lower portion of the outer cover on the lower part of the inner cover 2 and the inner surface 24 of the cover have been received. The channel 20 of the outer cover has been inserted into the interior of the upper portion of the outer cover 3, a central pin 29 is inserted through the opening 27 for coupling to the elbow 11a of the pipe 11 attached to the drainage port 9. The combination of the foam collars 42, the control boxes 19, and the coupling of the elbow 11a by the central pin 29 all this acts to maintain a substantially constant interstitial space 4 between the inner cover 2 and the outer cover 3.

In this semi-assembled state, the upper part of the outer cover 3 of the water heater 1 is placed in a support 47 mounted on a truck 48. The water heater 1 is subsequently rotated to be oriented vertically in an inverted position in the truck 48. The truck 48 is subsequently placed below the pressure plate 49. A number of cylinders 60 mounted between the corners of the truck 48 and the pressure plate 49 compress the lower part of the outer cover 3 in the upper portion of the outer cover 3. The cylinders 60 cause the pressure plate 49 to maintain an even pressure at the joint where the upper and lower portions of the outer cover 3 have been reassembled to ensure that the connection of a water heater finished 1 is properly aligned. The pressure plate 49 has openings formed therethrough to allow access to a plurality of filling holes 50 punched through the bottom portion of the outer cover 3. See Figure 4. The insulating foam material 5 is subsequently introduces into the interstitial space 4 between the inner and outer covers through the filling holes 50. Typically, a small length of flexible pipe 51 is inserted through one of the filling holes 50 into the interstitial space 4. The pipe 51 extends around the lower part of the inner cover 2 so that the foam can be injected through this flexible pipe 51 to flow in the interstitial space 4 directly into the space between the upper parts of the inner and outer covers 2, 3 As indicated above, the insulating foam material 5 is both expandable and curable, and reacts with moisture in the air that fills the space interstitial 4 to expand rapidly and fill the interstitial space 4 from the top of the water heater 1 to the bottom of the water heater 1. The flexible tubing 51 that was used to inject foam material 5 into the interstitial space 4 is removed from filling holes 50 and discarded. Alternatively, the flexible tubing 51 can be introduced into the interstitial space 4 as the expandable foam material 5 will enclose the flexible tubing 51 completely without any loss in insulating capacity or adverse effects to the function of the water heater 1. A As the insulating foam 5 expands, the air escapes through the filling holes 50 in the lower part of the outer cover 3 of the water heater 1. The indicator holes 51 are likewise separated around the underside of the rounded ring 32. See figure 4. Typically, somewhere between 4 and 7 indicator holes 52 are drilled through the bottom surface of the rounded ring 32. The indicator holes 52 are located such that when the water heater 1 is located in a vertically installed position, the indicator holes 52 can not be seen. The air displaced by the rapidly expanding foam 5 also escapes through the indicator holes 52. As the foam expands on the underside of the outer cover 3, the foam will exert force on the underside of the cover outer 3 which will tend to eject the inner surface 24 of the channel structure 20 from the inside of the upper portion of the outer cover 3. In addition, amounts of expandable foam material 5 will escape from the indicator holes 52. When the material escapes from expandable foam 5 of all the indicator holes 52 drilled through the bottom surface of the rounded ring 32, one can assure with reasonable certainty that all the interstitial space 4 between the inner and outer covers 2, 3, have been filled by the material of expandable foam 5. When one or more indicator holes 52 remain free of foam material 5, it is likely that there is an air cavity within the interstitial space 4. In this example, the water heater will be rejected. Once a predetermined amount of time has passed and the foam material 5 has been cured, the center pin 29 is removed and the water heater 1 is tilted back on its side and the tap 12 is attached to the pipe or conduit 11. Next, a contour 46 having a standard flush cutting tool 56 of the type typically used to fix laminate materials, is used to make a penetration cut through the wall of the outer cover 3 on the open face of the control box 19 attached to the flange 22 as illustrated in Figure 8. The flush cutting tool which is held in the contour 46 subsequently moves along with the side walls of the control box 19 and moves around the total perimeter of the open face of the control box 19 for trimming the waste portion 54 and exposing the entire interior of the control box 19.

The waste portion 54 of the wall of the outer cover corresponding to the open face of the control box 19 is removed and discarded. A cover of the control box 39 as described in the patent application of E.U.A. co-pending serial No. 09/211, 218 and comprising an intermediate plate and a convex cover panel is secured to the outside of the outer cover 3 on the control box 19. Finally, the electrical connection box 38 is secured to the surface of the outer cover 3 at the upper end of the duct 36b extending through the opening 37. The foregoing is considered as illustrative only of the principles of the invention. In addition, since numerous modifications and changes can easily be presented to those skilled in the art, it is not desired to limit the invention to the exact construction and operation that is shown and described. Although the preferred embodiment has been described, the details may be changed without departing from the invention, which is defined by the claims.

Claims

NOVELTY OF THE INVENTION CLAIMS

1. - A method for constructing a double-walled container, the walls of the double-walled container comprise an inner cover and an outer cover, respectively, the method comprises the steps of: providing an inner cover having a predetermined size and shape; providing an outer cover having a predetermined size and shape sufficient for the inner cover to be contained therein so that the walls of the respective covers are separated from each other to define an annular space therebetween; sectioning said outer cover to allow insertion of the inner cover into the interior of the outer cover; arranging the inner cover within the outer cover in a predetermined relationship with the outer cover; reassemble and thus close the outer cover around the inner cover; and injecting an expandable foam into the annular space between the inner and outer covers, the expandable foam expands to substantially fill the space between the inner and outer covers, the expandable foam becomes substantially rigid after a predetermined healing time to permanently place the inner cover inside the outer cover in its predetermined relation with the outer cover.

2. - The method according to claim 1, further characterized in that it comprises the step of: installing at least one accessory of the element together with the wall of the inner cover.

3. The method according to claim 1, further characterized in that it comprises the step of: securing a bottom surface of at least one control housing to the outer surface of the inner cover, the control housing being measured to cover the space between the inner and outer covers, the control housing having a top surface comprising an open face surrounded by a flange arranged and constructed to make contact with the inner surface of the outer cover in a substantially flush manner.

4. The method according to claim 1, further characterized in that it comprises the steps of: securing a bottom surface of at least two control housings to the outer surface of the inner cover, the control housings being measured to cover the space between the inner and outer covers, each control housing has an upper surface comprising an open face surrounded by a flange arranged and constructed to make contact with the inner surface of the outer cover in a substantially flush manner, and to install a conduit between the control housings to create a physical connection between them.

5. The method according to claim 2, further characterized in that it comprises the step of: securing a lower surface of the at least one housing of the control to the outer surface of the inner cover in correspondence with the accessory of the element formed integrally to the inner cover wall, the control housing being measured to cover the space between the inner and outer covers, the control housing has an upper surface comprising an open face surrounded by a flange arranged and constructed to make contact with the inner surface of the outer cover in a substantially flush manner.

6. The method according to claim 2, further characterized by comprising the steps of: securing a bottom surface of at least two control housings to the outer surface of the inner cover, each in correspondence with an accessory of the formed element integrally to the wall of the inner cover, the control housings being measured to cover the space between the inner and outer covers, each control housing has an upper surface comprising an open face surrounded by a flange arranged and constructed to make contact with the inner surface of the outer cover in a substantially flush manner, and install a conduit between the control housings to create a physical connection between them.

7. The method according to claim 1, further characterized in that the outer cover comprises a structure of the channel formed around the circumference of the same, the structure of the channel comprises an inner surface that is radially outwardly inward from the surface of the outer shell around the circumference of the outer shell, the inner surface is joined by upper and lower circumferential transition areas which are attached to the inner surface of the channel structure to the outer surface of the shell, and wherein the pitch sectioning the outer cover further comprises the step of: removing the material from the outer covering comprising the upper transition area of the channel structure, thereby separating the upper portion of the cover from a base portion of the cover to allow the insertion of the inner cover into the interior of the outer cover.

8. The method according to claim 7, further characterized by including the step of: re-assembling the outer cover around the inner cover by inserting the inner surface of the channel structure into the inner diameter of the upper portion of the outer cover.

9. The method according to claim 3, further characterized in that it comprises the step of: removing a portion of the wall of the registered outer cover on the open face of the control housing to gain access to the interior of the control housing.

10. The method according to claim 9, further characterized in that: a portion of the wall of the outer cover is removed by cutting it through the wall of the outer cover along a cutting path defined by the flange of the control housing. The method according to claim 3, further characterized in that it comprises the step of: installing a heating element and a control apparatus in at least one control housing, and securing a cover of the control housing to the surface outside of the outer cover on the open face of the control housing. 12. A method for manufacturing a double-walled container comprising inner and outer containers for providing access to the inner container through the outer container, the method comprising the steps of: forming an outer container having at least one reaming channel. assembly formed around it; forming an inner container having at least one accessory of the element formed integrally therein; sectioning the outer container of the reassembly channel; securing a bottom surface of the at least one control housing to the outer surface of the inner cover so that an opening formed in the control housing is in correspondence with the element fitting formed integrally to the wall of the inner cover , the housing of the control measured to cover the space between the inner and outer covers, the control housing having an upper surface comprising an open face surrounded by a flange arranged and constructed to make contact with the inner surface of the outer cover in a substantially flush; inserting the inner container into the outer container so that the control housing is in substantially flush contact with the inner surface of the outer container; reassembling the outer container to enclose the inner container therein; injecting a curable foam material into the space between the inner and outer container to maintain its constant spatial relationship and to ensure the structural integrity of the outer container; and, removing a portion of the wall of the outer container corresponding to the open face of the control housing to allow access to the interior of the control housing.