GB2178142A - A foam insulated water heater and method of making same - Google Patents

Abstract

A water heater 10 comprising a water tank 11 having a component 16a,b 17 intended to be kept substantially free from contact with an expandable foam insulating material, and a method of making same, is provided. The water heater has a jacket 12 surrounding the tank and providing an insulating space 13 therebetween. Positioned within this space is a pair of flexible sheets 21,22 forming an apron 20. The sheets are joined to form a seal 18, 19, 26 protecting the component from contact with the foam. The apron is positioned over a part of the tank surface so that the seal surrounds the component. The sheets of the apron are substantially unsealed along their top and sides. Foam having an initial viscosity of <300 cps, a flow index >/= about 0.7 and a gel index >/= about 0.8 is introduced between the sheets of the apron and flows out of the unsealed sides of the apron to fill the space between the tank and the jacket. Also described, (Fig. 5 not shown) is a method in which a flexible lining tube (130) is placed inside the outer jacket, and the foam is introduced between the lining tube and the water tank. Also described is a method of introducing the foam in which a plurality of consecutive injections rather than a single injection are used. <IMAGE>

Description

SPECIFICATION A foam insulated water heater and method of making same The present invention relates to foam insulated water heaters and methods of making same.

More particularly, the present invention relates to a method of insulating a water heater tank with an expandable foam insulation material such as polyurethane foam. Still more particularly, the present invention relates to a method of insulating a water heater tank with a novel, low viscosity expandable polyurethane foam insulation material.

The advantage of using rigid polyurethane foam insulation in water heater construction has been recognized for several years. For example, the heat conductivity of polyurethane foam is lower than that of fiberglass, thereby providing superior insulation properties. Thus, it is possible to obtain the same insulation properties utilizing a substantially reduced insulation wall thickness, as compared to conventional insulation materials, such as fiberglass. This results in water heaters having a reduced size thereby providing lower packaging and shipping costs.

In addition, the rigidity of the foam insulation, when compared with that of fiberglass, provides improved resistance to dents in the exterior jacket of the tank. This factor permits the use of less sophisticated (and therefore less expensive) shipping containers.

Although the superior insulating properties of expandable foam materials such as polyurethane have been well recognized for many years, the use of foam as an insulating material in water heaters has been to date quite limited. This is due at least in part to the production problems encountered using expandable foam materials. One of the major problems associated with water heater manufacturing, and particularly the production of foam insulated water heaters, has been the method by which the foam insulation layer is formed about the tank. Generally, the foam is injected as a liquid which continually expands and eventually sets into a rigid foam layer. Usually the liquid foam is injected into the annular space between the inner tank and the outer jacket.

Unfortunately, the liquid foam has a tendency to leak out of any small openings in the seams of the outer jacket. In addition, the sides of the tank generally are provided with openings such as a drain opening or with valves such as a temperature and pressure release valve. Also attached to the sides of the tank are electric controls and other components such as thermostats. In the past, it has been a serious problem in preventing these openings and components from becoming covered with foam, interfering with subsequent servicing, repair, adjustment, etc.

One way of shielding these areas from the expanding foam has been to pack the regions surrounding the nipples and controls with fiberglass insulation material. The fiberglass insulation material then serves as a "foam dam" during the foaming operation.

Other processes utilize a plastic bag filled with the expanding foam material, the bag being positioned around the tank. In U.S. Patent No. 4,372,028 the liquid foam material is first injected into a bag. The bag is then sealed and positioned circumferentially or longitudinally about the tank. The bag may have welded cut out openings which fit over any components attached to the exterior wall of the tank. Because the foam is wholly contained within an enclosed plastic bag, there is no danger of the foam leaking into unwanted areas. Once the foam within the bag expands sufficiently, it forms an effective dam about the electrical control or other area. Subsequently, the remaining annular space between the tank and the outer jacket may be foamed without danger of the foam leaking into the components.

U.S. Patent No. 4,447,377 utilizes another type of plastic bag used in foam insulated water heaters. The bag has a shape which may extend substantially around the entire circumference of the tank. The bag is first positioned around the tank and then the outer jacket is positioned around the bag. Cut out weld holes may be provided in the bag and positioned about any components such as electrical controls, thermostats, drain lines, etc. The top pan is then positioned over the jacket and foam is injected (through an opening in the top pan) into the bag.

Since the expanding foam is wholly contained within the bag, there is no danger of unwanted foam leakage.

Unfortunately, the foaming bags or envelopes used in the prior art have encountered serious problems. In applications such as electric water heaters, the bags are typically used over only a portion of the tank surface. Those areas of the tank surface having electrical control components and other devices (such as thermostats, temperature and pressure relief valves and drain openings) are packed with blocks of conventional insulation materials such as foam or fiberglass. In these applications it is necessary to tailor the size and shape of the bag so that it precisely dovetails with these blocks of fiberglass or foam. This is difficult from both design and production standpoints since the positioning of the bag on the tank surface prior to foam injection becomes quite critical.

In addition, the enclosed bags or envelopes, typically composed of airtight materials such as polyethylene sheet, have a strong tendency to trap air in the corners of the bag, thereby forming voids when the foam eventually sets. The problem of foam voids becomes especially acute as the size of the insulation cavity is reduced. Additionally, the mass of the bag impedes the flow and expansion of the foam and prevents the foam from completely filling the cavity.

In addition, further problems are encountered when foam is injected through a single opening in the top pan. Due to the single opening, the injected foam is typically injected in a short single shot in a rather localized space between the tank side wall and the outer jacket. As the injected foam begins to expand, there is a tendency for the expanding foam to push the tank off center with respect to the outer jacket, and in some extreme cases to cause bulging to occur in the thin flexible jacket. Thus, it is an object of the present invention to provide a foaming method which will alleviate these localized high pressure areas caused by the expanding foam material.

A further major problem associated with the production of foam insulated water heaters concerns the method by which the foam insulation layer is injected. Although many kinds of foamable materials can be used to insulate water heaters, two kinds which are readily available on a commercial basis are HPIM (High Pressure Impingement Mixing) foams and low pressure frothing foams. In both of these types of foam systems, two components, typically an isocyanate component and a resin component are mixed immediately prior to injection into the annular space. In addition, the low pressure frothing foam system injects a gas such as freon into the liquid component mixture just prior to injection. In both of the above-mentioned foam systems and in many other foam systems as well, the foam is typically injected in a single shot into the annular space between the tank and the outer jacket.A typical single shot may take anywhere from a fraction of a second to several seconds depending upon the type of foam injected and the volume of the annular space. The foam nozzle is stationary during the foam injection step so that all of the foam material is injected in a rather localized portion of the annular space. This localized injection of the foamable liquid, and its subsequent foaming action, has a tendency to push the tank and the outer jacket off center with respect to one another and in some extreme cases to cause bulging to occur in the outer jacket adjacent the foam injection site.

The single injection foaming also tends to generate more severe pressures, as the foam expands, which can cause distortions in the shape of the outer jacket, foam leakage and in severe cases can even effect the alignment of openings in the outer jacket with components, such as electric thermostats, positioned on the outside of the water tank.

It has now been discovered that remarkable advantages are achieved by letting the expanding foam material flow freely, without containing it within a bag. It has now been discovered that the expanding foam material gains viscosity and volume as it is being formed and that a surprisingly improved product is obtained by controlling the flow only when the foam is in its most liquid state. Thus, it is an object of the present invention to provide a method of injecting foam insulation into the annular space between a hot water tank and the outer jacket wherein the injected foam is controlled only at the very initial stage of this injection, and is later allowed to freely expand within the annular space.

It has further been discovered that the problem of localized pressure buildups can be alleviated by injecting the foam material before the top pan is secured over the outer jacket. In this way, the shot of injected foam can be articulated around the annular space between the tank and the jacket. In addition, multiple single shots of the foam material can be injected without the necessity (and attendant costs) of providing a number of holes and corresponding plugs in the top pan.

It has further been discovered that the disadvantages associated with the prior art bags and envelopes may be overcome utilizing a foam composition having an unusually low initial viscosity, having high flow and gel indices and which generates lower foaming pressures than the prior art foams. It has also been discovered that using these new foams it is no longer necessary to use the foam restrictive bags and envelopes of the prior art which were so troublesome from the production and void formation standpoints.

Certain embodiments of the present invention may also utilize a novel sleeve configuration which wholly obviates the problems encountered with attempting to dovetail the enclosed bags and envelopes of the prior art against insulation blocks.

It has now further been discovered that remarkable advantages are achieved by providing a plurality of serial injections of the foam insulation material into the annular space between a hot water tank and the outer jacket.

One or more of the problems indicated above may be ameliorated, and one or more of the advantages and objects obtained, by embodiments of the present invention. In one aspect this provides a water heater including a tank and an outer jacket surrounding the tank and spaced therefrom in order to provide an annular space therebetween, wherein a foam insulating material is provided in the annular space, and wherein the foam insulating material is formed by injecting an expandable foam, such as liquid polyurethane foam, into a plastic apron member having open sides. The plastic apron is typically provided with welded dam portions positioned to protect components attached to the exterior wall of the tank, such as electrical controls, thermostats, drain pipes, etc.

In another aspect the invention provides a method of making a water heater including a tank and an outer jacket surrounding the tank and spaced therefrom in order to provide an annular space therebetween, wherein a foam insulating material is provided in the annular space, and wherein the foam insulating material is formed by injecting a foamable liquid having a low initial viscosity, high flow and gel indices and which generates low foaming pressures as it expands.

These foams are preferably injected into a plastic sleeve whose bottom end is fixed around the circumference of the tank providing a seal therebetween. The tank wall may typically have a component, such as a relief valve, an electrical control, a thermostat, drain opening, etc., which must be kept substantially free from contact with the expandable liquid foam material. In such cases the plastic sleeve contains a dam of insulating material, the dam positioned to protect the component attached to the exterior wall of the tank, and forming a seal between the sleeve and the tank thereby preventing the foam from contacting the components.

The foams are preferably injected into the annular space between the tank and the outer jacket prior to securing the top pan over the jacket. In this way, the foam injection can be articulated around the tank in order to avoid localized pressure buildup caused by the expanding foam.

In another aspect the invention provides a method of making a water heater including a tank and an outer jacket surrounding the tank and spaced therefrom in order to provide an annular space therebetween, wherein a foam insulating material is provided in the annular space, and wherein the foam insulating material is formed by injecting a plurality of serial shots of an expandable foam, such as liquid polyurethane foam, into said annular space.

The multiple shot foam injection methods of the present invention can be used in both electric and gas water heaters. Furthermore, the multiple shot foaming methods can be used in water heaters having no envelope, bag, fiberglass dam, or apron as well as in water heaters having an envelope(s), bag(s) and/or apron(s).

Brief Description of the Drawings Figure 1 is a side elevational view, shown partly in section, of a water heater including a water tank and an outer jacket with an apron during a preferred form of foam injection step in accordance with this invention.

Figure 2 is a side elevational view of a water tank with an apron, with the outer jacket removed, during the foam injection step of Fig. 1.

Figure 3 is a side elevational view, shown partly in section, of a top portion of the heater shown in Fig. 1 with a top cover secured in place.

Figures 4A-4D are side elevational views, with parts thereof shown in section, of a single water heater during several successive production stages, with Fig. 4A showing an initial production stage and Fig. 4D showing a later production stage.

Figure 5 is a side elevational view, shown partly in section, of a water heater including a water tank and an outer jacket with a sleeve during a preferred foam injection step in accordance with this invention.

Figure 6 is a side elevational view, shown partly in section, of a water heater including a water tank and an outer jacket with an apron during an initial foam injection step in accordance with this invention.

Figure 7 is a side elevational view of a water tank with an apron, with the outer jacket removed for ease of illustration, during an initial foam injection step.

Figure 8 is a side elevational of the water tank and apron shown in Fig. 7 during a subsequent foam injection step.

Figure 9 is a side elevational view, shown partly in section, of a top portion of the heater shown in Fig. 6 with a top cover secured in place.

Figure 10 is a sectional view of the water tank and apron shown in Fig. 6 taken along lines X-X, illustrating the relative locations of the foam injection sites illustrated in Figs. 7 and 8.

Although specific forms of apparatus embodying the invention have been selected for illustration in the drawings, and although specific terminology will be resorted to in describing those forms in the specification which follows, their use is not intended to define or limit the scope of the invention which is defined in the appended claims. Although a gas or an electric type of water heater has in some cases been selected for illustration as a matter of convenience, the invention applies as well to either type of heaters or any others. Although a preferred plastic sleeve has been selected for illustration in the drawings, the foaming methods of the present invention may be used with or without aprons, bags, envelopes, or ordinary fiberglass foam dams.

Description of the Preferred Embodiments Referring to the drawings wherein like reference numerals refer to the same features in the several drawings, and especially referring to Fig. 1, there is shown electric water heater 10.

Water heater 10 consists of a water tank 11 having a cold water inlet nipple 14 and a hot water outlet nipple 15. Nipples 14, 15 are each surrounded with a block 41 of fiberglass or other insulating material in order to effectively prevent the injected foam from leaking through the openings (provided for the nipples 14, 15) in the top of the water heater. Surrounding tank 11 is outer jacket 12, typically constructed of sheet metal. The diameter of jacket 12 is greater than the diameter of tank 11, thereby creating an annular insulating space 13 therebetween.

Electric water heater 10 is provided with a number of components on the exterior wall of the tank 11. For instance, near the bottom of the tank 11 there is provided a drain opening 17. In addition, components 16a, 16b are attached to the side wall of tank 11 at areas 18, 19, respectively. Components 16a, 16b appear in Fig. 2 but have been deleted from Fig. 1 for ease of illustration. Typically, components 16a, 16b comprise electrical control components such as thermostats or similar devices. However, other types of components may also be positioned on the outer wall of tank 11, such as temperature and pressure release valves or other types of electrical control equipment.

It is important for purposes of proper operation or maintenance of components 16a, 16b that they be effectively shielded from the injected foam insulation material 40. Apron 20 comprises a pair of flexible sheets 21, 22 covering only a limited area of the tank 11 at the foam injection site. Flexible sheets 21, 22 are preferably composed of a flexible, water-tight material which serves to contain and distribute liquid foam 40. Typically, apron 20 is composed of a plastic sheet such as polyethylene.

Apron 20 has a length which is somewhat longer than the height of tank 11, but is much narrower than the circumference of tank 11. Furthermore, apron 20 is open to permit expanding foam to flow circumferentially without confinement by the apron 20. In the particular embodiment of apron 20 illustrated in Fig. 2 (with the outer jacket 12 removed for ease of illustration) the apron 20 has a width equal to about one-half the circumference of tank 11. However, in many cases the width of the apron 20 may be substantially less than that shown in Fig. 2. In certain cases, the width of the apron 20 may be even less than 25% of the circumference of the tank 11.

Apron 20 is provided with a number of cut out openings 24, 25, 26 defined by weld lines, along which weld lines the flexible sheets 21, 22 are welded together. The positions of openings 24, 25 and 26 correspond to the positions of components 16a, 16b and drain opening 17, respectively.

In the manufacture of the foam insulated water heater 10, apron 20 is appropriately positioned on tank 11 so that components 16a, 16b and drain opening 17 are positioned within the cut out openings 24, 25, 26, respectively. Once the apron 20 has been appropriately positioned, the inner flexible sheet 22 is pressed over hot water outlet nipple 15 so that the apron 20 securely hangs on tank 11. Appropriate openings or slits in flexible sheet 22 may be provided in order to facilitate the hanging of the apron 20 on nipple 15.

As a further step, outer jacket 12 is placed over apron 20 and tank 11. Once the outer jacket 12 is secured, the upper end of flexible sheet 21 is pulled outwardly over the top edge of jacket 12.

An expandable foam insulation material 40 is injected into the space between the tank and the jacket, under control of the apron 20. This is accomplished by introducing the liquid foam components through an injection nozzle 30 which extends into the apron 20. The amount of expandable liquid foam material injected may be predetermined depending upon the size of the cavity 13, the type and amount of foam, etc.

It will be appreciated that wide varieties of foams may be utilized in the practice of this invention. Self-foaming materials may be used, in which the foaming process occurs from chemical reactions brought about by merely mixing the foam producing components with each other. In other forms the foam is created by high pressure gas injection, or other means. In any event, the foaming material tends to be highly flowable and of relatively low viscosity during the initial stages of its formation and to become less flowable and of higher viscosity as the reactions proceed, ultimately setting up completely as a solid and rigid foam block.

The liquid foam 40 is injected, at an early stage of the foam-forming process and is freely flowable. Accordingly, it initially flows downwardly and outwardly to the bottom portion of apron 20. In the embodiment shown in Fig. 2, the bottom edges of flexible sheets 21, 22 are joined along seam 23, typically a heat welded seam. However, it is within the scope of the present invention to utilize a single flexible sheet which is simply folded at the bottom at 23, or to use a pair of flexible sheets which are not joined along their bottom edges.

As is clearly shown in Fig. 2, the side edges of flexible sheets 21, 22 are not sealed together. However in other embodiments, the sides of the flexible sheets may be joined for a short distance (about 6") adjacent their bottom edges. In either case, the side edges of sheets 21, 22 remain substantially unsealed. Thus, as the foam 40 is injected into apron 20 it is not confined by the apron 20 but is directed by the apron 20 to flow in a circumferential direction as the foam is generated. As more foam 40 is injected into apron 20, and as it begins to expand and to increase in viscosity, the foam 40 is forced out through the open sides of apron 20. However, by the time the foam 40 begins to flow out of apron 20, it has already increased in viscosity and begun to set and is too thick to present a danger of substantial leakage through small cracks or openings in the outer jacket 12.Furthermore, because of the cut out seams 24, 25 and 26, the liquid foam 40 is effectively dammed from the areas containing components 16a, 16b and drain opening 17.

After the foam 40 has been injected, there is a period of approximately 1 to 5 minutes required for the foam 40 to expand to occupy the entire volume 13 surrounding tank 11 and to set. Thus, after injecting foam 40 through nozzle 30, the top cover 27, shown in Fig. 3, is placed over outer jacket 12. The top cover 27 has appropriate openings for nipple 14, 15.

Furthermore, the top cover also is provided with a hole 28 therein to allow air or gases to escape from cavity 13 as the foam expands.

It has been found that with delicate timing the apron 20 provides a unique means of guiding the foam 40 circumferentially during its initial formation, while it is freely flowable, and that apron 20 delays the flow of foam long enough to permit it to experience an increase of viscosity before it flows circumferentially beyond the open edges of the apron 20. In addition, the highly liquid foam 40 is prevented from contaminating the areas containing components 16a, 16b and drain opening 17. The apron 20 also provides an effective means of guiding the foam 40 in its most liquid stage, thereby preventing leakage of foam through the seams and joints of the outer jacket 12. In addition, all of these advantages are provided through only the temporary guiding of the foam 40 within the open apron 20.This provides significant advantages of uniform coverage, ease of application and insulating effectiveness over the enclosed bags and envelopes of the prior art which are undesirable from production, efficiency, and cost standpoints.

Once the foam 40 has been injected and the top cover 27 has been secured to the jacket 11, the foam 40 is allowed to expand and set. As mentioned before, this procedure typically takes several minutes. The progress of the expansion of the foam 40 may be determined by providing a suitable hole in the top cover 27. This hole 28 also provides a suitable escape outlet for gases displaced by the expanding foam 40. Once the foam 40 has expanded to fill the entire space 13 surrounding the tank 11, the hole 28 may be plugged in a known manner.

Alternatively, the top cover 27 may be installed on the outer jacket 12 before the foaming step. In such a case, the foam 40 is injected through a suitable hole provided in the top cover.

Likewise, in this alternative procedure, the expansion of the foam 40 may be observed through the hole in the top cover which is later plugged at a suitable time.

Referring to Fig. 5, there is shown gas water heater 110. Water heater 110 consists of a water tank 111 a side wall 112, a tank head 113, a tank base 119 and an internally baffled flue pipe 120 extending therethrough. Positioned beneath tank 111 is combustion chamber 116 containing gas burner 117 and gas supply line 118. A bottom pan 128 is provided beneath chamber 116. Heater 110 also has a cold water inlet nipple 114 and a hot water supply nipple 115. Nipples 114, 115 and flue pipe 120 are each surrounded with a block 141 of fiberglass or other insulating material above tank head 113 in order to effectively prevent the injected foam from leaking through the openings (provided for the nipples 114, 115 and flue pipe 120) in the top pan 121 of the water heater 110. Surrounding tank 111 and combustion chamber 116 is outer jacket 125, typically constructed of a thin guage sheet metal.The diameter of jacket 125 is greater than the diameter of tank 111, thereby creating an annular insulating space 126 therebetween.

The distance between the outer jacket 125 and the side wall 112 has typically been in the range of 1 to 3 inches. However, as a result of recent trends to decrease the overall size of water heaters, this distance is now more likely to be in the range of about one-half to about two inches.

Gas water heater 110 is provided with a number of components on the wall 112 of the tank 111. For instance, near the bottom of the tank 111 there is provided a drain opening 122 and thermostat 123. Both drain opening 122 and thermostat 123 are positioned near the bottom portion of tank 111 and are surrounded by a conventional fiberglass insulation blanket 142.

Fiberglass blanket 142 having cutout openings for drain 122 and thermostat 123 also surrounds the combustion chamber 116.~Fiberglass blanket 142 is secured to tank wall 112 with a wire tie 129.

In addition, a component 124 is attached to the side wall 112 of tank 111. As shown in Fig.

5, component 124 typically comprises a temperature and pressure relief valve. However, other types of components may also be positioned on the outer wall of tank 111, such as a thermostat or other type of electrical control device.

It is important for purposes of proper operation and maintenance of component 124 that it be effectively shielded from the foam insulation material 140 injected into the space 126 through nozzle 145. Sleeve 130 comprises a flexible tubular sheet having a diameter which is greater than the diameter of tank 111. Sleeve 130 is preferably composed of a flexible, water-tight material which serves to contain and distribute liquid foam 140. Typically, sleeve 130 is composed of a plastic sheet such as polyethylene.

The lower end of sleeve 130 is tightly secured around the fiberlgass blanket 142 with a wire tie 127. In this way, the bottom end of sleeve 130 is sealed to the side wall 112 of tank 111 since the fiberglass blanket 142 acts as a foam dam. The sleeve 130 extends to about the top edge of outer jacket 125. Positioned within the sleeve 130, and surrounding temperature and pressure relief valve 124, is a block of fiberglass insulation 143. Block 143 typically is somewhat compressable and has a width which is slightly greater than the distance between the outer jacket 125 and the side wall 112. In addition, block 143 has a hole therethrough providing access to component 124.

In the construction of water heater 110 (and referring to Figs. 4A-4D), the fiberglass blanket 142 is secured with wire tie 129 around the bottom portion of the tank with its openings aligned with the thermostat 123 and the drain opening 122. The insulation head 141 may also be secured over the top of tank 111 around nipples 114, 115 and flue 120 at this time. Block 143 is also hung on component 142. The sleeve 130 is then slid over the tank 111 and the block 143 and secured over blanket 142 at its lower end with wire tie 127. Outer jacket 125 is then slid over tank 111 and sleeve 130 and sits loosely within bottom pan 128. Jacket 125 compresses block 143 between wall 112 and sleeve 130.

A low viscosity foamable liquid 140 is injected into the space 126 between the tank 111 and the sleeve 130. This is accomplished by introducing the foamable liquid 140 through injection nozzle 145 which extends through opening 144 in block 141 into the sleeve 130. The amount of expandable liquid foam material injected may be predetermined depending upon the size of the cavity 126 and the type of foam.

It has recently been discovered that surprisingly good results are achieved when the foamable liquid has an initial viscosity (as defined herein) of less than about 300 centipoise (cps) at a temperature of 250C and under atmospheric pressure and a relative humidity of about 50%.

Preferably the foamable liquid has an initial viscosity of less than about 200 cps at the abovementioned conditions.

By the term "initial viscosity", it is meant the viscosity of the liquid 140 as it is pumped out of nozzle 145 into space 126. Of course, it will be readily appreciated by those skilled in the art, that shortly after the foamable liquid 140 is pumped into space 126, it begins to expand and mature thereby increasing its viscosity.

Typically foamable liquid 140 comprises two or more separate liquid components which are mixed immediately upstream from nozzle 145. Thus, the initial viscosity of the foamable liquid 140 is easily determined by measuring the viscosities of each of the individual liquid components and multiplying by their volume percent.

In a preferred embodiment, Stepn Company's STEPAN FOAMTM Rl-9338 having two components may be used. Component A has an initial viscosity of 200 cps at 250C while component B has an initial viscosity of 100 cps at 25 C. Components A and B are metered into nozzle 45 in a 1:1 volume ratio.

The initial viscosity of the foamable liquid mixture having one or more components A,B, C, etc. may thus be computed using the following formula: UM =UA(VA) +U5(V5) + UC(VC) wherein U is the initial viscosity of the foamable liquid mixture, UA is the initial viscosity of component A, U5 is the initial viscosity of component B, Uc is initial viscosity of component C, VA is the volume fraction of component A, V8 is the volume fraction of component B and Vc is the volume fraction of component C.

Using the above mentioned formula, the initial viscosity of the STEPAN FOAMTM Rl-9338 is computed to be about 150 cps at a temperature of 250C and under standard pressure and humidity.

Another important foam property required of the foams used to manufacture water heaters according to the present invention is the flow index. The flow index is simply the ratio of the time it takes the foam to begin to solidify (sometimes called "gel time" or "string time") to the time it takes the foam to rise to 95% of its maximum height as measured in a standard cylindrically shaped open foaming vessel. For foaming water heaters, it is preferable that the foam have a flow index greater than about 0.7, more preferably greater than 0.8.

Another important property of the foams used in the manufacturing methods of the present invention comprises the gel index. The gel index is the ratio of the height of the foam at its gel time to its maximum rise height as measured in a standard cylindrically shaped open foaming vessel. In the methods of the present invention, the foam preferably has a gel index above about 0.8, more preferably above about 0.85.

The foams used in the present invention preferably develop low foaming pressures as they expand. Maximum foaming pressure may be measured using a jacketed cylindrical column having a height of about 24" and a diameter of about 5". The jacketed column is maintained at a temperature of about 1 100F and has a transducer rated 0-5 psig in the wall of the column about two inches from the bottom. A standard amount of foam is then injected into a foaming cup which is then secured to the base of the column. The foam then expands to fill the cup and begins to rise through the column: Pressure from th,e transducer is measured for a period of about ten minutes in order to determine the maximum generated pressure. Typically, the maximum pressure is recorded about ;two minutes after the foam is injected.

The foams used in the present. invention preferably generate a maximum pressure of less than about 1.0 psig, more preferably less than about 0.75 psig.

It will be appreciated that wide varieties of foams may be utilized in the practice of this invention. Self-foaming materials may be used, in which the foaming process occurs from chemical reactions brought about by merely mixing the foam producing components with each other. In other forms the foam is created by high pressure gas injection, or other means. In any event, the foaming material tends to be highly flowable and has an initial viscosity below about 300 cps, a flow index greater than or equal to about 0.7, a gel index greater than or equal to about 0.8 and which generates a maximum pressure of less than about 1.0 psig. The foaming material becomes less flowable and of higher viscosity as the reactions proceed, ultimately setting up completely as a solid and rigid foam block.

The foamable liquid 140 is injected at an early stage of the foam-forming process and is freely flowable. Accordingly, it initially flows downwardly within sleeve 130.

The foamable liquid 140 is unable to flow past the seal between sleeve 130 and tank wall 112 on account of the wire ties 127, 129 and fiberglass blanket 142. In addition, foamable liquid 140 is unable to come into contact with component 124 due to the damming action of fiberglass block 143 which provides a seal between tank wall 112 and sleeve 130 surrounding component 124.

As shown in Figs. 4 and 5, the foam 140 is preferably injected into annular space 126 through nozzle 145 while the top cover 121 is removed. This enables the nozzle 145 to be moved during foam injection thereby allowing the foam to be injected around a wider arc of the circumference of the tank 111. The foam may be injected continuously as the nozzle 145 is moved around tank 111 or in the alternative, a number of discreet shots of foam 140 may be made at different locations within the annular space 126. By spreading the injected foam around the circumference of tank 111, there is a much lesser likelihood that the outer jacket 125 and tank 111 will be pushed off center with respect to one another. This is true even in cases where the thin flexible outer jacket 125 simply sits loosely within bottom pan 128.In addition, there is less likelihood of bulging occurring in the thin flexible outer jacket 125 adjacent the foam injection site.

Once the liquid 140 has been injected, typically in an amount predetermined by the size of the cavity 126, the nozzle 145 is removed and a top pan 121 is then lowered into place (see Fig.

5).

As the liquid 140 is injected into sleeve 130 it is not confined by the sleeve 130 but is directed by the sleeve 130 to flow in a circumferential direction as the foam is generated. As more liquid 140 is injected into sleeve 130, it begins to expand and to increase in viscosity, and eventually fills the entire space 126.

After the liquid 140 has been injected, there is a period of approximately 1 to 5 minutes required for the liquid 140 to foam and expand to occupy the entire volume 126 surrounding tank 111 and to set. Thus, after injecting liquid 140 through nozzle 145, the top cover 121, shown in Fig. 4D, is lowered and secured over outer jacket 125. The top cover 121 has appropriate openings for nipples 114, 115 and flue 120.

As the' foam expands, there is some increase in pressure within cavity 126. This increase in pressure insures that the foamable liquid 140 will flow into all parts of cavity 126.

In addition, the liquid 140 is prevented from contaminating the component 124. The sleeve 130 also provides an effective means of containing the liquid 140 in its least viscous stage, thereby preventing leakage of foam through the seams and joints of the outer jacket 125. This provides significant advantages of uniform coverage, ease of application and insulating effectiveness over the enclosed bags and envelopes of the prior art which were undesirable from production, efficiency, and cost standpoints. However, these skilled in the art will realize that the methods of the present invention can be used to form a wide variety of water heaters, including those having a bag or envelope as well as those having none.

Once the liquid 140 has been injected and the top cover 121 has been secured to the jacket 125, the foamable liquid 140 is allowed to expand and set. As mentioned before, this procedure typically takes several minutes. The progress of the expansion of the foam 140 may be determined by providing a suitable hole in the top cover 121. This hole can also provide a suitable escape outlet for gases displaced by the expanding foam 140. Once the foam 140 has expanded to fill the entire space 126 surrounding the tank 111, the hole may be plugged in a known manner.

Alternatively, the top cover 121 may be installed on the outer jacket 125 before the foaming step. In such a case, the foam 140 is injected through suitable holes provided in the top cover.

Likewise, in this alternative procedure, the expansion of the foam 140 may be observed through one of the holes in the top cover which is later plugged at a suitable time.

Referring to the drawings wherein like reference numerals refer to the same features in the several drawings, and especially referring to Fig. 6, there is shown electric water heater 210.

Water heater 210 consists of a water tank 211 having a cold water inlet nipple 214 and a hot water outlet nipple 215. Nipples 214, 215 are each surrounded with a block 241 of fiberglass or other insulating material in order to effectively prevent the injected foam from leaking through the openings (provided for the nipples 214, 215) in the top pan 227 (shown only in Fig. 9).

Surrounding tank 211 is outer jacket 212, typically constructed of sheet metal. The diameter of jacket 212 is greater than the diameter of tank 211, thereby creating an annular insulating space 213 therebetween.

Electric water heater 210 is provided with a number of components on the exterior wall of the tank 211. For instance, near the bottom of the tank 211 there is provided a drain opening 217.

In addition, components 21 6a, 216b are attached to the side wall of tank 211 at areas 218, 219, respectively. Components 216a, 216b appear in Fig. 7 but have been deleted from Fig. 6 for ease of illustration. Typically, components 216a, 216b comprise electrical control components such as thermostats or similar devices. However, other types of components may also be positioned on the outer wall of tank 211, such as temperature and pressure release valves or other types of electrical control equipment.

It is important for purposes of proper operation and maintenance of components 216a, 21 6b that they be effectively shielded from the injected foam insulation material 240. Apron 220 comprises one of a number of means which may be used to provide a dam around components 216a, 216b and drain 217 during foaming of water heater 210. Although the following description will be directed specifically to a foaming operation utilizing apron 220, those skilled in the art will appreciate that the multiple shot foaming methods of the present invention may be used equally as well with water heaters containing no apron, sleeve, bag or envelope, with water heaters containing fiberglass dams as well as with water heaters containing a bag(s), sleeve(s) or envelope(s).

Apron 220 comprises a pair of flexible sheets 221, 222 covering only a limited area of the tank 211 at the foam injection site. Flexible sheets 221, 222 are preferably composed of a flexible, water-tight material which serves to contain and distribute liquid foam 240. Typically, apron 220 is composed of a plastic sheet such as polyethylene.

Apron 220 has a length which is somewhat longer than the height of tank 211, but is much narrower than the circumference of tank 211. Furthermore, the sides of apron 220 are open to permit expanding foam to flow circumferentially without confinement by the apron 220. In the particular embodiment of apron 220 illustrated in Fig. 7 (with the outer jacket 212 removed for ease of illustration) the apron 220 has a width equal to about one-half the circumference of tank 211. However, in many cases the width of the apron 220 may be substantially less than that shown in Fig. 7. In certain cases, the width of the apron 220 may be even less than 25% of the circumference of the tank 211.

Apron 220 is provided with a number of cut out openings 224, 225, 226 defined by weld lines, along which weld lines the flexible sheets 221, 222 are welded together. The positions of openings 224, 225 and 226 correspond to the positions of components 216a, 216b and drain opening 217, respectively.

In the manufacture of the foam insulated water heater 210, apron 220 is appropriately secured, preferably with a sprayed adhesive, on tank 211 so that components 216a, 216b and drain opening 217 are positioned within the cut out openings 224, 225, 226, respectively.

Alternatively, the inner flexible sheet 222 may be pressed over hot water outlet nipple 215 so that the apron 220 securely hangs on tank 211. Appropriate openings or slits in flexible sheet 222 may be provided in order to facilitate the hanging of the apron 220 on nipple 215.

Prior to the foam injection steps, tank 211 is preferably heated to a temperature of about 5-10 F higher than the temperature of the foamable liquid components. The tank 211 preheating step is strictly a preferred step which aids in the foaming and maturing of certain foamable materials.

As a further step, outer jacket 212 is placed over apron 220 and tank 211. Once the outer jacket 212 is secured, the upper end of flexible sheet 221 is pulled outwardly over the top edge of jacket 212.

An exandable foam insulation material 240 is then injected into the space between the tank and the jacket, under control of the apron 220. This is accomplished by introducing the liquid foam components through an injection nozzle 230, which extends into the apron 220, in two or more shots. The combined amount of expandable liquid foam material injected may be predetermined depending upon the size of the cavity 213, the type of foam, etc.

Referring to Figs. 7 and 8, there is illustrated a two-shot foaming method. Fig. 7 shows the first foam shot through nozzle 230 wherein the foam 240 is injected between sheets 221 and 222. Typically, openings 224, 225 are provided at a central portion of apron 220. The first injection of foam 240 is made slightly off center with respect to apron 220 as shown in Fig. 7.

As the foam is injected, it is freely flowable and typically falls to the bottom of apron 220.

Since the bottom edges of flexible sheets 221, 222 are joined along seam 223 (typically a heat welded seam) the foam 240 flows outwardly to either side as shown by the arrows. The first foam injection typically takes anywhere from a fraction of a second to several seconds, depending upon the type of foam and the size of the cavity. For the initial foam injection step, it is preferable to foam under free rise conditions i.e., lower pressures, preferably c1.0 psig, as will be described in more detail hereinafter.

As is clearly shown in Fig. 7, the side edges of flexible sheets 221, 222 are not sealed together. However in other embodiments, the sides of the flexible sheets may be joined for a short distance (about 6") adjacent their bottom edges. In either case, the side edges of sheets 221, 222 remain substantially unsealed. Thus, as the foam 240 is injected into apron 220 it is not confined by the apron 220 but is directed by the apron 220 to flow in a circumferential direction as the foam is generated. As more foam 240 is injected into apron 220, and as it begins to expand and to increase in viscosity, the foam 240 is forced out through the open sides of apron 220.However, by the time the foam 240 begins to flow out of the apron 220, it has already increased in viscosity and begun to set and is too viscous to present a danger of substantial leakage through small cracks or openings in the outer jacket 212. Furthermore, because of the cut out seams 224, 252 and 226, the liquid foam 240 is effectively dammed from the areas containing components 216a, 216b and drain opening 217.

After the injection of the first foam shot, the nozzle 230 may be moved to the position illustrated in Fig. 8. In the alternative, a second foam nozzle can also be used. Two foam nozzles are especially preferred when two different types of foams are injected in the first and second foam injection steps. In any event, there is typically a time period of 5-300 seconds between the first injection and the second injection in order to allow the foam injected in the first shot to reach a solid state. This time period is typically referred to as the foam's "gel time" or "string time" which will, of course, vary upon the particular foam used to insulate water heater 210. The amount of foam injected in the first shot is purposefully predetermined to be insufficient to foam and occupy the entire annular space 213.This, combined with the fact that the first shot is made before the top pan 227 is secured over the outer jacket, ensures that the foam injected during the first injection will be subjected to lower pressure (since the foam is not expanding within a closed container) as it foams, thereby resulting in the formation of a lower density foam having good structural strength properties. Fig. 8 clearly illustrates that at the time of the second foam injection, the earlier injected foam 240 has expanded to completely surround the lower 1/3-1/2 of tank 211. Thus, at the time of the second foam injection step, the outer jacket 212 is secured with respect to tank 211 by reason of the low density high structural strength foam material injected in the first injection step.

Fig. 8 clearly illustrates the second foam injection step through nozzle 230. The second foam shot is also made between sheets 221 and 222, slightly off center with respect to apron 220 as shown in Fig. 8.

The foam which is injected in the second injection step may be of the same or different type from the foam injected during the first injection step.

In the case of a two shot foaming method using the same kind of foam in both shots, the top pan 227 is immediately secured over the outer jacket 212 upon completion of the second shot.

This ensures that the foam injected in the second shot will be expanding within a closed container and will, therefore, be subjected to higher pressures as it foams. This causes the foam injected in the second shot to form a denser foam than the free rising foam injected in the first shot. Having a higher density foam surrounding the upper 1/2-2/3 portion of tank 211 is preferable from a heating efficiency standpoint since denser foam tends to have better insulating properties. Furthermore, the upper portions of water tank 211 tend to experience the greatest heat loss so it is desirable to have higher density foam surrounding these heat loss prone areas.

Referring to Fig. 10 of the drawings, there is shown a sectional view of the water heater 210 illustrated in Fig. 6 looking towards the bottom of heater 210. Fig. 10 clearly illustrates the first and second foam injection sites 250, 251, respectively. Sites 250, 251 are separated by about a 600 arc along the circumference of the apron 220. Injection sites 250, 251 are preferably equally spaced from the center portion of the apron 220.

It has surprisingly been discovered that using two, three, four or more foam injection steps results in a more uniform cell structure in the matured foam resulting in better insulation properties. In addition, it has also surprisingly been discovered that less foam material needs to be injected into the annular space when using two or more shots of foam resulting in savings of approximtely 1/2 Ib. of foam material for a 50 gallon size tank. This is true even in cases where the multiple shots are all of the same kind of foam.

It is well within the scope of the present invention to provide each shot of foam through a plurality of foam injection nozzles. For instance, it is possible to position a plurality of nozzles 230 around the circumference of tank 211 so that there will be two or more foam injection sites in each of the plurality of "shots".

In addition, it is well within the scope of the present invention to use foams having different densities in different shots.

Those persons skilled in the art will readily appreciate that the multiple shot foaming methods of the present invention may be utilized in any number of ways to provide different foams having specific desired properties within different portions of annular space 213. For instance, in the case of gas water heaters there are certain portions of the annular space, specifically those surrounding the combustion chamber and those surrounding the flue pipe, which become much hotter than other portions of the tank. It is possible using the foaming methods of the present invention to provide a foam insulation material having exceptional burn resistance properties in these high temperature areas.In addition, other foam properties such as structural strength, foaming pressure, insulation value as well as many other properties may be selectively used in the multiple shot foaming methods of the present invention in order to "customize" the various portions of the annular space 213 surrounding tank 211.

Thus, it is possible to provide foams having better insulating properties adjacent more critical areas such as those near the heating elements. In addition, low pressure foaming used in the initial foam injection shot relieves the problems encountered in the prior art wherein the tank and the outer jacket tended to be pushed off center with respect to one another.

It will be appreciated that wide varieties of foams may be utilized in the practice of this invention. Self-foaming materials may be used, in which the foaming process occurs from chemical reactions brought about by merely mixing the foam producing components with each other. In other forms the foam is created by high pressure gas injection, or other means. In any event, the foaming material tends to be highly flowable and of relatively low viscosity during the initial stages of its formation and to become less flowable and of higher viscosity as the reactions proceed, ultimately setting up completely as a solid and rigid foam block.

Once the last injection of foam 240 has been made and the top cover 227 has been secured to the jacket 211, the foam 240 is allowed to expand and set. This procedure typically takes several minutes. The progress of the expansion of the foam 240 may be determined by providing a suitable hole in the top cover 227. This hole 228 also provides a suitable escape outlet for gases displaced by the expanding foam 240. Once the foam 240 has expanded to fill the entire space 213 surrounding the tank 211, the hole 228 may be plugged in a known manner.

Alternatively, the top cover 227 may be installed on the outer jacket 212 before the foaming steps. In such a case, the foam 240 is injected through a plurality of suitable holes provided in the top cover. Likewise, in this alternative procedure, the expansion of the foam 240 may be observed through the hole in the top cover which is later plugged at a suitable time.

Although this invention has been described in the specification with reference to specific forms thereof. it will be appreciated that a wide variety of equivalents may be substituted all without departing from the spirit and scope of the invention as defined in the appended claims.

Claims (50)

1. In a water heater comprising a water tank having a component intended to be kept substantially free from contact with an expandable foam insulating material and a jacket surrounding the tank and providing an insulating space therebetween, a pair of flexible sheets forming an apron, the sheets being joined to form a seal protecting said component from contact with the foam, the apron being positioned over a part of the tank surface in a position whereby the seal surrounds said component, the apron being substantially unsealed along its top and sides wherein the foam introduced between the sheets flows out of the unsealed sides of the apron to fill said space.

2. The water heater according to Claim 1, wherein the apron is composed of plastic.

3. The water heater according to Claim 1 or 2 wherein the foam comprises polyurethane.

4. The water heater according to any of Claims 1-3 wherein the component comprises a thermostat.

5. The water heater according to any of claims 1-4 wherein the heater is an electric water heater.

6. The water heater according to any of Claims 1-5 wherein the sheets are joined along their bottom edges.

7. The water heater according to any of Claims 1-6 wherein the pair of sheets comprises two portions of a single sheet.

8. The water heater according to any of Claims 1-7 wherein the component comprises a drain opening.

9. The water heater according to any of Claims 1-8, wherein the seal defines a closed shape which is cut out from the sheets.

10. The water heater according to any of Claims 1-9 wherein the component comprises a valve.

11. In a method of insulating a water heater having a water tank with a component intended to be kept substantially free from contact with an expandable foam insulating material, the steps comprising: (a) placing over a part of the tank surface a pair of flexible sheets forming an apron, the sheets being joined to form a seal protecting said component from contact with the foam, the apron being positioned on the tank whereby the seal surrounds said component, the apron being substantially unsealed along its top and sides; (b) securing a jacket around the tank and over the apron, the jacket being dimensioned to provide a space therebetween in which said apron is positioned;; (c) introducing an expandable foam insulating material between the sheets, and (d) securing a cover on the top of the jacket to close off the top of the jacket, whereby the foam expands and flows out of the unsealed sides of the apron to fill said space.

12. The method according to Claim 11, wherein the apron is composed of plastic.

13. The method according to Claim 11 or 12 wherein the foam comprises polyurethane.

14. The method according to any of Claims 11-13 wherein the component comprises a thermostat.

15. The method according to any of Claims 11-14 wherein the component is a valve.

16. The method according to any of Claims 11-15 wherein the heater is an electric water heater.

17. The method according to any of Claims 11-16 wherein the sheets are joined along their bottom edges.

18. The method according to any of Claims 11-17 wherein the pair of sheets comprises two portions of a single sheet.

19. The method according to any of Claims 11-18 wherein the component comprises a drain opening.

20. The method according to any of Claims 11-19 wherein the seal defines a closed shape which is cut out from the sheets.

21. In a method of insulating a water heater having a water tank with an expandable foam insulating material, the steps comprising: (a) placing a flexible sleeve over the tank surface, the sleeve being open along its top end and fixed around the circumference of the tank along its bottom end; (b) securing a jacket around the tank and over the sleeve, the jacket being dimensioned to provide a space therebetween in which said sleeve is positioned; (c) introducing an expandable foam insulating material having an initial viscosity as defined herein of less than about 300 cps, a flow index 2 about 0.7, a gel index 2 about 0.8 and which generates a maximum pressure of S about 1.0 psig, between the sleeve and the tank; and (d) securing a cover on the top of the jacket to close off the top of the jacket, whereby the foam expands within the sleeve to fill said space.

22. The method according to Claim 21, wherein the sleeve comprises a plastic tube.

23. The method according to Claim 21 or 22 wherein the foam comprises polyurethane.

24. The method according to any of Claims 21-23 wherein the heater is a gas water heater.

25. The method according to any of Claims 21-24 wherein a lower portion of the sleeve is tied around the tank.

26. The method according to any of Claims 21-25 wherein a component intended to be kept substantially free from contact with the expandable foam insulating material is provided on the tank wall, said component being surrounded by a dam of insulating material, the dam being positioned between the sleeve and the tank and forming a seal therebetween to prevent the foam from contacting the component.

27. The method according to Claim 26 wherein the component comprises a valve.

28. The method according to Claim 26 or 27 wherein the component comprises a thermostat.

29. The method according to any of Claims 26-28 wherein the component comprises a drain opening.

30. The method according to any of Claims 26-29 wherein the dam is composed of fiberglass.

31. In a method of insulating a water heater having a water tank with an expandable foam insulating material, the steps comprising: (a) securing a jacket around the tank, the jacket being dimensioned to provide a space between the tank and the jacket, the space being capable of containing an expandable foam insulating material in an initial liquid state; (b) introducing an expandable foam insulating material having an initial viscosity of less than about 300 cps, a flow index I about 0.7, a gel index I about 0.8 and which generates a maximum pressure of ' about 1.0 psig, between the tank and the jacket, and (c) thereafter securing a cover on the top of the jacket to close off the top of the jacket, whereby the foam expands within the jacket to fill said space.

32. The method according to claim 31, wherein the expandable foam insulating material is introduced into the space at least around a portion of the circumference of the tank.

33. The method according to claim 32, wherein the foam is injected continuously.

34. The method according to claim 32, wherein a plurality of discreet shots of the foam are injected into the space.

35. In a method of insulating a water heater with an expandable foam insulating material, said heater including a tank and a jacket, the steps comprising: a. securing the jacket around the tank, the jacket being dimensioned to provide a space therebetween; b. introducing a plurality of serial injections of an expandable foam insulating material into the space; and c. securing a cover on the top of the jacket to close off the top of the jacket, whereby the foam expands to fill said space.

36. The method according to claim 35, wherein the foam comprises polyurethane.

37. The method according to Claim 35 or 36 wherein the heater is an electric water heater.

38. The method according to any of Claims 35-37 wherein two serial injections are introduced into the space.

39. The method according to any of Claims 35-38 wherein each of the plurality of injections are made through a single foam injection nozzle.

40. The method according to any of Claims 35-38 wherein at least one of the injections is made through a plurality of foam injection nozzles.

41. The method according to any of Claims 35-40 wherein there is provided a period of delay between a first and second injection.

42. The method as defined in Claim 41, wherein the period of delay is in the range of about 5-300 seconds.

43. The method as defined in any of Claims 35-42 wherein a first injection injects an expandable foam insulating material which is allowed to expand under free rise conditions and which is subjected to low pressures as it expands.

44. The method according to Claim 43, wherein the foam is subjected to pressures c about 1.0 psig.

45. The method according to Claim 43 or 44 wherein a second injection of an expandable foam insulating material comprises injecting a foamable material which is subjected to higher pressures than those subjected to the first foam injection.

46. The method as defined in any of Claims 35-45 wherein the plurality of serial injections are made into a plastic apron having a cut out opening therein.

47. The method according to Claim 46, wherein two serial injections are made on either side of the cut out opening.

48. The method according to any of Claims 35-47 wherein different foams having selected physical properties are injected into different portions of said space in said serial injections.

49. The method according to any of Claims 35-48 wherein one shot of foam is caused to expand with the cover off and wherein a subsequent shot of foam is injected with the cover off and the cover is affixed to the jacket to enclose the space while the foam of the subsequent shot is still expanding in said space.

50. A foam insulated water heater or a method of insulating a water heater substantially as any herein described with reference to and as illustrated in the accompanying drawings.