Abstract:
A foam dam in the insulation cavity of an electric water heater comprises a plastic bag into which liquid foam insulation is injected, the bag having an essentially closed top edge portion with only a small opening for receiving the injected insulation. A small portion of the insulation injected into the bag is forced outwardly therefrom via small metering holes to form external protrusions on the bag that mechanically interlock with a second batch of insulation subsequently injected into the cavity and prevent the hardened second insulation batch from pulling away from the bag. The substantially closed top edge of the bag permits the insulation injected into the bag to pack therein and increase the top-to-bottom hardened foam density uniformity. Side edges of the bag may be pleated to increase the sealing area of the foam dam.

Description:
BACKGROUND OF THE INVENTION 
     The present invention generally relates to the manufacture of insulated structures and, in a preferred embodiment thereof, more particularly relates to water heater structures and associated manufacturing and insulation methods therefor. 
     A conventional water heater of either the electric or fuel-fired type normally comprises a water storage tank, typically of a metal construction, adapted to hold a quantity of pressurized, heated water for on-demand delivery to various plumbing fixtures such as sinks, tubs, showers, dishwashers or the like. Outwardly surrounding the tank is a jacket, typically of a metal construction, which defines around the tank a cavity which is filled with a suitable insulation material, usually a hardened foam insulation material which is initially injected into the cavity in liquid form during the fabrication of the water heater. Various control structures, such as thermostats and electric heating element structures project outwardly from the tank and are aligned with associated access openings in the jacket. 
     In order to shield these control structures from the insulation, and to prevent the insulation from being forced outwardly through the jacket access openings during the liquid insulation injection process, it is common practice to circumscribe the control structure areas within the tank/jacket cavity with insulation barriers commonly referred to as “foam dams”. One previously proposed method of providing a foam dam around a control structure projecting outwardly from a water heater tank, illustrated and described in U.S. Pat. No. 4,372,028 to Clark et al, is to provide a plastic bag having a peripherally sealed aperture extending therethrough, place the bag in the empty tank/jacket cavity with the aperture aligned with and circumscribing the control structure location, expanding the bag into sealing engagement with the tank and jacket by injecting foam insulation into the bag, and then permitting the injected foam to harden within the bag. 
     The empty remainder of the insulation cavity is then injected with additional liquid foam insulation which is prevented from encroaching into the control structure locations, or flowing outwardly through the associated jacket access openings, by the previously formed plastic bag-based foam dam. This second batch of injected liquid foam insulation contacts the periphery of the foam dam and hardens within the tank/jacket cavity to complete the tank insulation process. 
     Several well known problems, limitations and disadvantages are typically associated with this conventional plastic bag-based foam dam construction. First, after the second or main batch of foamed-in insulation hardens it tends to pull away from the plastic bag in a manner creating a gap between the second foam batch and the bag along the entire length of the water heater. This gap, caused by shrinkage of the second foam batch, undesirably permits appreciable heat loss from the tank therethrough. 
     Second, the current practice for filling the foam bag with the first batch of foam insulation is to inject a shot of foam into the bag and then let the injected foam “free rise” within the bag to fill it. This results in an undesirably decreased foam density in a top portion of the bag, resulting in a lesser insulation efficiency in the top portion of the bag. 
     Third, bags of this conventional type are typically of a flat construction, but are used to sealingly fill a three dimensional portion of the tank/jack insulation cavity. The result tends to be a filled bag with marginal foam coverage around the control or other structure around which the filled foam bag protectively extends. 
     As can readily be seen from the foregoing, a need exists for an improved plastic bag-based foam dam structure and related insulated tank apparatus and associated fabrication methods. It is to this need that the present invention is directed. 
     SUMMARY OF THE INVENTION 
     In carrying out principles of the present invention, in accordance with a preferred embodiment thereof, a method of insulating a tank, such as a water heater tank, is carried out by steps including placing an outer jacket on the tank to define a cavity extending outwardly around a portion of the tank, and positioning a flexible bag in a first portion of the cavity, the bag having a spaced series of metering openings in a wall portion thereof. A first quantity of flowable, hardenable insulation is forced into the bag in a manner expanding the bag into sealing engagement with the tank and outer jacket, and causing a small portion of the insulation to be forced outwardly through the metering openings and subsequently form spaced apart hardened external protrusions on the bag. Representatively, the bag is of a plastic material, and the insulation material is a liquid foam insulating material. 
     After the first insulation quantity has hardened, a second quantity of flowable, hardenable insulation, preferably a liquid foam insulation, is flowed into a second portion of the cavity and into contact with the wall portion of the bag and the hardened insulation protrusions thereon. The second insulation quantity is permitted to harden and become mechanically interlocked with the previously hardened insulation protrusions in a manner substantially preventing shrinkage-created separation of the second insulation quantity from the wall portion of the bag. In this manner, in the finished insulated tank apparatus which also embodies principles of the present invention, there is no appreciable heat loss gap or void between the second batch of insulation and the foam filled bag. 
     Illustratively, the locking insulation protrusions have generally knob-like configurations which have surfaces that are spaced outwardly apart from and generally face the bag. These protrusion surfaces abut facing portions of the hardened second insulation quantity to facilitate the mechanical interlock between the hardened protrusions and the hardened second insulation quantity within the tank/jacket cavity. 
     In accordance with another aspect of the present invention, the bag has an essentially closed upper end with a relatively small inlet opening therein through which the first insulation quantity is injected into the bag. Small insulation vent openings are formed in the bag adjacent this injection inlet opening. Because of this configurational aspect of the bag, insulation injected into the bag is pressure-packed into the bag, as opposed to being permitted to merely “free rise” therein. This results in a desirably increased hardened insulation density uniformity along the vertical dimension of the bag. According to a further aspect of the present invention, this vertical insulation density uniformity is additionally enhanced by arranging the metering openings vertically along opposite vertical side edge portions of the bag and configuring the metering openings in a manner such that their cross-sectional areas increase in an upward direction along such side edge portions of the bag. 
     In one embodiment of the present invention, principles thereof are representatively incorporated in an electric water heater in which a component, representatively a heating element thermostat, projects outwardly from the tank toward an opening in the outer jacket. The insulation-filled bag functions as a foam dam which sealingly engages facing portions of the tank and jacket that circumscribe the component. The component extends through a peripherally sealed opening in the bag. According to a feature of the invention, this opening has, prior to the expansion of the bag caused by injection of foam insulation into its interior, a generally hourglass-shaped configuration with concave opposite vertical side portions. When the bag is subsequently expanded by the foam injected into its interior, these concave opposite side portions are is caused to generally straighten so that this component-receiving bag opening is more nearly rectangular to more closely correspond in shape to the generally rectangular shape of the thermostat. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic side elevational view of an electric water heater embodying principles of the present invention; 
         FIG. 2  is an enlarged scale schematic cross-sectional view through the water heater taken along line  2 — 2  of  FIG. 1 ; 
         FIG. 3  is an enlarged scale, partially cut away front side elevational view of a specially configured plastic foam bag used in the fabrication of the water heater, the foam bag being in a flattened pre-use orientation; 
         FIG. 4  is a right side edge view of the plastic foam bag; 
         FIG. 4A  is a right side edge view of the plastic bag after it has been filled and expanded with foam insulation; 
         FIG. 5  is an enlarged scale detail view of the dashed area “5” in FIG.  3  and illustrates a portion of the insulation metering holes formed in the plastic bag; 
         FIGS. 5A and 5B  are detail views similar to that in  FIG. 5  but illustrating representative alternate patterns for the metering holes; 
         FIG. 6  is an enlarged scale schematic cross-sectional view taken along line  6 — 6  through a portion the foam insulation-filled bag of FIG.  4 A and illustrating the unique mechanical interlock between insulation injected into the bag and another body of hardened foam insulation within the water heater; 
         FIG. 7  is an enlarged scale detail view of the dashed area “7” in  FIG. 6 ; 
         FIG. 8  is an enlarged scale partially cut away front side elevational view of an alternate embodiment of the plastic foam bag in a flattened, pre-use orientation; 
         FIG. 9  is a right side edge view of the  FIG. 8  bag in its generally flat pre-use orientation; and 
         FIG. 9A  is a right side edge view of the  FIG. 8  bag after it has been filled and expanded with foam insulation. 
     
    
    
     DETAILED DESCRIPTION 
     Referring initially to  FIGS. 1 and 2 , the present invention provides a water heater, representatively an electric water heater  10 , which is constructed and insulated in a unique manner using a specially designed foam dam structure  12  (see  FIG. 2 ) which will be subsequently described herein. Water heater  10  includes a vertically oriented, representatively cylindrical metal storage tank  14  adapted to hold a quantity of pressurized hot water  16  for on-demand delivery to various plumbing fixtures such as sinks, tubs, showers, dishwashers and the like. Extending upwardly from the upper end of the tank  14  are the usual cold water inlet, hot water outlet, and temperature and pressure relief fittings  18 , 20  and  22 . On the side of the tank  12 , near its bottom end, is an outwardly projecting drain fitting  24 . 
     Outwardly circumscribing the tank  14 , and forming therewith an insulation cavity  26 , is a metal jacket of a suitable, conventional construction. To heat the water  16  within the tank  14 , the water heater  10  is provided with heating apparatus representatively in the form of upper and lower electrical resistance type immersion heating elements  30 , 32  which project horizontally through the vertical side wall of the tank  14  into the water  16  therein. The outer ends of the heating elements  30 , 32  are secured to thermostatic control structures  34  that project outwardly from the tank  14 , through the insulation cavity  26 , and are aligned with access openings  35  in the jacket  28 . The access openings  35  are covered with suitable removable cover panels  36  secured to the jacket  28 , and the drain fitting  24  projects outwardly through a hole  38  in the jacket  28 . 
     To substantially reduce undesirable heat loss from the tank  14  outwardly through the outer jacket  28 , liquid foam insulation  40  is injected into the cavity  26  in a conventional manner and is allowed to harden in the cavity  26 . In a manner subsequently described herein, prior to this foam insulation injection the foam dam structure  12  is installed in the insulation cavity  26  and functions to prevent the pressurized liquid foam insulation  40  being injected into the cavity  26  from contacting the thermostats  34  or being forced outwardly through either of the jacket access openings  35  or the drain fitting hole  38 . 
     The foam dam structure  12  includes a vertically elongated, generally rectangular plastic bag  42  which is illustrated in  FIGS. 3 and 4  in a flattened, pre-use orientation thereof. Bag  42  has front and rear side walls  44  and  46 , top and bottom edges  48  and  50 , and left and right vertical edges  52  and  54 . Edges  50 , 52 , 54  of the bag  42  are sealed along their lengths, and the top edge  48  is substantially closed with the exception of a relatively small central insulation injection opening  56  formed therein. Horizontally spaced vent openings  58  are formed through the front and rear side walls  44 , 46  inwardly adjacent the top edge  48  on opposite sides of the injection opening  56 , and vertically spaced series of what may be termed pinhole metering openings  60  extend through the front and rear side walls  44 , 46  inwardly adjacent the left and right edges  52 , 54 . Representatively, metering openings  60  are arranged in single vertical rows inwardly adjacent the bag side edges  52  and  54 , but other metering opening arrangements and patterns could be utilized if desired. Horizontally aligned, vertically spaced rectangular thermostat openings  62  extend through the front and rear bag side walls  44 , 46  above a circular drain fitting opening  64  also extending through the front and rear bag side walls  44 , 46 . Each of the openings  62  and  64  has a sealed periphery. 
     To form the foam dam structure  12  within the insulation cavity  26 , the still flattened plastic bag  42  is suitably secured against the outer side of the tank  14 , before the outer jacket  28  is installed, with the thermostats  34  extending through the rectangular bag openings  62 , and the top edge  48  of the bag  42  adjacent the top end of the tank  14 . The outer jacket structure  28  is then installed in a manner aligning the jacket access openings  35  with the bag openings  62  and the jacket drain fitting opening  64  with the jacket drain fitting hole  38 . The drain fitting  24  may then be operatively connected to the tank  14  through the jacket hole  38  and the bag opening  64 . 
     Next, an initial quantity of liquid foam insulation  66  is injected downwardly into the bag  42  through its relatively small top edge opening  56 . Because the top end edge  48  of the bag  42  is substantially closed except for this relatively small injection opening, the injected insulation  66  tends to be packed into the bag under pressure (as opposed to being simply being permitted to “free rise” within the bag) as itis being injected. When the bag  42  is filled with insulation  66 , and begins to flow out of the small vent openings  58  near the top edge  48  of the bag, the bag injection process is stopped. The density of the foam  66  within the insulation-filled bag  42 , quite desirably, is substantially uniform from the bottom of the bag  42  to the top thereof, thereby correspondingly increasing the overall thermal insulation efficiency of the insulation-filled bag  42 . 
     The filling of the bag  42  with the insulation  66  expands the bag  42  in a forward direction (as may be seen by comparing  FIGS. 4 and 4A ) to cause the filled bag  42  to come into forcible sealing contact with the outer side surface of the tank  14  and the interior surface of the jacket  28  (see  FIG. 2 ) to thereby wall off the thermostats  34  and the drain fitting  24  (or their installation locations if they are subsequently mounted) from the balance of the insulation cavity  26 . 
     The pressurized filling of the bag  42  with the injected foam insulation  66  also causes the insulation  66  to ooze outwardly in small quantities through the diminutive metering openings  60  in the bag  42  (which, as the bag is expanded by the foam  66 , are re-oriented so that they face generally parallel to the front and rear bag side walls  44 , 46  as shown in FIG.  4 A). The metering openings  60  are substantially smaller in cross-section than the vent openings  58 . After the bag  42  is filled with the insulation  66 , the injected insulation  66  is permitted to harden. The very small portions of the insulation  66  which oozed out of the metering openings  60  during the pressurized insulation injection of the bag harden to form a series of mutually spaced apart, generally knob-shaped locking protrusions  68  on what are now the expanded vertical side edge portions of the bag  42  which circumferentially face the balance of portion of the insulation cavity  26  which horizontally extends around the tank  14 . 
     After the insulation  66  in the bag  42 , and the resulting exterior insulation protrusions  68  harden, the previously mentioned batch of insulation  40  is injected into the tank/jacket cavity  26  and allowed to harden. Due to the prior placement in the cavity  26  of the bag-based foam dam structure  12 , substantially none of the injected foam insulation  40  enters the bag openings  62  and  64 , contacts either of the thermostats  34  or the drain fitting  38 , or escapes outwardly through any of the jacket openings  35  or  38 . When the insulation  40  subsequently hardens, it becomes mechanically interlocked, as at locations  70  that may be best seen in  FIG. 7 , with the various hardened insulation protrusions  68  spaced apart along the expanded vertical side edges of the in-place bag  42 . 
     This mechanical interlock between the insulation  40  and the completed foam dam structure  12  substantially prevents the pulling away of the insulation  40  from the vertical bag side edges as the insulation  40  shrinks during its post-injection hardening. There is thus no appreciable gap created between the hardened insulation  40  and the expanded vertical side edges of the bag  42  (see  FIG. 7 ) for tank heat to leak outwardly through. Thus, the overall heating efficiency of the water heater  10  is appreciably and economically improved in a unique and simple manner. 
     Representatively, as shown in  FIG. 5 , the cross-sectional areas of the pinhole metering openings  60  are substantially uniform, and each of the openings  60  has a circular cross-section. Alternatively, the metering openings  60  may have other shapes such as, for example, the vertical elongated slot configurations shown in FIG.  5 A. Another modification which can be made to the configurations of the metering openings  60  is shown in  FIG. 5B  in which the cross-sectional areas of the representatively round metering openings  60  increase vertically along the opposite vertical side edges  52 , 54  of the bag  42  so that the cross-sectional areas of upper ones of the openings  60  are greater than the cross-sectional areas of lower ones of the openings  60 . Such increase in the metering opening areas vertically along the bag  42  has been found to further increase the desirable insulation density uniformity vertically along the interior of the bag  42 . 
     Illustrated in simplified form in  FIGS. 8-9A  is a representative alternate embodiment  42   a  of the previously described plastic foam dam bag  42 . To facilitate comparison between the two bag embodiments  42  and  42   a , features in the bag  42   a  similar to those in the bag  42  have been given identical reference numerals with the subscripts “a”. 
     In the bag  42   a , the vent openings  58   a  are formed by clipping off small top corner portions of the bag, and the thermostat openings  62   a  have vertically elongated, generally hourglass shapes with concave vertical sides  72  (see FIG.  8 ). When the bag  42   a  is filled with foam  66 , opening sides  72  generally straighten to their dotted line positions so that the resulting shapes of the openings  62   a  are more rectangular to more closely conform to the rectangular shapes of the thermostats  34  they receive. 
     The left and right side vertical side edge portions  74 , 76  of the bag  42   a  have pleated configurations which expand in a forward direction in response to filling the bag  42   a  with foam insulation  66  (compare the empty bag configuration in  FIG. 9  to the insulation-filled bag configuration in  FIG. 9A ) to increase the bag&#39;s sealing contact area around the thermostats  34  and the drain fitting  24 . The metering openings  60   a  are formed in the pleated side edge portions  74 , 76 , and when the foam insulation  66  is injected into the bag  42   a  and allowed to harden, the locking projections  68   a  are formed exteriorly along the pleated side edge portions  74 , 76  for mechanically interlocking with the subsequently injected batch of insulation foam  40  within the remainder of the insulation cavity  26  and preventing undesirable separation of such insulation  40  from the bag  42   a.    
     While the previously described fabrication and insulation technique has been representatively utilized in an electric water heater, those of skill in this particular art will readily appreciate that it could also be advantageously employed in a variety of other tank insulating applications, such as with boilers or gas-fired water heaters, without departing from principles of the present invention. 
     The foregoing detailed description is to be clearly understood as being given by way of illustration and example only, the spirit and scope of the present invention being limited solely by the appended claims.