Abstract:
The present invention is a vacuum insulated panel (VIP) for increasing the thermal insulation surrounding a structure or volume, and a novel method for manufacturing the VIP. The VIP comprises at least two pieces of thin metal foil welded together adjacent the edges of said metal foil, said thin metal foil material defining the exterior of a sealed and gas evacuated vacuum enclosure; and a vacuum insulation panel core located between said at least two pieces of welded thin metal foil material, said vacuum insulation panel core located inside said sealed and gas evacuated vacuum enclosure.

Description:
This is a continuation-in-part of provisional application Ser. No. 61/599,622 filed Feb. 16, 2012. Applicants claim priority to provisional application Ser. No. 61/599,622 to the extent allowed by law. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to the structure of a vacuum insulation panel of arbitrary size, the method of making the panel and ways of using the panel. 
     BACKGROUND OF THE INVENTION 
     Vacuum insulation panels (VIP) are panels that are poor thermal conductors and used where a temperature gradient needs to be maintained. These panels consist of a core that is a poor thermal insulator when placed in a low pressure environment (less than 100 microns), a getter (materials which adsorbs moisture and gas) and an outer envelope. 
     A vacuum insulated panel (VIP) is a form of thermal insulation made up of a nearly gas-tight enclosure surrounding a rigid core, from which the gas has been evacuated. Vacuum insulation panels are used to decrease the heat leakage from a structure or volume and therefore increase energy efficiency. Vacuum insulation panels are typically used inside refrigerator cabinets, freezers, vending machines, mobile refrigeration solutions, building construction, medical related fields, as well as in association with any products that require low energy loss due to heat transfer. 
     There have been changes to some of the materials that have been used in VIPs, particularly the “core material”, such as shown in U.S. Pat. Nos. 5,330,816; 7,517,576 and U.S. patent application No. 2012/00009376 A1. However, current processes of manufacturing VIPs have remained the same for some time and one such process is typically set forth in U.S. Pat. No. 5,364,577: 
     1. The core material, usually an inorganic “board” or panel, is manufactured and placed in a dry environment. 
     2. The panel is then heated and placed into a large chamber that is able to go to the desired pressures. 
     3. A getter is then placed next to the core material. 
     4. The getter and the core material are heat sealed in an envelope. The envelope is made of aluminum, a form of metalized plastic, or thick (&gt;0.003 inches) stainless steel. 
     5. Sometimes manufacturers will place some helium in the envelope prior to sealing for quality control purposes once the process is done. 
     Commercially available VIPs are clad in an aluminum/plastic foil laminate, and since aluminum has high thermal conductivity, edge losses can significantly reduce the effective insulation value of these VIPs. Both aluminum clad and metalized plastic envelopes are extremely fragile, and the requirement of a superstructure to attach a VIP to a building increases the retrofitting costs and represents additional thermal edge losses. The current method of manufacturing VIPs limits the maximum size of the VIPs. Gas is evacuated in the entire chamber where the VIP is present, and then the plastic VIP envelope is hot sealed all around the perimeter. 
     During the manufacturing of VIPs, the getter/desiccant in the enclosure is exposed to the manufacturing ambient and can lose effectiveness. The hermetic seal of the enclosure is by a plastic to plastic weld and is more permeable than a metal to metal weld. The current VIP envelopes are easily punctured, thus quickly reducing the effective R value of the VIP. One other problem with small VIPs is that the edge thermal losses can easily exceed the area thermal losses. For a VIP encased in 0.3 mil aluminum foil the significant thermal short at the edges of the VIP greatly reduces the effective R value of the VIP. 
     It is an objective of the present invention to create inexpensive hermetically sealed, puncture resistant vacuum insulated panels of arbitrary size and shape with high R value and reduce the VIPs&#39; thermal edge losses. One other objective of the present invention is to create and deliver a non-evaporable getter with high porosity to the enclosure of the VIPs. A further objective is to minimize water permeation and corrosion of the VIPs. 
     SUMMARY OF THE INVENTION 
     Aspects and advantages of the disclosure will be set forth in part in the following description, or may be apparent from the description, or may be learned through practice of the disclosure. 
     The present invention is a vacuum insulated panel (VIP) for increasing the thermal insulation surrounding a structure or volume, and a novel method for manufacturing the VIP. The VIP comprises at least two thin pieces of metal foil material, such as stainless steel or titanium alloy, welded together initially adjacent to all but one of the edges of the metal foil, forming an enclosure between the pieces of metal foil. A support core material is disposed in the enclosure or an enclosure is placed around the outside of a core material. The opening between the non-welded edges of metal foil forming the enclosure are clamped together, and gas, such as air, is evacuated from the enclosure through an aperture in one of the pieces of metal foil, the aperture located adjacent the clamped opening. A molecule-absorbing getter is also inserted into the enclosure before, during or after the gas evacuation process. Upon the completion of the gas evacuation from the enclosure, the opening formed between the metal foil pieces is welded shut along a line to the interior of the evacuation aperture. The clamped portion of metal foil material, along with the gas evacuation aperture, is then removed from the completed VIP and recycled. 
     The VIP disclosed in this application is made by welding two thin stainless steel or titanium alloy foils together with a seam welder on three sides of the enclosure, clamping the remaining side in a fixture and evacuating the enclosure through an aperture in one of the metal foils. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front-side perspective view of an embodiment of the vacuum insulating panel of the present invention, shown prior to evacuation of gas from the enclosure formed by the two welded metal foil pieces. 
         FIG. 2  is a cross-sectional schematic view of the vacuum insulating panel of  FIG. 1 , taken along line  2 - 2  of  FIG. 1 , showing a supporting core inside the enclosure. 
         FIG. 3  is a schematic illustration of a plurality of several trapezoidal shaped vacuum insulting panels of the present invention assembled side by side. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention relates to vacuum insulation panels that have arbitrary sizes.  FIG. 1  shows a top perspective view of the metal foil enclosure prior to the VIP being formed.  FIG. 2  is a cross-sectional view of the VIP along line  2 - 2  of  FIG. 1 . Current aluminum/plastic clad VIPs are puncture prone, can have significant thermal losses at their edges, and lose R value when exposed to the environment. The advantage of certain thin metals with low thermal conductivity, high corrosion resistance, and high strength is that they have a higher puncture resistance than aluminum foil, or metalized plastic film, and that edge losses, which are proportional to the product of thickness and thermal conductivity of the edge material are reduced. 
     During their service life, VIPs will be subjected to outdoor conditions that include such potentially detrimental factors as high/low temperatures, humidity, and sun irradiation. In addition, direct interaction with atmospheric precipitation, wind, and creatures can also degrade the VIPs. Since aluminum foil has a thermal conductivity around 15 times greater than stainless steel, using stainless steel foil eliminates the puncture prone and high thermally conductive aluminum exterior of the current VIPs. Other non-corrosive foil materials with a low thermal conductivity can also be used, such as titanium alloy. Certain titanium alloy foils can have half the thermal conductivity of stainless steel, but are about ten times the price of stainless steel per square foot. Titanium alloy can be used in applications where the local price of energy justifies the higher cost, and transportation of valuable cargo such as vaccines, blood, or human organs for transplantation, where better temperature isolation is justified by the price of loss of cargo and the high cost of air shipment. 
     An illustrated embodiment of the VIP  10  in  FIG. 1  is clad in 51 μm (0.002 inch) thick metal foils  12 ,  14  having exceptionally low corrosion rates. The foils  12 ,  14  are made from the following low thermal conducting materials, preferably having thermal conductivity lower than 26 W/(m×K); 321, 316 L or 304 L stainless steel; titanium alloys such as Ti (15 Mo-3 Nb-3 Al-2 Si), Ti (6 A1-5 Zr-0.5 Mo-0.25 Si), Ti (3 Al-2.5 V), and Ti (3 Al-2.5 V-0.05 Pd), or other low thermal conducting materials such as Hastelloy C™. The foils  12 ,  14  form the outer envelope  16  of the VIP  10 , and also form the interior walls  18 ,  20  that create an enclosure  24  housing the supporting core  22 . The core  22  aids in maintaining the shape of enclosure. The core  22  is adapted to support external pressures of approximately one atmosphere while minimizing the transfer of heat across the vacuum insulated panel. 
     The core  22  of the VIP  10  is also selected from materials having a high ratio of strength to thermal conductivity. In an embodiment of the present invention, the core  22  is made of fumed silica, a tensile structure or other mechanical structures. Fumed silica is produced by pyrolysis of SiCl 4 , which is generated during the production of polycrystalline silicon. In an embodiment, the fumed silica of the illustrated embodiment is comprised of the raw materials: (1) 60% amorphous silica (SiO 2 ), (2) 35% ilmenite (FeTiO 3 ) as an opacifier, and (3) 5% ceramic fiber used to strengthen the material. SiO 2  has a lower thermal conductivity than stainless steel. The fumed silica core  22  maintains the shape of the outer envelope  16 , as shown in  FIG. 2 . 
     The core  22  is inserted between metal foils  12 ,  14 , and the two foils are welded together along single connected paths on three sides  26 ,  28 ,  30  of the envelope  16  by a seam welder, laser, plasma welder, brazing system or other welder as is known in the art. In other embodiments of the present invention, the foils can also be welded along multiply connected paths to create desired continuous interior paths to meet the users&#39; needs. The remaining open side  32  is clamped in a fixture  34  to hermetically close the opening between the two foils  12 ,  14  along side  32 . The fixture  34  can include two gaskets, and the remaining side  32  is clamped between two gaskets  36 . An aperture  40  is located in one of the foils  12  a predetermined short distance from remaining side  32 . A diffuser  38  is inserted beneath aperture  40  such that aperture  40  communicates with enclosure  24  formed between foils  12 ,  14 . 
     Next, a vacuum tube (not shown) is connected to aperture  40  such as by mechanical or magnetic means as are known in the art, and the gas, such as air, is evacuated from enclosure  24 . Supporting core  22  maintains the shape of VIP  10  as shown in  FIG. 2 . Upon completion of the evacuation process to the parameters described below, the VIP  10  is welded along weld line  42  shown in  FIGS. 1 and 2  to complete the hermetic sealing of enclosure  24 . Weld line  42  is located on the side of aperture  40  opposite fixture  34 . 
     After the welding process along line  42  is complete, the fixture  34  is opened, and the foil material  12 ,  14  remaining between weld line  42  and remaining side  32  is trimmed and recycled. This completes the manufacturing process of VIP  10 . 
     Other polygon shaped VIP  10  packages can be used, i.e. hexagon. Round shaped packages can also be welded by having a curved fixture  34  to seal the remaining side  32 . 
     In the present invention, the enclosure  24  will be evacuated between about 10 −2  torr and 10 −6  with a dual stage roughing pump (not shown) in around 300 seconds through the aperture  40  prior to resistance weld sealing. The resistance welding occurs at between 7 m/sec and 1.3 cm/s. The evacuation will be through a 25 mm or larger inner diameter tube in the illustrated embodiment. Multiple apertures  40  can be used at one or more sides of the VIP  10  to speed up the pumping process if increasing the diameter of the pumping aperture  40  and minimizing diffuser  38  impedance does not reduce pumping time to a satisfactory level. Outgassing is minimized by baking out all components prior to use, and heating the VIP during the sealing process. 
     Maintaining the vacuum level in enclosure  24  is very important to the VIP  10  because if the vacuum level decreases, the R factor of the VIP decreases. During the step of evacuating the VIP, activated getters  44  ( FIG. 2 ) will be added into the enclosure  24  through the evacuation aperture  40 , just before the seal along weld line  42  is complete. The getter&#39;s role is to absorb chemical molecules that permeate through the metal foils  12 ,  14  or outgas from the enclosure  24  or the fumed silica core  22 , thereby keeping the vacuum below 10 −2  torr in the enclosure  24 , and extending the VIP&#39;s lifetime to possibly several decades. The getters used in prior VIP construction degrade with time. This is primarily due to water vapor penetrating the aluminum/plastic exterior foil at 1-4 ng/(m 2 ×s×Pa). It has been observed that without a getter, a VIP&#39;s internal pressure can exceed 10 −2  torr in a few minutes after completion, and the thermal insulation would deteriorate. Stainless steel and titanium alloys have a much lower permeability to water vapor and an upper limit was set by Norton at 10 −13  torr×L/(cm 2 ×s) at 25° C. with 0.025 inch thick material. Scaling this limit to 0.002 inch thick foil, the permeation would be below 12 pg/(m 2 ×s×Pa). A VIP made of stainless steel or titanium alloy would need much less getter and desiccant than a presently available VIP. 
     A typical getter  44  used for the present VIP invention is non-evaporable with a high specific surface area per gram of getter in the range of 800 to 2000 meters 2 /gm of getter. The getter material can also be selected from materials that meet the previous criteria and have a surface area per cubic centimeter of getter in the range of 300 to 3000 meters 2 /cubic centimeter of getter A form of getter  44  is distributed by SAES with a capacity of 10 torr×L and may contain 0.17, 0.85, or 2.7 gm of BaLi 4 , Cao, Co 3 O 4  respectively. This represents about 2% of the capacity or approximately one H 2 O molecule for every 50 getter molecules. Because the getter is placed into the enclosure  24  just before the enclosure  24  is completely sealed, the getter  44  can be stored prior to use at high temperature and in a high vacuum so that its full pumping capacity can be preserved for the VIP. The contact between the getter  44  and the ambient gas is greatly eliminated by inserting the getter into aperture  40  immediately prior to sealing the VIP along weld line  42 . 
     Other getters can be used including Carbide Derived Carbon (CDC), and Calcium. CDC has numerous advantages as a getter for VIPs. CDC is inexpensive, and has extremely high porosity so it has a very high surface area. CDC has very high affinity for H 2 O, O 2 , N 2 , and H 2 . Properly prepared, CDC is non-toxic which minimizes waste disposal issues, and can be reused. 
     To obtain a calcium getter, calcium chloride powder is evacuated in a silica test tube and heated until it decomposes. After the chlorine gas is evolved, the calcium will be allowed to cool, and remain in vacuum until needed. If the calcium agglomerates after being reduced, the calcium chloride will be mixed with an inert powder such as Al 2 O 3 . 
     The getter  44  will be pressed into a pellet if necessary to facilitate delivery and/or localization within the VIP enclosure  24 . A recess can be embossed into the walls of enclosure  24  to mechanically secure the getter pellet. 
     If necessary for storage before use without breaking the vacuum, the getter  44  will be poured into thin aluminum foil bags. These bags will be sealed by ultrasonic welding and their edges notched to facilitate opening under vacuum. They will in effect be similar to sugar packets used in restaurants, however they will contain a getter material that is prevented from reacting with the atmosphere by the aluminum foil which has negligible permeability. Keeping powders of the getter materials under ultra-high vacuum (UHV) conditions allows costs to be efficiently controlled. 
     If a leak appears on the clamped side along the edge  32  of VIP  10 , the leak can be eliminated by seam welding along the welding line  42  after the diffuser  38  is inserted into the bag, or the leak can be made manageable by pumping on the edge leaks with an additional vacuum pump, seal, and aperture. The VIP  10  components will be kept in a nitrogen environment at an elevated temperature to minimize absorbed moisture. 
     After the VIP  10  is completely evacuated and welded on the remaining side  32 , the foil edges of the VIP are trimmed along the welding lines adjacent sides  26 ,  28  and  30 . 
     Turning to  FIG. 3 , four VIPs with beveled lateral edges  46 ,  48  are shown tiled along their beveled edges  46 ,  48  with minimum gaps. The beveled edges configure the VIPs with a trapezoidal cross-section. Beveled edges  46  and  48  reduce heat loss by lengthening the thermal path of the VIP, and minimizing gaps between panels. The VIPs of the illustrated embodiment of the VIP have a uniformed bevel angle  50  of θ. Beveling the edges of the VIP lengthens the heat path by 
               1     sin   ⁢           ⁢   ϑ       .         
The perimeter of a square VIP is 4×S_VIP, ( FIG. 2 ) and the heat flow along a beveled edge will be
 
               Q   bevel_edge     =       K   edge     ×   4   ×   S_VIP   ×   t_SS   ×       Δ   ⁢           ⁢   T   ×   sin   ⁢           ⁢   ϑ     t_VIP             
where K edge  is the thermal conductivity of the edge material, and assuming the sheet metal foil material  12 ,  14  thickness is approximately unchanged. In making the VIPs, decreasing the bevel angle  50  and thinning the foil  12 ,  14  could further reduce the edge heat losses. The crossover size is where there are equal heat flows through the area and edge of a square VIP, and a smaller crossover size requires lower edge losses.
 
     The heat flow through the area of a square VIP Q VIP     —     area  is given by 
               Q   VIP_area     =       K   VIP_area     ×     S_VIP   2     ×         Δ   ⁢           ⁢   T     t_VIP     .             
K VIP     —     area  is the effective thermal conductivity, the thermal conductivity K VIP     —     area  is around 0.0025 W/(m×K) with a fumed silica core, as long as the pressure in the enclosure  24  is below around 10 −2  torr (1.3 Pa). The thermal conductivity of the 0.002 inch thick titanium alloy is K Ti =8.3 W/(m×K) and this gives a crossover size of 1.6 feet if θ=45°. S_VIP 2 ×t_VIP is the volume of the square VIP. The thickness of the VIP is t_VIP ( FIG. 2 ). Researchers measured a maximum mass loss of 5 mg/(m 2 ×year) from mechanically polished stainless steel samples exposed to precipitation with a pH of 2. This corresponds to a loss of 0.6 nm/year from the 51 μm thick stainless steel.
 
     One embodiment of the presently disclosed VIP will be sealed within wax paper to prevent moisture from condensing on the foils  12 ,  14 . Moisture touching the foils is undesirable since it can lead to corrosion, and possibly permeation through the foils in the form of atomic hydrogen. 
     The VIPs of the present invention can be manufactured with openings for wires and conduits, and in a variety of shapes. Except for the shape with trapezoidal cross-section mentioned above, other shapes include: square, rhomboid, circular, rectangular, and pillow-shaped. Unlike cellular plastic insulation, such as polyurethane foam, the present VIP is non-flammable, does not emit toxic gasses when exposed to a flame, and will not lose R value over decades since the VIP does not leak and there is no foaming agent to diffuse out of the material. Unprotected foam can lose 20% of its R value in 2 years. 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural or method elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.