Cast pressure vessel

Abstract

A single or multi-section cast pressure vessel (100) includes one or more longitudinally extending sections (104) positioned laterally adjacent to one another. Interior cavities (120) of the sections (104) may be connected via apertures (144) extending through interfaces between laterally adjacent sections (104). A base (132) may be included for supporting the pressure vessel (100) in an upright orientation. A method of manufacturing the single or multi-section cast pressure vessel (100) includes locating (148) a core (166) within an outer mold (168) to form a mold cavity (170), filling the cavity (170) with molten metal, and subjecting (164) the resulting casting to a heat treatment process.

Description

CAST PRESSURE VESSELTECHNICAL FIELD

[0001] The present disclosure relates generally to pressure vessels. More particularly, the present disclosure relates to multi and single-section pressure vessels suitable for, without limitation, holding a pressurized gas such as an air supply for hostile or rescue environments, an air supply for underwater diving, and / or an oxygen supply for medical applications.BACKGROUND

[0002] The use of pressure vessels, or pressurized gas vessels, for breathable primary or supplemental air supplies has become widely accepted in recreational, industrial, medical, and public safety arenas. Pressure vessels are used underwater for recreational underwater diving, termed “SCUBA” (Self Contained Underwater Breathing Apparatus) diving, and are also used for industrial or commercial diving applications such as ship repair, offshore drilling operations, underwater salvage, pipeline repair, as well as to military applications, search and rescue operations, and in underground environments such as mines.

[0003] In above-water applications, pressure vessels used as Self-Contained Breathing Apparatuses (SCBAs) are invaluable for personnel working in hostile or rescue environments. SCBAs are used by fire fighters entering smoke filled or toxic environments, police working at contaminated crime scenes, underground mine rescue teams entering “bad air” or smoke, HAZMAT teams working in contaminated environments, and industrial maintenance personnel working in confined spaces or in toxic environments. SCBAs are also strategically placed in chemical plants, laboratories, refineries, nuclear facilities, paper mills and underground mines for employees to be used as a “self-rescuer” during an emergency.

[0004] In medical applications, a pressure vessel containing pressurized oxygen (i.e., an oxygen tank) may be vital to medical professionals where patients require a supplemental oxygen supply to maintain an adequate blood oxygen level. In emergency scenarios, an oxygen tank may be used to resuscitate a patient whose breathing has been impaired due to a medical complication, such as during cardiac arrest. An oxygen tank may also be used in non-emergency scenarios, such as to provide oxygen to a patient whose breathing has slowed due to the administration of anesthesia during an operation, or to administer oxygen therapy to patients suffering from a respiratorycondition. Furthermore, many persons regularly carry an oxygen tank for personal medical use, such as to self-administer oxygen therapy throughout the day.

[0005] Some pressure vessels have been formed of aluminum. Historically, aluminum pressure vessels have been manufactured through a reverse extrusion process, in which an aluminum slug is pressed into a cup shape to form the body of the pressure vessel. A spin-forming process is subsequently used to form the open-end of the cup shape into the neck of the pressure vessel. These methods have inherent limitations in design, materials, and performance. For example, spin-forming tends to degrade the material properties of affected areas of the pressure vessel and is prone to folding. Folding can result in neck cracking, which is a common source of aluminum cylinder failure.SUMMARY

[0006] Disclosed herein are implementations of cast pressure vessels and methods for making the cast pressure vessels.

[0007] A pressure vessel (e.g., a cast pressure vessel) may define a longitudinal direction, a lateral direction, and a transverse direction that are substantially orthogonal to one another. In selected implementations, a cast pressure vessel may comprise a first longitudinally extending section that is connected to a second longitudinally extending section. Each of the first section and the second section may comprise a first head having a curved shape (e.g., comprise a first substantially hemispherical head or have a substantially hemispherical shape), a second head having a curved shape (e.g., comprise a second substantially hemispherical head or have a substantially hemispherical shape), a semi-cylindrical side wall that extends between the first head and the second head, and a cavity that is defined at least partially by the first head, the second head, and the side wall. The side wall may monolithically extend from the first head at a first transition defined by a change from the curved shape of the first head to the substantially semi-cylindrical shape of the side wall. Similarly, the side wall may monolithically extend from the second head at a second transition defined by a change from the curved shape of the second head to the substantially semi- cylindrical shape of the side wall. One of the first section or second section may extend longitudinally beyond the other and the corresponding head (e g., the head that extends longitudinally beyond an adjacent head) may form or include a base upon which the pressure vessel may stand. A first aperture may be located inside the pressure vessel and provide fluid communication between the cavity of the first section and the cavity of the second section. The firstaperture may extend in the lateral direction and may be positioned longitudinally outboard of the first transition.

[0008] Another aspect of the disclosure is a method of casting a pressure vessel comprising locating a sacrificial inner core within an outer mold to define a mold cavity. The method may also include connecting a reservoir containing molten metal therein to a mold cavity to provide fluid communication between the reservoir and the mold cavity. The method may further include transferring the molten metal into the mold cavity. Finally, the method may include controlling a thermal profile of the mold cavity to cool the molten metal within the mold cavity so the solidification front propagates in a particular manner (e.g., inside to outside and top to bottom).

[0009] Yet another aspect of the disclosure is a method of casting a pressure vessel. The method may comprise liquifying an aluminum-copper alloy. The method may also include transferring the molten alloy into a mold cavity. The method may further include solidifying the molten alloy in the mold cavity to form an as-cast pressure vessel. Finally, the method may include producing a treated pressure vessel having a fracture toughness greater than or equal to about 42 ksi^ in by subjecting the as-cast pressure vessel to a T4 heat treatment or a modified T4 heat treatment.BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The disclosure is best understood from the following detailed description when read in conjunction with the accompanying drawings. It is emphasized that, according to common practice, the various features of the drawings may not be to-scale. On the contrary, the dimensions of the various features may be arbitrarily expanded or reduced for clarity.

[0011] FIGS. 1 A and IB are perspective view illustrations of an implementation of a cast pressure vessel in accordance with the present disclosure.

[0012] FIG. 2 is a cut-away perspective view illustration showing an interior of the cast pressure vessel of FIGS. lA and IB.

[0013] FIG. 3 is a cross-sectional view of the cast pressure vessel of FIGS. 1 A and IB.

[0014] FIGS. 4 A and 4B are perspective view illustrations of another implementation of a cast pressure vessel in accordance with the present disclosure.

[0015] FIG. 5 is a cross-sectional view of the cast pressure vessel of FIGS. 4A and 4B.

[0016] FIGS. 6A and 6B are perspective view illustrations of another implementation of a cast pressure vessel in accordance with the present disclosure.

[0017] FIG. 7 is a flowchart that shows a process for casting a pressure vessel in accordance with the present disclosure.

[0018] FIG. 8 is a perspective, exploded view illustration showing implementations of an outer mold, a core, and a base mold for casting the pressure vessel of FIGS. 1A and IB.

[0019] FIG. 9 is a perspective view illustration of the outer mold, the core, and the mold base ofFIG. 8 in an assembled configuration.

[0020] FIG. 10 is a perspective view illustration of one half of the outer mold of FIG. 8.

[0021] FIG. 11 A is a perspective view illustration of a first half of the core of FIG. 8.

[0022] FIG. 1 IB is a perspective view illustration of a second half of the core of FIG. 8.

[0023] FIG. 12 is a perspective view illustration of the base mold of FIG. 8.

[0024] FIG. 13 is a perspective view illustration of another implementation of a base mold for casting the pressure vessel of FIGS. 4A and 4B.

[0025] FIG. 14 is a cross-sectional view of the assembly of FIG. 9 taken along line A-A.

[0026] FIG. 15 is a cross-sectional view of the assembly of FIG. 9 taken along line B-B.

[0027] FIG. 16 is a cross-sectional, schematic view illustration showing the assembly of FIG. 9 connected to an implementation of a reservoir.

[0028] FIG. 17 is a flowchart that shows a process for casting a pressure vessel in accordance with the present disclosure.DETAILED DESCRIPTION

[0029] The present disclosure relates to implementations of a method of casting a pressure vessel having properties suitable for, without limitation, holding a pressurized gas to be used as an air supply for hostile or rescue environments, an air supply for underwater diving, an oxygen supply for medical applications, a gas supply for welding applications, or the like. The disclosure also relates to implementations of single and multi-section pressure vessels that may be manufactured using the implementations of the method disclosed herein. Selected implementations of the disclosed pressure vessels comprise a seamless unitary structure of metal material and are configured to operably contain an internal gas pressure of at least about 2000 psi at ambient atmospheric external pressure. For example, an implementation of the pressure vessel for use in selected medical applications (e.g., storing oxygen for medical use) may configured to operably contain an internal gas pressure of at least about 2200 psi at ambient atmospheric external pressure. Alternatively, an implementation of the pressure vessel for use in selected underwater or SCUBA applications may be configured tooperably contain an internal gas pressure of at least about 3442 psi at ambient atmospheric external pressure. Certain implementations of the pressure vessel of the present disclosure have been broadly discussed as a vessel for containing air (e.g., breathable air). However, it is contemplated that the pressure vessel can be used to store other gases or liquids for other applications including medical gases, welding gas, automotive or aerospace fuel cells, or the like.

[0030] Implementations of the pressure vessel provide a volumetrically efficient configuration that enables a user to store air in a smaller, less obtrusive pressure vessel than is possible with conventional pressure vessel designs. Since the contained volume of air may be distributed across a series of semi-cylindrical sections, selected implementations offer a thinner, or lower, profile than a conventional air cylinder. The low-profile pressure vessel reduces the user's entrapment risk when entering a confined space or an area with reduced clearance. Additionally, the semi-cylindrical sections may be formed where a center point of each section lies on a shallow arc. This allows the sections to be substantially contoured around a user's back, further reducing the distance the pressure vessel extends away from the user.

[0031] With respect to underwater applications, implementations of the pressure vessel offer improved hydrodynamics in comparison to a conventional air cylinder due to their lower profile, shorter length, and closer conformity to a diver's body. A conventional air cylinder protruding above the user's back has an effect similar to the rudder of a sailboat in that as water moves past the cylinder, the cylinder tends to “steer” the diver. While the propensity of the air cylinder to steer a diver is negligible under most circumstances, it can be significant if the diver is swimming across or against a strong current, or if the diver is using an underwater sled or other propulsion device.

[0032] U.S. Patent No. 8,020,722 disclosing a seamless, multi-section pressure vessel is hereby incorporated by reference.

[0033] Referring to FIGS. 1A, IB, 2, and 3, in selected implementations, a pressure vessel 100 (e.g., a cast pressure vessel) may include a body 102 configured to hold pressurized gas therein. In some implementations, the body 102 may be seamless (e.g., monolithic), such that it is formed as a unitary structure having a closed geometry (excluding any included valve or cleanout ports) for containing pressurized gas therein without the use of joining means such as fastening, welding, brazing, or the like. The body 102 may be formed from an aluminum alloy (e.g., a casting aluminum alloy, an aluminum-copper alloy, A206 aluminum, an aluminum alloy 2xxx, or the like).

[0034] The body 102 may comprise one or more sections 104 extending longitudinally and positioned laterally adjacent to one-another. For example, the body 102 may comprise three of thesections 104, such as an intermediate section 106 sandwiched between two symmetrical implementations of the outer sections 108. In some implementations, however, the outer sections 108 may not be symmetrical. More than three of the sections 104, or even more than one row of the sections 104, may also be employed. That is, a different number of the sections 104 may be disposed in an additional row of the sections 104, such a row being offset from the first row. With such an arrangement, wasted space between the sections 104 may be minimized as the sections 104 of the additional row may be partially received in recesses between the sections 104 of the first row.

[0035] Each of the sections 104 may comprise a side wall 110 that extends between, and is a monolithic extension of, an upper head 112 and a lower head 114. An upper transition 116 may be located where the upper head 112 monolithically extends from the side wall 110, and a lower transition 118 may be located where the lower head 114 monolithically extends from the side wall 110. Each of the sections 104 may include a cavity 120 at least partially defined by the side wall 110, the upper head 112, and the lower head 114, and inside which pressurized gas may be stored. In certain implementations that include multiple of the sections 104, the sections 104 may include a dividing wall 122 (e g., a dividing wall 122 that is substantially flat) positioned at a common interface between each adjacent section. In such implementations, the cavity 120 of the sections 104 may be further defined by the dividing wall 122.

[0036] Due to the pressure vessel 100 being formed through a casting process as opposed to conventional methods such as reverse extrusion, complex geometries may be achieved. For example, a geometry of an exterior surface 124 of the body 102 may substantially deviate from a geometry of an interior surface 126 of the body 102. This enables the interior surface 126 to be optimized to withstand high pressure-induced forces, while the exterior surface 124 may include other geometries to accommodate various features thereon.

[0037] For example, in select implementations where the body 102 comprises at least three of the sections 104, such as two of the outer sections 108 and one or more of the intermediate sections 106, the exterior surface 124 of the side wall 110 of the outer sections 108 may be substantially semi-cylindrical, while the interior surface 126 of the side wall 110 (which includes portions of the dividing wall 122) may remain substantially cylindrical, which is an advantageous geometry for withstanding pressure-induced forces. Furthermore, in such an implementation, the exterior surface 124 of the side wall 110 of the one or more of the intermediate sections 106 may be arcuately curved, while the interior surface 126 of the side wall 110 may also remain substantially cylindrical.

[0038] The interior surface 126 of the upper head 112 of one or more of the sections 104 may be substantially hemispherical, which is an advantageous geometry for withstanding pressure-induced forces. Alternatively, the interior surface 126 of the upper head 112 of one or more of the sections 104 may be substantially semi-ellipsoidal, tori spherical, or the like. The exterior surface 124 of the upper head 112 may include features such as a neck 128 on which a valve port 130 may be located. The neck 128 and the valve port 130 may be positioned at a central location of the upper head 112 (i.e., in axial alignment with a longitudinal axis of the corresponding one of the sections 104) and may extend through the upper head 112 to provide fluid communication between the cavity 120 and an exterior of the pressure vessel 100. The valve port 130 may include threads that are configured to engage corresponding threads of a valve 131 (shown schematically) for filling the pressure vessel 100 with gas and dispensing gas therefrom.

[0039] Although the neck 128 and the valve port 130 are shown disposed on the upper head 112 of the intermediate section 106, the neck 128 and the valve port 130 may be disposed on the upper head 112 or the lower head 114 of any of the sections 104. Furthermore, additional necks and corresponding valve ports (not pictured) may be disposed on the upper head 112 and / or lower head 114 of any of the sections 104 on which the neck 128 is not already disposed. In underwater applications (i.e., SCUBA applications), for example, the neck 128 and the valve port 130 may support a primary regulator while an additional neck and corresponding valve port may support a secondary regulator.

[0040] In selected implementations, the interior surface 126 of the lower head 114 of one or more of the sections 104 may be substantially hemispherical. Alternatively, the interior surface 126 of the lower head 114 of one or more of the sections 104 may be substantially semi-ellipsoidal, torispherical, or the like. The exterior surface 124 of one or more of the lower heads 114 may include features such as a base 132 (or a portion of the base 132) to support the pressure vessel 100 in an upright position. The base 132 may be formed integrally (e.g., monolithically) with the body 102 and may extend in the longitudinal direction away from one or more of the sections 104 and terminate at a plane 134. In select implementations, the base 132 may include a rib 136 that extends continuously from the side wall 110 of one or more of the sections 104 in the longitudinal direction and terminates at the plane 134. In selected implementations, the rib 136 may extend from the exterior surface 124 of the intermediate section 106.

[0041] In certain implementations, the base 132 may include a central portion 138 that extends downward from the lower head 114 of one or more of the sections 104. In other implementations,the base 132 may not be formed integrally with the body 102, and rather may comprise a plastic or vinyl boot (not pictured) having struts or fins extending therefrom that may cap the lower head 114 of one or more of the sections 104.

[0042] In selected implementations, one or more cleanout ports 140 may be disposed on the lower head 114 of one or more of the sections 104 and may be operable to facilitate the removal of a sacrificial inner core that may be used to form the body 102. Moreover, the cleanout ports 140 may be positioned at a central location of the lower head 114 (i.e., in axial alignment with a central longitudinal axis of the corresponding one of the sections 104) and may extend through the lower head 114 of one or more of the sections 104. The cleanout ports 140 may define a profile on the sections 104 having any suitable shape, including but not limited to a circular shape or an elliptical shape. In implementations where the body 102 includes the base 132, the cleanout ports 140 may extend therethrough.

[0043] The cleanout ports 140 may also be configured to accommodate plugs 142 to seal the cleanout ports 140 after the removal of the sacrificial inner core from the body 102. The plugs 142 may engage the cleanout ports 140 via corresponding threads, interference fit, or any other means suitable for the plugs 142 to remain sealed when the pressure vessel 100 is pressurized.

[0044] Furthermore, to aid in the removal of the sacrificial inner core, it may be beneficial to maximize a size of the cleanout ports 140. For example, the size of the cleanout ports 140 may maximized while still providing a safety factor of at least ten (10) with a minimum of six (6) full threads engagement. Therefore, in certain implementations and depending on the size of the pressure vessel 100, the cleanout ports 140 may have a diameter between about 2 inches and about 2.625 inches. In other implementations that include only one of the sections 104 and the side wall 110 is substantially cylindrical, the cleanout port 140 may have a diameter of about one-half of a diameter of the exterior surface 124 of the side wall 110.

[0045] As illustrated, the cleanout ports 140 may be located on the lower head 114 of the outer sections 108. However, in other implementations, the cleanout ports 140 may be located on the upper head 112 or the lower head 114 of any of the sections 104. Furthermore, additional cleanout ports (not pictured) may be located on the upper head 112 and / or lower head 114 of any of the sections 104 on which the cleanout ports 140 are not already located.

[0046] In implementations in which the interior surface 126 of the upper head 112 and the lower head 114 are substantially hemispherical, the upper transition 116 and the lower transition 118 may be referred to as tangent portions, as in such implementations the side wall 110 may extendtangentially away from the curvature of the substantially hemispherical portions of the upper head 112 and the lower head 114. Despite implementations of the interior surface 126 of the side wall 110 being described as substantially cylindrical, and implementations of the interior surface 126 of the upper head 112 and the lower head 114 being described as substantially hemispherical, a traverse cross-section of the interior surface 126 of the sections 104 may nevertheless be characterized as substantially semi-circular, square, rectangular, trapezoidal, or the like.

[0047] In implementations including multiple of the sections 104, one or more communication apertures 144 may be provided on the dividing wall 122 of the sections 104 to provide fluid communication between the cavity 120 of the sections 104 that are adjacent to one-another. The communication apertures 144 enable the cavity 120 of each of the sections 104 to be fdled or discharged from the valve 131 of only one of the sections 104. Furthermore, the presence of communication apertures 144 may serve to equalize pressure between sections, enabling a relatively high internal gas pressure to be safely accommodated.

[0048] Furthermore, where gas pressure is exerted upon the interior of a pressure vessel having cylindrical side walls and hemispherical heads, the resulting stress acting along the cylindrical side walls, termed tangential or “hoop” stress, may be approximately two times greater than the longitudinal or axial stress acting on the hemispherical heads of the pressure vessel. Therefore, in certain implementations, to minimize the pressure induced stresses that may act upon the material forming or surrounding the communication apertures 144, the communication apertures 144 may be positioned on the upper head 112 or the lower head 114 of the sections 104, rather than on the side walls 110. In other words, the communication apertures 144 may be extending laterally or side-to- side at a position that is outboard of the upper transition 116 and the lower transition 118 (i.e., the tangent portions) of adjacent sections in the longitudinal direction. In such implementations, portions of the upper head 112 and the lower head 114 of the sections 104 adjacent to one-another may be connected, and the exterior surfaces 124 thereof may be monolithically formed as a single unit.

[0049] The communication apertures 144 may define a profile on the dividing wall 122 having any suitable shape, including but not limited to a circular shape or an elliptical shape. A size of the communication apertures 144 may be dependent upon a thickness of the dividing wall 122. Furthermore, the communication apertures 144 may include radiused edges that extend around the circumference of the communication apertures 144 on the dividing wall 122. Furthermore, in selected implementations, the communication apertures 144 may be reinforced with correspondingcollars or thicker regions (not pictured) that are formed in the dividing wall 122 and that extend circumferentially around each of the communication apertures 144. However, including these collars may result in increased manufacturing complexity due to their placement on the interior of the body 102. Accordingly, in order to support or enable use of a single piece core, all such collars may be omitted and a thickness of the dividing wall 122 (e.g., a thickness of an entire dividing wall 122) may be increased to properly resolve the increase in stress occasioned by the communication apertures 144. As a result, the dividing wall 122 may be thicker than side wall 110. For example, in selected implementations, the dividing wall 122 (e.g., each dividing wall 122) may be between about 1.2 and about 2.0 times thicker than the side wall 110. In certain implementations, the dividing wall 122 may be about 1.5 times thicker than the side wall 110.

[0050] In selected implementations, a mass of the pressure vessel 100 may be reduced by varying the thickness of the side walls 110, the upper head 112, and the lower head 114. As noted above, the tangential stress or “hoop” stress that acts upon the side walls 110 of the sections 104 may be approximately two times greater than the longitudinal or axial stress acting on the upper head 112 and the lower head 114 of the sections 104. Accordingly, in certain implementations, the thickness of the upper head 112 and the lower head 114 may be less than that of the side wall 110. Additionally, the thickness of the side wall 110 may be reduced if the corresponding one of the sections 104 is reinforced with a filament-wound belt (not pictured). Such a belt can be constructed using a lightweight material such as fiberglass, graphite, Kevlar, or a combination of materials. In order to avoid gaps formed under the filament- wound belt, the exterior surface 124 of the body 102 between the sections 104 must be substantially planar. This may be accomplished by providing lightweight shims (not pictured) configured to fill the gaps between adjacent ones of the sections 104 on either side of each interface, or by configuring the sections 104 of the body 102 such that the exterior surface 124 is planer. Filament- wound pressure vessels may offer an optimal capacity to weight ratio and may be ideal for above-water SCBA applications.

[0051] In selected implementations, the body 102 may be formed as a monolithic or unitary structure using a semi -permanent mold, permanent mold with sacrificial sand core, or investment casting methods. The body 102 may be cast of a low melting point alloy of aluminum using, for example, a semi-permanent mold or a permanent mold with a sacrificial sand core. In other implementations, the body 102 may be formed from ductile iron. In still other implementations, high melting point alloys of a steel, such as a stainless steel, may be used with investment castingtechniques. Other casting methods and metal materials are also contemplated as suitable for implementing implementations of the pressure vessel 100.

[0052] Referring to FIGS. 4A, 4B, and 5, in selected implementations, the body 102 may comprise only two of the sections 104. In such implementations, the exterior surface 124 of the side wall 110 of the sections 104 may be substantially semi-cylindrical, while the interior surface 126 of the side wall 110 (which includes a portion of the dividing wall 122) may remain substantially cylindrical. The rib 136 may extend from the exterior surface 124 of one of two of the sections 104

[0053] Referring to FIGS. 6A and 6B, in certain implementations, the body 102 may comprise only one of the sections 104. In such implementations, the exterior surface 124 of the side wall 110 may be substantially cylindrical, while the interior surface 126 of the side wall 110 may also be substantially cylindrical. The rib 136 may extend from the exterior surface 124 of the single one of the sections 104.

[0054] Referring to FIGS. 7-15, one implementation of a method 146 of casting the body 102 of the pressure vessel 100 is illustrated. The method 146 may include locating 148 an inner core 166 (e.g., an inner core 166 that is sacrificial) within an outer mold 168 (e.g., an outer mold 168 that is permanent) to define a mold cavity 170. The mold cavity 170 may substantially match the geometry of the body 102. In select implementations, locating 148 the inner core 166 may be facilitated by a base mold 172. The inner core 166, the outer mold 168, and the base mold 172 may be collectively referred to as a mold assembly 174.

[0055] The method 146 may further include liquifying 150 (i.e., melting) the metal (e.g., an aluminum alloy, casting aluminum alloy, aluminum-copper alloy, bronze metal alloy, steel alloy, or the like) that will be used to form the pressure vessel 100. Once in molten form, if required based on the casting equipment configuration, the metal may be transferred 152 into a reservoir that will support the casting process. Alternatively, a vessel used to liquify 150 the metal may also function as (or be moved into the role of) a molten metal reservoir. In such an implementation, the transferring 152 may be omitted.

[0056] At some point, a mold cavity 170 may be connected 154 to a reservoir such that a path is established for molten metal to flow from the reservoir to the mold cavity 170. Thereafter, molten metal may be transferred 156 from the reservoir into the mold cavity 170. In selected implementations, this may be accomplished by pressurizing the reservoir with an inert gas to force or push molten metal out of the reservoir and up into the mold cavity 170. Alternatively, or in addition thereto, pressure within the mold cavity 170 may be reduced. Accordingly, molten metalcontained in the reservoir may be subjected to an external pressure that is higher than a pressure of gas within the mold cavity 170. Thus, in selected implementations, a low-pressure casting process may be used.

[0057] With molten metal in the mold cavity 170, a thermal profile of the mold cavity 170 may be controlled 158 so that a solidification front propagates through the mold cavity 170 such that the desired microstructure and resultant post heat treatment mechanical properties are achieved. In selected implementations, the thermal profile may ensure that a solidification front does not cut off or separate any pockets of molten metal (or metal that is insufficiently cool and will yet experience significant contraction) from the reservoir. Accordingly, as a molten metal cools, solidifies 160, and contracts, fresh molten material may be available and pressurized to fill in as necessary. Thus, by controlling 158 the thermal profile of the mold cavity 170, the method 146 may prevent the formation of any voids, cracks, or undesirable microstructure caused by uncontrolled reductions in volume that accompany reductions in temperature and solidification without available fresh molten material to form a continuous microstructure.

[0058] When the solidifying 160 is complete, an as-cast pressure vessel without subsequent heat treatment may be formed. Accordingly, the as-cast pressure vessel may be removed from the outer mold 168. Furthermore, in implementations where the inner core 166 is sacrificial, the inner core 166 may be removed 162 from within the as-cast pressure vessel. Thereafter, the as-cast pressure vessel may be subjected 164 to a heat-treating process and become a treated pressure vessel. For example, the method 146 may include producing a treated pressure vessel having a fracture toughness greater than or equal to about 42 ksi / tn by subjecting the as-cast pressure vessel to a T4 heat treatment or a modified T4 heat treatment. Final machining (e.g., cutting off remaining sprue material, trimming flashing, cutting threads into the valve port 130 or the cleanout ports 140, or the like or a combination or sub-combination thereof) may be performed after the heat treatment. Alternatively, with certain alternate materials and designs, such machining or a portion thereof may precede the heat treatment.

[0059] Referring to FIGS. 8-10, 11 A, and 11B, in selected implementations, the mold assembly 174 may define the mold cavity 170 consistent with the body 102 having three of the sections 104. In other implementations, the mold assembly 174 may be consistent with the body 102 having one of the sections 104, two of the sections 104, or any other number of the sections 104.

[0060] In certain implementations, the outer mold 168 may comprise multiple portions (e.g., two halves). In some implementations of the mold assembly 174 defining the mold cavity 170 consistentwith the body 102 including sections 104 that are symmetrical, the halves of the outer mold 168 may be identical. In other implementations, however, the halves of the outer mold 168 may not be identical.

[0061] Each half of the outer mold 168 may include an inner core cavity 176 into which the inner core 166 may be received and may also include a base mold cavity 178 into which the base mold 172 may be received. The inner core cavity 176 may further include a core locating portion 179 configured to receive a corresponding portion of the inner core 166 to locate the outer mold 168 with respect thereto. Each half of the outer mold 168 may include a compression surface 180 (e.g., a compression surface 180 that is flat) upon which the compression surface 180 of a corresponding half of the outer mold 168 may be pressed against when assembled. Each half of the outer mold 168 may also include a locating feature 182 or more than one locating feature 182 (e.g., two locating features) for locating a half of the outer mold 168 to a corresponding half of the outer mold 168. The locating features 182 may, for example, be corresponding convex and concave domes or corresponding apertures and alignment rods located on the compression surface 180, and which fit into one-another when the halves of the outer mold 168 are assembled.

[0062] Furthermore, the outer mold 168 may include one or more purge ports 184 that extend from the inner core cavity 176 to the external environment. The purge ports 184 may enable gas to be purged from within the mold cavity 170. The purge ports 184 may also enable a vacuum to be formed and maintained within the mold cavity 170. FIGS. 10, 14, and 16 show the purge ports 184 being formed by corresponding recesses located on the compression surface 180 of each half of the outer mold 168 that cooperatively form the purge ports 184 when the outer mold 168 is assembled. Furthermore, FIGS. 10, 14, and 16 show the purge ports 184 extending through a top of the outer mold 168. In other implementations, however, the purge ports 184 may be formed and extend through the outer mold 168 at other locations.

[0063] In certain implementations, the inner core 166 may comprise multiple portions (e.g., two halves) that, when assembled or secured to one another form a single-piece core. In some implementations of the mold assembly 174 that define the mold cavity 170 consistent with the body 102 including symmetrical implementations of the sections 104, the halves of the inner core 166 may be identical. However, when one of the halves is reversed (e.g., rotated 180 degrees) and mated with the other half, an inner core 166 that may be defined as a single-piece core may be formed. In other implementations, however, the halves of the inner core 166 may not be identical. They may, however, still combine to form what may be considered a single-piece core.

[0064] The inner core 166 may be formed from a sacrificial material (e.g., sand with a thermoset binder) which, in certain implementations, may be removed from within the body 102 subsequent the casting process via the cleanout ports 140. In such implementations, after solidification 160, the inner core 166 may be broken down into small portions that may pass through the cleanout ports 140 of the body 102. Breaking down the inner core 166 may be facilitated by a baking or vibration process, which may become longer in proportion to the amount of material forming the inner core 166. Therefore, it may be advantageous for the inner core 166 to be hollow to minimize the amount of material that needs to be broken down and removed via the cleanout ports 140.

[0065] In certain implementations, to form an inner core 166 that is hollow, the inner core 166 may be formed through a shell molding process in which the sacrificial material is placed within a mold defining the exterior shape of the inner core 166 and subsequently rotated in order to distribute the sacrificial material all around an inner surface of the mold. In selected implementations, heat applied through such a mold may activate a bonding agent or the like that may solidify the sacrificial material coming into contact therewith. Alternatively, to form an inner core 166 that is hollow, multiple portions (e.g., two halves) of the inner core 166 may be independently formed and subsequently assembled to form the inner core 166. In implementations where the inner core 166 is hollow, the inner core 166 may include a vent hole 186 for discharging gas from within the hollow cavity of the inner core 166. This may prevent the hollow cavity from becoming pressurized by expanding gas when the inner core 166 is heated during the casting process.

[0066] Where the inner core 166 is formed by assembling two halves, each half of the inner core 166 may include a surface 187 for which the surface 187 of a corresponding half of the inner core 166 may be connected when assembled. Each half of the inner core 166 may also include locating features 188 (e.g., four of the locating features 188) for locating a half of the inner core 166 to a corresponding half of the inner core 166. The locating features 188 may, for example, be corresponding convex and concave domes or the like located on the surface 187 that fit into one- another when the halves of the inner core 166 are assembled.

[0067] In certain implementations, to locate the inner core 166 with respect to the outer mold 168, the inner core 166 may include a mold locating portion 190 configured to engage with the core locating portion 179 of the outer mold 168. In such implementations, the geometry of the mold locating portion 190 of the inner core 166 may closely match the geometry of the core locating portion 179 of the outer mold 168 such that any gap therebetween is minimized when the inner core166 is assembled within the outer mold 168. The mold locating portion 190 may be located anywhere on the inner core 166. However, it may be convenient to position the mold locating portion 190 at a location that corresponds to the valve port 130 of the body 102 because the portion of the inner core 166 that forms the valve port 130 extends outwardly into the outer mold 168. Furthermore, in implementations where the inner core 166 is hollow, the vent hole 186 may extend through the mold locating portion 190.

[0068] In selected implementations, the inner core 166 may also include base locating portions 192 configured to receive a corresponding portion of the base mold 172 for locating the inner core 166 with respect thereto. The base locating portions 192 may be located anywhere on the inner core 166. However, it may be convenient to position the base locating portions 192 at a position that corresponds to the cleanout ports 140 of the body 102 because the portion of the inner core 166 that forms the cleanout ports 140 extends outwardly toward the base mold 172.

[0069] Referring to FIG. 12, in certain implementations, to locate the base mold 172 to the outer mold 168, the base mold 172 may include a base 194 configured to engage the base mold cavity 178 of the outer mold 168. In such implementations, the geometry of the base 194 may closely match the geometry of the base mold cavity 178 of the outer mold 168 such that any gap therebetween is minimized when the base mold 172 is assembled to the outer mold 168. Furthermore, to locate the base mold 172 to the inner core 166, in some implementations, the base mold 172 may further include one or more locating members 196 (e.g., two of the locating members 196) that extend upwardly from the base 194 and are configured to engage the base locating portions 192 of the inner core 166. In such implementations, the geometry of the locating members 196 may closely match the geometry of the base locating portions 192 of the inner core 166 such that any gap therebetween may be minimized when the base mold 172 is assembled to the inner core 166. Furthermore, in selected implementations, the locating members 196 of the base mold 172 may be received within the base locating portions 192 of the inner core 166.

[0070] Additionally, the base mold 172 may include protrusions 198 that are operable to form portions of the base 132 of the body 102. In select implementations, the base mold 172 may also include a sprue 200 that extends through the base 194 and that is operable to provide fluid communication between an area outside of the mold assembly 174 and the mold cavity 170. However, in other implementations the sprue 200 may be located at a different location on the mold assembly 174.

[0071] Referring to FIG 13, as described above, implementations of the mold assembly 174 may be configured to define implementations of the mold cavity 170 consistent with the body 102 having one of the sections 104, two of the sections 104, or any other number of the sections 104. Accordingly, in selected implementations, the base mold 172 may be shaped and sized for use in a mold assembly 174 for forming the body 102 having two of the sections 104.

[0072] Referring to FIGS. 14-16, in selected implementations, three points of contact and / or support (e.g., at least three points of contact and / or support) may hold the inner core 166 in a fixed position with respect to a combination formed by the outer mold 168 and the base mold 172. The three points of contact may be two of the base locating portions 192 corresponding to the cleanout ports 140 and one mold locating portion 190 corresponding to the valve port 130.

[0073] In certain implementations, liquifying 150 may include melting metal to form a molten metal 202, which may eventually be used to fill the mold cavity 170 and form the body 102 of the pressure vessel 100. As described above, various metal materials may be employed to form the body 102. One such metal material may include or be a casting aluminum alloy (e.g., aluminum-copper alloy, an Axxx.x series aluminum alloy, or the like). A casting aluminum alloy and / or aluminumcopper alloy may have properties that are advantageous for the formation of pressure vessels, such as having low density when compared to alternative materials suitable for casting, as well as having high fracture toughness after being subjected to certain heat treatments. In select implementations, the metal material that is liquified and used to form the body 102 may be A206 aluminum alloy or a modified version of an A206 alloy (e.g., an A206 alloy modified with titanium and / or boron (TiBor)).

[0074] Referring to FIG. 16, in certain implementations, the transferring 1 2 following the liquifying 150 may include transferring the molten metal 202 into a reservoir 204. The reservoir 204 may be positioned within a chamber 206. The chamber 206 may be substantially sealed from an outside environment except for through the purge ports 184 of the outer mold 168. The chamber 206 may include a pressure port 208 that enables gas to be injected into the chamber 206 to establish a gas pressure 210 therewithin. The gas injected into the chamber 206 may be inert or substantially inert with respect to the molten metal 202. Accordingly, the molten metal 202 may have minimal to no chemical reactivity with the gas, which may reduce the formation of unwanted compounds (e.g., oxides) on or in the molten metal 202. Furthermore, the mold cavity 170 and the chamber 206 may be purged via the purge ports 184 prior to the liquifying 150 and the transferring 152. Purging the mold cavity 170 and the chamber 206 prior to the liquifying 150 and thetransferring 152 may expel contaminants from within the mold cavity 170 and chamber 206 and prevent the formation of oxides in the pressure vessel 100. Alternatively, or in addition thereto, the mold cavity 170 and the chamber 206 may be purged via the purge ports 184 subsequent to the liquifying 150 and the transferring 152.

[0075] In selected implementations, the connecting 154 may include connecting the reservoir 204 to the mold cavity 170 to provide fluid communication therebetween. To connect the reservoir 204 to the mold cavity 170, the chamber 206 may further include a fill port 212 that extends from the reservoir 204 to the mold cavity 170 and that provides fluid communication therebetween.Moreover, once the molten metal 202 has been transferred into the reservoir 204, impurities may form in the molten metal 202 nearest the top of the reservoir 204 because of oxidation and / or other chemical reactions. Therefore, it may be advantageous to position the fill port 212 such that an end of the fill port 212 is positioned in the molten metal 202 near the bottom of the reservoir 204. Additionally, in some implementations, the fill port 212 may connect to the sprue 200 of the base mold 172.

[0076] In certain implementations, the transferring 156 may include transferring the molten metal 202 from the reservoir 204 to the mold cavity 170 by pressurizing the molten metal 202 within the reservoir 204. Pressurizing the molten metal 202 may be facilitated by injecting gas into the chamber 206 via the pressure port 208. When the gas pressure 210 inside the chamber 206 is sufficiently high, the molten metal 202 may travel through the fill port 212 and into the mold cavity 170 through the sprue 200. Furthermore, in select implementations, the transferring 156 may further include purging the mold cavity 170 with an inert gas (e.g., nitrogen gas) prior to pressurizing the molten metal 202 within the reservoir 204 to prevent impurities from forming while the mold cavity 170 is filling with the molten metal 202.

[0077] Additionally, as described above, in select implementations the purge ports 184 may enable a vacuum to be formed and maintained within the mold cavity 170. In such implementations, the vacuum may cooperate with the gas pressure 210 inside the chamber 206 to facilitate the transferring 156. The purge ports 184 may be positioned at strategic locations on the outer mold 168 to enable a vacuum to be established and maintained at select locations in the mold cavity 170. The magnitude of the vacuum may be adjusted to control the transferring 156 of the molten metal 202 into the mold cavity 170. For example, where the purge ports 184 extend through the top of the outer mold 168, a vacuum may be maintained at the top of the mold cavity 170 to facilitate the transferring 156 of the molten metal 202 into the mold cavity 170. Once the molten metal 202 hassolidified (or partially solidified) at the top of the mold cavity 170, the vacuum may be reduced or discontinued. The purge ports 184 may extend through other locations of the outer mold 168 in order to establish adjustable vacuums at other locations in the mold cavity 170 to further control the transferring 156 of the molten metal 202 into the mold cavity 170.

[0078] The controlling 158 may follow the transferring 156 and may include controlling a thermal profile of the mold cavity 170 to control a solidification front 216 of the molten metal 202 within the mold cavity 170. Defects in the body 102 of the pressure vessel 100 (e.g., cracks, voids, etc.) may form due to shrinkage of the molten metal 202 as it cools and solidifies within the mold cavity 170. Therefore, to prevent such defects from forming in the body 102, the molten metal 202 within the mold cavity 170 may be cooled in a controlled manner. For example, defects may be prevented by ensuring that the molten metal 202 begins to solidify at a point along a flow path 218 of the molten metal 202 that is furthest from the sprue 200 of the mold assembly 174. This may allow for any potential gaps in the metal material resulting from shrinkage of the molten metal 202 to be immediately filled with more of the molten metal 202 that is traveling along the flow path 218. As the molten metal 202 further solidifies within the mold cavity 170, the thermal profile (e.g., the thermal profile of the outer mold 168) may be controlled so the solidification front 216 travels in a direction opposite the flow path 218 of the molten metal 202 to ensure that any potential gaps resulting from contraction associated with decreasing temperature may continue to be filled.

[0079] Generally, the points along the flow path 218 of the molten metal 202 that are furthest from the sprue 200 are located within portions of the mold cavity 170 that correspond to the thicker portions of the body 102, as well as the inner most portions of the body 102. In some implementations, these may be portions of the mold cavity 170 that correspond to the upper head 112 of the sections 104, and / or portions of the mold cavity 170 that correspond to the dividing wall 122. Therefore, to prevent defects resulting from the molten metal 202 contracting within the mold cavity 170 as it cools and solidifies, the thermal profile of the mold cavity 170 may be controlled so that the solidification front 216 travels generally from portions of the mold cavity 170 corresponding to the upper head 112 to the lower head 114 of the sections 104 (e.g., top to bottom), and generally from the dividing walls 122 to the side wall 110 (e.g., inside to outside) of the sections 104.

[0080] In selected implementations, an outer mold 168 may define a mold cavity 170 comprising a distal end, a proximal end, and a side-wall volume extending from the distal end to the proximal end. The distal end of the mold cavity 170 may correspond to or define an upper head 112 of thepressure vessel 100. The proximal end of the mold cavity 170 may correspond to or define a lower head 114 of the pressure vessel 100. The side-wall volume of the mold cavity 170 may correspond to or define a side wall 110 of the pressure vessel 100. Accordingly, in certain implementations, a thermal profile of the outer mold 168 may be controlled 158 to cool and solidify the molten metal 202 (i.e., the casting aluminum alloy in molten form) corresponding to a distal end before the molten metal 202 corresponding to the side-wall volume. This may ensure that a solidification front 216 does not cut off or separate any pockets of molten metal 202 (or metal that is insufficiently cool and will yet experience significant contraction) from molten metal 202 in the reservoir 204 that can flow into the mold cavity 170 and fill in or resolve any contraction resulting from solidification.

[0081] To control the thermal profile of the mold cavity 170, any suitable heat sources and / or heat sinks may be employed. As one example, heat sinks 220 may be positioned on portions of the mold assembly 174 (e.g., portions of the outer mold 168) that correspond to the upper head 112 of the sections 104 to facilitate heat transfer away from such portions (and, therefore, ensure that they solidify first or early in the solidification process. Alternatively, or in addition thereto, a heating element 222 or more than one heating element 222 may be positioned on portions of the mold assembly 174 (e.g., may be positioned on or wrapped around the exterior sides of the outer mold 168) that correspond to the side wall 110 areas of the mold cavity 170. This may ensure that the molten metal 202 in those areas (which areas may be relatively thin and prone to rapid cooling and solidification) may stay molten longer and may continue to flow toward a solidification front 216 and backfill or fill in for any contraction associated with cooling and solidification. In certain implementations, if desired or necessary, portions of the mold assembly 174 (e.g., the inner core 166 or selected portions of the inner core 166) may include other heat sinks formed thereon or may be cooled prior to filling the mold cavity 170 with the molten metal 202.

[0082] In selected implementations, the removing 162 may follow the solidifying 160, and may include removing the inner core 166 from the body 102 of the pressure vessel 100. As described above, the inner core 166 may be formed from a sacrificial material (e.g., sand with a thermoset binder), which may be broken down via a baking or vibration process and removed from within the body 102 via the cleanout ports 140 after the solidification 160.

[0083] The subjecting 164 may include subjecting the body 102 of the pressure vessel 100 to a heat treatment process to improve certain desirable properties of the metal used to form the body 102. One such property may be referred to as leak-before-break (LBB), wherein the pressure vessel 100 forms detectable leaks prior to any catastrophic fracturing or failure of the body 102. Toachieve a LBB pressure vessel, a fracture toughness greater than or equal to about 42 ksi fin may be desired. Another such property may be a “safe-life” greater than about 20,000 cycles, where “safe-life” may be defined as the minimum number of pressure cycles expected before an undetectable flaw could develop into a leak. To achieve one or more of these properties, in select implementations where A206 aluminum is used to form the body 102, a T4 heat treatment process or a modified T4 heat treatment process may be employed. AT4 heat treatment may comprise a solution heat treat, followed by a natural aging process. A T4 heat treatment applied to a body 102 formed of A206 aluminum and by the method 146 disclosed hereinabove may result in the body 102 being LBB and having a “safe-life” of about 20,000 cycles.

[0084] Referring to FIG. 17, another implementation of a method 224 of casting the body 102 of the pressure vessel 100 is illustrated. The method 224 may be similar to the method 146 disclosed above except as described herein. The method 224 may include determining 226 casting parameters for the casting of the body 102 of the pressure vessel 100. The casting parameters may include the geometry of the mold cavity 170. The casting parameters may also include the geometries of the inner core 166, the outer mold 168, and the base mold 172, as well as locations and geometries of features included therewith (e.g., locations and configurations of the purge ports 184, the sprue 200, etc.). The casting parameters may also include the locations and configurations of the heat sinks 220 and the heating elements 222 on the outer mold 168. The casting parameters may also include a transfer rate of the molten metal 202 into the mold cavity 170. The casting parameters may also include the gas pressure 210 used to transfer the molten metal 202 into the mold cavity 170. Other casting parameters may also be determined.

[0085] The determining 226 of the casting parameters may be performed by alloy specific analytical cooling rate and solidification prediction software (“prediction software”), which may determine at least some of the casting parameters based in part on some combination of the desired geometry of the body 102, the desired properties of the body 102, and known properties of the metal selected to form the body 102. The prediction software may use such information to determine actual cooling and solidification rates of the molten metal 202 during subsequent casting of the body 102, which may influence the casting parameters.

[0086] The method 224 may further include assembling 228 the inner core 166 (e.g., an inner core 166 that is sacrificial) within the outer mold 168 to form the mold assembly 174. The mold assembly 174 may also include the base mold 172. As described above, assembling 228 the inner core 166 within the outer mold 168 defines the mold cavity 170. Assembling 228 the inner core 166within the outer mold 168 may include locating the inner core 166 to the outer mold 168, which may be facilitated by the base mold 172.

[0087] The method 224 may further include removing 230 contaminants (e.g., particulates, oil, etc.) from pressurized casting equipment and the mold assembly 174. The pressurized casting equipment may include the reservoir 204, the chamber 206, the fill port 212, and other components that may contact the molten metal 202 when casting the body 102 of the pressure vessel 100. In some implementations, the removing 230 may be accomplished by purging the pressurized casting equipment and the mold assembly 174 via the purge ports 184 and / or the pressure port 208. The removing 230 may also be accomplished by other suitable means.

[0088] The method 224 may further include liquifying 232 (e.g., melting) a metal alloy (e.g., an aluminum alloy, casting aluminum alloy, aluminum-copper alloy, bronze metal alloy, steel alloy, or the like) that will be used to form the body 102 of the pressure vessel 100 to form the molten metal 202. In some implementations, the liquifying 232 may be performed in an inert gas environment. The inert gas environment may be a specialized liquification chamber that is purged and fdled with the inert gas prior to the liquifying 232. In select implementations, the inert gas environment may be the chamber 206, such that the metal alloy is liquefied within the reservoir 204. In such an implementation, the inert gas may be injected into the chamber 206 via the pressure port 208 prior to the liquifying 232. The inert gas may be nitrogen gas or some other gas that is inert or substantially inert with respect to the molten metal 202.

[0089] The method 224 may further include transferring 234 the molten metal 202 from the inert gas environment (e.g., the specialized liquification chamber) to the reservoir 204. In order to prevent oxidation and other chemical reactions from affecting the molten metal 202 when transferring the molten metal 202 from the inert gas environment to the reservoir 204, the transferring 234 may be performed under an inert gas blanket. Furthermore, the chamber 206 may be purged with the inert gas prior to the molten metal 202 being transferred into the reservoir 204 within the chamber 206. Of course, the transferring 234 may be omitted from the method 224 in implementations where the liquifying 232 is performed within the chamber 206.

[0090] The method 224 may further include connecting 236 the mold assembly 174 to the pressurized casting equipment to establish fluid communication between the mold cavity 170 and the reservoir 204. The connecting 236 may be facilitated by the fill port 212, which may extend from the molten metal 202 within the reservoir 204 to the sprue 200 of the mold assembly 174.

[0091] The method 224 may further include purging 238 the mold cavity 170 and the pressurized casting equipment with an inert gas to remove any gas that may react with the molten metal 202 (e.g., oxygen) from the mold cavity 170 and the pressurized casting equipment. In some implementations, the purging 238 may be achieved by injecting the inert gas into, and / or forming a vacuum within, the mold cavity 170 and the pressurized casting equipment. The purging 238 may be facilitated by the purge ports 184 and / or the pressure port 208.

[0092] The method 224 may further include introducing 240 the molten metal 202 into the mold cavity 170. The introducing 240 may be accomplished by injecting an inert gas into the chamber 206 via the pressure port 208 to establish the gas pressure 210 within the chamber 206. Once the gas pressure 210 is sufficiently high, the molten metal 202 may be forced out of the reservoir 204 and into the mold cavity 170. Importantly, the gas pressure 210 may be carefully controlled to achieve the casting parameters (e.g., the transfer rate of the molten metal 202 into the mold cavity 170) determined by the prediction software. As shown in FIG. 16, in some implementations, the chamber 206 and the reservoir 204 may be positioned beneath the mold assembly 174. Thus, in such implementations, the gas pressure 210 must be sufficiently high to force the molten metal 202 upwards and into the mold cavity 170.

[0093] The method 224 may further include controlling 242 the thermal profile of the mold cavity 170 and the solidification rate of the molten metal 202 that has been introduced to the mold cavity 170. By controlling the thermal profile and the solidification rate, propagation of the solidification front 216 through the mold cavity 170 may also be controlled such that the desired microstructure and resultant post heat treatment mechanical properties of the pressure vessel 100 are achieved. In select implementations, the thermal profile and the solidification rate may be determined by the prediction software. The controlling 242 may be accomplished by controlling the transfer rate of the molten metal 202 into the mold cavity 170, for example, by controlling the gas pressure 210 within the chamber 206. The controlling 242 may also be accomplished by controlling a size and location of openings in the mold assembly 174 such as, for example, the size and location of the purge ports 184, the sprue 200, or other openings.

[0094] The controlling 242 may also be accomplished by preheating specific areas of the mold cavity 170. In some implementations, preheating specific areas of the mold cavity 170 may be accomplished by preheating portions of the mold assembly 174. For example, the inner core 166 (or portions thereof) may be preheated prior to the assembling 228. As another example, portions of the outer mold 168 may be preheated before or after the assembling 228 via the heating elements 222.The controlling 242 may also be accomplished by controlling the cooling rate of the molten metal 202 that has been introduced into the mold cavity 170. Controlling the cooling rate of the molten metal 202 may be accomplished by precooling portions of the mold assembly 174. For example, the inner core 166 (or portions thereof) may be precooled prior to the assembling 228. Controlling the cooling rate of the molten metal 202 may also be accomplished, for example, by positioned the heat sinks 220 at strategic locations on the outer mold 168. As another example, other heat sinks may be formed on the inner core 166 that facilitate controlled cooling of the molten metal 202.

[0095] The method 224 may further include disconnecting 244 the mold assembly 174 from the pressurized casting equipment to terminate the fluid communication between the mold cavity 170 and the reservoir 204.

[0096] The method 224 may further include disassembling 246 the mold assembly 174 to extract the body 102 of an as-cast pressure vessel. The disassembling 246 may include, for example, separating halves of the outer mold 168. Furthermore, in implementations where the inner core 166 is sacrificial, the disassembling 246 may also include removing the inner core 166 from within the body 102 of the as-cast pressure vessel. As described above, removing the inner core 166 from within the body 102 of the as-cast pressure vessel may be accomplished by breaking down the inner core 166 via a baking and / or vibration process and removing pieces of the inner core 166 from within the body 102 via the cleanout ports 140.

[0097] The method 224 may further include subjecting 248 the body 102 of the as-cast pressure vessel to a prescribed heat treatment schedule to form the body 102 of a treated pressure vessel (e.g., the pressure vessel 100). The subjecting 248 of the body 102 of the as-cast pressure vessel may improve certain desirable properties of the metal used to form the body 102. For example, the prescribed heat treatment schedule may improve the fracture toughness of the body 102 to about 42 ksi in (e.g., to achieve a LBB pressure vessel). As another example, the prescribed heat treatment schedule may improve properties of the body 102 such that the body 102 has a “safe-life” greater than about 20,000 cycles. In select implementations where A206 aluminum is used to form the body, a T4 heat treatment process or a modified T4 heat treatment process may be employed. In some implementations, the prescribed heat treatment schedule is determined by the prediction software.

[0098] While implementations of the pressure vessel 100, the method 146 corresponding to FIG. 7, and the method 224 corresponding to FIG. 17 are susceptible to various modifications and alternative forms which will be readily apparent to those of ordinary skill in the art, specificimplementations have been shown by way of example in the drawings and have been described in detail herein. However, it should be understood the pressure vessel 100, the method 146 corresponding to FIG. 7, and the method 224 corresponding to FIG. 17 are not intended to be limited to the particular forms disclosed. Rather, the pressure vessel 100, the method 146 corresponding to FIG. 7, and the method 224 corresponding to FIG. 17 include all additions, deletions, and modifications, as well as equivalents, and alternative implementations falling within the scope of this disclosure as defined by the following appended claims and their legal equivalents.

[0099] An example of the foregoing may be a pressure vessel comprising a first section connected to a second section.

[0100] The example may include one or more functions or structures set forth above combined with the pressure vessel defining a longitudinal direction, a lateral direction, and a transverse direction that are substantially orthogonal to one another.

[0101] The example may include one or more functions or structures set forth above combined with each of the first section and the second section extending in the longitudinal direction.

[0102] The example may include one or more functions or structures set forth above combined with each of the first section and the second section comprising a first head having a curved shape that is substantially hemispherical, semi-ellipsoidal, or tori spherical.

[0103] The example may include one or more functions or structures set forth above combined with each of the first section and the second section comprising a second head having a curved shape that is substantially hemispherical, semi-ellipsoidal, or tori spherical.

[0104] The example may include one or more functions or structures set forth above combined with each of the first section and the second section comprising a side wall having a substantially semi-cylindrical shape and extending in the longitudinal direction between the first head and the second head.

[0105] The example may include one or more functions or structures set forth above combined with each of the first section and the second section comprising a cavity defined at least partially by the first head, the second head, and the side wall.

[0106] The example may include one or more functions or structures set forth above combined with the side wall extending monolithically from the first head at a first transition defined by a change from the curved shape of the first head to the substantially semi-cylindrical shape of the side wall.

[0107] The example may include one or more functions or structures set forth above combined with the side wall extending monolithically from the second head at a second transition defined by a change from the curved shape of the second head to the substantially semi-cylindrical shape of the side wall.

[0108] The example may include one or more functions or structures set forth above combined with the pressure vessel comprising a first aperture located inside the pressure vessel and providing fluid communication between the cavity of the first section and the cavity of the second section.

[0109] The example may include one or more functions or structures set forth above combined with the first aperture extending in the lateral direction and being positioned longitudinally outboard of the first transition.

[0110] The example may include one or more functions or structures set forth above combined with the pressure vessel comprising a second aperture located inside the pressure vessel and providing fluid communication between the cavity of the first section and the cavity of the second section.

[0111] The example may include one or more functions or structures set forth above combined with the second aperture extending in the lateral direction and being positioned longitudinally outboard of the second transition.

[0112] The example may include one or more functions or structures set forth above combined with the first head, second head, and side wall of both the first section and the second section being formed of a casting aluminum alloy.

[0113] The example may include one or more functions or structures set forth above combined with the casting aluminum alloy being an aluminum-copper alloy.

[0114] The example may include one or more functions or structures set forth above combined with the casting aluminum alloy being A206.

[0115] The example may include one or more functions or structures set forth above combined with the first head, second head, and side wall of both the first section and the second section being a single monolithic casting.

[0116] Another example of the foregoing may include a method for manufacturing a pressure vessel. The example may include locating an inner core within an outer mold to define a mold cavity comprising a distal end, a proximal end, and a side-wall volume extending from the distal end to the proximal end.

[0117] The example may include one or more steps, functions, or structures set forth above combined with connecting a reservoir containing a casting aluminum alloy in molten form to the mold cavity to provide fluid communication between the reservoir and the mold cavity.

[0118] The example may include one or more steps, functions, or structures set forth above combined with pressurizing gas above the reservoir to push the casting aluminum alloy in molten form out of the reservoir and into the mold cavity.

[0119] The example may include one or more steps, functions, or structures set forth above combined with controlling a thermal profile of the outer mold to solidify the casting aluminum alloy corresponding to the distal end before the casting aluminum alloy corresponding to the side-wall volume.

[0120] The example may include one or more steps, functions, or structures set forth above combined with the controlling the thermal profile of the mold cavity controlling a solidification front of the casting aluminum alloy within the mold cavity.

[0121] The example may include one or more steps, functions, or structures set forth above combined with the reservoir being connected to the mold cavity at a sprue located at the proximal end, and the solidification front traveling generally from a distal end to the proximal end.

[0122] The example may include one or more steps, functions, or structures set forth above combined with the controlling being facilitated by at least one heat sink or heating element connected to the outer mold.

[0123] The example may include one or more steps, functions, or structures set forth above combined with the casting aluminum alloy being A206.

[0124] The example may include one or more steps, functions, or structures set forth above combined with the locating comprising positioning at least one locating feature of the inner core to engage a corresponding locating feature of the outer mold.

[0125] The example may include one or more steps, functions, or structures set forth above combined with the locating feature of the inner core extending away from the mold cavity, and the locating feature of the outer mold comprising an aperture that extends through a portion of the outer mold.

[0126] The example may include one or more steps, functions, or structures set forth above combined with the inner core being substantially hollow.

[0127] The example may include one or more steps, functions, or structures set forth above combined with subjecting the pressure vessel to a T4 heat treatment.

[0128] The example may include one or more steps, functions, or structures set forth above combined with the pressure vessel comprising a first section and a second section, the first section extending longitudinally, the second section extending longitudinally and being connected to the first section.

[0129] The example may include one or more steps, functions, or structures set forth above combined with each of the first section and the second section comprising a first substantially hemispherical head.

[0130] The example may include one or more steps, functions, or structures set forth above combined with each of the first section and the second section comprising a second substantially hemispherical head.

[0131] The example may include one or more steps, functions, or structures set forth above combined with each of the first section and the second section comprising a semi-cylindrical side wall extending between the first substantially hemispherical head and the second substantially hemispherical head.

[0132] The example may include one or more steps, functions, or structures set forth above combined with each of the first section and the second section comprising a cavity defined at least by the first substantially hemispherical head, the second substantially hemispherical head, and the semi-cylindrical side wall.

[0133] The example may include one or more steps, functions, or structures set forth above combined with the pressure vessel comprising a first aperture providing fluid communication between the cavity of the first section and the cavity of the second section.

[0134] The example may include one or more steps, functions, or structures set forth above combined with the cavity of the first section and the cavity of the second section cooperating to contain pressurized gas therein.

[0135] Another example of the foregoing may include a method for manufacturing a pressure vessel. The example may include heating an aluminum-copper alloy to produce molten metal.

[0136] The example may include one or more steps, functions, or structures set forth above combined with transferring the molten metal to a mold cavity via a low-pressure casting process.

[0137] The example may include one or more steps, functions, or structures set forth above combined with solidifying the molten metal to form an as-cast pressure vessel.

[0138] The example may include one or more steps, functions, or structures set forth above combined with subjecting the as-cast pressure vessel to a T4 heat treatment to produce a treated pressure vessel having a fracture toughness greater than or equal to about 42 ksi "Vin.

[0139] The example may include one or more steps, functions, or structures set forth above combined with the transferring comprising connecting a reservoir containing the aluminum-copper alloy therein to the mold cavity to provide fluid communication between the reservoir and the mold cavity.

[0140] The example may include one or more steps, functions, or structures set forth above combined with the transferring comprising subjecting the aluminum-copper alloy contained in the reservoir to an external pressure that is higher than a pressure of gas within the mold cavity.

[0141] The example may include one or more steps, functions, or structures set forth above combined with the mold cavity being defined by a sacrificial inner core and an outer mold.

[0142] The example may include one or more steps, functions, or structures set forth above combined with the sacrificial inner core comprising sand.

[0143] The example may include one or more steps, functions, or structures set forth above combined with the pressure vessel comprising a first section and a second section, the first section extending longitudinally, the second section extending longitudinally and being connected to the first section.

[0144] The example may include one or more steps, functions, or structures set forth above combined with each of the first section and the second section comprising a first substantially hemispherical head.

[0145] The example may include one or more steps, functions, or structures set forth above combined with each of the first section and the second section comprising a second substantially hemispherical head.

[0146] The example may include one or more steps, functions, or structures set forth above combined with each of the first section and the second section comprising a semi-cylindrical side wall extending between the first substantially hemispherical head and the second substantially hemispherical head.

[0147] The example may include one or more steps, functions, or structures set forth above combined with each of the first section and the second section comprising a cavity defined at least by the first substantially hemispherical head, the second substantially hemispherical head, and the semi-cylindrical side wall.

[0148] The example may include one or more steps, functions, or structures set forth above combined with the pressure vessel comprising a first aperture providing fluid communication between the cavity of the first section and the cavity of the second section.

[0149] The example may include one or more steps, functions, or structures set forth above combined with the cavity of the first section and the cavity of the second section cooperating to contain pressurized gas therein.

[0150] While the disclosure has been described in connection with certain implementations, it is to be understood that the disclosure is not to be limited to the disclosed implementations but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the scope of the appended claims, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures as is permitted under the law.

Claims

What is claimed is:

1. A pressure vessel defining a longitudinal direction, a lateral direction, and a transverse direction that are substantially orthogonal to one another, the pressure vessel comprising: a first section connected to a second section, each of the first section and the second section extending in the longitudinal direction and comprising a first head having a curved shape that is substantially hemispherical, semi- ellipsoidal, or tori spherical, a second head having a curved shape that is substantially hemispherical, semi- ellipsoidal, or tori spherical, a side wall having a substantially semi-cylindrical shape and extending in the longitudinal direction between the first head and the second head, and a cavity defined at least partially by the first head, the second head, and the side wall, wherein the side wall extends monolithically from the first head at a first transition defined by a change from the curved shape of the first head to the substantially semi- cylindrical shape of the side wall, and the side wall extends monolithically from the second head at a second transition defined by a change from the curved shape of the second head to the substantially semi-cylindrical shape of the side wall; and a first aperture located inside the pressure vessel and providing fluid communication between the cavity of the first section and the cavity of the second section, wherein the first aperture extends in the lateral direction and is positioned longitudinally outboard of the first transition.

2. The pressure vessel of claim 1, further comprising a second aperture located inside the pressure vessel and providing fluid communication between the cavity of the first section and the cavity of the second section, the second aperture extending in the lateral direction and being positioned longitudinally outboard of the second transition.

3. The pressure vessel of claim 1, wherein the first head, second head, and side wall of both the first section and the second section are formed of a casting aluminum alloy.

4. The pressure vessel of claim 3, wherein the casting aluminum alloy is an aluminum-copper alloy.

5. The pressure vessel of claim 3, wherein the casting aluminum alloy is A206.

6. The pressure vessel of claim 1, wherein the first head, second head, and side wall of both the first section and the second section are a single monolithic casting.

7. A method of manufacturing a pressure vessel, the method comprising: locating an inner core within an outer mold to define a mold cavity comprising a distal end, a proximal end, and a side-wall volume extending from the distal end to the proximal end; connecting a reservoir containing a casting aluminum alloy in molten form to the mold cavity to provide fluid communication between the reservoir and the mold cavity; pressurizing gas above the reservoir to push the casting aluminum alloy in molten form out of the reservoir and into the mold cavity; and controlling a thermal profile of the outer mold to solidify the casting aluminum alloy corresponding to the distal end before the casting aluminum alloy corresponding to the side-wall volume.

8. The method of claim 7, wherein the controlling the thermal profile of the mold cavity controls a solidification front of the casting aluminum alloy within the mold cavity.

9. The method of claim 8, wherein the reservoir is connected to the mold cavity at a sprue located at the proximal end, and the solidification front travels generally from a distal end to the proximal end.

10. The method of claim 7, wherein the controlling is facilitated by at least one heat sink or heating element connected to the outer mold.

11. The method of claim 7, wherein the casting aluminum alloy is A206.

12. The method of claim 7, wherein the locating comprises positioning at least one locating feature of the inner core to engage a corresponding locating feature of the outer mold.

13. The method of claim 12, wherein the locating feature of the inner core extends away from the mold cavity, and the locating feature of the outer mold comprises an aperture that extends through a portion of the outer mold.

14. The method of claim 7, wherein the inner core is substantially hollow.

15. The method of claim 7, further comprising subjecting the pressure vessel to a T4 heat treatment.

16. The method of claim 7, wherein the pressure vessel comprises: a first section and a second section, the first section extending longitudinally, the second section extending longitudinally and being connected to the first section, each of the first section and the second section comprising: a first substantially hemispherical head, a second substantially hemispherical head, a semi-cylindrical side wall extending between the first substantially hemispherical head and the second substantially hemispherical head, and a cavity defined at least by the first substantially hemispherical head, the second substantially hemispherical head, and the semi-cylindrical side wall; and a first aperture providing fluid communication between the cavity of the first section and the cavity of the second section, wherein the cavity of the first section and the cavity of the second section cooperate to contain pressurized gas therein.

17. A method of casting a pressure vessel comprising: heating an aluminum-copper alloy to produce molten metal; transferring the molten metal to a mold cavity via a low-pressure casting process; solidifying the molten metal to form an as-cast pressure vessel; and subjecting the as-cast pressure vessel to a T4 heat treatment to produce a treated pressure vessel having a fracture toughness greater than or equal to about 42 ksi / in.

18. The method of claim 17, wherein the transferring comprises: connecting a reservoir containing the aluminum-copper alloy therein to the mold cavity to provide fluid communication between the reservoir and the mold cavity; and subjecting the aluminum-copper alloy contained in the reservoir to an external pressure that is higher than a pressure of gas within the mold cavity.

19. The method of claim 17, wherein: the mold cavity is defined by a sacrificial inner core and an outer mold; and the sacrificial inner core comprises sand.

20. The method of claim 17, wherein the pressure vessel comprises: a first section and a second section, the first section extending longitudinally, the second section extending longitudinally and being connected to the first section, each of the first section and the second section comprising: a first substantially hemispherical head, a second substantially hemispherical head, a semi-cylindrical side wall extending between the first substantially hemispherical head and the second substantially hemispherical head, and a cavity defined at least by the first substantially hemispherical head, the second substantially hemispherical head, and the semi-cylindrical side wall; and a first aperture providing fluid communication between the cavity of the first section and the cavity of the second section, wherein the cavity of the first section and the cavity of the second section cooperate to contain pressurized gas therein.