Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
  • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
  • F17C1/00—Pressure vessels, e.g. gas cylinder, gas tank, replaceable cartridge
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21C—MANUFACTURE OF METAL SHEETS, WIRE, RODS, TUBES OR PROFILES, OTHERWISE THAN BY ROLLING; AUXILIARY OPERATIONS USED IN CONNECTION WITH METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL
  • B21C23/00—Extruding metal; Impact extrusion
  • B21C23/02—Making uncoated products
  • B21C23/20—Making uncoated products by backward extrusion
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21C—MANUFACTURE OF METAL SHEETS, WIRE, RODS, TUBES OR PROFILES, OTHERWISE THAN BY ROLLING; AUXILIARY OPERATIONS USED IN CONNECTION WITH METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL
  • B21C23/00—Extruding metal; Impact extrusion
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21C—MANUFACTURE OF METAL SHEETS, WIRE, RODS, TUBES OR PROFILES, OTHERWISE THAN BY ROLLING; AUXILIARY OPERATIONS USED IN CONNECTION WITH METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL
  • B21C23/00—Extruding metal; Impact extrusion
  • B21C23/22—Making metal-coated products; Making products from two or more metals
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
  • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
  • F17C2201/00—Vessel construction, in particular geometry, arrangement or size
  • F17C2201/01—Shape
  • F17C2201/0104—Shape cylindrical
  • F17C2201/0114—Shape cylindrical with interiorly curved end-piece
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
  • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
  • F17C2203/00—Vessel construction, in particular walls or details thereof
  • F17C2203/06—Materials for walls or layers thereof; Properties or structures of walls or their materials
  • F17C2203/0602—Wall structures; Special features thereof
  • F17C2203/0612—Wall structures
  • F17C2203/0614—Single wall
  • F17C2203/0617—Single wall with one layer
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
  • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
  • F17C2209/00—Vessel construction, in particular methods of manufacturing
  • F17C2209/21—Shaping processes
  • F17C2209/2181—Metal working processes, e.g. deep drawing, stamping or cutting

Definitions

• the present invention relates to a method of manufacture of vessels adapted to contain pressurised fluids, the manufacturing apparatus thereof and pressure vessels manufactured using this method. More particularly, the present invention concerns a backward extrusion method for the manufacture of metallic vessels capable of containing fluids under pressure, the extrusion apparatus thereof and pressure vessels manufactured according to that method. In particular, but not exclusively, the present invention relates to apparatus and a manufacturing method for closed-ended hoop wrap gas cylinders adapted to contain gases at pressures above atmospheric pressure and to the closed-ended hoop wrap gas cylinders produced by the method.
• Type I pressure vessels are formed solely of metallic material such as steel or aluminium alloys.
• Type II pressure vessels comprise a metallic vessel (usually made of aluminium) which has a filamentous composite sleeve, formed for example of an epoxy resin, aramid and/or carbon fiber, surrounding the cylindrical side wall only of the vessel (referred to herein as hoop wrap).
• Type II pressure vessels are generally lighter in weight than Type I pressure vessels because the metallic vessel wall of a Type ⁇ pressure vessel can be thinner than a Type I pressure vessel without loss of performance.
• repeated dispensing and vessel re-filling of gas under pressure causes the vessel to flex and such flexing can encourage the propagation of cracks in the vessel wall.
• autofrettage has been used to improve pressure vessel fatigue resistance.
• Autofrettage involves applying a pressure within the bore of the vessel sufficient to plastically deform the metal at the inner surface. The technique produces compressive residual stresses at or near the internal surface, and this enhances the fatigue resistance of the vessel subjected to cyclic internal pressure loading.
• W096/1 1759 describes the use of autofrettage in the manufacture of pressure vessels to cause regions of peak stress in the pressure vessel wall to move away from an internal or external wall surface.
• the present invention seeks to provide a pressure vessel manufacturing method, manufacturing apparatus and pressure vessels manufactured using the method which improves the pressure vessel's resistance to fatigue.
• the present invention also seeks to provide a pressure vessel manufacturing method, manufacturing apparatus and pressure vessels manufactured using the method which reduces the likelihood of premature failure.
• the present invention further seeks to provide a cold extrusion manufacturing method and manufacturing apparatus particularly suited to manufacturing AA6XXX and AA7XXX series aluminium high pressure cylinders and cylinder liners.
• the present invention seeks to provide closed-ended hoop wrap pressure vessels with improved performance in comparison to conventional closed-ended hoop wrap pressure vessels.
• the present invention separately seeks to provide pressure vessels which meet the regulatory requirements of pressure vessel standards such as: EN 12257 and/or IS01 1 119-1 and which have a compound curve internal surface.
• the present invention therefore provides a method of forming a closed-ended pressure vessel, the method comprising: positioning a billet of an extrudable metal into a die, said billet having an axis and a forward surface; using a ram with a longitudinal axis of symmetry, an end face region and a substantially cylindrical side wall to cause the metal to extrude by driving the end face region of the ram into the forward surface of the billet along the axis of the billet so as to cause the metal to extrude into the space between the ram and the die and along the cylindrical side wall of the ram to form an extrudate; and removing the extrudate from the die and shaping the open end of the extrudate to form a shoulder and a neck, whereby the end face region of the ram has a surface profile comprising a central section, at least one intermediate ring and an outermost ring with intersecting but differing curvatures of radii: R, r, and Rc respectively, the central section, the at least one intermediate ring and the
• the axial distance H is in the range 0.3ID and 0.4ID.
• the axial distance H is substantially equal to ID/3.
• the central section preferably has a radius of curvature R in the range 0.5ID and 1.2ID.
• the central section has a radius of curvature R substantially equal to 1.1 ID.
• the intermediate ring has a radius of curvature r in the range between 0.1 ID and 0.5ID.
• the intermediate ring preferably has a radius of curvature r in the range 0.12ID and 0.13ID.
• the end face region of the ram may have a surface profile including at least two intermediate rings each with a different radius of surface curvature.
• the outermost ring has a radius of curvature Rc in the range ID/(3 ⁇ 2).
• the outermost ring has a radius of curvature Rc in the range ID/(3 ⁇ 1 ).
• the outermost ring preferably has a radius of curvature Rc substantially equal to ID/2.
• the method may further comprise the step of subjecting the pressure vessel to autofrettage.
• the billet may comprise a AA6XXX series aluminium alloy.
• the billet comprises a AA7XXX series aluminium alloy.
• the present invention provides extruding apparatus for use in the manufacture of a closed-ended pressure vessel, the extruding apparatus comprising a die for receiving a billet of an extrudable metal and a ram having a longitudinal axis of symmetry, an end face region and a substantially cylindrical side wall, the end face region of the ram having a surface profile comprising a central section, at least one intermediate ring and an outermost ring with intersecting but differing curvatures of radii: R, r, and Rc respectively, the central section, the at least one intermediate ring and the outermost ring connecting a central point where the end face intersects the longitudinal axis of the ram with the cylindrical side wall of the ram at an axial distance H from the central point, the axial distance H having a range 0.28ID to 0.5ID, where ID is the cross-sectional diameter of the cylindrical side wall of the ram.
• the axial distance H is in the range 0.3ID and 0.4ID.
• the axial distance H is substantially equal to
• the central section preferably has a radius of curvature R in the range 0.5ID and 1.2ID.
• the central section has a radius of curvature R substantially equal to 1.1 ID.
• the intermediate ring preferably has a radius of curvature r in the range between 0.1 ID and 0.5ID.
• the intermediate ring has a radius of curvature r in the range between 0.12ID and 0.13ID.
• the end face region of the ram may have a surface profile including at least two intermediate rings each with a different radius of surface curvature.
• the outermost ring preferably has a radius of curvature Rc in the range ID/(3 ⁇ 2).
• the outermost ring has a radius of curvature Rc in the range ID/(3 ⁇ 1 ).
• the outermost ring has a radius of curvature Rc substantially equal to ID/2.
• the present invention provides a closed-ended pressure vessel formed of an extrudable metal, the pressure vessel comprising a closed-end section, a substantially cylindrical side wall with a cross sectional internal diameter ID, a shoulder and a neck and having a longitudinal axis of symmetry, the internal surface profile of the closed-end section comprising a central section, at least one intermediate ring and an outermost ring with intersecting but differing curvatures of radii: R, r, and Rc respectively, the central section, the at least intermediate ring and the outermost ring connecting a central point where the closed-end section intersects the longitudinal axis with the cylindrical side wall at an axial distance H from the central point, the axial distance H having a range 0.28ID to 0.5ID.
• the axial distance H is in the range 0.3ID and 0.4ID.
• the axial distance H is substantially equal to ID/3.
• the central section preferably has a radius of curvature R in the range 0.5ID and 1.2ID.
• the central section has a radius of curvature R substantially equal to 1.1 ID.
• the intermediate ring preferably has a radius of curvature r in the range between 0.1 ID and 0.5ID.
• the intermediate ring has a radius of curvature r in the range between 0.12ID and 0.13ID.
• the internal surface profile of the closed-ended section may include at least two intermediate rings each with a different radius of surface curvature.
• the outermost ring preferably has a radius of curvature Rc in the range ID/(3 ⁇ 2).
• the outermost ring has a radius of curvature Rc in the range ID/(3 ⁇ 1 ).
• the outermost ring has a radius of curvature Rc substantially equal to ID/2.
• the closed-ended pressure vessel may comprise a AA6XXX series aluminium alloy.
• the closed-ended pressure vessel comprising a AA7XXX series aluminium alloy.
• a composite pressure vessel comprises a closed-ended pressure vessel as described above and a sleeve of a composite material.
• the composite material may be selected from a carbon fibre composite, basalt fibre, aramid and/or fibre glass fibre.
• the manufacturing method and manufacturing apparatus of the present invention enables closed-ended high pressure vessels to be manufactured using cold or warm extrusion which have an equivalent or improved lifetime in contrast to equivalent high pressure vessels manufactured using hot extrusion and which achieve equivalent performance even with lower pressure autofrettage.
• Fig. 1 illustrates schematically a series of stages in backward extrusion of a metallic billet to form a closed-ended pressure vessel
• Fig. 2 is perspective view through a cross section of the closed end of a pressure vessel according to the present invention
• Fig. 3 is a detailed cross-section of the closed end of the pressure vessel of Fig. 2;
• Fig. 4 illustrates the relationship of the surface curvature radii of the closed end of the pressure vessel of Fig. 2;
• Figs. 5a and 5b illustrate the first principal stresses and the Von Mises stresses using finite element analysis of the base of a conventional hoop wrap pressure vessel liner; and Figs. 6a and 6b illustrate the first principal stresses and the Von Mises stresses using finite element analysis of the base of a hoop wrap pressure vessel liner in accordance with the present invention.
• hot extrusion in which the extrusion is typically performed above the recrystallization temperature
• cold and/or warm extrusion in which the extrusion is performed below the recrystallization temperature
• Warm extrusion is typically performed with a starting billet temperature at 100-250°C
• cold extrusion is typically performed with a starting billet temperature at below 100°C, preferably ambient temperature.
• the precise extrusion conditions are not material to this invention and conventional conditions for extrusion may be employed.
• the method of manufacturing a closed-ended pressure vessel as shown in Fig. 1 involves the use of extrusion apparatus 1 in the backward extrusion of a metallic billet 2.
• the billet of metallic material for example an aluminium alloy
• a ram 5 which is preferably cylindrical in cross-section and with substantially parallel side walls, is arranged for reciprocal movement along a common axis X of the ram 5, the die 4 and the billet 2.
• the ram 5 is inserted into the die cavity 3 so that the end face 6 of the ram 5 engages the surface of the billet 2 facing towards the opening of the die cavity 3.
• the radial separation of the side wall of the ram 5 from the cylindrical inner surface of the die 4 generally corresponds to the thickness of the cylindrical side wall of the pressure vessel.
• the internal profile of the closed end of the pressure vessel corresponds to the external profile of the ram 5.
• Formation of the closed end of the pressure vessel results in an initial generally cup- shaped extrudate with a base, parallel side walls and an open top.
• the open top of the extrudate is then squared off and heated, typically induction heated to 300-450°C, prior to the formation of a neck using conventional swaging or spinning techniques.
• the resulting hollow body is solution heat treated; quenched, generally in cold water; and finally aged.
• Conventional finishing processes such as autofrettage and shot peening, may also be performed to complete manufacture of the pressure vessel.
• the extrusion method described above differs from conventional backward extrusion of a metallic billet by virtue of the use of novel and inventive extrusion apparatus 1.
• the features of the extrusion apparatus 1 are generally conventional in design with the exception of the external surface 10 of the end face of the ram 5, which is described in greater detail below.
• the internal surface profile of the closed end of the pressure vessel corresponds to the profile of the external surface 10 of the ram 5 and so the external surface 10 of the ram 5 is described herein by reference to Figs. 2 to 4 which show in cross section the closed end of a pressure vessel manufactured using the die 4 and ram 5 of the extrusion apparatus 1.
• the pressure vessel has an external or outer diameter OD, which is substantially equal to the internal diameter of the cylindrical side wall of the extrusion sleeve or die 4, and an internal diameter ID which is substantially equal to the external cylindrical diameter of the external side wall of the ram 5.
• Key features of the profile of the external surface 10 of the ram 5 include a central point 12 where the end of the ram 5 intersects its longitudinal axis of symmetry X, a central section 13 and at least two rings 14, 15 which connect the central point 12 to the substantially cylindrical side wall 1 1 of the ram 5.
• the central section 13 and the two rings 14 and 15 are all rotationally symmetric with respect to the axis X and concentric with respect to each other.
• the surface profiles of the central section 13 and the two rings 14 and 15 in the vertical cross-section of Figs. 3 and 4 can be clearly seen to have differing but intersecting surface curvatures.
• the surface curvature of the central section 13, the intermediate ring 14 and the outermost ring 15 extends between their boundaries and has a radius of R, r, and Rc respectively.
• the central point 12 lies at the centre of the central section 13.
• the surface profile of the central section 13 has a curvature of radius R between 0.5ID and 1.2ID, more preferably between 0.8ID and 1.2ID, and more preferably still 1 ID ⁇ R ⁇ 1.2ID.
• the outer edge of the central section 13 joins or intersects the inner edge of the first knuckle section, referred to herein as an intermediate ring 14, which has a curvature of radius r between 0.1 ID and 0.5ID, more preferably between 0.1 ID and 0.25ID, and more preferably still 0.1 ID ⁇ r ⁇ 0.15ID.
• Rc ID/(3 ⁇ 2)
• Rc ID/(3 ⁇ 1 )
• the radius R of the central section's surface curvature is measured from a point (origin) a distance R along the axis X. Furthermore the intersection of the central section 13 with the intermediate ring 14, the intersection of the intermediate ring 14 with the outermost ring 15, and the intersection of the outermost ring 15 with the cylindrical side wall 11 are each blended to ensure no discontinuities in the surface profile of the end of the ram 5 that might be detrimental to the strength of the cylinder.
• a cross section taken through the ram 5 at the junction of the outermost ring 15 with the cylindrical side wall 1 1 intersects the axis X a distance H above the central point 12.
• the radius Rc of the outermost ring's surface curvature is measured from a point (origin) that lies in a cross-sectional plane through the ram 5 at height H above the central point 12.
• the radius r of the intermediate ring 14 is measured from a point (origin) corresponding to the intersection of Rc-r and R-r.
• the cross sectional diameter IDC of the center of the intermediate ring 14 is less than or equal to OD-(3xa), where OD is the external cylindrical diameter of the pressure vessel (equal to the internal cylindrical diameter of the die 4) and a is the thickness of the pressure vessel wall (equal to the separation of the cylindrical side walls of the die 4 and the ram 5).
• the internal surface profile of the pressure cylinder may comprise more than one intermediate ring with each intermediate ring having its own radius of surface curvature and with each of the intermediate rings blending at its edges with the edges of adjacent rings i.e. the tangents to the surface curvature of each intermediate ring at the edges of the intermediate ring being substantially aligned with the tangents to the surface curvatures of adjacent rings.
• the central 13 may consist of an inner central section which is substantially flat and an outer central section, concentric to the inner central section, which has a surface curvature of radius R.
• a first set of exemplary dimensions for a die 4 and ram 5 of extrusion apparatus according to the present invention and the corresponding dimensions of the 5 litre AA7060 cylinder liner produced using the die and ram are set out below. total height of cylinder
• Shape A A second set of exemplary dimensions for a conventional 2 litre carbon fibre hoop wrap AA7060 alloy liner (and the corresponding dimensions of the die 4 and ram 5 of conventional extrusion apparatus) (Shape A) and similarly for a 2 litre carbon fibre hoop wrap AA7060 alloy liner (and its corresponding die and ram) (Shape B) in accordance with the present invention are set out below: Shape A Shape B
• Failure site 0 leak, position unknown
• Failure site 1 rupture at cylinder bottom
• test pressure vessels having the dimensions set out in Example 1 were tested to failure.
• Five groups each of five pressure vessels were subjected to a pressure cycling test with each group of pressure vessels having had a different amount of autofrettage.
• the remaining two pressure vessels (having had no autofrettage) were subjected to a burst test.
• Each of the test pressure vessels was a 5 litre carbon fibre hoop wrap 7060 aluminium alloy pressure vessel manufactured in a cold backward extrusion process using a die 4 and ram 5 having the dimensions set out in Example 1. Details of the amount of autofrettage for each group of pressure vessels and the results of the tests are set out below in Table 3. Table 3
• (b) represents failures at different parts of the cylinder.
• Aluminium high pressure gas cylinders are usually designed so that the stress in the cylindrical side wall at service pressure does not exceed half the alloy yield stress, and that the cylinder burst pressure is at least 2.5 times the operating pressure.
• the design should be such that wall stresses do not exceed 225 MPa.
• Finite element analysis (FEA) of a hoop wrap pressure vessel manufactured using the method and apparatus described above has revealed that the internal profile of the closed end of pressure vessels according to the present invention results in noticeably lower maximum stresses in comparison to pressure vessels with a conventional internal profile at the closed end.
• FEA With FEA the structure (in this case the closed end of the pressure vessel) is broken down into many small pieces (finite number of elements) of various types, sizes and shapes.
• the elements are assumed to have a simplified pattern of deformation (linear or quadratic etc.) and are connected at 'nodes' normally located at corners or edges of the elements.
• the elements are then assembled mathematically using basic rules of structural mechanics i.e. equilibrium of forces and continuity of displacements, resulting in a large system of simultaneous equations.
• the deformed shape of the structure under load may be obtained and internal stresses and strains may be calculated from the deformed shape.
• Figs. 5a and 5b show the principal stresses and the Von Mises stresses for Analysis 1 and Figs. 6a and 6b show the principal stresses and the Von Mises stresses for Analysis 4.
• Figs. 5 and 6 show that the location of maximum stress in the knuckle region remains substantially the same for Analysis 1 and Analysis 4 (the same is also true for Analysis 2 and Analysis 3, not shown).
• Figs. 5 and 6 also show that for Type II pressure vessels manufactured using the method and apparatus described above, the maximum Von Mises stress remains at the inner surface of the pressure vessel even after autofrettage.
• Table 4 clearly show that the absolute value of the first principal stress and the Von Mises stress are significantly lower for Analysis 4 than for any of the other Analyses.
• the FEA shows that the main factors contributing to the lowering of the maximum stress are the value of H and Rc.
• the above method and apparatus are particularly suited, but not limited, to the cold extrusion manufacture of pressure vessels for AA6XXX and AA7XXX series of aluminium alloys (according to the Aluminum Association Inc. Register 2009) and to both Type I cylinders and Type II cylinder liners respectively which meet the fatigue requirements of hoop wrapped pressure vessel standards, for example, EN12257 and IS01 1 1 19-1 and corresponding standards in other regions of the world.
• Type ⁇ cylinders which at least match and often exceed the failure performance of equivalent conventional cylinders may be manufactured using autofrettage at lower pressures.

Landscapes

• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Filling Or Discharging Of Gas Storage Vessels (AREA)
• Pressure Vessels And Lids Thereof (AREA)
• Shaping Metal By Deep-Drawing, Or The Like (AREA)
• Extrusion Of Metal (AREA)

Priority Applications (7)

Applications Claiming Priority (2)

Publications (1)

Family

ID=51688186

Family Applications (1)

Country Status (11)

Families Citing this family (5)

Citations (8)

Family Cites Families (7)

• 2014
  • 2014-06-13 FR FR1455433A patent/FR3022164B1/fr active Active
• 2015
  • 2015-05-26 CN CN201580031312.1A patent/CN106457327B/zh active Active
  • 2015-05-26 PL PL15728083T patent/PL3154719T3/pl unknown
  • 2015-05-26 WO PCT/GB2015/051527 patent/WO2015189561A1/en active Application Filing
  • 2015-05-26 AU AU2015273346A patent/AU2015273346B2/en active Active
  • 2015-05-26 DK DK15728083.5T patent/DK3154719T3/en active
  • 2015-05-26 RU RU2017100331A patent/RU2683676C2/ru active
  • 2015-05-26 GB GB1508964.2A patent/GB2527203B/en active Active
  • 2015-05-26 ES ES15728083.5T patent/ES2672802T3/es active Active
  • 2015-05-26 EP EP15728083.5A patent/EP3154719B1/en active Active
  • 2015-05-26 TR TR2018/07783T patent/TR201807783T4/tr unknown

Patent Citations (8)

Also Published As

Similar Documents

Legal Events