Conformable pressure vessel concepts offer improved storage efficiencies and reduced system weights compared to traditional cylindrical designs. These pressure vessels may be comprised of a plurality of smaller cylindrical vessels that can be stacked or bundled to fit into a predetermined packaging space.
Production of conformable pressure vessels requires the fabrication of a polymeric pressure vessel liner to act as a barrier layer to prevent permeation of the liquids and gasses contained by the pressure vessel at high pressures. One method for production of pressure vessel liners is to extrude a continuous plastic tube and send the plastic tube through a corrugation process that creates the desired profile comprising rigid main body sections and flexible return lines.
One limitation of existing fabrication methods is insufficient speed of the corrugator, which restricts production capacity. Fabricating the larger main body sections and smaller return lines requires speed reductions in the corrugator, further restricting production volumes. Producing larger amounts of plastic pressure vessel liners therefore requires numerous pieces of expensive production equipment and significant floor space.
An additional limitation of existing equipment is that the number of mold elements in the repeating pattern is constrained by the equipment design. Some pressure vessel liner geometries are only possible to achieve by adding an excessive amount of additional mold elements to the pattern. This lengthens the equipment, which adds to the cost and overall size of the equipment. Other pressure vessel liner geometries are not possible to achieve because the pattern of mold elements required would be too large to be practical.
An additional fabrication method for pressure vessel liners involves the separate production of extruded main body sections and formed return lines. This improves throughput, but joining the segments together introduces several potential leak paths that are exacerbated by high pressure, extreme temperatures, and pressure cycling.
Another limitation of existing fabrication methods is inconsistent mechanical properties, including variability of wall thickness and material properties of the pressure vessel liners. This is caused by the limitations of the forming equipment which has difficulties creating a larger outer diameter and a smaller return line diameter from a single extruded tube.
Another limitation of existing fabrication methods is the inflexibility of the forming equipment, which cannot produce flexible main body lengths without stopping the process and reconfiguring the equipment. Stopping production and reconfiguring equipment further reduces effective production capacity and results in more connections between varying length pressure vessels, leading to additional potential leak paths.
Several alternative polymeric pressure vessel liner production methods and apparatuses are disclosed. The methods include improving the flexibility of pressure vessel production by introducing automated methods for changing out mold elements without stopping the production run. Alternative forming methods are also disclosed for producing variable lengths of main body sections with improved mechanical properties at high extrusion rates without the need for reconfiguration of a corrugator.
One method for forming a pressure vessel liner includes forming an extruded tube by extruding a parison through a die and a mandrel; forming main body sections and return line sections in the extruded tube according to a first pattern, wherein a cross-sectional area of the return line sections is smaller than a cross-sectional area of the main body sections; changing the pattern according to which the main body sections and the return line sections are formed from the first pattern to a second pattern without stopping the forming of the extruded tube; and forming the main body sections and the return line sections in the extruded tube according to the second pattern.
One apparatus for forming pressure vessel liners includes an extruder that drives a parison through a die and a mandrel to form an extruded tube; and a formation unit that forms the extruded tube into main body sections and return line sections according to a first pattern, changes the pattern according to which the main body sections and the return line sections are formed to a second pattern without stopping the extrusion of the extruded tube; and forms the extruded tube into the main body sections and the return line sections according to the second pattern.
Another method for forming a pressure vessel liner includes forming an extruded tube by extruding a parison through a die and a mandrel; using a corrugator having a set of mold elements, forming main body sections and return line sections in the extruded tube according to a pattern; using an interchange mechanism, selectively replacing large diameter mold elements in the set of mold elements with small diameter mold elements; and using the corrugator and the selectively replaced mold elements, forming the main body sections and the return line sections in the extruded tube according to the pattern.
Another method for forming a pressure vessel liner includes forming an extruded tube by extruding a parison through a die and a mandrel; and forming main body sections and return line sections in the extruded tube by alternating application of small diameter sections and large diameter sections of a pair of drums to the extruded tube. A cross-sectional area of the return line sections is smaller than a cross-sectional area of the main body sections, and a pattern of the main body sections and the return line sections is formed without stopping the forming of the extruded tube by applying the pair of drums to form the small diameter sections on the extruded tube.
Another method for forming a pressure vessel liner includes forming an extruded tube by extruding a parison through a die and a mandrel; and forming main body sections and return line sections in the extruded tube by clamping opposing sections of a molding press together onto the extruded tube. A cross-sectional area of the return line sections is smaller than a cross-sectional area of the main body sections. A pattern of the main body sections and the return line sections is formed without stopping the forming of the extruded tube by expanding the opposing sections of the molding press in a longitudinal direction along an axis parallel to a longitudinal axis of the extruded tube or controlling a frequency with which the opposing sections press together onto the extruded tube.
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 are not to-scale. On the contrary, the dimensions of the various features are arbitrarily expanded or reduced for clarity.
Pressure vessel liners can be formed using various types of formation units that includes components such as corrugators, mold presses, and/or opposed drums used to shape an extruded plastic parison. Flexibility in application of these various components can improve production speed, reduce space within a production facility, and allow flexibility in parison type and grade when compared to a more standard corrugation process.
Operation of the corrugator 600 can include applying circulating pairs of active mold elements 610 in a first pattern to the extruded tube 614, where the pairs of active mold elements 610 form a profile of an outside geometry of each section of a pressure vessel liner 626. Operation of the corrugator 600 can also include removing pairs of inactive mold elements 612 forming the first pattern from the corrugator 600 and replacing the removed pairs of inactive mold elements 612 with pairs of alternative mold elements 618 to form a second pattern. Circulating pairs of the alternative mold elements 618 can be applied according to the second pattern to the extruded tube 614.
With this apparatus, the mold elements 610, 612 for the corrugator 600 can be selectively removed and replaced with the alternative mold elements 618, enabling the pattern of mold elements 610, 612 to be controlled and varied. For example, since the mold elements 610, 612 rotate between positions in which the active mold elements 610 are applied to the extruded tube 614 to form the main body sections 616 and the return line sections 618 and in which the inactive mold elements 612 are not applied to the extruded tube 614, the alternative mold elements 618 can be swapped for particular inactive mold elements 612. This enables the same corrugator 600 to produce pressure vessel liners 626 with a variety of lengths for the main body sections 616 and the return line sections 618. Automated mold element 610, 612 selection and replacement also allows forming a variety of patterns of repeating or variable main body sections 616 and return line sections 618 without the corrugator 600 being taken off-line for manual reconfiguration, improving process timing.
The embodiments of
The molding press 802 can be horizontally stationary with the opposing sections 804 moving up and down to clamp around the extruded tube 806. The molding press 802 can also be configured to translate horizontally at the same speed as the extruded tube 806 to avoid breaking, tearing, or bunching up of the extruded tube 806 proximate to the molding press 802. In other words, in some implementations the molding press 802 can be stationary relative to longitudinal motion of the extruded tube 806 and in other implementations the molding press 802 can move along an axis parallel to a longitudinal axis of the extruded tube 806 at a speed at which the extruded tube 806 is extruded.
Lead-in features in the horizontally axial direction may also be used to avoid abrupt geometry changes. The molding press 802 may also incorporate heating and vacuum features similar to those described in respect to
The expanding molding press 1000 expands the extruded tube 1004 in a targeted region in order to reduce the specific weight of material, for example in regions of the return line sections 1008, in order to reduce wall thickness and enable improved material properties. The expanding molding press 1000 can be fitted with a progressive die, for example, a spring-loaded die, that guides the extruded tube 1004 into a proper shape at the selected region. The progressive die can be connected to the expanding molding press 1000, where the progressive die forms the extruded tube 1004 into the main body sections 1006 and the return line sections 1008 in a region of the extruded tube 1004 where the opposing sections 1002 of the expanding molding press 1000 clamp together. The expanding molding press 1000 can also be fitted with cutters that can be used to trim off excess material after shaping.
In some implementations, as the extruded tube 1202 passes through the drums 1200a,b, the drums 1200a,b are rotated to the large diameter section 1206 to allow the extruded tube 1202 to pass through the drums 1200a,b without touching either of the drums 1200a,b. When it is time to form a return line section 1210, the drums 1200a,b are rotated such that a small diameter section 1204 of the drums 1200a,b forms the main body sections 1208 and the return line sections 1210 as the extruded tube 1202 and the drums 1200a,b move together. In some implementations, the drums 1200a,b can be stationary relative to longitudinal motion of the extruded tube 1202. In other implementations, the drums 1200a,b can move along an axis parallel to a longitudinal axis of the extruded tube 1202 at a speed at which the extruded tube 1202 is extruded. This can allow the extruded tube 1202 to be created with varied lengths of main body sections 1208 having return line sections 1210 in between.
Operation of the drums 1200a,b can include moving the extruded tube 1202 in a longitudinal direction through the drums 1200a,b where an outside radial surface of each drum 1200a, 1200b has a small diameter section 1204 and a large diameter section 1206. The operation of the drums 1200a,b can also include rotating each of the opposing drums 1200a, 1200b about an axis perpendicular to a longitudinal axis of the extruded tube 1202 and forming the main body sections 1208 and the return line sections 1210 into the extruded tube 1202 by applying the small diameter sections 1204 of each opposing drum to the extruded tube 1202 according to a first pattern.
A frequency with which the small diameter sections 1204 of each opposing drum 1200a, 1200b are applied to the extruded tube 1202 can be changed to form a second a pattern. Operation of the drums 1200a,b can also include forming the main body sections 1208 and the return line sections 1210 by applying the small diameter sections 1204 of each opposing drum 1200a, 1200b to the extruded tube 1202 according to the second pattern. In some implementations, the operation of the drums 1200a,b can include changing speed of the extruded tube 1202 relative to the drums 1200a,b before and after the small diameter sections 1204 of the drums 1200a,b are applied to the extruded tube 1202 to change a wall thickness of the extruded tube 1202. In other words, the extrusion speed and relative motion of the extruded tube 1202 before and after the extruded tube 1202 passes through the drums 1200a,b can be manipulated to ensure the proper wall thickness is produced in the return line sections 1210. In some implementations, multiple drum pairs can be used to produce multiple different shapes on the same extruded tube. For example, one set of drums can form the ends of an extruded tube section without corrugations to enable the attachment of end fittings, and another set can form return line sections.
The embodiments of
While the disclosure has been described in connection with certain embodiments, it is to be understood that the disclosure is not to be limited to the disclosed embodiments but, on the contrary, is intended to cover various modifications and equivalent arrangements.
This application claims priority to U.S. Provisional Patent Application Ser. No. 62/411,918, titled “Continuous Polymeric Liner Production Methods for Conformable Pressure Vessels,” filed Oct. 24, 2016, the entirety of which is incorporated herein.
Number | Date | Country | |
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62411918 | Oct 2016 | US |