Abstract
A double-walled tube section for constructing a double-walled tube segment suitable for underpressure applications such as an evacuated tube transport system.
Claims
1. A double-walled tube section for constructing a double-walled tube segment suitable for underpressure applications, wherein the double-walled tube segment comprises an elongated curved outer shell part forming the outer wall of the double-walled tube segment and a plurality of inner shell parts, wherein the elongated curved outer shell part comprises an outer shell part curved central portion having outer shell part long edges, and an outer shell part portion folded portion at at least one of the outer shell part long edges wherein the outer shell part folded portion forms a flange folded towards the centrepoint M of the curvature, wherein each inner shell part comprises an inner shell part flat central portion having inner shell part long edges, and an inner shell part folded portion folded away from the centrepoint of the curvature at at least one of the inner shell part long edges, the inner shell part folded portion having an inner shell part curved edge to match the curvature of the elongated curved outer shell part, wherein the plurality of inner shell parts are joined together along their inner shell part long edges, and wherein the plurality of inner shell parts are joined to the inner surface of the elongated curved outer shell part along the curved edge of the inner shell part folded edge portion.
2. The double-walled tube section according to claim 1, wherein the angle between the inner shell part flat central portion and the inner shell part folded edge portion is between 85 and 95°.
3. The double-walled tube section according to claim 1, wherein each inner shell part flat central portion also has short edges, wherein each folded portion of the elongated curved outer shell part also has a respective edge, wherein each inner shell part is also joined along at least one of the short edges of the inner shell part flat central portion to the edge of the at least one folded portion of the elongated curved outer shell part.
4. The double-walled tube section according to claim 1, wherein the inner shell part long edge of the inner shell part flat central portion overlaps another said inner shell part edge of the inner shell part flat central portion of the adjoining inner shell part of said plurality of inner shell parts, and wherein these inner shell part edges are joined.
5. The double-walled tube section according to claim 1, wherein both of the outer shell part long edges of the elongated curved outer shell part is respectively provided with the outer shell part folded portion, wherein the outer shell part folded portions form outer shell part flanges folded towards the centrepoint M of the curvature, and wherein each inner shell part is also joined along both of the inner shell part short edges to the edge of the folded portions of the elongated curved outer shell part.
6. The double-walled tube section according to claim 1, wherein the curved portion of the elongated curved outer shell part is provided with protruding or intruding outer shell part reinforcements against buckling.
7. The double-walled tube section according to claim 6, wherein the outer shell part reinforcements against buckling are intruding dimples in the surface of the tube, wherein the dimples are circular, elliptic or polygonal wherein the number of sides in the polygon is 5 or more.
8. The double-walled tube section according to claim 1, wherein the flat portion of one, more or all of the inner shell parts is provided with protruding or intruding inner shell part reinforcements against buckling.
9. The double-walled tube section according to claim 8, wherein the protruding inner shell part reinforcements against buckling comprise one or more longitudinal dimples parallel to the inner shell part long edges.
10. The double-walled and airtight tube segment consisting of a plurality of double-walled tube sections according to claim 1, wherein the double-walled tube sections are airtightly joined along the outer shell part long edges to form a tube segment wherein the folded edges of the inner shell part in adjoining double-walled tube sections are aligned to form a plurality of ribs around the internal circumference of the tube segment distanced apart, and wherein the folded portions of the elongated curved outer shell part form longitudinal rims (“stringers”).
11. The double-walled and airtight tube segment according to claim 10, wherein the double-walled tube sections are also joined to the adjoining double-walled tube section along the edges inner shell part 4f and 4g of the adjoining inner shell parts.
12. The double-walled and airtight tube segment according to claim 10 with an incircle having a diameter of at least 3 m.
13. A tube for an evacuated tube transport system (ETT) comprising a plurality of double-walled tube segments according to claim 10.
14. The double-walled tube section according to claim 1, wherein the angle between the flat central portion and the folded edge portion is 900 (orthogonal).
15. The double-walled tube section according to claim 1, wherein each inner shell part flat central portion also has short edges, wherein each folded portion of the elongated curved outer shell part also has a respective edge, wherein each folded portion of the inner shell part also has short side edges and a respective curved edge, wherein each inner shell part is also joined along at least one of the short edges of the inner shell part flat central portion to the edge of the at least one folded portion of the elongated curved outer shell part, and also along the short side edges of the folded portion of the inner shell part.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0045] The invention will now be further explained by means of the following, non-limitative drawings.
[0046] FIG. 1 shows a double-walled tube segment according to the invention. The tube segment shows embossed hexagonal dimples (indentation) to increase the buckling resistance of the tube when operated under external pressure. The tube segment in this example is constructed from eleven double-walled tube sections (dwts) according to the invention. The outside of the tube segment is formed by a plurality (11 in this example) of elongated outer skin panels (eosp) that have a curvature so as to form a smooth and cylindrical surface. The inside surface (as seen from the tube segment) consists of inner sheel parts (isp). The cross section in FIG. 1 is circular, and this is also the preferable shape. It is conceivable that the cross section may be non-circular, e.g. oval, but in that case the curvature of the eosp is not the same for each one making up the circumference of the tube segment, and this is not preferable from a process efficiency point of view. However, it may be applicable e.g. to house switches. The eosp's are joined together, e.g. by welding (such as laser welding, laser hybrid welding, gas metal arc welding, or any other suitable form of welding) along the entire length to obtain an airtight connection. The number of double-walled tube sections needed to produce a tube segment depends on the width of the available metal sheet and the desired diameter of the tube segment. It is preferable to produce the eosp from coiled steel sheet. In that case the width of the eosp is determined by the width of the coil. Assuming a width of 1.50 m and 4 mm thick steel strip and a 6 cm high folded portion a tube segment with an external diameter of 5 m requires 11 eosp's. A 4 m diameter tube segment requires 9 eosp's.
[0047] FIG. 2 shows the double-walled tube segment according to the invention of FIG. 1 but without the flat central portion of the isp's and without the curved portion of the eosp, so that the internal structure is clearly visible. The cell size (the rectangular space between the annular ribs and the longitudinal ribs (stringers)) is visible, particularly in the enlarged section. The folded edge portions of the isp's are aligned to form a continuous circumferential rib. The height of the rib is not constant, because of the flat central portion of the isp's providing an even deeper twin wall section away from the stringers, but nevertheless it contributes greatly to the buckling strength. The distance between the ribs is determined by the width (4f, 4g) of the flat central portion of the isp's. Ideally (but not necessarily) the width of the isp is the width of the coiled steel sheet. Producing these isp's from hot rolled strip appears to be a very economical and efficient way of producing these parts because the strip is supplied in the form of coiled strip that can be uncoiled on site and the parts can be cut, provided with protruding or intruding reinforcements against buckling and folded in line. In this particular example the length of the eosp is 30 m, and the width (4f, 4g) of the flat central portion of the isp is 1 m. The eosp's are joined together, along the entire length so the flange along the long edge(s) of the eosp act as longitudinal ribs (or stringers). The eleven longitudinal ribs are clearly visible in FIG. 2.
[0048] FIG. 3 shows one eosp 3 and thirty individual isp's 4 of which the first seven are already welded to the eosp and the others are shown in an exploded view. These will be welded to the eosp finally resulting in the assembled double-walled tube section 2. In this example the thickness of the eosp is 4 mm and the thickness of the isp's is 2 mm. By itself the eosp is insufficiently stiff to be handled, despite the curvature, but in the form depicted in FIG. 4 where the isp's are welded to each other and to the eosp the assembly is stiff enough to be handled for transportation, e.g. by truck, or during constructed of a tube, through the tube already constructed. During construction, the system as depicted in FIG. 9 could be used. FIG. 5A shows two dwts's joined airtightly. The eosp may be provided with a groove G to receive the edge of the adjoining eosp to enable the resulting outer surface of the double-walled and airtight tube segment to be flush and smooth after connecting the edge to the adjoining eosp (see FIG. 6). In the enlarged section (FIG. 5B) the two dwts are still separated so that the internal structure is visible. The second enlargement (FIG. 5C) shows that the eosp in this case has only one flange, so that the structure on the other long side is open. In addition to the airtight connection between the adjoining eosp's, it is preferable that the adjoining dwts's are also connected, preferably airtightly, at the side which forms the inside of the tube section along the edges 4f and 4g of the isp's in the dwts's.
[0049] FIG. 3D also shows the locations where a connection (k, k′) needs to be made between the isp's and the eosp, and where a fold is already present (fold). The connection indicated with k.sub.1 or k.sub.2 is preferably a full joint, such as a welding k.sub.1 along the entire length of the edge 4e is the isp connecting the isp to the eosp, and the welding k.sub.2 along the entire length of the edge 4f to connect the isp to the flange 3d of the eosp, but could also be stitch welded. The connections k′ can also be full connections, but could also be spot welds, stitch welds or glued connections. The connection k″ can be the same as k.sub.2 if the eosp also has a flange similar to 3d at edge 3b, or a connection between two dwts on the inside of the tube segment. This can be a full joint, such as a weld along the entire length of the dwts or a different type of joint, optionally using a connector such as a corner bracket that is fixed in place. Note that the joint at the short upstanding edges of flange 4d are not indicated. These may or may not be joined.
[0050] FIG. 6 shows a cross-section of the connection between two dwts, where the surface of the left eosp is indented to receive the edge of the right eosp and thereby produce a flush connection by welding in the groove G.
[0051] FIG. 7 shows the eosp with the curvature R, and FIG. 8 shows the isp with the same curvature of edge 4e on flange 4d.
[0052] It should be noted that the dimensions of the edges 4b/4c and 4f/4g in the isp depicted in FIG. 8 is such that edge 4b/4c is shorter than edge 4f/4g. However, according to the invention the edge 4b/4c can also be chosen longer than edge 4f/4g. In that case the ribs formed by the flanges 4d are distanced further apart, and the amount of welding is reduced, because there are less isp's needed along the length of the dwts.
[0053] FIG. 9 shows the sequence of producing a tube 6 from tube segments 1, and from double walled tube sections (dwts) 2. In this example 11 dwts's are needed to produce one tube segment 1.
[0054] FIG. 10 shows a schematic process of producing double-walled and airtight tube segments from double-walled tube sections. A first dwts is placed on a roller bed. A second dwts is provided, and fixedly connected to the first dwts. After fixing the two dwts's the connected dwts's rotate on the roller bed. Another dwts is provided, and fixedly connected to the already connected dwts's and this is repeated until the double-walled tube segment is complete.
[0055] FIG. 11 shows the embodiment wherein the dwts is produced by using the eosp according to the invention and a flat isp (optionally with reinforcements against buckling) without flanges and insert pieces that act as the connection between the curved surface of the eosp and the flat isp, wherein the insert pieces provide the annular rib in the tube segment produced from the dwts's.
