SYSTEM AND METHOD FOR MANUFACTURING A HOLDER FOR A FUEL CELL PRODUCED BY TIPPING MIXING

Abstract

Method for manufacturing a fuel cell holder made of aluminum castings by tilt casting process for a fuel cell, the method comprising: Providing a negative mold (30) with cavities for forming the holder, the holder comprising: a plurality of support legs (32) connected to each other and configured to form a frame (34) with a first and a second side (36, 38) for supporting the fuel cell, the frame (34) having horizontal and vertical casting orientations for casting the support, each support leg (32) having circumferential edges (40) extending around it, each support leg (32) having a first and a second outer ridge (42, 44) formed on the circumferential edges (40) with respect to the vertical casting orientation on the second side (38) of the frame (34), each of the outer ridges (42, 44) extending along the second side (38), at least one support leg (32) having an inner ridge (46) formed away from the circumferential edges (40) and extending over them on the second side (38); a plurality of circumferential projections (50) formed on the second side (38) of the frame (34) for structural fastening, each circumferential projection (50) having a projection diameter (D) B ) has, wherein each circumferential projection (50) is formed on one of the supporting legs (32) and is located either on the first outer ridge (42) or on the inner ridge (46); a plurality of primary ribs (52) arranged on the second side (38) of the frame (34) for reasons of structural integrity, each primary rib (52) bearing against a circumferential projection (50) and extending vertically upwards with respect to the vertical casting orientation to the first outer ridge (42), where the primary rib (52) defines a riser contact area (54), each primary rib (52) having a width of at least 70% of the projection diameter (D B ) and extends at a draft angle of at least 3 degrees from the circumferential projection (50); Providing a feeding mechanism (14) arranged around the mold (30) and fluidically connected to its cavities, the feeding mechanism (14) comprising: a sprue channel (80) which is arranged around the mold (30) and fluidically connected to it; a plurality of gates (82) which are fluidically connected to the sprue (80) and the cavities of the mold (30), each gate (82) having a first side (84) which is connected to the sprue (80) and extends to a second side (86) which is connected to the mold (30); a plurality of primary risers (90) which are fluidically connected to cavities of the mold (30), wherein each primary riser (90) is connected in one of the riser contact areas (54) to the first outer edge of a support leg (32) and is arranged next to the one circumferential projection (50), wherein each primary riser (90) is arranged vertically above the one circumferential projection (50) with respect to the vertical casting orientation of the frame (34); Melting a first metallic material at a predetermined temperature to form a molten metallic material; Moving the mold (30) and the feed mechanism (14) from the horizontal casting orientation to the vertical casting orientation around a rotational axis, while molten metallic material is fed through the sprue (80) to the cavities of the mold (30); Cooling the molten metallic material for a first solidification period in the mold (30) and for a second solidification period in the plurality of risers (90) in order to form a solidified metallic material with the dimensions of the aluminum die-cast fuel cell holder in the risers (90) and in the mold (30), wherein the second solidification period is longer than the first solidification period, so that the shrinkage of the solidified metallic material in the risers (90) takes place outside the mold (30); and Removing the solidified metallic material from the negative sand casting mold (30) to form the fuel cell holder made of aluminum casting using the tilt casting process.

Description

INTRODUCTION

[0001] The present disclosure relates to fuel cell holders made of aluminum casting produced by tilt casting and in particular to systems and methods for producing fuel cell holders produced by tilt casting which compensate for shrinkage during casting.

[0002] A method for casting a part from a molten light metal, in particular from aluminium or an aluminium alloy, is known, for example, from WO 2010 / 058 003 A1.

[0003] A fuel cell bracket is used to hold a fuel cell in place during installation in a vehicle. Many fuel cell brackets are cast from a metallic material such as a metal or metal alloy. During the solidification of the metallic material, undesirable shrinkage can occur in the mold. SUMMARY

[0004] Although the current systems and processes for manufacturing fuel cell brackets fulfill their purpose, there is a need for a new and improved system and process for manufacturing a tilt-cast aluminum fuel cell bracket for a vehicle fuel cell.

[0005] Therefore, one of the aims of the invention is to improve the production of a fuel cell holder made of cast aluminum.

[0006] This problem is solved by a method with the features of claim 1 and a system with the features of claim 9. Advantageous embodiments can be found in the dependent claims, the description, and the drawings.

[0007] According to claim 1, a method for manufacturing a fuel cell bracket made of cast aluminum using the tilt casting process is provided. The method comprises providing a negative mold with cavities for forming the bracket. The bracket comprises a plurality of support legs connected to one another and configured to form a frame with a first and a second side for supporting the fuel cell. The frame has horizontal and vertical casting orientations for casting the bracket. Each support leg has circumferential edges extending around it. Furthermore, each support leg has a first and a second external ridge formed on the circumferential edges with respect to the vertical casting orientation on the second side of the frame. Each of the external ridges also extends along this second side.In addition, at least one support leg has an internal ridge that extends away from the circumferential edges and across them on the second side.

[0008] The bracket further comprises a multitude of circumferential projections formed on the second side of the frame for structural fastening. Each circumferential projection has a projection diameter. Furthermore, each circumferential projection is formed on one of the support legs and abuts either the first outer ridge or the inner ridge.

[0009] The support further comprises a multitude of primary ribs, which are arranged on the second side of the frame for structural integrity. Each primary rib abuts a circumferential projection and extends vertically upwards with respect to the vertical casting orientation to the first outer ridge, where it establishes a riser contact area. Furthermore, each primary rib has a width of at least 70% of the projection diameter and extends from the circumferential projection at a demolding angle of at least 3 degrees.

[0010] The method further comprises providing a feeding mechanism arranged around the mold and fluidically connected to its cavities. The feeding mechanism includes a sprue arranged around the mold and fluidically connected to it. The feeding mechanism further comprises a plurality of gates fluidically connected to the sprue and the cavities of the mold. Each gate also has a first side connected to the sprue and extending to a second side connected to the mold.

[0011] The feeding mechanism further comprises a multitude of primary risers that are fluidically connected to cavities in the mold. Each primary riser is connected to the first outer edge of a support leg in one of the riser contact areas and is located next to a single circumferential projection. Furthermore, each primary riser is positioned vertically above the single circumferential projection with respect to the vertical casting orientation of the frame.

[0012] The process further comprises melting a first metallic material at a predetermined temperature to form a molten metallic material. The process further comprises moving the mold and the feeding mechanism from the horizontal casting orientation to the vertical casting orientation about a rotational axis, while molten metallic material is fed through the sprue to the cavities of the mold.

[0013] The process further comprises cooling the molten metallic material for a first solidification period in the mold and for a second solidification period in the multiple risers to form a solidified metallic material with the dimensions of the aluminum fuel cell mounting bracket in the risers and in the mold. The second solidification period is longer than the first, so that the shrinkage of the solidified metallic material in the risers occurs outside the mold. The process further comprises removing the solidified metallic material from the negative sand casting mold to form the aluminum fuel cell mounting bracket produced by the tilt casting process.

[0014] In one example, each primary riser has a height at least twice the diameter of the projection. In another example, each primary riser has a width greater than the projection diameter. In yet another example, at least one secondary projection is positioned next to a circumferential projection on the second side of the frame and points downwards with respect to the vertical casting orientation. Each secondary projection has the same diameter as the projection.

[0015] In one example, the support further includes a secondary rib located on the second side of the frame. In this example, the secondary rib abuts the secondary projection and extends vertically upwards towards the circumferential projection with respect to the vertical casting orientation. In another example, the secondary rib has a width of at least 70% of the projection diameter and extends from the secondary projection at a demolding angle of at least 3 degrees.

[0016] In one example, at least one support leg is arranged vertically with respect to the vertical casting orientation and defines a second leg. Furthermore, the feeding mechanism includes a lateral riser, which is arranged in the respective riser contact area on the secondary leg of the mold and fluidically connected to it. In this example, the lateral riser is provided with a connector through which the molten metallic material flows. The connector has a neck that is fluidically connected to the at least one mold cavity. The connector has an open end configured to extend to the at least one mold cavity in the riser contact area and to form a riser connection angle of at least 45° to a horizontal plane.

[0017] In one example, the first metallic material comprises the following: 7.0 wt% silicon (Si), 0.4 wt% magnesium (Mg), 0.14 wt% iron (Fe) and the remainder aluminum (Al).

[0018] According to claim 9, a system for manufacturing a fuel cell bracket made of cast aluminum using a tilt casting process is provided. The system comprises a mold unit configured to form a negative mold for the cast aluminum fuel cell bracket manufactured using the tilt casting process. The mold includes at least one shaped cavity with a pattern having the dimensions of the cast aluminum bracket.

[0019] The bracket comprises multiple support legs connected to each other and configured to form a frame with a first and a second side for supporting the fuel cell. The frame has horizontal and vertical casting orientations for casting the bracket. Each support leg has edges running around its circumference. Furthermore, each support leg has a first and a second external ridge formed on the circumferential edges with respect to the vertical casting orientation on the second side of the frame. Each of the external ridges extends along this second side. In addition, at least one support leg has an internal ridge extending away from the circumferential edges and across them on the second side.

[0020] Furthermore, the bracket includes a multitude of circumferential projections formed on the second side of the frame for structural fastening. Each circumferential projection has a projection diameter. In addition, each circumferential projection is formed on one of the support legs and abuts either the first outer ridge or the inner ridge.

[0021] The support further comprises a multitude of primary ribs, which are arranged on the second side of the frame for structural integrity. Each primary rib abuts a circumferential projection and extends vertically upwards to the first outer ridge with respect to the vertical casting orientation, which defines a riser contact area. Each primary rib has a width of at least 70% of the projection diameter and extends from the circumferential projection at a demolding angle of at least 3 degrees.

[0022] The system further comprises a feeding mechanism arranged around the mold and fluidically connected to its cavities. The feeding mechanism includes a sprue, also arranged around the mold and fluidically connected to it, and a plurality of gates fluidically connected to the sprue and the mold cavities. Each gate has a first side connected to the sprue and extends to a second side connected to the mold.

[0023] The feeding mechanism further comprises a multitude of primary risers that are fluidically connected to cavities in the mold. Each primary riser is connected to the first outer edge of a support leg in one of the riser contact areas and is located next to a single circumferential projection. Furthermore, each primary riser is positioned vertically above the single circumferential projection with respect to the vertical casting orientation of the frame.

[0024] The system further comprises a furnace configured to melt a first metallic material at a predetermined temperature to form a molten metallic material. The system also includes a tilting device movably connected to the mold and the feeding mechanism. The tilting device is configured to move the mold and the feeding mechanism from the horizontal casting orientation to the vertical casting orientation about a rotational axis, while molten metallic material is fed through the sprue to the cavities of the mold.

[0025] The system further includes a cooling area designed to cool the molten metallic material for a first solidification period in the mold and for a second solidification period in the multiple risers, in order to form a solidified metallic material with the dimensions of the aluminum die-cast fuel cell holder in both the risers and the mold. The second solidification period is longer than the first, so that the shrinkage of the solidified metallic material in the risers occurs outside the mold.

[0026] The system also includes a separation unit designed to remove the solidified metallic material from the negative mold in order to form the aluminum die-cast fuel cell holder produced by tilt casting.

[0027] The system also includes a control unit that communicates with the molding unit, the oven, the feeding mechanism, the tilting device, and the separating unit. The control unit is designed to operate the molding unit, the oven, the feeding mechanism, the tilting device, and the separating unit.

[0028] The system also includes a power source designed to supply power to the forming unit, the oven, the feeding mechanism, the tilting device, the separating unit and the control system.

[0029] In one embodiment, each primary riser has a height that is at least twice the diameter of the projection. In another embodiment, each primary riser has a width that is greater than the projection diameter.

[0030] In one embodiment, the holder further comprises at least one secondary projection adjacent to a circumferential projection on the second side of the frame, which is directed downwards with respect to the vertical casting orientation. Each secondary projection has a projection diameter. In one example of this embodiment, the holder further comprises a secondary rib arranged on the second side of the frame. The secondary rib abuts the secondary projection and extends vertically upwards with respect to the circumferential projection with respect to the vertical casting orientation. In one example, the secondary rib has a width of at least 70% of the projection diameter and extends from the secondary projection at a demolding angle of at least 3 degrees.

[0031] In one embodiment, at least one support leg is arranged vertically with respect to the vertical casting orientation and defines a second leg. In this embodiment, the feeding mechanism further comprises a lateral riser, which is arranged in the respective riser contact area on the secondary leg of the mold and fluidically connected to it. The lateral riser is provided with a connecting piece through which the molten metallic material flows. The connecting piece has a neck that is fluidically connected to the at least one mold cavity. Furthermore, the connecting piece has an open end that is configured to extend to the at least one mold cavity in the riser contact area and to form a riser connection angle of at least 45° to a horizontal plane.

[0032] In another embodiment, the first metallic material comprises the following: 7.0 wt% silicon (Si), 0.4 wt% magnesium (Mg), 0.14 wt% iron (Fe) and the remainder aluminium (Al).

[0033] According to yet another aspect of the present disclosure, a fuel cell support bracket made of cast aluminum, manufactured by tilt casting, is provided for a fuel cell. The bracket comprises a plurality of support legs connected to one another and configured to form a frame with a first and a second side for supporting the fuel cell. The frame has horizontal and vertical casting orientations for casting the bracket. Each support leg has edges extending around it. In addition, each support leg has a first and a second external ridge formed on the circumferential edges with respect to the vertical casting orientation on the second side of the frame. Furthermore, each of the external ridges extends along these edges on the second side. At least one support leg has an internal ridge formed away from the circumferential edges and extending over them on the second side.

[0034] Furthermore, the bracket includes a multitude of circumferential projections formed on the second side of the frame for structural fastening. Each circumferential projection has a projection diameter. In addition, each circumferential projection is formed on one of the support legs and abuts either the first outer ridge or the inner ridge.

[0035] The support further comprises a multitude of primary ribs, which are arranged on the second side of the frame for structural integrity. Each primary rib abuts a circumferential projection and extends vertically upwards with respect to the vertical casting orientation to the first outer ridge, where it establishes a riser contact area. Furthermore, each primary rib has a width of at least 70% of the projection diameter and extends from the circumferential projection at a demolding angle of at least 3 degrees.

[0036] In one embodiment, the holder further comprises at least one secondary projection adjacent to a circumferential projection on the second side of the frame, which is directed downwards with respect to the vertical casting orientation. Each secondary projection has a projection diameter of [missing information].

[0037] In another embodiment, the support further comprises a secondary rib arranged on the second side of the frame. The secondary rib rests against the secondary projection and extends vertically upwards towards the circumferential projection with respect to the vertical casting orientation.

[0038] In yet another embodiment, the secondary rib has a width of at least 70% of the projection diameter and extends from the secondary projection at a demolding angle of at least 3 degrees.

[0039] Further areas of application arise from the description given here. The description and the specific examples serve only for illustration and are not intended to limit the scope of this disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The drawings described here are for illustrative purposes only and are not intended to limit the scope of the present disclosure in any way. Fig. Figure 1 is a schematic representation of a system for manufacturing a fuel cell holder made of aluminum casting using the tilt casting process, according to an embodiment of the present disclosure. Fig. Figure 2A is a side view of the front of a feed mechanism and a mold for the fuel cell mount of the system in Fig. 1 according to one embodiment. Fig. 2B is a side view of the rear of the feeding mechanism and the mold in Fig. 2A. Fig. 2C is a front face of a fuel cell bracket made of cast aluminum using the tilt casting process, taken from the mold in Fig. 2A and Fig. 2B. Fig. Figure 3 is an enlarged view of the feeding mechanism and the mold in circle 3 of Fig. 2B. Fig. Figure 4 is an enlarged view of the feeding mechanism and the mold in circle 4 of Fig. 2B. Fig. Figure 5 is an enlarged view of the feeding mechanism and the mold in circle 5 of Fig. 2B. Fig. Figure 6 is an enlarged view of the feeding mechanism and the mold in circle 6 of Fig. 2B. Fig. Figure 7 is a partial side view of the feeding mechanism and the mold according to another embodiment of the present disclosure. Fig. Figure 8 is an enlarged view of the feeding mechanism and the mold in circle 8 of Fig. 2B. Fig. Figure 9 is a flowchart of a process for manufacturing a fuel cell holder made of aluminum casting using the tilt casting process, according to an example in the present disclosure. DETAILED DESCRIPTION

[0041] The following description is merely exemplary and is not intended to limit the present disclosure, its application or use.

[0042] Aspects of the present disclosure provide systems and methods for manufacturing an improved, tilt-cast aluminum fuel cell bracket for a vehicle, wherein the bracket exhibits high elasticity and strength. The systems and methods offer a means of compensating for the shrinkage of the aluminum casting in a mold during solidification when casting the bracket. Consequently, the metal shrinkage occurs in overflow risers outside the mold.

[0043] Fig. Figure 1 shows a system 10 for manufacturing a low-porosity aluminum fuel cell bracket produced by tilt casting for a vehicle according to an embodiment of the present disclosure. As shown, the system 10 comprises a mold unit 12 which is equipped with a negative mold 30 ( Fig. 2A and Fig. 2B) for the fuel cell holder 100 made of cast aluminum using the tilt casting process ( Fig. 2C). The mold 30 comprises at least one formed cavity, preferably a plurality of formed cavities, with one or more patterns to define the dimensions of the aluminum die-cast fuel cell holder produced by tilt casting. In one example, the mold 30 has patterns made of wet-cast or chemically bonded sand. A core arrangement can then be provided in the mold 30 to further define the dimensions or structure of the pattern. It is understood that the mold 30 can also be produced in any other suitable manner without departing from the spirit or scope of this disclosure.

[0044] With reference to Fig. 1-2B has the negative mold 30 dimensions that define the support. This comprised a plurality of support legs 32, which are connected to one another and configured to form a frame 34 with a first and a second side 36, 38 for supporting the fuel cell. In this embodiment, the first side 36 ( Fig. 2A) a front side and the second side 38 ( Fig. 2B) a back side of frame 34. As shown, the back side of frame 34 has a waffle structure, which is described in more detail below.

[0045] Frame 34 has horizontal and vertical casting orientations for casting the bracket. In Fig. 2A and Fig. Figure 2B shows the frame 34 in a vertical casting orientation along a vertical plane. In one embodiment, the vertical plane defines a front cutting half and a rear cutting half of the mold. As shown in Fig. 2A and Fig. As shown in Figure 2B, the frame 34 has a pivot axis X about which the frame 34 can be moved, tilted or rotated during a process for manufacturing the bracket (see below).

[0046] With reference to Fig. 2B Each support leg 32 has edges 40 extending around it. Furthermore, each support leg 32 has a first outer ridge 42 and a second outer ridge 44 formed on the circumferential edges 40 on the second side 38 of the frame 34. In this embodiment, each of the outer ridges extends along the second side 38. In addition, at least one support leg 32 has an inner ridge 46 extending away from the circumferential edges 40 and extending along the second side 38. As shown, the inner ridge 46 can be perpendicular or parallel to one of the outer ridges. As shown, at least one support leg 32 is arranged vertically with respect to the vertical casting orientation and defines a second leg 48 (secondary leg 48). Fig. 7).

[0047] As in Fig. As shown in Figure 2B, the bracket further comprises a plurality of circumferential projections 50 formed on the second side 38 of the frame 34 for structural fastening. Each circumferential projection 50 has a projection diameter. In addition, each circumferential projection 50 is formed on one of the support legs 32 and abuts either the first outer ridge 42 or the inner ridge 46.

[0048] The support further comprises a plurality of primary ribs 52, which are arranged on the second side 38 of the frame 34 for reasons of structural integrity. Each primary rib 52 abuts a circumferential projection 50 and extends vertically upwards with respect to the vertical casting orientation to the first outer ridge 42. At the outer ridge 42, each primary rib 52 defines a riser contact area 54. In this respect, each primary rib 52 has a width of at least 70% of the projection diameter.

[0049] Furthermore, each primary rib 52 extends from the circumferential projection 50 at a first demolding angle 60 (e.g., at least 3 degrees) to a first rib side 62, which forms a first plane 64 thereof, to the first outer ridge 42. In addition, each primary rib 52 extends from the circumferential projection 50 at a second demolding angle 66 (e.g., at least 3 degrees) to a second rib side 68, which forms a second plane 69 thereof, to the first outer ridge 42. In this embodiment, the first demolding angle 60 is at least 3 degrees with respect to the first plane 64, and the second demolding angle 66 is at least 3 degrees with respect to the second plane 69.

[0050] With reference to Fig. 2B and 6-7, the holder further comprises at least one second projection 70, which is arranged next to a circumferential projection 50 on the second side 38 of the frame 34. As shown, the at least one secondary projection 70 is arranged below the one circumferential projection 50 with respect to the vertical casting orientation. Each secondary projection 70 has a projection diameter. The holder further comprises a secondary rib, which is arranged on the second side 38 of the frame 34. The secondary rib abuts the secondary projection 70 and extends vertically upwards with respect to the circumferential projection 50 ( Fig. 7) In one example, the secondary rib has a width of at least 70% of the projection diameter.

[0051] Furthermore, each secondary rib extends from the secondary projection 70 at a third demolding angle 74 (e.g., at least 3 degrees) to a third side 75, which forms a third plane 76 thereof, to the circumferential projection 50. Additionally, each secondary rib extends from the secondary projection 70 at a fourth demolding angle 77 (e.g., at least 3 degrees) to a fourth side 78, which forms a fourth plane 79 thereof, to the circumferential projection 50. In this embodiment, the third demolding angle 74 is at least 3 degrees to the third plane 76, and the fourth demolding angle 77 is at least 3 degrees to the fourth plane 79.

[0052] With reference to Fig. 1 and Fig. In 2B, the system 10 further comprises a feeding mechanism 14 configured to direct the molten metallic material into the at least one cavity of the mold 30, which defines the dimensions of the holder to be cast. In this embodiment, the feeding mechanism 14 is arranged around the mold 30 and fluidically connected to its cavities. In one example, the feeding mechanism 14 comprises a ladle (not shown), a sprue (not shown), a filter (not shown) fluidically connected to the sprue, and a runner 80 fluidically connected to the sprue and the mold 30. As shown, the runner is arranged around the mold 30. In this example, the ladle receives molten metallic material (e.g., aluminum alloy) and pours the molten metallic material into the sprue, with the filter removing oxides from the molten metallic material.As already mentioned, the inlet is fluidically connected to the sprue (here a double sprue with a first and a second vane) through which the molten metallic material flows from the filter.

[0053] As in Fig. 2B and Fig. As shown in Figure 3, the feeding mechanism 14 further comprises a plurality of gates 82 which are fluidically connected to the sprue and the cavities of the mold 30. Each gate 82 has a first gate side 84 which is fluidically connected to the sprue 80. The first gate side 84 extends to a second gate side 86 which is fluidically connected to the mold 30.

[0054] With reference to Fig. 2B and 4-6, the feeding mechanism 14 further comprises a plurality of primary risers 90 which are fluidically connected to cavities of the mold 30. Each primary riser 90 is connected to the first outer edge of a support leg 32 in one of the riser contact areas 54. In addition, each primary riser 90 is arranged next to a circumferential projection 50.

[0055] Furthermore, each primary riser 90 is arranged vertically above the circumferential projection 50 with respect to the vertical casting orientation of the frame 34. Preferably, each primary riser 90 has a height H R (referring to the vertical orientation), which is at least twice the diameter D B The lead is 50. Furthermore, each primary riser has a width of 90. R , which is preferably larger than the projection diameter D B .

[0056] As in Fig. 2B and Fig. As shown in Figure 8, the feeding mechanism 14 further comprises a lateral riser 92, which is arranged in the respective riser contact area 54 on the secondary leg 48 of the mold 30 and fluidically connected to it. The lateral riser 92 is provided with a connecting piece 94 through which the molten metallic material flows. The connecting piece 94 has a neck 96, which is fluidically connected to at least one mold cavity. In addition, the neck 96 has an open end 98, which is configured to extend to the at least one mold cavity in the riser contact area 54 and to form a riser connection angle of at least 45° to a horizontal plane.

[0057] As shown, the horizontal plane can be defined in relation to the vertical casting orientation of the frame 34. Thus, the riser connection angle can be defined by a wall of the neck 96 and the horizontal plane, as shown in Fig. Figure 8 is shown. Consequently, each riser of the feed mechanism 14 is designed to receive the overflow of molten metallic material from the mold 30 at a corresponding riser connection angle, thus enabling shrinkage to occur in the risers outside the mold 30.

[0058] With renewed reference to Fig. In Figure 1, the system 10 further comprises a furnace 16 configured to melt a first metallic material at a predetermined temperature to form a molten metallic material. In one example, the furnace 16 can be operated at a temperature between 650 °C and 900 °C. In another embodiment, the furnace 16 can be charged with aluminum. The furnace 16 can be an electric arc furnace, an induction furnace, or another suitable furnace, without thereby departing from the spirit or scope of the present disclosure. Furthermore, the first metallic material can comprise 7.0 wt% silicon (Si), 0.4 wt% magnesium (Mg), 0.14 wt% iron (Fe), and aluminum (Al) as the remainder.

[0059] As in Fig. As shown in Figure 1, the system 10 further comprises a tilting device 18, which is movably connected to the mold 30 and the feed mechanism 14. The tilting device 18 is configured to move the mold 30 and the feed mechanism 14 from the horizontal casting orientation to the vertical casting orientation about a rotational axis, while molten metallic material is fed through the sprue to the cavities of the mold 30. The tilting device 18 is configured to move or tilt the mold 30 and the feed mechanism 14 at a controlled speed, e.g., 2 degrees per second (° / sec). It is understood that the controlled speed is between 1° / sec and 10° / sec, 1° / sec, 2° / sec, 4° / sec, 6° / sec, 8° / sec. or may be at another suitable regulated speed, without departing from the spirit or scope of the present disclosure.The tilting device 18 can have a clamping, bed, or rod mechanism attached to the frame 34 and the mold 30. Such a mechanism can be equipped with a motor configured to rotate the frame 34 and the mold 30 about the axis of rotation at a controlled speed.

[0060] The mold 30 can then be cast or sealed with chemically bonded sand. The molten metallic material in the mold 30 and in the risers is then cooled to a specific temperature, e.g., to approximately 450 °C, in a designated cooling area (see below), so that the molten metallic material can solidify in the numerous formed cavities of the mold 30 and form a final component with the dimensions of the holder. Preferably, the holder is made of an aluminum alloy of the composition described above.

[0061] With reference to Fig. The system 10 further comprises a cooling area 20, which is designed to cool the molten metallic material for a first solidification period in the mold 30 and for a second solidification period in the multiple risers, in order to form a solidified metallic material with the dimensions of the aluminum die-cast fuel cell holder in the risers and in the mold 30. It is understood that the second solidification period is longer than the first, so that the shrinkage of the solidified metallic material in the risers occurs outside the mold 30. That is, during the solidification of the molten metallic material, the shrinkage of the metallic material is compensated for by allowing the shrinkage to occur in the respective risers outside the mold 30. This compensation is achieved in part by the geometry of the risers (e.g., the height of the risers), the geometry of the ribs (e.g.,the width of the ribs) and the connection angle (e.g. 45°) of the lateral risers 92 is achieved.

[0062] In one example, the first metallic material of the bracket is preferably an aluminum alloy, e.g., A356. In another example, the solidified metallic material has a Young's modulus or modulus of elasticity (E) of about 75 GPa. Preferably, the solidified metallic material has a tensile strength (UTS) of about 310 megapascals (MPa), a yield strength (YS) of more than 250 MPa, and an elongation (EL) between 5% and 12%. Furthermore, the solidified metallic material exhibits a porosity of preferably less than 10%.

[0063] With reference to Fig. In Figure 1, the system 10 further comprises a separation unit 22 configured to remove the solidified metallic material from the negative mold 30 to form the aluminum die-cast fuel cell holder produced by tilt casting. In one embodiment, the separation unit 22 is configured to shake or remove the mold 30 containing the chemically bonded sand from the target component. An automated unit can be used to separate the mold 30 from the target component by breaking the mold apart and obtaining the target component. For example, a vibrating unit or a vibrating table with a lower collection grid for collecting mold particles can be used. It is understood that the mold can also be broken apart in any other suitable manner without deviating from the spirit or scope of this disclosure.

[0064] In this embodiment, the separating unit 22 is further configured to remove the sprue after the mold 30 has been removed from the target component. As is known in the prior art, removing the sprue from the target component can also include removing portions of the bonded sand that was used to fill the mold 30 during casting and gating.

[0065] In one embodiment, the separating unit 22 is further configured to clean the target component after the sprue has been removed. For example, a sandblasting machine can be used to apply or blast beads (e.g., metal beads) onto the surfaces of the target component. To meet the alloy design requirements, the separating unit 22 can also include a testing area in which the target component is tested for its mechanical dimensions, mechanical properties, chemical composition, and microstructure. For example, a computer-based system such as a coordinate measuring machine (CMM) can be used to measure the mechanical dimensions of the target component, thereby enabling the fixture 100, as shown in Fig. 2C is shown and specified. Any suitable methods and equipment may be used to evaluate the dimensions, mechanical properties, chemical composition, and microstructure of the bracket without deviating from the spirit or scope of this disclosure.

[0066] As in Fig. As shown in Figure 1, the system 10 further comprises at least one control unit 24, which is connected to the molding unit 12, the oven 16, the feeding mechanism 14, the tilting device 18, and the separating unit 22. The control unit 24 is configured to control the molding unit 12, the oven 16, the feeding mechanism 14, the tilting device 18, and the separating unit 22. The system 10 further comprises a power source 26, which is configured to supply current to the molding unit 12, the oven 16, the feeding mechanism 14, the tilting device 18, the separating unit 22, and the control unit 24.

[0067] Fig. Figure 9 shows a method 110 for manufacturing a low-porosity aluminum fuel cell bracket produced by tilt casting for a vehicle according to an example of the present disclosure. In this example, the method 110 can be combined with the system 10 consisting of Fig. 1. Method 110 comprises, in box 112, the provision of a negative mold 30 with cavities for forming the bracket. The mold 30 comprises at least one formed cavity, preferably a plurality of formed cavities, to form the aluminum casting fuel cell bracket produced by tilt casting. The mold 30 has a pattern with dimensions of the aluminum casting bracket. In one example, the mold 30 has patterns made of wet-casting or chemically bonded sand. A core arrangement can then be arranged in the mold 30 to further define the dimensions or structure of the pattern. It is understood that the mold 30 can also be produced in any other suitable manner without departing from the spirit or scope of this disclosure.

[0068] As above and in Fig. As explained in Figures 2A-2C, the bracket comprises a plurality of support legs 32, which are interconnected and configured to form a frame 34 with a first and a second side 36, 38 for supporting the fuel cell. As mentioned earlier, the first side 36 is a front and the second side 38 is a back of the frame 34. Furthermore, the back of the frame 34 has a waffle-like structure, which will be described in more detail below.

[0069] Frame 34 has horizontal and vertical casting orientations for casting the bracket. In Fig. 2A and Fig. Figure 2B shows the frame 34 in a vertical casting orientation along a vertical plane. In one embodiment, the vertical plane defines a front cutting half and a rear cutting half of the holder. As explained above, the frame 34 has an axis of rotation about which the frame 34 can be moved, tilted, or rotated during a process for manufacturing the holder.

[0070] As in Fig. As shown in Figure 2B, each support leg 32 has edges 40 extending around it. Furthermore, each support leg 32 has a first outer ridge 42 and a second outer ridge 44, which are formed on the second side 38 of the frame 34 with respect to the vertical casting orientation at the circumferential edges 40. In this respect, each of the outer ridges extends along the second side 38. In addition, at least one support leg 32 has an inner ridge 46, which extends away from the circumferential edges 40 and along the second side 38.

[0071] With reference to Fig. 2B The bracket further comprises a plurality of circumferential projections 50, which are formed on the second side 38 of the frame 34 for structural fastening. Each circumferential projection 50 has a projection diameter. In addition, each circumferential projection 50 is formed on one of the support legs 32 and abuts either the first outer ridge 42 or the inner ridge 46.

[0072] As in Fig. As shown in Figures 2B and 4-6, the support further comprises a plurality of primary ribs 52, which are arranged on the second side 38 of the frame 34 for reasons of structural integrity. Each primary rib 52 abuts a circumferential projection 50 and extends vertically upwards to the first outer ridge 42 with respect to the vertical casting orientation, which defines a riser contact area 54. In this respect, each primary rib 52 has a width of at least 70% of the projection diameter and extends at a demolding angle of at least 3 degrees from the circumferential projection 50 (as explained above).

[0073] With reference to Fig. 2B and Fig. In this embodiment, the holder further comprises at least one secondary projection 70 adjacent to a circumferential projection 50 on the second side 38 of the frame 34, which is directed downwards with respect to the vertical casting orientation. Each secondary projection 70 has a projection diameter. In one example of this embodiment, the holder further comprises a secondary rib arranged on the second side 38 of the frame 34. The secondary rib abuts the secondary projection 70 and extends vertically upwards with respect to the circumferential projection 50. In one example, the secondary rib has a width of at least 70% of the projection diameter and extends from the secondary projection 70 at a demolding angle of at least 3 degrees.

[0074] As in Fig. As shown in Figure 9, the method 110 further comprises, in Box 114, the provision of a feeding mechanism 14 which is arranged around the mold 30 and fluidically connected to its cavities. The feeding mechanism 14 of the system 10 from Fig. 1 can be implemented in method 110. Preferably, the feeding mechanism 14 is configured to direct the molten metallic material into the at least one cavity of the mold 30, which defines the dimensions of the holder to be cast.

[0075] As described above, the feeding mechanism 14 comprises a ladle (not shown), a sprue (not shown), a filter (not shown) fluidically connected to the sprue, and a runner fluidically connected to the sprue and the mold 30. As shown, the runner is arranged around the mold 30. In this example, the ladle receives molten metallic material (e.g., aluminum) and pours the molten metallic material into the sprue, with the filter removing oxides from the molten metallic material. As mentioned previously, the sprue is fluidically connected to the runner (here a double runner with a first and a second vane) through which the molten metallic material flows from the filter.

[0076] As mentioned above and in Fig. As shown in Figure 2B-3, the feeding mechanism 14 further comprises a plurality of gates 82 which are fluidically connected to the sprue and cavities of the mold 30. Each gate 82 has a first gate side 84 which is connected to the sprue 80 and extends to a second gate side 86 which is connected to the mold 30. As shown in Fig. As shown in Figure 2B, the feeding mechanism 14 further comprises a plurality of primary risers 90 which are fluidically connected to cavities of the mold 30. Each primary riser 90 is connected to the first outer edge of a support leg 32 in one of the riser contact areas 54 and is arranged next to a circumferential projection 50. Furthermore, each primary riser 90 is arranged vertically above the circumferential projection 50 with respect to the vertical casting orientation of the frame 34. Preferably, each primary riser 90 has a height H R , which have at least twice the diameter D BThe lead corresponds to 50. In addition, each primary riser 90 preferably has a width W. R , which is larger than the projection diameter D B .

[0077] As explained, the feeding mechanism 14 further comprises a lateral riser 92, which is arranged in the respective riser contact area 54 on the secondary leg 48 of the mold 30 and fluidically connected to it. The lateral riser 92 is provided with a connecting piece 94 through which the molten metallic material flows. The connecting piece 94 has a neck 96, which is fluidically connected to the at least one mold cavity. Furthermore, the neck 96 has an open end 98, which is configured to extend to the at least one mold cavity in the riser contact area 54 and to form a riser connection angle θ of at least 45° to a horizontal plane, as explained above.Consequently, each riser of the feed mechanism 14 is designed to receive the overflow of molten metallic material from the mold 30 at a corresponding riser connection angle, thus enabling shrinkage to occur in the risers outside the mold 30.

[0078] With reference to Fig. 9 further comprises, in Box 116, the melting of a first metallic material at a predetermined temperature to form a molten metallic material. The melting step can be carried out using the furnace 16 of system 10. Fig. 1. The furnace 16 is configured to melt a first metallic material at a predetermined temperature to form a molten metallic material. In one example, the furnace 16 can have a temperature between 650 °C and 900 °C. In one embodiment, the furnace 16 can be charged with aluminum. The furnace 16 can be an electric arc furnace, an induction furnace, or another suitable furnace, without thereby departing from the spirit or scope of the present disclosure. Furthermore, the first metallic material can comprise 7.0 wt% silicon (Si), 0.4 wt% magnesium (Mg), 0.14 wt% iron (Fe), and aluminum (Al) as the remainder.

[0079] As in Fig. As shown in Figure 9, the method 110 further comprises, in box 118, moving the mold 30 and the feeding mechanism 14 from the horizontal casting orientation to the vertical casting orientation about a rotational axis, while molten metallic material is fed through the sprue to the cavities of the mold 30. In one example, the tilting device 18 of the system 10 is Fig. The tilting device 18 is used to move the mold 30 and the feed mechanism 14. As explained above, the tilting device 18 is movably connected to the mold 30 and the feed mechanism 14. The tilting device 18 is configured to move the mold 30 and the feed mechanism 14 from the horizontal casting orientation to the vertical casting orientation about a rotational axis, while molten metallic material is fed through the sprue to the cavities of the mold 30. The tilting device 18 is configured to move or tilt the mold 30 and the feed mechanism 14 at a controlled speed, e.g., 2 degrees per second.

[0080] The mold 30 can then be cast or sealed with chemically bonded sand. The molten metallic material in the mold 30 and in the risers is then cooled to a specific temperature, e.g., to approximately 450 °C, in a designated cooling area (see below), so that the molten metallic material solidifies in the numerous cavities of the mold 30 and forms a final component with the dimensions of the holder. Preferably, the holder is made of an aluminum alloy of the composition described above.

[0081] With reference to Fig. 9 further comprises the process 110 in box 120, cooling the molten metallic material for a first solidification period in the mold 30 and for a second solidification period in the plurality of risers, in order to form a solidified metallic material with the dimensions of the fuel cell holder made of aluminum casting in the risers and in the mold 30. In one example, the cooling area 20 of the system 10 is made of Fig. 1. The system is designed to allow the molten metallic material to solidify for a first solidification period in the mold 30 and for a second solidification period in the multiple risers. It is understood that the second solidification period is longer than the first, so that the shrinkage of the solidified metallic material in the risers occurs outside the mold 30. That is, during the solidification of the molten metallic material, the shrinkage is compensated for by allowing the shrinkage to occur in the risers outside the mold 30. This compensation is achieved in part by the geometry of the risers, the geometry of the ribs, and the riser connection angle of the lateral risers 92.

[0082] In one example, the first metallic material of the bracket is preferably an aluminum alloy, e.g., A356. Furthermore, the solidified metallic material has a Young's modulus or modulus of elasticity (E) of approximately 75 GPa. Additionally, the solidified metallic material has a tensile strength (UTS) of approximately 310 megapascals (MPa), a yield strength (YS) of more than 250 MPa, and an elongation (EL) between 5% and 12%. Finally, the solidified metallic material exhibits a porosity of less than 10%.

[0083] Fig. Figure 9 further shows process 110, in which the solidified metallic material is removed from the negative sand casting mold 30 in box 122 to form the fuel cell holder made of cast aluminum using the tilt casting process. The separation step can be performed with the separation unit 22 of system 10. Fig.1. As explained, the separation unit 22 is configured to remove the solidified metallic material from the negative mold 30 to form the aluminum die-cast fuel cell holder produced by tilt casting. In one embodiment, the separation unit 22 is configured to shake or remove the mold 30 containing the chemically bonded sand from the target component. An automated unit can be used to separate the mold 30 from the target component by breaking the mold 30 apart and obtaining the target component. For example, a vibrating unit or a vibrating table with a lower collection grid for collecting mold particles can be used. It is understood that the mold can also be broken apart in any other suitable manner without deviating from the spirit or scope of this disclosure.

[0084] In this example, the separation unit 22 is further configured to remove the sprue after the mold 30 has been removed from the target component. As is known in the prior art, removing the sprue from the target component can also involve removing some of the bonded sand that was used to fill the mold 30 during casting and gating. Furthermore, the separation unit 22 is also configured to clean the target component after the sprue has been removed. As explained above, a sandblasting machine can be used to apply or blast beads (e.g., metal beads) onto the surfaces of the target component. To meet the alloy design requirements, the separation unit 22 can also include a testing area where the target component is tested for its mechanical dimensions, mechanical properties, chemical composition, and microstructure.In one example, a computer-based system such as a coordinate measuring machine (CMM) can be used to measure the mechanical dimensions of the target component, thereby determining the fixture. Any suitable methods and equipment can be used to evaluate the dimensions, mechanical properties, chemical composition, and microstructure of the fixture without deviating from the spirit or scope of this disclosure.

[0085] The term "approximately" used here means up to + / - 10% of the parameter's value. For example, approximately 270 °C can encompass a range between 243 °C and 297 °C. In another example, approximately 40 micrometers can encompass a range between 36 micrometers and 44 micrometers.

Claims

[1] Method for manufacturing a fuel cell holder made of aluminum castings by tilt casting process for a fuel cell, the method comprising: Providing a negative mold (30) with cavities for forming the holder, the holder comprising: a plurality of support legs (32) connected to each other and configured to form a frame (34) with a first and a second side (36, 38) for supporting the fuel cell, the frame (34) having horizontal and vertical casting orientations for casting the support, each support leg (32) having circumferential edges (40) extending around it, each support leg (32) having a first and a second outer ridge (42, 44) formed on the circumferential edges (40) with respect to the vertical casting orientation on the second side (38) of the frame (34), each of the outer ridges (42, 44) extending along the second side (38), at least one support leg (32) having an inner ridge (46) formed away from the circumferential edges (40) and extending over them on the second side (38); a plurality of circumferential projections (50) formed on the second side (38) of the frame (34) for structural fastening, each circumferential projection (50) having a projection diameter (D) B ) has, wherein each circumferential projection (50) is formed on one of the supporting legs (32) and is located either on the first outer ridge (42) or on the inner ridge (46); a plurality of primary ribs (52) arranged on the second side (38) of the frame (34) for reasons of structural integrity, each primary rib (52) bearing against a circumferential projection (50) and extending vertically upwards with respect to the vertical casting orientation to the first outer ridge (42), where the primary rib (52) defines a riser contact area (54), each primary rib (52) having a width of at least 70% of the projection diameter (D B ) and extends at a draft angle of at least 3 degrees from the circumferential projection (50); Providing a feeding mechanism (14) arranged around the mold (30) and fluidically connected to its cavities, the feeding mechanism (14) comprising: a sprue channel (80) which is arranged around the mold (30) and fluidically connected to it; a plurality of gates (82) which are fluidically connected to the sprue (80) and the cavities of the mold (30), each gate (82) having a first side (84) which is connected to the sprue (80) and extends to a second side (86) which is connected to the mold (30); a plurality of primary risers (90) which are fluidically connected to cavities of the mold (30), wherein each primary riser (90) is connected in one of the riser contact areas (54) to the first outer edge of a support leg (32) and is arranged next to the one circumferential projection (50), wherein each primary riser (90) is arranged vertically above the one circumferential projection (50) with respect to the vertical casting orientation of the frame (34); Melting a first metallic material at a predetermined temperature to form a molten metallic material; Moving the mold (30) and the feed mechanism (14) from the horizontal casting orientation to the vertical casting orientation around a rotational axis, while molten metallic material is fed through the sprue (80) to the cavities of the mold (30); Cooling the molten metallic material for a first solidification period in the mold (30) and for a second solidification period in the plurality of risers (90) in order to form a solidified metallic material with the dimensions of the aluminum die-cast fuel cell holder in the risers (90) and in the mold (30), wherein the second solidification period is longer than the first solidification period, so that the shrinkage of the solidified metallic material in the risers (90) takes place outside the mold (30); and Removing the solidified metallic material from the negative sand casting mold (30) to form the fuel cell holder made of aluminum casting using the tilt casting process. [2] Method according to claim 1, wherein each primary riser (90) has a height (H R ) has a projection diameter at least twice the diameter (D B ) of the circumferential margin (50). [3] Method according to claim 1, wherein each primary riser (90) has a width (W R ) which is larger than the projection diameter (D B ). [4] Method according to claim 1, wherein the holder further comprises at least one secondary projection (70) adjacent to a circumferential projection (50) on the second side (38) of the frame (34), which is arranged downwards with respect to the vertical casting orientation, wherein each secondary projection (70) has the projection diameter (D B ) has. [5] Method according to claim 4, wherein the holder further comprises a secondary rib arranged on the second side (38) of the frame (34), wherein the secondary rib abuts the secondary projection (70) and extends vertically upwards to the circumferential projection (50) with respect to the vertical casting orientation. [6] Method according to claim 5, wherein the secondary rib has a width of at least 70% of the projection diameter (D B) and extends from the secondary projection (70) at a demolding angle of at least 3 degrees. [7] Method according to claim 1, wherein at least one support leg (32) is arranged vertically with respect to the vertical casting orientation and defines a secondary leg (48), and wherein the feeding mechanism (14) further comprises a lateral riser (92) which is arranged in the respective riser contact area (54) on the secondary leg (48) of the mold (30) and is fluidically connected to it, wherein the lateral riser (92) is provided with a connecting piece (94) through which the molten metallic material flows, wherein the connecting piece (94) has a neck (96) which is fluidically connected to the at least one mold cavity, and wherein the connecting piece (94) has an open end (98) which is configured to extend to the at least one mold cavity in the riser contact area (54) and to form a riser connection angle (θ) of at least 45° to a horizontal plane. [8] Method according to claim 1, wherein the first metallic material comprises 7.0 wt% silicon (Si), 0.4 wt% magnesium (Mg), It contains 0.14 wt% iron (Fe) and the remainder aluminum (Al). [9] System (10) for manufacturing a fuel cell support made of aluminum castings for a fuel cell produced by tilt casting, the system (10) comprising: a molding unit (12) configured to form a negative mold (30) for the aluminum die-cast fuel cell holder produced by tilt casting, wherein the mold (30) comprises at least one shaped cavity with a pattern having the dimensions of the aluminum die-cast holder, the holder comprising: a plurality of support legs (32) connected to each other and configured to form a frame (34) with a first and a second side (36, 38) for supporting the fuel cell, the frame (34) having horizontal and vertical casting orientations for casting the support, each support leg (32) having circumferential edges (40) extending around it, each support leg (32) having a first and a second outer ridge (42, 44) formed on the circumferential edges (40) with respect to the vertical casting orientation on the second side (38) of the frame (34), each of the outer ridges (42, 44) extending along the second side (38), at least one support leg (32) having an inner ridge (46) formed away from the circumferential edges (40) and extending over them on the second side (38); a plurality of circumferential projections (50) formed on the second side (38) of the frame (34) for structural fastening, each circumferential projection (50) having a projection diameter (D) B ) has, wherein each circumferential projection (50) is formed on one of the supporting legs (32) and abuts either the first outer ridge (42) or the inner ridge (46); and a plurality of primary ribs (52) arranged on the second side (38) of the frame (34) for reasons of structural integrity, each primary rib (52) bearing against a circumferential projection (50) and extending vertically upwards with respect to the vertical casting orientation to the first outer ridge (42), where the primary rib (52) defines a riser contact area (54), each primary rib (52) having a width of at least 70% of the projection diameter (D B ) and extends at a draft angle of at least 3 degrees from the circumferential projection (50); a feeding mechanism (14) arranged around the mold (30) and fluidically connected to its cavities, the feeding mechanism (14) comprising: a sprue channel (80) which is arranged around the mold (30) and fluidically connected to it; a plurality of gates (82) which are fluidically connected to the sprue (80) and the cavities of the mold (30), each gate (82) having a first side (84) which is connected to the sprue (80) and extends to a second side (86) which is connected to the mold (30); and a plurality of primary risers (90) which are fluidically connected to cavities of the mold (30), wherein each primary riser (90) is connected in one of the riser contact areas (54) to the first outer edge of a support leg (32) and is arranged next to the one circumferential projection (50), wherein each primary riser (90) is arranged vertically above the one circumferential projection (50) with respect to the vertical casting orientation of the frame (34); a furnace (16) which is equipped to melt a first metallic material at a predetermined temperature in order to form a molten metallic material; a tilting device (18) which is movably connected to the mold (30) and the feed mechanism (14), wherein the tilting device (18) is configured to move the mold (30) and the feed mechanism (14) from the horizontal casting orientation to the vertical casting orientation about an axis of rotation, while molten metallic material is fed through the sprue (80) to the cavities of the mold (30); a cooling area (20) configured to allow the molten metallic material to solidify for a first solidification period in the mold (30) and for a second solidification period in the plurality of risers (90) in order to form a solidified metallic material with the dimensions of the aluminum die-cast fuel cell holder in the risers (90) and in the mold (30), wherein the second solidification period is longer than the first solidification period, so that the shrinkage of the solidified metallic material in the risers (90) takes place outside the mold (30); and a separation unit (22) which is designed to remove the solidified metallic material from the mold (30) in order to form the fuel cell holder made of aluminum casting produced by tilt casting; a control unit (24) which is connected to the molding unit (12), the oven (16), the feeding mechanism (14), the tilting device (18) and the separating unit (22), wherein the control unit (24) is configured to control the molding unit (12), the oven (16), the feeding mechanism (14), the tilting device (18) and the separating unit (22); and a power source (26) which is configured to supply power to the forming unit (12), the oven (16), the feeding mechanism (14), the tilting device (18), the separating unit (22) and the control unit (24). [10] System according to claim 9, wherein each primary riser (90) has a height that is at least twice the advance diameter (D) B ) of the circumferential margin (50).

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