Metal seal

Abstract

The present invention is provided with: an annular U-shaped seal part (3) having a U-shaped cross section and having a pair of seal lip parts (2) for sealing between a pair of flat surfaces; an annular centering guide part (6) having a pair of rectangular cross-section locking bulge parts (5) respectively bulging from a pair of base part-side axial side surfaces (3b) of the U-shaped seal part (3) toward both sides in the axial direction; a pair of first seal protrusions (7) formed so as to protrude at the tips of the pair of seal lip parts (2), respectively abutting the pair of flat surfaces; and a pair of second seal protrusions (9) provided in a protruding manner respectively at positions separated from corner parts between the pair of locking bulge parts (5) and the pair of base part-side axial side surfaces (3b). A distance (A) between the root outer peripheral surface of the pair of seal lip parts (2) and the top part of the second seal protrusions (109) is set to A ≥ 0.3.

Description

Metal seal

[0001] The present invention relates to a metal seal used in pipe connections and the like in semiconductor manufacturing equipment.

[0002] Conventionally, as disclosed in Patent Document 1, for example, a metal seal has been known which has a U-shaped seal portion that seals between two mutually parallel planes, and which has a locking bulge protruding from the axial side of the U-shaped seal portion near the base, and which has an integrally formed centering guide portion.

[0003] In this metal seal, a first seal ridge is formed at the tip end of a pair of elastic leg pieces of the U-shaped seal portion, and further, a second seal ridge smaller than the first seal ridge is formed on each of the axial side surfaces near the base of the U-shaped seal portion at the corner between the axial side surface near the base and the bulge portion.

[0004] This metal seal can be centered without machining a concave seal groove into the two parallel planes to be sealed, making it easy to replace conventional seal materials.It can also withstand use in high-temperature areas, making it fully applicable to modern semiconductor manufacturing equipment, etc.

[0005] Patent No. 6424124

[0006] However, while metal seals such as those described in Patent Document 1 can exert a certain degree of tightening force by fastening a pair of flanges with multiple bolts, there is a risk that chain clamps made of aluminum alloys will be damaged if tightened with a high tightening force. For this reason, there is a demand for seals that can exert the required sealing performance with a lower tightening force.

[0007] The present invention has been made in view of the above points, and an object of the present invention is to reduce the tightening force required to achieve the desired sealing performance.

[0008] In order to achieve the above object, in the present invention, the shape and position of the second seal ridge are improved.

[0009] Specifically, the first invention comprises: a U-shaped seal portion which is annular and has a U-shaped cross section and has a pair of seal lip portions which seal between a pair of flat surfaces; an annular centering guide portion which has a pair of locking bulges which have a rectangular cross section and which bulge out axially from a pair of base-near axial side surfaces of the U-shaped seal portion to both axial sides; a pair of first seal ridges which protrude from the tips of the pair of seal lip portions and abut against the pair of flat surfaces, respectively; and a pair of second seal ridges which protrude away from the corners between the pair of locking bulges and the pair of base-near axial side surfaces, and the distance A between the root outer peripheral surfaces of the pair of seal lip portions and the tops of the second seal ridges is A≧0.3.

[0010] If the distance A is less than 0.3, the flexural rigidity of the seal lip portion cannot be maintained, causing the seal lip portion to tilt too much. However, by setting A ≥ 0.3, the second seal ridge is appropriately spaced from the base of the U-shaped seal portion, maintaining the flexural rigidity of the base of the U-shaped seal portion and suppressing its deformation. This reduces the sinking of the first seal ridge side and suppresses tilting of the U-shaped seal portion. This allows the U-shaped seal portion to maintain high surface pressure at the contact points with the pair of flat surfaces. This prevents a decrease in sealing performance due to insufficient surface pressure.

[0011] In a second aspect of the present invention, in the first aspect, the second seal ridge has an isosceles triangular cross section, and a ratio of a height X to a base length Y satisfies X / Y≦0.70.

[0012] If X / Y is greater than 0.7, the second seal ridge has a pointed shape and its tip is easily deformed, resulting in significant sinking of the first seal ridge and a significant tilt of the U-shaped seal portion, reducing the surface pressure on the first seal ridge and deteriorating sealing performance. However, by setting X / Y≦0.70, the second seal ridge is not too pointed and deformation of its tip is suppressed, resulting in less sinking of the first seal ridge and suppressing tilt of the U-shaped seal portion. This allows the U-shaped seal portion to maintain high surface pressure at the contact point with the pair of flat surfaces. This prevents a decrease in sealing performance due to insufficient surface pressure.

[0013] In a third aspect of the present invention, in the first or second aspect of the present invention, the cross section of the first seal ridge is circular or triangular, and the ratio X / Z of the height X of the second seal ridge to the height Z of the first seal ridge satisfies 0.6≦X / Z≦1.6.

[0014] If X / Z is less than 0.6, the height of the second seal ridge becomes too low, resulting in only the first seal ridge contacting the pair of flat surfaces. Conversely, if X / Z is greater than 1.6, the height of the second seal ridge becomes too high, resulting in only the second seal ridge contacting the pair of flat surfaces. However, by satisfying the ratio 0.6≦X / Z≦1.6, it is possible to prevent the pair of flat surfaces from contacting only one of the first seal ridge and the second seal ridge, thereby achieving high sealing performance. Furthermore, by tapering the first seal ridge, the contact area between the first seal ridge and the pair of flat surfaces is reduced, allowing for high surface pressure to be maintained.

[0015] In addition, a fourth invention comprises: a U-shaped seal portion which is annular and has a U-shaped cross section and has a pair of seal lip portions which seal between a pair of flat surfaces; an annular centering guide portion which has a pair of locking bulge portions with a rectangular cross section which bulge out axially from a pair of base-near axial side surfaces of the U-shaped seal portion to both axial sides; a pair of first seal ridges which are formed to protrude from tips of the pair of seal lip portions and abut against the pair of flat surfaces, respectively; and a pair of second seal ridges which protrude from and are spaced apart from corners between the pair of locking bulge portions and the pair of base-near axial side surfaces, wherein the ratio of the distance A between the root outer peripheral surface and the top of the second seal ridge to the distance B between the outer peripheral surfaces of the locking bulge portions and the root outer peripheral surfaces of the pair of seal lip portions is A / B≦0.26.

[0016] With the above configuration, the pair of second seal ridges on both axial sides are located at a distance A / B of 0.26 or less from the outer peripheral surfaces of the roots of the pair of seal lips, and therefore are closer to the pair of seal lips than when A / B is more inward than 0.26, making the portion directly below the second seal ridges more easily deformable and requiring less force to press the second seal ridges. As a result, when the metal seal is fastened to the sealing portion with a chain clamp, it can be fastened with a lower clamping force than conventional products, preventing damage to the chain clamp.

[0017] In a fifth aspect of the present invention, in the fourth aspect, the ratio of the axial thickness E of the seal lip portion at a portion closer to the base than the first seal ridge to the axial thickness C of the base of the U-shaped seal portion is E / C≦0.15.

[0018] With the above configuration, the E / C value is 0.15 or less, and the axial thickness E of the seal lip portion in the area without the first seal ridge is thinner than in the conventional case, making it easier to deform and allowing the metal seal to be fastened with a lower tightening force.

[0019] In a sixth aspect of the present invention, in the fourth or fifth aspect of the present invention, a ratio of a radial length D of the seal lip portion to an axial thickness C of a base of the U-shaped seal portion is D / C≧1.35.

[0020] According to the above configuration, by setting the D / C value to 1.35 or more, the seal lip portion is more easily deformed than in a case where the length D of the seal lip portion is shorter and the D / C value is smaller than 1.35, and the metal seal can be fastened with a lower tightening force.

[0021] As described above, according to the present invention, it is possible to further reduce the tightening force required to achieve the desired sealing performance, and to prevent a decrease in sealing performance due to insufficient surface pressure.

[0022] FIG. 5A is an enlarged cross-sectional view of line VB-VB in FIG. 5A. FIG. 5A is an enlarged cross-sectional view of line VB-VB in FIG. 5A. FIG. 5A is an enlarged cross-sectional view of line VB-VB in FIG. 5A. FIG. 5A is an enlarged cross-sectional view of line VB-VB in FIG. 5A. FIG. 5A is an enlarged cross-sectional view of line VB-VB in FIG. 5A.

[0023] Hereinafter, a first embodiment of the present invention will be described with reference to the drawings.

[0024] 1A to 1C show a metal seal 1 according to a first embodiment of the present invention, which is used in pipe connections in semiconductor manufacturing equipment, vacuum equipment, liquid crystal panel manufacturing equipment, and the like. The metal seal 1 has excellent corrosion resistance, radical resistance, heat resistance, and the like. The metal seal 1 is made of, for example, stainless steel, copper alloy, or heat-resistant and corrosion-resistant alloy (Inconel, Hastelloy, etc.), and may be surface-coated (gold, silver, copper, nickel, etc.), and can exhibit sealing performance even at 200°C (the heat-resistant temperature of general sealing materials is approximately 150°C).

[0025] The metal seal 1 includes a U-shaped seal portion 3 having an annular shape and a U-shaped cross section, and a pair of seal lip portions 2 that seal between a pair of flat surfaces 50a, 51a (shown in FIG. 1C ). The pair of flat surfaces 50a, 51a are, for example, formed on first and second flanges 50, 51 of a pair of pipe connections and are parallel to each other. The U-shaped seal portion 3 has a root outer peripheral surface 3a that extends in the radial direction and has a substantially arc-shaped cross section on the root side of the pair of seal lip portions 2, and the base portion has a generally rectangular shape.

[0026] A pair of locking bulges 5 having a rectangular cross section bulge outward in the axial direction from a pair of axially proximal side surfaces 3b of the U-shaped seal portion 3, forming an annular centering guide portion 6. The outer peripheral surface 5a of this centering guide portion 6 abuts against the inner peripheral surfaces 50b, 51b of the first and second flanges 50, 51 that form the pair of flat surfaces 50a, 51a, thereby centering the metal seal 1 so that its center coincides with the center of the first and second flanges 50, 51.

[0027] First seal ridges 7 are formed at the tips of the pair of seal lip portions 2 so as to protrude toward the pair of flat surfaces 50 a, 51 a, respectively. The cross-sectional shape of the first seal ridges 7 shown in the figure is semicircular, but it may also be a polygonal shape such as a triangle, as shown in FIG. 9 , which will be described later. As shown in FIG. 1C , when the pair of first seal ridges 7 abut against the pair of flat surfaces 50 a, 51 a, respectively, the pair of seal lip portions 2 are pressed toward each other in the axial direction and deformed.

[0028] A pair of second seal ridges 9 are provided at a predetermined distance from the corners 8 between the pair of locking bulges 5 and the pair of axial side surfaces 3b near the base. The second seal ridges 9 have a triangular cross section, for example, and in this embodiment, the positions of their apexes are set.

[0029] Specifically, as shown in FIG. 1B , the ratio of the distance A between the root outer peripheral surface 3 a and the top of the second seal ridge 9 to the distance B between the outer peripheral surface 5 a of the locking bulge portion 5 and the root outer peripheral surface 3 a (at the smallest diameter portion) of the pair of seal lip portions 2 is A / B≦0.26.

[0030] Furthermore, it is desirable that the ratio of the axial thickness E of the portion of the seal lip portion 2 closer to the base than the first seal ridge 7 to the axial thickness C of the base of the U-shaped seal portion 3 be E / C≦0.15.

[0031] Furthermore, it is desirable that the ratio of the radial length D of the seal lip portion 2 to the axial thickness C of the base of the U-shaped seal portion 3 be D / C≧1.35.

[0032] Next, a method of using the metal seal according to this embodiment will be described.

[0033] 1C, the metal seal 1 is placed so as to be sandwiched between the pair of flat surfaces 50a, 51a of the pair of first and second flanges 50, 51. Specifically, the metal seal 1 is placed so that the outer peripheral surface 5a of the locking bulge 5 of the metal seal 1 abuts against the inner peripheral surface 51b of the first flange 51, which has the lower flat surface 51. This causes the center of the metal seal 1 to be centered with the centers of the first and second flanges 50, 51.

[0034] Next, the metal seal 1 is sandwiched from above by the first flange 50 having the flat surfaces 50 a. As a result, the pair of first seal ridges 7 contact the pair of flat surfaces 50 a, 51 a. At this stage, the pair of second seal ridges 9 have not yet contacted the pair of flat surfaces 50 a, 51 a.

[0035] Next, the pair of first and second flanges 50, 51 are clamped with a predetermined clamping force using a known chain clamp, which causes the pair of seal lip portions 2 to deform and move closer to each other, as shown in Figure 1C, and the second seal ridge 9 is pressed against the pair of flat surfaces 50a, 51a and deforms accordingly.

[0036] As a result, the metal seal 1 can be deformed appropriately with a smaller tightening force than conventional metal seals, and exhibits its sealing performance.

[0037] Examples 1 to 3 (1) Relationship between the position of the apex of the second seal ridge 9 and the line load A metal seal 1 with A / B = 0.26 was prepared as Example 1. Also, a metal seal with A / B = 0.38 but other dimensions being the same was prepared as Comparative Example 1.

[0038] FIG. 2 shows the amount of crushing of the metal seal when each metal seal is sandwiched between a pair of first and second flanges 50, 51 and the line load is gradually increased.

[0039] As can be seen from Figure 2, in the region where the crushing amount at which sealing performance is achieved is greater than approximately 0.14 mm, the line load is higher in Comparative Example 1 than in Example 1. In Example 1, the line load is maintained at 25 N / mm or less when the crushing amount of the metal seal 1 is between 0.14 and 0.20 mm. In Comparative Example 1, the line load exceeds 25 N / mm when the crushing amount is greater than 0.18 mm. This shows that it is desirable for A / B to be ≦0.26.

[0040] (2) Relationship between Length of Seal Lip Portion 2 and Line Load A metal seal 1 with D / C = 1.35 was prepared as Example 2. Also, a metal seal with D / C = 1.25 but other dimensions being the same was prepared as Comparative Example 2.

[0041] FIG. 3 shows the amount of crushing of the metal seal when each metal seal is sandwiched between a pair of first and second flanges 50, 51 and the line load is gradually increased.

[0042] As can be seen from Figure 3, in the region where the crushing amount at which sealing performance is achieved is greater than approximately 0.14 mm, the line load is higher in Comparative Example 2 than in Example 2. In Example 2, the line load is maintained at 25 N / mm or less when the crushing amount of the metal seal 1 is between 0.14 and 0.20 mm. In Comparative Example 2, the line load exceeds 25 N / mm when the crushing amount is greater than 0.15 mm. This demonstrates that it is desirable for D / C to be 1.35 or greater.

[0043] (3) Relationship between thickness of seal lip portion 2 and line load A metal seal 1 with E / C = 0.150 was prepared as Example 3. Also, a metal seal with E / C = 0.186 and other dimensions being the same was prepared as Comparative Example 3.

[0044] FIG. 4 shows the amount of crushing of the metal seal when each metal seal is sandwiched between a pair of first and second flanges 50, 51 and the line load is gradually increased.

[0045] As can be seen from Figure 4, in the region where the amount of compression that demonstrates sealing performance is greater than approximately 0.14 mm, the line load is higher in Comparative Example 3 than in Example 3. In Example 3, the line load is maintained at 25 N / mm or less when the amount of compression of the metal seal 1 is between 0.14 and 0.20 mm. In Comparative Example 3, the line load exceeds 25 N / mm when the amount of compression is greater than 0.18 mm. This demonstrates that it is desirable for E / C to be ≦0.15.

[0046] - He Leak Test - At room temperature of 5°C to 35°C, the metal seal 1 was sandwiched between the first and second flanges 50, 51 from above and below, and a general-purpose chain clamp (not shown) was attached from the outside, and the chain clamp was tightened with a torque wrench.

[0047] The test was carried out using the hood method by covering the first and second flanges 50, 51 and the chain clamp with a polypropylene bag or the like, and spraying He gas into the bag. The He leak rate was measured using a He leak detector connected to the first flange 50 that did not have the metal seal 1 placed on it.

[0048] As a result, the amount of He leak was 1 x 10 at a tightening torque of 3.0 N m. －８ P.A.M. ３ / sec level, and showed sealing properties equal to or better than those of commercially available fluororubber seals.

[0049] As described above, in this embodiment, the pair of second seal ridges 9 on both axial sides are located at a position where A / B is 0.26 or less from the root outer peripheral surfaces 3 a of the pair of seal lip portions 2, so the portion directly below the second seal ridges 9 is more easily deformed than when A / B is located more inward than 0.26, and less force is required to press the second seal ridges 9. Therefore, when fastening the metal seal to the sealing portion with a chain clamp, it can be fastened with a lower clamping force than conventional products, preventing damage to the chain clamp due to overtightening.

[0050] Furthermore, in this embodiment, the value of E / C is 0.15 or less, and the axial thickness E of the seal lip portion 2 in the area where the first seal ridge 7 is not present is thinner than in the conventional case, making it easier to deform and allowing the metal seal 1 to be fastened with a lower tightening force.

[0051] Furthermore, in this embodiment, by setting the D / C value to 1.35 or more, the seal lip portion 2 is more easily deformed than when the D / C value is less than 1.35 and the length of the seal lip portion is shorter, and the metal seal 1 can be fastened with a lower tightening force.

[0052] Therefore, with the metal seal 1 according to this embodiment, it is possible to further reduce the tightening force required to achieve the desired sealing performance.

[0053] 5A and 5B show a metal seal 101 according to a second embodiment of the present invention, which differs from the first embodiment in particular in the shape of the second seal ridge 109. In this embodiment, the same parts as those in FIGS. 1A to 1C are designated by the same reference numerals, and detailed descriptions thereof will be omitted.

[0054] The second seal ridge 109 of this embodiment has an isosceles triangular cross section, unlike that of the first embodiment. The ratio of the height X to the base length Y of the second seal ridge 109 is X / Y≦0.70.

[0055] In this embodiment, the distance A between the root outer peripheral surfaces of the pair of seal lip portions 2 and the top of the second seal ridge 109 satisfies A≧0.3.

[0056] Furthermore, in this embodiment, the ratio X / Z of the height X of the second seal ridge 109 to the height Z of the first seal ridge 7 is set to 0.6≦X / Z≦1.6.

[0057] The other shapes are the same as those of the first embodiment, and the materials are also the same as those of the first embodiment.

[0058] --Example 4 Regarding Distance A-- In Example 4, distance A is 0.3 mm. On the other hand, in Comparative Example 4, distance A is 0.2 mm, and other shapes and the like are the same as those of Example 4. For Example 4 and Comparative Example 4, the change in surface pressure when the contact lens is sandwiched between a pair of flat surfaces 50a, 51a and the amount of displacement is gradually increased was compared.

[0059] 6, the surface pressure begins to increase at a displacement of about 0.13 mm in both Example 4 and Comparative Example 4. However, it was found that the rate of increase in Example 4 was significantly greater than that in Comparative Example 4.

[0060] When the distance A is less than 0.3, as in Comparative Example 4, the flexural rigidity of the seal lip portion cannot be maintained, and the seal lip portion tilts too much. However, by satisfying A≧0.3 as in Example 4, the second seal ridge 109 is appropriately spaced from the base of the U-shaped seal portion 3, thereby maintaining the flexural rigidity of the base of the U-shaped seal portion 3 and suppressing its deformation. This reduces the sinking of the first seal ridge 7, suppressing the tilt of the U-shaped seal portion 3 and allowing the U-shaped seal portion 3 to maintain high surface pressure at the contact points with the pair of flat surfaces 50a, 51a. Therefore, it was found that satisfying A≧0.3 is advantageous in that it can prevent a decrease in sealing performance due to insufficient surface pressure.

[0061] Example 5 with respect to the ratio X / Y In Example 5, the ratio X / Y is 0.28. On the other hand, in Comparative Example 5, the ratio X / Y is 0.8, and other aspects such as the shape are the same as those of Example 5. Example 5 and Comparative Example 5 were compared with respect to the change in surface pressure when the substrate was sandwiched between a pair of flat surfaces 50a, 51a and the amount of displacement was gradually increased.

[0062] 7, in Example 5, the surface pressure begins to increase at a displacement of 0.13 mm. On the other hand, in Comparative Example 5, the surface pressure does not begin to increase until the displacement reaches 0.16 mm. Moreover, it was found that the rate of increase in Example 5 was significantly greater than that in Comparative Example 5.

[0063] When X / Y is greater than 0.7, as in Comparative Example 5, the second seal ridge 109 has a pointed shape and its tip is easily deformed. As a result, the first seal ridge 7 sinks more, causing the U-shaped seal portion 3 to tilt too much, reducing the surface pressure at the first seal ridge 7 and deteriorating sealing performance. However, by satisfying X / Y≦0.70 as in Example 5, the second seal ridge 109 does not have an excessively pointed shape and suppresses deformation of its tip. As a result, the first seal ridge 7 sinks less, reducing the tilt of the U-shaped seal portion 3. This allows the U-shaped seal portion 3 to maintain high surface pressure at the contact points with the pair of flat surfaces 50a, 51a. Therefore, it was found that by satisfying X / Y≦0.70, deterioration of sealing performance due to insufficient surface pressure can be prevented.

[0064] Example 6 with respect to the ratio X / Z In Example 6, the ratio X / Z is 1.0. On the other hand, in Comparative Example 6, the ratio X / Z is 1.7, and in Comparative Example 7, the ratio X / Z is 0.5, with the other shapes and the like being the same as in Example 6. Example 6 and Comparative Examples 6 and 7 were compared with respect to the change in surface pressure when the contact lens was sandwiched between a pair of flat surfaces 50a, 51a and the amount of displacement was gradually increased.

[0065] As can be seen from Figure 8, in Example 6, the surface pressure begins to increase when the displacement reaches 0.13 mm. On the other hand, in Comparative Example 6, the surface pressure finally begins to increase when the displacement exceeds 0.15 mm. In Comparative Example 7, the second seal ridges do not come into contact with the pair of flat surfaces 50a, 51a for a long time, and the surface pressure does not increase at all even when the displacement exceeds 0.16 mm. It was also found that the rate of increase in Example 6 was significantly greater than that of Comparative Example 6.

[0066] Thus, when X / Z is less than 0.6, as in Comparative Example 7, the height of the second seal ridge is too low, resulting in only the first seal ridge contacting the pair of flat surfaces 50a, 51a. Furthermore, when X / Z is greater than 1.6, as in Comparative Example 6, the height of the second seal ridge is too high, resulting in only the second seal ridge contacting the pair of flat surfaces 50a, 51a. If only one of the ridges contacts the pair of flat surfaces 50a, 51a, the surface pressure does not increase easily. However, by setting the ratio of X / Z to 0.6≦X / Z≦1.6 as in Example 7, the pair of flat surfaces 50a, 51a contacts both the first seal ridge 7 and the second seal ridge 109, thereby achieving high sealing performance. Furthermore, by tapering the first seal ridge 7, the contact area between the first seal ridge 7 and the pair of flat surfaces 50a, 51a is reduced, allowing for high surface pressure to be maintained.

[0067] Therefore, the metal seal 101 according to this embodiment can stably maintain sealing performance.

[0068] It should be noted that the above-described embodiments are essentially preferred examples and are not intended to limit the scope of the present invention, its applications, or uses.

[0069] For example, in each of the above-described embodiments, the cross section of the first seal ridge 7 is circular, but as shown in Fig. 9, it may be a triangular first seal ridge 107. In this case, the same effects can be obtained.

[0070] 1, 101 Metal seal 2 Seal lip portion 3 U-shaped seal portion 3a Root outer peripheral surface 3b Axial side surface 5 Locking bulge portion 5a Outer peripheral surface 6 Centering guide portion 7, 107 First seal ridge 8 Corner portion 9, 109 Second seal ridge 50, 51 Flange 50a, 51a Flat surface 50b, 51b Inner peripheral surface

Claims

1. A metal seal comprising: a U-shaped seal portion having an annular shape and a U-shaped cross section, and a pair of seal lip portions that seal between a pair of flat surfaces; an annular centering guide portion having a pair of locking bulges with a rectangular cross section that bulge out axially from a pair of base-near axial side surfaces of the U-shaped seal portion; a pair of first seal ridges that protrude from the tips of the pair of seal lip portions and abut against the pair of flat surfaces, respectively; and a pair of second seal ridges that protrude from and are spaced apart from the corners between the pair of locking bulges and the pair of base-near axial side surfaces, wherein the distance A between the root outer peripheral surfaces of the pair of seal lip portions and the tops of the second seal ridges is A ≧ 0.

3.

2. The metal seal according to claim 1, characterized in that the second seal ridge has an isosceles triangular cross section, and the ratio of height X to base length Y is X / Y≦0.

70.

3. A metal seal according to claim 1 or 2, characterized in that the cross section of the first seal ridge is circular or triangular, and the ratio X / Z of the height X of the second seal ridge to the height Z of the first seal ridge satisfies 0.6≦X / Z≦1.

6.

4. A metal seal comprising: a U-shaped seal portion having an annular shape and a U-shaped cross section, and a pair of seal lip portions that seal between a pair of flat surfaces; an annular centering guide portion having a pair of locking bulges with a rectangular cross section that bulge out axially from a pair of base-near axial side surfaces of the U-shaped seal portion; a pair of first seal ridges that protrude from the tips of the pair of seal lip portions and abut against the pair of flat surfaces, respectively; and a pair of second seal ridges that protrude from and are spaced apart from corners between the pair of locking bulges and the pair of base-near axial side surfaces, wherein the ratio of the distance A between the base outer circumferential surface and the top of the second seal ridge to the distance B between the outer circumferential surfaces of the locking bulges and the base outer circumferential surfaces of the pair of seal lip portions is A / B≦0.

26.

5. A metal seal as described in claim 4, characterized in that the ratio of the axial thickness E of the portion of the seal lip portion closer to the base than the first seal ridge to the axial thickness C of the base of the U-shaped seal portion is E / C≦0.

15.

6. A metal seal according to claim 4 or 5, characterized in that the ratio of the radial length D of the seal lip portion to the axial thickness C of the base of the U-shaped seal portion is D / C≧1.35.

Images