JP7644480B2 - Lid holder frame for underground structures - Google Patents

Description

The present invention relates to a frame for receiving a lid for an underground structure that defines an opening leading to an underground structure and closes the opening by being covered with a lid for an underground structure.

At locations where underground structures such as underground buried objects and underground facilities for sewage, water supply, electricity, gas, and communications, etc., connect to the ground, a lid receiving frame set for an underground structure may be installed, which includes an underground structure lid receiving frame that defines an opening that connects to the underground structure, and an underground structure lid that is supported by the underground structure lid receiving frame to close the opening. In this specification, the underground structure lid receiving frame may be abbreviated to the receiving frame, the underground structure lid to the lid, and the underground structure lid receiving frame set to the lid receiving frame set. In addition, the state in which the lid is supported by the receiving frame and the opening is closed (the state in which the lid is fitted into the receiving frame) may be referred to as the closed lid state.

Inside the underground structures mentioned above, such as sewerage pipeline facilities, hydrogen sulfide and other gases are generated, particularly in places where sewage stagnates, creating a corrosive atmosphere. The lid and frame are generally made of metal such as cast iron, and the back surface of the lid and the exposed parts of the frame when the lid is closed are exposed to a harsh environment of corrosive atmosphere, so corrosion prevention performance that can withstand this is required. For this reason, measures such as electrostatically painting an epoxy resin-based powder paint or the like on the back surface of the lid and the exposed parts of the frame to provide a corrosion prevention coating are sometimes taken.

In addition, it is difficult to uniformly apply an anticorrosive coating to the outer peripheral surface of the lid body and the inner peripheral surface of the receiving frame (the mating portion of the lid body and the receiving frame), which come into surface contact when the lid is closed. Even if an anticorrosive coating is applied, it will come into contact with (come into) the lid body when it is opened and closed, and rusting (corrosion) will occur easily. For this reason, the applicant has proposed a receiving frame in which an anticorrosive sheet made of synthetic rubber or the like is provided on the inner peripheral surface of the receiving frame (see, for example, Patent Document 1, etc.). The receiving frame described in Patent Document 1 makes it difficult for a corrosive atmosphere to get between the outer peripheral surface of the lid body or the inner peripheral surface of the receiving frame and the anticorrosive sheet, making it possible to prevent corrosion of the outer peripheral surface of the lid body and the inner peripheral surface of the receiving frame.

JP 2020-159113 A

However, when installing the receiving frame, if workers do not notice the presence of the anti-corrosion sheet, which may be made of rubber, and mistakenly assume that the anti-corrosion sheet is made of metal like the frame itself, there is a risk that the anti-corrosion sheet may be inadvertently damaged. In addition, during maintenance inspections, a means is also desired that can easily and clearly determine whether the anti-corrosion sheet is in a state where it is not damaged or peeled off. In this way, a new problem has been found for preventing corrosion of the outer surface of the lid body and the inner surface of the receiving frame in a more stable manner over the long term.

In view of the above circumstances, the present invention aims to provide a lid support frame for underground structures that prevents inadvertent damage to anticorrosive sheets during frame installation work, etc., and is designed to facilitate inspection during maintenance and management.

The present invention provides a lid receiving frame for an underground structure that solves the above-mentioned object,
In a frame for receiving a cover for an underground structure, the frame defines an opening leading to an underground structure, and the opening is blocked by being closed with a cover for an underground structure,
A metal frame body having an inner peripheral surface that is inclined in a direction in which the inner diameter narrows downward;
A corrosion prevention sheet is attached to the inner peripheral surface by an adhesive and is in surface contact with the underground structure cover in a closed state,
The frame body is black,
The anticorrosive sheet is gray in color,
The frame body and the front surface of the anticorrosive sheet are characterized in that the brightness difference in Munsell scale is 3.0 or more and less than 7.0 .

Here, the anticorrosive sheet may be made of synthetic rubber or plastic. As the synthetic rubber, NBR (nitrile rubber), CR (chloroprene rubber), and IIR (butyl rubber) are preferable, and as the plastic, PP (polypropylene) and PVC (polyvinyl chloride) are preferable. In addition, the cover receiving frame for the underground structure has a track record of being painted black so as not to impair the scenery after installation, and the anticorrosive sheet may be gray in its entirety or only the front surface may be gray . In addition, the frame body may be made of, for example, a cast iron casting. The inclination angle of the inner peripheral surface is not particularly limited, and may be, for example, about 8° to 12°.

According to the underground structure lid receiving frame of the present invention, the anticorrosive sheet is gray , so that it can attract the attention of workers during installation work, etc. This can prevent mistakes such as workers mistaking the anticorrosive sheet for something made of metal like the frame body and accidentally damaging the sheet. In addition, since the anticorrosive sheet is easy to distinguish from the frame body, defects such as damage or peeling of the anticorrosive sheet can be easily found during maintenance inspections.

In an embodiment in which the anticorrosive sheet is made of synthetic rubber such as NBR, if a pigment is added to give a predetermined color, the adhesive strength (bonding strength) of the anticorrosive sheet is reduced when the anticorrosive sheet is bonded to the frame body by, for example, a two-liquid mixed reactive adhesive. Therefore, if the anticorrosive sheet is made gray, it can be formed by adding a white pigment to carbon black, and the amount of pigment used can be reduced. As a result, the adhesive strength of the anticorrosive sheet to the frame body can be suppressed from decreasing. In addition, by making the brightness difference between the front surface of the frame body and the anticorrosive sheet 3.0 or more in the Munsell symbol, the anticorrosive sheet and the frame body can be clearly distinguished, and the attention of workers during installation work and the like and the ease of inspection for maintenance and management can be fully ensured. Furthermore, if the brightness difference in Munsell symbols between the frame body and the front surface of the corrosion-prevention sheet exceeds 7.0, the distinguishability between the corrosion-prevention sheet and the frame body will be improved, but the amount of white pigment added to the corrosion-prevention sheet will increase, resulting in a decrease in adhesive strength, which is not preferable.
In addition, in the cover receiving frame for an underground structure of the present invention, the frame body is made of cast iron and is painted black with an epoxy resin-based or acrylic resin-based paint,
The anticorrosive sheet may be made of synthetic rubber and adhered to the inner peripheral surface by a two-part reactive adhesive.

Furthermore, in the underground structure cover receiving frame of the present invention, the anticorrosive sheet has a black upper end surface,
The frame body and the upper end surface of the anticorrosive sheet may have a brightness difference of within 2.0 in Munsell symbols.

In the closed state, the upper end surface of the anticorrosion sheet is located between the frame body and the underground structure cover and is exposed above ground. Here, if the surface of the underground structure cover is also black like the frame body, there is a risk of creating an incongruous feeling if only the upper end surface of the anticorrosion sheet is a different color. In addition, the underground structure cover may have various designs and colors on its surface, but if the color of the upper end surface of the anticorrosion sheet is different from that of the frame body, there is a risk of losing the sense of unity in the design. Therefore, by adopting an aspect in which the upper end surface of the anticorrosion sheet is black with a brightness difference of 2.0 or less in Munsell notation from the frame body, it is possible to reduce the sense of incongruity and the loss of the sense of unity in the design.

In addition, in the underground structure lid receiving frame of the present invention, the inner circumferential surface may not be provided with the anticorrosive sheet in the portion facing the keyhole in the underground structure lid when the lid is closed.

The part of the inner circumferential surface facing the keyhole in the underground structure cover is not in contact with the outer circumferential surface of the underground structure cover (the part where the underground structure cover and the underground structure cover receiving frame do not fit together), and is less susceptible to corrosion even without the anticorrosive sheet. Furthermore, when the valve cover that closes the keyhole is rotated with an opening and closing tool or the like, the tip of the valve cover is likely to come into contact with the valve cover, and if the anticorrosive sheet is provided, it is likely to peel off due to contact with the tip of the valve cover. And peeling of a part of the anticorrosive sheet may trigger peeling of other parts of the anticorrosive sheet. Therefore, by adopting an embodiment in which the anticorrosive sheet is not provided on the part of the underground structure cover that faces the keyhole, peeling due to contact with the tip of the valve cover, etc., can be prevented, and as a result, peeling of other parts of the anticorrosive sheet can also be suppressed.

The portion of the inner circumferential surface that faces the pry hole in the underground structure cover in the closed state is also a portion that does not come into contact with the outer circumferential surface of the underground structure cover, and the anticorrosive sheet may not be provided.

The present invention provides a cover receiving frame for underground structures that prevents inadvertent damage to the anticorrosive sheet during frame installation work and that is designed to facilitate inspection during maintenance.

1A is a cross-sectional view of a lid receiving frame set consisting of a receiving frame and a lid body, and FIG. 1B is a plan view of the lid receiving frame set shown in FIG. 1A is an enlarged view of a portion A surrounded by a dashed circle in FIG. 1A, and FIG. 1B is a cross-sectional view taken along line CC in FIG. 2A is a plan view of the receiving frame shown in FIG. 1 , and FIG. 2B is an enlarged view of a portion D surrounded by a dashed line circle in FIG. FIG. 4 is a bottom view of the receiving frame shown in FIG. 3(a) is a front view (viewed from below) of the receiving frame shown in FIG. 3(a), and FIG. 3(b) is a rear view (viewed from above) of the receiving frame shown in FIG. 3(a).

The following describes an embodiment of the present invention with reference to the drawings.

Figure 1(a) is a cross-sectional view of a lid receiving frame set 10 consisting of a receiving frame 3 and a lid body 2, and Figure 1(b) is a plan view of the lid receiving frame set 10 shown in Figure 1(a). Note that the cross-sectional view shown in Figure 1(a) is a cross-sectional view taken along line B-B in Figure 1(b). Also, Figure 1(a) shows the ground G, but in Figure 1(b), the ground G is omitted.

Figure 1 shows a cover frame set (cover frame set for underground structure) 10 including a cover (cover for underground structure) 2 according to one embodiment of the present invention and a frame (cover frame for underground structure) 3 that supports the cover 2. A sewerage drainage pipe, which is an underground buried object, is buried at a predetermined depth from the ground surface, and a manhole is provided as an underground facility midway along the sewerage drainage pipe. Both the sewerage drainage pipe and the manhole correspond to underground structures. The manhole is formed as a vertical hole leading from the sewerage drainage pipe to the ground surface by a structure made of stacked prefabricated concrete molded products. The frame 3 is provided on the structure and defines an opening H that leads to the manhole, which is an underground structure. The inside of this underground structure is in a corrosive atmosphere due to the generated hydrogen sulfide, etc.

The lid body 2 is circular in plan view and can be freely opened and closed to cover an opening H that leads to a manhole, which is an underground structure. The lid body 2 shown in FIG. 1 covers the opening H. The lid body 2 shown in FIG. 1 is made of cast iron formed by casting, for example, made of FCD700 material. Note that the lid body 2 may be made of iron other than cast iron, or may be made of metal other than iron.

Figure 2(a) is an enlarged view of part A, which is circled by a dashed line in Figure 1(a).

As shown in Figures 1 and 2(a), the lid body 2 comprises a disk-shaped top plate portion 21, an annular wall portion 22 provided on the outer periphery of the top plate portion 21 and surrounding the top plate portion 21, and a lid rib 23 protruding downward from the back surface of the top plate portion 21. A corrosion-resistant coating is formed by electrochemical deposition on the back surface of the top plate portion 21 and the lid rib 23. On the outer periphery of the annular wall portion 22, an outer peripheral surface 221 is formed that is inclined in a direction in which the outer diameter narrows downward.

1 and 2(a), the receiving frame 3 includes a frame body 5 and an anticorrosive sheet 7. The frame body 5 is made of cast iron, for example, made of FCD700, and is painted black (for example, with a Munsell value of 1.5 (N1.5)) with an epoxy resin or acrylic resin paint. The frame body 5 includes a cylindrical body 51 formed in a ring shape in a plan view, a flange portion 52 that protrudes outward from the lower end portion of the cylinder 51, and a frame rib 53 provided on the upper surface of the flange portion 52. The inner peripheral portion of the cylinder 51 is provided with a stop portion 512 that protrudes in a ring shape toward the inside of the receiving frame 3. When the lid body 2 slides down due to long-term use, the lower end of the annular wall portion 22 of the lid body 2 abuts against this stop portion 512, preventing further sliding.

As shown in FIG. 2(a), an inner peripheral surface 511 is formed on the upper side of the stop portion 512 in the inner peripheral portion of the cylinder 51, the inner diameter of which is inclined downward so that the inner diameter narrows, and an anticorrosive sheet 7 is provided on the surface of the inner peripheral surface 511. The inclination angle of the inner peripheral surface 511 is set to be approximately the same as the inclination angle of the outer peripheral surface 221 of the lid body 2 (e.g., 8° to 9°).

In FIG. 2(a), the anticorrosion sheet 7 provided on the frame body 5 is shown enlarged and surrounded by a dashed line circle. In this embodiment, the anticorrosion sheet 7 is made of synthetic rubber NBR, and is adjusted to a gray color (for example, a Munsell value of 6.5 (N6.5)) by adding carbon black and white pigments. The thickness of the anticorrosion sheet 7 is set in the range of 0.5 to 5.0 mm so that it will not cut or crack even when the lid body 2 and the receiving frame 3 interfere with each other when the lid body 2 is opened or closed, and will not be scratched or expose the cast iron base of the lid body 2 or the receiving frame 3.

The anticorrosion sheet 7 has its back surface 71 adhered to the inner circumferential surface 511 of the frame body 5 by an adhesive, with its lower end surface 74 supported by the stop portion 512 of the frame body 5. The anticorrosion sheet 7 is not limited to being made of NBR, but may be made of other synthetic rubbers such as CR or IIR, or may be made of plastics such as PP or PVC. Furthermore, it may be a combination of these materials.

As shown in FIG. 2(a), in the closed state, the outer peripheral surface 221 of the lid body 2 and the anticorrosive sheet 7 provided on the inner peripheral surface 511 of the frame body 5 are in surface contact with each other, and the lid body 2 is supported by the receiving frame 3. This makes it difficult for a corrosive atmosphere to get between the anticorrosive sheet 7 and the outer peripheral surface 221 of the lid body 2, preventing corrosion of the outer peripheral surface 221 of the lid body 2. In addition, the inner peripheral surface 511 of the frame body 5 is prevented from corrosion by the anticorrosive sheet 7 provided on its surface.

The frame body 5 is black, and in this embodiment, the front surface 72 of the anticorrosive sheet 7 is gray. This makes it possible to alert workers during installation work, etc. This prevents mistakes such as accidentally damaging the anticorrosive sheet 7 because they mistake it for something made of metal like the frame body 5. In addition, because the anticorrosive sheet 7 is easy to distinguish from the frame body 5, defects such as damage or peeling that occur in the anticorrosive sheet 7 can be easily found during maintenance inspections. As a result, corrosion of the outer peripheral surface of the lid body 2 and the inner peripheral surface of the receiving frame 3 can be prevented more stably over a long period of time.

In particular, in this embodiment, the anticorrosive sheet 7 is gray, and as described above, it can be formed by adding white pigment to carbon black, reducing the amount of pigment used. As a result, it is possible to prevent a decrease in the adhesive strength of the anticorrosive sheet 7 to the frame body 5.

Furthermore, in this embodiment, the brightness difference between the frame body 5 and the anticorrosion sheet 7 in the Munsell symbols is 3.0 or more (specifically, the frame body 5 is N1.5 and the anticorrosion sheet is N6.5, so the brightness difference is 5.0), so the anticorrosion sheet 7 and the frame body 5 can be clearly distinguished. Note that if the brightness difference between the frame body 5 and the anticorrosion sheet 7 in the Munsell symbols exceeds 7.0, the amount of white pigment added to the anticorrosion sheet 7 will increase, which is not preferable as it will reduce the adhesive strength.

As shown in FIG. 2(a), when the lid is closed, the upper end surface 73 of the corrosion prevention sheet 7 is located between the frame body 5 and the lid body 2 and is exposed above ground. For this reason, it is preferable to color the upper end surface 73 of the corrosion prevention sheet 7 black, for example by painting, with a Munsell brightness difference of 2.0 or less from that of the frame body 5. This makes it less likely that a sense of incongruity will arise due to the difference in color between the frame body 5 and the upper end surface 73 of the corrosion prevention sheet 7.

The anticorrosion sheet 7 may be provided around the entire inner periphery 511 of the frame body 5, but in this embodiment, the anticorrosion sheet 7 is not provided on the peripheral portion of the top plate portion 21, which faces the keyhole 211 formed on the upper side in FIG. 1(b). This keyhole 211 is a notched hole for inserting an opening/closing tool, and the portion of the receiving frame 3 facing the keyhole 211 is not in contact with the lid body 2. This point will be described in detail below.

Figure 3(a) is a plan view of the frame 3 shown in Figure 1, and Figure 3(b) is an enlarged view of the portion D surrounded by a dashed line circle in Figure 3(a). Figure 4 is a bottom view of the frame 3 shown in Figure 3(a). Figure 5(a) is a front view (viewed from below) of the frame 3 shown in Figure 3(a), and Figure 5(b) is a rear view (viewed from above) of the frame 3 shown in Figure 3(a). Note that the right side view (viewed from the right side) of the frame 3 shown in Figure 3(a) and the left side view (viewed from the left side) of the frame 3 shown in Figure 3(a) are omitted because they are the same as Figure 5(a). Also, Figure 5(c) is a cross-sectional view of the frame 3 shown in Figure 3(a) along line E-E. Note that in Figures 3(b) and 5(c), the anticorrosive sheet 7 is shaded to distinguish it from the frame body 5.

As shown in Figures 3(b) and 5(c), the anticorrosive sheet 7 is not provided in the keyhole facing region 511a of the frame body 5 that faces the keyhole 211 (see Figure 1(b)). The widthwise length S of the keyhole facing region 511a (the distance between both side end faces 75, 75 of the anticorrosive sheet 7) is set to be approximately the same as the widthwise length of the keyhole 211.

Figure 2(b) is a cross-sectional view taken along line C-C in Figure 1(b). In this Figure 2, the side end surface 75 on one side (the right side in Figures 3(b) and 5(c)) of the anticorrosive sheet 7 is shown.

As shown in FIG. 2(b), a locking member 9 is provided on the back side of the keyhole 211. The locking member 9 has a pair of shafts 92, 92 supported on the back side of the lid body 2, a valve cover 91 that closes the keyhole 211, a locking claw 93 provided below the valve cover 91, a weight 94, and a spring 95 as a biasing means. In addition, a claw receiving piece 514 that protrudes diagonally downward is provided in a position below the inner peripheral surface 511 in a portion of the frame body 5 corresponding to the locking member 9, and a space R is formed below the claw receiving piece 514.

The locking member 9 can rotate around a pair of shafts 92, 92 between a closed state in which the valve cover 91 closes the keyhole 211 and an open state in which the valve cover 91 opens the keyhole 211. The locking member 9 is applied with a force toward the closed state by the weight 94 and is biased toward the closed state by the spring 95, and is inserted into the locking claw 93 space R. Therefore, when the cover body 2 floats up, the locking claw 93 engages with the claw receiving piece 514, preventing the opening from being opened.

To open the lid 2, the valve lid 91 is pushed down with an opening/closing tool (not shown) and the locking member 9 is rotated counterclockwise, which opens the keyhole 211 and causes the locking claw 93 to retract from below the claw receiving piece 514 and move out of the space R. This allows the lid 2 to be opened. Note that in FIG. 2(b), in order to simplify the drawing, only the valve lid 91 is shown with a dashed line with respect to the rotated locking member 9.

When the locking member 9 rotates, the tip of the valve cover 91 approaches the frame body 5. If an anticorrosion sheet 7 is provided in the keyhole-facing area 511a of the inner circumferential surface 511, the tip of the valve cover 91 will come into contact with it and will likely peel off. Peeling off part of the anticorrosion sheet 7 may trigger peeling off of other parts of the anticorrosion sheet 7.

In this embodiment, the anticorrosion sheet 7 is not provided in the keyhole-facing area 511a of the inner surface 511, so it will not peel off due to contact with the tip of the valve lid 91, and as a result, peeling off of the entire anticorrosion sheet 7 can be suppressed.

In FIG. 1(b), the cover 2 is likened to a clock face, and pry holes 212 are provided near the 4 o'clock and 8 o'clock positions. The pry holes 212 are holes for inserting a rod-shaped opening and closing tool (not shown) to pry the cover 2 when the cover 2 has not been opened for a long time and the cover 2 and the receiving frame 3 are tightly fitted together due to rust or repeated loads such as the passing of vehicles, making it difficult to open the cover 2. Since these pry holes 212, 212 are also formed in a notch shape like the keyhole 211, the part of the receiving frame 3 facing the pry hole 212 is not in contact with the cover 2. For this reason, the part of the inner surface 511 facing the pry hole 212 may also be provided with no anticorrosive sheet 7.

Next, we will explain an example of the process for attaching the anticorrosive sheet 7 to the frame body 5.

For example, the anticorrosion sheet 7 is prepared by using synthetic rubber NBR as the material and adding carbon black and white pigments to give it a gray color (e.g. N6.5). The height dimension of the anticorrosion sheet 7 is the same as the height dimension of the inner peripheral surface 511 of the frame body 5, and the total length of the anticorrosion sheet 7 is formed to be approximately the same as or slightly longer than the total circumference of the inner peripheral surface 511 of the frame body 5. If necessary, the upper end surface 73 of the anticorrosion sheet 7 is painted black.

Next, with the inner circumferential surface 511 of the frame body 5, excluding the keyhole-facing region 511a, and the front surface 72 covered with masking tape, a two-part reactive adhesive is applied to the back surface 71 of the anticorrosive sheet 7. The thickness of the anticorrosive sheet 7 and the adhesive are adjusted taking into account functionality, workability, etc., and the thickness of the anticorrosive sheet 7 may be about 1.5 mm, for example.

Then, the anticorrosion sheet 7 is overlapped on the inner circumferential surface 511 of the frame body 5 using the stopper portion 512 of the frame body 5 as a support, and the portion of the anticorrosion sheet 7 that overlaps the keyhole-facing region 511a is then cut. Here, if the anticorrosion sheet 7 is provided around the entire inner circumferential surface 511 of the frame body 5, the anticorrosion sheet 7 must be cut where it overlaps, which can be difficult to do. In contrast, if the anticorrosion sheet 7 is not provided in the keyhole-facing region 511a as in this embodiment, the work of cutting the anticorrosion sheet 7 becomes easier.

Next, the frame body 5 and the anticorrosive sheet 7 are clamped with clips or the like and left to cure until adhesion is complete. Here, instead of using clips or the like, the lid body 2 may be set in a closed state to allow curing. In other words, the lid body 2 can also be used as a jig for curing.

Once the preparation is complete, remove the masking tape and the installation of the anti-corrosion sheet 7 onto the frame body 5 is complete.

The above-described receiving frame 3 can provide a receiving frame for a lid body of an underground structure that prevents inadvertent damage to the anticorrosive sheet during the installation work of the receiving frame, and is designed to facilitate inspection during maintenance and management.

The present invention is not limited to the above-described embodiment, and various modifications can be made within the scope of the claims. For example, in the above-described embodiment, a gray anticorrosive sheet 7 is used as an example, but a non-gray anticorrosive sheet 7 may be used as long as it is a color that can be sufficiently distinguished from the frame body 5. In addition, an embodiment in which the entire anticorrosive sheet 7 is gray is described, but a black anticorrosive sheet 7 with only the front surface 72 painted gray may be used. If this embodiment is adopted, the gray paint may peel off due to interference (contact) during opening and closing of the lid, but since it can be constructed without adding pigment, the decrease in adhesive strength due to the addition of pigment is prevented, and the black paint of the upper end surface 73 is also unnecessary.

10 Lid receiving frame set 2 Lid body 21 Top plate portion 211 Keyhole 22 Annular wall portion 221 Outer peripheral surface 3 Receiving frame 5 Frame main body 511 Inner peripheral surface 511a Keyhole facing region 512 Stop portion 7 Anticorrosive sheet 73 Upper end surface 75 Side end surface 9 Locking member 91 Valve lid H Opening

Claims (4)

In a frame for receiving a cover for an underground structure, the frame defines an opening leading to an underground structure, and the opening is blocked by being closed with a cover for an underground structure,
A metal frame body having an inner peripheral surface that is inclined in a direction in which the inner diameter narrows downward;
A corrosion prevention sheet is attached to the inner peripheral surface by an adhesive and is in surface contact with the underground structure cover in a closed state,
The frame body is black,
The anticorrosive sheet is gray in color,
A lid support frame for underground structures, characterized in that the frame body and the front surface of the corrosion prevention sheet have a brightness difference in Munsell symbols of 3.0 or more and less than 7.0. The frame body is made of cast iron and is painted black with epoxy resin or acrylic resin paint.
2. The lid receiving frame for underground structures according to claim 1, wherein the anticorrosive sheet is made of synthetic rubber and is adhered to the inner peripheral surface by a two-part reactive adhesive . The anticorrosive sheet has a black upper end surface,
3. The lid receiving frame for underground structures according to claim 1 or 2, characterized in that the difference in brightness between the frame body and the upper end surface of the corrosion protection sheet is within 2.0 in Munsell symbols. The cover receiving frame for underground structures according to any one of claims 1 to 3, characterized in that the anticorrosive sheet is not provided on the inner peripheral surface in the portion facing the keyhole in the cover for underground structures when the cover is closed.

Images