JPH04330111A - Elastic dam expandable/contractile and its manufacture - Google Patents

Abstract

PURPOSE:To preclude generation of crevice or through hole due to unnatural damage and prevent loss of the function of elastic rubber by laminating a base layer of rubber and an elastic protection layer integrally and forming a dam sheet of tubing body in laminate structure. CONSTITUTION:A base layer 9 of rubber and an elastic protection layer 10 outside thereof are laminated integrally, and a dam sheet 8 of laminate structure is constructed. The elastic protection layer 10 is embodies in a flexible rubber sheet, in which small pieces 12 of ceramics in thin, long column form having a dia. of 2-4mm and a length of approx. 2-8mm are buried at random. The thickness of this protection layer 10 shall range 4-12mm, and the amount of buried small pieces 12 of ceramics shall range 4-8kg/m. This allows preventing puncture or burst even though unnatural damage is given such as with a harpoon or bullet.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an expandable and contractible elastic dam used for intake weirs, estuary weirs, diversion/flow control sluices, etc., and a method for manufacturing the same.

0002

[Prior Art] Intake weirs for irrigation, water supply, power generation, industrial use, etc., estuary weirs for backflow prevention, sand control, wave prevention, etc., sewage use, etc.
For diversion and flow rate control sluice gates, etc. for retarding ponds and reservoirs, etc.
A scalable elastic dam is provided.

[0003] This elastic dam consists of a tube body that is installed transversely on the bed of a river and is deformed to expand and contract through the injection of fluid. That is, when a fluid such as air or water is injected into the tube body from the operation chamber, the tube body expands and expands to form a dam that obstructs the water flow of the river. On the other hand, when the fluid inside the tube body is discharged by operation from the operation room, the tube body contracts and becomes flat, allowing water to flow out of the river without interfering with it.

[0004] Therefore, the tube body forming the elastic dam consists of a seal sheet that is installed on the river bed and forms the bottom of the tube body, and a rubber dam sheet that is attached to this seal sheet. Both side edges are airtightly or watertightly fixed to both side edges of the sealing sheet, and when fluid is injected, the dam sheet is expanded and expanded to stand up.

[0005]

[Problems to be Solved by the Invention] In order to ensure the durability of the elastic dam, the dam sheet is embedded with multiple plies of canvas in an effort to improve its strength. Therefore, it has sufficient resistance to river water flow under natural conditions, and if natural shrubs etc. are washed away by water flow and collide with the elastic dam, slight damage to the dam sheet will not be practical. does not interfere with

However, in recent years, it has been observed that elastic dams have been artificially damaged, resulting in so-called puncture or burst accidents. The inventor investigated the cause and found that as the number of people fishing, boating, and playing in the water increases, these people intentionally or negligently harpoon elastic dams, cut them with knives, etc. It has been discovered that there are cases where the damage can be artificially caused by some method. It has also been found that in rivers in the mountains, hunters fire their guns at elastic dams, and bullets fired at birds and animals sometimes hit elastic dams as stray bullets, damaging them. .

[0007] In the case of such artificial damage,
The current situation is alarming as cracks and through holes occur in the dam sheet, causing fluid in the tube body to leak, resulting in a serious accident in which the original elastic dam function is lost.

[0008]

[Means for Solving the Problems] The present invention aims to protect an elastic dam from the above-mentioned human-induced accidents, and is characterized by providing a protective layer on a dam sheet constituting a tube body.

[0009] As a method of providing such a protective layer, for example, it is possible to cover the outer periphery of an existing or ready-made elastic dam with a separate protective net or protective sheet, but this is not preferred in practice. That is, as mentioned above, elastic dams are characterized by being expandable and deformable through the injection of fluid, but when the elastic dam is surrounded by separate nets or sheets, these nets It becomes difficult to completely follow the expansion and contraction of the elastic dam and deform the sheet, which impairs the characteristics mentioned above. In addition, elastic dams are usually long because they span the entire width of the river bed.
When installing this on-site, it is disadvantageous to install a separate net or sheet at the same time because it reduces work efficiency and increases installation cost.

Therefore, the inventor of the present invention has found that it is advantageous to integrally mold the protective layer with the dam sheet instead of using such a separate net or sheet. That is, by constructing the dam sheet into a laminated structure consisting of a rubber base layer and an elastic protective layer laminated and integrated on the outer surface of the rubber base layer, elasticity with excellent breakage resistance can be achieved without causing the above-mentioned problems. It became possible to provide a dam.

By the way, since the elastic protective layer guarantees the flexibility of the dam sheet and prevents it from being damaged artificially as described above, it will not penetrate even when harpooned. Furthermore, it must be so strong that bullets will not penetrate it even when fired with a rifle.

Therefore, in order to satisfy the two seemingly contradictory demands of flexibility and high strength, the present inventor has developed a flexible protective layer comprising a large number of ceramic pieces embedded in the elastic protective layer constituting the outer layer of the dam sheet. It has been found that it is most advantageous to construct the rubber sheet layer with a rubber sheet layer. That is, as a result, the rubber sheet layer does not lose its flexibility as a whole and guarantees the expansion and contraction deformation of the elastic dam in exactly the same way as before, while the embedded ceramic pieces prevent the penetration of harpoons and bullets, and prevent the penetration of harpoons and bullets. It is possible to prevent tearing caused by, etc. At this time, by embedding a large number of small ceramic pieces so that they are spread out and adjacent to each other in the plane direction of the rubber sheet layer, the entire dam sheet has a protective function and prevents the formation of local weak parts. was completed. In addition, by not only spreading the ceramic pieces in the plane direction but also embedding them so that they overlap vertically within the thickness of the rubber sheet layer, we can reliably prevent the penetration of harpoons and bullets. This is what was created.

[0013] The elastic dam provided by the present invention is a tubular elastic dam made of a rubber dam sheet that is installed in a transverse direction on the bed of a river and is deformed to expand and contract through the injection of fluid. In the dam sheet, the dam sheet is composed of a laminated structure of a rubber base layer and an elastic protective layer laminated and integrated on the outer surface of the rubber base layer, and the elastic protective layer has a large number of ceramic pieces embedded at random. It is composed of a flexible rubber sheet layer, and a large number of the ceramic pieces are scattered and spread adjacent to each other in the plane direction of the rubber sheet layer, and are also scattered vertically and overlappingly within the thickness of the rubber sheet layer. It is characterized by becoming.

In order to meet the above-mentioned two requirements of flexibility and high strength, in a preferred embodiment of the present invention,
The ceramic piece has a diameter of about 2 to 4 mm and a length of about 2 mm.
It has an elongated, almost cylindrical shape with a length of ~8 mm. In addition, when the thickness of the elastic protective layer is approximately 4 to 12 mm, the amount of ceramic pieces embedded in the rubber sheet layer is approximately 4 kg/m.
It is preferable to set it at 2 to 8 kg/m2.

Furthermore, the present invention provides a method for manufacturing an elastic dam equipped with the above-mentioned elastic protective layer, and its feature is that a large number of ceramic pieces coated with a rubber adhesive on the surface are unvulcanized. After thinly depositing and scattering ceramic pieces on a short sheet of rubber, ceramic pieces are buried in the short sheet using a non-vulcanizing press mold to obtain a preliminary sheet for a protective layer in an unvulcanized state; A step of obtaining a belt-like long base layer preliminary sheet made into an unvulcanized state by a continuous sheet of rubber, and applying the unvulcanized protective layer preliminary sheet on top of the unvulcanized base layer preliminary sheet. After being laid one after another, the preliminary sheet for the base layer and the preliminary sheet for the protective layer are vulcanized and integrated using a vulcanizing press mold to form a dam sheet, and the obtained dam sheet is used to form a tube-like elastic material. The point is that it consists of the process of manufacturing a dam.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention will be described in detail below with reference to the drawings.

(Embodiment of an elastic dam) As shown in FIGS. 1 and 2, an elastic dam 1 is a tube that is installed in a transverse direction on a river bed 3 of a river 2 and is deformed to expand and contract through injection of fluid. Consists of 4 bodies. A fluid such as air or water can be injected and discharged into the tube body 4 from an operation room 5 installed on the riverbank via a supply/discharge pipe 6. Therefore, when fluid is injected into the tube body 4, the tube body 4 expands and expands as shown in FIG. 1 to form a dam that blocks the water flow of the river 2. On the other hand, when the fluid inside the tube body 4 is discharged, the tube body 4 contracts and becomes flat as shown in FIG.
The water is discharged without impeding the water flow.

As shown in FIG. 3, the tube body 4 forming the elastic dam 1 includes a seal sheet 7 installed on the riverbed 3 and forming the bottom of the tube body 4, and a rubber seal sheet 7 attached to the seal sheet 7. Both side edges of the dam sheet 8 are airtightly or watertightly fixed to both side edges of the seal sheet 7, and when a fluid is injected, the dam sheet 8 is expanded and expanded to stand up. In the case of the illustrated example, both side edges of the seal sheet 7 are fixed to the riverbed 3 with anchor bolts, and flanges on both side edges of the dam sheet 8 are fastened onto the seal sheet 7 using metal fittings attached to the anchor bolts. There is.

The tube body 4 of the elastic dam 1 may be constructed by separately forming a sealing sheet 7 and a dam sheet 8 as shown in the figure, or by, for example, bending a wide band-shaped dam sheet 8 into a cylindrical shape and butting them together. It is also possible to have a single-piece structure in which the edges are fixed by baking, bonding, or fastened with metal fittings.

As shown in FIG. 3, the dam sheet 8 is composed of a laminated structure including a rubber base layer 9 and an elastic protective layer 10 laminated and integrated on the outer surface of the rubber base layer 9. The rubber base layer 9 has a canvas 11 in the rubber layer, as shown in FIG. 4(A).
are embedded and integrated into multiple plies. In the example shown, the weir height of the elastic dam 1 is approximately 2 m, and the thickness of the rubber base layer 9 is approximately 4 m.
．． 1mm, canvas 11 is two ply. However, if the weir height of the elastic dam 1 is about 7 m, the thickness of the rubber base layer 9 will be about 16 mm, and the canvas 11 will have three or more plies.

The elastic protective layer 10 is shown in FIGS. 4(A) and 4(B).
As shown in the figure, it is composed of a flexible rubber sheet layer in which a large number of small ceramic pieces 12 are randomly embedded. The ceramic piece 12 may have a small rectangular parallelepiped shape, a cube shape, or a ball shape, but it is most preferable that it has an elongated substantially cylindrical shape as shown in the figure. In the case of the illustrated embodiment, the ceramic small piece 1
2 is made of α-alumina and other ceramics,
If the elastic protective layer 10 has a diameter of about 2 to 4 mm (most preferably about 2 mm) and a length of about 2 to 8 mm (most preferably about 4 mm), and the thickness of the elastic protective layer 10 is about 4 to 12 mm, the ceramic pieces 12 can be buried. Approximately 4kg/m2 to 8kg/m
2. However, a large number of small ceramic pieces 12
They may all be of the same shape and size, or they may be of different shapes and sizes.

The reason for this is that if the size of the ceramic small piece 12 is too large, when the dam sheet 8 expands and deforms, the small piece 12 may break through the deformed rubber sheet layer of the elastic protective layer 10; , ceramic pieces 12
If the dimension of is too small, not only will it be difficult for the small pieces 12 to be uniformly scattered throughout the rubber sheet layer during preforming of the elastic protective layer 10 described later, but the protective function described above will be inferior.

[0023] Furthermore, the amount of embedded ceramic pieces 12 is 4.
If the weight is less than 12 kg/m2, 12 small pieces are added within the rubber sheet layer.
On the other hand, if the weight exceeds 8 kg/m2, the small pieces 12 are scattered too densely and the flexibility of the elastic protective layer 10 cannot be satisfied. be.

As shown in FIG. 4(B), a large number of the ceramic pieces 12 are scattered and spread adjacent to each other in the plane direction of the rubber sheet layer, and the elongated cylindrical ceramic pieces 12 have a directionality. Since there is no adjacent piece 1
2 are arranged at random in a mutually interlocking manner in the front, back, left and right directions. Therefore, even if the tip of a thin harpoon or a small-caliber bullet pierces any part of the elastic protective layer 10, the small ceramic piece 12 is always present at a position that inhibits the penetration. Moreover, even if an attempt is made to cut the elastic protective layer 10 with a cutting tool such as a knife, the small ceramic piece 12 is always located so as to block the cutting line.

Furthermore, as shown in FIG. 4(A), a large number of ceramic pieces 12 are scattered in a vertically overlapping manner within the thickness of the rubber sheet layer. That is, in the case of the illustrated example, many of the ceramic pieces 12 are attached to the elastic protective layer 10.
A first layer 1 that spreads in the plane direction in a portion close to the surface of
3, a second layer 14 located below the first layer 13, and a third layer 15 located further below. The ceramic pieces 12 in the other layer are arranged so as to close the adjacent spaces between the ceramic pieces 12 in the other layer. Therefore, the tip of a thin harpoon or a bullet with a small diameter pierces the space between adjacent ceramic pieces 12 of the first layer 13 (between two ceramic pieces 12 adjacent in the plane direction) from the surface of the elastic protective layer 10. Even if the ceramic pieces 12 are pushed aside laterally and the ceramic pieces 12 are pushed aside, the ceramic pieces 12 in the lower layers 14 and 15 block the ceramic pieces 12 from entering.

(Embodiment of manufacturing method) The dam sheet 8 provided with the elastic protective layer 10 described above can be manufactured by the following steps.

(Production process of preliminary sheet for protective layer) First,
As shown in FIG. 5A, a rubber adhesive 16 is applied to the surface of the prepared ceramic piece 12 and dried. The adhesive 16 is mainly composed of chlorinated rubber dissolved in a solvent and a reactive phenolic resin added thereto. For example, adhesives commercially available under the trademarks of Chemlock 205 and 220 are be. In this adhesive application method, a large number of small ceramic pieces 12 may be placed in a basket and dipped into the adhesive, but a sprayer may be used to apply the adhesive to a large number of small pieces 12.
2 may be applied by spraying. In addition, the applied adhesive 1
6 is air dried.

Next, as shown in FIG. 5(B), a large number of the ceramic pieces 12 are placed on a short sheet 1 of unvulcanized rubber.
7 while being thinly deposited and scattered. The amount of scattered ceramic pieces 12 is approximately 4 kg/m2 as described above.
~8 kg/m2, and the dimensions of the short sheet 17 are, for example, 1350 mm (width) x 2000 mm (length), or other appropriate dimensions.

Thereafter, as shown in FIG. 5(C), a large number of small ceramic pieces 12 are placed on a short sheet 17 of unvulcanized rubber, and a press die for unvulcanization with upper and lower molds 18 and 19 is used to press the short sheet 17 of unvulcanized rubber. The ceramic pieces 12 are pressed and buried in a short sheet 17 of unvulcanized rubber, and the thickness is approximately 4 to 12 m.
A preliminary protective sheet 20 in an unvulcanized state having a size of about 100 m is obtained. A large number of buried ceramic pieces 12 are embedded in the elastic protective layer 1
They are arranged randomly in the same way as described above for 0. In this pressing step, the unvulcanized short sheet is only pressed at room temperature and is not vulcanized. Alternatively, if the non-vulcanization press mold is heated to 60 to 80 degrees Celsius, the rubber will not be vulcanized, but the rubber will be softened and the ceramic pieces 12 will be formed by plastic deformation of the short sheet 17. embedment becomes easy. In this way, the protective layer preliminary sheet 20 pressed by the non-vulcanizing press type leaves the rubber material in an unvulcanized state. Or, even if a semi-vulcanized state due to natural vulcanization, which is at least referred to as rubber burning, occurs after mold release,
It is said to be in a "non-vulcanized state" which allows it to be fully vulcanized later by hot pressing.

As shown in FIG. 6, this protective layer preliminary sheet 20 has joints 21a and 21b formed by slanting the cross sections located on both side edges (in the illustrated example, slanting at an angle of 45 degrees). is formed. This inclined joint 21
a, 21b, the inner surfaces of the molds 18, 19 are provided with slopes corresponding to the joint portions, and the short sheets 17 are deformed through plastic deformation during pressing with the non-vulcanizing press mold. Although it is preferable that the protective layer preliminary sheet 20 is press-molded, the protective layer may be formed by cutting the side edges diagonally using a cutter means.

(Manufacturing process of preliminary sheet for base layer) Separately from the process of manufacturing the preliminary sheet for protective layer 20, a preliminary sheet for base layer 22 for molding the rubber base layer 9 of the dam sheet described above is manufactured. The manufacturing process of this base layer preliminary sheet 22 is not shown because it is the same as the intermediate process of manufacturing the dam sheet in conventional elastic dams, but as in the past, it is made of a continuous sheet of unvulcanized rubber. The canvas 11 has as many plies as necessary and is embedded inside. As a method for manufacturing such a preliminary sheet 22 for the base layer, unvulcanized rubber sheets may be laminated in a sandwich manner with each of the necessary number of canvases 11 sandwiched between them, It may also be manufactured by using a rubberized cloth having a predetermined thickness and laminating the required number of such rubberized cloths. The thickness and width of this base layer preliminary sheet 22 are determined depending on the target weir height of the elastic dam, as described above.

[0032] Like the preliminary protective layer sheet 20, this base layer preliminary sheet 22 is also kept in an "unvulcanized state" so that it can later be fully vulcanized by hot pressing.

(Dam sheet forming process) As shown in FIG. 6, the unvulcanized preliminary sheet 20 for the protective layer is successively placed on the preliminary sheet 22 for the base layer that has been rendered unvulcanized. and spread it out. At this time, the protective layer preliminary sheets 20, 20 that are laid out adjacently are connected to each other at the connecting portions 21a, 2.
1b is polymerized. In addition, when laying the preliminary sheet 20 for the protective layer on the preliminary sheet 22 for the base layer, the rubber compositions of both preliminary sheets 20 and 22 are different from each other, and the vulcanization progress speed in the subsequent vulcanization step is different from each other. In case,
Another unvulcanized rubber sheet may be added and interposed between the two preliminary sheets, or a coating film of a rubber adhesive may be interposed therebetween. However, if the vulcanization progress speeds of both preliminary sheets 20 and 22 are approximately the same, both preliminary sheets can be vulcanized and integrated by subsequent hot pressing even without such an additional intervening layer. Ru.

The base layer preliminary sheet 22, on which the protective layer preliminary sheet 20 has been laid out in sequence, is continuously conveyed in a band shape to a continuous vulcanizer, as shown in FIG. 5(D). The dam sheet 8 is hot-pressed by the upper and lower molds 23 and 24 of the vulcanizing press mold, and both sheets 20 and 22 are vulcanized and integrated to form the above-mentioned dam sheet 8.

During this hot press vulcanization, the joint parts 21a and 21b of each protective layer preliminary sheet 20 are vulcanized and integrated, so that the surface of the elastic protective layer 10 after molding does not have seams or joints. First, they are seamlessly integrated. Further, within the protective layer preliminary sheet 20 during vulcanization, a large number of ceramic pieces 12 are firmly adhered to the rubber around the entire circumference via the rubber adhesive 16.

(Manufacturing process of elastic dam) The dam sheet 8 manufactured in this way has the elastic protective layer 1 of the present invention on the surface layer.
Since it is the same as a conventional dam sheet except that 0 is laminated and integrated, it is bent into a tube shape by the same method as the conventional method and used as an elastic dam 1 as shown in FIGS. 1 to 3.

[0037]

Effects of the Invention According to the present invention as set forth in claims 1 to 3,
It is possible to provide an elastic dam that is expandable and deformable as in the past, but does not suffer from punctures or bursts due to artificial hazards such as harpoons or bullets.

In particular, an elastic protective layer composed of a flexible rubber sheet layer in which a large number of small ceramic pieces are randomly embedded is arranged such that a large number of small ceramic pieces are scattered and spread adjacent to each other in the plane direction of the rubber sheet layer. Moreover, since they are scattered vertically and overlapping within the thickness of the rubber sheet layer, someone may try to pierce the outer surface of the elastic protective layer with the thin tip of a harpoon or a small-caliber bullet, etc. Even if an attempt is made to cut the elastic protective layer with a knife, the small ceramic pieces block the piercing or tearing direction from both the plane direction and the wall thickness direction, thereby preventing damage. Therefore, it is outstanding as a dam sheet that satisfies the two requirements of flexibility and high strength.

According to the fourth aspect of the present invention, there is an effect that the elastic dam as described above can be manufactured by a simple method.

In particular, when manufacturing the dam sheet, the preliminary sheet for the protective layer and the preliminary sheet for the base layer are both prepared in an unvulcanized state, and then they are polymerized and vulcanized into one piece. Elastic deterioration due to rubber deterioration unlike in the case of double vulcanization does not occur, and it is possible to provide a dam sheet with the desired rubber properties. Moreover, in the preliminary manufacturing process, the preliminary sheet for the protective layer was simply produced in large numbers in short sheets in which a large number of small ceramic pieces were embedded, and then these were laid out in a continuous strip on the preliminary sheet for the base layer. After that, in the dam sheet forming process, the dam sheet is integrally molded by vulcanization, so manufacturing is simple and the dam sheet can be manufactured extremely efficiently.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing an expanded state of an elastic dam according to an embodiment of the present invention.

FIG. 2 is a perspective view showing a contracted state of an elastic dam according to an embodiment of the present invention.

FIG. 3 is a longitudinal cross-sectional view of an elastic dam according to one embodiment of the present invention.

FIG. 4 shows a dam sheet in an elastic dam according to an embodiment of the present invention, in which (A) is an enlarged longitudinal sectional view and (B) is a plan view.

FIG. 5 shows a method for manufacturing a dam sheet used in an elastic dam according to an embodiment of the present invention, in which (A) is a perspective view showing a step of applying a rubber adhesive to a small ceramic piece, and (B) (C) is a vertical cross-sectional view showing a state in which a large number of ceramic pieces are thinly deposited on a short sheet of unvulcanized rubber, and (C) is a vertical cross-sectional view showing a state in which a preliminary sheet for a protective layer is formed by cold pressing. (D) is a longitudinal cross-sectional view showing a state in which a preliminary sheet for a base layer and a preliminary sheet for a protective layer are vulcanized and integrated by hot pressing to form a dam sheet.

FIG. 6 is a longitudinal cross-sectional view showing a method of successively laying out a protective layer preliminary sheet on a base layer preliminary sheet.

[Explanation of symbols]

1 Elastic dam 2 River 3 Kawadoko 4 Tube body 8 Dam seat 9 Rubber base layer 10 Elastic protective layer 12 Ceramic pieces 16 Rubber adhesive 17 Short sheet of unvulcanized rubber 20 Protective spare sheet 22 Preliminary sheet for base layer

Claims (4)

[Claims] 1. A tubular elastic dam comprising a rubber dam sheet that is installed transversely on a river bed and is expandably deformed through injection of fluid, the dam sheet comprising a rubber base layer; It consists of a laminated structure with an elastic protective layer laminated and integrated on the outer surface of the rubber base layer, and the elastic protective layer is constituted by a flexible rubber sheet layer in which a large number of ceramic pieces are randomly embedded, and the ceramic A freely expandable and contractible elastic dam characterized in that a large number of small pieces are scattered and spread adjacent to each other in the planar direction of a rubber sheet layer, and are overlapped vertically within the thickness of the rubber sheet layer. . [Claim 2] The ceramic pieces have a diameter of approximately 2 to 4 m.
2. The expandable and contractible elastic dam according to claim 1, wherein the expandable and contractible elastic dam has an elongated, substantially cylindrical shape with a length of about 2 to 8 mm. 3. The elastic protective layer has a thickness of about 4 to 12 mm, and the amount of ceramic pieces embedded in the rubber sheet layer is about 4 kg/m2 to 8 kg/m2. An elastic dam that can be expanded and contracted. 4. A large number of small ceramic pieces coated with a rubber adhesive on the surface are thinly deposited and scattered on a short sheet of unvulcanized rubber, and then a press mold for non-vulcanization is used to form small ceramic pieces in the short sheet. a step of embedding the unvulcanized rubber to obtain a preliminary sheet for the protective layer in an unvulcanized state; a step of obtaining a preliminary sheet for the base layer in a long belt-like state rendered unvulcanized by a continuous sheet of unvulcanized rubber; After sequentially and consecutively laying out the unvulcanized preliminary sheets for the protective layer on the preliminary sheet for the base layer in the cured state, the preliminary sheets for the base layer and the preliminary sheet for the protective layer are vulcanized using a vulcanizing press mold. A method for manufacturing a expandable and contractible elastic dam, comprising the steps of forming a dam sheet by integrating the dam sheet, and manufacturing a tubular elastic dam using the obtained dam sheet.