Method for conserving steel bridge

Abstract

To provide a method for conserving a steel bridge, the method being capable of improving work efficiency of conservation work of the steel bridge.SOLUTION: A method for conserving a steel bridge performs a projection step for projecting a mixed projection material obtained by mixing grit and shots at a prescribed ratio on the surface of a steel bridge, and a coating step for coating paint on the surface of a steel material 31 after the projection step. In this conservation method, it is possible to remove substances 32 adhering to the surface of the steel material 31 and adjust the base and apply compressive residual stress by the projection method. In addition, minor scratches 34 remain on the surface of the steel material 31, and thus, it is possible to improve adhesion properties between the surface of the steel material 31 and a coating film 35.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a maintenance method for steel bridges to be implemented on steel bridges.

Background Art

[0002] Conventionally, preventive maintenance has been carried out for steel bridges, whether newly constructed or existing, in order to prevent the occurrence of rust and the like, or particularly in the case of existing steel bridges, for the renewal of paint whose corrosion has progressed due to aging deterioration. Since such preventive maintenance requires the removal of rust and the like or the removal of old paint films, in recent years, rust and paint films have been removed by blasting (type 1 keren), and then new paint has been applied.

[0003] As a maintenance method for existing steel bridges and the like, for example, Patent Document 1 proposes a method in which a blasting process for removing rust and paint films and preparing the base, a shot peening process for introducing compressive residual stress to the surface of the steel material to improve fatigue strength, and a painting process for applying rust preventive paint are sequentially executed. And in this conventional method, the blasting process and the shot peening process are carried out using the same injection device by switching the grit and the shot.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] By the way, in the conventional maintenance method described in Patent Document 1 mentioned above, since the blasting process and the shot peening process are carried out using the same injection device, compared with the case of using an injection device for the blasting process and an injection device for the shot peening process, the time and labor required for transporting and installing the injection device can be reduced, so that the working efficiency of the maintenance work can be improved. However, in this conventional maintenance method, since an operation of replacing grit and shot is required, there is a limit to the effect of improving the working efficiency.

[0006] The present invention proposes a maintenance method for a steel bridge that can improve the working efficiency of the maintenance work of the steel bridge as compared with the conventional maintenance method.

Means for Solving the Problems

[0007] The present invention is a maintenance method for a steel bridge that removes deposits adhering to the base surface of the steel bridge and paints the base surface, and includes a mixed projection material containing grit, which is a projection material having an angular and angular shape, and shot, which is a spherical projection material. By projecting the mixed projection material onto the surface of the steel bridge, a projection step of removing the deposits to adjust the base and applying compressive residual stress to the surface of the steel bridge, and after the projection step, a painting step of applying a predetermined paint to at least the surface of the steel bridge onto which the mixed projection material was projected in the projection step. It is a maintenance method for a steel bridge characterized by including.

[0008] Here, the base surface of the steel bridge corresponds to the surface of the steel material constituting the steel bridge, and the deposits indicate a paint film, rust, etc. Also, the spherical shape of the shot includes a spherical shape and a shape close to a spherical shape, and the shot may be a mixture of a spherical shape and a shape close to a spherical shape, or may be only one of a spherical shape and a spherical shape.

[0009] In such a maintenance method, by means of a spraying process of spraying a mixed spraying material in which grit and shot are mixed, it is possible to perform surface preparation of the steel materials constituting the steel bridge and impart compressive residual stress to the steel materials. That is, the surface preparation performed by the conventional blasting treatment and the imparting of compressive residual stress performed by the shot peening treatment can be executed in a single spraying process. Accordingly, according to the maintenance method of the present invention, there is no need for the replacement work of grit and shot as in the above-described conventional maintenance method, and the working time of the maintenance work can be shortened as compared with the conventional maintenance method.

[0010] Furthermore, in this spraying process, since a mixed spraying material in which grit and shot are mixed is sprayed, the surface of the steel bridge can be made rougher than in the conventional method. More specifically, in the conventional maintenance method, after the surface of the material is damaged by grit in the blasting treatment, the shot peening treatment is performed. Therefore, the damage caused by the blasting treatment is removed by the collision of spherical shots. As a result, a large number of curved recesses are formed on the surface of the steel bridge after the shot peening treatment. On the other hand, in the spraying process of the present invention, since the mixed spraying material is sprayed, a large number of fine scratches caused by the collision of grit are present on the surface of the steel bridge after this process. Thereby, the adhesiveness with the paint applied in the painting process is remarkably improved as compared with the conventional method. As described above, according to the configuration of the present invention, in addition to the effect of shortening the working time as compared with the conventional method, there is an effect of improving the paint adhesiveness that cannot occur in the conventional method.

[0011] Also, in the projection process of the present invention, by setting conditions such as the ratio of mixing grit and shot that make up the mixed projection material, the sizes of the grit and shot, the projection amount of the mixed projection material, and the projection time, etc., it is possible to appropriately change the adjustment level of substrate adjustment, the imparting level of compressive residual stress, etc. to a desired level. Here, the compressive residual stress is applied for the purpose of improving fatigue strength. And generally, when compressive residual stress is applied by shot peening treatment, it is said that the fatigue strength is improved by two grades, and when an operator performs the treatment using a grinder, it is said that the fatigue strength is improved by one grade. The projection process of the present invention can change the fatigue strength according to the usage environment and desired level between one grade and two grades by setting conditions such as the above-mentioned ratio of grit and shot. Thus, the present invention has an excellent advantage that a desired fatigue strength can be generated without the need for the above-mentioned replacement work of grit and shot by setting the conditions of the projection process.

[0012] In the steel bridge maintenance method of the present invention described above, there is proposed a method including a recovery process of recovering the mixed projection material projected in the projection process and sending it to a projection material storage tank that stores the mixed projection material projected in the projection process, and a replenishment process of replenishing the grit to the projection material storage tank when predetermined replenishment conditions are satisfied.

[0013] Here, by performing the recovery process, the mixed projection material projected in the projection process can be reused. However, the grit of the reused mixed projection material is worn by projection. This is because when the mixed projection material is used in the projection process, the angular portions on the surface of the grit are worn down and deformed into a curved surface shape due to collisions between grits, collisions between grit and shot, and collisions between grit and the steel bridge. For this reason, if the mixed projection material is repeatedly reused, there is a risk of reducing the effect of the treatment for adjusting the steel material substrate.

[0014] Such a maintenance method performs a replenishment process in addition to a recovery process for reusing mixed projection materials. By replenishing grit in this replenishment process, the substrate adjustment by the projection process can be sufficiently and stably performed over a relatively long period. Therefore, according to this method, the effect of reducing the usage amount of mixed projection materials by the recovery process and the effect of stably performing the substrate adjustment process by the replenishment process can be achieved in good balance, and overall, the cost required for maintaining the steel bridge can be reduced.

[0015] Here, as the replenishment conditions, it is preferable to set according to the state where the grit of the mixed projection material is worn. Specifically, it can be set on the condition that the number of executions of the projection process, the time when the projection process is performed, or the area of the steel material on which the projection process is performed reaches a predetermined value.

Effects of the Invention

[0016] According to the steel bridge maintenance method of the present invention, substrate adjustment and application of compressive residual stress can be performed without the need for the replacement work of grit and shot as in the conventional maintenance method described above, and the work efficiency of the maintenance work can be dramatically improved compared to the conventional method. In addition, due to the projection process, fine scratches can be left on the surface of the steel bridge, so the adhesiveness of the paint applied in the painting process can be improved.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Figure 3

Figure 4

Modes for Carrying Out the Invention

[0018] An embodiment embodying the maintenance method for steel bridges according to the present invention will be described below. The maintenance method for the steel bridge of this embodiment is carried out for the purpose of maintaining an existing steel bridge. As shown in FIG. 1, first, a temporary curing facility is installed on the steel bridge to be maintained (S101). Specifically, a scaffold is temporarily installed on the steel bridge, and a dust-proof sheet is temporarily installed so that dust does not diffuse to the outside. Then, curing of the non-painted part is performed, and a projection device 1 (see FIG. 2) for projecting a mixed projection material described later is installed.

[0019] Next, the type and thickness of the old paint film applied to the steel bridge, or the condition of the steel bridge, etc. are investigated (S102). Then, based on the investigation results, a mixed projection material in which grit and shot are mixed, and the injection speed etc. of the mixed projection material are determined. Here, since the mixed projection material relates to the main part of the present invention, details will be described later.

[0020] Next, the mixed projection material determined in S102 is supplied to a hopper tank 21 described later, and a projection process is performed (S103). Here, the supply amount of the mixed projection material supplied to the hopper tank 21, the ratio of grit to shot in the mixed projection material, etc. are determined by S102. By this projection process, the old paint film and rust adhering to the surface of the steel material 31 (see FIG. 3) constituting the steel bridge are removed to perform substrate conditioning, and compressive residual stress can be applied to the surface of the steel material 31. Here, the surface of the steel material 31 corresponds to the substrate surface according to the present invention, and the old paint film and rust correspond to the deposits according to the present invention. Note that since the projection process relates to the main part of the present invention, details will be described later.

[0021] Next, the surface of the steel material 31 after the projection process is confirmed (S104). This confirmation process includes not only visual inspection, but also comparison using, for example, an ISO8501 blast photo album, or roughness confirmation using a surface roughness measuring instrument. By this, confirmation is performed as to whether there is any remaining unp peeled paint film, or whether the roughness of the material surface is within the standard. Here, if it is determined to be qualified by this confirmation, the next painting process is performed. On the other hand, if it is determined to be unqualified (if there are insufficient parts), the projection process (S103) is performed again.

[0022] Next, a painting process is performed (S105). In this embodiment, heavy anticorrosive painting is performed on the area where the mixed projection material was projected in S103. This heavy anticorrosive painting is, for example, rust-proof painting with an epoxy resin paint for undercoating, and then a fluororesin paint is used for intermediate coating to protect the rust-proof painting, and further top-coated with a fluororesin paint on top of this. Thereby, a new coating film covering the surface of the steel material 31 is formed.

[0023] After completion of the painting process, confirmation is performed (S106). This confirmation includes not only confirmation of the film thickness after the paint has dried, but also, for example, confirmation of the wet film thickness using a wetness gauge during the painting operation. Also, such confirmation is performed not only after the top coating, but also during the undercoating and intermediate coating. By completing this painting confirmation, the painting work is terminated.

[0024] After completing the painting confirmation, the site is tidied up (S107). Specifically, scaffolds, dust sheets, etc. are collected, and the projection device 1 is withdrawn. By the completion of such tidying up, all the processes according to the steel bridge maintenance method are completed.

[0025] Also, together with the processes of S101 to S107 described above, a dust collection process (S111) and a replenishment process (S112) for replenishing the grid are performed. In the collection process, dust containing the used mixed projection material (grit and shot) used in the projection process (S103) and the old coating film, rust, etc. generated in the projection process is collected while being separated, and the used mixed projection material is sent to the hopper tank 21 described later. Thereby, the used mixed projection material can be reused in the projection process. Note that the replenishment process will be described in detail later since it relates to the main part of the present invention.

[0026] The projection device 1 used in the above-described projection process will be described. This projection device 1 is capable of injecting the grit and shot that constitute the mixed projection material described above, and is of a circulation type that can collect and separate the used mixed projection material (grit and shot) and the peeled coating film, etc.

[0027] As shown in Fig. 2, the projection device 1 includes a device main body 2 installed adjacent to the work site α of the steel bridge K to be worked on. This device main body 2 is equipped with a pressure hose 4, and an injector 3 is connected to the tip of the pressure hose 4. A detachable nozzle (not shown) is attached to the tip of the injector 3, and a mixed projection material (grit and shot) is ejected from the nozzle. Further, the device main body 2 is equipped with a suction hose 5, and the tip of the suction hose 5 is arranged at the work site α. Thereby, through the suction hose 5, it is possible to suck the used mixed projection material generated at the work site α and the dust X composed of foreign matters including the peeled paint film and rust. Note that a dust-proof sheet (not shown) is stretched at the work site α so that the dust X does not leak to the outside, and a blower, a dust collector, etc. are also installed as appropriate.

[0028] Further, the projection device 1 is provided with a hopper tank 21. The hopper tank 21 has a function of storing a mixed projection material and a used mixed projection material (hereinafter, these mixtures are referred to as a mixed projection material), and a pressure tank 22 for pumping the mixed projection material stored in the hopper tank 21 to the work site α is connected. Note that the hopper tank 21 in this embodiment corresponds to the projection material storage tank according to the present invention.

[0029] A dry compressed air supply means 25 is connected to this pressure tank 22 via a dry compressed air pipe 26. Such dry compressed air supply means 25 is composed of an air compressor and an air dryer for supplying dry compressed air. Further, the pressure hose 4 is connected to the grit pressure tank 22. And with such a configuration, the mixed projection material is ejected from the nozzle 7 of the injector 3 through the pressure hose 4 by the air pressure of the dry compressed air supplied from the dry compressed air supply means 25.

[0030] Dust containing used mixed projection materials deposited at the work site α and foreign substances such as peeled coating films is collectively sucked from one end of the suction hose 5. Then, the dust sucked by the suction hose 5 reaches the separation chamber 11 disposed above the hopper tank 21. A dust hose 28 is attached to this separation chamber 11, and a dust collection unit 12 as a peeled coating film recovery unit is connected to the dust hose 28. Further, an air suction device 13 as a dust suction means is connected to the dust collection unit 12, and the dust can be sucked by the air suction force of the air suction device 13. In the separation chamber 11, the dust is separated into used mixed projection materials and foreign substances including the peeled coating film. The discharged foreign substances are introduced into the dust collection unit 12 through the dust hose 28, deposited in the dust collection unit 12, and discharged into the waste bag 29 at a desired timing for treatment as industrial waste.

[0031] Next, the main part of the present invention will be described. As described above, in the projection process of this embodiment, a mixed projection material in which grit and shot are mixed is projected onto the surface of the steel bridge by the projection device 1. Here, the mixed projection material is a mixture of grit, which is a projection material having an angular and angular shape, and shot, which is a spherical projection material, and in this embodiment, the ratio of grit to shot is determined so that the fatigue strength of the steel material is improved by one grade or more in the projection process. Further, both the grit and shot of the mixed projection material are made of steel, and the grit has a higher hardness than the shot.

[0032] As for the grit contained in the mixed projection material, abrasive grains defined in JIS Z 0310:2004 and JIS Z 0311:2004 (in the state before use, having an angular and angular shape, and particles with rounded parts less than 1 / 2 of the particles) can be applied. Also, as for the shot, particles defined in JIS Z 0311:2004 (in the state before use, having no sharp corners, crushed surfaces or other sharp surface defects, and spherical particles with a major axis within 2 times the minor axis) and JIS G 0951:2004 (spherical or nearly spherical hard particles) can be applied. Also, regarding the fatigue strength grade, it is described in "Fatigue Design Guidelines for Steel Structures - Explanation - Design Examples - Revised Edition 2012" (edited by the Japan Institute of Steel Construction).

[0033] As described above, such a mixed projection material is stored in the hopper tank 21 of the projection device 1 and is projected from the injector 3 by air pressure, thereby being projected onto the surface of the steel bridge. When the grit of this mixed projection material collides with the surface of the steel bridge, the old paint film and rust adhering to the surface of the steel material constituting the steel bridge can be removed. Also, when the shot of the mixed projection material collides with the surface of the steel bridge, compressive residual stress can be applied. More specifically, by projecting the mixed projection material, the grit and the shot randomly and repeatedly collide with the surface of the steel bridge. Therefore, at the part where the shot collides with the old paint film, the old paint film is broken, and the grit that collides later makes it easier to remove the old paint film. Also, the base surface (the surface of the steel material 31) from which the old paint film has been removed is curved and recessed by the collision of the shot, and is finely scraped compared to the shot by the collision of the grit (see Figure 3). Due to the collision of this grit, it becomes easier to generate residual stress in the surface layer than by the collision of only the shot. And since the collision of the grit also causes scratches in the curved concave part recessed by the collision of the shot, residual stress can be generated in the surface layer in the same way.

[0034] When the mixed projection materials collide in this way, the old paint film and the like can be removed to adjust the substrate, and compressive residual stress can be applied to improve the fatigue strength and stress corrosion cracking resistance. That is, by one projection process, substrate adjustment and application of compressive residual stress can be performed simultaneously. And the peak of the compressive residual stress can be generated on the surface layer, and the fatigue strength can be improved by one grade or more.

[0035] Furthermore, when the projection process is executed, as described above, the surface of the steel material is curved and recessed in a curved shape due to the impact of the shot, and a large number of scratches 34 generated by the impact of the grit remain on the surface. Thereby, the adhesiveness of the surface of the steel material to the paint film formed in the painting process after the projection process is remarkably improved.

[0036] Specifically, when the mixed projection materials are projected onto the old paint film 32 adhering to the surface of the steel material 31 shown in Fig. 3(A), as shown in Fig. 3(B), the old paint film 32 is removed, and a large number of recesses 33 generated by the impact of the shot and a large number of scratches 34 generated by the impact of the grit remain on the surface of the steel material 31. Thereby, the surface of the steel material 31 has a rough surface having the recesses 33 and the scratches 34. When the paint is applied to the steel material 31 having such a rough surface in the painting process, as shown in Fig. 3(C), a new paint film 35 is formed on the surface of the steel material 31. This paint film 35 has extremely high adhesiveness to the rough surface having the recesses 33 and the scratches 34.

[0037] The preservation method of this present embodiment is compared with the conventional preservation method. In the conventional preservation method, shot peening treatment is performed after blasting treatment. For the sake of comparison, the steps before the blasting treatment and the steps after the shot peening treatment are the same as those in the embodiment. In the blasting treatment, the same grit as in the embodiment is used, and in the shot peening treatment, the same shot as in the embodiment is used. When blasting treatment is performed on the surface of the steel material 31 to which the old paint film 32 is attached (Fig. 4(A)), as shown in Fig. 4(B), the old paint film 32 is removed due to the collision of the grit. And on the surface of the steel material 31, scratches 34 caused by the collision of the grit remain. Next, when shot peening treatment is performed, as shown in Fig. 4(C), although curved recesses 37 caused by the collision of the shot remain on the surface of the steel material 31 due to the collision of the shot, the scratches 34 are removed by the collision of the shot. When paint is applied to the surface in this state, as shown in Fig. 4(D), a paint film 35 is formed on the surface.

[0038] When comparing such a conventional preservation method with the preservation method of the present embodiment described above, according to the projection process of the present embodiment, the surface of the steel material before the painting process can be roughened compared with the conventional preservation method. Thereby, according to the preservation method of the present embodiment, the adhesiveness between the surface of the steel material and the paint film can be improved.

[0039] Also, in the preservation method of the present embodiment, as described above, a recovery process (S111) for recovering and reusing the mixed projection materials (grit and shot) used in the projection process and a replenishment process (S112) for replenishing the grit to the hopper tank 21 are performed. Here, when the mixed projection material is projected in the projection process, the corners of the grit are worn down due to collisions between the grits generated by the projection, collisions between the grit and the shot, and collisions between the grit and the steel material. Then, as the reuse by the recovery process is repeated, the surface of the grit is deformed into a curved surface shape. In the used mixed projection material due to such reuse, the effect of adjusting the substrate by the collision of the grit in the projection process (such as removing the old coating layer and scratching the steel material surface) is reduced. Therefore, in this embodiment, in order to suppress this reduction, grit is replenished into the hopper tank 21 by the replenishment process.

[0040] The replenishment process is executed every time the projection amount of the mixed projection material projected in the projection process reaches a preset threshold value, and grit is replenished into the hopper tank 21. That is, in this embodiment, grit is replenished every time the projection amount reaches the threshold value, and no grit is replenished when the threshold value is not reached. In this way, the grit is replenished (the replenishment process is performed) on the condition that the projection amount of the mixed projection material reaches the threshold value (replenishment condition). Here, the threshold value and the replenishment amount of the grit are set based on the amount of the mixed projection material used in the projection process (the storage amount in the hopper tank 21), the ratio of the grit, and the projection amount.

[0041] In addition, the projection device 1 of this embodiment is provided with replenishment means (not shown) for replenishing grit into the hopper tank 21. This replenishment means can be configured to include control means for detecting the projection amount and determining whether the threshold value has been reached, and means for automatically replenishing grit into the hopper tank 21 when the threshold value is reached. Or, it may be configured to include means for notifying when the control means reaches the threshold value, and the operator replenishes the grit by this notification.

[0042] As described above, the preservation method of this embodiment can simultaneously perform substrate adjustment and imparting of compressive residual stress by one projection process. In addition, the peak of the compressive residual stress can be generated on the surface layer to improve the fatigue strength by one grade or more. Furthermore, since fine scratches caused by the collision of grit remain on the surface of the material, the adhesiveness with a new coating film can be improved. Also, in this embodiment, since a replenishment process for replenishing grit is performed, problems (the effect of adjusting the substrate of steel materials is reduced) caused by repeatedly using the used mixed projection material by the recovery process can be suppressed. Thereby, it is possible to achieve a good balance between the effect of suppressing the usage amount of the mixed projection material by the recovery process and the effect of being able to stably perform the substrate adjustment process over a relatively long period by the replenishment process.

[0043] The present invention is not limited to the above-described embodiments, and can be appropriately modified within the scope not departing from the gist of the present invention. For example, the ratio of grit to shot constituting the mixed projection material can be appropriately changed. Specifically, the ratio may be set so that the fatigue strength is improved by two grades, or the ratio may be set so as to be between one grade and two grades (for example, a level corresponding to 1.5 grades). Also, in the embodiment, the replenishment condition for replenishing grit in the replenishment process is set such that the projection amount of the mixed projection material reaches a predetermined threshold value, but this replenishment condition can be appropriately changed. For example, it may be conditioned that the area on which the mixed projection material is projected reaches a predetermined threshold value, or it may be conditioned that the projection time of the mixed projection material reaches a predetermined threshold value.

Explanation of Signs

[0044] 1 Projection device 31 Steel material 32 Old coating film (adhesion) K Steel bridge

Claims

1. A method for preserving steel bridges, which involves removing deposits from the base surface of a steel bridge and painting the base surface, a projection process in which a mixed projection material containing grit, which is an angular projection material having an angular shape, and shot, which is a spherical projection material, is projected onto the surface of the steel bridge to remove the deposits, adjust the base material, and impart compressive residual stress to the surface of the steel bridge; After the projection step, a painting step is performed in which a predetermined paint is applied to at least the surface of the steel bridge onto which the mixed projection material has been projected in the projection step. A steel bridge preservation method comprising the steps of:

2. a recovery process for recovering the mixed projection material projected in the projection process and sending it to a projection material storage tank that stores the mixed projection material projected in the projection process; a refilling step of refilling the blast material storage tank with the grit when a predetermined refilling condition is met; 2. The method for preserving a steel bridge according to claim 1, further comprising:

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