JP4502622B2 - Thermal spraying method - Google Patents

Description

  The present invention relates to a thermal spraying method for forming a metal spray coating for corrosion protection on the surface of a metal body, and particularly to a thermal spraying method suitable for on-site repair of a steel structure or the like.

  Conventionally, the painting method is generally used as an anti-corrosion measure for steel structures such as steel towers, bridges, elevated facilities, and tanks. However, this painting method has a problem that the coating cost is high, the service life is limited, and the repair cost is high because it requires periodic repainting. Therefore, a method of forming a sprayed coating on the steel surface has been proposed as an anti-corrosion measure to replace the painting method. For example, Patent Document 1 discloses an anticorrosion structure for a steel structure in which a thermal environment is sprayed on a poor environment portion of the steel structure, and a weather resistant steel is used for a portion other than the poor environment portion. According to this anti-corrosion structure, it is said that the corrosion resistance of the entire steel structure is improved, and the construction cost and the repair cost can be reduced.

  For offshore structures that have been exposed to severe corrosive environments for a long time, a conventional method of forming a resin lining film has been used, and a thermal spraying method has been proposed as a method for repairing damaged parts of this lining film on site. . For example, after a ground treatment is performed to roughen the defective part generated in the lining film, the defective part is preheated to a required temperature, and then a polymer compound powder is sprayed onto the defective part to repair the defective film. Patent Document 2 describes a method for repairing an anticorrosion lining film that forms a film. According to this repair method, it is said that it is possible to perform on-site repair with a long life and high reliability as compared to the conventional method of repairing with a room temperature curing type paint.

  Thermal spray coating has excellent properties such as corrosion resistance, heat resistance, and wear resistance, and thermal spraying is not limited to steel materials that are members of steel structures, but is used in a wide range of fields as a surface modification technology for various materials and products. Has been. Thermal spraying involves spraying a thermal spray material heated to a molten or semi-molten state onto a sprayed body to form a thermal spray coating, and there are a gas flame spraying method and a plasma spraying method as main thermal spraying methods.

  Gas flame spraying uses a flame of oxygen and combustible gas to heat a thermal spray material in the form of a wire, rod, or powder, and melts it or sprays it to the sprayed body to form a coating. Is the law. This gas flame spraying method is most popular because it is easy to operate and has low equipment and operating costs.

  The plasma spraying method is a spraying method in which a thermal spray material is heated and accelerated using a plasma jet, and is melted or sprayed onto a thermal sprayed body to form a coating. In this plasma spraying method, a high melting point ceramic, a metal, and a plastic can be used as a spraying material, and spraying in an air atmosphere, an inert atmosphere, or a reduced pressure atmosphere is possible. Although the thermal spray material of plasma spraying is mainly powdery, in recent years, plasma arc torches using linear or rod-like thermal spray materials have been proposed in Patent Documents 3 to 5.

JP 2001-89880 A JP 2002-69604 A Japanese Patent Publication No. 5-80273 Japanese Patent Publication No. 6-39682 Japanese Patent No. 3261518

  By the way, when performing thermal spraying, as a pretreatment for the thermal sprayed object, a process of removing the paint, plating film, oxide, etc. on the surface of the thermal sprayed object and roughening the surface is required. By roughening the surface of the object to be sprayed, a so-called anchor effect is produced in which the thermal spray particles mechanically mesh with the irregularities on the roughened surface and the adhesion between the sprayed coating and the object to be sprayed is improved. This roughening is usually performed by a method called blasting. There are several methods for blasting, but the most common method is to project natural minerals, artificial minerals, metallic grit, non-metallic grit, cut wire, etc. onto the sprayed object using compressed air. Thus, the substrate is exposed on the surface, and irregular minute irregularities are formed on the surface.

  In order to perform this blasting process, large-scale devices such as a blast material hopper, a tank, an air compression device, a compressed air pipe, a blast material supply tube, a torch, a blast material recovery device, and a dust collecting device are required. In the case of a construction process where these devices are installed in a material processing plant for steel structures, etc., blasting is performed at the material processing stage, and the thermally sprayed material is transported to the construction site after blasting to assemble steel structures etc. There is no problem as compared with the implementation of blasting. However, in the case of on-site repairs, there are major problems in terms of cost, work and environment, and implementation is very difficult. In order to perform the blasting process at the repair site, it is difficult to arrange the above-described apparatus set at the repair site. Moreover, in the case of on-site repairs of large structures, the work is often performed at high places, and it is difficult to install necessary equipment at high places. Further, it is difficult to collect the blast material during processing and to collect the generated dust, and there is a problem that the working environment is deteriorated by the scattered blast material and dust and the environment is contaminated.

  Therefore, when spraying in the field repair, blasting cannot actually be performed, so it is necessary to take a roughening method instead of blasting. Even when blasting is performed at a material processing plant, the working environment is inevitably deteriorated. Therefore, if a roughening method can be applied instead of blasting, there is no surpassing this.

  The problem to be solved by the present invention is that a thermal sprayed body that provides a practically sufficient adhesion between the thermal sprayed coating and the thermal sprayed body when a thermal sprayed coating for corrosion protection is formed by spraying a metal thermal spray material on the metal body. It is intended to improve the workability of the surface roughening process and reduce the thermal spraying cost while elucidating the surface roughening conditions and thermal spraying conditions and maintaining the anticorrosion effect.

  The present inventors have intensively studied the influence of the roughening condition and spraying condition of the sprayed body as a pretreatment for spraying on the adhesion between the sprayed coating and the sprayed object, and used a relatively simple tool. In order to complete the present invention, it has been found that even a thermal sprayed surface to be roughened can obtain a practically sufficient adhesion of a thermal spray coating by spraying under specific thermal spraying conditions. It came.

That is, the thermal spraying method according to the present invention is a thermal spraying method in which a metal thermal spray material is sprayed on a metal body, in particular, a thermal spraying method by plasma spraying to form an anticorrosive thermal spraying coating, and a thermal spraying method is applied by using a grinding tool A step of performing a surface roughening treatment so that the average roughness Ra of the surface is in a range of 2 to 10 μm, and an average of the molten particles per particle when the molten particles of the thermal spray material adhere to the surface of the sprayed body And a step of performing thermal spraying on the condition that the area becomes 10,000 to 100,000 μm ² .

  Here, it is desirable to use a thermal spraying apparatus using a linear or rod-shaped metal spraying material as the plasma spraying apparatus, and it is desirable to use an aluminum alloy, more preferably an aluminum-magnesium alloy as the metal spraying material. Moreover, the process of performing a sealing process can also be included in the film after thermal spraying.

By performing plasma spraying under the condition that the average area per grain when the molten particles adhere to the surface of the sprayed body is within a predetermined range, the temperature of the surface of the sprayed body rises and the droplets on the surface of the sprayed body Improves wettability. As a result, even when the surface is roughened by a grinding tool, the degree of surface roughening is lower than in the case of blasting, it is possible to obtain the adhesion strength of the thermal spray coating that is the same as that in the case of a combination of blasting and gas flame spraying. it can. Roughening with a grinding tool does not require a large-scale device as in the case of blasting, and it can be used for high-level work in on-site repairs if it is a small portable tool. There is little scattering and less risk of environmental pollution. Further, if the average area per grain of plasma spraying in place of the arc spraying method a molten particles using performs spraying under the condition that the 10000～100000Myuemu ^2, effects similar to the above, has the advantages it can.

  The object of thermal spraying in the present invention is a metal body. Although thermal spraying itself can be applied to non-metallic bodies, the present invention is premised on plasma spraying, and for the purpose of strengthening the anti-corrosion function of metal structures and reducing repair costs, the metal structure or its members are applied. A thermal spraying method for forming a metal spray coating is adopted.

  In the present invention, the roughening treatment as a pretreatment for thermal spraying is performed using a grinding tool. The grinding tool here refers to a power tool in which abrasive grains are fixed to a disk-shaped or belt-shaped base material, a power tool in which a flap or wire is implanted on the outer peripheral surface of the wheel, etc. These tools are hand-held work There is also a small one that can be used, so it can be suitably used especially for on-site repairs. When the surface of the sprayed object is ground using such a grinding tool, a large number of parallel line marks are generated on the surface. When the grinding tool is moved in a certain direction, the linear trace becomes a constant direction, and when the moving direction is crossed, the linear trace also intersects. In order to form a large number of irregularities as in the case of blasting, it is preferable to cross the moving direction of the grinding tool, but the roughening treatment of the present invention provides sufficient adhesion even with linear traces in a certain direction. be able to. In addition, although the intersection angle in the case of making a linear trace cross | intersect may be many times, Preferably an intersection angle shall be 60-90 degree | times.

  The surface roughness obtained by this roughening treatment is optimal when the average roughness Ra is 2 to 10 μm, more desirably 5 to 8 μm. Moreover, it is preferable that the maximum roughness Rz is 20 to 100 μm and the roughness peak count value RPc is 30 to 100. When the surface roughness is in the above range, when the molten particles collide with the rough surface during spraying, the surface spreads without gaps and the anchor effect of biting into the rough surface becomes strong.

  If the average roughness Ra of the surface roughness is less than 2 μm, a sufficient anchor effect cannot be obtained and the adhesion of the sprayed coating is lowered. When the average roughness Ra is larger than 10 μm, it is rather preferable in terms of the adhesion force of the sprayed coating. However, in order to generate such a rough surface, it is necessary to increase the grain size of the abrasive grains used in the grinding tool. The resistance increases and the burden on the operator operating the grinding tool increases, which is not practical. Further, when the surface roughness becomes extremely large, the molten metal cannot be sufficiently flattened and spread over the rough surface, and a gap is generated between the surface and the molten particles, and conversely the adhesion of the sprayed coating is reduced.

  When the maximum roughness Rz is smaller than 20 μm, it is necessary to obtain a uniform surface roughness in order to obtain an appropriate average roughness, and it becomes difficult to perform the roughening process using the grinding tool as described above. When the maximum roughness Rz is larger than 100 μm, a grinding tool having a large grinding particle diameter is required. However, since the large grinding particles are consumed quickly, it is difficult to perform uniform construction and workability is lowered. When the roughness peak count value RPc is less than 30, the number of irregularities is small and there are many small smooth portions, and the adhesion of molten particles is reduced. On the contrary, if the peak count value RPc is larger than 100, the interval between the concaves and convexes becomes too small, and the molten particles do not become sufficiently familiar with the surface without any gaps, and gaps are formed and the adhesion of the molten particles is reduced.

In the present invention, a plasma spraying apparatus, preferably a thermal spraying apparatus using a linear or rod-shaped metal spraying material is used as the spraying apparatus. Such a thermal spraying device itself is known as described in Patent Documents 3 to 5, and a known thermal spraying device can also be used in the present invention. In the present invention, using such a plasma spraying apparatus, spraying is performed so that the average area per one molten particle when the molten particle of the sprayed material adheres to the surface of the sprayed body is 10,000 to 100,000 μm ^2. On condition that this is done.

In the case of thermal spraying with a plasma spraying apparatus using a linear or rod-like metal spray material, as shown in FIG. 1A, the molten particles collide with the surface of the sprayed body S and are flattened and laminated. Therefore, the adhesion between the individual sprayed coatings m increases, and the adhesion of the sprayed coating M as a whole also increases. Further, by performing the thermal spraying so that the average area per molten particle when the molten particles of the thermal spray material adhere to the surface of the thermal sprayed object becomes 10,000 to 100,000 μm ² , the temperature of the surface of the thermal sprayed object increases. This improves the wettability of the droplets against the surface of the sprayed body.

  On the other hand, in the case of thermal spraying with a gas flame spraying apparatus, as shown in FIG. 1 (b), the initial molten particles fill the recesses on the surface of the sprayed body S, and each sprayed coating m is Since it becomes a thin scaly piece, the coating surface becomes smooth, and the adhesion with the coating laminated thereon is lowered, and there is a problem that the adhesion with the thermal spray coating M is lowered as a whole. For this reason, in the case of thermal spraying with a gas flame spraying apparatus, surface irregularities having the same degree of roughness as in the case of roughening by blasting are required. When the surface roughness is large, the individual sprayed coatings m of the thin scaly pieces are formed along the concavo-convex surface of the surface of the sprayed body S and are sequentially laminated as shown in FIG. Since the decrease in the adhesion force between the m is suppressed, the adhesion force of the sprayed coating M as a whole is sufficient.

In the present invention, plasma spraying is performed on the surface of the thermal sprayed body having an average roughness Ra of 2 to 10 μm by pretreatment. When the molten particles of the sprayed material adhere to the surface of the thermal sprayed body at this time By spraying under the condition that the average area per molten particle of 10000 to 100000 μm ² is obtained, a laminate of individual sprayed coatings as shown in FIG. Can be obtained. Even if the average area per one molten particle is too small or too large than the above range, gaps are generated between the individual sprayed coatings, and the temperature of the sprayed body surface cannot be sufficiently raised, and sufficient The adhesion of the thermal spray coating cannot be obtained. In the case of gas flame spraying, the average area per one molten particle is several hundred to several thousand μm ² , and in the arc spray coating, the average area per one molten particle is several hundred to several thousand μm ^2. Although molten particles slightly larger than those in the case of thermal spraying are included, if the average roughness Ra of the surface of the sprayed body is about 2 to 10 μm, sufficient adhesion of the thermal spray coating cannot be obtained.

  There are no special requirements other than the above roughening treatment, surface roughness and thermal spraying conditions. What is necessary is just to select an appropriate film thickness in the range of 50-200 micrometers according to the anticorrosion performance requested | required as the thickness of a sprayed coating. Various metals such as conventionally known aluminum, zinc, copper, cobalt, titanium, and alloys thereof can be used as the metal as the thermal spray material. Among these, aluminum or an aluminum alloy such as an aluminum-magnesium alloy or zinc-aluminum alloy is particularly suitable from the viewpoint of sufficiently exhibiting the sacrificial anodic action. Moreover, you may perform a sealing process after sprayed coating formation. In particular, in the case of on-site repairs, it is better to perform the sealing process as soon as possible after spraying. Conventionally known resins and organic chemicals can be used as the sealing material.

  Hereinafter, an example in which the thermal spraying method of the present invention is applied to on-site repair of a steel structure will be described in the order of main steps. Here, an existing steel structure is a structure in which a coating is applied on a galvanized steel material, and the case where the coating is peeled off locally and the galvanized corrosion portion is repaired by thermal spraying will be described as an example. .

[Roughening treatment process]
FIG. 2 is a perspective view showing an example of a grinding tool used in this embodiment.
The grinding tool 1 is an electric grinding tool called a grinding roller type sander, and a sandpaper 3 is attached to the roller 2 and the surface of the damaged portion of the steel material is ground by rotating the sanding tool 3. Abrasive grains such as silicon carbide and alumina having a grain size number # 20 to # 40 (average grain size 1000 to 425 μm) are fixed to the sandpaper 3 with a resin binder. By grinding the steel surface with this grinding tool 1, the damaged portion of the coating and plating is ground, and the steel surface becomes a rough surface with an average roughness Ra of about 5 to 8 μm. In addition to the grinding roller type sander, a belt sander, a disk sander, a flap wheel, a rotating brush, or the like can be appropriately used as the grinding tool.

[Spraying equipment]
FIG. 3 is a view showing the structure of the main part of the plasma spraying apparatus used in the present embodiment under the thermal spraying condition.
An electrode 8 of a plasma torch (the internal structure of the main body portion is omitted) 7 of the plasma spraying device 6 is provided so as to protrude forward from the rear wall portion 10 having insulation properties of the nozzle 9. The nozzle 9 has a cylindrical peripheral wall 11 connected to the rear wall portion 10 and a conical tapered tube portion 12 provided on the front side of the peripheral wall 11 and whose cross-sectional outer shape is rapidly reduced toward the front side. is doing. In the peripheral wall 11, inlets 13 through which plasma gas flows into the nozzle 9 along the circumferential direction are formed at a plurality of locations. As the plasma gas, an inert gas such as nitrogen, argon, or helium can be used alone or in combination.

  An outer peripheral nozzle 19 is provided on the outer peripheral portion of the tapered tube portion 12 of the nozzle 9 to eject gas to the tip side of the center line of the nozzle 9 along the outer peripheral surface. As the gas, air, nitrogen, argon, helium, or the like is used. Further, on the outer side of the outer peripheral nozzle 19, a supply device 15 that sends out an Al—Mg alloy wire 14 as a thermal spray material is provided on the front side of the center line of the nozzle 9 and on the base side of the gas ejection portion. ing. The supply device 15 includes a guide member 16 and an extrusion roller 17.

  The electrode 8 is connected to the negative pole of the DC power supply device 18, and the wire 14 is connected to the positive pole of the DC power supply device 18. The DC power supply device 18 can supply a DC voltage of about 30 to 200 V and a DC current of about 50 to 500 A. The DC power supply 18 can apply a high voltage of about 3000 V in a short time.

[Spraying process]
The plasma spraying device 6 is arranged so that the center line of the nozzle 9 of the plasma spraying device 6 is perpendicular to the surface of the steel material 4 that is the sprayed body.
When plasma gas is introduced from the inlet 13 of the plasma spraying device 6, the plasma gas generates a swirling flow along the peripheral wall 11. In this state, when a voltage of 3000 V is applied by the DC power supply device 18, a spark discharge is generated between the electrode 8 and the wire 14. The plasma gas swirls and the pressure in the central portion decreases, and the plasma gas in the central portion is preferentially discharged by spark discharge. When the spark discharge occurs, the plasma gas between the electrode 8 and the wire 14 is ionized to create an ionization state, and a direct current flows. When a direct current flows in the plasma gas, the gas is further converted into plasma, and a plasma arc flow is formed. The plasma arc flow flows along the central portion of the plasma gas decompressed by the swirling flow, and the plasma gas is heated by the plasma arc flow and is blown out vigorously as a plasma flame from the outlet 20 of the nozzle 9.

  The tip of the wire 14 is rapidly heated and melted by the plasma arc flow. The melted wire 14 becomes molten particles 21 and is blown off to the steel material 4 side by the plasma frame. Since the plasma gas uses an inert gas, the amount of oxygen in contact with the molten particles 21 is reduced, and oxidation of the formed thermal spray coating 5 is prevented. Further, the wire 14 whose tip has been melted and lost is moved to the front side by the extrusion roller 17 so that the tip coincides with the center line of the nozzle 9. The outer peripheral nozzle 19 allows the compressed gas to flow from the rear and ejects it from the front in a conical shape. By blowing the gas to the molten particles 21 from the outer peripheral side, the molten particles 21 are miniaturized and become an optimum size for forming the thermal spray coating 5. The refined molten particles 21 collide with the surface of the steel material 4 and become flat. A large number of the molten particles 21 are stacked, bonded, and cooled to form the sprayed coating 5.

[Adhesion strength measurement results]
In order to confirm the effect of the thermal spraying method of the present invention, a known gas flame spraying apparatus and the plasma shown in FIG. 3 are used when the surface of the sprayed body is roughened by blasting and grinding. The surface roughness after the surface roughening treatment and the adhesion of the thermal spray coating were measured when each thermal spraying was performed with a thermal spraying apparatus. The measurement results are shown in Table 1. In the description of ISO (International Organization for Standardization) 2063, the practically sufficient adhesion is 4.5 N / mm ² or more. In this embodiment, this numerical value is adopted as a necessary value for the adhesion.

注）密着力の測定は、ＪＩＳ Ｈ８６６１に準拠したエルコメータを用いて行った。

Note) The adhesion was measured using an elcometer in accordance with JIS H8661.

As can be seen from Table 1, in the case of gas flame spraying, if the surface roughness Ra is about 20 μm by performing blasting as the roughening process, the adhesion of the sprayed coating is about 6-7 N / mm ^2, which is sufficient Can be obtained, but when the surface roughness Ra is less than 15 μm by grinding, the adhesion of the sprayed coating is 4 N / mm ² or less, and practical adhesion cannot be obtained. . Usually, the surface roughness Ra in the case of blasting is about 15 to 40 μm, and an adhesion force of about 6 to 7 N / mm ² is obtained by gas flame spraying. On the other hand, in the case of plasma spraying, even if the surface roughness Ra by grinding is in the range of ^{2 to} 10 μm, the adhesion of the sprayed coating is 6 to 7 N / mm ² , and sufficient adhesion can be obtained. However, if the surface roughness Ra is less than 2 μm, the adhesion is reduced, which is not practically desirable.

  As described above, the thermal spraying method of the present invention has been described by taking a steel structure as an example of a metal body. However, the thermal spraying method of the present invention can be applied to various metal structures including a steel structure and corrosion protection of members thereof. Moreover, it can be applied to structures and members other than metal bodies by appropriately selecting the material and spraying conditions of the metal spray material.

It is a figure which shows typically the lamination | stacking state of a thermal spray coating. It is a perspective view which shows an example of the grinding tool used in the Example. It is a figure which shows the structure of the principal part of the plasma spraying apparatus used in the Example under a thermal spraying state.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Grinding tool 2 Roller 3 Sand paper 4 Steel 5 Thermal spray coating 6 Plasma spray apparatus 7 Plasma torch 8 Electrode 9 Nozzle 10 Rear wall part 11 Peripheral wall 12 Tapered cylinder part 13 Inlet 14 Wire 15 Supply apparatus 16 Guide member 17 Extrusion roller 18 DC power supply Device 19 Outer peripheral nozzle 20 Outlet 21 Molten particles

Claims (3)

A thermal spraying method for forming a thermal spray coating for corrosion protection by spraying a metal thermal spray material on a metal body,
Grinding the surface of the object to be sprayed using a grinding tool to produce linear marks, and performing a surface roughening treatment so that the average roughness Ra of the surface of the object to be sprayed is in the range of 2 to 10 μm;
Using the plasma spraying apparatus using a linear or rod-shaped metal sprayed material on the surface of the thermal sprayed surface after the roughening treatment, the melting when the molten particles of the thermal sprayed material adhere to the surface of the thermal sprayed material And a step of performing plasma spraying so that an average area per particle becomes 10,000 to 100,000 μm ² . Aluminum as the metal spraying material of aluminum - spraying method according to claim 1, wherein the use of magnesium alloy or zinc aluminum alloy. The thermal spraying method of Claim 1 or 2 including the process of performing a sealing process after spraying coating formation.

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