JP2017176938A - Coating method of metal pipe inner surface - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coating method of a metal pipe inner surface which can obtain a low-cost powder coating film without damaging a coating film appearance and adhesiveness of powder coating.SOLUTION: A coating method of a metal pipe inner surface for applying powder coating by spraying powder coating material on a metal pipe inner surface includes a first process of coating the metal pipe inner surface with the power coating material, a second process of supplying and depositing silica sand on the coated powder coating material by air pressure feeding, and a third process of coating the deposited silica sand with the powder coating material again to sandwich the silica sand with powder coating material layers.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for coating an inner surface of a metal tube, and more particularly to a method for performing powder coating on the inner surface of a metal tube at a low cost.

  In metal pipes, particularly cast iron pipes used in water and sewage systems, in recent years, a coating film made of an epoxy resin powder coating is generally formed on the inner surface of the pipe from the viewpoints of corrosion resistance and environmental considerations. One method of forming an epoxy coating film with this epoxy resin powder coating is to apply an epoxy resin powder coating to the inner surface of a heated rotating tube by spraying, etc., and melt and cure.

  A resin powder coating used for coating a metal tube is generally composed of a resin, a curing agent, a pigment, and an additive. The pigment includes a colored pigment and an extender pigment, and the colored pigment includes an inorganic component and an organic component, and is added for the purpose of coloring. On the other hand, extender pigments are inorganic components such as barium sulfate, talc, calcium carbonate, and silica, and are added as fillers to improve the performance of the coating film and to increase the coatability of the coating film. It also plays a role of improving kneadability and grindability during production, and improving workability and fluidity during coating.

  On the other hand, as a technique for using silica sand for coating a metal surface, Patent Document 1 discloses that a powder gun is applied to a metal surface, and a plastic gun is formed on the formed plastic film while the plastic film is in a softened or molten state. Using A, together with a flame, spray inorganic coarse particles such as glass, ceramic, sand, iron, etc. with a particle size of around 0.05 to 3.0 mm, and embed and fix the exposed inorganic coarse particles partially, A method for obtaining a rough surface structure is disclosed.

JP 2003-127282 A

  As described above, the epoxy resin powder coating is able to ensure anticorrosion without using a solvent, and is very excellent with little impact on the environment, but the price of the epoxy resin itself is high, In order to obtain a coating film having a certain thickness, the cost may be a problem.

  On the other hand, it is conceivable to increase the blending amount of extender pigments such as silica, which is an excellent filler in terms of cost, while suppressing the amount of epoxy resin relatively, but in reality, the load on the equipment during melt kneading Is not realistic. Silica sand with a large particle size can be obtained at a lower cost than fine particle silica, but when mixed with a paint, the resulting coating film has irregularities due to the silica sand on the finished surface, which is not preferable in appearance. It also affects the life of the coating.

  Then, this invention aims at providing the coating method which can obtain a low-cost powder coating film, without impairing the coating-film external appearance and adhesiveness in powder coating.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors spread silica sand on a metal tube coated with a powder coating that is less than the target film thickness, and the powder coating is again made to have the target film thickness. The present invention found that even silica sand having a relatively large particle size can be included in the coating film without particularly affecting the coating film surface, and the amount of powder paint used can be reduced. Was completed.

  That is, the present invention provides a metal tube inner surface coating method in which powder coating is performed by spraying a powder coating on the inner surface of a metal tube, and a first step of coating the powder coating on the inner surface of the metal tube, The second step of supplying and depositing silica sand by pneumatic feeding and the third step of re-coating the powder coating on the deposited silica sand are arranged so that the silica sand is sandwiched between the powder coating layers. .

  Accordingly, it is possible to increase the bulk by the silica sand while ensuring the adhesion with the undercoat of the metal tube and the smooth surface state after the coating.

  Further, the above-described metal pipe inner surface coating method is performed by a coating apparatus including a paint discharge unit that discharges the powder paint and a silica sand discharge unit that discharges the silica sand, and the coating apparatus includes the paint discharge unit. And a moving mechanism that relatively moves the silica sand discharge part and the metal pipe body in the tube axis direction, and the paint discharge part and the silica sand discharge part are spaced apart along the tube axis direction of the pipe to be coated. The powder coating material is disposed in the first step by changing the position of the coating material discharge portion and the silica sand discharge portion in the tube axis direction with respect to the metal tube body by the moving mechanism. It can be performed by coating from one end side to the other end side, and then re-coating the powder coating material from the other end side to the one end side of the metal tube body in the third step. Further, the deposition of the silica sand in the second step is performed from one end side to the other end side of the metal tube in combination with the first step, or in addition to the metal tube in addition to the third step. It can be done from one end to the other, or both. A high working efficiency can be obtained by reciprocating an apparatus capable of continuously discharging paint and silica sand in the pipe to be coated.

  According to the metal tube inner surface coating method of the present invention, since a predetermined amount of silica sand can be sandwiched between the coating films, the amount of the powder coating itself can be reduced while suppressing costs, In addition, it is possible to obtain a good coating film that is excellent in adhesion and that the silica sand hardly affects the finish of the coating film surface.

It is the schematic for demonstrating one Embodiment of the metal pipe inner surface coating method of this invention. It is the schematic explaining the formation process of the coating film obtained by one Embodiment of the metal pipe inner surface coating method of this invention. It is the schematic explaining the formation process of the coating film obtained by one Embodiment of the metal pipe inner surface coating method of this invention. It is the schematic explaining the cross section of the coating film obtained by one Embodiment of the metal pipe inner surface coating method of this invention.

  Hereinafter, the metal pipe inner surface coating method of the present invention will be described with reference to FIGS. FIG. 1 is a schematic view for explaining an embodiment of the method for painting an inner surface of a metal pipe of the present invention. 2 and 3 are schematic views for explaining the process of forming a coating film obtained by the metal tube inner surface coating method of the present invention. FIG. 4 is a schematic diagram for explaining a cross section of a coating film actually obtained by an embodiment of the metal tube inner surface coating method of the present invention.

  First, the structure of a pipe inner surface coating apparatus (hereinafter simply referred to as a coating apparatus) D used in the metal pipe inner surface coating method of this embodiment will be described with reference to FIG. In addition, the coating apparatus D shown by FIG. 1 is an example to the last, and is not limited to the structure shown in FIG.

  As shown in FIG. 1, the coating apparatus D of the present embodiment includes a discharge device 1 that discharges the powder coating material 4 and the silica sand 5, and a tube rotation device 2 that supports the tube P and rotates the tube P. And. As will be described later, the discharge device 1 includes a paint supply device 11 and a silica sand supply device 12, and the paint supply device 11 and the silica sand supply device 12 include a paint discharge portion 11a and a silica sand discharge portion 12a, respectively. Moreover, in this embodiment, the coating apparatus D is provided with the moving mechanism 3 which moves the coating material discharge part 11a and the silica sand discharge part 12a along a pipe-axis direction, as FIG. 1 shows.

  In the present embodiment, as shown in FIG. 1, the tube rotating device 2 has a preheated metal pipe P (hereinafter simply referred to as a metal pipe or a pipe body) P placed thereon and the metal pipe P around the axis. A rotating roller 21 is provided for rotation. The rotating roller 21 rotates the metal tube P during painting by the discharge device 1, and the paint discharge unit 11 a and the silica sand discharge unit 12 a are moved along the tube axis direction by the moving mechanism 3, whereby the inner peripheral surface of the metal tube P The whole is painted. In addition, although the kind of metal pipe P is not specifically limited, For example, it can be set as a cast iron pipe. Moreover, the shape of the metal pipe P is not particularly limited. For example, the metal pipe P can be a straight pipe having a receiving port on one end side and an insertion port on the other end side.

  The discharge device 1 is a device that discharges the powder paint 4 and the silica sand 5 and paints the inner surface of the metal pipe P. In the present embodiment, as shown in FIG. 1, the discharge device 1 includes a powder paint supply device 11 having a paint discharge portion 11 a that discharges powder paint 4 and a silica sand having a silica sand discharge portion 12 a that discharges silica sand 5. And a supply device 12.

  In addition, the powder coating 4 used in the present invention can be used without particular limitation as long as it is melted by heat and then cured after being applied to the metal tube P. For example, in the case of a ductile cast iron pipe for water supply, an epoxy powder resin paint conforming to the standard is used. Further, the silica sand 5 used in the present invention is not particularly limited. For example, the silica sand 5 has a mode diameter of about 0.1 to 0.2 mm and a particle size distribution of 0.05 mm to 0.3 mm. Generally, it is preferable to use what is marketed as No. 7 silica sand and No. 8 silica sand.

  In this embodiment, as shown in FIG. 1, the powder coating material supply apparatus 11 is supplied to a coating material supply mechanism 11c for supplying a powder coating material 4 from a powder coating material supply source (not shown) and a coating material supply mechanism 11c. A paint pipe 11b that is connected to supply the powder paint 4 to the paint discharge part 11a and a paint discharge part 11a that is connected to the paint pipe 11b and discharges the paint are provided.

  The coating material supply mechanism 11c is not particularly limited as long as it can supply the powder coating material 4 to the coating material discharge unit 11a.

  The paint pipe 11b forms a passage for supplying the paint 4 to the paint discharger 11a. In the present embodiment, the paint pipe 11b is provided between the paint supply mechanism 11c and the paint discharge part 11a and extends substantially parallel to the tube axis of the metal pipe P.

  The paint discharger 11 a is a part that discharges the powder paint 4. The structure of the coating material discharge unit 11a is not particularly limited as long as it can discharge the powder coating material 4, but a known nozzle used for discharging the coating material can be used.

  In the present embodiment, as shown in FIG. 1, the silica sand supply device 12 is connected to a silica sand supply mechanism 12c for supplying the silica sand 5 from a silica sand supply source (not shown) and the silica sand supply mechanism 12c. A silica sand pipe 12b to be supplied to the silica sand discharge part 12a and a silica sand discharge part 11a connected to the silica sand pipe 12b to discharge the silica sand 5 are provided.

  The silica sand supply mechanism 12c is not particularly limited as long as the silica sand 5 can be supplied by pneumatic feeding.

  The silica sand pipe 12b forms a passage for supplying the silica sand 5 to the silica sand discharge part 12a, and basically has the same configuration as the paint pipe 11b of the powder paint supply device 11 described above, and thus detailed description thereof is omitted. To do.

  The silica sand discharge part 12a is a part for discharging the silica sand 5, and the structure of the silica sand discharge part 12a is not particularly limited as long as the silica sand 5 can be discharged, and is generally known for use in discharging paint. Depending on the particle size of the silica sand 5 to be used such as a nozzle, an appropriate one can be used.

  The moving mechanism 3 is a mechanism that relatively moves the paint discharge part 11a, the silica sand discharge part 12a, and the metal pipe P in the tube axis direction of the metal pipe P. In the present embodiment, the moving mechanism 3 is configured to move the paint discharge part 11a and the silica sand discharge part 12a along the pipe axis direction inside the metal pipe P. The metal pipe P may be moved without moving the 11a and the silica sand discharge part 12a, or both the metal pipe P and the paint discharge part 11a and the silica sand discharge part 12a may be moved. . Although details will be described later, the inner surface of the metal pipe P can be painted by relatively moving the metal pipe P, the paint discharge part 11a and the silica sand discharge part 12a in the pipe axis direction of the metal pipe P. In FIG. 1, the moving mechanism 3 is schematically exemplified by a moving body that moves by wheels. However, the moving mechanism 3 only needs to move at least the paint discharging unit 11 a and the silica sand discharging unit 11 b. The structure is not particularly limited.

  Moreover, in this embodiment, the coating material discharge part 11a is arrange | positioned at intervals in the pipe-axis direction with the silica sand discharge part 12a, as FIG. 1 shows. More specifically, when coating is started from one end side of the metal pipe P, the coating material discharge part 11a is arranged at an interval so as to be positioned on the other end side with respect to the silica sand discharge part 12a. In addition, although the space | interval of the pipe-axis direction between the coating material discharge part 11a and the silica sand discharge part 12a is not specifically limited, For example, it is preferable that it is 100-300 mm.

  Next, the metal pipe inner surface coating method of the present invention will be described with reference to FIGS. In the following description, the above-described coating apparatus is described as an example, but a coating apparatus having another structure may be used as long as the same effect can be obtained.

  The metal tube inner surface coating method of the present embodiment is a metal tube inner surface coating method in which powder coating is applied to the inner surface of the metal tube to perform powder coating. A second step of supplying and depositing silica sand by pneumatic feeding on the powder coating, and a third step of re-coating the powder coating on the deposited silica sand. The second step is the first step. And the third step.

  The first step is a step in which the inner surface of the metal tube P is painted from one end side to the other end side of the metal tube P, and the second step is also performed. That is, as shown in FIG. 2, the powder coating 4 is first applied to the inner surface 6 of the metal tube P along the tube axis direction, and the front end 4a of the uncured powder coating is applied in the tube axis direction. The coating is performed such that the front end 5a of the silica sand discharged along the chase follows. In this embodiment, first, in a state where the paint pipe 11b and the silica sand pipe 12b are arranged at intervals along the pipe axis direction from the opening on one end side (receiving side) of the metal pipe P, the metal pipe P to be coated is provided. (Direction of FIG. 1 → A: forward path, FIG. 2). Next, the discharge of the powder coating material 4 from the front end (paint discharge portion 11a) of the paint pipe 11b is started before the paint required area R on the inner surface of the pipe, and similarly the front end (silica sand discharge portion 12a) of the silica sand pipe 12b in turn. ) Starts discharging the silica sand 5. In accordance with these discharges, the coating mechanism 11 performs coating from one end side to the other end side of the metal pipe P by moving the paint discharge region 11a and the silica sand discharge portion 12a in the direction of → A by the moving mechanism 3 in the direction of required coating R.

  The third step is a step in which coating is performed in the opposite direction to the first step, that is, from the other end side of the metal pipe P toward the one end side, and the second step is also performed. That is, as shown in FIG. 3, the powder coating material 4 is again applied to the portion where the powder coating material 4 and the silica sand 5 formed in the first step and the second step are laminated. In the present embodiment, in the third step, after the first step is completed up to the other end side of the metal pipe P, for example, when the paint discharge unit 11a and the silica sand discharge unit 12a penetrate the tube P, the moving mechanism 3 causes the powder to be discharged. The body discharge part 11a and the silica sand discharge part 12a are moved in the direction of → B (return path) in FIG. As a result, the necessary coating region R is repainted in the reverse direction. Thereafter, the discharge of the paint 4 and the silica sand 5 is stopped at a point (substantially starting position) where the paint discharge part 11a and the silica sand discharge part 12a have passed the required paint region R, and the paint pipe 11b (paint discharge part) 11a) and the silica sand pipe 12b (including the silica sand discharge part 12a) are extracted.

  Thus, according to the metal tube inner surface coating method in the present embodiment, the silica sand is sandwiched between the powder coating layers in the first step and the third step. As a result, a predetermined amount of silica sand can be sandwiched into the coating film, reducing the amount of powder coating used and reducing the cost while maintaining excellent adhesion between the coating film and the inner surface of the metal tube. Can be secured. Furthermore, since silica sand is deposited on the uncured powder coating material, and the powder coating material is further coated thereon, a good coating film that hardly affects the finish of the coating film surface can be obtained.

  Moreover, in this embodiment, as FIG. 2 and FIG. 3 shows, it has the structure which has arrange | positioned the coating material discharge part 11a and the silica sand discharge part 12a at intervals along the pipe-axis direction. In this case, the paint discharge unit 11a and the silica sand discharge unit 12a are simultaneously reciprocated to perform coating, whereby the silica sand 5 is discharged immediately after the powder coating material 4 is discharged, and the paint discharge unit 11a is applied during the coating process. The coating is performed in a state in which the silica sand discharge part 12a is kept at a constant interval. Therefore, it is possible to obtain a coating film having a uniform film thickness with the silica sand 5 sandwiched between the paints 4. Specifically, as shown in FIG. 2, in the forward path (first step and second step), the paint 4 is first discharged from the paint discharge portion 11a as the coating progresses, and the paint 4 is applied to the inner surface 6 of the metal tube. The Subsequently, the silica sand 5 discharged from the silica sand discharge portion 12a disposed behind the paint discharge portion 11a with respect to the traveling direction is deposited on the previously applied paint 4 to form a two-layer structure. At this time, since the silica sand 5 is deposited before the paint 4 is cured, the silica sand 5 is buried to some extent in the painted paint 4. Furthermore, since the metal pipe P to be coated is rotated around the pipe axis, the silica sand 5 having a high specific gravity moves to the pipe side with time, and is buried in the paint layer (see FIG. 4). When the forward coating is completed, the coating material discharge part 11a and the silica sand discharge part 12a are temporarily removed from the pipe and then run backward to perform the backward coating. In the return path (second process and third process), as shown in FIG. 3, as the coating progresses, first, the silica sand 5 is discharged from the silica sand discharge part 12a and deposited on the coating film formed in the forward path. . Subsequently, the coating material 4 is discharged from the coating material discharge portion 11 a and a coating film is formed so as to cover the silica sand 5. Thus, by the first step and the third step, the silica sand 5 is buried in the layer of the paint 4, and the powder paint 4 is further applied thereon, and is applied to the inner surface of the metal pipe P after painting. Unevenness caused by the silica sand 5 hardly occurs, and the finished state of the coating of the metal pipe P can be improved (see FIG. 4). Further, in the case where the first and third steps are simultaneously reciprocated between the paint discharge unit 11a and the silica sand discharge unit 12a as in the present embodiment, the first step and the third step are combined, or By performing the second step in combination with both steps, the silica sand can be sandwiched between the powder coating layers in one reciprocation, so the time required for the coating step can be shortened and efficient coating can be performed. .

  Moreover, as the silica sand 5 used for this invention, it is preferable to use what is marketed as 7 silica sand and 8 silica sand as mentioned above. Normally, No. 7 silica sand has a particle size in the range of 0.1 to 0.3 mm and a mode diameter of approximately 0.2 mm, and No. 8 silica sand has a mode in which the particle size ranges from 0.05 to 0.15 mm. The diameter is approximately 0.1 mm. When silica sand having a smaller particle size range and mode diameter is used, the structure of the present embodiment makes it easy to roll up due to air at the time of discharge, and when the rolled silica sand 5 adheres to the surface coating layer, the surface becomes rough, etc. May not be preferable. On the other hand, when No. 7 silica sand or No. 8 silica sand having a relatively large particle size is used as the silica sand 5, the silica sand hardly rolls up when discharging the silica sand, and the silica sand that has floated and floated on the finished surface of the powder coating layer Adhesion can be prevented. In addition, when silica sand with a relatively large particle size is used to prevent the silica sand from rolling up, depending on the coating method, such as mixing with the paint itself, the silica sand on the finished surface of the powder coating is caused by the silica sand. In the present invention, as described above, it is possible to suppress the unevenness generated on the finished surface of the coating by sandwiching the silica sand with the powder coating from both sides as described above.

  The powder coating 4 and the silica sand 5 can be used in various proportions as long as the unevenness caused by the silica sand 5 does not become a problem on the surface of the coating film to be obtained. In the embodiment in which the powder is discharged, it is preferable to use the powder coating 4 equal to or more than the weight of the silica sand 5, and more preferably 3/2 or more of the weight of the silica sand 5. Moreover, it is preferable to use the powder coating material 4 in the quantity of 2 times or less of the weight of the silica sand 5, and when using more than twice the weight of the silica sand 5, there exists a tendency for the cost reduction effect of this invention to become difficult to be acquired. is there.

  Further, the coating amount of the powder coating 4 on the forward path and the return path can be set as appropriate. However, increasing the coating amount on the forward path more than the coating amount on the forward path is preferable because smoothness becomes better. As a means for increasing the amount of paint on the return path from the amount of paint on the forward path, not only increasing the discharge amount of the powder paint 4 on the return path, but also reducing the paint speed of the return path from the forward path while maintaining the discharge amount. And so on. In the embodiment in which the silica sand is discharged on both the outward path and the backward path, if the coating speed of the outbound path is decreased, the amount of silica sand 5 deposited on the return path also increases, but it does not particularly affect the smoothness, but rather the silica sand 5 Since the transition to the metal tube side proceeds, the surface smoothness becomes better, which is preferable. In that case, for example, the painting speed of the return path is preferably half or less of the coating speed of the outbound path, and more preferably about one third or less.

  Furthermore, the overall coating speed can be appropriately set according to the powder coating used, the discharge amount, etc., and is not particularly limited.

  By the embodiment shown in FIG. 1 to FIG. 3, the inner surface of the metal tube was coated using the method for coating the inner surface of the metal tube of the present invention.

  As a pipe to be coated, a ductile cast iron pipe (straight pipe) for water supply having a nominal diameter of 150 and a length of 50 cm was used.

  After removing the rust on the inner surface of the pipe to be coated with a flap wheel, it was heated in an electric furnace set at 250 ° C. and placed in a tube rotating device, and coating was started at 200 ° C. (± 10 ° C.) (number of rotations: 200 m / min). Paint pipe and silica sand pipe are inserted from the receiving side with the interval of both discharge parts set to 150mm, and the discharge of paint and silica sand is started in the receiving area, and the inlet side is at a constant speed (1m / min to 6m / min) The inner surface of the pipe was painted. Then, after the silica sand discharge port has come out of the pipe, it is turned back and applied at a constant speed (1m / min to 6m / min) from the insertion side to the receiving side in the order of silica sand deposition and powder coating. went. Upon entering the receiving area, the discharge of paint and silica sand was stopped, and the paint pipe and silica sand pipe were extracted from the pipe body.

  Epoxy powder resin paint (gel time: 92 seconds) used for the inner surface coating of ordinary ductile cast iron pipes for water supply is used for the paint, and silica sand No. 7 or No. 8 (manufactured by Miku Kaiun Co., Ltd.) is used for the silica sand. Using. Table 1 shows the particle size distribution of each silica sand. Both the powder paint and silica sand are discharged using an injector-type powder coating device, and the paint and silica sand discharge amounts so that the coating thickness on the inner surface of the pipe is 400 to 600 μm by the forward and return coating. The ratio of paint and silica sand is such that the ratio is 1: 1, 3: 2, and 2: 1 and the return coating speed is the same as that of the outbound path, or half or one third. The discharge rate and coating speed were adjusted.

  From the above, the coating film on the inner surface of the metal pipe obtained in both cases of silica sand No. 7 and No. 8 was not particularly affected by the silica sand on the coating film surface and was excellent in adhesion to the metal pipe. Also, when the discharge ratio of paint and quartz sand is 3: 2 or 2: 1, the surface smoothness is better than when the ratio is 1: 1, and the forward coating speed is higher than the forward coating speed. When the speed was set to 1/2 or 1/3, the silica sand moved to the pipe side and the surface smoothness was better than that at the same speed (see FIG. 4).

  In the above-described embodiment, the silica sand is discharged in both the outward coating and the backward coating. However, the outward coating is performed by discharging only the powder coating in the first step, without discharging the silica sand. In this case, the discharge of the silica sand in the second step may be performed together with the third step, or only the powder paint in the third step may be discharged and the discharge of the silica sand may be stopped in the backward coating.

  Furthermore, although the example which the coating material piping 11b and the silica sand piping 12b extended separately was shown in embodiment mentioned above, the coating material piping 11b and the silica sand piping 12b may be fixed with the joining member which is not shown in figure. Moreover, as shown in FIGS. 1 to 3, the paint pipe 11 b and the silica sand pipe 12 b may be arranged vertically in the vertical direction or in the horizontal direction.

  In the above-described embodiment, the paint pipe 11b and the silica sand pipe 12b are configured to move by one moving mechanism 3, but separate moving mechanisms may be provided to move each independently. Absent. In the present embodiment, the paint pipe 11b and the silica sand pipe 12b are both inserted from one opening (receiving port) of the metal pipe P. However, either the paint pipe 11b or the silica sand pipe 12b is one side. The other of the paint pipe 11b and the silica sand pipe 12b may be inserted through the other opening. In the present embodiment, the coating is started from the receiving side of the metal pipe P. However, the coating may be started from the insertion side of the metal pipe P.

  Furthermore, in the above-described embodiment, the paint discharge part 11a provided at the tip of the paint pipe 11b and the silica sand discharge part 12a provided at the tip of the silica sand pipe 12b are accompanied by the movement of the paint pipe 11b and the silica sand pipe 12b. For example, a guide rail that guides the paint discharge part and the silica sand discharge part is inserted into the metal pipe, and the paint discharge part and the silica sand discharge part are moved directly along the guide rail by the moving mechanism. It doesn't matter.

D Coating Device 1 Discharge Device 11 Paint Supply Device 11a Paint Pipe 11b Paint Discharge Unit 11c Paint Supply Mechanism 12 Silica Sand Supply Device 12a Silica Sand Pipe 12b Silica Sand Discharge Unit 12c Silica Sand Supply Mechanism 2 Tube Rotating Device 21 Rotating Roller 3 Moving Mechanism P Metal Tube 4 Paint 5 Silica sand 6 Metal pipe inner surface

Claims (3)

In the metal tube inner surface coating method, where powder coating is performed by spraying powder paint on the inner surface of the metal tube,
The first step of painting powder coating on the inner surface of the metal tube,
It includes a second step of supplying and depositing silica sand on the coated powder paint by pneumatic feeding, and a third step of re-coating the powder paint on the deposited silica sand, whereby the silica sand is applied to the powder paint. Method of painting the inner surface of a metal tube sandwiched between layers. The metal pipe inner surface coating method is performed by a coating apparatus including a coating material discharging unit that discharges the powder coating material and a silica sand discharging unit that discharges the silica sand, and the coating device includes the coating material discharging unit and the silica sand. A moving mechanism for moving the discharge unit and the metal tube body relatively in the tube axis direction;
The paint discharge part and the silica sand discharge part are arranged at intervals along the tube axis direction of the pipe to be coated,
By the moving mechanism, the coating material discharge section and the silica sand discharge section change the position of the tube axis direction with respect to the metal tube body, so that the powder coating material is removed from one end side of the metal tube body in the first step. The metal pipe inner surface coating method according to claim 1, wherein the coating is applied to the end side, and then the powder coating is re-coated from the other end side to the one end side of the metal pipe body in the third step. The silica sand is deposited in the second step from one end side to the other end side of the metal tube together with the first step, or the other end side of the metal tube is combined with the third step. The method for coating an inner surface of a metal pipe according to claim 2, wherein the method is performed from the first end to the one end side or both.

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