JP2018161680A - Method for treating shell internal surface - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for treating a shell internal surface that can reduce pin-hole defects.SOLUTION: A method for treating a shell internal surface comprises a shell casting process S1, an internal surface grinding process S3 that performs grinding on a shell internal surface by a grind stone rotating about an axis nearly parallel with an axis of a shell, a water-pressure test process S4 to be performed preceding or succeeding to the internal surface grinding process S3, and an abrasion process S5 that performs abrasion on the shell internal surface by an abrasion brush rotating about an axis nearly parallel with the axis of the shell. The abrasion brush in the abrasion process S5 rotates reverse to the grind stone in the internal surface grinding process S3.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for treating an inner surface of a tubular body.

  Cast iron pipes widely used for water pipes, etc., have a cylindrical straight part with a constant inner and outer diameter, a receptacle provided at one end with a larger inner and outer diameter, and an inner diameter provided at the other end and a straight part. Many are made up of equal inserts. The cast iron pipe is annealed after casting the pipe, and then the inner surface is polished with a grindstone. Usually, after the inner surface polishing is performed, a water pressure test is performed by applying water pressure in the pipe, and a ground treatment such as rust removal is performed. Thereafter, after the inside of the tube is heated, so-called powder coating is performed in which, for example, a thermosetting epoxy resin powder coating is introduced to form a resin layer on the inner surface of the tube.

  A cast iron pipe that has been subjected to internal coating such as powder coating is usually subjected to pinhole inspection. This pinhole inspection is performed in order to inspect the pinhole defect of a coating film using a holiday detector. In order to clear this pinhole inspection, reducing the pinhole defect of the cast iron pipe leads to improving the productivity of the cast iron pipe.

  As a countermeasure against such a pinhole defect, for example, Patent Document 1 discloses a cast iron pipe that is ground so that a rotating milling cutter is brought into contact with the inner surface of the cast iron pipe and the inner surface of the pipe is held by the blade of the rotating milling cutter. An inner surface treatment method is disclosed.

  Patent Document 2 discloses a method for coating powder on the inner surface of a cast iron pipe, in which a high-frequency coil is inserted inside the cast iron pipe to remove residual moisture.

JP 2002-200514 A JP-A-5-131168

  Although the method disclosed in Patent Documents 1 and 2 can be expected to have a certain effect on pinhole defects, it can further reduce pinhole defects in cast iron pipes that have been internally coated such as powder coating. It has been demanded.

  Then, in view of such a problem, an object of the present invention is to provide a method for treating an inner surface of a tubular body that can reduce pinhole defects.

  The tubular body inner surface treatment method according to the present invention includes a tubular body casting step, an inner surface polishing step in which the inner surface of the tubular body is ground by a grindstone rotating about an axis substantially parallel to the axis of the tubular body, and the inner surface A water pressure test step performed before or after the polishing step, and a polishing step of cleaning the inner surface of the tube with a polishing brush rotating about an axis substantially parallel to the axis of the tube. The polishing brush in the sweeping process rotates in a direction opposite to the grindstone in the inner polishing process.

  Moreover, it is preferable that the said polishing brush is a wheel brush extended radially with respect to the rotating shaft of the said cleaning brush.

  The tubular body is a cast iron pipe on which powder coating is performed, and the inner surface treatment method of the tubular body further includes a heating step of heating the inner surface of the tubular body, and a powder paint on the inner surface of the heated tubular body. It is preferable to provide a powder coating process to be applied.

  According to the method for treating an inner surface of a tubular body of the present invention, it is possible to reduce pinhole defects and to obtain a good coating finish.

It is a flowchart of the inner surface treatment method of the tubular body of one Embodiment of this invention. It is the schematic which looked at the inner surface grinding | polishing apparatus used for the inner surface grinding | polishing process of a tubular body from the upper side. It is the schematic which shows the state by which the inner surface of a tubular body (straight part) is grind | polished with the grindstone of an inner surface grinding | polishing apparatus. It is the schematic which looked at the scouring apparatus used for the scouring process of a tubular body from the upper side. It is the schematic which shows the state in which the inner surface of a pipe body is being cleaned by the cleaning brush of the polishing apparatus.

  Hereinafter, a method for treating an inner surface of a tubular body according to an embodiment of the present invention (hereinafter simply referred to as an inner surface treatment method) will be described with reference to the accompanying drawings. The inner surface treatment method described below is merely an example, and the inner surface treatment method of the present invention is not limited to the following embodiment.

  As shown in FIG. 1, the inner surface treatment method of the present embodiment includes a casting step S1, an annealing step S2, an inner surface polishing step S3, a hydraulic pressure test step S4, a polishing step S5, a heating step S6, and a powder coating step S7. Have. In addition, the said process is an illustration to the last, You may have another process, and if a desired inner surface process can be performed, you may change a part of said process.

  The casting step S1 is a step of casting the pipe body. In the present embodiment, the tubular body is a cast iron pipe having a receiving port, a straight part, and an insertion port. After the casting step S1, an annealing step S2 is performed in order to perform an annealing process on the cast iron pipe.

  After the annealing step S2 is performed, an inner surface polishing step S3 for polishing the inner surface of the tubular body with a grindstone is performed. After the inner surface polishing step S3 with a grindstone, the tube is filled with water, the internal water is pressurized under predetermined conditions, and the water pressure test step S4 is performed.

  After the water pressure test step S4 is performed, a scouring step S5 with a scouring brush is performed in order to perform ground treatment such as rust removal. In the cleaning step S5, the rust removal polishing step may be performed using a grindstone before the cleaning with the cleaning brush.

  After the polishing step S5 is performed, a heating step S6 for heating the inner surface of the tube body to a predetermined temperature is performed in order to perform powder coating. After the heating step S6 is performed, a powder coating step S7 is performed in which a powder coating is applied to the inner surface of the heated tube. As the powder coating used in the powder coating process, for example, in the case of a ductile cast iron pipe for water supply, an epoxy powder resin coating conforming to the standard can be used.

  Through the above steps, the inner surface of the cast iron pipe can be painted. Next, an inner surface treatment apparatus used in the inner surface treatment method of the present embodiment will be described. FIG. 2 is a schematic view of the inner surface polishing apparatus used in the inner surface polishing step S3 of the tube body as viewed from above. FIG. 3 shows the inner surface of the tube body (direct portion) being polished by the grindstone of the inner surface polishing apparatus. It is the schematic which shows a state. FIG. 4 is a schematic view of the scouring device used in the tube scouring step S5 as viewed from above. FIG. 5 shows the scouring brush of the scouring device with the inner surface of the scouring device. It is the schematic which shows the state which is.

  As shown in FIG. 2 and FIG. 3, the inner surface polishing apparatus 1 used in the inner surface polishing step S <b> 3 has a grindstone 11 that rotates about an axis substantially parallel to the axis X of the tube P, and the tube is formed by the grindstone 11. The inner surface Pa of P is polished. As shown in FIGS. 2 and 3, the grindstone 11 has a substantially cylindrical shape, and polishes the inner surface Pa of the tubular body P while rotating around the rotating shaft 12. Although the rotation speed around the rotating shaft 12 of the grindstone 11 is not specifically limited, For example, it can be set to 500-4000 rpm.

  In this embodiment, the inner surface polishing apparatus 1 has a moving carriage 13 to which a rotating shaft 12 is connected. The moving carriage 13 moves in the direction of the axis X of the tubular body P, whereby the grindstone 11 is moved to the axis of the tubular body P. It is moved in the X direction, and polishing is performed in the axis X direction of the tube P.

  Further, the inner surface polishing apparatus 1 includes a tube rotating device (not shown) that supports the tube body P and rotates the tube body P about the axis X. When the tube body P rotates, the inner surface Pa of the tube body P is reduced. Polishing in the circumferential direction by the grindstone 11. The number of rotations around the axis X of the tube body P is not particularly limited, but can be, for example, 20 to 120 rpm. Even if the rotating shaft 12 for rotating the grindstone 11 is moved in the circumferential direction with respect to the inner surface Pa of the tube P without rotating the tube P, the inner surface Pa of the tube P is polished in the circumferential direction. I do not care.

  In the present embodiment, the tubular body P rotates clockwise as viewed from the receiving side of the tubular body P. The tube body P may rotate counterclockwise as viewed from the receiving side of the tube body P. In the present embodiment, the grindstone 11 rotates clockwise (same direction as the tube P) when viewed from the receiving side of the tube P. The grindstone 11 may rotate counterclockwise when viewed from the receiving side of the tube P.

  In the present embodiment, the inner surface polishing apparatus 1 is provided as a pair on the receiving port side and the insertion port side. However, the inner surface polishing apparatus 1 has one inner surface polishing inserted from one of the receiving port and the insertion port. It may be a device.

  As shown in FIGS. 4 and 5, the scouring device 2 used in the scouring step S5 has a scouring brush 21 that rotates about an axis substantially parallel to the axis X of the tube P, and the scouring brush. 21 cleans the inner surface Pa of the tube P. The polishing brush 21 is not particularly limited. For example, the polishing brush 21 may be a wheel brush in which a plurality of wires extend radially with respect to the rotation axis of the polishing brush 21. In the present embodiment, a wheel brush having a plurality of brass wires is used. In addition, the material of the polishing brush 21 is not specifically limited, For example, you may use the wheel brush of other materials, such as a product made from nylon. The scouring brush 21 scours the inner surface Pa of the tubular body P while rotating around the rotating shaft 22 and performs rust removal after the water pressure test. The number of rotations around the rotation shaft 22 of the scouring brush 21 is not particularly limited, but can be set to, for example, 500 to 4000 rpm.

  In this embodiment, the scouring apparatus 2 has a moving carriage 23 to which a rotating shaft 22 is connected. The moving trolley 23 moves in the direction of the axis X of the tubular body P, whereby the cleaning brush 21 is moved to the tubular body P. Are moved in the direction of the axis X of the tube P, and are cleaned in the direction of the axis X of the tube P.

  Further, the scouring device 2 includes a tube rotating device (not shown) that supports the tube P and rotates the tube P around the axis X. When the tube P rotates, the inner surface Pa of the tube P is reduced. Abrasion brush 21 is used for circumferential cleaning. The number of rotations around the axis X of the tube body P is not particularly limited, but can be, for example, 30 to 120 rpm. In addition, without rotating the tube P, the rotating shaft 22 that rotates the scouring brush 21 is moved in the circumferential direction with respect to the inner surface Pa of the tube P, and the inner surface Pa of the tube P is cleaned in the circumferential direction. It doesn't matter.

  In the present embodiment, the polishing brush 21 is configured to rotate in a direction opposite to the grindstone 11 in the inner surface polishing process. In other words, when the grindstone 11 rotates clockwise as viewed from the receiving side, the polishing brush 21 rotates counterclockwise as viewed from the receiving side, and the grindstone 11 rotates counterclockwise as viewed from the receiving side. When rotating clockwise, the polishing brush 21 rotates clockwise as viewed from the receiving side. In the polishing step S5, in this embodiment, the tube P rotates counterclockwise as viewed from the receiving side of the tube P, and the cleaning brush 21 also rotates counterclockwise (in the same direction as the tube P). However, the rotating direction of the tube P may be clockwise.

  As described above, the present inventors rotate the polishing brush 21 in the polishing step S5 in the direction opposite to the grindstone 11 in the inner surface polishing step S3, as shown in the following examples. It has been found that the rate can be significantly reduced.

  Next, the present invention will be specifically described with reference to examples and comparative examples, but the present invention is not limited to these examples.

  For each of Examples 1 to 3, Comparative Examples 1 to 3, and Reference Examples 1 to 3, the inner surface polishing apparatus 1 and the polishing apparatus 2 shown in FIGS. Through S7, a total of 2307 cast iron pipes were manufactured. In addition, about an Example, a comparative example, and the reference example, the rust removal grinding | polishing with a grindstone was performed on the apparatus similar to the internal surface grinding | polishing apparatus 1 and the same conditions between the hydraulic-pressure test process S4 and the polishing process S5, respectively.

(Polishing and polishing conditions)
In Examples 1 to 3, in the inner surface polishing step S3, the tube P and the grindstone 11 are rotated clockwise (clockwise) when viewed from the receiving side, and in the rust removal polishing step, the tube P and the grindstone are received. The tube P and the cleaning brush 21 were rotated counterclockwise (counterclockwise) when viewed from the receiving port side in the scouring step S5 as viewed from the mouth side.

  For Comparative Examples 1 to 3, in the inner surface polishing step S3, the tube P and the grindstone 11 are rotated clockwise when viewed from the receiving side, and in the rust removal polishing step, the tube P and the grindstone are viewed from the receiving side. In the scouring step S5, the tube P was rotated counterclockwise when viewed from the receiving side, and the scouring brush 21 was rotated clockwise when viewed from the receiving side.

  For Reference Examples 1 to 3, in the inner surface polishing step S3, the tube P and the grindstone 11 are rotated clockwise when viewed from the receiving side, and in the rust removal polishing step, the tube P and the grindstone are viewed from the receiving side. In the scouring step S5, the tube P was rotated counterclockwise when viewed from the receiving side, and the scouring brush 21 was rotated clockwise when viewed from the receiving side.

  For the cast iron pipe coated by the above-mentioned method, the pinhole ratio is calculated by pinhole inspection using a holiday detector, and the grinding wheel and sharpening in the inner surface polishing step S3, the rust removal polishing step, and the polishing step S5, which are considered to be normally performed, Degree of decrease in pinhole ratio relative to Reference Examples 1 to 3 in which the sweeper brush was rotated in the same direction (all clockwise) ((Pinhole ratio of Example or Comparative Example) / (Pinhole ratio of Reference Example)) Was calculated. The evaluation criteria are shown below.

(Evaluation criteria)
◎: The degree of pinhole ratio decrease is ¼ or less of the reference example. ○: The pinhole ratio decrease degree is 1/4 to 1/2 of the reference example. △: Pinhole ratio. The degree of decrease in the pinhole ratio was 1/2 to 3/4 of the reference example. ▲: The pinhole ratio was decreased to 3/4 to 1 in the reference example. Table 1 shows the results of evaluation based on the above evaluation criteria.

  As shown in Table 1, Examples 1 to 3 in which the grindstone 11 and the cleaning brush 21 were rotated in the reverse direction in the inner surface polishing step S3 and the polishing step S5 are the inner surface polishing step S3 and the polishing step. In S5, it was found that the pinhole ratio was significantly reduced compared to Comparative Examples 1 to 3 and Reference Examples 1 to 3 in which the grindstone 11 and the polishing brush 21 were rotated in the same direction. Further, according to Comparative Examples 1 to 3 and Reference Examples 1 to 3, even if the grindstone 11 in the inner surface polishing step S3 and the grindstone in the rust removal polishing step are rotated in the opposite directions, the pinhole ratio does not decrease. all right. From the above, it can be seen that it is meaningful that the rotation direction of the grindstone 11 in the inner surface polishing step S3 is opposite to the rotation direction of the polishing brush 21 in the polishing step S5. In this case, a very excellent pin It can be seen that the Hall ratio is reduced.

  As described above, according to the tubular body inner surface treatment method of the present invention, the pinhole ratio can be greatly reduced, and pinhole defects can be reduced. Thereby, the favorable coating finish of a tubular body can be obtained. Moreover, since the pinhole defect can be reduced by a simple method of reversing the rotation direction of the grinding wheel in the inner surface polishing process and the rotation direction of the polishing brush in the polishing process, the productivity of the cast iron pipe is reduced. improves. Moreover, according to the present invention, it is not necessary to increase the film thickness of the inner surface coating in order to reduce pinhole defects as in the prior art, and the production cost can be reduced.

  In the inner surface treatment method of the above embodiment, the inner surface treatment of the cast iron pipe on which powder coating is performed has been described as an example, but the pipe body is not limited to the cast iron pipe. In the inner surface treatment method of the above embodiment, the case where the powder coating is applied to the inner surface of the tube has been described as an example. However, other synthetic resin coatings that may cause pinhole defects similar to the powder coating may be used. The inner surface treatment method can also be applied when applying a mixture of a powder coating material and other materials such as silica sand.

  In the inner surface treatment method of the above embodiment, the hydraulic pressure test step is performed after the inner surface polishing step, but the hydraulic pressure test step may be performed before the inner surface polishing step.

DESCRIPTION OF SYMBOLS 1 Inner surface polisher 11 Grinding wheel 12 Rotating shaft 13 Moving trolley 2 Abrasive device 21 Abrasive brush 22 Rotating shaft 23 Moving trolley P Tube Pa Inner surface of tube S1 Casting step S2 Annealing step S3 Inner surface polishing step S4 Hydraulic pressure test step S5 Polishing Sweeping process S6 heating process S7 powder coating process X tube axis X

Claims (3)

Tube casting process;
An inner surface polishing step of polishing the inner surface of the tubular body with a grindstone rotating around an axis substantially parallel to the axis of the tubular body;
A hydraulic pressure test step performed before or after the inner surface polishing step;
A scouring step of scouring the inner surface of the tubular body with a scouring brush that rotates about an axis substantially parallel to the axis of the tubular body,
An inner surface treatment method for a tubular body, wherein the polishing brush in the polishing step rotates in a direction opposite to a grindstone in the inner surface polishing step. The method for treating an inner surface of a tubular body according to claim 1, wherein the polishing brush is a wheel brush that extends radially with respect to a rotation axis of the polishing brush. The pipe body is a cast iron pipe on which powder coating is performed,
The method for treating the inner surface of the tubular body further includes:
A heating process for heating the inner surface of the tubular body;
A method for treating an inner surface of a tubular body according to claim 1 or 2, further comprising a powder coating step in which a powder coating is applied to the inner surface of the heated tubular body.

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