JPH081506A - Polishing method for pipe inner surface - Google Patents

Abstract

PURPOSE:To perform finish polishing at high smoothness by pressing an abrasive material to a pipe inner surface by magnetic force. CONSTITUTION:A pair of magnets 4 and 5 are arranged at positions opposing to each other with a pipe 1, a material to be polished, in-between to insert a block-like ferromagnetic body 2 and abrasives 3 into the pipe 1. The abrasives 3 are pressed to the inner surface of the pipe 1 by the ferromagnetic body 2 magnetized in the magnetic fields of the magnets 4 and 5 so as to polish the inner surface. The abrasives 3 in a condition of suspension in liquid is supplied to the inside of the pipe 1. Or, an abrasive cloth/paper or an abrasive nonwoven fabric stuck to the ferromagnetic body 2 can be used instead of the abrasives 3. Consequently, loss due to leakage flux is eliminated, and magnetic force is efficiently consumed for pressing an abrasive material to the inner surface of the pipe 1, allowing finish polishing to high smoothness.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for polishing an inner surface of a pipe to have extremely high smoothness.

[0002]

2. Description of the Related Art Pipes used in manufacturing equipment for foods, chemicals, fine chemicals, etc. are designed to prevent bacteria, impurities, passing substances, etc. from adhering and to facilitate fan-shaped removal of bacteria and foreign substances. It is required to polish the inner surface to a state close to a mirror surface. As this type of pipe, a stainless steel sanitary pipe is generally used. The inner surface of the sanitary pipe has the best surface condition, and the surface roughness is R _max 0.4 μm or less.

Buff polishing, electrolytic polishing, etc. are employed for finish polishing of the inner surface of the pipe. In the buff polishing, a buff having polishing abrasive particles adhered to the surface thereof or the polishing abrasive particles and the buff are inserted together into a pipe, and are passed while polishing the inner surface of the pipe by a rod-shaped or rope-shaped moving device. But,
Since it is necessary to move the buff over the entire length of the pipe to be polished, the device itself becomes large. Particularly in the case of a long pipe having a total length of 4 m or more like a sanitary pipe, it becomes difficult to move the buff, and polishing takes a long time. Also, since the buff is passed inside the pipe, if the inner surface of the pipe is uneven, the buff cannot be pressed against the inner surface of the pipe with a constant pressure, and the inner surface of the pipe has a uniform surface state over the entire length. Difficult to finish.

In electropolishing, a stainless steel pipe whose inner surface corresponds to a buffed surface is immersed in an electrolytic solution, a cathode over the entire length of the pipe is inserted and fixed inside the pipe, and electrolysis is performed by using the pipe as an anode. Polish the inner surface of the pipe. In this case as well, since it is necessary to insert and fix the cathode over the entire length of the pipe, the same problem as buffing occurs. Further, since the eluate from the pipe stays in the electrolytic solution after polishing, a facility for managing and treating the electrolytic solution and a facility for removing the electrolytic solution from the polished pipe are required. As described above, the buff polishing and the electrolytic polishing cannot avoid an increase in the number of steps and working time and an increase in the size of the polishing equipment, and have a drawback that an auxiliary equipment such as an electrolytic solution treatment equipment is required. Therefore, as a solution to these drawbacks, a magnetic polishing method has been developed in which polishing is performed while applying a magnetic field from the outer surface of the pipe.

For example, in Japanese Patent Laid-Open No. 63-221965, a magnetic abrasive material in which magnetic particles and abrasive grains are integrated is inserted into a pipe together with a small piece of a plastic magnet, and a magnetic field is applied from the outer surface of the pipe to generate a magnetic field. The inner surface of the pipe is polished while rotating the pipe. In addition, JP-A-6
In JP-A-3-300856, a method is introduced in which a block-shaped magnet or ferromagnetic material is inserted inside a pipe, and the magnet or ferromagnetic material is pressed against the inner surface of the pipe by a magnetic field applied from the outside of the pipe and polished. .

[0006]

In the method of inserting a plastic magnet into a pipe and polishing it, there is a small gap between the plastic magnets which causes a magnetic field leakage. Therefore, the magnetic force that presses the plastic magnet or the magnetic polishing material against the inner surface of the pipe decreases, and the force necessary for polishing the inner surface of the pipe may be insufficient. Further, as the inner diameter of the pipe to be polished increases, the amount of plastic magnets to be inserted into the pipe also increases. Along with this quantitative increase, the gap also increases, and it becomes impossible to hold the plastic magnet and the magnetic abrasive in the pressed state on the inner surface of the pipe only by the magnetic field applied from the outside of the pipe.

In the method in which a blocked magnet or ferromagnetic material is inserted into a pipe and polished, a magnetic field is applied from one side of the outer surface of the pipe in order to obtain a magnetic force that presses the magnet or ferromagnetic material against the inner surface of the pipe. When the magnetic field is applied in this way, there is a magnetic field leakage in the longitudinal direction of the pipe, and the force for pressing the magnet or the ferromagnetic material against the inner surface of the pipe in the vicinity of the pipe end is likely to decrease. As a result, there is a difference in the force with which the magnet or the ferromagnetic material is pressed between the inner surface of the end portion and the inner surface of the central portion of the pipe, and uniform polishing finish tends to be uneven in the longitudinal direction. The present invention has been devised to solve such a problem, and by polishing the inner surface of the pipe with high inner surface smoothness by generating a magnetic field so as to increase the magnetic force that presses the abrasive against the inner surface of the pipe. The purpose is to do.

[0008]

In order to achieve the object, the method for polishing a pipe inner surface according to the present invention has a pair of magnets arranged at opposite positions with a pipe as a material to be polished being sandwiched therebetween, and a block-shaped strong magnet. Insert the magnetic material and abrasive grains into the pipe,
The abrasive grains are pressed against the inner surface of the pipe by the ferromagnetic material magnetized by the magnetic field of the magnet, and the magnet or the pipe is relatively moved. The abrasive grains can be supplied inside the pipe in a state of being suspended in a liquid. Alternatively, an abrasive cloth paper or an abrasive woven cloth attached to a block-shaped ferromagnetic material can be used as the abrasive material. The pipe polished according to the present invention is not restricted by its material, and any of ordinary steel, austenitic stainless steel and the like can be similarly polished on the inner surface.

[0009]

The larger the pressing force of the abrasive grains or the abrasive against the inner surface of the pipe, the more the polishing efficiency improves. To increase the pressing force, apply a magnetic field with magnets placed at opposite positions on the outside of the pipe that sandwiches the pipe to be polished, and use a block-shaped ferromagnetic material that reduces the leakage of the magnetic field inside the pipe. It is effective to insert into. The abrasive grains or abrasives inserted inside the pipe move relative to the longitudinal direction of the pipe by moving the magnetic field outside the pipe or the pipe itself. The magnetic fields formed by the magnets installed at the positions opposite to each other are substantially linear instead of the wraparound flow that occurs when the magnets are arranged in parallel. Therefore, the magnetic field leaking out of the magnet surface is reduced. Magnetic field leakage is further suppressed by the ferromagnetic material inserted inside the pipe. The type of the block-shaped ferromagnet used in the present invention is not limited as long as it is a substance exhibiting ferromagnetism. For example, ordinary steel, special steel, Ni, Co, alloys or compounds thereof are used as the ferromagnetic material. It is preferable that the block-shaped ferromagnetic material has a surface with rounded corners so that it is not scratched due to friction with the inner surface of the pipe, and that an elastic material such as buff, leather or rubber is attached. .

As the polishing abrasive grains, those used in ordinary polishing and grinding are used. For example, there are alumina, silicon carbide, diamond, CBN and the like. Alternatively, it is possible to use an abrasive that is mounted on the surface of the block-shaped ferromagnetic material. Examples of such an abrasive include abrasive cloth paper, abrasive non-woven cloth, and abrasive film having abrasive particles adhered to the surface thereof. It is also possible to inject a liquid in which polishing abrasive grains are suspended into the inside of the pipe for polishing. A magnetic field is applied from the outside of the pipe by a permanent magnet, an electromagnet or the like to the pipe in which a block-shaped ferromagnetic material is inserted together with abrasive grains or an abrasive. At this time, in order to obtain a uniform pressing force against the inner surface of the pipe, it is preferable to dispose magnetic field applying means such as a permanent magnet or an electromagnet at positions facing each other outside the pipe. In this state, the pipe is rotated or stopped to relatively move the magnetic field outside the pipe or the pipe itself in the longitudinal direction of the pipe.

When a block-shaped ferromagnetic material is inserted into a pipe which is a material to be polished and a magnetic field is applied by magnetic field applying means arranged at opposite positions outside the pipe with the pipe interposed, leakage of the magnetic field is suppressed, The pressing force of the abrasive grains or the abrasive against the inner surface of the pipe can be increased. Therefore, it is possible to use a magnetic field applying means that is less expensive than the conventional one, and it is possible to use the abrasive grains and the abrasives that have been used in the conventional polishing and grinding. Further, since a general-purpose material such as ordinary steel is also used as the block-shaped ferromagnetic material, the inner surface of the pipe can be polished at a low processing cost. Moreover, since the inner surface is polished over the entire length of the pipe while moving the magnetic field outside the pipe or moving the pipe, the working time can be shortened and the polishing method is easy to ride on the automated line.

[0012]

【Example】

Example 1 As a material to be polished, a cored material of TIG welded round pipe made of stainless steel SUS304 having an outer diameter of 28.58 mm, a length of 200 mm and a wall thickness of 1 mm was used. As shown in FIG. 1, a block-shaped ferromagnetic material 2 and a liquid 3 in which abrasive grains were suspended were inserted into a pipe 1. As the ferromagnetic material 2, a normal steel block having a rectangular parallelepiped corner with a height of 8 mm, a width of 10 mm and a length of 19 mm was used. The liquid 3 in which the polishing abrasive grains are suspended is mixed by adding 1 part by weight of tap water to 1 part by weight of alumina abrasive grains having a particle size of # 240 and mixing.
Prepared by stirring. A pair of electromagnets 4 and 5 were arranged at opposite positions on the outer surface of the pipe with the pipe 1 interposed therebetween. For the electromagnets 4 and 5, a copper wire is attached to an iron core with a diameter of 30 mm.
In this embodiment, which uses 2,000 windings and has a trapezoidal cross section with a tip width of 10 mm and a length of 40 mm, the electromagnets 4 and 5 are fixed on the table of the lathe, and the pipe 1 is moved in the longitudinal direction. Arranged as possible. The pipe 1 was attached to the chuck of a lathe, and the liquid 3 in which the abrasive grains were suspended together with the block-shaped ferromagnetic body 2 was inserted into the pipe 1 in an amount of 100 cc. The rotation speed of the pipe 1 is 75 m / min, the relative movement speed of the electromagnets 4, 5 is 105 mm / min, the electromagnets 4, 5
The inner surface of the pipe 1 was polished in one pass with a current of 2 A supplied to the pipe.

Comparative Example 1: As shown in FIG.
2.5 μm and 5 mm long carbon steel short metal fibers 6
A magnetic abrasive 7 containing alumina abrasive grains having a particle size of 80 μm and a grain size of # 240 was inserted into the pipe 1 in an amount of 2.5 g, and the pipe 1 was internally polished under the same conditions. When the magnetic flux density during polishing was measured, as shown in FIG. 3, in Example 1 in which the block-shaped ferromagnetic body 2 and the liquid 3 in which polishing abrasive grains were suspended were used together, short metal fibers and a magnetic polishing material were used. The magnetic flux density was about twice as high as that of Comparative Example 1 in which It is presumed that this is because the generated magnetic field was effectively consumed for pressing the polishing abrasive grains against the inner surface of the pipe, and the influence of leakage was suppressed. As a result, the inner surface of the pipe after polishing had a greatly reduced surface roughness as compared with Comparative Example 1 as shown in FIG. 4, and was finished in an extremely smooth surface state.

Example 2: The same stainless steel S as in Example 1
Using core material of US304 TIG welded round pipe,
As shown in FIG. 5, a block-shaped ferromagnetic body 2 having a surface coated with a polishing paper or a polishing nonwoven fabric 8 was inserted into a pipe 1. As the abrasive cloth paper, those having abrasive grains of grain size # 30 adhered thereto were used, and as the abrasive non-woven fabric, those having abrasive grains of grain size # 60, 120, 320 adhered thereto were used. The inner surface of the pipe 1 was polished while applying a magnetic field under the same conditions as in Example 1. However, the polishing using the polishing cloth paper or the polishing nonwoven fabric 8 having the polishing grain sizes of # 30, 30, 120, and 320 was performed for each one pass, for a total of four passes.

Comparative Example 2: Grain size # 30, 60, 120, 3 containing 2.5 g of metal short fiber 6 made of carbon steel and having a diameter of 100 μm and a length of 5 mm, and alumina abrasive grains having a diameter of 80 μm.
Twenty magnetic abrasives 7 were inserted into the pipe 1 in an amount of 2.5 g. Then, the granularity # 30, 60, 120, 320
The inner surface was polished with a total of 4 passes, one pass for each. When the inner surface of the polished pipe was compared with that of Example 2 and Comparative Example 2, the inner surface of the pipe obtained in Example 2 had a remarkably small surface roughness as shown in FIG.

Example 3: The same stainless steel S as in Example 1
Using core material of US304 TIG welded round pipe,
As shown in FIG. 5, a block-shaped ferromagnetic body 2 having a surface coated with a polishing paper or a polishing nonwoven fabric 8 was inserted into a pipe 1. As the abrasive cloth paper, those having abrasive grains of grain size # 30 adhered thereto were used, and as the abrasive non-woven fabric, those having abrasive grains of grain size # 60, 120, 320 adhered thereto were used. The inner surface of the pipe 1 was polished while applying a magnetic field under the same conditions as in Example 1. However, the polishing using the polishing cloth paper or the polishing nonwoven fabric 8 having the polishing grain sizes of # 30, 30, 120, and 320 was performed for each one pass, for a total of four passes.

Comparative Example 3: An electromagnet 9, 9 in which a ferromagnetic material 2 to which an abrasive cloth paper or an abrasive nonwoven cloth 8 is attached is inserted into a pipe 1 and N pole and S pole are arranged in parallel as shown in FIG.
Was placed on only one side of pipe 1. Others were set to the same conditions as in Example 1 described above, and the inner surface of the pipe 1 was polished.
When the magnetic flux density was measured during polishing, it was found to be 0.
While it was 8 Tesler, in Comparative Example 3, it remained at 0.4 Tesler. From this, it was confirmed that when the electromagnets 9, 9 were arranged only on one side of the pipe 1, the leakage of the magnetic field increased. Observation of the inner surface of the pipe after polishing revealed that in Example 3 in which a pair of magnets were arranged so as to sandwich the pipe 1, it was an extremely smooth surface with R _{max of} 0.4 μm as shown in FIG. On the other hand, the surface roughness obtained in Comparative Example 3 has a surface roughness exceeding R _{max of} 7 μm, and the force of pressing the abrasive against the inner surface of the pipe is small due to the leakage magnetic flux. I understand.

[0018]

As described above, according to the present invention, a magnetic field is applied by magnets which are arranged at positions opposite to each other with a pipe as a material to be polished being sandwiched therebetween, so that a large pressing force is applied to polishing abrasive grains and polishing. Since the inner surface of the pipe is abraded with a polishing material such as a cloth paper or a non-woven fabric, the inner surface of the pipe is polished, so that a high surface smoothness can be achieved. In addition, there is no loss of magnetic force due to the leakage magnetic flux, the action of the magnetic field is effectively consumed by the pressing force, and the working time can be shortened and inexpensive magnetic field applying means can be used. Moreover, since the automation of polishing becomes relatively easy, a low-cost and efficient polishing line is constructed.

[Brief description of drawings]

FIG. 1 is a polishing state in Example 1 of the present invention.

2 is a polishing state in Comparative Example 1. FIG.

FIG. 3 Comparison of magnetic flux densities during polishing

FIG. 4 is a comparison of surface roughness when polished with abrasive grains of grain size # 240.

FIG. 5: Polished state in Example 2 of the present invention

FIG. 6 is a comparison of surface roughness when the abrasive grains have a grain size of # 30 to 320.

FIG. 7: Polished state in Comparative Example 3

FIG. 8 is a comparison of surface roughness between Example 3 and Comparative Example 3 in which the abrasive grains have a particle size of # 30 to 320.

[Explanation of symbols]

1: Pipe as a material to be polished 2: Block-shaped ferromagnetic material 3: Liquid in which abrasive grains are suspended 4,5: Electromagnet 6: Metal short fiber 7: Magnetic abrasive material 8: Abrasive cloth paper or abrasive non-woven fabric 9: Electromagnet

Front page continued (72) Inventor Issei Nakamoto 1 Tsurumachi, Amagasaki City, Hyogo Prefecture Nisshin Steel Co., Ltd.

Claims (3)

[Claims] 1. A pair of magnets are arranged at positions opposed to each other with a pipe being a material to be polished interposed therebetween, and a block-shaped ferromagnetic material and abrasive grains are inserted into the pipe and magnetized by a magnetic field of the magnet. A method of polishing an inner surface of a pipe, characterized in that the abrasive grains are pressed against the inner surface of the pipe by the ferromagnetic material, and the magnet or the pipe is relatively moved. 2. The method for polishing an inner surface of a pipe according to claim 1, wherein the abrasive grains suspended in a liquid are supplied into the pipe. 3. A pair of magnets are arranged at positions opposite to each other with a pipe being a material to be polished interposed therebetween, and a block-shaped ferromagnetic material having abrasive cloth paper or abrasive non-woven fabric attached thereto is inserted into the pipe, and A method for polishing an inner surface of a pipe, comprising: pressing the polishing cloth paper or the polishing nonwoven fabric against the inner surface of the pipe by the ferromagnetic material magnetized by a magnetic field of a magnet, and relatively moving the magnet or the pipe.