JP7612442B2 - Manufacturing method of fluorescent magnetic particles for wet magnetic particle testing - Google Patents

Description

The present invention relates to a method for producing fluorescent magnetic powder for wet magnetic particle testing. More specifically, the fluorescent magnetic powder produced by the present invention is a fluorescent magnetic powder formed by coating the surface of composite particles, in which a fluorescent pigment is attached to the surface of magnetic powder particles via a water-soluble resin, with a water-soluble resin. Therefore, the fluorescent pigment is unlikely to peel off or fall off in the fluorescent magnetic powder liquid or during a flaw detection test. Therefore, background phenomena due to peeled or fallen fluorescent pigment are unlikely to occur, and a large proportion of the fluorescent pigment remains on the surface of the magnetic powder particles, resulting in a clear defect indication pattern. This is a method for producing fluorescent magnetic powder for wet magnetic particle testing that can produce a fluorescent magnetic powder liquid that can detect fine open defects and non-open defects just below the surface with high detection sensitivity.

As is well known, the wet magnetic particle inspection method is standardized in JIS-Z-2320, and this test method involves applying commercially available magnetic powder for wet magnetic particle inspection (a fluorescent pigment such as Lumogen Yellow S0790 (manufactured by BASF) or Festa A (manufactured by Swada) to conductive particles such as iron tetraoxide particles or pure iron particles using a synthetic resin binder such as a cellulose acetate synthetic resin or a vinyl butyral synthetic resin, and having an average particle diameter of 3 to 30 μm (volume-based distribution display, the same applies below), a true specific gravity of 2 to 5 g/cm, to a magnetized inspection object, for example, a steel part such as a shaft, a steel material such as a magnetic body or a billet, or a magnetic body. In this test method, a magnetic powder liquid prepared by dispersing the powder of ^{No. 3} (hereinafter referred to as "magnetic powder") in water is applied to the test object, and the magnetic powder dispersed in the magnetic powder liquid is caused to gather at the open defect portion of the test object (fine cracks or pinholes present on or near the surface of the test object) to form a defect indication pattern, and the open defect portion is detected by this defect indication pattern (hereinafter this test method is referred to as "wet magnetic particle testing").

There are two methods for producing magnetic powder: one known to those skilled in the art as the "pulverization method" and the other as the "spray method."

The pulverization method is a method in which a fluorescent pigment is dispersed in a solution of an organic solvent-soluble synthetic resin used as a binder, which is dissolved in a volatile organic solvent, and then magnetic powder is mixed and kneaded to form a paste. The paste is then dried to form a mass, which is then pulverized into fine particles using a grinder such as a ball mill, and classified using a sieve to obtain fluorescent magnetic powder of the desired particle size.

The spray method involves adding magnetic powder, fluorescent pigment, and a binder made of water-dispersible or water-soluble synthetic resin to water to form a paste, which is then sprayed or scattered into the air using a spray nozzle or centrifugal disk, followed by drying and granulation to obtain spherical fluorescent magnetic powder of the desired particle size, in which the magnetic powder and fluorescent pigment are attached via the synthetic resin.

Fluorescent magnetic powder is dispersed in a dispersion liquid such as water to create a fluorescent magnetic powder liquid. However, if the fluorescent pigment peels off or falls off from the surface of the magnetic powder particles in the fluorescent magnetic powder liquid or during flaw detection testing, the peeled off or fallen fluorescent pigment will adhere to the surface of the test object other than the defective area and emit fluorescence, making it difficult to see the defect indication pattern. This is known as the background phenomenon, and there is a problem in that the detection sensitivity of the defective area is reduced.

In addition, when the fluorescent pigment peels off or falls off, the amount of fluorescent pigment covering the surface of the magnetic powder particles decreases, resulting in a problem of reduced brightness of the defect indication pattern and reduced detection sensitivity of defective areas.

Therefore, there is a need to develop a fluorescent magnetic powder that can be used to create a fluorescent magnetic powder liquid with high detection sensitivity that allows the fluorescent pigment to adhere firmly to the surface of magnetic powder particles, making it difficult for the fluorescent pigment to peel off or fall off in the fluorescent magnetic powder liquid or during flaw detection testing, making it less likely to cause background phenomena, and in which a high proportion of the fluorescent pigment that covers the surface of the magnetic powder particles remains, resulting in clear defect indication patterns.

JP2004-101193

Patent document 1 describes fluorescent magnetic powder produced by dissolving or dispersing magnetically conductive particles, a fluorescent colorant, and a binder in a solvent to form a paste, drying the paste, and pulverizing the dried material, and by spray-drying a paste made by dispersing magnetically conductive particles, a fluorescent colorant, and a synthetic resin emulsion in water.

However, if fluorescent magnetic powder liquid is made from fluorescent magnetic powder manufactured by the manufacturing method described in Patent Document 1, the fluorescent pigment on the surface of the magnetic powder particles is likely to peel off and fall off in the fluorescent magnetic powder liquid. Also, during flaw detection testing, the fluorescent pigment on the surface of the magnetic powder particles is likely to peel off and fall off, resulting in low brightness of the defect indication pattern and background phenomena that are likely to occur, resulting in low detection sensitivity.

The inventors of the present invention set out to solve the above-mentioned problems as a technical task, and as a result of repeated trial and error trial and error trials, they have discovered that a mixture containing 20% by weight or more and 40% by weight or less of magnetic powder having a median diameter of 2 μm or more and 7 μm or less, 5% by weight or more and 12% by weight or less of a resin content of a water-soluble resin-containing emulsion having a glass transition temperature of 10° C. or less, 5% by weight or more and 25% by weight or less of a fluorescent pigment, and water is granulated, and 10% by weight or more and 55% by weight or less of a fluorescent pigment is added to an aqueous solution containing 5% by weight or more and 35% by weight or less of the resin content of the water-soluble resin-containing emulsion. The above-mentioned granulated particles are dispersed and then granulated again to produce fluorescent magnetic powder, which has fluorescent pigment firmly attached to the surface of the magnetic powder particles. Therefore, the fluorescent pigment is unlikely to peel off or fall off in the fluorescent magnetic powder liquid or during flaw detection testing, making it difficult for background phenomena to occur. Furthermore, a high proportion of the fluorescent pigment remains on the surface of the magnetic powder particles, resulting in a clear defect indication pattern with a noticeable difference between defective and non-defective areas. This is the remarkable discovery that a fluorescent magnetic powder liquid can be produced that can detect open defects and non-open defects just below the surface with high detection sensitivity, thereby achieving the above-mentioned technical objective.

The above technical problems can be solved by the present invention as follows:

The present invention is a method for producing fluorescent magnetic powder for wet magnetic particle inspection testing, which comprises granulating a mixture containing 20% by weight or more and 40% by weight or less of magnetic powder having a median diameter of 2 μm or more and 7 μm or less, 5% by weight or more and 12% by weight or less of a resin content of a water-soluble resin-containing emulsion having a glass transition temperature of 10° C. or less, 5% by weight or more and 25% by weight or less of a fluorescent pigment, and water, dispersing 10% by weight or more and 55% by weight or less of the granulated particles in an aqueous solution containing 5% by weight or more and 35% by weight or less of the resin content of the water-soluble resin-containing emulsion, and then granulating again to produce fluorescent magnetic powder.

The present invention also relates to a method for producing fluorescent magnetic powder for wet magnetic particle inspection, in which the granulation method is spraying.

The present invention also relates to a method for producing the fluorescent magnetic powder for wet magnetic particle inspection, wherein the solid content in the mixture consisting of the magnetic powder, the fluorescent pigment, and the resin content of the water-soluble resin-containing emulsion is 65% by weight or less.

The present invention also relates to a method for producing fluorescent magnetic powder for wet magnetic particle inspection, in which the particles granulated from the mixture are composite particles in which a fluorescent pigment is attached to a magnetic powder.

The present invention also relates to a fluorescent magnetic powder liquid for wet magnetic particle testing, in which the fluorescent magnetic powder produced by the above-mentioned manufacturing method is dispersed.

The fluorescent magnetic powder of the present invention is manufactured by granulating a mixture containing 20% by weight to 40% by weight of magnetic powder having a median diameter of 2 μm to 7 μm, 5% by weight to 12% by weight of a resin content of a water-soluble resin-containing emulsion having a glass transition temperature of 10° C. or less, 5% by weight to 25% by weight of a fluorescent pigment, and water to produce composite particles in which the fluorescent pigment is attached to the surface of the magnetic powder particles via the water-soluble resin, and then dispersing 10% by weight to 55% by weight of the composite particles in an aqueous solution containing a water-soluble resin-containing emulsion in which the resin content of the water-soluble resin-containing emulsion is 5% by weight to 35% by weight, and then granulating again, so that the composite particles become fluorescent magnetic powder coated with the water-soluble resin.

The fluorescent magnetic powder produced by the manufacturing method of the present invention has less fluorescent pigment that peels off or falls off in the fluorescent magnetic powder liquid or during flaw detection testing, making it possible to produce a fluorescent magnetic powder liquid that is less likely to cause the so-called background phenomenon in which peeled-off fluorescent pigment adheres to the surface of the test object other than the defective area and emits fluorescence.

In addition, with the fluorescent magnetic powder of the present invention, the amount of fluorescent pigment that peels off and falls off in the fluorescent magnetic powder liquid is small, so a high percentage of the fluorescent pigment remains on the surface of the magnetic powder particles, and when re-sprayed, the fluorescent pigment that peels off and falls off the surface of the magnetic powder particles and the fluorescent pigment that does not adhere to the surface of the magnetic powder particles are dispersed in the water-soluble resin-containing emulsion to coat the surface of the composite particles, resulting in a clear defect indication pattern, making it possible to produce a fluorescent magnetic powder liquid with high detection sensitivity that can detect even fine open defects and non-open defects just below the surface.

In particular, by granulating either method by spraying, fluorescent magnetic powder with a uniform particle size can be produced, making it possible to produce a fluorescent magnetic powder liquid with high detection sensitivity that can detect even minute open defects and non-open defects just below the surface.

In addition, if the total solid content of the magnetic powder, fluorescent pigment, and water-soluble resin in the mixture is 65% by weight or less, the mixture is suitable for granulation by the spray method.

The fluorescent magnetic powder liquid in which the fluorescent magnetic powder of the present invention is dispersed is less likely to cause background phenomena and the fluorescent pigment of the fluorescent magnetic powder remains at a high rate, resulting in a clear defect indication pattern with a noticeable difference between defective and non-defective areas. This fluorescent magnetic powder liquid can detect fine open defects and non-open defects just below the surface with high detection sensitivity.

FIG. 13 is a diagram comparing peeling water. FIG. 1 is a diagram showing a method for measuring peel brightness.

The fluorescent magnetic powder of the present invention is produced by granulating composite particles from a slurry-like mixture of magnetic powder, a water-soluble resin-containing emulsion, a fluorescent pigment, and water, and then dispersing the composite particles in an aqueous solution containing a water-soluble resin-containing emulsion and spraying it again, so that the composite particles become fluorescent magnetic powder coated with the water-soluble resin.

(Magnetic powder)
The magnetic powder contained in the mixture of the present invention is not particularly limited.
Examples of the magnetic powder include reduced iron powder, electrolytic iron powder, γ-ferric oxide powder, and iron tetroxide powder.

The median diameter of the magnetic powder particles is preferably 2 μm to 7 μm, and more preferably 3 μm to 5 μm.

If the median diameter is less than 2 μm, the brightness of the fluorescent magnetic powder liquid may be low, resulting in a risk of reduced sensitivity in detecting open defects. If the median diameter exceeds 7 μm, the fluorescent magnetic powder liquid may flow, resulting in an unstable magnetic powder pattern.

The magnetic powder content in the mixture is preferably 20% to 40% by weight, and more preferably 30% to 37% by weight.

If the magnetic powder content is less than 20% by weight, the amount of fluorescent pigment that does not adhere to the surface of the magnetic powder particles increases, making it easier for background phenomena to occur in which the fluorescent pigment adheres to the surface of the test object other than the defective area and emits fluorescence, which may reduce the detection sensitivity of the defective area.

Furthermore, if the content exceeds 40% by weight, the solid content in the mixture becomes too high, making it difficult to granulate using the spray method.

(Water-soluble resin-containing emulsion)
The mixture in the present invention is an emulsion containing a water-soluble resin having a glass transition temperature of 10° C. or lower.

If the glass transition temperature exceeds 10°C, the resin will harden easily, and there is a risk that fine powder of the water-soluble resin will precipitate after spraying.

There are no particular limitations on the water-soluble resin with a glass transition temperature of 10°C or less.

Examples of the water-soluble resin-containing emulsion in the present invention include acrylic ester emulsion, styrene acrylic emulsion, and styrene butadiene emulsion.

The resin content of the water-soluble resin-containing emulsion contained in the mixture is preferably 5% to 12% by weight, more preferably 6% to 10% by weight.

If it is less than 5% by weight, the amount of fluorescent pigment that peels off and falls off from the composite particles increases, making the background phenomenon more likely to occur, and if it is more than 12% by weight, clumps of the water-soluble resin attached to the fluorescent pigment will form, either of which may reduce the detection sensitivity.

(Fluorescent pigment)
The mixture according to the present invention contains a fluorescent pigment.

The fluorescent pigment is not particularly limited, but examples include Lumogen Yellow S0790 (manufactured by BASF) and Festa A (manufactured by Swada).

The content of fluorescent pigment in the mixture is preferably 5% to 25% by weight, more preferably 10% to 15% by weight.

If it is less than 5% by weight, the brightness of the defect indication pattern will be low, which may reduce the detection sensitivity.

Also, if the content exceeds 25% by weight, the solid content in the mixture increases, causing the viscosity to become too high, making it difficult to granulate using the spray method.

It is preferable that the mixture is in a slurry state with a viscosity of 100 cP or less, because this makes it easier to granulate using the spray method.

It is preferable that the solid content of the mixture, consisting of magnetic powder, fluorescent pigment, and water-soluble resin, is 65% by weight or less.

If it exceeds 65% by weight, the viscosity becomes too high, making granulation by spraying difficult.

The mixture can be granulated using a spray dryer by spraying it into the air at high temperature to remove the water from the droplets and dry them.

This makes it possible to obtain composite particles in which the fluorescent pigment is attached to the surface of the magnetic powder particles via the water-soluble resin.

The fluorescent magnetic powder of the present invention is prepared by dispersing composite particles in an aqueous solution consisting of water and a water-soluble resin-containing emulsion with a glass transition temperature of 10°C or less, and then granulating the mixture again.

In an aqueous solution containing a water-soluble resin-containing emulsion in which composite particles are dispersed, the fluorescent pigment that has peeled off and fallen off the surface of the magnetic powder particles is dispersed, and if the particles are granulated again, the water-soluble resin in which the fluorescent pigment is dispersed coats the surface of the composite particles.

The composite particles to be dispersed in the aqueous solution containing the water-soluble resin-containing emulsion are preferably 10% to 55% by weight, and more preferably 40% to 45% by weight.

If the composite particle content is less than 10% by weight, the surface of the composite particle will be coated with a large amount of water-soluble resin, which may not be fully absorbed into defective areas. If the content exceeds 55% by weight, the solid content will increase, causing the viscosity to become too high, making it difficult to granulate again by the spraying method.

(Aqueous solution containing water-soluble resin-containing emulsion)
The aqueous solution in which the composite particles are dispersed can be prepared by mixing an emulsion solution containing a water-soluble resin having a glass transition temperature of 10° C. or less with water.

If the glass transition temperature exceeds 10°C, the resin will harden easily, and there is a risk that fine powder of the water-soluble resin will precipitate after spraying.

Water-soluble resin-containing emulsions with a glass transition temperature of 10°C or less are not particularly limited, and examples include acrylic ester emulsions, styrene acrylic emulsions, and styrene butadiene emulsions.

The resin content of the water-soluble resin-containing emulsion in the aqueous solution is preferably 5% to 35% by weight.

If the proportion of resin in the aqueous solution is less than 5% by weight, the coating effect will be weak and there is a risk that peeling or falling off of the fluorescent pigment will not be prevented.

Furthermore, if the content exceeds 35% by weight, the solid content becomes too high, which increases the viscosity and may make it difficult to granulate using the spray method.

(Fluorescent magnetic powder liquid)
The prepared fluorescent magnetic powder can be dispersed in an organic solvent such as water or kerosene to produce a fluorescent magnetic powder liquid.

The fluorescent magnetic powder contained in the fluorescent magnetic powder liquid is preferably 0.3 g/L to 2.0 g/L.
This is because minute defects can be detected with high detection sensitivity.

In order to improve the dispersibility of the fluorescent magnetic powder, a commercially available magnetic powder dispersant for wet magnetic particle testing may be added to the fluorescent magnetic powder liquid in the present invention.

(Wet magnetic particle testing method)
1 shows an embodiment of a wet magnetic particle inspection using a fluorescent magnetic powder liquid in which fluorescent magnetic powder is dispersed according to the present invention.

The test object is magnetized using the standard axial current method, then fluorescent magnetic powder liquid is applied, and the defect indication pattern is observed by shining an ultraviolet light in a dark place, and the number and size of defects are measured.

The fluorescent magnetic powder liquid of the present invention can be suitably used to detect open defects with a width of 0.02 mm or more, and non-open Ketos No. 7 defects just below the surface.

The present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited thereto.

As shown in the table, iron oxide powder, acrylic ester emulsion, melamine-based fluorescent pigment (Shinroihi Color 5005/Shinroihi Co., Ltd.) and water were mixed to prepare a slurry-like mixture.

The "Water-soluble resin" column in each table shows the glass transition temperature (Tg) and resin content (wt%) of the acrylic ester resin in the mixture or aqueous solution.

The mixture was sprayed into the air at high temperature using a spray dryer to remove moisture from the droplets, and then dried and granulated.

The resulting composite particles were divided into those that were not re-sprayed and those that were re-sprayed.

An aqueous solution containing an acrylic ester emulsion was prepared by dissolving the acrylic ester emulsion in water.

The composite particles to be re-sprayed were dispersed in the prepared aqueous solution containing the acrylic ester emulsion, and then granulated again using a spray dryer to obtain the re-sprayed fluorescent magnetic powder.

In the following, those that were not re-sprayed will be referred to as composite particles, and those that were re-sprayed will be referred to as re-sprayed fluorescent magnetic powder.

(Sprayability)
When the re-spraying was possible, the sample was evaluated as ◯, and when the sample could not be dispersed in the aqueous solution containing the water-soluble resin-containing emulsion and could not be sprayed, the sample was evaluated as ×.

(Detection sensitivity)
A type A test piece as specified in JIS Z2320 was attached to 60 square steel materials, and while magnetizing them by an axial current method, magnetic powder liquid was applied to them. The detection state of artificial defects in the type A test piece was visually observed and evaluated.

If the detection sensitivity of the fluorescent magnetic powder liquid in which the re-sprayed fluorescent magnetic powder was dispersed was equal to or greater than the detection sensitivity of the fluorescent magnetic powder liquid in which the composite particles were dispersed, it was evaluated as ◯, and if it was lower, it was evaluated as ×.

(peel brightness)
0.5 g of each of the re-sprayed fluorescent magnetic powder and composite particles of the Examples and Comparative Examples was dispersed in 1 L of water by adding a dispersant (Ecomagna Dispersant EC-4/Marktec Co., Ltd.).

After that, as shown in Figure 2, the water from which the fluorescent magnetic particles had been removed using a magnet (hereafter referred to as "stripped water") was poured into a transparent Teflon (registered trademark) tube with a diameter of 6 mm, ultraviolet light was irradiated onto the outer surface of the Teflon (registered trademark) tube, and the emitted light was read by a photosensor.

In this specification, the brightness of the peeled water read by the photosensor using the above method is referred to as peeling brightness.

The peeling brightness of the composite particles in Example 1 before re-spraying was 0.714, and the peeling brightness of the re-sprayed fluorescent magnetic powder after re-spraying was 0.155 (Figure 1).

The reduction rate of peeling brightness was calculated using the following formula.
(Formula) 0.155/0.714×100=21.7%

Similarly, re-sprayed fluorescent magnetic powder that had a reduction in peeling brightness of 50% or less compared to the peeling water of the fluorescent magnetic powder liquid in which the composite particles were dispersed before re-spraying was evaluated as ◯, and those that exceeded 50% were evaluated as ×.

The results are shown in Tables 1 and 2.
In the table, "resin precipitation" indicates that fine powder of water-soluble resin was generated after spraying.

A comparison of the stripping water from composite particles and re-sprayed fluorescent magnetic powder is shown in Figure 1.

As shown in Tables 1 to 3, the re-sprayed fluorescent magnetic powder of the present invention is less likely to peel off or fall off when dispersed in water, and it has been shown that a fluorescent magnetic powder liquid can be produced that is less likely to cause background phenomena.

Therefore, it has been proven that the fluorescent magnetic powder liquid in which the fluorescent magnetic powder of the present invention is dispersed can produce clear defect indication patterns and is a fluorescent magnetic powder liquid with high detection sensitivity.

The fluorescent magnetic powder of the present invention is a fluorescent magnetic powder in which composite particles having a fluorescent pigment attached to the surface of magnetic powder particles via a water-soluble resin are further coated with a water-soluble resin. Since the fluorescent pigment is firmly attached to the surface of the magnetic powder particles, the fluorescent pigment is unlikely to peel off or fall off in the fluorescent magnetic powder liquid or during flaw detection testing, making it possible to produce a fluorescent magnetic powder liquid in which background phenomena are unlikely to occur.
In addition, since there is little peeling or falling off of the fluorescent pigment, a large proportion of the fluorescent pigment remains on the surface of the magnetic powder particles, and further, any fluorescent pigment that peels off or falls off during the production of the composite particles is dispersed in an aqueous solution containing an emulsion containing a water-soluble resin, and when the composite particles are sprayed again, the water-soluble resin in which the peeled fluorescent pigment is dispersed coats the surface, making it possible to produce a fluorescent magnetic powder liquid that can produce a clear defect indication pattern.
Therefore, the fluorescent magnetic powder liquid in which the fluorescent magnetic powder of the present invention is dispersed can detect minute open defects and non-open defects immediately below the surface with high detection sensitivity.
Therefore, the present invention has high industrial applicability.

Claims (5)

A method for producing fluorescent magnetic powder for wet magnetic particle inspection testing, comprising: granulating a mixture containing 20% by weight or more and 40% by weight or less of magnetic powder having a median diameter of 2 μm or more and 7 μm or less, 5% by weight or more and 12% by weight or less of a resin content of a water-soluble resin-containing emulsion having a glass transition temperature of 10° C. or less, 5% by weight or more and 25% by weight or less of a fluorescent pigment, and water; dispersing 10% by weight or more and 55% by weight or less of the granulated particles in an aqueous solution containing 5% by weight or more and 35% by weight or less of the resin content of the water-soluble resin-containing emulsion, and then granulating again to produce fluorescent magnetic powder. The method for producing fluorescent magnetic powder for wet magnetic particle inspection according to claim 1, wherein all of the granulation methods are spraying. 3. The method for producing fluorescent magnetic powder for wet magnetic particle inspection according to claim 1, wherein the solid content of said mixture consisting of said magnetic powder, said fluorescent pigment and the resin content of said water-soluble resin-containing emulsion is 65% by weight or less. The method for producing fluorescent magnetic powder for wet magnetic particle testing according to any one of claims 1 to 3, wherein the particles granulated from the mixture are composite particles in which a fluorescent pigment is attached to the surface of magnetic powder particles. 5. A fluorescent magnetic powder liquid for wet magnetic particle inspection, comprising a fluorescent magnetic powder produced by the method according to claim 1 dispersed therein.