JP7684813B2 - 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 in which a fluorescent pigment is firmly attached to the surface of the magnetic powder particles via a water-soluble resin, so that the fluorescent pigment is unlikely to peel off or fall off in the fluorescent magnetic powder liquid or during the flaw detection test, making it difficult for background phenomena due to peeled or fallen fluorescent pigment to occur, and since a high proportion of the fluorescent pigment remains on the surface of the magnetic powder particles, a highly bright defect indication pattern is obtained. 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 a highly bright defect indication pattern.

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 have set the technical task of solving the above-mentioned problems, and as a result of repeated trial and error trials and experiments, have discovered that a magnetic powder having a median diameter of 2 μm or more and 7 μm or less is 20% by weight or more and 40% by weight or less, a water-soluble resin-containing emulsion having a glass transition temperature of 10° C. or less having a resin content of 5% by weight or more and 12% by weight or less, a fluorescent pigment having a glass transition temperature of 10° C. or less and water is granulated, and the granulated particles are heated at a temperature of 80° C. or more and 180° C. or less to produce a magnetic powder having a median diameter of ... μm or more and 7 μm or less and water is granulated, and the magnetic powder is granulated. The fluorescent magnetic powder thus produced is a fluorescent magnetic powder in which the fluorescent pigment is firmly attached to the surface of the magnetic powder particles via the water-soluble resin, and the fluorescent pigment is unlikely to peel off or fall off in the fluorescent magnetic powder liquid or during flaw detection testing, making it less likely 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 highly bright defect indication pattern.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 provides 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, and heat-treating the granulated particles at a temperature of 80° C. or more and 180° C. or less to produce fluorescent magnetic powder.

The present invention also relates to a method for producing fluorescent magnetic powder for wet magnetic particle inspection, which comprises spraying the mixture and granulating it.

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

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

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 produced 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 component 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 fluorescent pigment, and water to produce composite particles in which the fluorescent pigment adheres to the surfaces of the magnetic powder particles via the water-soluble resin, and then heat-treating the composite particles at 80° C. to 180° C., resulting in fluorescent magnetic powder in which the fluorescent pigment adheres firmly to the surfaces of the magnetic powder particles.

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, because there is little peeling or falling off of the fluorescent pigment, a high percentage of the fluorescent pigment remains on the surface of the magnetic powder particles, resulting in a highly bright defect indication pattern, 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 particular, if the mixture is made into a slurry and then granulated by a spraying method, fluorescent magnetic powder with a uniform particle size can be produced, making it possible to produce a fluorescent magnetic powder liquid that can detect fine open defects and non-open defects just below the surface with even higher detection sensitivity.

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 produces a highly bright defect indication pattern, making it a fluorescent magnetic powder liquid that can detect minute 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 in the present invention is a fluorescent magnetic powder 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 heat-treating the composite particles at 80°C to 180°C.

(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 decrease in the detection sensitivity of open defects. If the median diameter exceeds 7 μm, the fluorescent magnetic powder liquid may flow, resulting in an unstable magnetic powder pattern.

The content of magnetic powder 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 used in the present invention is a water-soluble resin-containing emulsion that contains 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.

Water-soluble resin-containing emulsions with a glass transition temperature of 10°C or less are not particularly limited.

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.

The mixture preferably has a viscosity of 100 cP or less in the form of a slurry.
This is because granulation is easy by 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 in this invention is produced by heat treating composite particles.

The temperature for the heat treatment is preferably 80°C to 180°C, and more preferably 100°C to 160°C.

If the heating temperature is less than 80°C, the amount of fluorescent pigment peeling off and falling off from the fluorescent magnetic powder liquid will not decrease, and if the temperature is heated to more than 180°C, the brightness of the fluorescent magnetic powder will decrease, and either of these may result in a decrease in detection sensitivity.

The heating process can be carried out in an oven preset to 80°C to 180°C.

(Fluorescent magnetic powder liquid)
The prepared fluorescent magnetic powder can be dispersed in an organic solvent such as water or kerosene to prepare 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 opening 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 that appears when exposed to ultraviolet light in a dark place is observed, 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 defects just below the surface, such as Ketos No. 7.

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 the table shows the glass transition temperature (Tg) of the acrylic ester resin in the mixture and the resin content (wt%).

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 composite particles obtained were divided into those that were not subjected to heat treatment (hereafter referred to as "unheated fluorescent magnetic powder") and those that were subjected to the heat treatment described in each table (hereafter referred to as "heated fluorescent magnetic powder").

(Heat Treatment)
The mixture was heated in a pre-heated oven for 20 minutes.

(Sprayability)
Those which could be sprayed with the spray gun were rated as ◯, and those which could not be dispersed in water and therefore could not be sprayed were rated 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 heated fluorescent magnetic powder was equal to or greater than that of the fluorescent magnetic powder liquid in which unheated fluorescent magnetic powder was dispersed, it was evaluated as ◯, and if it was lower, it was evaluated as ×.

(peel brightness)
0.5 g of each of the heated fluorescent magnetic powders or unheated fluorescent magnetic powders 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 unheated fluorescent magnetic powder in Example 1 was 0.774, and the peeling brightness of the heated fluorescent magnetic powder was 0.174 (Figure 1).

The reduction rate of peeling brightness was calculated using the following formula.
(Formula) 0.174/0.774×100=22.5%

Similarly, samples where the peeling brightness of heated fluorescent magnetic powder was reduced by 50% or less compared to the peeling brightness of unheated fluorescent magnetic powder were evaluated as ◯, and samples where the reduction rate 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.

The stripping water for Examples 1 to 3 and Comparative Example 9 is shown in Figure 1.

As shown in Tables 1, 2 and Figure 1, the heated 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 it is possible to create a fluorescent magnetic powder liquid that is less likely to cause background phenomena.

It was also confirmed that the brightness did not decrease even when heated at temperatures between 80°C and 180°C, demonstrating that a highly bright defect indication pattern could be obtained.

Therefore, it has been proven that the fluorescent magnetic powder liquid in which the fluorescent magnetic powder of the present invention is dispersed 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 the fluorescent pigment is firmly attached to the surface of the magnetic powder particles, and therefore the fluorescent pigment is not easily peeled off or fallen off in the fluorescent magnetic powder liquid or during flaw detection testing, making it possible to prepare a fluorescent magnetic powder liquid in which background phenomena are less likely to occur.
Furthermore, since there is little peeling or falling off of the fluorescent pigment, it is possible to prepare a fluorescent magnetic powder liquid that can provide a defect indicating pattern with high brightness.
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 (4)

A method for manufacturing 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 with 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 with 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, and heat-treating the granulated particles at 80°C or more and 180°C or less. The method for producing fluorescent magnetic powder for wet magnetic particle inspection according to claim 1, in which the mixture is sprayed and granulated. The method for manufacturing fluorescent magnetic powder for wet magnetic particle inspection according to claim 1 or 2, wherein the solid components of the mixture, consisting of the magnetic powder, the fluorescent pigment, and the water-soluble resin, are 65% by weight or less. 4. The method for producing fluorescent magnetic powder for wet magnetic particle inspection according to claim 1, wherein the particles granulated from the mixture are composite particles in which a fluorescent pigment is attached to the surface of magnetic powder particles.