JPH0253744B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for producing colored magnetic particles for magnetic particle flaw detection.

[Technical background of the invention and its problems]

As is well known, in the magnetic particle flaw detection method, when a magnetizable inspection object is magnetized and there is a defect such as a crack or pinhole near the surface of the inspection object, the magnetic reluctance of the defective area is higher than that of other healthy parts. This method utilizes the phenomenon in which magnetic flux drifts only in this area and leaks into the air, and when excited by white or yellow pigment or ultraviolet irradiation on the surface of magnetically conductive powder particles, yellow or yellow color is generated. Powder (hereinafter referred to as colored magnetic powder) made by attaching a fluorescent substance that emits green light (hereinafter referred to as coloring material) using synthetic resin as a binder.
is sprayed wet or dry on the surface of the object to be inspected,
By aggregating and adhering colored magnetic particles to the leakage magnetic flux portion on the surface of the object to be inspected, in other words, to the defective part, forming a defect indicator magnetic particle pattern by the aggregate of colored magnetic particles, and observing the pattern, it is possible to detect the defective magnetic particles. This is a method for non-destructively detecting the presence of defects on an object to be inspected. The magnetic conductive powder is colored with a coloring material in order to improve the contrast with the surface of the object to be inspected and to facilitate observation of the defect indicator magnetic powder pattern.

The oldest method for producing colored magnetic powder is to disperse or dissolve a coloring material in a solution of a synthetic resin, etc. as a binder, dissolved in a solvent, and then mix magnetically conductive powder into this solution. The mixture is kneaded to form a paste, and this paste is dried and then ground into fine particles using a grinder such as a ball mill, and then classified using a sieve or the like to obtain colored magnetic powder of the desired particle size. It's a method.

The above method has the disadvantage that during the grinding process, a considerable amount of the coloring material bound to the magnetically conductive powder by synthetic resin, etc., inevitably peels off and falls off together with the binding material, such as the synthetic resin. Yes, if the colored magnetic powder contains coloring material and binder released from the magnetically conductive powder, or if the colored magnetic powder contains uncolored magnetically conductive powder,
It is well known to those skilled in the art that accurate flaw detection results cannot be obtained.

Therefore, in the industry, various methods for producing colored magnetic powder that do not require a pulverization process have been proposed.
One of them is JP 58-142253, which belongs to the spray drying method.
There is a method disclosed in the publication No.

The method for producing colored magnetic powder disclosed in the above-mentioned publication uses a thermoplastic synthetic resin and paraffin, which are so-called "hot melt materials," as binders, and a coloring agent and triiron tetroxide powder, which is a magnetically conductive powder. By heating, melting and stirring a mixture of the three to form a liquid, spraying the liquid into the air using a heated spray gun, and allowing it to cool naturally in the air,
Method for obtaining colored magnetic powder (hereinafter referred to as known method)
It is.

In the known method, when triiron tetroxide powder with a particle size of 1 to 3 microns is used as the magnetically conductive powder, peeling and falling off of the colorant and binder is more difficult than in the production method that requires the above-mentioned pulverization step. The shortcomings of the above have been improved.

However, according to the experimental results of the present inventors, when pure iron powder or stainless steel powder is used as the magnetically conductive powder, a considerable amount of the colorant and binder peels off or falls off during spraying and cooling. was unavoidable. Furthermore, as the particle size of the target powder increased to 5 microns, 10 microns, etc., there was a tendency for more peeling and falling off.

By the way, as for the magnetically conductive powder used for the colored magnetic powder, it is desirable that the powder itself be light in color and have a high light reflectance.

This is because, as mentioned above, when the colorant is a pigment, white, yellow, or red pigments are usually used, but when coloring with such pigments, the magnetic conductive powder itself This is because it is easier to color gray than black, and when the colorant is a fluorescent substance, it is usually a fluorescent substance that emits yellow to yellow-green light when excited by ultraviolet irradiation. (For example, Lumogen Brilliant Yellow, dye name) is used, but in such cases, it is better to have the magnetically conductive powder itself gray in color and have a higher light reflectance than black. This is because the fluorescence brightness upon excitation increases.

Now, as is well known, the color of triiron tetroxide powder itself is black and its particle surface is rough, but the color of pure iron powder itself and stainless steel powder itself is gray, and the particle surface is rough. The surface is smooth compared to the surface of triiron tetroxide powder particles.
Therefore, from the viewpoint of coloring, pure iron powder and stainless steel powder are better than triiron tetroxide powder as magnetically conductive powder used for colored magnetic powder.

Furthermore, the magnetic sensitivity of triiron tetroxide powder is low compared to that of pure iron powder and stainless steel powder. Therefore, in producing colored magnetic powder that requires high magnetic sensitivity, it is preferable to use pure iron powder and stainless steel powder, particularly pure iron powder, as the magnetically conductive powder.

However, when the known method is applied to pure iron powder or stainless steel powder, a considerable amount of the colorant and binder will peel off or fall off during spraying and cooling, as described above.

Of course, the present inventor has conducted numerous experiments and trial productions by variously changing the types of thermoplastic synthetic resin and paraffin used as the hot melt materials used as binders, the blending ratio, melting conditions, spraying conditions, etc. Although we have even tried using a rotating disk type atomizer instead of the atomizer, the result is that when using pure iron powder and stainless steel powder, it is difficult to prevent the colorant and binder from peeling off or falling off. I learned that it is impossible. The reason for this is that while the particle surface of triiron tetroxide powder is rough, the particle surface of pure iron powder and stainless steel powder is smooth, resulting in poor wettability with the hot melt material used as the binder. In the case of triiron tetroxide powder, fine particle powder with a particle size of 1 to 3 microns is commercially available, but in the case of pure iron powder and stainless steel powder, it is commercially available as fine powder. At most, the particle size is less than 20 microns and the average particle size is 5.
This is thought to be due to two reasons: the particle size is on the order of microns, and it is necessary to use particles with a larger particle size than when using triiron tetroxide powder.

[Purpose of the invention]

The present invention solves the above-mentioned problems, namely, the coloring agent and the coloring agent that occur during spraying and cooling when a known method is applied to pure iron powder or stainless steel powder with a particle size of 20 microns or less and an average particle size of about 5 microns. The purpose is to solve the problem of peeling and falling off of the bonding material.

[Summary of the invention]

The present invention comprises 10 to 60 parts of pure iron powder or stainless steel powder with a particle size of 20 microns or less and an average particle size of 4 to 6 microns as a magnetically conductive powder, 5 to 60 parts of a pigment or fluorescent substance as a coloring agent, and a binder. 10 to 80 parts of one or more of hot melt materials selected from polyethylene wax, atactic polypropylene, and paraffin wax, and chlorinated paraffin, dioctyl phthalate,
Using a rotating disk type atomizer, heat and melt a viscosity of 200 cp or less consisting of 5 to 30 parts of one or more selected from trioctyl phosphate, tributoxyethyl phosphate, dibutyl maleate, dibutyl sebacate, and butyl diglycol. This is a method for producing colored magnetic powder for magnetic particle flaw detection, which is characterized in that it is sprayed into the air and naturally cooled to obtain granules. First, each compound and its compounding ratio in the method of the present invention will be explained.

As the magnetically conductive powder, pure iron powder or stainless steel powder with a particle size of 20 microns or less and an average particle size of about 5 microns, which are commercially available and easily available, is used. The blending ratio is 10 to 60 parts.
If the amount is less than 10 parts, the magnetic sensitivity will be low and it will be difficult to obtain colored magnetic powder with sufficient flaw detection accuracy. When the amount is 60 parts or more, it becomes difficult to reduce the viscosity of the heated melt to 200 cp or less.

Examples of colorants include commercially available white pigments (e.g., titanium white), yellow pigments (e.g., α-FeOOH pigments), which have been conventionally used in the production of colored magnetic powder.
Pigments such as red pigments (for example, Bengara) and fluorescent substances (for example, fluorescent dyes such as Lumogen Brilliant Yellow) are used. The blending ratio is 5 to 60 parts. When the amount is less than 5 parts, it is difficult to obtain a sufficient coloring effect. When the amount is 60 parts or more, it becomes difficult to reduce the viscosity of the heated melt to 200 cp or less.

As the binder, commercially available polyethylene wax, atactic polypropylene, paraffin wax, etc., which are well known as hot melt materials, are used. The blending ratio is 10 to 80 parts.
When the amount is less than 10 parts, it is difficult to obtain sufficient adhesive strength, and the viscosity of the heated melt cannot be reduced to less than 200 cp. If the amount exceeds 80 parts, it will become impossible to incorporate other ingredients in the necessary amounts.

As mentioned above, it is almost impossible to produce colored magnetic powder using the above three materials without peeling or falling off the coloring material and the binding material. Therefore, in the present invention, commercially available chlorinated paraffin, dioctyl phthalate, trioctyl phosphate,
Tributoxyethyl phosphate, dibutyl maleate, dibutyl sebacate, butyl diglycol, etc. are used. All of these have the effect of improving the wettability of the pure iron powder or stainless steel powder with the hot melt material.

That is, when the above-mentioned bonding aid is present, even if the surface of the pure iron powder particles or stainless steel powder particles is smooth compared to the surface of the triiron tetroxide powder particles, the bonding with the above-mentioned hot melt material will be difficult. This improves the wettability between hot melt materials and prevents them from peeling off or falling off even when the hot melt material changes from a molten state to a solid state during spraying.

Further, the bonding auxiliary material has good compatibility with the bonding material and also has the effect of lowering the viscosity of the heated melt.

The blending ratio of the above bonding aid is 5 to 30 parts.
When the amount is less than 5 parts, it is difficult to obtain the effect of improving wettability and it is difficult to obtain the effect of lowering the viscosity. When the amount is more than 30 parts, the surface of the colored magnetic powder obtained becomes sticky and
The colored magnetic powder itself causes blocking.

Next, the viscosity of the heated melt of each of the above-mentioned formulations will be explained.

The viscosity of the heated melt must be less than 200 cp.

This is because when a heated molten material is sprayed into the air using a rotating disc type atomizer and then naturally cooled to obtain granules, the higher the viscosity of the heated molten material to be sprayed, the more difficult it is to obtain granules. This is because the diameter of the particles tends to become larger.

The present invention uses pure iron powder or stainless steel powder with a particle size of 20 microns or less and an average particle size of about 5 microns, and obtains colored magnetic powder by adhering a binding material, a coloring material, and a binding auxiliary material to the pure iron powder or stainless steel powder. , the resulting colored powder has a particle size of less than 30 microns and an average particle size of 10
It must be on the order of microns. The reason is that when implementing the magnetic particle testing method,
Normally, it is required to be able to detect defects with a depth of 5 microns or more, and in order to meet this requirement, the colored magnetic powder used must have a particle size of 30 microns or less on average.
It needs to be about 10 microns.

When heating and melting each of the above-mentioned compounds, if the viscosity is set to 200 cp or less, the granules obtained by spraying into the air using a rotating disk atomizer and cooling naturally will have a particle size of 30 cp. We can guarantee that the average particle size will be about 10 microns or less.

When each compound is blended within the above-mentioned proportions, a heated melt having a viscosity of 200 cp or less can be easily prepared.

In addition, in preparing the heated melt, first put a predetermined amount of the above binding material and the above binding auxiliary material into a container, heat it to about 90 to 150°C to melt the binding material, and stir. The melt (binding material) and the binding auxiliary material are thoroughly mixed, then a predetermined amount of the above-mentioned magnetically conductive powder and coloring material are added, and stirred for 30 to 60 minutes using a stirrer such as a homomixer. It is preferable to adopt such an embodiment, and by preparing according to such an embodiment, a heated melt having a viscosity of 200 cp or less can be easily obtained.

Next, granulation using a rotating disk type atomizer will be explained.

Rotating disk type atomizer (rotating disk type atomizer)
utilizes the principle that when liquid is poured into the center of a disk rotating at high speed, the centrifugal force of the disk causes the liquid to atomize around the disk, and is often used as a type of granulator using the spray drying method. Various types of rotary disks are commercially available (such as those in which the rotating disk is disk-shaped, plate-shaped, bowl-shaped, etc.).

In the present invention, using a commercially available rotary disk type atomizer, a heated molten product having a viscosity of 200 cp or less is sprayed into the air and then naturally cooled to obtain a granulated product.

Naturally, when spraying, care must be taken as usual to prevent the heated molten material from being cooled down before reaching the rotating disk of the rotating disk type atomizer.

Under normal conditions, the temperature of the heated melt is 100-170℃ at the atomizer inlet, 80-150℃ near the rotating disk, and 15-35℃ at the atomizer outlet.
It is preferable to adopt an embodiment in which the temperature is about ℃. Also,
It is preferable that the rotation speed of the rotating disk is usually set to 26,000 to 32,000 rpm.

By adopting the above-mentioned method and spraying the heated melt with a viscosity of 200 cp or less into the air and allowing it to cool naturally, the above-mentioned colorant, binder and bonding auxiliary material will hardly peel or fall off. Without any doubt, one or more of the magnetically conductive powder particles are coated with a mixture of the binder and the bonding auxiliary material colored with the colorant and have a particle size of 30 microns or less. Powder with an average particle size of about 10 microns can be easily obtained.

This powder has satisfactory performance as a colored magnetic powder for magnetic particle flaw detection, as shown in the Examples below.

[Embodiments of the invention]

The present invention will be described in detail with reference to examples as follows. Note that "parts" in each example mean parts by weight.

Example 1 Polyethylene wax (molecular weight 500, viscosity 4cp
(95°C)) and 10 parts of chlorinated paraffin are placed in a stainless steel tank, heated to approximately 95°C under stirring to melt them, and added to the Add 25 parts of pure iron powder and 15 parts of Lumogen Brilliant Yellow and stir for about 50 minutes using a homomixer to obtain a viscosity of 160 cp (95°C,
(measured using a Type B viscometer) was prepared.

Next, using a rotating disk type atomizer, the heated molten material was heated at a temperature of about 110°C near the atomizer inlet.
The temperature near the rotating disk is about 90℃, the temperature near the atomizer outlet is about 20℃, and the rotation speed of the rotating disk is 26,000 rpm. Spray into the air and cool naturally, and one pure iron powder particle becomes Lumogen. Particle size 25 coated with a mixture of brilliant yellow colored polyethylene wax and chlorinated paraffin (as confirmed by optical microscope x400)
Colored magnetic powder with an average particle size of 8 microns or less -
It is generally called fluorescent magnetic powder. - Obtained 98 copies.

The colored magnetic powder thus obtained was used without being classified to carry out the following magnetic particle flaw detection method.

Add 2 g of the above colored magnetic powder per 1 water to 20 g per 1 water.
Magnetic powder liquid dispersed in water using cc dispersant (surfactant) is PC-
When the surface of the inspected object (ordinary carbon steel: billet material) is magnetized by applying a current of 1000A for 2 seconds, and the surface of the inspected object is irradiated with ultraviolet rays using a black light, the depth of approximately 5 microns existing on the inspected object surface is applied. It was confirmed with the naked eye that the defective part was clearly indicated by a defect indicating pattern exhibiting yellow-green fluorescence. This fact indicates that peeling and falling off of the colored material and the like hardly occurred.

The fluorescence brightness of the above-mentioned colored magnetic powder was measured using a Yagi type fluorescence meter, and the fluorescent brightness of the commercially available fluorescent magnetic powder LY- was measured as a standard product.
1500 (product name: Special Paint Co., Ltd.) fluorescent brightness is 100%
When measured as , it was 400%.

For comparison, the fluorescence brightness of colored magnetic powder produced under the same conditions as above, except that triiron tetroxide powder was used instead of pure iron powder, was measured in the same manner as above and found to be 98%.

Example 2 25 parts of atactic polypropylene (molecular weight 400, viscosity 1 cp (150°C)) and 15 parts of dioctyl phthalate were placed in a stainless steel tank and heated to about 150°C while stirring.
50 parts of stainless steel powder with a particle size of 20 microns or less and an average particle size of 5 microns and 10 parts of titanium white are added to this, and the mixture is stirred for about 60 minutes using a homomixer. Viscosity 195cp (150
℃, measured using a B-type viscometer) was prepared.

Next, using a rotating disk type atomizer, the heated molten material was heated to a temperature of about 170℃ near the atomizer inlet.
The temperature near the rotating disk is 150℃, the temperature near the atomizer outlet is about 35℃, and the rotation speed of the rotating disk is 30,000 rpm. Spray into the air and cool naturally, and each stainless steel powder particle is colored with titanium white. 97 parts of white magnetic powder having a particle size of less than 28 microns and an average particle size of 9 microns was obtained which was coated with a mixture of the atactic polypropylene and dioctyl phthalate (as confirmed using a x400 optical microscope).

The white magnetic powder thus obtained was used without being classified, and a magnetic powder solution prepared by dispersing 5 g of the white magnetic powder per 1 water in water using a dispersant of 20 c.c. per 1 water was prepared as described in Example 1. When sprayed on the surface of a magnetized object to be inspected in the same manner as in the case, under white light, defects approximately 5 microns deep on the surface of the object to be inspected are clearly indicated by a white defect indicator pattern. It was confirmed with the naked eye that

Example 3 Polyethylene wax (molecular weight 400, viscosity 0.8cP
(90°C)) and 5 parts of trioctyl phosphate are placed in a stainless steel tank, heated to approximately 90°C under stirring to melt, and the average particle size is 10μ or less.
Add 10 parts of 4μ pure iron powder and 10 parts of Bengara and stir for about 30 minutes using a homomixer to obtain a viscosity of 125 cp.
A heated melt (measured at 90°C using a B-type viscometer) was prepared.

Next, using a rotating disk-type atomizer, the heated molten material is heated to a temperature of about 100°C near the atomizer inlet.
At a temperature of approximately 80℃ near the rotating disk, a temperature of approximately 17℃ near the atomizer outlet, and a rotation speed of the rotating disk of 32,000 rpm, each pure iron powder particle is sprayed into the air and cooled naturally. 98 parts of red magnetic powder having a particle size of less than 15 microns and an average particle size of 7 microns, coated with a mixture of colored polyethylene wax and trioctyl phosphate (confirmed using an optical microscope x400), was obtained.

When the obtained red magnetic powder was used without being classified and subjected to magnetic particle flaw detection under exactly the same conditions as in Example 2, under white light, the depth existing on the surface of the object to be inspected was approx. It was confirmed with the naked eye that the 5 micron defective area was clearly indicated by the red defect indicator pattern.

〔Effect of the invention〕

According to the present invention, pure iron powder or stainless steel powder with a particle size of 20 microns or less and an average particle size of about 5 microns is used as the magnetically conductive powder, and a hot melt material is used as the binder, and the powder is granulated by a spray drying method. Colored magnetic powder can be produced without peeling or falling off of the coloring material.

Further, due to the use of pure iron powder or stainless steel powder as the magnetically conductive powder, it is possible to provide colored magnetic powder for magnetic particle flaw detection that is excellent in color or fluorescence brightness and magnetic sensitivity.

Furthermore, since the present invention uses a rotating disk type atomizer as the spray drying means, temperature control and operation during spraying are easy, and granulation can be performed with a high yield.

Claims (1)

[Claims] 1 10 to 60 parts of pure iron powder or stainless steel powder with a particle size of 20 microns or less and an average particle size of 4 to 6 microns as a magnetic conductive powder, 5 to 60 parts of a pigment or fluorescent substance as a coloring agent, and a hot melt material as a binder. 10 to 80 parts of one or more selected from polyethylene wax, atactic polypropylene, and paraffin wax, and chlorinated paraffin, dioctyl phthalate, trioctyl phosphate, tributoxyethyl phosphate, and maleic acid as binding agents. A heated melt of 5 to 30 parts of one or more selected from dibutyl, dibutyl sebacate, and butyl diglycol with a viscosity of 200 cp or less is sprayed into the air using a rotating disk type atomizer, and then naturally cooled and granulated. A method for producing colored magnetic powder for magnetic particle flaw detection, which is characterized by obtaining colored magnetic particles.