JPH01210854A - Flaw detection of surface of material to be inspected - Google Patents

Abstract

PURPOSE:To obtain a flaw detection method which allows the observation of the defects on the surface of a material to be inspected even by naked eyes and does not impair productivity by coating a colored flaw detecting liquid consisting of a solvent for a polymer consisting of about 0.5-5wt.% film formable polymer, about 0.5-15wt.% pigment and the balance solvent for the polymer on the surface of the material to be inspected and drying the coated film. CONSTITUTION:The colored flaw detecting liquid film consisting of about 0.5-5wt.% film formable polymer, about 0.5-15wt.% pigment and the balance solvent for the polymer is coated on the surface of the material to be inspected having the color different from the color of said liquid and is dried. The presence or absence of the colored part different from the color of the colored film formed in such a manner is then observed. At least one kind of the polymers used as the material for vehicles for paint, for example, polyvinyl alcohol, etc., are used as the film formable polymer. At least one kind of alcohol such as, for example, methanol, are used as the solvent for the polymer according to the kind of the polymer used. For example, at least one kind of titanium white, etc., are used for the pigment.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for detecting defects on the surface of an object to be inspected.

More specifically, the present invention relates to a flaw detection method that allows defects on the surface of an object to be detected, which are difficult to detect with the naked eye, to be detected with the naked eye.

[Conventional technology]

Defects such as cracks and cracks often occur on the surface of molded or processed products made of various resins and metal scraps.
Large defects can be observed with the naked eye, but small defects such as
Pinholes cannot be observed with the naked eye and require observation using a microscope. Therefore, various flaw detection methods that do not require microscopic observation have been proposed, for example, as follows.

(1) The object to be tested is immersed or coated in a mainly aqueous fluorescent penetrating liquid containing a fluorescent dye dissolved therein, so that it penetrates into the defective areas on the surface of the testing object, and then the penetrating liquid adhering to the surface is immersed in or coated with a fluorescent penetrating liquid that is mainly aqueous. In the case of a liquid, it is removed by washing with water) and then irradiated with ultraviolet rays to find the defective area using the fluorescence emitted by the penetrant remaining in the defect area.In the case of this method, the fluorescent penetrant that has been applied removal work,
It requires an ultraviolet irradiation device and a dark room, and is not an easy method due to operational and equipment considerations, and it is not possible to confirm minute cracks, pinholes, etc. that can only be confirmed with a microscope.

(2) A colored solution that easily penetrates into scratches and cracks, mainly a red solution, is coated on the area where the defect is thought to be occurring and allowed to penetrate.After removing the remaining colored solution, a white pigment dispersion is applied. Then, the colored penetrating liquid remaining in the defect area oozes out to the surface, and the defect is detected by coloring the white pigment red etc. This method does not require any special equipment. However, since it requires wiping off the penetrating liquid with a dry cloth, it is not suitable for large-scale inspections.

(3) When a large current is passed through a magnetic object to be tested, or if it is placed in a strong magnetic field and energized, defects such as cracks and cracks on the surface of the object become discontinuous, causing the magnetic field to bend. , electric current leaks and creates a magnetic pole, and when magnetic powder such as iron powder is applied to it, it is attracted.
A method that allows defects that are difficult or invisible to the naked eye to be easily identified. Application of this method is limited to magnetic objects to be inspected.
It also requires large equipment.

[Problem to be Solved by the Invention] The method (2) or (3) above is partially used to detect surface defects in resin molded products, such as tetrafluoroethylene resin molded products and phenol resin molded products. However, the application of these methods has not only been a factor that greatly hinders productivity in terms of work efficiency, but also problems have been seen in terms of accuracy.

The present invention allows you to see defects on the surface of an object that are difficult to observe with the naked eye! ! ! The aim is to provide a flaw detection method that can detect defects without sacrificing productivity.

[Means for Solving the Problems] and [Operation] The flaw detection method of the present invention for the surface of an object to be tested achieves the above objects by using a film-forming polymer of about 0.5 to 5% by weight and a pigment of about 0.5 to 5% by weight. 1
A colored flaw detection liquid consisting of 5% by weight and the balance being a solvent for the polymer is applied to the surface of the object to be flawed with a color different from that, and the coating film is dried, thereby forming a colored part different from the color of the colored film formed. This is done by checking the presence or absence of [9].

A colored flaw detection liquid consisting of a film-forming polymer, a solvent for the polymer, and a pigment is applied to the surface of a resin or metal molded or processed product.

Film-forming polymers include at least one type of polymer used as a material for paint vehicles, varnishes, etc., such as polyvinyl alcohol, polyvinyl butyral, polystyrene, polymethyl methacrylate, and ABS resin. It is used in a proportion of about 0.5 to 5% by weight in the liquid.

Solvents for these polymers include, for example, methanol,
At least one of alcohols such as ethanol, n-propatool, isopropatool, ethers such as methyl cellosolve and cellosolve, hydrocarbons such as toluene and xylene, and ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone. , depending on the type of polymer used.

Further, as the pigment, at least one type of pigment such as titanium white, graphite, carbon black, red bean etc. is used in a proportion of about 0.5 to 15% by weight in the colored wound liquid. The color of the pigment selected is symmetrical to the color of the object to be inspected; if it is a bright color such as white, it will be black-based, and if it is a dark color such as black, it will be white-based. It is preferable.

In the colored flaw detection liquid prepared with the above-mentioned components as essential ingredients, an antisedimentation agent to prevent pigment sedimentation, a viscosity modifier to adjust the viscosity of the flaw detection liquid, etc. can be added as necessary.

When a colored flaw detection liquid is applied to the surface of an object to be tested by dipping or spraying, and the coating is dried, a colored film is formed thereon. At that time, cracks, cracks,
When a defect such as a pinhole exists, the thickness of the film formed in that area tends to become thinner, and the color of the object to be inspected, which is a different color from that of the colored film, appears as a line depending on the defect state. It has been found that there are phenomena that appear in shapes, dots, areas, etc. In other words, by detecting the presence or absence of a colored part that is different from the color of the formed colored film, it is possible to determine the presence or absence of a defect on the surface of the object being tested. It is possible to identify them.

The present invention is based on the discovery that the thickness of the film formed at the defective location becomes thinner, and the following are thought to be the causes of this.

(a) The coating shrinks in the thickness direction and in the coating surface direction as the solvent evaporates.

(b) Paint, which is a colored flaw detection liquid, has entered the gap between the defective parts.

(c) The paint film on the surface gradually dries, but since the solvent in the paint that has entered the gaps evaporates more slowly than on the surface, drying is slightly slower than on the surface.

(d) The coating film on the surface shrinks as it dries, but because the solvent evaporates slowly, the film on the defective area is softer than the film on the surface, and is stretched by the shrinkage of the surface and becomes thinner. Evaporation is accelerated and the material is eventually dried and fixed in a thin film.

In relation to these causes, we investigated increasing the difference in shading in the colored areas, and found that lowering the concentration of the film-forming polymer increases the amount of shrinkage and increases the difference between the thick and thin parts of the film. However, when the limit is exceeded and the temperature is lowered to 1 degree, the detection accuracy decreases as seen in Comparative Example 2 below, and when the amount of pigment is greater than the amount of polymer, the density increases. The difference becomes even bigger. The amount of the film-forming polymer and the amount of pigment in the colored flaw detection liquid described above were selected and determined from this viewpoint.

〔Effect of the invention〕

With the method of the present invention, defects on the surface of an object to be detected that are difficult to detect with the naked eye can be detected with the naked eye! Moreover, even when the object to be tested is a tetrafluoroethylene resin molded product that requires inspection in large quantities, it can be applied without substantially impeding productivity.

〔Example〕

Next, the present invention will be explained with reference to examples.

Comparative Example 1 A cylindrical preformed product of tetrafluoroethylene resin in which graphite is dispersed is subjected to an impact to generate many microcracks, then placed in an electric furnace and fired at 375°C to create a black cylindrical preformed product (inner diameter 21mm, outer diameter 25+m, length 10
0+nm) was obtained.

This cylindrical molded product was immersed in a water-soluble fluorescent penetrating liquid (Taseto Check N-4P, a product of NOF Corporation) for 5 minutes, then taken out and washed in the shower for 10 minutes. Tetrafluoroethylene resin is water-repellent, so if you shake a washed molded product to remove water droplets and irradiate it with a black lamp (ultraviolet irradiation device), you will notice that it has yellow-green glowing linear parts, cracks, and
It was found that there were defects such as cracks.

Large cracks on the surface of the molded product can be seen with the naked eye if you pay close attention, but small cracks, etc., are difficult to see with the naked eye.Up to such areas, the above method illuminates, making it possible to observe the defects, but beyond that. The minute cracks, which could only be seen by observing them under a microscope, did not glow yellow-green.

Example 1 67.5 g of titanium white (titanium oxide) was added to a solution in which 45 g of polyvinyl butyral (Denka Butyral 2000L, an electrochemical product) was dissolved in 887.5 g of ethanol.
was dispersed to prepare a white solution with a total weight of I kg.

Comparative Example 1 in which microcracks were formed in this white solution
A black cylindrical molded article was immersed, immediately taken out and stood on a cloth to dry the coating film. The surface of the molded product was completely covered with a white film, but black lines were partially observed. Therefore, the coating on this part was dissolved and removed with ethanol.
When inspected visually and under a microscope, the areas where black lines were observed included both areas that could be observed with the naked eye and areas that could only be observed using a microscope.

Example 2 In Example 1, when the white solution was diluted 3 times with ethanol and used, the white color was pale overall, but the black lines were clearly discernible.

Comparative Example 2 In Example 1, when the white solution was diluted 15 times with ethanol and used, the black line at the defective area did not clearly appear up to the area visible under a microscope [0].

Example 3 An annular body having a substantially H-shaped vertical cross-section, with an annular rib-like piece integrally extending outward at the center of the outer circumferential side and inward at the upper end of the inner circumferential side. The top and bottom of a black phenolic resin molded product was held in a vise to generate radial cracks. This crack can be visually observed from a height of 50 cm.
If you look carefully under 0W fluorescent light, you can clearly see it.

The same white solution as in Example 1 was prepared by substituting half of the ethanol with methanol. The reason why methanol was used in combination here is that in the case of a phenolic resin molded product with such a complex shape, it may be partially dried. (This is to prevent the brightness of minute parts of cracks from fading). When this is applied to the entire surface of the cracked phenol resin molded product using a brush, as the paint film dries, it becomes grayish-black. A streak appeared. These streaks were clearly observed under the brightness of a 20W desk fluorescent lamp placed about 2 meters away, and cracks were clearly observed when viewed under a microscope.

Claims (1)

[Claims] 1. Approximately 0.5 to 5% by weight of film-forming polymer, approximately 0.0% pigment.
A colored flaw detection liquid consisting of 5 to 15% by weight and the balance being a solvent for the polymer is applied to the surface of the object to be flawed with a color different from that, and the coating film is dried, and the color of the colored film is different from that of the formed colored film. A flaw detection method for the surface of an object to be flawed, characterized by observing the presence or absence of colored parts.