DE2329318A1 - Composite magnetic particles - for crack detection in ferromagnetic workpieces - Google Patents

Abstract

In magnetic particles, contg. ferromagnetic particles in combination with an optically contrasting additive, particularly for magnetic crack testing of workpieces the particles consist of optically contrasting bodies in which >=1 ferromagnetic particle is embedded.

Description

PATENT LAWYERS

· DIPL.-ING. P. WIRTH DI PL.-I NG. G. DAN N EN BERC DR.V. SCHMIED-KOWARZIK DR. P. WEINHOLD DR. D. GUDEL

6 FRANKFURTAM MAIN

CR.ISCHENHtIMElI STRASSC 39

Günther Dibus, Kronberg / Ts. and Heinrich Kolbe, Bad Homburg v.d.H.

Magnetic particles and processes for their manufacture

The invention relates to magnetic particles, the ferromagnetic particles in conjunction with an optical Contrasting addition included.

It is known in the magnetic crack test of ferromagnetic workpieces or the like. Defects such as To make cracks or surface inclusions visible through so-called magnetic powder. The powder particles stick to you magnetize test specimens where the lines of force emerge.

Black iron powder, such as iron carbonyl powder or iron oxide powder, or rust-brown iron oxide powder is used, as well as iron file or iron grinding powder.

As a rule, air or a liquid, for example water, is used as the carrier medium for the magnetic powder and especially oil with suitable physical properties

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shafts and favorable physiological behavior. In the The test will either let the liquid e.g. water with magnetic powder whirled up in it run over the test piece, or the test piece is immersed in a bath of this liquid.

To increase the contrast between magnetic powder accumulations and test body surface is largely the magnetic powder mentioned type used in connection with substances that fluoresce under UV light. The manufacture of such magnetic Particles are made in such a way that iron powder is intimately mixed with a fluorescent substance a binder or the like. Is hardened and then finely ground. In the magnetic particles obtained in this way are ferromagnetic particles of the magnetic powder in an irregular manner - due to the production - with Parts of the fluorescent substance affected. Another known means of increasing contrast is through use light-reflecting particles, e.g. aluminum flakes, in connection with the magnetic powder, however, these particles or flakes are not firmly connected to the ferromagnetic powder particles, but usually only loosely with them You are mixed.

In special cases, e.g. in the stick test, an additional spraying of the test specimen surface with a lighter, preferably white color has recently appeared, whereby the accumulation of magnetic powder on the cracks is no coherent Allow the formation of a layer of paint and thus be recognizable as dark caterpillars on a lighter background. That However, because of the required surface preparation, e.g. sandblasting, spraying on paint is costly, especially the paint has to be removed frequently.

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The most widely used material is therefore the fluorescent magnetic particles described above. They do have the advantage of using UV lighting in a darkened room on light and dark surfaces to become equally visible from test specimens, but the serious disadvantages of the required darkening and the UV lighting of the workplace with all the resulting uncomfortable physical and psychological consequences for the personnel involved in the examination, such as rapid fatigue, eye strain, frequent occurrence of inflammatory irritation of the UV and

particularly areas of skin exposed to IR radiation, etc. As / disadvantageous It also turns out that the cracks found under UV illumination do not or under normal illumination are difficult to see and must therefore also be marked with a color sign. There are also sources of error in the manner of the irregular connection of fluorescent and ferromagnetic substances in the individual particles, the manufacturing process of which is otherwise relatively expensive.

Non-fluorescent magnetic powders have the disadvantage that they are either only light-colored or only dark-colored Surfaces of test specimens are visible, i.e. cannot be used unversely, which means that cracks can be identified to a large extent difficult, imprecise, or in many cases impossible.

It is therefore an object of the invention to provide magnetic particles similar to that described above fluorescent magnetic powder ferromagnetic particles in conjunction with an optically contrasting one Contain additive, which are however easier and more economical to manufacture and which also appear in normal light light and dark surfaces of test specimens are easily recognizable.

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This object is achieved according to the invention by magnetic Particles dissolved, which are characterized in that the particles consist of optically contrasting bodies in the at least one ferromagnetic particle is embedded. The term contrasting optically is also used here as for example with the known fluorescent magnetic particles, the optical contrast effect compared to the Understand the surface of a test body. By the invention Embedding ferromagnetic particles in such an optically effective body is achieved that the magnetic particle has an optically effective side opposite the viewer in every position, in contrast to the irregular side known particles contaminated with fluorescent substances. The optical effect is therefore multiplied and in addition, the embedding in an extremely simple manner by, for example, the most diverse, known per se Process for producing coatings on particles can be carried out. A further advantage results from this, that such a coating or such a casing inevitably has more or less rounded contours and thus easier mobility of the individual particles relative to one another, in the carrier medium and on the test piece surface results. Particles according to the invention are therefore able to follow magnetic lines of force more quickly and more accurately.

A preferred embodiment of the invention is characterized in that the optically contrasting Body contain a colorant, preferably from a signal color or another in the visible Spectral range is made of brightly colored and / or fluorescent substance.

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However, within the scope of the invention it is also possible to use the optically contrasting body instead or in addition to train highly reflective, by appropriate choice of its material and / or its contour. Particularly in the latter respect, an essentially spherical shape is advantageous, the body being made of a transparent material such as glass or plastic, with or without the inclusion of a colorant. For example, glass beads containing ferromagnetic particles can be used in the manner customary in projection screens Find. However, it can also contain magnetic particles and a colorant or the like. Body in the form of microcapsules are produced and used by the methods known for this purpose.

Colorants in the context of the invention are both dyes and pigments, which are preferred in a suitable solvent or, if it is a pigment, in a suitable binder, are added together with the ferromagnetic particles. For the sake of simplicity, in the description and In the claims, the terms binder and solvent are summarized in the term colorant carrier.

Another preferred embodiment of the invention is characterized in that the optically contrasting Bodies are formed from a dispersible substance. This enables the magnetic particles to be manufactured according to the invention as a disperse phase in a dispersion. The dispersible substance is preferably a colorant containing colorant carrier. This gives magnetic particles, which essentially consist of a There are colorant carriers in which the colorant and the magnetic particles are embedded. In particular is

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It is advantageous that the colorant carrier consists of a substance which is used in the manufacture of the magnetic particles is dispersible or finely divided and not solid, such as paraffins, inorganic and organic oils and Fats, thermoplastics and thermosetting plastics, synthetic resins, inorganic glasses etc. Y / ie already mentioned, the magnetic ones can Particles according to the invention are present as microcapsules, the colorant and ferromagnetic particles containing Body is formed from the colorant carrier, which can be completely or partially liquid or pasty.

Particular advantages of the magnetic particles according to the invention, not previously known, are the following:

If, in the case of microencapsulated magnetic particles, the wall thickness of the microcapsule is chosen so that the capsule wall is at the caterpillar formation, i.e. when it adheres to the test specimen, bursts by the forces acting on it, the content can step out. The magnetic particles are grounded by the stray magnetic field present at a crack drawn close to the crack, but not the colorant carrier, so that an overlaying of the ferromagnetic Particles through the colorant carrier with the colorant takes place, so the bead on the free surface in the The color of the colorant used appears. Also non-microencapsulated magnetic particles according to the invention behave in the same way if the colorant carrier enveloping the magnetic particles is liquid and has a viscosity which is in a suitable manner corresponding to the respective surface tensions of the colorant carrier in the carrier medium of the magnetic particles and is selected according to the size of the magnetic particles. The carrier medium can for example be water, and the surface tension then acts like an outer skin that contributes to

Force breaks during a test process under the influence of the magnetic field,

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In the case of magnetic particles according to the invention, their optical contrasting body is formed from a colorant carrier, the specific gravity of the particles can be determined by corresponding V. 'number of the colorant carrier and / or the quantitative ratio between ferromagnetic particles and colorant carrier can easily be chosen so that the specific gravity of the magnetic particles that of the carrier medium in to which they are applied, is approximately adapted. This gives the further advantages of ease of suspension and this results in a low tendency to heel, which only requires a correspondingly low turbulence in the carrier medium during use makes, also better mobility in magnetic Stray field and rapid formation of particularly thick beads, supported by the preferably spherical shape of the magnetic particles.

If in microencapsulated or coated with non-solid colorant carrier magnetic particles according to the invention the colorant carrier is air-drying, the bead that forms in the magnetic field results in a contrast to the previous ones known magnetic particles not easily wiped off and easily visible color marking of the even in daylight Cracks.

Magnetic particles whose optically contrasting body is solid, for example made of glass or a solid Plastic with or without color, also have considerable advantages over the previously known magnetic particles good both in terms of economic production and in terms of use in normal light recognizable caterpillars.

The invention also relates to a method for producing the magnetic particles according to the invention, which is thereby indicates that magnetic particles with a

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Substance are coated, which forms an optically contrasting body. The procedure is preferably such that a colorant carrier containing a colorant is used for coating and according to a colloidal chemical process is applied to the particles. This is a particularly simple, economical and reliable one Way of producing optically effective magnetic particles, i.e. particles in the sense of the known magnetic powder Can be used because they are able to due to ferromagnetic components address magnetic lines of force. The most varied of known colloid chemical working methods can be used are used as they are customary for the production of dispersions, in particular suspensions and emulsions are. According to a preferred embodiment, the procedure is so that the magnetic particles with a Colorants are mixed, that this mixture is then added a colorant carrier and the whole then in a carrier medium optionally containing an emulsifier is emulsified. The thus from disperse phase Magnetic particles formed in the carrier medium can be used directly for a crack test, wherein the carrier medium serves as a means of application. According to the invention, however, one embodiment is also this Process provided in which the magnetic particles dispersed in the carrier medium undergo surface hardening subjected to microencapsulation of the Particles can be achieved.

Another embodiment of the method according to the invention is characterized in that the magnetic Particles are provided with an approximately spherical coating made of glass. Magnetic particles are then obtained of strong reflectivity, the application of which in a magnetic field also without additional colorant, which is, however,

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can optionally be used, results in a clearly visible marking of magnetic lines of force without special lighting would be required.

The preparation of magnetic particles according to the invention however, it can also take place in that the magnetic particles are embedded in microcapsules in a manner known per se that contain a colorant. The use of electrostatic or other suitable coating processes is also possible and suitable within the scope of the invention, to coat magnetic particles with a substance that forms an optically contrasting body.

The following are some embodiments of methods of making magnetic particles in accordance with the invention described:

1. Manufacture of magnetic particles according to the invention after the emulsification process.

1 part by volume of carbonyl iron powder is triturated with 5 parts by volume of color pigment, e.g. Lumogen LT as colorant, to form a homogeneous mixture, to which a viscous oil, e.g. Cetiol, is added as a colorant carrier until a paste is formed. This paste is mechanically emulsified in water mixed with an emulsifier (e.g. Mulgafarin 2% strength can be used as an emulsifier) as a carrier medium. The magnetic particles obtained in this way as the disperse phase of an emulsion are approximately spherical bodies with a dimensional stability that depends on the surface tension with respect to the carrier medium and on the particle radius. These magnetic particles can be used in the carrier medium for crack testing 409881/1075

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find, forming caterpillars at cracks, which are covered with a closed layer of colorant Colorant carriers are coated. The iron powder can expediently be commercially available carbonyl iron, that in the form of spherical particles about 3-7 ^ u in diameter is available.

2. Production of magnetic particles according to the invention according to a variant of the emulsification process.

1 part by volume of carbonyl iron powder is mixed with 5 parts by volume of color pigment, linseed oil until it is viscous added and in 8 to 10 parts by volume of water, which as an emulsifier, for example, approx. 0.001 parts by volume Contains saponin, emulsified by shaking. In example 1, the magnetic ones are also used here Particles obtained as the disperse phase of the emulsion.

3. Production of magnetic particles according to the invention by a combined emulsification and microencapsulation process.

5p carbonyl iron powder and 1p Lumogen LT (luminous color pigment) are mixed by rubbing. Then 3p linseed oil varnish with 3% cobalt siccative is added and rubbed into a paste. This paste is emulsified by shaking in 100 ml of 15% H ₂ O ₂ , in which 3 ρ Mulgafarin has swelled as an emulator and which contains 0.1 p saponin. A sufficient amount of catalase is added to this emulsion in a pressure-resistant container to cause the surface hardening of the ferromagnetic particles, the color pigment, by the oxygen released as a result

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as well as particles containing the colorant carrier (linseed oil varnish and siccative) and therefore a microencapsulation to achieve.

Instead of the colorant carriers mentioned in Examples 1 to 3, paraffins, inorganic and organic fats and oils, thermoplastics and thermosets and synthetic resins can be used. Using of synthetic resins that can be hardened by hardeners, the hardener can be added to the carrier medium (water in the examples) be added, which must be a suitable liquid. In all three exemplary embodiments Carbonyl iron powder is only called because it is particularly strong magnetic force fields. It goes without saying, however, that if appropriate, instead all other ferromagnetic substances can also be used.

Below are some exemplary embodiments based on the schematic, greatly enlarged drawing magnetic particles according to the invention, namely show:

1 and 1a each show a section through a magnetic particle according to the invention with optical contrasting body.

Fig. 2 and 2a each show a section through a magnetic Particles according to the invention containing a colorant.

Fig. 3 is a section through a magnetic

Particles according to the invention in microencapsulated form;

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Fig. 4 is a section through a to be tested

Workpiece and magnetic particles according to FIG. 1 or 2 in the magnetic stray field of a crack.

FIG. 5 is a section corresponding to FIG. 4 with a different type of magnetic particles; FIG.

and

6 again a section corresponding to FIG. 4 in the case of magnetic particles Fig. 3

1 and 1a show basic shapes of magnetic particles according to the invention. Here's in a visually contrasting one Body 2 embedded at least one ferromagnetic particle, as shown in Figure 1, while body 2 also two, as shown in Fig. 1a, or more magnetic ones Particles 1 may contain. The optically contrasting body 2 consists here of glass, for example In addition to colored glass, colorless glass can also be used, as it is essentially due to the reflective properties this material matters.

2 and 2a are examples of magnetic obtained in the emulsification process, for example according to Example 1 above Particles in which the optically contrasting body consists of a colorant carrier in which a Colorant 4 is embedded, and this body has a ferromagnetic particle 1 (Fig.2) or more has such particles (Fig 2a).

3 shows a magnetic particle produced as a microcapsule according to the invention with a ferromagnetic one Particles 1, an optically contrasting body 2 and a skin 5 forming the capsule shell. Also in

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In this case, several particles 1 can be present within a capsule.

4 to 6 show, enlarged and coarsened, the use of magnetic particles according to the invention for crack testing in workpieces 6. Only a section in the area of a crack 9 is shown in each case. 4 shows the arrangement of the particles in the magnetic stray field when particles are used which were obtained as the disperse phase of an emulsion. The ferromagnetic particles then crowd together following the magnetic field, while their soft shell, containing a dye, forms ^{an easily recognizable bead 3 1 in the outer area.} FIG. 5, on the other hand, shows the arrangement in the case of particles with a solid body, for example according to FIG. 1. It becomes clear that in each case the envelope of the ferromagnetic particles designated here by 7 forms the optically decisive outer surface of the bead. The particles 7 can be designed according to FIGS. 1 and 1a or FIGS. 2 and 2a.

Finally, FIG. 6 shows the use of magnetic particles according to the invention, which are present as microcapsules, for example Fig. 3. The ferromagnetic particles

1 are strongly compressed under the effect of the magnetic stray field, so that the shells 5 of the microcapsules burst into individual pieces 8 and the mass 2 ^{1 of} the optically contrasting body 2 is forced outwards. Since this mass 2 ′ usually contains a colorant, the result is again a bead that clearly stands out from the workpiece 6.

The embodiment according to FIG. 1 illustrates the basic principle of the invention, the optically contrasting body

2 of course not to the example above

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cited glass is limited. Glass or more transparent Plastic are only examples of how to achieve optical contrast effects due to reflective Properties of the material, while instead or in addition to coloring agents or fluorescent substances can be used.

Patent attorney:

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Claims (26)

Claims (T) Magnetic particles, the ferromagnetic particles combined with an optically contrasting additive included, in particular for magnetic crack testing of workpieces, characterized in that the particles consist of optically contrasting bodies in which at least one ferromagnetic Particle is embedded. 2. Particles according to claim 1, characterized in that the optically contrasting bodies contain a colorant. 3. Particles according to claim 2, characterized in that the coloring agent is a signal color. 4. Particles according to one of the preceding claims, characterized in that the optically contrasting body contain a fluorescent substance. 5. Particles according to one of the preceding claims, characterized in that the optically contrasting body are highly reflective. 6. Particles according to one of the preceding claims, characterized in that the optically contrasting body are substantially spherical. 7. Particles according to claim 6, characterized in that the optically contrasting bodies are in the form of microcapsules. 409881/1075 8. Particles according to one of the preceding claims,
characterized in that the optically contrasting bodies are formed from a dispersible substance. 9. Particles according to claim 8, characterized in that the dispersible substance is a colorant containing Colorant carrier is. 10. Particles according to claim 9, characterized in that the colorant carrier is a paraffin. 11. Particles according to claim 9, characterized in that the colorant carrier is an oil or fat. 12. Particles according to claim 9, characterized in that the colorant carrier is a plastic. 13. Particles according to claim 9, characterized in that the colorant carrier is an inorganic glass. 14. Particles according to claim 9, characterized in that the colorant carrier is air dry. 15 · Particles according to one of the preceding claims, characterized in that the optically contrasting bodies are present as a disperse phase of a dispersion, the individual body containing the ferromagnetic particles or particles embedded in a colorant carrier containing a colorant. 16. Particles according to claim 15, characterized in that the colorant carrier is an emulsifiable substance. 409881/1075 17. Particles according to one of claims 8-16, characterized in that that the dispersible substance is at least partly in a viscous state. 18. Particles according to one of claims 15-17, characterized in that that the dispersible substance of one by its surface tension in the dispersant and viscosity determined by the size of the magnetic particle. 19. Particles according to one of the preceding claims, characterized characterized in that the quantitative ratio between ferromagnetic particles and the substance of the embedding them optically contrasting body is dimensioned for a specific weight of the magnetic particles, which is the one of these particle-absorbing carrier medium comes close. 20. A method for making magnetic particles according to one of the preceding address, characterized in that the magnetic particles are coated with a substance that forms an orcisch contrasting body. 21. The method according to claim 20, characterized in that a colorant carrier containing a colorant is used for coating and by a colloid-chemical process is applied. 22. The method according to claim 21, characterized in that the magnetic particles mixed with a colorant that A colorant carrier is added to this mixture and the whole is then added to one, optionally containing an emulsifier Carrier medium is emulsified. 409881 / Ί075 23 · The method according to claim 22, characterized in that the particles dispersed in the carrier medium one
Be subjected to surface hardening. 24. The method according to claim 20, characterized in that the magnetic particles with an approximately spherical Covering made of glass can be provided. 25. The method according to claim 20 , characterized in that the magnetic particles in a known manner
be embedded in microcapsules containing a colorant. 26. The method according to claim 20, characterized in that the magnetic particles electrostatically with a
a colorant-containing substance can be coated. Godparents 409881/1075