DE102008048592B4 - Adjustable hand magnet - Google Patents

Abstract

Device (1) for non-destructive material testing with a magnetization arrangement (2a, 2b, 2C, 2d) which can be adjusted between an active position and a passive position
- At least one magnetizable element (10a, 10b, 10c, 10d, 11a, 11b, 11c, 11d, 12, 13, 14, 15, 16) and
At least one permanent magnet (3, 4, 5, 6, 7)
comprising at least one permanent magnet (3, 4, 5, 6, 7) and at least one magnetizable element (10a, 10b, 10c, 10d, 11a, 11b, 11c, 11d, 12, 13, 14, 15, 16) in such a way can be adjusted relative to one another that an external magnetic field strength of the magnetizing arrangement (2a, 2b, 2e, 2d) is variable between a minimum value associated with the passive position and a maximum value associated with the active position.

Description

The The invention relates to a device for non-destructive Materials testing.

The Materials testing represents a central measure for quality assurance in connection with modern production methods. For new components, Materials or manufacturing processes is a review of required material properties just as essential as in the current production of proven products, as every manufacturing process brings a certain error rate. In addition to the destructive material testing, at the workpiece damaged is and therefore only for random sampling is suitable, in particular the non-destructive material testing has significance. This has the advantage that the tested workpiece is undamaged after the test and can be used. For one, this will cost saved, on the other hand it is possible the quality a particular workpiece to consider, which actually after that is used.

A possible Weak point of workpieces are cracks in the material. Initially, such cracks can be dimensions of a few microns, so they are invisible to the naked eye. The same applies to Cracks that are below the surface of the workpiece lie. A proven Procedure, with which also such small superficial or at least near the surface To detect cracks in ferromagnetic materials is magnetic particle inspection.

in this connection will be the to be tested workpiece magnetized at least in a partial area. The magnetic field lines in this case run essentially in the region of the surface of the workpiece under the surface and parallel to this. However, if the workpiece has a crack, so The field lines are due to the much lower magnetic permeability of there existing medium (typically air) displaced from the crack and come out of the surface out. To make these stray fields visible, the surface of the workpiece colored Applied iron powder. This can be colored fluorescent or in a color that contrasts with the respective surface (eg black on white). Possibly. must be the surface therefor also colored become. The application can be either in a wet process, with oil or water as a powder carrier, or dry. By emerging from cracks from the surface Magnetic field lines there is an accumulation of iron particles, which also with mere Eye is visible. In this case, fluorescent particles by means of UV radiation made more visible.

To The prior art is used to magnetize the workpiece either an electromagnet or a permanent magnet used. In both make the magnet must be practically directly on the surface of the workpiece be set up, as well as distances lead by a few millimeters that part of the field lines does not penetrate into the workpiece, whereby the test result significantly impaired becomes. However, the two devices mentioned have considerable Disadvantage. Permanent magnets, the one sufficient for carrying out the method field strength supply, develop in the immediate vicinity of the workpiece attractions up to over 100 N, whereby a controlled application to the surface of the workpiece and in particular peeling after the end of the testing process almost impossible are. In the worst case it can even be damaged here the surface come. It should also be remembered that the handling of a strong permanent magnet generally brings problems, such. B. unwanted attraction nearby objects or impairment from magnetic storage media such as check cards.

Adjustable magnets are, for example, from the documents US 2 479 363 A . FR 775 082 A . US 5,382,935 A . DE 27 25 306 A1 and DE 41 02 102 C2 known from the documents, in particular the DE 41 02 102 C2 known permanent magnets are designed to change the magnetic strength rotatable. For controllable devices for Magnetpulverprüfung previously controllable electromagnets were used, as for example. From the DE 82 06 754 U1 are known. In the form adjustable permanent or electromagnets are from the DE 17 82 986 U , of the DE 18 21 047 U and US 2 479 363 A known.

through of an electromagnet, the required magnetic field, although in principle set in a wide range and above all as needed be switched on and off. However, to generate the necessary field strengths comparatively strong currents required, which in turn leads to corresponding active power. Therefore are such devices can only be operated by means of mains supply, what their application possibilities severely limits. On the one hand, there are only locations with suitable power supply possible, on the other hand, the device is through the power cord bad to handle.

In front It is an object of the invention to provide a device for magnetic particle testing which is easy to handle.

The Task is solved through a device for non-destructive Materials testing according to claim 1 and by a method according to claim 17. Advantageous Further developments of the invention are described in the dependent claims.

The Device according to the invention comprises In this case, a magnetizing arrangement which is between an active position and a passive position is adjustable. The term "magnetizing arrangement" denotes Here, an arrangement which is designed to be a ferromagnetic Magnetize material, which is thus capable of an external magnetic field to create. As an external magnetic field In this case, a magnetic field is referred to, at least in some areas exits the Magnetisieranordnung and thus outside of the same causes magnetic interactions.

The magnetizing arrangement in this case comprises at least one magnetizable element and at least one permanent magnet. As a magnetizable element in this case each component is referred to, which is at least partially, preferably completely ferromagnetic or ferrimagnetic, that has a magnetic permeability μ _r , which is significantly greater than 1, preferably greater than 10, more preferably greater than 100. Preferred materials for this purpose Ferroalloys and ferrites. There are preferred those materials which are magnetically soft, which thus show a low residual magnetization in the absence of external magnetic field. In this context, a single magnetizable element is rigid in itself. There may be interconnected ferromagnetic components, but these will not be considered hereinafter as parts of a magnetizable element, but as a plurality of magnetizable elements.

When Permanent magnet is here called a component, which also at least partially, preferably completely ferromagnetic or ferrimagnetic is, in which case materials are preferred, the magnetically possible hard, such as bismanol, aluminum-nickel-cobalt, samarium-cobalt or neodymium-iron-boron, the latter being particularly preferred. The basic form of a permanent magnet in the context of the present invention is a dipole magnet with exactly a north and a south pole. In addition, you can but also higher Multipole magnets, in particular quadrupole magnets are used.

Basically it desirable that said magnetic properties in one possible huge Temperature range are given so that the device can be used at all conceivable temperatures is where a workpiece inspection is to be performed. In practice, such testing usually takes place at temperatures take place between -150 ° C and 300 ° C, although in certain cases Even temperatures are conceivable that are outside this range. As the device according to the invention in particular intended for manual handling (although the integration in a robot or the like is readily possible), should the above magnetic properties at least in be given a temperature range, within which to a manual handling is to think, so at least between 0 ° C and 50 ° C, preferably at least between -40 ° C and 80 ° C. Too too non-manual handling to allow the magnetic properties at least in be given a temperature range between -150 ° C and 300 ° C.

At least according to the invention a permanent magnet and at least one magnetizable element so relative to each other adjustable that an external magnetic field strength the Magnetisieranordnung assigned between one of the passive position Minimum value and one of the active position associated maximum value variable is.

in this connection the term "adjustable" describes the possibility a change in position, the controlled brought about can be. The corresponding position change can be done in one rotation, a shift or a combination thereof. If the device a housing, a handle or similar which gives a kind of "frame of reference" is, it is conceivable that at least one permanent magnet or at least one magnetizable element or both with respect to this Reference frames are adjustable. It is conceivable that when adjusting Intermediate positions are adjustable. It can be a continuous one or discontinuous adjustability. The history the magnetic field strength between the maximum value and the minimum value may be different be. The term magnetic field strength refers here primarily in the physical Senses on the H field, measured in amps / meter. Is the magnetic permeability known the respective medium, the magnetic field strength results directly from the magnetic flux density (ie the B-field, measured in Tesla) and vice versa. In this sense, qualitative statements are regarding one of the two sizes the other size transferable.

The external magnetic field strength of the magnetizing arrangement is a field strength which prevails outside the magnetizing arrangement and which results from this, ie a field strength of a magnetic field emerging from the magnetizing arrangement. This magnetic field is used in the material testing to magnetize a workpiece to be examined. The maximum value is the largest among all values which the magnetic field strength can assume in all possible positions of the magnetizing arrangement, that is, it corresponds mathematically to the global maximum. Accordingly, the minimum value is the smallest among all possible values, corresponding to the global minimum. The terms of the maximum and minimum values here and in the following always refer to the magnitude of the field strength, ie, not field strengths are understood as "positive" and "negative" depending on the orientation.

By the relative displacement of permanent magnet and magnetizable Element takes a remagnetization of the latter. For example can use a rotatably mounted, rod-shaped permanent magnet whose two poles are in the passive position of a magnetizable Element are spaced while in the active position, a pole towards the magnetizable element is aligned and a small distance to this, for example 0.5 mm, has. In the passive position is a comparatively weak Magnetization of the magnetizable element given, in particular the magnetic field strength on the side facing away from the permanent magnet side comparatively weak be. In the active position, however, by the magnetic pole, the is aligned with the magnetizable element, a strong magnetization, a high field strength forms in the magnetizable element, which is also outside of the same. With a suitable geometry this works magnetizable element here as a kind of "conductor" and "amplifier" of the permanent magnet outgoing magnetic field. In the present case, for example the magnetizable element stretched-cylindrical and formed the permanent magnet arranged on an end face, so is in the active position a high field strength at the opposite face determine.

In In the case described, the magnetization is in the passive position weaker as in the active position. However, this is not necessarily the case Case. Rather, the direction of magnetization is essential, d. H. the course of the field lines within the magnetizable Element. In a preferred embodiment of the invention in the passive position the field lines of two poles opposite polarity in a sense "short-circuited". For this are at least one permanent magnet and at least one magnetizable Element so relative to each other adjustable that in the passive position at least two magnetic poles of opposite polarity to the magnetizable element are arranged adjacent, and that in the active position of only one of the two poles to the magnetizable element is arranged adjacent, while the other pole spaced from the magnetizable element is. This is explicit the possibility included that said poles to different permanent magnets belong.

is a pole disposed adjacent to a magnetizable element, so The field lines occur practically directly from the magnetic pole into the magnetizable one Element on or vice versa. Are two magnetic poles of opposite polarity arranged adjacent to the magnetizable element, so run the Field lines within the same from one pole to another, they are virtually short-circuited. That is, the magnetization may be local relatively strong, but the field lines are again directly to the magnet back and it steps outward towards only a small magnetic field strength. Is in contrast in the Active position only one of said poles to the magnetizable Element arranged adjacent while the other pole spaced from the magnetizable element is, then the field lines, as already described above, by this directed and reinforced, so that outward, So z. B. on a side facing away from the magnet side of the magnetizable Elements, a high field strength exit. The effect will be natural even stronger, if in the active position at least one other pole of the same polarity is arranged adjacent to the magnetizable element.

In This connection determines the question to which magnetic pole a certain area of the surface of the permanent magnet belongs, accordingly the general definition according to whether the magnetic field lines in this area from the surface exit or enter. So every pole is a magnet Of course a broad area and not a single point. Has preferred at least a portion of a pole referred to as being "adjoining" a distance of less than 1 mm, more preferably less than 0.7 mm, more preferably less than 0.4 mm, to the surface of the magnetizable element. In contrast, each part has preferred a pole that is considered "spaced arranged "designated is, a distance of at least 1 mm, more preferably at least 5 mm to the surface of the magnetizable element. At this point it should be noted that a minor one Deviation from this preferred embodiment is not critical. So leads it is still too useful, albeit worse results, if a small subarea, z. B. 5%, the other pole not in above "sensed", but is arranged adjacent to the magnetizable element.

In principle, there are no restrictions with regard to the geometry of the magnetizable element (s) within the scope of the invention. However, since the magnetization of the workpiece to be examined can be optimized by contacting as closely as possible, in a preferred embodiment of the invention at least one magnetizable element is designed as a contact element for placement on a surface of a workpiece. Such a contact element has at least one surface which allows the most direct possible placement on a workpiece surface. These Surface will therefore be flat for flat workpiece surfaces. For curved surfaces, an area with correspondingly opposite curvature may possibly be provided. Of course, such a surface must also allow an approach to the workpiece and is therefore usually located on an outside of the device. Preferably, the surface is exposed, since already thin layers of paint, plastic o. Ä. can affect the contact with the workpiece. In addition, for a further improved adaptation to the surface geometry of the workpiece, at least one contact element can be removable or exchangeable.

Around a usability of the device for as possible size Variety of workpieces to ensure, is preferably at least one contact element for adaptation to a Surface geometry of the workpiece adjustable. A corresponding adjustment can be in a pan or move. This is usually when interacting makes sense at least two contact elements, as in this way their Distance and / or angle can be adjusted to each other. So can two contact elements by pivoting at least one of the two with their contact surfaces either (for plane Surfaces) parallel or (for curved or angled surfaces) be set at an angle to each other. It is also conceivable that a contact element extended by moving to some extent is to engage in a recess in the workpiece surface.

Out In the prior art, the horseshoe shape for electromagnets as well as for permanent magnets known. Also in the present invention, this form, in in a sense two polarities be redirected in one direction, prefers. For this purpose, the device comprises two horseshoe-shaped magnetizable elements and a permanent magnet disposed therebetween. One at least approximately Mirror-symmetric arrangement is preferred, wherein each of the magnetizable Elements roughly L-shaped is formed so that it forms one half of the horseshoe. The however, both magnetizable elements do not abut each other; Rather, a permanent magnet is arranged between them. This can be combined with another magnetizable element, which opposite the L-shaped Elements is movable. However, the permanent magnet is preferred itself movable and is in at least one position of the L-shaped elements at most separated by a gap of 1 mm (or less). The magnet can be mounted displaceably, but it is preferably rotatable stored. A design that in a special way to a rotation adapted is that of a cylinder, being the separation plane runs between the poles through the axis of symmetry of the cylinder and the latter coincides with the axis of rotation.

Next Magnetizing arrangements which are simply horseshoe-shaped, so to speak "two-legged", can also three- or four-legged versions be used. The latter, the z. B. with electromagnets also As cross magnets are known, can for example, four L-shaped include magnetizable elements. Here are each two L-shaped elements opposite each other and together form a hoof-shaped senform. The two "horseshoes" are here across from rotated each other by 90 °. Leaves accordingly made up of three L-shaped ones Build elements a three-legged arrangement. Between the magnetizable Elements in the area where these adjoin one another can be one Permanent magnet be rotatable, depending on the orientation the individual magnetizable elements magnetized. Opposite the bipedal arrangement, although magnetic fields of variable strength, but firmer Alignment allowed, has such a three- or four-legged arrangement additional Advantages because cracks that are at an angle of about 30 ° or less to the magnetic field direction, are hereby better detectable. On a u. U. required turning, as if necessary in a two-legged Arrangement is required, can be dispensed with. This is why because a three- or four-legged arrangement magnetic fields different Alignment can produce what the detection of cracks different Location is possible without turning the arrangement.

If also a permanent magnet is sufficient to realize the invention, can the device As already indicated, a plurality of permanent magnets include. This concludes in particular the combination of magnets, opposite to one magnetizable element stationary are, with those that are adjustable, one. For example, in a variation of the example just described another permanent magnet be provided in the nature and dimensions with the first Permanent magnet is identical, but not rotatable, but across from the L-shaped Stationary elements is arranged. Will now the first magnet with the second parallel aligned, which corresponds to the active position, so there is a high field strength in each of the magnetizable elements leading to the ends of the horseshoe is redirected. The first magnet becomes antiparallel by rotation aligned with the second magnet, which corresponds to the passive position, in each case the field lines between the south pole of the one and the north pole the other one over a magnetizable element shorted, bringing at the ends the horseshoe only a small field strength occurs.

As already stated, an adjustment of a permanent magnet by displacement exercise and / or by rotation. Here, however, the rotation is preferred. This has two main advantages. First, the rotation represents a space-saving movement; when the magnet rotates about an axis of symmetry, it always occupies the same space. This makes it possible to make the magnetizing device and thus the entire device more compact. The second advantage arises when a periodic adjustment between the active position and the passive position is to be made. This is necessary if magnetic fields are to be generated with the device according to the invention, as is possible in the prior art only with electromagnets. In a shift of the permanent magnet must be constantly reciprocated in this case, which is possible, but energetically inefficient and can lead to unwanted vibrations. In contrast, in an adjustment by rotation of the magnet can be kept simply in rotation, whereby the periodic adjustment takes place. Here are no acceleration forces, but only forces due to friction and magnetic interaction.

One Periodic adjustment can basically by simple manual " and switching ", however, this is not true at frequencies above a few hertz possible. Therefore, the device includes preferably means for periodically adjusting between the active position and the passive position. Such remedies can be in the simplest form be operated manually. So z. B. a hand crank available be that attached to a simple transmission gear is coupled. In this way, z. B. in the case of a translation from 1: 5 with a turn of the hand crank with 1 U / sec a turn a permanent magnet with 5 U / sec done. Alternatively, a Connection point for be provided an external drive. So could in the simplest case the End of an axis, either directly or via a translation to the Magnetisieranordnung docked to the outside of the device accessible be to connect to this the drill chuck of a cordless screwdriver. Herewith become higher Frequencies accessible as by a manual operation and it can more accurately adhere to a frequency become. The means for periodically adjusting can in any case a transmission and, if the adjustment is made by moving, a connecting rod include. By the periodic adjustment, it is possible with the device according to the invention alternating fields to produce, which in the prior art only by means of a can be generated by alternating current operated electromagnets.

advantageously, includes the device motor means for adjusting the Magnetisieranordnung. These are particularly useful when a periodic adjustment done should, since they are an adjustment with higher frequencies (eg. 10 Hz or more), the device independent from an external drive is. About that can out Such motor means serve as a servo motor, creating a power-saving and precise Adjustment of the magnetizing arrangement is possible. This is special interesting, if intermediate positions between the active position and the passive position should be set. A user can do this via a Control element, a switch or regulator, a setting of Choose magnetization arrangement, which is controlled by the servo motor. The motor means can consist of one or more motors. You can use the magnetizer arrangement directly or via drive a gearbox.

To In the state of the art, the magnetic particle testing method is either static Magnetic field or an alternating field with a frequency of usually 50 Hz, ie the frequency of the mains voltage used. It has however, shown that sometimes a better picture of Achieves material defects, when other frequencies are used. Furthermore, the optimal Frequency depends on the material and possibly also on the geometry of the workpiece. Therefore is in a further development of the device according to the invention, the magnetizing adjustable by the motor means with a plurality of frequencies. Here, a controller or switch may be provided with which the User select a frequency can. The frequency can be continuous or discontinuous be adjustable. A frequency choice can be made by experience or by Look up in a corresponding table or by plain Try it out. It should be noted here that the amplitude the magnetic field strength is frequency dependent, not only the nature of the device, but also the one of near located workpiece are decisive. With regard to the frequency range, it has been shown on the one hand magnetic fields with higher frequencies than 50 Hz are advantageous because the magnetic susceptibility of many ferromagnetic Materials only becomes maximum above the mains frequency. Besides However, it should be taken into account that high-frequency fields increased Losses due to eddy currents can bring with it. Because of these considerations it is preferred that the magnetizing arrangement by the motor Medium adjustable with at least one frequency between 1 Hz and 200 Hz is.

Eddy currents can form on the one hand in the workpiece, on the other hand, but also in a magnetizable element. The latter can sometimes be reduced by the fact that a magnetizable element is not made of one piece, but of parts that are firmly connected to each other, but electrically isolated from each other. So can one such element z. B. consist of stacked sheets, which are each provided with an insulating varnish. If the lacquer layer is very thin (eg 0.1 mm or less), it has little effect on the magnetic field, while eddy currents in the individual metal sheets are much weaker than in a single, solid element.

in principle Various types of motors are used as motor means suitable, so for example, internal combustion engines. by virtue of the much easier handling, especially with regard to On and off and speed control, it is preferred that the motor means an operable by means of a battery Electric motor include. As batteries come here in particular Rechargeable batteries that remain for charging either on the device can, if a corresponding charging device is integrated, or can be removable for external recharging.

The Results of the material testing carried out with the device according to the invention depend on it from whether reaches a certain minimum magnetization of the workpiece becomes. If the magnetization is insufficient, no accumulation occurs of the test powder at material defects, whereby u. U. a faultless workpiece would be simulated. at proper maintenance of the device can one workpieces, whose properties are known, based on experience, assume that at a certain frequency reaches a certain magnetic field strength which in turn corresponds to a sufficient magnetization of the workpiece. To one as possible However, it does make sense to ensure the versatility of the device that while the use of the device possibility exists to check if a certain field strength is reached. For this purpose, the device comprises in a further development gauge for the determination of the external magnetic Field strength. Such a measuring device is suitably arranged so that it is close to the surface of the workpiece, when this is contacted, as for the magnetization of the workpiece mainly the magnetic field strength is crucial in this area. The meter can, if only AC fields be measured, as an essential component comprise a coil, in an alternating field induces a voltage. However, it is preferred that the meter includes a Hall probe, as this works much more precise and also in time can measure constant fields.

The from the meter determined values can in certain circumstances be evaluated internally. To give the user a control option However, it is preferable that the device has means for displaying a measured magnetic field strength includes. Such means could be formed differently. It can, for. B. an analog or digital display on which the magnetic field strength - or, in the case of alternating fields whose amplitude - can be read. alternative or in addition this can z. B. at least one control LED be provided which lights up when a manufacturer specified minimum value the magnetic field strength is reached. Also acoustic signals, possibly also a voice output, can used to help the user achieve or not reach a certain field strength display. Vibrationsignals are conceivable, but not preferred as they transfer to the workpiece and thus can falsify the result of the test.

In a further development of the device this includes a control loop, by means of which a frequency einregelbar for generating a predetermined magnetic field strength is. Such a control circuit in this case comprises both a measuring device for measuring the outer magnetic Field strength, as also means for controlling the frequency with which the magnetizing arrangement is adjusted. The control circuit further comprises a control unit, which evaluates the measured values and from this a new frequency value which is passed to the means for controlling the frequency becomes. In this case, the control unit tries a certain minimum value the magnetic field strength to reach. This value is typically specified by the manufacturer, but it is also conceivable that this is entered by the user becomes. Also in combination with a control loop, it makes sense that the device has means for Display of a measured magnetic field strength has, z. B. via an LED, the user over the Reaching or not reaching the given magnetic field strength informed.

Besides can the device different additional Have components that are familiar to the expert. These include z. B. a digital or analog display of the set frequency, a Display for the state of charge of a used battery and an automatic shutdown at longer Non-use of the device. As already indicated, the device can of course a housing, for example Made of plastic material, surrounded by the most components are. In this case, however, it is preferred that contact elements at least as far outside of the housing are located that a direct contacting of the workpiece is possible.

details The invention will be described below with reference to embodiments with reference explained on the figures. This shows

1 a schematic representation of a Embodiment of a device according to the invention for non-destructive material testing;

2 a schematic sectional drawing of the device 1 ;

3a a schematic representation of the magnetizing of the device 1 in the passive position;

3b a schematic representation of the Magnetisieranordnung 3a in the active position;

4a a schematic representation of a second embodiment of a magnetizing in the passive position;

4b a schematic representation of the Magnetisieranordnung 4a in the active position;

5 a schematic representation of a perspective view of a third embodiment of a Magnetisieranordnung and

6 a schematic representation of a perspective view of a fourth embodiment of a Magnetisieranordnung.

That in the 1 and 2 illustrated device 1 for non-destructive material testing can be performed by a user (not shown) with one hand. For this purpose is on a housing 40 made of plastic, which largely surrounds the functional components, a handle 41 formed. There is a switch button on this 42 by which the user the device 1 with one hand on and off. Furthermore, on the outside of the housing 40 a function selector switch 44 and a frequency selector switch 43 appropriate. The function selector switch 44 can be adjusted between a constant field position and an alternating field position. The device works in the constant field position 1 with temporally constant magnetic field, in the alternating field position with periodically varying magnetic field. The frequency of the variation is via the frequency selector 43 adjustable. In this device 1 four frequencies, namely 10 Hz, 20 Hz, 50 Hz and 60 Hz, can be selected. Furthermore, located on the housing 40 an LED 45 which indicates to the user by lighting up that an external magnetic field strength has reached or exceeded a factory preset value of 2 kA / m. This value, which in air corresponds to a magnetic flux density of approx. 2.5 mT, is considered sufficient to magnetize the workpiece to be tested 100 , This is the value prescribed by DIN EN 9934-1 for the tangential field strength directly on the surface of the workpiece.

As in the sectional drawing in 2 is recognizable, is located inside the housing 40 a magnetizing arrangement 2a , This comprises as a core piece a permanent magnet 3 made of neodymium-iron-boron, which is designed as a cylindrical dipole magnet with a diameter of 30 mm. The permanent magnet 3 is between a first magnetizable element 10a and a second magnetizable element 11a arranged, wherein it is rotatably mounted relative to this about its cylinder axis. The mentioned magnetizable elements 10a . 11a are each L-shaped and arranged together horseshoe-shaped. They are with the case 40 rigidly connected. With the L-shaped magnetizable elements 10a . 11a are a first and a second contact element 12 . 13 connected. The contact elements 12 . 13 can be adjusted by rotation, allowing an adaptation to different shaped workpieces 100 can be done. Both the L-shaped elements 10a . 11a as well as the contact elements 12 . 13 consist of soft iron and have a magnetic permeability of about 12000. As in 1 can be seen, protrude the contact elements 12 . 13 at the bottom of the device 1 out of the case 40 out. One of the contact elements 12 . 13 Outgoing external magnetic field strength can be used to magnetize the workpiece to be tested 100 be used.

In the 3a and 3b is the operation of the Magnetisieranordnung 2a shown. 3a shows the Magnetisieranordnung 2a in the liability position. The permanent magnet 3 is polarized perpendicular to the cylinder axis, ie north and south pole 50 . 51 of the permanent magnet 3 each have a semicircular cross section. The border between the North Pole 50 and the South Pole 51 of the permanent magnet 3 is marked by the dashed line. Here is the permanent magnet 3 aligned so that both the North Pole 50 as well as the South Pole 51 at each of the L-shaped magnetizable elements 10a . 11a are arranged adjacent; between the permanent magnet 3 and each of the L-shaped elements 10a . 11a there is an air gap with a width of 0.3 mm. Due to the small width of the air gap, the field lines are in each case via the magnetizable elements 10a . 11a shorted. It occurs at the contact elements 12 . 13 practically no external field strength.

By a rotation of the permanent magnet 3 by 90 °, the magnetizing device 2a in the active position adjusted, what in 3b is shown. Here, based on each of the L-shaped elements 10a . 11a one pole each 50 . 51 arranged adjacent to the magnet, while the other pole is arranged at a distance. Because the L-shaped elements 10a . 11a as well as the contact elements 12 . 13 have a high magnetic permeability, the Magnetic field amplified by this and diverted, so that at the contact elements 12 . 13 a high external magnetic field strength occurs.

As in 2 is recognizable, is the permanent magnet 3 via an axle (not shown) with a first gear 21 connected. This gear 21 can have a toothed belt 23 from an electric motor 20 at which a second gear 22 is attached, be controlled. The gear ratio between the first gear 21 and the second gear 22 this is 2.5: 1. Therefore, the permanent magnet leads 3 two turns off while the engine is running 20 five turns. By the translation, on the one hand, a reduction of the rotational speed is achieved, on the other hand is in this way on the permanent magnet 3 a higher torque available, whereby a frequency-stable rotation can be ensured even with strong Ummagnetisierungskräften.

The motor 20 is via a control and evaluation unit 30 with an accumulator 31 connected by three series-connected lithium polymer elements. For simplicity, the electrical connections between various components are not shown. The accumulator 31 feeds the engine 20 with energy while on the control and evaluation unit 30 the speed of the motor 20 is controlled. The control and evaluation unit 30 is your turn with the frequency selector switch 43 , the function selector switch 44 and the switch button 42 connected. Will the switch button 42 pressed while the function selector switch 44 is in the constant field position, the control and evaluation unit rotates 30 the permanent magnet 3 by means of the engine 20 so that the magnetizing device 2a is in the active position, the button is 42 let go, turns the control and evaluation unit 30 the permanent magnet 3 by means of the engine 20 so that the magnetizing device 2a is in the passive position. Is the function selector switch located 44 in the alternating field position and the switch button 42 is pressed, then turns the control and evaluation unit 30 the permanent magnet 3 with a frequency caused by the setting of the frequency selector 43 is predetermined. This results in a time-periodic adjustment of the magnetizing 2a between the active and the passive position.

At the first contact element 12 is a Hall probe 32 attached, which serves to measure the external magnetic field strength. This is with the control and evaluation unit 30 connected. Join the Hall probe 32 a magnetic field strength of 2 kA / m or more, so sets the control and evaluation unit 30 a voltage to the LED 45 , whereupon this lights up informing the user about the achievement of the necessary field strength. In the case of an alternating field, this is based on the amplitude of the field strength.

In the present case, the Hall probe 32 on the first contact element 12 arranged; Alternatively, it is also conceivable, a Hall probe 32 to attach to a probe or the like, so that a measurement on the workpiece surface between the two contact elements 12 . 13 is possible.

For testing a workpiece 100 According to the prior art, ferromagnetic powder (not shown), which has been fluorescently colored, is applied to the workpiece 100 applied. Then the user guides the device 1 to the workpiece 100 zoom in and put this with the contact elements 12 . 13 on the surface of the workpiece 100 on. Should the workpiece 100 be checked by an alternating field, the function selector switch 44 placed in the alternating field position and the frequency selector switch 43 set a frequency, z. B. 10 Hz. Subsequently, the user presses the button 42 , whereby a periodic adjustment of the magnetizing arrangement 2a with 10 Hz. The motor 20 works in this case with 25 rpm. Indicates a flashing of the LED 45 If the user is told that the required field strength has been reached, the test can continue. If a light stays off, the user can adjust the frequency selector switch 43 another frequency, z. For example, select 20 Hz to repeat the test.

After successful testing, the user leaves the button 42 again, causing the control and evaluation unit 30 the permanent magnet 3 so that turns the magnetizer 2a in passive position. Then the device can 1 from the surface of the workpiece 100 be removed.

As an alternative to the embodiment shown here, the control and evaluation unit 30 also be designed to independently determine a frequency at which a maximum field strength is achieved. If this is at least equal to the predetermined field strength of 2 kA / m, this in turn can be achieved by an LED 45 are displayed. In this alternative design forms the control and evaluation unit 30 together with the Hall probe 32 , the engine 20 and the magnetizing arrangement 2a a control cycle. The frequency selector switch 43 does not apply in this case.

As already stated, the magnetizing arrangement 2a . 2 B . 2c be constructed in different ways. 4a and 4b show an embodiment of a magnetizing arrangement 2 B using a quadrupole magnet 16 , Again, there are again two L-shaped magnetizable elements 10b . 11b present, so that there is a horseshoe-like structure. Between the L-shaped elements 10b . 11b is a cylindrical quadrupole magnet 4 rotatably mounted. Unlike in the 3a and 3b shown Magnetisieranordnung 2a shows this two opposite north poles 52 . 53 and two south poles facing each other 54 . 55 on. The border between two adjacent poles is again marked by dashed lines. Relative to the axis of rotation of the quadrupole magnet 4 opposite the L-shaped elements 10b . 11b there is a U-shaped magnetizable element 14 that, as well as the L-shaped elements 10b . 11b , from the quadrupole magnet 4 separated by an air gap of 0.3 mm width. In the in 4a Passive position shown are the fields of two poles by the L-shaped elements 10b . 11b shorted, while the fields of three poles through the U-shaped element 14 are shorted. In this state, practically no external magnetic field strength is present.

By a 45 ° rotation of the quadrupole magnet 4 becomes the magnetizing device 2 B adjusted to the active position, the in 4b is shown. Here are a first North Pole 52 and a first south pole 54 adjacent to each of the L-shaped elements 10b . 11b arranged, which in turn causes the magnetic field lines through the L-shaped elements 10b . 11b to get redirected. A second North Pole 53 and a second South Pole 55 are adjacent to the U-shaped element 14 arranged, whereby their field lines are short-circuited. This ensures that any disturbing stray field is prevented.

In the 5 illustrated Magnetisieranordnung 2c resembles in its construction strongly in the 3a and 3b illustrated arrangement 2a , However, here are between two L-shaped elements 10c . 11c two cylindrical dipole magnets 5 . 6 arranged. A stationary magnet 5 is coaxial with a rotatable magnet 6 arranged. The stationary magnet 5 is here compared to the L-shaped elements 10c . 11c stationary arranged while the rotatable magnet 6 opposite the L-shaped elements 10c . 11c is rotatably mounted. Here is one pole of the stationary magnet 5 adjacent to one of the L-shaped elements 10c . 11c arranged. In the passive position is the rotatable magnet 6 oriented so that its north pole adjoins that magnetizable element to which the south pole of the stationary magnet 5 adjoins and vice versa. In this way, the field lines of poles with opposite polarity are shorted. An adjustment to the active position is made by a 180 ° rotation of the rotatable magnet 6 in that each pole of the same polarity is adjacent to one of the L-shaped elements 10c . 11c are arranged.

6 shows a further embodiment of a magnetizing arrangement 2d , Here are four L-shaped magnetizable elements 10d . 11d . 15 . 16 arranged in the manner of a cross magnet. Here are a first pair of magnetizable elements 10d . 11d opposite each other and together form a horseshoe shape. Accordingly, there are a second pair of magnetizable elements 15 . 16 opposite each other and in turn form a horseshoe shape, opposite to the first pair 10d . 11d rotated by 90 °. Between the magnetizable elements 10d . 11d . 15 . 16 , in the area where they adjoin one another, is a cylindrical permanent magnet 7 rotatably mounted, whose rotational and symmetry axis with the axis of symmetry of the arrangement of the magnetizable elements 10d . 11d . 15 . 16 coincides. The permanent magnet 7 can be designed here as a dipole magnet or as a quadrupole magnet. The Magnetisieranordnung shown here 2d has the advantage that it is possible to generate magnetic fields not only of variable strength, but also of different orientation, whereby the detection of cracks of different position is possible without turning the device.

There are in addition to the Magnetisieranordnungen shown here 2a . 2 B . 2c . 2d numerous other variations with which the invention can be realized. This concerns the integration of several magnets, of displaceable magnets or the use of magnetizable elements which are not arranged in a horseshoe shape.

Claims (17)

Device ( 1 ) for the non-destructive testing of materials with a magnetizing arrangement which can be adjusted between an active position and a passive position ( 2a . 2 B . 2C . 2d ), which - at least one magnetizable element ( 10a . 10b . 10c . 10d . 11a . 11b . 11c . 11d . 12 . 13 . 14 . 15 . 16 ) and - at least one permanent magnet ( 3 . 4 . 5 . 6 . 7 ), wherein at least one permanent magnet ( 3 . 4 . 5 . 6 . 7 ) and at least one magnetizable element ( 10a . 10b . 10c . 10d . 11a . 11b . 11c . 11d . 12 . 13 . 14 . 15 . 16 ) are adjustable relative to one another such that an external magnetic field strength of the magnetizing arrangement ( 2a . 2 B . 2e . 2d ) between a passive position associated with the minimum value and one of the active position associated maximum value is variable. Apparatus according to claim 1, characterized in that at least one permanent magnet ( 3 . 4 . 5 . 6 . 7 ) and at least one magnetizable element 10a . 10b . 10c . 10d . 11a . 11b . 11c . 11d . 12 . 13 . 14 . 15 . 16 ) are adjustable relative to one another such that in the passive position at least two magnetic poles ( 50 . 51 . 52 . 53 . 54 . 55 ) of opposite polarity to the magnetizable element ( 10a . 10b . 10c . 10d . 11a . 11b . 11c . 11d . 12 . 13 . 14 . 15 . 16 ) are arranged adjacent, and that in the active position of one of the two poles ( 50 . 51 . 52 . 53 . 54 . 55 ) to the magnetizable element ( 10a . 10b . 10c . 10d . 11a . 11b . 11c . 11d . 12 . 13 . 14 . 15 . 16 ) is disposed adjacent, while the other pole ( 50 . 51 . 52 . 53 . 54 . 55 ) of the magnetizable element ( 10a . 10b . 10c . 10d . 11a . 11b . 11c . 11d . 12 . 13 . 14 . 15 . 16 ) is arranged at a distance. Device according to at least one of claims 1 or 2, characterized in that at least one magnetizable element ( 10a . 10b . 10c . 10d . 11a . 11b . 11c . 11d . 12 . 13 . 14 . 15 . 16 ) as a contact element ( 12 . 13 ) for placing on a surface of a workpiece ( 100 ), wherein preferably at least one contact element ( 12 . 13 ) for adaptation to a surface geometry of the workpiece ( 100 ) is adjustable. Device according to at least one of the preceding claims, characterized by two magnetizable elements arranged in horseshoe shape ( 10a . 10b . 10c . 10d . 11a . 11b . 11c . 11d . 15 . 16 ) and a permanent magnet ( 3 . 4 . 5 . 6 . 7 ). Device according to at least one of the preceding claims, characterized by a three- or four-legged arrangement of the magnetizable elements ( 10d . 11d . 15 . 16 ). Device according to at least one of the preceding claims, characterized by a plurality of permanent magnets ( 5 . 6 ). Device according to at least one of the preceding claims, characterized in that at least one permanent magnet ( 3 . 4 . 6 . 7 ) is adjustable by rotation between the active position and the passive position. Device according to at least one of the preceding claims, characterized by means ( 20 . 21 . 22 . 23 ) for the periodic adjustment between the active position and the passive position. Device according to at least one of the preceding claims, characterized by motor means ( 20 ) for adjusting the magnetizing arrangement ( 2a . 2 B . 2c . 2d ). Device according to claims 8 and 9, characterized in that the magnetizing arrangement ( 2a . 2 B . 2c . 2d ) by the motor means ( 20 ) is adjustable with a plurality of frequencies and / or at least one frequency between 1 Hz and 200 Hz. Device according to at least one of claims 8 or 9, characterized in that the motor means by means of a battery ( 31 ) operable electric motor ( 20 ). Device according to at least one of the preceding claims, characterized by a measuring device ( 32 ) for determining the external magnetic field strength. Apparatus according to claim 11, characterized by means ( 45 ) for displaying a measured magnetic field strength. device according to the claims 9 and 11, characterized by a control circuit, by means of which a frequency for generating a predetermined magnetic field strength einregelbar is. Using a device ( 1 ) according to at least one of claims 1 to 13 for magnetic particle inspection. Method for magnetic particle inspection of a workpiece ( 100 ) with a device ( 1 ) according to at least one of claims 1 to 13, comprising the steps of - bringing the device ( 1 ) to the workpiece ( 100 ), - adjusting the Magnetisieranordnung ( 2a . 2 B . 2c . 2d ) in the active position for at least partial magnetization of the workpiece ( 100 ), - adjusting the Magnetisieranordnung ( 2a . 2 B . 2c . 2d ) in the passive position and - Removing the device ( 1 ) of the workpiece ( 100 ). A method according to claim 16, characterized in that after the introduction of the device ( 1 ) to the workpiece ( 100 ) a periodic adjustment between the active and the passive position takes place.