US2355940A - Demagnetizing system - Google Patents

Description

Aug. 15, 1944. ZUSCHLAG 2,355,940

DEMAGNETIZING SYSTEM Filed Nov. 25, 1940 \NVENTOR T/ftODO/F 2050/1 AG ATTORNEY5 Patented Aug. 15, 1944 DEMAGNETIZING SYSTEM Theodor Zuschlag, West Englewood, N. J assignor to Magnetic Analysis Corporation, Long Island City, N. Y., a. corporation of New York Application November 23, 1940, Serial No. 366,873

6 Claims.

This invention relates to the demagnetization of magnetic bodies and is directed especially to immovements in demagnetizing systems and sup paratus. Ihe invention is an improvement, for example, on the system disclosed in U. S. Letters Patent No. 2,207,392, granted July 9, 1940.

Products manufactured of magnetic materials such as iron and steel are susceptible to magnetization, and such magnetization in many cases interferes with their satisfactory use. While this is true of articles of any shape it is particularly true of elongated steel and iron products such as rods, bars and tubes.

The unavoidable or inadvertent magnetization of steel or similar products sometimes results as the natural consequence of normal manufacturing processes which mechanically affect or influence the arrangement of molecules in the body or product, or, again, as a consequence of the subjection of the product to one or more mag netic fields at a stage in the process when the material thereof is comparatively fluid and thus susceptible to the influence of magnetic fields. Such magnetic fields may, for example, comprise the normal magnetic field of the earth or artificial fields set up by electrical circuits or apparatus in the neighborhood.

Furthermore, it has become quite common, especially in connection with the manufacture of steel products, to subject them to a testing operation to determine their physical or structural and metallurgical characteristics such, for example, as the existence of strains or flaws. In the course of such testing the steel products are sometimes passed through an electromagnetic field which is likely to leave a certain degree of residual magnetism in the products.

Whatever the source of the residual magnetism in steel or like products it is usually desirable that all traces of such residual magnetism be erased or removed before the material is shipped from the mill. Such undesired residual magnetism may readily be removed as described in my U. S. Letters Patent 2,207,392, and it is the purpose of the present invention to simplify the apparatus disclosed in that patent so that the required equipment may have certain electrical advantages, and be much lighter, more compact and considerably cheaper.

As in the system of the previous patent, the present invention contemplates the subjection of the article to be demagnetized simultaneously to an alternating-current field and to a direct-current field, both suitably controlled, but in the present case by a greatly simplified apparatus as illustrated in the drawing, wherein:

Fig. l is a circuit diagram showing the com nections of all of the essential components of the system;

Fig. 2 is a circuit diagram of an alternative and preferred form of the system illustrated in Fig. 1; and

Fig. 3 is a circuit diagram of a system similar to that of Fig. 1 wherein a different but equiva lent type of rectifier has been substituted.

Referring first to Fig. l, the alternating current supply line i which may be of, say, 120 volts and of any commercial frequency between 25 and cycles, for example, is connectible through a line switch 2 to the demagnetizing system shown above. This system includes an A. C. (alternating current) energizing coil 3, the ter minals of which are connected to the source of A. C. current 2, which in this instance is the line switch. This coil should normally be of sufficient reactance to permit direct connection across the power line at the prescribed voltage. Coil 3 is preferably wound on a diameter large enough to allow the product or body to be demagnetized to be placed within it or to be passed through it, depending upon the dimensions of thebody. A secondary or neutralizing coil 5 is disposed in inductlve relation to coil 3 and so as to be also in inductive relation to the body to be demagnetized. To this end, coil 5 would usuall be wound and positioned to be concentric with coil 3. Coils 3 and 5 together comprise an activator coil assem bly, and coil 5 comprises not only the secondary of an alternating-current transformer of which coil 3 is the primary, but in addition it performs the function of a D. C. (direct current) neutralizing coil, as will be explained below.

Across the terminals of coil 5, as shown in Fig. 1, a polarizing or reversing switch 6 is connected so that the direct-current polarity of coil 5 may be selected at will. The two pairs of contacts of this reversing switch are connected respectively to the anode of a half-wave diode rectifier l and to an adjustable resistor or rheostat 9. The adjustable contact ll of this rheostat is connected to the indirectly heated cathode 15 of rectifier 1, preferably through a fixed current-limiting resistor 8. Anode l4 and cathode l5 of rectifier diode l are connected across coil 5 and are not otherwise coupled to the alternating current source, so as to isolate the rectifier circuit from the alternating current source except by the electromagnetic coupling between coils 3 and 5. The cathode heater filament IU of rectifier tube 7 is preferably connected directly across the A. C. supply line as shown, and may be so connected if the tube be of a type having a suitable heater, such for example, as is found in the type 11726 tube. Of course, if the heater be designed for a lower voltage, it should be coupled to the line by a suitable heating transformer, or in series with a voltage-dropping resistor, in a manner well known in the art. With either arrangement the cathode heater is not connected to the rectifier circuit. If the rectifierbe of the type requiring no supply transformer, the entire demagnetizing sys. tem will operate substantially independently of the frequency of the alternating current source, because, as will be noted from the figures, no ironcored transformers will then be required in the entire system. To this end, the rectifier need not be of the vacuum tube type, but may, for example, be of the copper oxide type which requires no cathode heating current. Such a rectifier is represented in Fig, 3. If a large rectified current output be required, two or more rectifiers of the type chosen may be connected in parallel, as is shown in Fig. 3.

As an illustration of typical apparatus useful in the system above described the following circuit components may be suggested: rectifier tube, type 11726; coil 5, wound to provide about 200 volts A. C. across its terminals; resistor 8, approximately 400 ohms; rheostat 9, approximately 10,000 ohms. In practice it has been found that for most purposes no control is required for the current flowing through the energizing coil I as long as the coil is of sufiicient reactance to restrict the current to a reasonable value. However, in certain instances some control of the current in this coil may be desired and for that reason a variable resistor, or a reactance coil I 3 as shown, may be connected in series with coil 3, but no value need be given for this element.

Referring to Fig. 2 it will be seen that the system illustrated is identical with that of Fig. 1 except that in this embodiment the rheostat of Fig. 1 is replaced by a potentiometer ll. Assuming the same illustrative examples suggested in connection with Fig. 1, the resistance of potentiometer i i may be of about 2,000 ohms.

The operation of the system in accordance with all of the figures is essentially the same. However, referring to Fig. 1, it will be seen that closure of line switch 2 causes alternating current the line frequency to fiow through energizing coil 3, and, by reason of the electromagnetic coupling between coils 3 and 5, an alternating potentia will be developed across secondary coil 5. Due to the unilateral conducting property of half-wave rectifier element 1, this alternating potential causes a unidirectional pulsating current to fiow through the rectifier circuit comprising limiting resistor 8, control rheostat 9, reversing switch 5 and coil 5 which, being disposable in electromagnetic relation to the body i, may be considered as a neutralizing coil. By adjustment of slider I! on rheostat 8 and manipulation of switch 8 there may be established a unidirectional current of such magnitude and direction as to create a unidirectional electromagnetic field equal in intensity and opposite in sign to the resultant field created in the neighborhood. of the body i by all extraneous unidirectional magnetic forces acting on the body. Th A. C. field of coil 3, acting in conjunction with this D. C. field reduces the residual magnetism in the body to a very low value, or substantially to zero.

As just explained, coil 5 functions as the seconda "y of a transformer 3, 5 supplying alternating potential to rectifier 1, and through this same coil 5 fiows no appreciable alternating current but only the rectified current producedby the rectifier I. The alternating-current potential induced in coil 5 is impressed across the cathode and anode of rectifier I and consequently current flows in the series circuit including coil 5 and resistors 9 and 8 connected across the anode and cathode of rectifier I when the alternating potential'renders the anode positive with respect to the cathode but not when it renders the anode negative with respect to the cathode. The resulting rectified current actually comprises a succession of unidirectional current peaks occurring at the frequency of the current in power line I. Although this rectified current is not actually a continuous direct current, the effect of it is to produce a polarized or unidirectional electromagnetic field about coil 5, and for the purpose of the present invention such a field is equivalent to one produced by a continuous direct current.

From the foregoing it will be evident that since the energy source for the rectifier circuit is coil 3 which is also the source of the alternating demagnetizing field, any change or variation in this demagnetizing field or in the current in the circuit of coil 3 will automatically result in a corresponding change or variation in the unidirectional neutralizing field, so that the relative strength of the two fields remains the same even though variations occur in the circuit of coil 3 which cause variations in the demagnetizing field. For example, it frequently happens that, as the body under treatment moves simultaneously through the fields of coils 3 and 5, structural or metallurgical variations in the body react magnetically on coil 3 to produce changes in the magnitude of current in the coil and hence in the strength of its field, and if the rectifier circuit were coupled independently to an energy source the neutralizing field would remain constant while the demagnetizing field varied. This is a serious disadvantage in demagnetizing equipment for the present purpose and is here obviated by deriving the energy for the rectifier circuit solely from the coil which generates the demagnetizing field. The arrangement according to this invention has the further advantage that the single adjustment of current control means i3 automatically effects corresponding adjustments or changes in both the A. C. and unidirectional fields. The relative strength of the two fields can, of course, always be adjusted by means of manual control II.

The operation of the arrangement of Fig. 2 is the same as that of Fig. 1 just described, except that by th use of potentiometer H in the place of rheostat 9, a more satisfactory control of the magnitude of the rectified current is obtainable, especially at the lower values of the ad- Justable range. Such an improved control is particularly desirable in connection with the demagnetization of a body which is weakly magnetized.

The system shown in Fig. 3 is similar to that of Fig. l, the only differences being in the specific type of rectifier employed and in the specific type of current control I3, which in this instance is aresistor requiring no iron core. Consequently the operation of the arrangements of Fig. 1 and Fig. 3 is the same. The rectifier 1 shown in Fig. 3 is represented to be of the copper Also, as units are oxide type, as previously mentioned. above proposed, a plurality of rectifier shown connected in parallel to increase the rec tilled current output. One advantage of this type of rectifier is that it requires no heating current. This feature is ordinarily advantageous only if a rectifier tube of the indirectly heated cathode type capable of operation without a transformer, as referred to, is not available. However, with either type of diode half-wave rectifier the operation is th same, because in either case the rectifier circuit is coupled to the altemating-current power source only by means of the coupling between. the demagnetizing coil and the neutralizing coil.

The demagnetization process may best be carried out in three stages. The first stage comprises merely the placing of a magnetization meter near the body and observing the deflection oi the meter to determine whether or not the body under observation is magnetized. If the body is not magnetized nothing further need be done to that particular body or portion thereof. However, if the magnetization meter indicates a defiection, the body is moved slowly through or past the coils 3, at say a speed of 100 feet per minute with only the energizing coil! energized. This may be accomplished by first setting the switch 8 at an open circuit position. The direction 01' deflection of the magnetization meter at this stage will furnish a guide as to the direction in which the reversing switch 6 should then be thrown. Th third stage of operation comprises passing the body again through the apparatus with power supplied to both the energizing coil 3 and neutralizing coil 5, and adjusting slider I2 until the magnetization meter reads zero.

While the system above described is especially adapted to the demagnetization of elongated bodies such as rods and tubes it may be used in connection with the demagnetization .of bodies of any shape which maybe disposed within the magnetic flelds of activator coils 3, 5. Thus rings,"

in the magnitude of said unidirectional current in said neutralizing coil.

2. In apparatus for demagnetizing a magnetic body movable with respect to said apparatus, the combination which includes a demagnetising coil connectible to a source 01' alternating current, said coil being disposable in inductive relation to said body, a neutralizing coil inductively rel 45. to said demagnetizing coil and disposableinductive relation to said body, said cells being positioned to be in inductive relation simultaneously to the same portion oi said body as said body moves with respect to said. coils, a tifler circuit for producing unidirectional neutralizing current in said neutralizing coll, said circuit including said neutralizing coil and a hall?- wave rectifier element, said circuit being coupled to said source only by means of said inductive relation to said demagnetizing coil, whereby changes in the magnitude of alternating current in said demagnetizing coil resulting from variestions in the magnetic effect of said body on said deinagnetizing coil as said body passes through the iield thereof automatically produce corre sponding changes in said unidirectional current in said neutralizing coil.

3. In apparatus for demagnetizing a magnetic body, the combination which includes aderaagnetizing coil connectible to a source oi alternat o ing current, said coil being of the air-core type disposable in inductive relation to said body, a

neutralizing coil inductively related to said debillets, plates and any other desired bodies may be treated. In such a case it is often desirable that the body to be demagnetized be allowed to remain in a stationary position during the process of demagnetization, in which event the effect of passing the body through the fields of the activator coils may be achieved by gradually and substantially reducing to zero the strength of both the A. C. and. D. C. fields simultaneously, varying the adjustment of reactance II,

as by or in some instances by a simultaneous adjustment oi slider 12 and reactance I3 by means of a uni control device interconnecting the two.

What I claim is: v

1. In apparatus for demagnetizing' a magnetic body, the combination which includes a demagnetizing coil connectible to a source of alternating current; said coll. being of the air-core. type disposable in inductive relation to said body, a neutralizing coil inductively related to said demagnetizing coil and being of the air-core type disposable in inductive relation to said bodyrsaid coils being positioned to be in inductive relation simultaneously to the same portion of said body, and a rectifier circuit for producing unidirectional neutralizing current in said neutralizing coil, said circuit including said neutralizingcoil and a unilateral conducting element, said circuit being electrically coupled to said source only by means of said inductive relation to said demagnetizing coil, whereby changes in the magnitude of the alternating current in said demagnetizing coll automatically produce corresponding changes magnetizing coil and being of the air-core type disposable in inductive relation to said body, said coils being positioned to be in inductive relation to the same portion of said body, and a rec tifier circuit for producing unidirectional hen-:- tralizing current in said neutralizing coil, said air edit comprising in series connection said neutralizing coil, as polarity-reversing switch, a hall wave rectifier element and current-limiting means for controlling the unidirectional current in said circuit, said circuit being coupled tosaid source only by means of said inductive relation to said demagnetizingcoil, whereby changes in magnitude oi the alternating current in said demagnetizing coil automatically produce corrcbody, "netizing coil connectible to a source ing current, control means for changing the mag spending changes in the magnitude of said unidirectional current in said neutralizing coil.

4. In apparatus for demagnetizing a magnetic thecombination which includes a oi alternat nitude oi' alternating current in said coil,'eaid coil being disposable in inductive relation to said,

, body to subject said body to an alternatingwur field, said coils being rent demagnetizing field, a neutralizing coil in ductively related to said 'dernagnetizing coil and relation to said body to unidirectional neutralizing positioned to be in inductive relation to the same portion of said body, and a rectifier circuit for producing unidirectional cur rent in said neutralizing coil, said circuit includ .ing said neutralizing coil and a hale-wave unilateral conducting element, said circuit coupled to said source only by means of said ductive relation to subject said body to a current in said demagnetizing coil produce corresponding changes ii said unidirectional current in coil and in the magnetic ileld pr so as automatically to maintain. strength of said fields tactic-ill 5. In apparatus for demagnetizing a magnetic body, the combination which includes a demagnetizing coil connectible to a source of alternating current, control means for changing the magnitude of alternating current in said coil, said coil being disposable in inductive relation to said body to subject said body to an alternating-current demagnetizing field, a neutralizing coil inductively related to said demagnetizing coil and disposable in inductive relation to said body to subject said body to a unidirectional neutralizing field, said coils being positioned to be in inductive relation to the same portion of said body, and a rectifier circuit for producing unidirectional current in said neutralizing coil, said circuit including in series connection said neutralizing coil, a halt-wave rectifier element and current-limiting means, said circuit being coupled to said source only by means of said inductive relation to said demagnetizing coil, whereby changes in magnitude of the alternating current in said demagnetizing coil automatically produce corresponding changes in magnitude of said unidirectional current in said neutralizing coil and in the magnetic iield produced thereby so as automatically to maintain the relative strength oi said fields substantially constant 6. In an apparatus for demagnetizing a magnetic body, first coil means for producing an alternating-current demagnetizing field, second coil means establishing an alternating-current potential solely by induction from said field, a rectifier, connections between said second coil means and said rectifier whereby to establish a unidirectional current and for conducting a unidirectional current through said second coil means whereby to produce a unidirectional neutralizing magnetic held, and means whereby a given portion of said body may be influenced by both oi said fields simultaneously.

THEODOR ZUSCHLAG.

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