US2403424A - Demagnetizing apparatus - Google Patents

Description

y 1946- v 1'. 'ZUSCHLAG I 2,403,424

DEMAGNETI Z ING APPARATUS Filed NOV. 1, 1943 I I INVENTORQ' m bw, MM

' A TTORNE Y5.

Pateuled July 2,

STATES PATENT QFFECE ZAGSBAM DEMAGNETIZING APPARATUS Theodore Zusclilag, West Englcwood, N. JL, as-

signor to Magnetic Analysis Corporation, Long Island City, N. iii, a corporation of New York Apolication November 1, 134:3, Serial No. 508,525

(Gil ll'5--ill1) 4 Claims. i

it, this application being filed as a continuaticn-in-part of the application which matured to o the last-named patent.

Products manufactured of magnetic materials such as iron and steel are susceptible to roagnctization, and such magnetization in many cases interferes with their satisfactory use. While this 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 oi steel or similar products sometimes results as the natural consequence oi normal manufactur lug orocesses which, mechanically affect or flue-rice the arrangement of molecules in the loody or product, or, again, as a consequence oi the action of the product to one or more mag netic fields at a stage in the process when material, thereof is comparatively fluid and time susceptible to the influence of magnetic Such magnetic fields may, for example, cot. the normal magnetic field of the o ar tiiiclal fields set up li y electrical circuits or a,

in the neighborhood, or a combination 5 products, to on t them a det t sir pnysical or allui teristics such, for e: the existence of strain or flaws, of; such testing steel products are tiirougii electromagnetic likely to leave a certain degree resle or like products it is usually d traces of such r sidual magi or removed the material is slug: is mill. Although such undesired resin 'isiri may readily lee r'rnoved in the in my mentioned patents, t'losc have certain inherent limitations which ourpose oi the present invention to overo oresent invention. makes possible a con sideralcla enlargement of the range of oath the alternating-cu rent and the direct-current vol v appar t s at once more simple to operate, more universally useful, and more economical in use,

iii?

than that heretofore known.

The apparatu of the present invention is illustrated in the drawing, in which is shown an alternating current supply 5 of, say, 120 volts oiconnnercial frequency, such as 60 cycles, which is couriectilile through a line switch 2 to the demagnetizing system shown above. This system includes an C. (alternating-current) energizlug coil the terminals of which are connected to h source of A. 53. current which, for convenience, may be considered as the lin switch 2. This cell should normally be of sufficient react once to permit direct connection across the power line at the prescribed voltage. In the particular embodiment of: the invention here described this coil comprise approximately 860 turns wound diameter large enough to allow the body l, which is to be demagcetized, to be placed within it to be passed through it, depending upon the of the body. Preferably connected in *s with energizing coil is a condenser Ell ed to a capacity value such as to resonate icing coil 3 at the applied line frequem e assumed case, 60 cycles, By thus tunez'iergizing circuit, which includes coil approximately to the frequency of the 5 current, a considerable gain in our e t, hence in the strength of the energizing is simply and economically achieved. across condenser is a bleeder re of a resistance suitable to permit the ge oi condenser ill. The secondary, neutralising, coil 5 is disposed in inductive relation to coil ll so as to be also in inductive relation. to the body to be demagnetized. To this end, soil it should preferably be wound outside of coil positioned to be concentric with coil like. the particular embodiment referred to, secondary coil 5 may be of about 2,000 turns, and of much il tier wire than that with which the coil 3 is wound. Coils 3 and 5 together may preferably be constructed as a unitary coil assembly of the air-core type, of which coil 5 comprises not only the secondary of an alternatmg-current transformer (coil 3 being the primary) but in addition performs the function of a D. C. (direct-current) neutralizing coil, as will be explained below.

A shown in the drawing, a polarizing or reversing switch 6 is connected across the terminals of coil 5 so that the direct-current polarity of coil 5 may be selected as required. The two pairs of contacts of this reversing switch are connected, respectively, to the anode 8 and cathode 9 of a triode rectifier tube 1. This tube may be of type 2A3 or 6A3, for example. Serially connected in the lead between switch 6 and cathode 8 is a switch I! the purpose of which will be described later.

A diode rectifier tube I2 is connected to the terminals of the A. C. current source 2 to furnish an adjustable control potential to the control grid of half-wave rectifier tube 1. To this end the cathode of diode I2 is connected to one terminal ot the A. C. voltage source 2 and the anode 2| of diode I2 is connected in series with a resistor H to the other terminal of source 2. The resistance value of resistor l4 may be about 2,000 ohms. A filter condenser l5, of say 25 microfarads, may be shunted across the terminals of resistor H, as shown. In the embodiment illustrated, resistor I4 is used as a potentiometer and has two adjustments, one of which is a switch l5 selectively connectible to a plurality of taps on the resistor for coarse voltage adjustment, and an adjustable slider I! on the resistor for fine voltage adjustment. The resistor I need not comprise a single element as shown in the draw ing. but may conveniently comprise a rheostat type resistor provided with taps cooperating with a selector switch 16, and connected in series with a potentiometer type resistor having an adjustable slider ll. I'h filaments or cathode heaters l and I3, respectively, of the tubes should, as is well known in the art, be connected to suitable secondary windings of a filament-heatin transformer, the primary of which should be connected to the current source 2.

The operation of this system is as follows: The closing of line switch 2 causes alternating current at the line frequency to flow through energizing coil 3. The value of this current is economically increased by reason of the resonance, or approach to resonance, produced by variable condenser 20 in combination with the inductance of coil 3. Thus, an A. C. energizing field of considerable strength is produced by coil 3. It is important that the strength of thi field be sufficient to effect rapid demagnetization, but it is unimportant if the field is stronger than necessary. Coil 5, being electromagnetically coupled to coil 3 and preferably arranged to be symmetrically spaced in relation thereto, acts as a secondary with re spect to coil 3 by reason of which an alternating potential will be developed across secondary coil 5. Due to the unilateral conducting property of rectifier I this alternating potential causes a unidirectional pulsating current to fiow through the rectifier circuit traced from coil 5 to switch 6, anode 8 of tube 1, cathode 9 thereof, switch l8, switch 6, and back again tocoil 5. This coil 5, being disposable in electromagnetic relation to the body I, also functions as a neutralizing coil. The connection of resistor M in series with rectifier l2 across the power line creates uni-directional current flow through resistor I4, thereby establishing the indicated polarities at the respective terminals of. the resistor. Filter condenser l5 tends to smooth out the pulsations so as to keep the potential difference of the mentioned terminals substantially constant.

Manipulation of the coarse adjustment i5 and the fine adjustment ll of the potentiometer H permits the very accurate control of the negative bias potential applied to grid H with respect to the cathode 9 of tube 1, over a wide range. By this means, in combination with the selection of polarity achieved by reversing switch 6, there may be established a uni-directional current in coil 5 of such magnitude and direction as to create a uni-directional electromagnetic field exactly equal in intensity and opposite in sign to the reultant field created in the neighborhood of body I by all extraneous magnetic forces acting on that body. The A. C. field of coil 3 acting in conjunction with this D. C. field thus reduces the residual magnetism in the body to an extremely low value, or substantially to zero.

As above explained, coil 5 functions as a secondary of transformer 3, 5 supplying alternating-- current potential to rectifier l, and through this same coil 5 fiows no appreciable alternating current, but only rectified current produced by rectifier 1. The alternating-current potential induced in coil 5, being impressed across the anode and cathode of rectifier 1, produces a flow of current in the circuit including coil 5 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. l'hus the rectifier passes either one half or the other half of the cycles, depending upon the position of switch 6. The rectified Zillllut flowing; in coil 5 actua ly comprises a succession of uni-dint, it current peak occurring at the frequency of the current in power line I. Although this rectified current is therefore not actually a continuous direct current the effect of it is to produce a polariZecl or uni-directional 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 of 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 causes 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 clemagnetizing equipment for the present purpose, and is here obviated by deriving the energy for the rectifier circuit solely from the coil which generates the dernagnetizing held (the electron energy from cathode Hl being disregarded). Similarly, when the voltage of the power line I fluctuates, relative strength of the alternating-current and directcurrentfields with respect to thebody will re.-

control potential applied to grid H of rectifier tube I is derived directly from rectifier I: which in'turii is energized by the same alternating 01.11: rent source. The relative strength of the .A, C.

with finer adjustment I1.

merely the placingof a magnetization meter near meter to determine whetherand to what degree the body under observation is magnetized. Meters suitable for this purpose and'methods for using them are described in more detail in my men-:

tioned patent. If the body is not magnetized,

nothing-further ne dbeuone to that particular y n is moved slowly through or past the coils 3 and 5,

circuit position. The direction of deflection of the magnetization meter at this stage will fursupplied to both the energizing coil 3 and the neutralizing coil 5 by closing switch I8 and adjusting tap switch l6 and finer adj stment I1 until the magnetization meter reads zero. Under some circumstances, as for example when the ficient to block entirely the output current from tube 1. In such event the switch It may remain closed during the entire operation, if desired.

Should a neutralizing field of greater strength i than that provided by a-single triode' rectifier tube of the types above mentioned be required, 1 two or more such tubes may be connected in parsuccess.

From the foregoing description of a preferred I embodiment of the invention and of the operation thereof it will be evident that a precise control of the strength of the neutralizing field can be readily obtained over a large range of field strength, and that the apparatus of the invention may without any structural change whatever, be satisfactorily employed on power supply lines which diifer'considerably as to voltage or frequency or both. Furthermore, the apparatus is, without change, adapted to the successful demagnetization of bodies of a wide variety of types and shapes and of any dimensions, so long as the bodies, or required portions thereof, can be symmetrically disposed within the m netic fields of coils 3 and 5. Rings, plates, billets and any other shapes and types of magnetizable bodies may thus be satisfactorilytreated. j What is claimed is: i

1. In apparatus for demagnetizing'a'magnetic mainsubstantially constant, first, for the rea--- son above described, and second, because the' 'and D. C. fields can, of course, always be adjusted by means of tap switch IS, in conjunction The demagnetizingprocess best be carried out in three stages. The first sta e requires the body and observing the deflection of. the

on thereof." However, it the mag-l netization meter indicates a deflection, the body;

- at say a speed-of 100 feet per'minute, with only the energizing coil '3 energized. This may be accomplished by setting-the switch [8' in its open nish a guide as to the direction in which the reversing switch 6 should-then be thrown. The 30 third stage of operationoomprises passing the body again through the apparatus with power body 4 is of fairly small size, the grldbias avail- 1 able through controls l6 and I] may be suftype of rectifier can be substituted with equal body movable with respect to said apparatus, the combination which includes a demagnetizing coil connectible to a source of alternating current,

said coil being disposable in inductive relation to 5 said body, a neutralizing coilinductively related to said demagnetizing coil and disposable in in-- ductive relation to said body, a rectifier tube having an anode, acontrol grid and a cathode,

said coils being positioned to be in inductive rela- 10 tion simultaneously to the same portion of said body as said body moves with respect to said coils. a rectifier circuit for producing unidirectional neutralizi'ngcurrent in said neutralizing -coil,isaid circuit includingsaid neutralizing coil and a half-wave rectifier including the anode and cathode of said tube, said circuit being coupled to said source only by means of said inductive relation tolsaid demagnetizing coil, where-' by changes in the magnitude of alternating cur- 0 rent in said. demagnetizin'g coil resulting from variations in, the magnetic effect of said body on said demagnetizing coil as said body passes throughthe field thereof automatically produce corresponding changes in said unidirectional cur- 5, rent insaid neutralizing'coil, a second rectifier,

a resistor connected in series with said second rectifier-f across said source, connections from the cathode and control grid of said half-wave rectifier tube to said resistor, whereby a bias potential derived from the second rectifier is impressed,

on said control grid, and, means for adjusting said bias potential. i 2. In apparatus for demagnetizing a magnetic body, the combination which includes a demagnetizing col-l connectible to a source of alternating current,.said coil being disposable in'inductive relation to said body, a'neutralizing coil inductively related to said demagnetizing coil and disposable in inductiverelation to said body, said 49 cells being positioned to be in inductive relation simultaneously to the same portion of said body,

a rectifier tube'having, an anode, a control grid and a cathode, a rectifier circuit for producing unidirectional neutralizing current in said neu-. 'tralizing coil, said circuit including said rieutralizing coil and a half-wave rectifier including the anode and cathode of said tube, said circuit being coupled to said source only by means of said inductive relation to said demag 50 netizing coil; whereby changes in the-magnitude of alternating current in said demagnetizing coil resulting from variations in the magnetic effect f of said body on said demagnetizing. coil when said body is in the field thereof automatically producecorresponding changes in said unidirec tional current in said neutralizing coil, a diode rectifier, a resistor connected in series with. saiddiode rectifier across said source, connections from the cathode and'control gridpf said hattwave rectifier tube to said resistor whereby a bias potential derived from said diode rectifier is impressed on said control grid, and variable,

contact means on said resistor included in at least one of said connections for adjusting said bias potential, whereby the strength of said domagnetizing field may be accurately adiusted' over a wide range.

i 3. In apparatus for demagnetizing a magnetic body, the combination which includes a demag- 7 netizing coil connectible to a source of alternating current, said coilbeing disposable in inductive relation to said body, a condenser connected in series with said coil, said condenser having a capacity such as at least approximately to resonate said coil with the frequency of said source,

7 v a bleeder resistor connected in shunt to said condenser, a neutralizing coil inductively related to said demasnetizing coil and disposable in inductive relation to said body, said coils being positioned to be in inductive relation simultaneously to the same portion of said body, a rectifier tube having an anode, a control grid and a cathode, and a rectifier circuit for producing unidirectional neutralizing current in said neutralizing coil, said circuit including said neutralizing coil and a half-wave rectifier including the anode and cathode of said tube, said circuit being coupled to said source only by means of said inductive.

relation to said demagnetizing coil, whereby changes in the magnitude 0! alternating current in said demagnetizing coil resulting from variations in the magnetic eflect of said body on said demagnetizing coil when said body isin the field thereof automatically produce corresponding changes in said unidirectional current in said neutralizing coil, a second rectifier, a resistor connected in series with said second rectifier across said source, connections from the oathode and control grid of said hall-wave rectifier tube to said resistor, whereby a bias potential derived from the second rectifier is impressed on said control grid, and means for accurately adjusting said bias potential.

4. In apparatus for demagnetizing a magnetic been, the combination which includes a demagnetlzing coil connectible to a source 01' alternat-- ing current, said coil being of the air-core type disposable in inductive relation to said body, a condenser connected in series with said coil, said condenser having a capacity such as at least approximately to resonate said coil with the ire- 8 quency or said source, a bleeder resistor connected in shunt to said condenser, a neutralizing coil inductively related to said demagnetizing coil and being the air-core type disposable in inductive relation to said body, said coils being positioned to be in inductive relation to the same portion or said body, a rectifier tube having an anode, a control grid and a cathode, a rectifier circuit (or producing unidirectional neutralizing current in said neutralizing coil, said circuit comprising in series connection said neutralizing coil, a. polarity-reversing switch, and a hall-wave rectifier including the anode and cathodeoi said tube, 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 the magnitude of said unidirectional current in said neutralizing coil, a diode rectifier, a second resistor connected in serieswith said diode rectifier across said source, coarse resistance-adjusting means and fine resistance-adjusting means in contact with said second resistor, a filter condenser connected in parallel with said second resistor, and connections from said adjusting means to the control grid and cathode, respectively, of said hall-wave rectifier tube for impressing on said control grid a closely adjustable biasing potential derived from said diode rectifier, whereby the polarity of said .demagnetizing field may be selected and the strength or said demasnetizing field may be accurately adjusted over a wide range.

I THEODORE ZUSCHLAG.

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