US2397497A - Method and means for demagnetizing - Google Patents

Description

M. L. MAGES METHOD AND MEANS FOR DEMAGNETIZING April 2, 1946.

2 Sheets-Sheet 1 Filed Aug. 13, 1943 10 z m my 5/ w 1 0 Win m u 7. w W fl. v

r mkwmz a ma 4/9 nv v at W v v\/ v y Patented Apr. 2, 1946 METHOD AND MEANS ron DEMAGNETIZING Morris L. Mages, Chicago, Ill., assignor to Magnaflux Corporation, Chicago, Ill., a corporation of Delaware Application August 13, 1943, Serial No; 498,524

Claims.

This invention relates to a method and means for demagnetizing and more particularly to a novel method and means for demagnetization with the use of transients.

Some of the troublesome problems encountered in the field are the demagnetization of large parts, in particular, crankshafts, or smaller parts of highly retentive material such as heavy springs. It is quite common today for manufacturers to test metal parts for flaws and other defects by magnetizing the part and then depositing paramagnetic powder on the part for the purpose of observing any special congregation of particles as would be the case if a flaw or other defect were present in the metal. It is usually considered desirable and in many cases it is absolutely necessar that a part which has been tested in such a manner be demagnetized after the test. Where a crankshaft or other large or special part has been magnetized, it is not always possible to obtain satisfactory demagnetization of the part by simply drawing the part through and out of an alternating magnetic field.'

I have found that a very satisfactory demagnetization of a part may be obtained by utilizing the starting transient when a demagnetizing coil 15 first connected to an alternating current power line. More particularly, I have found that if a rapid and successive series of transients is first to the time when a steady alternating current is caused to flow through the coil so as to enable the part to be gradually withdrawn from the influence of the field, that a much more satisfactory demagnetization will result.

It is an object of the present invention to provide a novel method and means for demagnetizing which includes the use of transients.

Another object of the present invention is to provide a novel demagnetizing apparatus wherein the alternating current energization circuit of the invention is to provide a novel timer control circuit for demagnetizing equipment.

The novel features which I believe to be characteristic of my invention are set forth with Darticularity in the appended claims. My invention itself, however, both as to its manner of construction and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description, taken in connection with the accompanying drawings, in which: v

Figure 1 is a schematic wiring diagram of the novel control circuit for a demagnetizer embodying thenovel principles and teachings of the present invention; T

Figure 2 illustrates in full lines the steady state voltage and current flowing in the demagnetizing coil while the transient is shown in dotted lines;

Figure 3 shows the nature of the resulting curve when the transient is combined with the steady current;

Figure 4 is a hysteresis curve showing the effect of the transient on the magnetization of the part being tested; 7

Figure 5 is a schematic wiring diagram illustrating a modified form of the present invention;

' and I introduced into the demagnetizing coil prior to demagnetizer is turned on and off a number of rapidly interrupting the flow of alternating cur-= rent to the energization circuit of the demagnetizer.

Another and still further object of the present Figure 6 is a schematic wiring diagram illustrating a third embodiment of the Present invention.

One embodiment of the present invention is illustrated in Figure 1 of the drawings wherein a demagnetizing coil in is arranged to be connected to alternating current supply conductors ii and i2 through contactors I! and Nb. Now the novel method of the present invention includes the placing of a part to be demagnetized (not shown) in the coil l0, turning thecurrent on and off in rapid succession to produce a plurality of starting transients (preferably at least ten or more) and then withdrawing the part from the coil during the time the coil is energized by the steady flow of alternating current from the power supply lines. and I2. The control circuit for carrying out such a method includes a synchronous timer l5 which is connected through a dropping resistorifi to the supply conductors II and the motor I1 is arranged to cause the swit h is to be opened after the elapse of a predetermine period of time.

As soon as switch :18 is closed, will be observed that the motor is energized through conductors ii and H8". The contacts and iilb in the main circuit are arranged to be closedupon ene1-= gization of a contactor coil which is connected through a normally closed contact 21' and switch it across'conductors ii and The normally closed contact will hereinafter be referred to as an interlock for this contact 28 is arranged to be opened as the contacts 09a and i319 are closed. It will thus be seen that as soon as the contacts 09a and 11% are closed, the contac'tor coil 89 becomes deenergized by the coercing of the interlock ill and the contacts i301 and i922 thereupon drop out. But as soon as the contacts 119a and 8% drop out, the interlock so is closed and the contactor coil 89 again becomes energized to cause the closing of the contacts lilo and [l-Sb. This results in a rapid opening closing of the energization circuit to the den-magnetizing coil ill.

Connected in shunt with the contactor coil iii and the interlock Bil is a timer coil 20 which is arranged to cause the movable contact element 26a which is connected to one end of the contactor coil ill through a conductor 23 to move from its full line position as shown in Figure l to its dotted line position as shown in Figure 1, After the timer coil 2i has caused the switch Zia to close, it will be observed the interlock is shmted out of effective control ofthe energizetion of the contactor coil 09 and the contactor coil is will remain continuously energized until the synchronous timer 15 has caused the switch ill to open. During this latter period the part which has been disposed within the demagnetizing coil it is gradually withdrawn.

In any circuit, when first making contact, a transient current will nearly always occur because the relationship between the voltage and current in that circuit at the particular instant of contact will not, in general, be the same as for the steady state condition. l ihen considering the demagnetizing coil id of Figure l by way of example, the steady state condition would be represented by a sine wave 2 3 of current lagging 90 approximately behind the ap-.

plied voltage wave (as shown Figure 2). This 90 lag is of course due to the fact that the resistance of the coil lb is negligible in comparison with the inductance. Now when the circuit to the demagnetizer coil i is closed (by closure of contacts 09a and 8%) at a time "01, the current at the instant of closing is zero, which obvi ously does not coincide with the finite value of current "g which would be present that instant under the steady state condition. As a result, a transient is established which makes up the difference in current and supplies the energy required to establish the held of the coil. The transient in the coil to has the shape shown by the dotted curve 2t (an exponential curve) and has a maximum value corresponding to the value My",

If an oscillogram is now taken of the line current starting at the time a, the picture would appear as shown by the full line curve ill in Figure 3. Figure 3 is derived by adding the steady state current to the transient.

The effect can be analyzed by considering a D. C. transient to be present for the first live or six cycles in addition to the normal steady state current. The magnitude oi. the transient will depend on the instant at which the switch is closed.

' netized part.

The maximum transient will made at an instant of time 12 corresponds to a closing of the contact at an ln stant of timewhen the current wave shoul" be maximum in a positive direction (b) or in negative direction (0). It the circuit at a time y'f or in other words at a when the current wave should be zero, there will of course be no transient at all. It will furthermore be observed from the above consideration that the transient may be either positive or negative, depending on the time oi the closing.

Use may be made or this C. transient by causing it to oppose the original field in the maglily energizing the coil a number of times it is believed a transient will always result of high magnitude which is in the proper direction to neutralize a substantial part or the field in the magnetized part or even to reverse it to some extent. From this point, the usual withdrawal of the part through the coil is sumcient to remove the remaining magnetism. Should another transient in the wrong direction he applied, the beneficial efiect of the first tronsient is not lost to any great extent. 'lhis has been conclusively proved in practice. It is believed that an explanation of this efiect may be explained by the hysteresis curve shown in Figure 4. The point 28 represents the residual mam netism left in the part after the original insane tization. Point 29 represents the amount left after a favorable transient. Point 3b shows how the residual magnetism is still considerably less than that at 28 in spite of an unfavorable transient being applied after point 29. Point ill is arrived at by a further favorable transient. Demagnetization from .point to will not be quite as good as that from point but nevertheless it is still substantially better than what it was at the point 28 where it originally started.

It has furthermore been found in practice that the beneficial effect obtained by rapidly interrupting'the energization circuit to the magnetizing coil to is due to the starting transient when the circuit is made and not due to the condition which exists at the break. Numerous tests have further shown that a beneficial result is always obtained by a series of openings and closings of the energization circuit of the coil iii A modified form of the present invention is shown in Figure 5 ofthe drawings. In this embodiment the demagnetizing coil ill is also connected to the power lines it and i2 through contactors lilo and i9?) as described in connection with Figure l. The parts are similar to those shown in Figure l and they have been given the same reference characters. A synchronous timer l5 having a motor l l and a timer switch ill is also connected across the lines it and i2 through a dropping resist-or id. The contactor coil 58 in this instance, however, is connected through a normally closed relay contact 32 and through the switch it to the lines ii and i2 rather than through the mechanical interlock previously described. A timer microswitch Zia is provided which is normally open but which is arranged to be closed after a brief interval of time by the timer coll 2| which is connected to the circuit in the same'manner as that described in connection with Figure 1. A relay coil 33 is connected across the demagnetizin coil iii so that it is on the same side of the contactors E o and lob as is the demagnetizer coil ill. It will thus be apparent that upon closure of the contacts Na and 8% by energization of the contactor coil ID, the contacts its and I9?) drop out and the magnetizing coil to as well as the relay coil 33 becomes deenergized. The cycle is rapidly repeated until the timer microswitch 2 la has closed thus holding the contactor coil l9 continually energized so long as the synchronous timer switch l8 remains closed. During this period the part is slowly withdrawn from the demagnetizing coil l0. After the elapse or a predetermined interval of time, the synchronous motor it opens the switch It and prevents further energization of the magnetizing coil l until the switch 13 has again been closed.

A third embodiment of the present invention is illustrated in Figure 6 of the drawings, wherein means is provided for obtaining a somewhat slower interruption of the contacts 130 and Nb. In this form of the invention, the contactor coil i3 is connected through a microswitch 33 and the switch it of the synchronous timer ll to the lines it and II. The microswitch 35a i controlled by a timer coil 35 which is connected through a mechanical interlock 36 and a microswitch 38a across the lines I I and I2. The microswitch 38a is operated by the timer coil 33 which is connected across the lines H and I2 through switch is or the synchronous timer ii. The synchronous timer I5 is connected across the, lines II and 12 through a. dropping resistor It in the same manner as previously described.

When the synchronous timer I5 is turned on by closing its switch I8, the contactor coil l3 and timer coil 38 are energized. The energization of the contactor i9 causes the contacts I31: and Nb to be closed to energize. the magnetizing coil ill. The interlock 38 is mechanically connected to the contactors Na, and l9b in such a manner that upon closure of the latter, the interlock 33 closes. When the interlock 38 closes, the timer coil 35 is energized and after theelapse of a predetermined period of time, such for example as twotenths of a second, the microswitch 33a opens after opening the energization circuit of the contactor coil is. Deenergization of the contactor coil l9 causes the contacts Isa and Nb to drop out and results in the deenergization of the demagnetizing coil ID. The opening of the contacts 18a and 19b causes the cycle to repeat itself at twotenths second intervals. After the elapse of a predetermined period of time, such for example as two seconds (or in other words twenty twotenths second intervals) the timer 38 causes its microswitch 38a to disconnect timer 35 from the circuit. This stops the intermittent action and causes the demagnetizer coil to remain energized until the synchronous timer shuts off the entire circuit.

It is evident that with this particular embodiment of the present invention, the rate at which the transients are produced, and the number of transients which occur before a steady operation is reached, are both controllable through the timers 33 and 38.

In practice it has been found that a circuit of the general type shown in Figure 6 is more uniform in satisfactory results, for it has been found that ii the duration of a transient is very short, it is not as effective in its demagnetizing action as where the duration of the transient is somewhat longer. I have found that under usual operating conditions, the minimum length of time is about six cycles (Where sixty cycle alternatin current is used) or one-tenth of a second. It has further been found in practice that the efiectivenessof the demagnetization increases with the number of transients used but practically the entire benefit of the process is obtained with ten to fifteen transients.

' While I have shown and described certain particular embodiments of my invention, 'it will, of course, be understood that I do not wish to be limited thereto, since many modifications may be made, and I, therefore, contemplate by the appended claims to cover all such modifications as fall within the true spirit and scope of my invention.

I claim as my invention:

1. Demagnetization apparatus comprising a demagnetizing coil in which a magnetized part is placed when it is to be demagnetized, means for energizing said coil with a series of A. C. starting transients for a predetermined period of time, and means for energizing said coil with a steady state A. C. after said predetermined period of energization.

2. Demagnetizationapparatus comprising a demagnetizing coil, means for introducing in rapid succession a series of alternating current transients insaid coil for a predetermined period of time, and means for causing an alternating current of substantially constant maximum amplitud to flow through said coil after the elapse of said predetermined period of time.

3. Demagnetization apparatus comprising a demagnetizing coil, means for energizing said coil with a plurality of A. C. starting transients in rapid succession, and means for thereafter energizing said coil with alternating current of susbtantially uniform amplitude.

4. Demagnetization apparatus comprising a demagnetizing coil, means for energizing said coil with a series of A. C. starting transients for a predetermined period of time, and means for energizing said coil with alternating current of substantially uniform amplitude for a second predetermined period of time immediately following said first period of time.

5. Demagnetization apparatus comprising a demagnetizing coil. means for energizing said coil with a successively applied group of A. C. starting transients, each transient being applied for a few cycles only, and means for thereafter energizing said coil with alternating current of substantially constant amplitude.

6. Demagnetization apparatus comprising a demagnetizing coil, means for energizing said coil with alternating current of substantial constant amplitude, and means for initially peaking the amplitude of the alternating current wave for a predetermined period of time.

7. A circuit for controlling the energization of a demagnetizer comprising supply conductors arranged to be connected to a source of alternating current, a demagnetizer including a circuit esswitch after the elapse of a of time.

8. A circuit for controlling the energization of a demagnetizer comprising supply conductors arranged-to be connected to a source of alternating current, a demagnetizer, means for connecting said demagnetizer to said supply conductors including a contactor having a contactor operating coil, and a contact interlock which opens when the contactor closes and which closes when the contactor opens, a synchronous timer connected to said supply conductors and having a synchronous timer switch which opens after the elapse of a predetermined period of time, said contactor coil and said interlock being connected in series with said synchronous timer switch, a microtimer switch connected in parallel with said interlock, said microtimer switch having a timer coil for closing said switch after a predetermined period of time, the predetermined period of time of said microtimer switch being shorter than the predetermined period of time of said synchronous timer.

9. A circuit for controlling the energization of a demagnetizer comprising supply conductors arranged to be connected to a source of alternating current, a demagnetizer, means for connecting said demagnetizer to said supply conductors including a contactor having normally open contacts and a contact operating coil which closes the contacts upon energization thereof, a normally closedrelay switch, a relay coil for opening said relay switch upon energization of said relay coil, said relay coil being connected in parallel with said demagnetizer and on the normally open side of said contacts, and means for conmeeting said contact operating coil and said relay switch in series to said supply conductors.

10. A circuit for controlling the energization of a demagnetizer comprising supply conductors arranged to be connected to a source of alternating current, a demagnctizer, means for connecting said demagnetizer to said supply conductors including a contactor having normally open contacts and a contact operating coil which closes the contacts upon energization thereof, a normally closed relay switch, a relay coil for opening said relay switch upon energization thereof, a micrbtimer having a normally closed microtlmer switch and a timer coil which opens said microtimer switch after the elapse of a predetermined period of .energization of said timer coil, said relay coil being connected in parallel with said demagnetizer and on the normally open side of said contactor, said contactor coil and said relay switch being connected in series across said supply conductors, said timer coil being connected across said supply conductors, and said timer microswitch being connected in parallel to said relay switch.

11. A circuit for controlling the energization of a demagnetizer comprising supply conductors arranged to be connected to a source of alternating current. a demagnetizer, means for connecting said demagnetizer to said supplysconpredetermined period ductors including a contactor having normally open contacts, and a contact operating coil which closes the contacts upon energization thereof, a normally closed relay switch, a relay coil for opening said relay switch upon energization thereof. said relay coil being connected in parallel with said demagnetizer and on the normally open side of said contactor, a microtimer including a normally open microtlmer switch and a timer coil for closing said switch a predeteracorns? mined period of time after the energlzation of said timer coil, and a synchronous timer having a timer motor and a synchronous timer switch which is opened by said motor after the elapse of a predetermined period of time, said last period of time being greater than the period of time for closing said microtimer switch, said contactor coil and said relay switch being connected in series through said synchronous timer switch, said microtimer switch being connected in pare allel with said relay switch and said microtimer coil being connected through said synchronous timer switch to said supply conductors.

12. A circuit for controlling the energization of a demagnetizer comprising supply conductors arranged to he connecmd to a source of alternating current, a demagnetizer, means for connecting said demagnetizer to said supply conductors including a contacto-r having normally open contacts, and a contact operating coil which closes the contacts upon energization thereof, a first microtimer having a timer coil and a normally closed microtimer switch, a second microtinier having a timer coil and a normally closed microtimer switch, an interlock switch on said contactor arranged to close when the contacts of said contactor are closed and to open when the contacts of said contactor are open, said contactor coil and said first microswitch being connected in series to said supply conductors, said first microtimer coil, said interlock switch and said second microswitch being connected in series to said supply conductors, said second microtimcr coil heing connected to said supply conductors, said first microtimer coil being arranged to open its associated microswitch after the elapse of a predetermined period of time, and said second microtimer coil being arranged to open its associated switch af ter the elapse or" a predetermined period of time which is greater than the predetermined period of time for said first microtimer. I

13. A circuit for controlling the energization of a demagnetizer comprising supply conductors rs mg current, a demagnetizer, means for connecting said demagnetizer to said supply conductors including a contactor having normally open contacts, and a contact operating coil which closes the contacts upon energization thereof, a first mi- 00 crotimer having a timer coil and a normally closed microtimer switch, a second mlcrotimer having a timer coil and a normally closed microtimer switch, said first microtimer coil being arranged to open its associated microswitch after the elapse of a predetermined period of time, said second microtimer coil being arranged to open its associated microswitch after the elapse of a predetermined period of time greater than the predetermined period of time of said first microtimer, a synchronous timer having a motor and a closable switch which is arranged to be opened a predetermined period of time after the closure thereof, said last mentioned predetermined period of time being greater than the predetermined period of time of said second microtimer, said contactor coil and said first microswitch being connected through said synchronous timer switch across said supply conductors, an interlock switch arranged to open and close with the contacts of 70 said contactor, said first timer coil, said interlock switch and said second microswitch being connected in series across said supply conductors, and said second timer coil being connected through said synchronous timer switch across said 7 supply conductors.

arranged to be connected to a source of a-lternatwenew 14. The method of eleetricagly demegnetizing magnetized parts which includes subjecting the part to the magnetic infiveme e2 magnetic fields preduced by eltemeting 0 event transients and then slewly withdrawing the peri; from a steady altemetimg magnetyie fl a megneisizeai per: whicl'a incfiudee subjecting fihe part 50 e, termpted series of magnetic fields gorndueee series of alternating current starting and then slowly withdrawing the per; magnetic field produced by a steady e5 netzlng current.

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