US2820632A

US2820632A - De-magnetizer for magnetic feed system

Info

Publication number: US2820632A
Application number: US359573A
Authority: US
Inventors: Fowler Alexander
Original assignee: Individual
Current assignee: Individual
Priority date: 1953-06-04
Filing date: 1953-06-04
Publication date: 1958-01-21
Anticipated expiration: 1975-01-21

Description

Jan. 21, 1958 A. FOWLER 2,320,532

DE-MAGNETIZER FOR MAGNETIC FEED SYSTEM Filed June 4, 1953 2 Sheets-Sheet 2 Ila) LINE 1 2/6 2/8 LINE 2 TEE.

IN V EN TOR. ALEXANDER FOWLER A TTOEA/E Y5 United States Patent DE-IWAGNETEZER FOR MAGNETIC FEED SYSTEM Alexander Fowler, Stamford, Conn.

Application June 4, 1953, Serial No. 359,573

Claims. (Cl. 271-18) This invention relates to magnetic feed systems, and more particularly to a de-magnetizer for the same.

In my copending applications Serial No. 129,662, filed November 26, 1949, and Serial No. 226,656, filed May 16, 1951, now Patent No. 2,661,208 of Dec. 1, 1953, I disclose magnetic sheet feed systems in which the uppermost sheet of a stack is raised and separated magnetically, the said sheet reaching a magnetic feed roller which feeds the sheet out from the stack. Inasmuch as the sheets are ferrous or ferromagnetic, they may retain residual magnetism. For certain purposes it may prove undesirable to leave residual magnetism in the sheets, and one object of the present invention is to provide de-magnetizing means. Another object is to improve my aforesaid sheet feed apparatus by combining the same with tie-magnetizing means adapted to eliminate residual magnetism caused by said apparatus.

In my aforesaid apparatus the sheet feed roller may be energized continuously, but I prefer to provide means for energizing the same intermittently in properly timed relation, thus economizing in the use of power. In accordance with a further feature and object of the present invention the de-magnetizer may also be excited only intermittently and in properly timed relation, in order to conserve in the consumption of power.

To accomplish the foregoing general objects, and other more particular objects which will hereinafter appear, my invention resides in the sheet separating, feeding, and de-magnetizing elements, and their relation one to another, as are hereinafter more particularly described in the following specification. The specification is accompanied by drawings, in which:

Fig. 1 is a plan view of sheet separating, feeding, and de-magnetizing apparatus embodying features of my invention;

Fig. 2 is a section taken in elevation approximately in the plane of the line 2-2 of Fig. 1;

Fig. 3 is explanatory of the theory of the invention;

Fig. 4 is a schematic representation of a modification for use with exceptionally high speed apparatus; and

Fig. 5 is a schematic wiring diagram for a complete apparatus energized from a single phase power supply.

Referring to the drawing, and more particularly to Figs. 1 and 2, the apparatus comprises a bed or table 12 for supporting a stack of sheets 14, and an induc-.

tion coil 16 which extends entirely around the stack 14 and the table 12. The axis of the coil extends in the direction in which the sheets are to be fed, which in this case is horizontally, from left to right. The apparatus further includes an electromagnetic feed roller 24 capable of feeding sheet 22 with the latter disposed beneath the roller. The roller is driven by motor 28. The latter may rotate one or more sets of later feed rollers, indicated schematically at 25, through a drive 27.

The sheets may be stacked between guide plates 30, supported within side plates 32, preferably by means of adjusting screws 34, so that sheets of diflerentwidth ICE may be accommodated. The sheets are aligned at their forward edge by means of front stops such as the posts 36.

The slip rings 38 (Fig. 1) and brushes 40 supply magnetizing current to the coils 42 of the feed roller 24. A feeler 44 (Fig. 2) controls switch contacts 46. When the topmost sheet 22 reaches the feed roller 24 the feeler closes the normally open contacts 46. This showing is merely schematic.

In accordance with the present invention the magnetic feed roller 24 is immediately followed by a de-magnetizer coil 39%). This is large enough in diametrical dimension to pass the sheets. More specifically, it is large enough in horizontal direction to pass the widest sheet to be handled by the apparatus, and it is dimensioned high enough in vertical direction to provide adequate clearance despite possible variation in the path taken by the sheet as it is delivered by the rollers. The coil has sufiicient windings and a suitable impedance relative to the supply voltage to provide adequate excitation for the dc-magnetizing operation.

The theory underlying the de-magnetizing operation may be explained with reference to Fig. 3 of the drawing. The coil 30% (Figs. 1 and 2) is supplied with an alternating current of constant magnitude, as indicated by the lines 35192 (Fig. 3). However, the sheet is in motion, and in respect to any transverse zone or increment of the sheet it is excited a maximum amount when that increment is in the plane of the coil 3%, and the excitation falls away or is effectively damped as it leaves the coil and becomes more and more remote. This is illustrated by the damped wave shown at sea, and the excitation falls away to substantially zero. The excitation is alternating, and if at fairly high frequency relative to the speed of travel of the sheet, it will be seen that the increment at which the excitation approaches zero, or reaches the lowest value that is capable of reorienting the molecules in the increment, will be at random along the sheet, so that some molecules of the sheet may face one way and others face another way, depending on their last orientation just as the excitation became too feeble to further change the orientation of the molecules. Of course, if the molecules distributed along the sheet are oriented in different directions, the sheet has been de-magnetized.

For most practical purposes ordinary power line frequency of 60 cycles per second sufficiently high to accomplish the desired tie-magnetization. However, if the apparatus feeds sheets at exceptionally high speeds, so that it becomes desirable to increase the frequency of alternation in order to make certain of relatively ran dom disposition of the molecules, the frequency may be stepped up by using a suitable means, such as a motor generator, or vacuum tube oscillator. Thus refer ring to Fig. 4, the vacuum tube oscillator 1 is ener' gized from an ordinary 6O cycle power line 3%, and the much higher frequency output of the oscillator is supplied to the de-magnetizing coil.

Attention is next directed to Fig. 5 of the drawing, but by way of general introduction it may be explained that most of this diagram corresponds to one of a number of different systems disclosed in my aforesaid pattent applications, for energizing the induction coil 16 and magnetic feed roller 24 of Figs. 1 and 2. This circuit provides the induction coil in with a rising or socalled growth current each time the coil is energized to raise another sheet, and as explained in my copending applications, if the induction coil is energized in this manner the topmost sheet tends to be raised from the next subjacent sheet before the latter is raised at all, whereupon both rise before the third sheet. rises, so that the fanning out or divergence or separation of the sheets is maintain d as the ind c i n s il i ur er. ene gized In any event the topmost sheet alone reaches the' feed roller, and the induction coil may then be de-energized withoutdanger ofthe feed roller holding morethan one .sheet.

I The specific system 02 Fig. 5 employs a thyratronpand fires the thyratron by means of a trigger wave. The 1 maininduction coil of the apparatus receives the D. C. e or rectification increments. The trigger wave is shifted, and this provides a growth current because of the increas- 3 ing increments of plate current "as the firing point of the thyratron changes.

The plate and grid Waves of the thyratronmay be of like frequency and each of uniform magnitude, but relatively'shiftable in phase. With the waves 180 out of phase 110 current will flow. At intermediate values the current supplied by the thyratron may be varied by shifting the phase of the trigger wave supplied to the grid. On the other hand the trigger wave and the plate Wave may :be given a phase difference which is maintained I left, thus causing larger and larger chips of plate current quired in a particular application. the A. C. wave is brought down.

to flow through the thyratron. additional current control which may or may not be reit controls how far

Controls

142 and 160 overlap and it is not essential to have both.

The energization of the main coil 16 causes the sheet to rise untillitreacheshthe magnetic roller 24 and the trip switch 44, closing the latter, and energizing the relay 126, which functions to magnetize the feed roller 24 and to start the feed motor 2's. in the particular circuit here shown the magnet coils of the feed roller. 24 are energized through 'a thyratron tube172 controlled much constant, and theaxis of the trigger wave may be raised 7 or lowered'by changing the magnitude of a bias super,

de-magnetizing coil is shown at 300. Single phase power is supplied at

lines

1 and 2.

When the main switch is thrown on, the transformer 112 is energized, heat the filament of thyratron tube 114, through secondary 116. After the tube is warmed up a circuit breaker 118 is closed, and then the operating switch 120 is closed, which starts the cycle as follows:

Relay122 is energized from line 1 through the normally closed contacts124 of relay 126, which is still deenergized'because the trip switch 44is open. Actuation of relay 122 opens the contacts 128. When contacts 128 of relay 122 open the growth current starts'and the sheets begin to separate. The growth current is obtained from the transformer secondary 144, and is controlled by thyratron 114; A trigger wave is supplied from transformer secondary 130 to the grid.

The resistor 132 and capacitor 134 provide a phase shifting circuit for the trigger wave. The series resistor 136 limits the grid current. Resistor 132 of the phase shifting circuit is variable to permit fine control of the phase relation of trigger wave or grid voltage to plate voltage.

Secondary-138 of transformer 112, in conjunction with full-wave rectifier 140 and potentiometer 142, provides a positiveD. C. grid potential or bias which raises the axis of-the trigger wave and so increases the amountof- 7 plate current fed through the main sheet separating coil 16. This bias may be set for the maximum desired amount of thyratron plate current. Transformer secondary 146 and rectifier 148 supply a negative bias to;

lowerthe' axis of the trigger wave.v The thyratron plate current is in alternateor positive'halfjwaves; The

trigger wave from secondary 130 has its phase displaced by the resistor and

capacitor

132, 134, and has its horizontal axis raised by the bias supply 133, 140, the amount beingadjustably controlled by potentiometer 142. As

i as previously described, but with a view to providing two widely different stages or uniform amountsof magnetization of the feed roll, as well as a complete cut-off when the feed roll is not in use. A relatively small magnetization is adequatedto hold-the topmost sheet while the main ;coil 16 is being de-energized to permit descent of the other sheets; A substantially higher-degreeofii magnetization isemployed to actually feed the sheet. I,

Energization of relay- 126 opens contacts 124,. de:

' energizing relay 122,;and permitting contacts 128-to again close.- This bucks the trigger wave elevating potential of thyratron 114, and socollapses (either completely-or partially) the field in the main coil 16. The field in the main coil iscollapsed becausethe trigger I wave axis is lowered .by

rectifier supply

146, 148, thuspulling the A., C. trigger wave down to the point where. the thyratron does not fire (or fires at desired minimum);

At thesarne time relay 126 also closes its

contacts

162 and 164. Contacts 162initiate the cycle of the upper 1' thyratron tube 172 with theaid of secondaries 166 and 168 .of transformer 170. Secondary 166 provides the trigger wave, and resistor 174 and capacitor 176 provide the phase shiftof the trigger wave, which controls the firing of the thyratron and so controls the degree of. energization of the magnetic roller 24. The resistor 178 limits grid current. a

Secondary 168, through rectifier 186 and potentiometer 182, through relay contacts 162 leading to the capacitor 184 and resistors 186,188, 190 provide positive .gridpotential to, thyratron 172, thereby causing whatever plate current is required to energize the magnetic roller at its lower stage ofimagnetization.

Contactsf164 initiate the operation of a time delay relay builharound tube 194. Tube 1 94 is used with a decay circuit to act as atimer to; delay rotaiton of the feed roller after the sheet has reached the roller (as indicated by'closing of the trip switch 44). The time delay here is accomplished through grid rectification by means H W of resistor .136 and capacitor198. The resistor 200 is,

used to limit'grid current. I

Because .of grid rectification the capacitor applies a negativepotential on the grid ofthe tube, and plate current does not fiowg However, when the contacts 164 close the charge stored in capacitor 198 during the grid 3 rectification period then discharges through the grid cir cuit 200, 196, 198, 202, 222, and when the discharge has a reached a certain point the tube will fire. It is this time required'for discharge that results in the desired time delayaction'of thej'circuit.

When 'the tube 194 fires, a relay 192 is energized, clos- Y .2 ing contacts 20A and 2416. Contacts 264 increase the current through magnetic roller 24 by supplying more positive; potentialthan previously applied through conthe circuit goes into operation,'howev er,-the effect of the noneg or if desired, only a small-chip of plate current e flows; The amount-that it is pulled down thendecreases----- by reason--of--an R.-C. decay'circuit-152,'154. "As the axis of the A.-C. grid voltage wave risesits pointofi firing 'of- -the-thyratron keeps moving effectively to thetacts1-162 'of;relay-1 -26 to thegrid of thyratron 1'72.

this purpose-the adjustmentofpotentiometer 298 is made a higher than thatofpotentiometer-1'32. -At the same time the closingofrelay contacts 206'energizes the feed motor V 28 through;switch- 219, rectifier 212, and rheostat-214n As so far described the operation would be wholly automatic,-'the deliverykof'one sheetfollowing another but in many applications a manual-or pedal control iswanted-..

Potentiometer is an For and for this purpose it is merely necessary to add any convenient form of manual or pedal switch 220 in parallel with the switch 210 previously mentioned, the latter then being opened or omitted, and the switch 220 being a normally open switch. The motor is a shunt motor symbolized at 28, but electrically the terminals 216 represent the connections to the field of the motor, while the terminals 218 represent the connections to the armature of the motor.

When the sheet leaves the feed roller 24 the trip switch 44 opens and relay 126 is de-energized. This opens

con tacts

162 and 164, and permits closing of contacts 124. The opening of contacts 164 cuts off the current flow through tube 194, de-energizing relay 192, and opening

contacts

204 and 2%. The opening of contacts 2% stops the motor. The opening of contacts 224, in conjunction with the opening of contacts 162 of relay 126, completely de-energizes the roller after elapse of a time interval caused by the

delay circuit

184, 186 and 188. The closing of contacts 124 operates relay 122, thereby opening contacts 128, and so again initiating the growth current in the main sheet separating coil 16. This causes the cycle to repeat.

In a simpler form the circuit of Fig. 7 might provide for continuous fully automatic feed of sheets, one immediately after the other, with continuous energization of the feed motor 28 and the feed roller 24. In slightly more complex form the feed roller may be de-energized between feed operations. In still more complex form the feed roller may be energized with two degrees of magnetization, a lesser one for holding but not feeding a sheet, and a stronger one for feeding the sheet. In the present circuit there is the still further refinement of prolonging the full energization or magnetization of the roller beyond the rotation of the motor, a feature particularly useful for partial or incremental sheet feed, and also to energize the de-magnetizer coil, as explained later.

Circuit breaker 118 is used in this circuit to protect the thyratron 114, and the main coil, and to act as a cut-off device if the tube is operated at maximum load for too long a time. The circuit breaker includes a thermal time delay mechanism to take care of the possibility of a sheet not being raised. If no sheet is raised to the trip switch 44 after, say four seconds, the main coil 16 is cut off.

Secondary 116 of transformer 112 is the filament heating source for thyratron 114. Transformer secondary 222 of transformer 170 is used to heat the cathode of tube 194. The plate circuit of this tube is supplied directly from the line, rather than from a transformer secondary. Secondary 224 of transformer 170 is used to heat the cathode of thyratron 172. Secondary 226 of transformer 170 is used to supply plate current to thyratron 172, and consequently to magnetize the feed roller 24.

The rectifier 239 is a back rectifier across the main coil 16 and is used to give increased life to thyratron 114,

and incidentally add energy to the main coil 16. An

alternate idea which might be used but is thought less preferable is the use of a

shunt circuit

232, 234 across the thyratron 114, this being a series R. C. circuit of very small current value to just eifect the proper commutation time of the tube.

This back rectifier idea has here been employed also in connection with the feed roller circuit and even in connection with one of the relay circuits. Specifically the back rectifier 238 serves the purpose of improving commutation of thyratron 172 and at the same time adding energy to the circuit. The back rectifier of tube 194 is indicated at 242 and provides additional energy in the non-conducting cycle of tube 194, the additional energy going to relay 192. Resistor 244 is used in the circuit to connect the cathode and screen grid to the plate circuit to aid in grid rectification for the timing circuit.

The de-magnetizing coil 3% shown in the upper righthand corner of Fig. 5 is energized through

wires

310, 312.

The energization maybe continuous, and a circuit for that purpose is obtained by throwing the double pole double throw switch 314 to upward position, in which case wire 310 is connected through

wires

316 and 318 toline 2, while wire 312 is connected through

wires

320 and 322 to line 1.

However, for economy in the consumption of electricity the de-magnetizer coil 3% may be energized intermittently, and a circuit for this purpose is obtained by throwing the switch 314 to downward position, in which case the wire 310 is again connected through wire 318 to line 2, but the wire 312 is connected through wire 324 to the switch 210 previously referred to. This connects into the circuit which rotates the magnetic feed roller 24 which, it will be recalled, is rotated only intermittently during feed of a sheet. It therefore follows that the de-magnetizer coil 3% is also energized only intermittently, and also in properly timed relation if, as is here shown, the de-magnetizer coil is physically located immediately following the magnetic feed roller.

This does not mean that one must locate the de-magnetizer coil close to the feed roller. It may be spaced a substantial distance from the feed roller, but in that case it may either be energized continuously by throwing the switch 314 to upward position, or it may be energized intermittently as previously described, but with a time delay relay interposed, so that the energization of the de-magnetizer takes place an appropriate amount of time later than the rotation of the magnetic feed roller. Such a relay is shown at 326.

For exceptionally high speed delivery a frequency stepup means may be introduced, as explained in connection with Fig. 4. Such a means is indicated at 328 in Fig. 5. If it be a vacuum tube oscillator, the filament heater may be energized by wires brought in separately for continuous heating, even when the de-magnetizer coil 300 is energized only intermittently, so that the oscillator response will be instantaneous.

To summarize the operation of the circuit of Fig. 5, thyratron 114 acts as a valve to control the main sheet lifting coil 16. There are two bias circuits, one of which (138, 140, 142) elevates, and the other of which (146, 148, depresses the trigger wave, the latter being efiective when the main coil is not functioning, and the former being effective when it is. The growth of the plate current takes place because the trigger wave axis is raised by discharge of potential from the

decay circuit

152, 154.

Thyratron 172 acts as a valve to control the magnetization of the feed roller 24. The height of the axis of the trigger wave is established by bias potential supplied by transformer secondary 168, rectifier and potentiometer 182. This is adjusted to supply the needed current for the sheet holding stage. The magnetization is increased during the sheet feeding stage by raising the trigger wave axis. y

if it be desired to delay the start of the sheet feeding operation until after ample time for collapse of the main field and the fanned sheets, such delay is provided by a time delay circuit associated with tube 194 and using R. C. circuit 1%, 298. The delay in firing of tube 194 delays both rotation and full magnetization of the feed roller. if it be desired to briefly continue full energization of the roller after the motor stops, in order to compensate for inertia of the moving sheet, such prolongation is provided by the time delay or

decay circuit

184, 186, 188. This may be used to continue the excitation of the de-magnetizing coil 300, without using a time delay relay at 326, to insure decay of excitation for the increments in the trailing end of the sheet.

The sheets are de-magnetized by their passage through the de-magnetizer coil 300, the motion of the sheet corresponding to a damping of the excitation to zero, even though the actual excitation may be uniform. Since the 7 I polarity of the excitation of the coil alternates "at a frequency whichis high, relative to the speed of travel of the sheet,; the molecules are left in random. positions, and the sheet is file-magnetized.

It is believed that the construction and operation, as Well as the advantages of my improved apparatus for separatingtand feeding sheets, will be apparent from the foregoing detailed description thereof.

It will also be apparent that while I have shown and described the invention in a preferred form, changes may be made in the structure disclosed without departing from the scope of the invention as sought to be defined in the following claims. In some claims there is reference to a top sheet, and to the raising of a top sheet to a magnetic feed roller above the stack, but this is to be understood primarily inv a relative sense, because the sheets need not necessarily be initially stacked in horizontal position.

I claim:

1. In combination, a magnetic feed roller for feeding lengths of ferromagnetic material, a source of power for exciting said magnetic feed roller, means to intermittently energize the feed roller for the successive feeding operations, tie-magnetizing means for ridding the material of residual magnetism, said de-magnetizing means comprising a coil disposed with its axis in the approximate direction of motion of the material and large enough in diametral dimension to permit the material to pass through the coil in the course of the feed movement produced by said feed roller, and a source of alternating current power connected to said coil, the level of energization of the coil during treatment of a length of the material being maintained substantially constant but the individual increments of the material being subjected to alternating magnetization which falls oif or decays because of the travel of the increment through and away from the coil, exciter means to intermittently excite the de-magnetizing coil, and means to time said exciter means to make the demagnetizing coil eliective during the passage of a length of material therethrough.

2. In combination, de-magnetizing means for ridding ferromagnetic sheets of residual magnetism, means for feeding said sheets through said de-magnetizing means, said de-magnetizing means comprising a coil disposed with its axis in the approximate direction of motion of the sheets and large enough in diametral dimension to permit the sheets to pass through the coil in the course of the feed movement, and a source of alternating current power connected to said coil, the level of energization of the coil during treatment of a sheet being maintained substantially constant but the individual increments of the sheet being subjected to alternating magnetization which falls off or decays because of the travel of the sheet through and away from the coil, the frequency of alternation of thealternating current being made sufiiciently high relative to the speed of travel of the sheet to result in a random disposition of the molecules in the material, exciter means to intermittently excite the de-magnetizing coil, and means to time said exciter means to make the demagnetizing coil effective during the passage of the sheets therethrough.

3. In combination, a long magnetic feed roller for feeding sheets of ferromagnetic material, a source or" power for exciting said magnetic feed roller, means to intermittently energize the feed roller for the successive feeding operations, de-magnetizing means for ridding the sheets of residual magnetism, said de-magnetizing means comprising a coil disposed with its axis in the approximate direction of motion of the sheets, said coil having rectangular turns and being large enough in diametral dimension to permit the sheets to pass through the coil in the course of the feed movement produced by said feed'roller, and asource of alternating current power connected to said coil, the level of energization ofrthe. coil during treatment of a sheet being maintained. substantially constant but the individual increments of. the. sheet being subjected to alternating magnetizationwhi'ch. falls off or decays because of thetravel of the increment) through and away from thecoil, the frequency of alternation of the alternating current being made sufficiently high relative tothe speed of travel of the sheetv to resultv in a random disposition of the molecules in the sheet, exciter means to intermittently excite the de-magnetizing coil, and means to time said exciter means to makethe demagnetizing coil effective during the passage of the sheetthrough the coil.

4. in combination, intermittently operable magnetic, means to raise and separate the uppermost sheet of a. stack of ferromagnetic sheets, said means being an induction coil which extends entirely around the stack with its axis in the approximate direction of motion for. delivery of the sheets, means, to intermittently excite'said. induction coil, means to receive and feed the uppermost sheet our from the stack, and de-magnetizing means for ridding the sheets of residual magnetism, said de-magnetizing means comprising a coil disposed with its axis in the approximate direction of motion of the sheets, said; coil having rectangular turns and being large enough in diametral dimensions to permit the sheets to pass through the coil in the course of the feed. movement produced by said feed roller, and a source of alternating current power connected to said coil, the level of energization of the coil during treatment of a sheet being maintained substantially constant but the individual increments of the sheet being subjected to alternating'magnetization which falls ofi or decays because of the travel of the sheet through and away from the coil, the frequency of alternation of the alternating current being made sufiiciently high relative to the speed of travel of the sheet to result" in a random disposition of the molecules in the material, exciter means to intermittently excite the de-magnetizing coil, and means to time said exciter means to make the demagnetizing coil effective during the passage of the sheet through the d e-magnetizing coil.

5. In combination, intermittently operable magnetic means to raise and separate the uppermost sheet of a stack of ferromagnetic sheets, said means being an induction coil which extends entirely around the stack with its axis in the approximate direction of motion for deh'very of the sheets, and means, to intermittently-excite said induction coil, a magnetic feed roller for feeding; the sheets of ferromagnetic material, a source of power" for exciting said magnetic feed roller, means to intermit-- tently energize the feed roller for the. successive feeding operations, tie-magnetizing means for ridding the sheets:

of residual magnetism, said de-magnetizing means comprising a coil disposed with its axis in the approximate: direction of motion of the sheets and large enough in diametral dimension to permit the sheets to pass through the coil in the course of the feed movement produced by said feed roller, and a source of alternating current power connected to said coil, the level of energization of the coil during treatment of a sheet being maintained substantially constant but the individual increments of the material being subjected to alternating magnetization which falls off or decays because of the travel of the sheet through and away from the coil, the frequency of alternation of the alternating current being made su'fii ciently high relative to the speed of travel. of the mate; rial to result in a random disposition of the molecules in the material, and exciter means to intermittently excite the dot-magnetizing coil, said means being timed to make the demagnetizing coil efifective duringtthe passage of sheets through the tie-magnetizing coil.

(References on following page) 9 10 References Cited in the file of this patent 2,460,684 Farrow Feb. 1, 1949 2,650,824 Fowler Sept. 1, 1953 UNITED STATES PATENTS 2,661,208 Fowler Dec. 1, 1953 1,824,403 McKee Sept. 22, 1931 2,207,392 Zuschlag July 9, 1940 5 OTHER REFERENCES 2,306,584 Zuschlag Dec. 29, 1942 Demagnetizing parts of anti-friction bearings, Elec- 2,403,424 Zuschlag July 2, 1946 trical World, February 2, 1946.