US2171512A

US2171512A - Electrical apparatus

Info

Publication number: US2171512A
Application number: US742913A
Authority: US
Inventors: Prescott D Crout
Original assignee: Raytheon Manufacturing Co
Current assignee: Raytheon Co
Priority date: 1934-09-06
Filing date: 1934-09-06
Publication date: 1939-08-29
Anticipated expiration: 1956-08-29

Description

Aug. 29, 1939. P. D. cRouT 2,171,512

, ELECTRICAL APFARATUS INVENTOR PREscoTT D. CRouT ATTORNEY Aug. 29,v 1939.

P. D. cR'ouT 2,171,512

ELECTRICAL APPARATUS Filed Sept. 6, 1954 3 Sheets-Sheet 2 Hz e INVENTOR I 61 PREscoTT D. CRou-r w .3b @9m ya 3M FIG. 6

ATToRN EY Aug. 29, 1939. P. D, cRoUT ELECTRICAL APIARATUS Filed Sept. e, 1954 5 Sheets-Sheet 3 lNvENToR PREscoTT D. CRoUT bv Patented Aug.l 279, 1939 UNITED u STATES PATENT CFFICE r2,171,512 vELEc'rRIcAL APPARATUS Application September, 1934, Serial No. 742,913

8 Claims.

This invention relates to an electrical apparatus.

An object of this invention is to devise a novel movable reactor-bar control arrangement; for the apparatus.

The foregoing and other objectsof my invention will be bestunderstood from the following exemplication thereof, reference'being had to the accompanying diagrammatic drawi) ings, wherein:

Fig. l is a side view of the apparatus with portions broken away to show the interior thereof;

Fig. 2 is an end view of the apparatus;

Fig. 3 is a section taken along lines 3-3 of iii Fig. 1; y

Fig. 4 is ya top view of a combined transformer and inductance control unit which is incorporatedin the apparatus, the top baffle plate lbeing broken away to show the underlying structure;

- Fig. 5 is a side View of the device shown in Fig. 4, the side baiile plates being broken away to show the underlying coils;

Fig. 6 is a section vtaken along'line GWG of Fig. 4;

33. Fig. 7 is a, detail of the indicator dial-operating mechanismwith parts broken away to show the underlying structure; and

Fig. 8 is a diagram of the circuit arrangements of the apparatus. v

I have devised a novel electric arc-welding system comprising a gaseous discharge rectifier, a transformer for supplying power to said rectifier, and an* inductance control device in the primary circuit of said transformer for controlling the output current of the rectifier which is adapted to feed an electric welding arc. This system is described and claimed in my Patent No. 1,928,848 dated October 3, 1933. In the present invention the various elements of such a sys-V tem are mounted in a compact andunitary arrangement. .In the drawings, I represents a frame withinwhich is mounted a unitary power and control device 2 consisting of a transformer 3 and an inductance control unit 4. lOn top of the frame I is mounted the tube support 5 within which is supported the rectifier tube 6. This tube is preferably of the construction as shown in the copending application of Spencer and Marshall, Serial-No.'729,101, filed June 5, 1934, al-

though any other suitable rectifier could be used. On the frame are also mounted the front wall 1, carrying various terminals, indicating and adjusting members,.and the rear wall 8 carrying the Ventilating fans. A protecting screen 9 covers the air-inlet'opening in the rear wall 8. A cover tei thereof by shafts 26.

(Cl. 17T-242) I0 carried by the front and rear walls 'I and 8 encloses the space between the walls 'l and 8 and the frame Iwithin which the tube Slis supported. Handles I28 are secured to the upper wall of cover I0, but are free to rotate therein. 5 These handles I 28 are threaded at their inner ends and are adapted to engage corresponding threads in two blocks 28 fastened to the front and rear walls IlI and 8, respectively. In this Way cover Iii may be securely fastened in place 10 on the frame I or may bereadily removed for adjustment, inspection or repair of the internal assembly within the frame ik The structure is preferably provided with wheels il, I2 and I8 in order that it may easily 15 be moved from place to place. The front Wheel il is mounted on an axle id carried by a yoke i5.- The yoke Iii is carried at the lower end of a supporting stud I6, the upper end of whichA passes rotatably through a bushing in the upper 2o wall of frame I. A spring I8 is placed between the upper side of the yoke I5 and the upper Wall of the frame I. The upper end of said stud I6 has rigidly fastened toit the arm Ii'. The outer end of arm -I'II is formed as a yoke between the 25.

arms of which is rotatably mounted on a shaft E8 the lower end ofthe handle I9. The upper end of the handle is provided with a cross-bar 28 in order to provide a convenient means whereby the operator can graspthe handle i9 in order to 3e push or pull the apparatus to the desired location. On the upper side of the front wall 'i is mounted a catch 2I which engages the bar 20 and holds the handle I9 in the position shown when said handle is not in use. The catch 2I is prefer- 35 ably biased in its retaining position by means of a spring (not shown). The rear Wheels I2 and I3 are supported on

shafts

22 and 23 carried by supporting

arms

24 and 25, respectively. Each

arm

24 and 25 is formed with a bifurcated por- 40 tion at one end thereof, the wheels I2 and I3 being supported between the arms of said bifurcated portion. The supporting

arms

24 and 25 are rotatably mounted at approximately the cen- At the' rear end of 45 each of said arms is connected a spring 21, the upper end of which is connected to the top rear portion of the frame I. .'In this manner each of the wheels I2 and I3 is supprted by a cantilever arrangement. The wheels II, I2 and I3 are also 50 each preferably supplied with rubber tires 28.

' In order to enable the machine to be hoisted to any desired positionlthe front and rear walls 'I and 8 are each supplied with t-wo hoisting rings The unitryvpower and control device 2 is shown most clearly in Figs. 4, and 6. In the particular embodiment which I have illustrated, the transformer 3 has a three-phase primary and a six-phase secondary while the inductance control unit 4 has three inductance coils in series A a primary coiland a secondary coil with a center tap. Terminal conductors 3| to 36, inclusive, are provided to establish the connection to the ends of the primary coils. The ends of the secondary coils are brought out to terminalv conductors 31 to 42, inclusive, and the center taps of the secono dary coils are brought out to conductors 43, 44.

and 45. The combinedcore unit 291s also provided with three additional legs 46,41 and 48 upon which Vthe three inductance control coils 49,

and 5| are respectively mounted. 'I'he ends of the

coils

49, 56 and 5| are brought out to terminal conductors 52 to 51, inclusive, whereby the proper connection may be established to each of these coils. The magnetic circuit for the legs 30 is completed by a yoke 58 at the' rear end thereof and by a. yoke 59 at the other end thereof. The loke 59 also interconnects the three legs 46, 41 and 48 of the inductance control. A movable reactor bar 66 is disposed adjacent the outer ends of the legs 46, 41 and 48 which form the pole faces of these legs. By varying the distance between the reactor bar' and the pole faces, the inductance of the

coils

49, 56 and 5| is varied. 'I'he core member 29 and the coils 'mounted thereon are rigidly clamped between the upper -and lower sections of a frame 6| by means of trunnions 69 formed in its upperpand lower side.

- These trunni'ons are received in the upper and Aet lower plates and 66, respectively, so as to allow each block 68 4to rotate to some degree about the axis of trunnions 69. Each block 66 is provided with a bore through which passes a rod 10. The rod 10 is securely fastened against rotation in the bore of block 68 by suitable means, such as a taper pin or key, and is provided at its end with a nut 1| which prevents the bar 60 and its blocks 68 'from being pulled oi the rods 16. Each rod 10 is supported in position on the frame member 6| by two

bushings

12 and 12 held :drmly on the frame member 6|. Each rodv 10 is free to s lide in its bushings. At the end wheredzhe bushings are "supported, the frame member 6| is split so as to provide upper anc lower clamping

arms

13 and 14 for said bushings. Bolts 15 firmly clamp the

arms

13 and 14 around the bushings, whereby the bushings, the rods 10 and their associated structure are retained in their proper positions. In order to vary the positionof bar 66, each rod 16 is 12 and 12'. The internal threads of the sleeve 16 lit the external threadsgof the rod 16, and

- associated structure.

thus the rotation of the sleeve 16 will move the `rod 1|) forward or back'with respect to the frame 6| depending upon the direction` in which the sleeve 16 is rotated. In order to rotate the sleeves 16, each sleeve is provided with a sprocket 11 (see Fig. 3), and a single chain 18 passes around and engages both sprockets 11. A third sprocket 19 is mounted on a shaft 60 in the front wall 1, and may be rotated by an actuating wheel 8| mounted on the shaft 80 in front of the Wall 1. T he chain 18 also passes around and engages sprocket 19. By having the single chain 16 engage both sprockets 11, both rods 10 will be moved in synchronism when the actuating handle 8| is rotated.. Thus the ends of the bar 66 will always be parallel to the pole faces of the legs 46, 41 and 48 in any position to which the bar 60 is moved by the above-mentioned mechanism. Each rod 10 is provided with an adjustable stop 82 yso that the spacing between the pole faces of the legs 46, 41 and 48 and the bar 60 in itsl innermost position may be definitely predetermined. The arrangement of the

clampingvarms

13 and 14 affords a convenient way of assembling the reactor bar 60 and its associated structure in proper position on the frame 6|.

In the above arrangement the ends 16 could be rotatable and the sleeves 16 held stationary. In that case the sprockets 11 would be mounted on the ends 10..

In order' to afford the operator a convenient way of setting the bar 60 in the proper position, the shaft 80 has geared thereto an indicating disk |24. This disk |24 is mounted on a stud |25 rotatably mounted in the front wall 1. The disk |24 may be provided with any suitable markings, but is preferably calibrated in load amperes. The wall 1 isprovided with a'window |26 through which the operator may observe the markings on the disk |24. The window is preferably provided with indicating arrows |21. 'I'he machine is usually adapted to be used with various kinds of welding rods which operate on two different voltage ranges. The current through the load for each setting of the bar 66' will' be somewhat different at these two `voltage ranges. Thus the disk |24 preferably carries two calibrations, one for each voltage range, and the window |26 has correspondingly two indicatingA arrows |21.

^ The problem of supporting a movable reactor bar disposed adjacent a magnetic core excited by current has been a particularly troublesome one. Attempts have been made in various other relationships toA support such a movable reactor bar, but such previous efforts have resulted in very severe chattering of the reactor bar and its Inasmuch as any commercial application should be relatively quiet, such present invention I have devised an arrangement whereby a movable reactor bar may be supported at any of its adjusted positions without'chattering. Whenever a reactor bar is supported with a spacing between the pole faces of the reactor core legs and the reactor bar and the reactor core is energized, there is a force which tends to move the reactor bar toward the core. `In any sys# tem with a. movable reactor bar, there must be a mechanical4 structure winch will hold the reactor bar inplace against the action of the magnetic forces. Such mechanicalv structure constitutes an elastic system. In -any such system of support for the reactor bar, there ordinarily 60 excessive chattering is very objectionable. By my l exists a plurality of members with contacting surfaces which can leave each other. This separation may be slight, but if it occurs in the presence of the vibration of parts, chattering will result. When I use the term chattering, I means the action produced when such separa'- tion and subsequent engagement of such surfaces takes place. In addition to the chattering, the surfaces, upon coming in contact with each other after separation, will cause impact upon the members of the supporting system, and such impact might seriously damage the structure after a comparativelyshort time.

I have found that when a reactor bar is supported, as I have indicated above, and the core is energized by an alternating current, the reactor bar vis subjected to a plurality of forces First of all there may be a constant translatory* force tending to cause the reactor bar to approach the core. Ordinarily in a system where the legs are symmetrical and similarly energized, this constant translatory force acts over the cantral point of the legs. 'I'here also may be a -constant torque on the reactor bar in the plane of the reactor legs. In the usual case mentioned above, this torque is ordinarily zero. There also may be analternating translatory force tending to move the reactor bar toward and away from the pole faces of the reactor legs. In the case mentioned above, this alternating translatory force usually acts over the central point of the legs. There also may bean alternating torque acting in the plane of the reactor legs. If, for

example, the reactor is a two-legged, double-air gap, single-phase reactor, the forces acting are the constant translatory force and the alternating translatory force, bothof the torques mentioned above vanishing. If it is a three-legged,

three-air gap, three-phase reactor, such as dev scribedffor example, in the present application, the force system comprises the constant translatory force and the alternating torque. The above conditions describe the steady state of the reactor. If the amplitudev of the current energizing the reactor is permitted to vary, or if other transient conditions occur, other forces may exist. These forces likewise can be split up into constant and alternating forces. In any such system I have found that in order to eliminate chattering, the alternating displacement amplitudes produced by the above-mentioned alternating forces must be smaller than the displacements due. to the constant forces. Ordinarily in any system in which the reactor bar is supported by a supporting structure, there does exist under some conditions alternating displacements which are greater than the displacement due to the constant forces. In order to make sure that such a condition shall not exist in order to avoid any chattering whatsoever, I provide an additional constant force tending to move vthe reactor bar toward the pole faces of the core, and I make the magnitude of this addi tional unidirectional force great enough to satisfy the above requirement under all conditions to which the device may be subjected during operation. In the particular embodiment shown in the drawings I provide this additional force structure. The additional constant force which I exert on/the reactor bar by the springs i3 and 64 is made suiiiciently great so that the requirements set forth above. are satised over and above the forces necessary to take up all back-lash.

In order to provide means for attaching the

springs

63 and 84 to the reactor bar GII, the

plates

65 and 66 are extendedbeyond the frame 6I and carry at each end thereof a bail 83 whose ends 84 and 85 project freely through openings in the

plates

65 and 86, respectively. These ends are retained in place by some convenient means, such as cotter pins 86. One end of each

spring

63 and 84 is hooked over the middle portion of the respective bail 83, and the other end of each of said springs is held in place on the frame 6I by means of a retaining rod. 81. Each rod 81 passes freely through a stud 88 formed integrally with the frame 6I. Each rod 81 is provided with an eyelet 89 through which the other end of the

respective spring

83 or 64 can be hooked. Each rod 81 is threaded at its outer end and provided with a nut 90.

The unitary power and control device 2 is provided With four mounting brackets 9|. Two of these brackets are mounted on the studs 88. Two additional studs 92 are provided upon which the other two brackets 9| are mounted. A bushing of soft rubber 93 is interposed between each bracket SI and its associated stud in order to prevent any vibration set up in the combined transformer and inductance control unit from reaching the frame I. The unit is secured in the frame I by bolts 94 which pass through the frame I and engage the brackets 9|, as shown in Fig. 1. 'Ihe only other connection between the frame I -and the device 2 is the transmission system between the actuating wheel 8| and the bar 60. The chain 18 interposed in this transmission system constitutes a flexible member through which no vibration from the device 2 can be transmitted to the frame I.

I have arranged the various parts of my system so that a. fan with a rating suflicient to cool the transformer and inductance element may be used to cool the tube in addition. 'Ihe tube 6 is provided with a condensing chamber I3I from which a fairly large amount of heat must be removed.

. This condensing chamber I3I is disposed directly in the path of the blast of air blown into thelmachine by the fan 9, and is cooled thereby. Some of the velocit-y'head created by the fan 9 is dissipated by the turbulence around the tube 6. This turbulence, however, creates suillcient eirculation of air around the tube 6 to produce the desired cooling thereof. 'I'he remaining portion of the velocity head becomes a pressure head vwithin the chamber enclosed by the cover IU, The

cover III when fastened down by the handles |28 ts the front and back Walls 1 and 8 sufficiently close so that the air can escape from the chamber Within the cover III only through the opening around the transformer 3 and the inductancecontrolling unit 4. The pressure head created in the chamber within the cover III is converted into a velocity head around the

members

3 and 4, and air blows past them at a suiiicient rate to produce adequate cooling of these members. Thus we see that the air blown into the machine by the fan 9 venters with a velocity hea'd sufliciently to cool the tube 8 and also to build up a pressure head in the cham-ber within the cover III, which 'pressure head is again converted into a velocity ducts |33.

head around

themembers

3 and 4, whereby these members likewise are cooled.

In the arrangement; .shown in Figs. 4, 5 and 6, the various coils and core members 'are constructed in such a manner that when assembled in the apparatus they are capable of being easily cooled by the air which is blown past them by the pressure head .under the cover |0. The coils on the legs 30 are spaced apart from each other and the surfaces are curved in such a manner as to provide a plurality of air ducts |32 around them. The coils 49, 50 and 5| are likewise disposed in a `similar manner as to provide a plurality of air In order to confin the cooling air to the proper channels in the manner-as will be described below, the portion of the frame 6| which is not llled by the various coils and the air ducts |32 and |33 is covered by a baille plate |34, preferably of a light insulating -board material. It is desirable to cool the pole faces of the legs 46, 41 `and 48 andthe inner face of the movable reactor bar 60. In order that these surfaces may be properly cooled, I form the baille plate |34 with a plurality of air ducts |36, |31 and |38 disposed adjacent the faces of the legs 46, 41 and 48, respectively. The baille plate may be conveniently retained in place by fastening means, such'as bolts |39 and a screw |39'.

In order to conne the air to the proper channels adjacent the outside of ythe transformer coils on the outer legs of the transformer, baille plates |40 are provided on both sides of the transformer. Similar baille plates |4| arerprovided for the reactor coils.` Additional baie plates 42 are provided to direct cooling air past the ildes of the core between the transformer and thereactor.

The various elements described are electrically connected in a suitable electrical circuit, such as that shown in Fig, 11. Three line conductors L1, La and La from a three-phase line are con- ,nected` to the main contactor |43 which serves to connect the three line conductors L1, Ia and L3 to the three conductors |44, |45 and |46 leading to th three

terminals

52, 54 and 56 of the three reactor coils `49, and 5|. 'I'he three' primary coils |49, |50 and |5| of the transformer 3 are preferably connected in a delta connection, the three corners of which are connected to the

terminals

53, and 51 of the reactor coils 49, 50 and 5|. The-three center taps of the secondary -coils are connected together to the common conductor |52 which is in turn connected to contact |53 on the reversing switch |54. The six outer terminals 31v to 42, inclusive, of the secondary coils are connected to the six anodes |55 of the -rectifier 6. The cathode |56 o f the rectifier 6 is connected through a shunt |51 to contact |58 on the reversing switch |54. 'I'he reversing switch |54 is provided with two additional contacts |18 a'n'd |19 connected to two external binding posts 13,0 and |8| mounted on the front wall 1, as shown igiligs. 1 and 2. A pair of movable contact arms |85 and |83 selectively connect contacts |53 and either to contacts |18 and |19, respectively, or vice versa. The movable contact arms may be moved to either position by the operating lever |84, shown most clearly in Fig. 2.l 'Ihe lever |81! is mounted on a stub shaft |84' which passes rotatably through the front wall 1, and has secured to its inner end the insulating plate |65.l The insulating plate |95 carries the two contact arms |82 and |83. By shifting the operating lever |84 from one positionto another, the polarity of the binding posts |80 and |8| maybe reversed. Thus during operation the operator may readily reverse the polarity of his welding electrode and the piece to be welded without disconnecting the conductors connected to binding posts |80 and I 8|.

As is set forthin my Patent No. 1,928,848, it is dlarable to eliminate all inductance in the load circuit. Since the wall 1 is usually made of iron and the load circuit passes through the wall 1 by means of the binding posts |80 and |8|, the wall 1 would ordinarily form a closed magnetic -path around the conductors in the load circuit,

and might introduce some self-inductance. In order to eliminate this effect, a slot |86 is cut through the wall 1 between the binding posts |80 and |8|, This interrupts the otherwise complete magnetic path around each of said binding posts, and thus substantially prevents the introduction of any appreciable amount of.. selfinductance-at this point.

The protective contacts |62 provide protectionv for the machine against overload and fan failure. The fan 9 is connected to the three conductors |44, |45 and |46. In two of these conductors,'for example conductors |44 and |45, are connected heating elements |64 and |65, respectively. Each heating element |64 and |65, as its temperature rises, tends to open thevcontacts |62. Since the currentthrough the elements |64 and |65 varies with the load, the temperatures of these elements vary'with the load on the machine. The device is so calibrated that upon a sustained overload, lthe temperature of the heating elements |64 and |65 risesA sufficiently to open the contacts |62. This in turn deenergizes the coil |59 and opens the main contactor |43. The inherent time delay in the heating elements |64 and 65 permits temporary overloads to occur without opening the contacts |62. Since the machine is built to Withstand large temporary overloads, this operatior is desirable.:A A

A tube |61 is provided which extends from the chamber'within the cover |0 to a point adjacent the heating element 64. The pressure head of air created by the fan 9 inthe chamber within the cover |0 causes air to blow through the tubev |61 onto the heating element |64. This air cools the element |64 so that normally it will not open the contacts |62. -If, however, for any reason whatsoever the fan 9 fails to operate, the pressure head in the machine disappears and the air is so chosen that the current flowing heats it suiciently to open the contacts |62, thus shutting olf the machine. Since the failure of fan 9 would tend to overheat the machine and since such overheating occurs only after the fan has ceased to operate for some length of time, the heating element |64 may be designed to heat up slowly and openvthe contacts |62 at the necessary time. The machine at heavy loads would tend to heat up more rapidly than at light loads. This factor is taken care of by thefact that the current through the element |64 is-a function of load current. Thus as,the load increases, the element |64 heats up lfaster and tends to open the contacts |62 sooner.

|56 is turned on, it is usually advisable to wait until the cathode is heated sufiiciently to emit enough electrons to properly start the discharge within the tube 6 before a load is placed on the tube. In order to indicate to the operator when the cathode is at the proper temperature to start welding, a lamp |14 is connected from one of the anodes |55 to the cathode as, for example, by a conductor connected to one side of the shunt |51. Interposed in this circuit of the lamp |14 is a thermostat |15. This thermostat |15 is open when cold. A heating element |16 for the thermostat |15 is connected across the secondary of the filament transformer |69. Thus when the filament transformer is energized and starts heating the filament |68 at the same time it starts heating the heating element |16. When the cathode |56 reaches the proper temperature, the element |16 heats up suiciently to close the contacts of thethermostat |15. This closes the circuit Io'r the lamp |14 from the terminal 40, through the thermostat 15, the lamp |14, the cathode |56, the discharge space through the tube 6, the anode |55 connected to terminal 39 and back to the terminal 39. impresses a voltage on the said circuit, and causes a small discharge to occur between the cathode and one of the anodes, thus lighting the lamp |14. This indicates to the operator that the tube is ready to operate. The fact that the discharge space in the tube is includedvin the circuit of the' lampl |14 is an additional way of l determining whether the tube is ready for operation. The fact that the lamp |14 lights shows that the cathode |56 is emitting a considerable amount of thermionic electrons, in order to support the discharge to light the lamp |14. AThis shows that the thermionic emission is sufficient to start the main discharge in the tube.

The coil 39-40 v f drop which tends to return the potential of the cathode to that of the 'neutral point of the secondary Winding of the transformer 3. The in The arrangement of lamp .|14 also comprises a specialv starting device for the rectifier tube 6. During operation the voltage from the'neutral conductor |52 'to one of the secondary coil terminals isimpressed between-the cathode and each anode. In starting it is desirable to increase this voltage in order toinsure the initiation of the discharge. The circuit of the lamp |14 connects the cathode |56 directly to one of the anodes |55. Before the discharge starts, no current itiation of the discharge between the cathode |56 and the anode |55 connected to the terminal 39 enables the discharges to each of the other anodes to occur at the nornal running voltage. To insure the operation of this starting circuit even if lamp |14 burns out, a resistance |11 is connected in parallel with the lamp |14.

Of course' it isto be understood that this invention is not limited to the particular details of' vthe arrangement as described above as many equivalents will suggest themselves to vthose skilled in the art. Also various of the diierent parts of the machine may be used in other relationships. For example, the invention disclosed with respect to the movable reactor bar 6D may be utilized in any device 'where a magnetic member is to be moved in order -to vary an air gap. Likewise the Ventilating principle for the machine can be used in other devices aside from a welding machine. Various .other changes and uses 4in and for the various novel parts of my machine will readily suggest themselves. It is accordingly desired that the appended claims be given a broad interpretation commensurate with the scope of the invention within the art.

What is claimed is:

1. In a magnetic apparatus, a magnetic core, means for setting up a magnetic flux in said core, said magnetic core having a variable air gap between a pole face and a movable magnetic bar, supporting means for supporting said `magnetic bar spaced from said pole face,A and' additional means for exerting on said magnetic bar a unidirectional force tending to move saidbar toward said pole face, the magnitude of said unidirectional force being great enough to prevent chattering.

2. In amagnetic apparatus, a magnetic core, means for setting up a magnetic flux in said core, said magnetic core having a variable air gap between a pole face and amovable magnetic bar, supporting means for supporting said magnetic bar spaced. from said pole-face, and additional means for exerting on said magnetic bar a unidirectional force tending to move said bar toward'said'pole face, the magnitude of said unidirectional force being great enough to prevent able for varying the distance between saidA chattering, said supporting means being adjusting means for supporting said magnetic bar spaced from said pole faces, and additional means for exerting on said magnetic bar a unidirectional force tending to move said bar toward said pole faces, the magnitude of said unidirectional force being great enough to prevent chattering, said supporting means being adjustable for varying the distance between said magnetic barand said pole faces.

4. In a magnetic apparatus,a magnetic core, means for setting up a magnetic ux in said core, said core having a plurality of legs with pole faces thereon, a movable magnetic bar, supporting means for supporting said magnetic bar spaced from said pole faces, spring means for exerting on said magnetic bar a unidirectional force tending to move said bar toward said pole faces, the

magnitude of said unidirectional force being great enough to prevent chattering, said supporting means being adjustable for varying the distance between said magnetic bar and said pole faces.

5. In a magnetic apparatus, a magnetic core, means for setting up a magnetic fiux in said core, said core having a plurality of legs with pole faces thereon, a movable magnetic bar, supporting means forsupporting said magnetic bar spaced from said pole faces, said supporting means comprising a vplurality of rods secured to said magnetic bar at Vspaced points along said bar, said rods being threaded along a substantial length, each rod carrying an internally-threaded nut engaging the threads on its respective rod, means for mounting said nuts at a fixed distance from said magnetic core, said nuts and rods being relatively rotatable, sprocket means for ea'ch associated nut and rod for causing relative rotation between them, va single chain engaging all of said sprocket means,- means for moving said chain, andadditional means for exerting on said magnetic bar a unidirectional force tending to move means for setting up a magnetic flux in said'core,

said core having a plurality of legs with pole faces thereon, a movable magnetic bar, supportspaced from said pole faces, said supporting means comprising a plurality of rods secured to said magnetic bar at spaced points along said bar, said rods being threaded along a substantial length, each rod carrying` an internally-threaded nut engaging the lthreads on its respective rod,

' means for mounting said nuts at a xed distance from said magnetic core, said nuts and rods being relatively rotatable, means for causing relative rotation between said nuts and rods in synchroA nism, and additional means for exerting on said magnetic bar a unidirectional force tending to move said bar toward said pole faces, the mag- .ing means for supporting said magnetic bar y means comprising a plurality of rods secured to said magnetic bar at spaced points along said bar, said rods being threaded along a substantial length, eachl rod carrying an internally-threaded nutengaging the threads on its respective rod,

means for mounting said nuts at a xed distance l 'from said magnetic core, said nuts and rods being relatively rotatable, sprocket means for each associated nut and rod for causing relative rotation between them, a single chain engaging all of said sprocket means, means for moving said chain, and spring means for exerting on said magnetic bar a unidirectional force tending to move said bar toward said pole faces, the magnitude of said unidirectional force being great enough to prevent Y chattering.

8. In a magnetic apparatus, a magnetic core, means for setting up a magnetic flu in said core,

said core having a, plurality of legs with pole faces thereon, a movable magnetic bar, a plurality of supporting means at different; points on said magnetic bar, means for moving al1 of said supporting means in synchronism to move said mag- '.netic bar toward and away from said pole faces,

and additional means for exerting on said magnetic bar a unidirectional force tending to move said bar toward said pole faces, the magnitude of said unidirectional force being great enough to prevent chattering.

PRESCOTT D. CROUT.