US2394103A - Electromagnet - Google Patents

Description

Feb. 5, 1946.

L. T. RADER ELECTROMAGNET Filed Oct. 20, 1942 His Attorny Patented Feb. 5,

ELECTROMAGNET Louis T. Rader, Schenectady, N. Y., asslgnor to General Electric Company, a corporation of New York Application October 20, 1942, Serial No. 462,662

4 Claims.

The invention relates to electromagnets, and the principal object is to provide an improved form of alternating current electromagnet of the cast magnetic shell enclosed solenoid type having a separately sealed ofl movable laminated plunger cooperating with a, magnetic out-ofphase flux producing sealing member to provide a quiet and strong enough pull for operating valves or other relatively heavy loads.

Usually a cast magnetic shell type of solenoid has required energization with direct current in order to obtain a quiet and strong pull on the plunger as well as to prevent overheating. Upon alternating current energization of such an electromagnet, the plunger may tend to chatter when in closed position so as to create excessive noise under even a very light load. Likewise, the usual fluid-tight sealing tube for the plunger that extends from the body of the valve or other operated device inside the operating solenoid may be subject to excessive heating losses due to the eddy currents induced therein when the solenoid is energized with alternating current. Also, excessive heating losses due to hysteresis and eddy currents in the usual cast magnetic enclosing a sufliciently strong out-of-phase flux for maintaining the plunger quiet in the attracted positlon even under relatively heavy load when the solenoid is energized with alternating current.

Further objects and advantages of the improvements'of the present invention will become apparent from the following description of the accompanying drawing, in which the single figure is a sectional view of an alternating current solenoid of the enclosed cast magnetic shell type having a separately sealed off movable plunger for operating a valve and embodying the invention in a preferred form.

shell of the solenoid may result in case of alternating current energization thereof. Consequently, the temperature to which the usual direct current cast magnetic shell enclosed soleing transverse a wide and flat eddy current conductive path for reducing the magnetic losses and thereby increasing the eifective quiet magnetic pull on the plunger of an alternating current solenoid.

Another specific object is to provide an improved form of plunger sealing and guiding tube structure having relatively low eddy current losses in producing out-o'f-phase flux for holding the plunger firmly in attracted position during alternation of the current in an alternating current solenoid.

A more specific object is to provide the plunger guiding and sealing tube with an improved form of magnetic pole shader disc, for sealing the end thereof inside the solenoid as well as providing As shown in the drawing, the solenoid magnet winding I0 is of suitably insulated annular form and is providedwith the terminal leads II for energizing the solenoid from an alternating current source, such as an ordinary -cycle commercial supply line. The solenoid Ill is totally enclosed within a separable flux conducting cast iron shell indicated generally by the character l2 and comprising the top wall l3, the bottom wall It and the cylindrical side wall l5. Preferably, the top wall I! and the cylindrical side wall I5 are cast integrally of soft cast iron and provided with a series of radial heat radiating fins I6 for dissipating the heat produced, by eddy currents andhysteresis in the shell. Also, preferably a wiring connection box H is formed to project from one side of the enclosing shell wall l5 and provided with a threaded opening l8 for receiving the conduit pipe I9 carrying the alternating current supply lines so that the whole device becomes splashproof, waterproof, and even explosionproof. A removable sealing cover 20 provides the necessary access for connecting the solenoid terminal lead H with the supply lines.

The bottom wall it of the enclosingrshell l2 preferably is cast as an integral part of the enclosing sleeve 23 for the movable valve or other load device that is to be operated by the solenoid. As shown, the valve enclosing sleeve 23 is removably secured to the main body of valve 24 by the bolts 25 with a portion of the sleeve 23 cut away to show the pivot yoke 26 that is carried by the pivot pin 21 extending through the laminated washer 3|.

Since the particular structure of the valve 24 is not of the essence of the present invention, the details thereof are not shown. However,-for low pressure work, the operating stem 29 may be connected to operate the main valve parts directly, while for high pressure work, the operating stem and is sealed off fluid-tight from the other parts of the operating solenoid by the cylindrical sealing and guiding tube 33. To reduce the eddy currents induced therein, this tube 33 is formed of relatively thin high resistance non-magnetic material, such as stainless steel or Nichrome, and preferably is provided with a conically flared end 33a so that it can be tightly clamped in fluidtight engagement with the sloping shoulder 34 extending from the cylindrical wall of the opening 35 in the bottom shell wall I through which the plunger 28 operates. The conically flaring end 33a of the tube 33 is clamped in position by the extra elongated annular clamping nut 36 of soft steel which preferably closely surrounds the laminated plunger 28 so as to provide a magnetic flux path of low reluctance from the bottom shell wall I 4 to the plunger 28 with a minimum air gap therein. However, the annular clamping nut 36 preferably is of just slightly larger internal diameter than the internal diameter of the sealing and guiding tube 33 so that the plunger guiding tube will always prevent actual engagement of the plunger 28 with the clamping nut 36.

In accordance with the present invention, the end of the plunger sealing and guiding tube 33 that extends inside the solenoid I is sealed by a relatively thin out-of-phase flux producing and conducting plate or disc 39 of solid magnetic material. This out-of-phase flux producing and conducting plate or disc 39 preferably is formed of silicon steelso as to avoid the work hardening or aging characteristic of soft steel which may build up its residual so that it tends to become permanently magnetized and thus may tend to hold the plunger in its attracted position even though the solenoid I0 is deenergized. Preferably, the plate or disc 39 is provided with a peripheral shoulder 39a that engages with a complementary inwardly projecting shoulder 33b formed at the top of the sealing and guiding tube 33. Since the cylindrical side walls of the sealing and guiding tube 33 are relatively thin, preferably being only about .030 thick, this interlocking shoulder construction insures that the solid plate or disc 39 of magnetic material is securely anchored in the end of the tube so as to withstand the very high internal pressures to which the sealing tube and disc may be subjected in case the valve 24 is employed for controlling high pressure fluids. The plate or disc 39 may be pressed into position, as shown, at the inside end of the tube 33 and thereby provide a fluidtight joint. However, if desired, the plate or disc 39 may be further secured to the end of the tube 33 by suitable brazing or welding.

In order to minimize the eddy current losses in the sealing tube 33, this tube preferably is formed of a high resistance non-magnetic material, such as stainless steel or Nichrome, as previously noted. Also, the length of the tube 33 extending inside the solenoid I 0 is reduced to the bare minimum that will provide a suiliciently long stroke for the plunger 28 to effectively operate the valve. Thus by forming the tube 33 of high resistance non-magnetic material, as well as by minimizing the thickness and the length thereof, the heat loss produced by the eddy currents within the tube upon alternating current energization of the solenoid Hi can be reduced to a minimum. Moreover, since the inside of tube 33 is in direct contact with the fluid controlled by the valve 24, the heat generated in the tube 33 will be transmitted directly to and carried away by the fluid except, of course, when the fluid may have a higher temperature as, for example, high pressure steam.

A pole 40 of laminated magnetic material, preferably silicon steel, is adjustably mounted in flux conducting relation in the recess ll formed in the top wall [3 of the cast iron shell l2 opposite the central opening 35 in the bottom wall H through which the plunger 28 operates upon energization of the solenoid. The laminated pole 40 is clamped in intimate magnetic contact with plate or disc 39 by means of the enlarged stop screw 42 which is threaded centrally in the top wall 13 of the cast iron shell I2. This enlarged stop screw 42 not only facilitates the flux conduction between the pole 40 and shell l2 but also enables the pole 40 to be forced into firm engagement with the relatively thin out-of-phase flux producing and conducting plate or disc 39 so as to receive the impact of the plunger 28 when the plunger moves to the attracted position. Also, in this way, when the solenoid i0 is energized from the alternating current source, the relatively thin solid magnetic out-of-phase flux producing and conducting plate or disc 39 is interposed between the laminated plunger 29 and the laminated pole 40 in intimate flux conducting contact with each so as to provide a sufficiently strong out-of-phase flux for maintaining the plunger in firm and quiet engagement with plate or disc 39 during alternation of the solenoid energizing current under even heavy loads.

The out-of-phase flux producing action of the thin solid plate or disc 39 of magnetic material may be understood by considering the plate or disc 39 as a continuous series of concentric rings of solid conductive metal within each of which eddy currents are produced by inductive action upon movement of plunger 28 to the attracted position due to energization of the alternating current solenoid I0. Under these operating conditions the eddy currents inductively produced in each of the assumed concentric rings serve to provide an out-of-phase flux when the energizing alternating current of the solenoid I0 passes through the zero value, Since the assumed rings are concentric, the out-of-phase flux producing action thereof becomes cumulative along their axis and thus results in a very strong centralized out-of-phase magnetic field. Due to the intimate magnetic engagement of both the laminated plunger and the laminated pole with the opposite sides of the solid thin plate or disc 39 of magnetic material, the out-of-phase flux produced by the eddy currents in the disc is most effective in holding the plunger firmly and quietly in the attracted position during alternation of the solenoid energizing current since there is practically no air gap in the symmetrical local magnetic circuit between the pole 40 and plunger 28. In this local magnetic circuit the thin magnetic disc 39 is disposed between and normal to the opposite longitudinal laminations of the pole 40 and plunger 28 so as to interlink these longitudinal laminations through a short magnetic path extending transverse the wide and flat conductive path for concentric eddy current flow in -Letters Patent of the opposite said opening, a

the disc. Thus the plate or disc 39 serves to provide a very strong and effective out-of-phase flux for holding the plunger in the attracted position since the solid plate or disc 39 is relatively thin. In fact, it has been found that increasing the thickness of the disc 39 to much more than one-eighth of an inch merely increases the heat loss due to the increased eddy currents produced therein but does not materially increase the out-' of-phase flux efiective for holding the plunger in the attracted position. This one-eighth inch effective thickness limitation for the solid steel disc 39 corresponds substantially to twice the usual effective alternating flux penetration depth permitted by the so-called skin effect of any relatively thick solid steel body at the ordinary sixtycycle commercial frequency. Hence, in case the thickness of disc 39 should be increased materially beyond this limitation, the resulting skin eifect of the disc will tend to render the out-ofphase plunger holding action produced by a thin disc ineffective.

Since the plunger 28 and the pole 40 both are of laminated magnetic material, the heat loss produced by eddy currents and hysteresis therein during operation of the solenoid is practically negligible. An analysis of the total heat loss of a particular solenoid constructed as illustrated in the drawing shows that when energized with alternating current at the rated voltage, the total watts loss produced on continuous heat run in the solenoid and its magnetic circuit is 194. Of this the out-of-phase flux producing disc 39 generates only twenty-three watts, the sealing and guiding tube 33 twenty-six watts, the copper of the solenoid winding Ill four watts, and the remaining l4! watts areproduced by hysteresis and eddy currents in the cast iron shell l2. Thus the heat radiating fins l5 are located so as to dissipate the relatively large heat loss generated directly in the cast iron shell l2, while'the heat generated in the disc 39 and the tube 33 may be readily dissipated to the fluid. In this way, the operating temperature to which the solenoid I0 is subjected is maintained within permissive safe For best results, the solenoid It should be relatively short in length with the operating air gap between the plunger 28 and pole All located cen-' trally within the solenoid as shown, preferably the overall height of the solenoid coil l9 being approximately three times the air gap through which the plunger 28 must operate. It has been found that making the solenoid any larger with the expectation of increasing the permissible watt input thereto and thereby increasing the pull exerted on the plunger 28 produces negligible results. The increase in watts due to the added height of the coil and its shell simply increases the losses therein without appreciably increasing the effective quiet pull on the plunger.

What I claim as new and desire to secure by United States is:

1. In combination, a solenoid having a cast iron enclosing shell provided with a plunger opening and a longitudinally laminated magnetic pole projecting from said shell inside said solenoid load operating longitudinally laminated magnetic plunger movable through said opening into opposing attracted relation with said pole upon energization of said solenoid with alternating current, a tube formed ,of a high resistance nonmagnetic metal and having sealing connections with said opening and extending inside said solenoid for guidinl said tion of the alternating energizing current of said solenoid.

2. In combination, an alternating current solenoid having a magnetic circuit including a longitudinally laminated pole extending inside said solenoid and an opposing longitudinally laminated plunger attracted toward said pole upon energization of said solenoid, and a plunger guide tube formed of a high resistance nonmagnetic' material extending inside said solenoid around said plunger and having a thin disc of magnetic flux and eddy current conductive material extending across the end thereof in abutting engagement with said pole for receiving the impact of said plunger upon attraction thereof and for magnetically interlinking the opposite longitudinal laminations of both said pole and said plunger upon attraction thereof through a short magnetic path extending transverse a wide and flat eddy current conductive path to inductively produce out-of-phase flux for maintaining said plunger attracted upon alternation of the energizing current of said solenoid.

3. In combination, an alternating current solenoid having a laminated plunger and a magnetic circuit for conducting flux thereto including a laminated pole extending inside said solenoid, means providing a sealed enclosure for said plunger including a tube formed of a high resistance nonmagnetic metal extending inside said solenoid around said plunger and a thin plate of magnetic flux and eddy current conducting metal provided with peripheral connections 'for sealing said tube and supporting said plate in abutting engagement with said pole to receive the impact of said plunger upon attraction thereof, said plunger and pole each having the laminations thereof normal to and in contact with said plate upon attraction of said plunger to magnetically interlink said laminations through said plate to produce out-of-phase eddy currents in said plate for maintaining said plunger attracted upon alternation of the energizing current of said solenoid.

4. In combination, an alternating current solenoid having a longitudinally laminated plunger, a plunger guide tube formed of a high resistance nonmagnetic material extending inside said solenoid and having a thin plate of magnetic flux LOUIS 'r. as en

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