US2307113A

US2307113A - Refrigeration

Info

Publication number: US2307113A
Application number: US317380A
Authority: US
Inventors: George P Daiger
Original assignee: Hoover Co
Current assignee: Hoover Co
Priority date: 1940-02-05
Filing date: 1940-02-05
Publication date: 1943-01-05
Anticipated expiration: 1960-01-05

Description

G. P. DAIGER REFRIGERATION Ja is, 1943.

Filed Feb. 5; 1940 Patented Jan. 5, 1943 llI'I-IGEBATION George P. pm, Canton. Ohio, asaigner to The Hoover Company, North Canton, Ohio Application rem s, 1m, scan m. ums.

(Cl. ss-uas) Gains.

ratus are very high and may range from 250 pounds per square inch to over 400 pounds per.

square inch, depending upon the ambient temperatures involved and other operating conditions. It may also happen under certain abnormal conditions that the internal pressures may go to a much higher value.

The apparatus must therefore be suiilciently strong to withstand the high operating pressures involved under normal operation and also the higher abnormal pressures and at the same time be resistant to the corrosive action of the ammonia.

The use of a pressure equalizing medium ren ders it unnecessary to provide a large power unit for circulating the mediums, since there is only a small pressure head to overcome. It is therefore possible to circulate the mediums in such an apparatus with a. motor fan unit developing only a few inches of water pressure difference between the inlet and outlet side and requiring only a few watts power input.

This small motor unit must be so related to the apparatus that it will withstand the high pressures involved and also be protected from the corrosive action of the ammonia. One way of doing this is to position the motor rotor and fan interiorly of the apparatus and the motor fieldstructure exteriorly thereof. Due to the high pressures involved and the small size of the circulator unit required, this has been very dillcult to accomplish in prior machines of this type.

It is therefore one object of this invention to provide an absorption refrigerating apparatus of the type using a pressure equalizing medium and a smoll motor fan unit for circulating the mediums in which the motor rotor and fan are positioned interiorly of the apparatus and the motor field is positioned exteriorly thereof which will withstand the high pressures involved while pre serving the efficiency of the motor fan unit and in which the motor fan unit will be Protected from the corrosive action of the mediums being circulated.

More particularly it is an object of this invention to provide an absorption refrigerating apparatus of the type above referred to in which the motor rotor and fan unit is positioned interiorly of the apparatus and its stator positioned exteriorly thereof, in which the rotor and stator are separated by a thin shell of high strength corrosive resistant magnetic material with end sections of high strength corrosive resistant nonmagnetic material ioined to the shell and to the walls of the apparatus by welded Joints and in which the stator structure is so positioned relative to the thin shell as to reinforce it against internal pressures.

In absorption refrigerating apparati of the type under consideration, some means such "as a corrosion inhibitor is used to prevent the ammonia from attacking the metal of the boiler and the solution circuit. One such inhibitor is sodium chromate. This inhibitor has the property of reacting with iron to form a stainless steel surface which is resistant to further corrosion but has the disadvantage that it attacks other metals such as aluminum or other conductor bars and end rings for the induction rotor of the motor fan unit, some bearing materials and other parts of the motor fan unit.

It is therefore another object of this invention to provide an absorption refrigerating apparatus having a motor fan unit for circulating the mediums and using a corrosion inhibitor dissolved in the solution in which the motor fan unit is protected from coming into contact with the inhibitor.

Other objects and advantages of this invention will become apparent as the description proeeeds when taken in connection with the accompanying drawing in which:

Figure 1 is a diagrammatic representation of a refrigerating system embodying the present invention;

Figure 2 is a longitudinal sectional view of the motor fan unit separated from the system;

Figure 3 shows the details of construction of the shell between the rotor and stator of the motor; and

Figure 4 is a transverse cross-sectional view through the motor rotor and stator.

Referring to Figure 1 of the drawing, there is disclosed a three-fluid absorption refrigerating system comprising a boiler B, an analyzer D, an air-cooled rectifier R, a tubular air-cooled vertically positioned condenser C, an evaporator E, a gas heat exchanger G, a tubular air-cooled absorber A, a solution reservoir 8, a liquid heat exchanger L, and a circulating fan 1' which is driven by an electrical motor M.

The above described elements are interconof gas and liquid circuits constituting a complete refrigerating system to which reference will be made in more detail hereinafter.

The refrigerating system will be charged with a suitable refrigerant, such as ammonia, a suitable absorbent, such as water, a suitable inert pressure equalizing medium, such as nitrogen, and a corrosion inhibitor such as sodium chromate dissolved in the absorbent.

The boiler B will be heated in any suitable manner as by an electrical cartridge heater or by a gas burner as may be desired. The circulating motor M and the heater for the boiler 13 may be controlled in any suitable or desired manner.

The application of heat to the boiler B liberates refrigerant vapor from the strong' solution contained therein. The vapor so liberated passes upwardly through the analyzer 13 passing backwardly and forwardly across staggered baiile refrigerant vapor is liquefied in the condenser by heat exchange relation with atmospheric air and is discharged from the bottom portion thereof through a conduit i! into a downwardly extending conduit It. The bottom portion of the conduit It connects to the bottom portion of an upwardly ext nding conduit i1 through a ilbend II. The conduit II is appreciably longer than the conduit i1 for a purpose to be described hereinafter. The conduit ll opens at its upper end int-r a conduit 20 which discharges into the evaporator in a manner to be vdescribed more fully hereinafter.

The weak solution formed in the boiler by the generation of refrigerant vapor therefrom is conveyed from the boiler through a conduit 22, the outer pass of the liquid heat exchange L, and a condiut 23 into the solution reservoir 8. The weak solution is conveyed from the solution reservoir 8 through a U -shaped conduit 26 opening into a vertically extending tube 2!, of small diameter, forming a gas lift pump which dis- I culating fan F and leads to the junction of the conduits 24 and 2! which is below the solution level normally prevailing in the reservoir whereby the weak solution is elevated into the top of the absorber by gas lift action. I

In the absorber the weak solution flows downwardly by gravity in counterflow to the rich pressure equalizing medium refrigerant vapor mixture flowing upwardly therethrough. The refrigerant vapor content of the mixture is absorbed in the absorption solution and the heat of absorption is rejected to the surrounding air I 9,807,118 nected by various conduits to form a plurality by the air cooling nns'which are mounted on the exterior walls of the absorber vessel. The strong solution formed in the absorber discharges into a conduit 32 which opens into the inner pass of the liquid heat exchanger L. From the inner pass of the liquid heat exchanger L the strong solution is conveyed to the upper portion of the analyzer D by conduit 33 whereby it flows downwardly through the analyzer in counterflow to upwardly rising vapor generated in the boiler.

The lean pressure equalizing medium refrigerant vapor mixture formed in the absorber A is taken from the upper portion thereof through the conduit 35 into the'suction side of the circulating fan F in which it is placed under pressure and discharged through the conduit 28 into the outer pass of the gas heat exchanger G, through a downwardly extending conduit 8 into the bottom portion of the evaporator E.

The conduit 20 opens into the bottom portion of the conduit 36 whereby the liquid refrigerant supplied to the evaporator enters the same simultaneously with the pressure equalizing medium which is placed under pressure by the circulating fan F. The diameter of the conduits of the evaporator are relatively small whereby the pressure equalizing medium flows through them at a relatively high velocity. The rapidly flowing pressure equalizing medium sweeps or drags the liquid refrigerant with it through the evaporator into the box-cooling conduit ll as the refrigerant is evaporating by diffusion into the pressure equalizing medium to produce refrigeration. In the conduit 40 the velocity of the inert gas stream is relatively slow by reason of the large diameter of that conduit and the liquid refrigerant flows therethrough by gravity. Any liquid refrigerant not evaporated in the evaporator will flow through conduit 45, the inner pass of the gas heat exchanger and pipe 46 to the bottom of the absorber so as not to interfere with the operation of the motor fan unit.-'

- The rich pressure equalizing medium refrigerant vapor mixture formed in the evaporator is conducted therefrom into the inner pass of the gas heat exchanger G through a conduit 45. The opposite end of the gas heat exchanger G communicates with the bottom portion of the absorber A through a conduit 46. In the absorber A the rich pressure equalizing medium refrigerant vapor mixture flows upwardly in counterflow to absorption solution whereby the refrigerant vapor content of the mixture is absorbed by the weak solution.

The bottom coil of the evaporator E is provided with a drain conduit I which opens into the strong solution return conduit 32. The conduit 43 opens into the top portion of the bottom coil of the evaporator whereby it will not completely drain such conduit. The upper portion of the discharge conduit ll of the condenser is vented through a vent conduit ll into the inner pass of the gas heat exchanger'G. The solution reservoir 8 is vented through a conduit 0 into the suction conduit of the circulating fan.

The circulating fan Fplaces the pressure equalizing medium discharged therefrom \mder a small pressure in the neighborhood of a pressure of 4%" of water. In order to prevent this pressure,

which also prevails in the conduit 38, from bea pressure balancing column of liquid is formed in the conduit ll which extends above the point .of connection between the conduits l1 and 20 a distance sufiicient to overcome the pressure produced by the circulating fan F in the conduit 36.

Referring to Figures 2, 3 and 4 the motor fan unit comprises a fan casing 52 comprising an annular portion 54 with end plates 55 and ii welded thereto. The interior of-the fan casing is divided by a plate 58 into a suction chamber and a discharge chamber and has an opening 9 leading to the suction or eye side of the fan. Welded to the end plate 56 is a motor shell generally indicated at SI which separates the motor rotor 62 and the motor field structure 64. The shell 60 is made up of three sections of annular form welded together in end to end relationship. The three sections comprise a cup-shaped end section '66, a central annular section 68 and an end annular section 10 which is welded to the end plate 58 of the fan casing.

The sections 66 and 10 are made of a chrome nickel alloy steel which has the approximate percentages of 18% chromium, 8% nickel and a low percentage of carbon. This steel has a very high tensile strength, is very resistant to corrosion by the ammonia in the system and is nonmagnetic in that it has a high reluctance and low permeability.

The central section 68 is made of a chromium steel alloy having the approximate percentages of 16% to 18% chromium and a low percentage of carbon. This steel alloy has a very high tensile strength, is highly resistant to the corrosive action of ammonia and is magnetic in that it has a high permeability and low reluctance.

The motor rotor 82 is rigidly connected with the fan F by means of a shaft 12 supported at one end by a bearing assembly 14 in the cupshaped section 68 and at the other end by a bearing assembly 18 suitably supported on the end plate of the fan housing. The fan F may be made of aluminum or other metal not subject to attack by an ammonia atmosphere and includes a throwoff ring 18, the purpose of which will be described later. The rotor 62 is made of stainless steel laminations with cast aluminum conductor bars and end rings II for forming an induction rotor of a well known type. The motor field structure includes windings 82 and iron laminations 04 having a plurality of poles 85.

restricted to the absorption solution circuit. Yet; by reason of the novel arrangement of parts. I am enabled to employ a motor driven pump to circulate absorption solution without any danger of the inhibitor or solution coming into contact with any part of the motor pump assembly.

Any liquid refrigerant which is not vaporized in the evaporator E will be led through the conduit 45, the inner pass of the gas heat exchanger 10 .G and the conduit 46 to the bottom of the absorber. It can therefore be seen that none of this liquid refrigerant can reach themotor fan unit which is in the other half of the pressure equalizing medium circuit.

Furthermore, any condensate which may collect in the outer passage of the gas heat exchanger or in conduit 28 is prevented from reaching the pump assembly since such condensate is drained off through bleed conduit .21.

Sincethe fan F only develops a pressure difference of a few inches of water, the motor M may be made very small with a power input of approximately 12 to 15 watts. It can therefore be seen that it is essential that the shell between the rotor and stator be made as thin as possible consistent with withstanding the pres sures involved and at the same time have the best magnetic properties for the magnetic lines of force passing from the motor field structure to the rotor. In Figure 3, the section 88 whichseparates the rotor from the stator is shown enlarged but in actual practice its thickness is a few thousandths of an inch.

The making of the central section 68 of high strength stainless magnetic steel alloy is therefore very important since its high strength char- 'acteristics renders it suitable for withstanding the high pressures within the system, its corrosion resistant properties renders it suitable for resisting the corrosive atmosphere within the system and its magnetic properties renders it suitable for use as a part of the motor field structure itself. Sincethe field structure U is pressed tightly over the central section I, it can be seen that thesection ll forms a part of the field structure itself as it forms a magnetic path for the magnetic lines of force from the field The central section 68 which lies between the rotor and stator of the motor is made extremely thin so as to reduce the eflective air gap between therotor and stator. This section is machin'ed very accurately on the interior and exterior surfaces to. provide avery small air gap between the rotor and shell and to provide a liquid that might condense in the outer partof the gas heat exchanger G and tube 28 when the system is shut down will be immediately thrown oil by the throw-oil ring 18 and drain into the absorber through drain opening 88. None of the sodium chromate inhibitor in the solution circuit can ever reach the motor fan unit since this inhibitor is not vaporizable.

Hence. i Will be clear that 'the inhibitor is 75v structure to the rotor in addition to performing its function as a part of the system walls;

In small fractional horse power induction motors of this type it has been found that if the adjacent tips of the poles are connected by a magnetic bridge that the motor has better running characteristics. As can be seen from Figure 4, Y

the magnetic annulus 8, in addition to forming a part of the refrigerating system walls, forms a'magnetic path for the lines of force from the field structure to the rotor and also forms a-magnetic bridge between adjacent pole tips. This section therefore performs three separate and distinct functions in the complete system.

The non-magnetic sections" and 10 also perform two distinct functions in that in addition to forming part of the system walls they prevent magnetic flux leakage from adjacent poles of the field structure and also prevent magnetic flux leakage to other parts of the system itself.

The field structure 6i also performs a double erant in various parts oi the system without coming in contact with any of the liquid mediums within the system. which is inaccessible to the chromate inhibitor dissolved in the solution, in which the field structure is positioned extericrly of the system whereby it cannot be attacked by the corrosive atmosphere, and which is separated from the motor rotor by a thin magnetic shell which performs magnetic functions as well as mechanical flmctions.

While I have shown but one embodiment of my invention, I do not wish to be limited to the particular structure shown and described but to include all equivalent variations thereof except as limited by the claims.

I claim:

a 1. An absorption refrigerating apparatus of the type using an inert pressure equalizing medium and subject to an internal pressure in excess of 250 pounds per square inch, in combination with a motor-fan unit for circulating the mediums in the apparatus, said motor-tan unit comprising a fan and motor rotor positioned interiorly oi the apparatus and a motor ileld structure positioned exteriorly oi the apparatus, a thin shell of high strength chrome-alloy steel having magnetic properties separating the motor rotor and held structure, an annular section positioned between the thin shell and other parts of the apparatus walls, and an end section positioned at the other end of the thin shell and closing the interior oi the apparatus, said annular section and end section being 01' a high strength chrome-nickel alloy steel having nonmagnetic properties and being joined to the thin shell and to the walls of the apparatus by welded joints, said field structure being so relatedto the thin shell as to reinforce it against the pressure within the apparatus.

2. An absorption refrigerating apparatus of steel integrally connected in end to end relationthe type using an inert pressure equalizing medium in combination with a motor-fan unit for circulating the mediums in the apparatus, said motor-fan unit comprising a tan and motor rotor positioned interiorly oi the apparatus and a motor field structure positioned enteriorly of the apparatus, a thin shell of magnetic material separating the motor rotor and held structure, an annular section separating one end of the thin shell from other parts of the apparatus walls, and an end section positioned at the other end of the thin shell and closing the interior oi the apparatus, said annular section and end section being of non-magnetic material and being joined to the thin shell and the apparatus walls by welded joints, said field structure being so related to the thin shell as to reinforce it against the pressure within the apparatus.

3. An absorption refrigerating apparatus, a boiler, an absorber and an evaporator, conduits connecting said boiler and absorber to form a closed circuit for simulating an absorption solution between the boiler and absorber, conduits connecting said evaporator and absorber to form a closed circuit for circulating a pressure equalizing medium between the evaporator and ab sorber, power driven means in the evaporatorabsorber circuit for circulating the pressure moans accumulation of liquid mediumsunder certain conditions, said fan casing having means to: draining any accumulated liquid away from the motor-fan unit and said motor rotor casing comprising three annular sections connected in end to end relation with each other and the fan casing by welded joints, the end sections being oi non-magnetic material and the central section of magnetic material.

4. A shell for a iractional horse power induction motor for circulating a medium in an absorptlon refrigerating apparatus in which the rotor is subjected to the corrosive atmosphere andhighpressureontheinteriorottheshelland inwhichtheneldstructureisarrangedexternally oi the shell, comprising, a cup-shaped membcr ct non-magnetic strainless steel, a seamless annular section 0! annealed magnetic stainless ship to the open end of the cup-shaped member by a welded joint, and an annular member of non-magnetic stainless steel integralh connected in end to end relationship to the other end of ghientmag'netlc stainless steel section by a welded 5. An induction motor for circulating a medium in an absorption refrigerating apparatus which is subjected to the corrosive atmosphere and high pressure on the interior oi a casing and inwhich a multi-pole stator is positioned on the exterior oi the casing, comprising, an integral shell for separating the rotor from the stator, said shell comprising two end annular sections or non-magnetic steel and a relatively thin central annular seamless section of magnetic steel joined to the end annular setcions by welded joints, :1. multi-pole field structure positioned over said thin central section so as to support it against internal pressure, and an induction rotor positioned for rotation on the interior oi the shell with the rotor proper pomtioned at the central magnetic section, said magnetic section forming a bridge between the pole tips of the field structure to thereby improve the running characteristics of the motor as well as to form a portion of the enclosing casing for the rotor.

8. A hermeticaly sealed unit tor operation under high pressures within the interior of an absorption refrigerating apparatus, comprising a casing 01 magnetic material, a closed end annular shell secured thereto by a welded joint, said shell comprising an end annular member and an inner annular member of non-magnetic steel connected to prevent magnetic tiux leakage acrom adjacent poles, said thin annulus of magnetic steel serving to connect adjacent pole tips by a magnetic path and also to form a part of the enclosing casing, and mid inner annular section serving to prevent magnetic flux leakage trom the field structure to the magnetic casing as well as to form a portion of the casing.

7. A hermetically sealed unit for operation imacorns lar shellsecuredthereto by a:=welded ioint, said shell comprising an end cup-shaped member and an inner annular member; oi non-magnetic steel connected by a thin annulus oi seamless magnetic steel joined torthe-inner and'end members by welded joints, arotatable element inv said casing-subduction rotor secured to saidrotatable element. for rotation therewith, the rotor proper beingpositioned in said shell at the thin annulus oi magnetic steel, and a multiple pole stator positioned on .the exterior oi said thin annulus oi magnetic stainlesssteel. so as to support it against internal pressure.

8. A closed end annularv shell ior separating the rotor and stator oi an induction motor ior circulating a medium in an absorption reirigerating apparatus comprising, a continuous annular wall in which the metaloi the wall has molecular cohesion throughout, said wall being divided into an intermediate annular section oi magnetic material and end annular sections oi nonmagnetic material.

9. An annular shell for separating the rotor irom the stator or a dynamo electric machine ior circulating a medium in an absorption reirigerating apparatus comprising, a continuous annular wall having an uninterrupted crystalline structure, said wall being dividedv into an intermediate annular section oi magnetic material and end annular sections oi non-magnetic material.

10. An absorption refrigerating apparatus, comprising a boiler, an absorber and an ever orator, conduits connecting said boiler and absorber to iorm a closed circuit ior circulating an absorption solution between the boiler and absorber, conduits connecting said evaporator and absorber to iorm a closed circuit for circulating a pressure equalizing medium between the evaporator and absorber, power-driven means ior circulating said pressure equalizing medium in its circuit and utilizing aportion oi said medium. ior circulating the absorption solution between the boiler and absorber, said power-driven means comprising a motor ian unit having a rotor and a ian assembly hermetically sealed within the walls oi the a'pparatuaa stator outside the walls oi the apparatus and surrounding an annular 'section oi the wall the apparatus constructed to house said rotor, said annular section being made oi stainless magnetic steel and being separated irom and connected to other portions oi the apparatus walls by an annular section oi non-magnetic steel, said sections iorming an integral part 1 oi the apparatus walls and having a continuous uninterrupted crystalline structure throughout. 11. An absorption refrigerating apparatus, comprising a boiler, a condenser, an evaporator andan absorber, the top oi; said evaporator being positionedabove thebottom oi the condenser, a conduit connecting the bottom oi said condenser with the evaporator ior leading liquid reirigerant thereto, conduits connecting said boiler and absorber to iorm. a closed'circuit to circulate solution between the boiler and absorber, conduits connecting the evaporator and absorber to iorm' a-ciosed. circuit ior circulating inert pressure equalizing medium between. the evaporator andabsorber, power-operated means ior'circulatingmediums in their circuits,'said power-operated means comprising a motor-ran unit having a oi magnetic steel andheing separated irom and joined to other'parts oi the apparatus walls by an annular section oi non-magnetic steel, said sections iorming an integral part oi the apparatus walls and having a continuous uninterrupted crystalline' structure throughout. and means ior utilizing the pressure developed by the ian ior circulating the absorptionsolution between the boiler and absorber and tar moving liquid reirigerant along the evaporator.

I 12. In an absorption reirigerating apparatus, an evaporator and an absorber, conduits connecting the evaporator and absorber to form a circuit for circulating pressure equalizing medium between the evaporator and absorber and power-operated means ior circulating said medium in it circuit, said power-operated means comprising a motor rotor separated irom a motor field structure by a shell oi stainless steel, said shell comprising a closed end section, of nonmagnetic steel, a thin annular section oi magnetic steel between the rotor and stator and an annular section oi non-magnetic steelv separating the magnetic annular section from the remainder oi the apparatus walls, the sections oi said shell .iorming an integral portion oi the reirigerating apparatus walls and having a continuous uninterrupted crystalline structure throughout, saidiield structure being positioned to assist said magnetic section in supporting the internal pressure oi the apparatus, said magnetic annular section iorming a part oi'the magnetic circuit oithe neld structure-and rotor, and said non-magnetic section. serving to prevent magnetic flux leakage between adjacent pole oi the iicld structure and to other parts of the-reirigerating apparatus.

13. In combination with a plurality oi interconnected fluid circuits including a gaseousiluid circuit and liquid circuit having a part in common with saidgas circuit, a motor-driven pump tions on either side oi the stator, said casing consisting oi materials resistant to attack by the fluids being circulated.

. 14. In combination with a reirigerating system oi the hermetically sealed type, said system ineluding a casing having a continuous uninterrupted crystalline structure throughout subject on its interior to conditions within the system and iorming an intezral part oi the walls-thereof, a motor driven pumping mechanism housed by said casing and operable to circulate a medium within the system, said casing including an annular-magnetic section, interposed between two non-magnetic portions, a motor armature rotatably mounted within said annular section, a stator having a plurality oi spaced poles mounted about said annular section exteriorly thereoi and in such manner that portions oi said section bridge the gap between adjacent poles with mamotor rotor and ian assembly hermetically sealed to terial oi high permeability and low reluctance,

whereby portions of said casing are common to both said refrigerating system and to said motor.

15. In combination, an absorption refrigerating apparatus of the type subject to interior pressures in excess of 250 pounds per square inch and power means for circulating a medium in the apparatus, said power means including a multipole, fractional horse power induction motor having it field structure positioned exteriorly of the apparatus, its rotor interiorly of the apparatus and a casing having a continuous uninterrupted crystalline structure throughout separating the field structure and rotor and forming a part of the apparatus walls, said casing comprising a thin annular section of magnetic material separating the rotor and field structure and two end annular sections oi. non-magnetic material extending beyond the ends of the field structure and rotor, said field structure being pressed tightly over the thin annular magnetic section whereby the field structure supports the thin section against internal pressure as well as performs its electrical function, the thin annular section forms a part of the flux path of the motor'and serves to form magnetic bridges between adjacent poles as well as serve as part or the apparatus walls and said end non-magnetic sections serve to prevent flux leakage between adjacent poles and other parts of the apparatus as well as serve as part or the apparatus walls.

16. An annular shell for separating the rotor and stator of an induction motor for circulating a medium in an absorption refrigerating apparatus comprising, a continuous annular wall having an uninterrupted crystalline structure throughout, said wall being divided into an intermediate annular section of magnetic material and end annular sections of non-magnetic material with a sharp line of demarcation between said sections, the metal between said sections being free of oxides.

17. A shell for separating the stator and rotor oi a dynamoelectric machine for circulating a medium in an absorption refrigerating apparatus comprising, a unitary shell in which the iron of the end section is in an austenitic state and the iron of the central section in a ferretic state and in which the she l has a continuous uninterrupted crystalline structure throughout. I

18. A unitary shell for separating the rotor and stator of a dynamoelectric machine for circulating a medium in an absorption refrigerating apparatus comprising, a steel shell in which the atoms of the iron in the end sections are so arranged that the end sections are non-magnetic and those of the central section so arranged that the central section is magnetic.

19. A motor for circulating a medium in an I absorption refrigerating apparatus comprising, a casing, a rotor mounted for rotation in the interior of said casing and a stator pressed over the exterior of said casing, said casing comprising a closed end shell in which the metal of the shell has molecular cohesion throughout and said shell being divided into an intermediate annular section of magnetic material and end sections of non-magnetic material, said intermediate section being positioned immediately between said rotor and stator and said end sections being positioned outside the linear extent of said rotor and stator.

20. A motor for circulating a medium in an absorption refrigerating apparatus comprising, a casing, a rotor mounted for rotation in the interior of said casing and a stator pressed over the exterior of said casing, said casing comprising a shell having an uninterrupted crystalline structure throughout and being divided into an intermediate annular section of magnetic ma- .and said end sections being positioned outside the linear extent of said rotor and stator.

GEORGE P. DAIGER.