US2951686A - Heat exchangers - Google Patents

Description

P 1950 SANDMANN EI'AL 2,951,686

HEAT EXCHANGERS I Filed July 2, 1954 7 Sheets-Sheet 1 Fig. 1

Sept. 6, 1960 H. SANDMANN ETAL 2,951,686

HEAT EXCHANGERS Filed July 2, 1954 7 Sheets-Sheet 3 p 1960 H. SANDMANN ETAL 86 HEAT'EXCHANGERS Filed July 2, 1954 7 Sheets-Sheet 4 22 TW 5 ;\\\\\m\ 2 l9. llllllll/II/I 5 55 57 Sept. 6, 1960 H. SANDMANN ETAL 2,951,636

HEAT EXCHANGERS Filed July 2, 1954 7 she ts-sheet 5 H fimdm alt/1w Z?) Era/w H. SANDMANN ET AL 2,951,686

HEAT EXCHANGERS Sept. 6, 1960 7 Sheets-Sheet 6 Filed July 2, 1954 w- E1 H.'SANDMANN ETAL 2,951,686

HEAT EXCHANGERS Filed July 2, 1954 I 7 Sheets-Sheet 7 Unitecl States atent HEAT EXCHANGERS Herbert Sandmann, Kurfurst Heinrich Strasse '3, ()lpe,

Westphalia, Germany, and Herbert Brandt, Rothemuhle uber Olpe, Westphalia, Germany Filed July 2, 1954, Ser. No. 441,106

12 Claims. (Cl. 257-265) Regenerative air pre-heaters and similar heat exchangers" are known in which the regenerative storage elements are made of thin sheet metal which mounted in a strong casing constitute a rotor. According to the output such rotors have a high weight up to many tens of tons. Even though the journalling of such heavy bodies can be effected satisfactorily sealing of the media flowing through the heat exchanger from each other and from the outer air presents serious difiiculties. The provision of as small as possible a labyrinth gap is made very difficult by the large dimensions, the sag of the rotor, and finally through the heat expansion of the structure. A substantial improvement can be obtained by the use of flexible rubbing plates. Since the output requirements have become ever greater the dimensions of such heat exchangers have also become greater and the difficulties of satisfactory sealing of the media have accordingly increased.

In the know-n constructions the rotor itself performs the function of a control member because by its rotation the various regenerator chambers arranged in the direction of rotation are brought into and out of the zones of the difierent media in succession. Whereas it is desirable in technical apparatus for the control members to consti tute but a small fraction of the Weight and structure of the complete apparatus, in the known rotary heat exchangers the conditions are just the reverse.

It has already been proposed to unite the numerous storage elements into a separate body and fix this and to effect the direction of the media through it by rotation of the housing. Such a solution cannot be satisfactory, however, by such rotation of the housing alone, because the above mentioned difiiculties are not removed by this arrangement, but on the contrary are only increased by the necessity of mounting the housing so that it is rotatable.

According to the present invention an apparatus for heat exchange between flowing media, in particular for preheating the combustion air for furnaces, is provided which. comprises a stationary regenerator chamber of circular cylindrical form, stationary inflow and outflow members for one medium, and rotatable pipe connections between the inflow and outflow members and the regenerator chamber for the other medium, and one end of each of the pipe connections slides over one end surface of the regenerator chamber making a good joint and preferably being of sector form, while the other end is concentric to the axis of rotation and makes a joint with the inflow .or outflow member or pipe. The invention will be described in detail with reference to the accompanying drawings:

Figure l is a diagrammatic side view of a heat exchanger according to the invention.

Figure 2 is a horizontal section looking downwardly on the line IIH of Figure 1.

Figure 3 is a horizontal section looking upwardly on the line ll-11 of Figure l and showing diagrammatically an example of only one sector form opening of the rotating pipe connection.

Figure 4 is a view from below on the line LLI-LH of Figure 1.

Figure 5 is a vertical section showing the sealing arrangements and mounting of the upper pipe connection.

Figure 6 is a cross section on an enlarged scale taken on the line Vl--VI of Figure 5.

Figure 7 is a fragmentary vertical section of the mounting of the upper pipe connection close to the central shaft on an enlarged scale taken on the line V1I-VH of Figure 2.

Figure 8 is a fragmentary vertical section on an enlarged scale taken on the line VIII VIH of Figure 2.

Figure 9 is a fragmentary plan view of the mounting of the upper rotating sealing frame with part of a compressed air cleansing device.

Figure 10 is a vertical section showing the mounting of the lower rotatable pipe connection and the journalling of the shaft.

Figure 11 shows the arrangements of the regenerator elements in the regenerator chamber seen from above.

Figure 12 is a fragmentary vertical section on line XIIXII thereof, and

Figure 13 illustrates diagrammatically an apparatus for grinding the elements in the regenerator chambers, as seen in side view.

A rigidly mounted cylindrical casing or regeneration chamber 15 which contains the regenerative material shown as being made up of packets of sheet metal elements or other storage elements by which the heat is taken up and then given out again is secured to a foundation 17 by means of feet 1 6. Combustion gases are supplied through an entry chamber 18 and led out through an outlet chamber 19, both chambers being fixed to the casing 15. The cold air is supplied from below through a bend 20, and thence flows through a pipe connection 21 rotating about the axis of the casing, which pipe connection if of 8 form and the outlet of which is so formed that it covers a part of the lower end surface of the easing 15, preferably being of sector form. This pipe connection 21 will be called the rotatable pipe connection.

It is obviously possible instead of using a single pipe connection of sector form to use two or more which are joined together about the axis of rotation. By the use of a plurality of such connections bending moments are avoided in the shaft.

In a corresponding fashion on the upper end surface of the regenerator chamber, that is to say, on its outlet side a corresponding rotatable pipe connection 22 is arranged in the combustion gas entry chamber 18 for the heated air into which the heated air from regenerator chamber 15 passes to flow upwardly through a pipe bend 23 leading to a pipe line 24.

The two rotatable pipe connections 21, 2 2, are mounted by shafts 25 and 26, respectively, in the axis of the exchanger to overhang the casing or chamber 15 and are so connected together by a longitudinally slidable coupling that they rotate in the same direction while adjustment of the pipe connection in relation to the end surfaces of the regenerator chamber 15 is possible. It is, however, also possible and often indeed advantageous to secure both rotatable pipe connections upon a single shaft passing right through.

The shaft 26 of the lower pipe connection 21 is, surrounded by a protecting tube 27 (Fig. 10), the purpose of which will be described later. The shaft 26 is mounted and supported in a journal bearing 28 and a thrust bearing 29. The drive of this shaft and thus of both pipe connections is effected by a motor 30 through transmission gearing 31 (Fig. l). The shaft 25 for the upper rotatable pipe connection 22 is externally mounted in a bearing 32 and internally in a bearing 33. However, if a single shaft passing right through is used, the upper axial bearing 32 and the lower thrust bearing 29 would suflice. Fig. 2 shows the sector-like inserts in the re generator chamber 15 seen from above and supporting rollers 35 of the sealing frames described in greater detail later which are carried'round with the pipe connections. This arrangement will be described in greater detail below.

Fig. 3 shows diagrammatically the upper rotating pipe connection 22 with only a single sector shaped opening and its connection to the pipe bend 23, whereby a good in and out flow of the media are ensured in all positions of the rotatable pipe connection.

Of particular importance in the heat exchanger according to the invention is the gas tight sealing of the rotatable pipe connections 21, 22, by sealing frames which are supported by adjustable rollers 35 on tracks 36 on the regenerator chamber. One construction of these parts of the heat exchanger is illustrated by way of example in Fig. 5. The rotatable pipe connection 22, which is cylindrical at its upper end and of sector shape at its lower end, is mounted on the shaft 25 by means of a hub 37 in such a way that its height can be adjusted, but so that it is not rotatable in relation to the shaft. Adjustment of height is effected by means of internally threaded adjusting rings 38 with looking rings 39. At the upper end the pipe connection is secured to the shaft by means of adjustable tension bolts 40. On the sealing frames which are axially adjustable in relation to the rotating pipe connection are a plurality of running rollers 35 which are preferably distributed roundthe periphery and either spring mounted or preferably fixed but adjustable in level. When the regenerator chamber 15 is constructed as a hollow annular cylinder it can with advantage be provided at the top and bottom on its inner end surface with a flange or some similar track 41, on which also rollers 42 run (Figs. 2 and and which can at the same time serve as a labyrinth packing or a track for a rubbing packing as is shown in detail in Figures 7 and 8.

The openings of the rotatable pipe connections facing the regenerator chamber 15 are each formed by a frame 43of channel section material, on which a sealing frame 44 is vertically slidably mounted which has projecting flexible blades or leaves 45 and can be pressed towards the regenerator chamber by spring members 46. This arrangement is shown on an enlarged scale in cross section in Fig. 6 for the upper pipe connection. Beneath the frame 43 to which the rotatable pipe connection 22 is secured in gas tight fashion is located the sealing frame 44 with an exchangeable packet of blades or leaves 45 which bear against the plates in chamber 15 and present a sealing surface which is a small multiple of the spacing of the plates forming the heat exchange elements. Both parts are secured together in vertically adjustable fashion by means of a band seal 47 and screws 48 passing through slots. Between the sealing frame 44 and the band seal 47 is a ring 49 of graphite or other sealing ma terial. At intervals of the sealing frame, as Fig. 5 shows, are spring heads 46, which contain plungers 50 under spring pressure which engage in cylindrical lugs 51 on the upper side of the sealing frame 44. The structure of the similar elements of connection 21 is the same. The spring pressure is adjustable by means of a screw 52 hearing against the abutment 53 for the spring. In this way the pressure of the sealing frame and thus of the blades 45 against the end of the regenerator chamber 15 can be regulated.

The sealing frame 44 on the inner side near the shaft 25 is also supported by rollers 42. Such an arrangement is shown in radial section on the line VII-VII of Fig. 2 and in Fig. 7 on an enlarged scale. On the running surface 41 which adjoins the top and bottom surface of the regenerator chamber 15 on the inside towards the shaft 25 or 26, run rollers 42. These rollers are loose on pins 54 supported at one end by the aid of adjusting screws 55 which pass through them and are thus adjustable in the vertical direction in guides 56. Service openings in the hub 37 can be closed gas tight by caps 57. Between a plate 58 carrying the rollers 42 and the hub is again provided a band seal 47 and sealing ring 49. Similarly, a sealing ring 61 is provided between the body of the track 41 and the roller-carrying plate 58.

Fig. 8 shows on an enlarged scale the internal sealing between the radial members of the sealing frame 44 and the stationary regenerator body 15. To the hub 37 is secured the frame 43 of the rotating pipe connection by which as already described the sealing frame 44 with the packet of blades 45 is carried along through sprung plungers 50. On the sealing frame 44 are inwardly projecting arms 62 traversed by bolts 63 which are screwed into the roller supporting plate 58. Between the plate 58 and the arms 62 lying above it are spring elements, for example dished plate springs 64 and adjust: ing means such as washers or shims 60.

In Fig. 9 the outer support of the sealing frame is shown. On the outer arcuate member 59 of the frame 44 are angle form carrying arms 65 provided with a guide block 66 for the pin 67 of the rollers 35. The height of. the pin 67 can be adjusted in a similar manner to that above described with reference to Fig. 7 for the inner carrying rollers 42. On the same track on which the rollers '35 run, a packet of blades 45 are provided to rub on the inner edge of the arcuate member 59 of the frame 44, pressure is applied by adjustable spring members in the same way as in the case of the radial members 44 of the frame.

It should here be mentioned that each sealing frame is not in itself. rigid but that the parts, arcuate member 59, two radial bars 44 and the hub-like carrying plate 58 (Figs. 2 and 8), are connected together with sufiicient play to allow a certain degree of relative movement. Just as the radial members 44 are connected to the plate58 through the parts 60, 63, 64, so is the arcuate member 59 attached to the two radial members. The arcuate member 59, the radial members 44, and the plate 58 each has its own packet of blades and in each packet of blades the length of the blades is transverse to the flow direction of the media.

In Fig. 9 another feature of the heat exchanger according to the invention is shown. Alongside one of the radial members of the sealing frame 44 is an apertured tube 68 which communicates with the interior of the shaft 25 which is made hollow. At its upper projecting end above the bearing 32 the shaft 25 is provided with a stuffing box for connection to a compressed air supply. The apertures in the tube 68 are directed towardsfthe regenerator chamber 15 so that by blowing in compressed air from time to time the regenerator can be cleaned. Further, at the periphery of the frame a scraper 69 is provided which frees the track surface for the outer rollers 35 from deposits.

The lower pipe connection 21 is sealed to the lower end surface of the regenerator chamber in exactly the same way as described in detail above for the upper pipe connection 22. At the inside adjacent the shaft the lower pipe connection is also sealed in the same way as the upper pipe connection by means of a band seal which perm-its axial movement.

In Fig. 10 the height adjustment of the lower rotatable pipe connection 21 is shown in vertical section. The pipe connection 21 is prevented from rotating in relation to the shaft 26 by means of a two part hub 70 and a key 71. A tube 27 extends downwardly from the hub 70.

mechanism as diagrammatically shown in Fig. 13.

Tube 27 is further connected to another'tube 72. This tube '72 .passes through a packing .73 'held by .two part housing parts 74, 75, mounted on the inlet bendc ZO and carries a flange 76 which rests on thethrust bearing 29. On its underside the lower race ofthe thrustbearing29 is heId by a nut'77, which runs on a threaded element :7 8'

so nut 77 -can'be moved vertically withrespect tozshaft 26. The shaft 26below the threaded elemerit178risshouldered and is-provided with oneThalf 79 lot a coupling of which the other half is connectedzto .the driving gear 30,31.

By rotating the nut 77 on threaded element .78 .an adjustment in height of the lower rotatable pipe connection 21- can be effectedfromthe-outsideduring operation. A similar arrangement couldalso beprovided forithe upper rotating pipe connection. While the adjustment illustrated in Figs. 7 and 8 can onlybe effected frominside, if an arrangement similar tothat shown inFig. 10 is provided at the top, then adjustment could beeffecte'd during operation. It will be noted that the adjusting means described enable the precise axial separation between the two rotating pipe connections to be adjusted as-well as each ofthem to be adjusted separately in relation to the stationarypart of the apparatus. Itmay here also be pointed out that as shown in Figs. 7 and Sthe hub -37 has a bore which widens outdownwardly. Thisenables a certaindegree of adjustment in relation to the horizontal planeto beefiectedby the aid of the tension bolt 40 shown in Fig. and above described. Manifestly the hub of thelower rotating pipe connection 21 is or can be similarly arranged.

In small exchangers the external axial adjustment shown in Fig. may not be necessary and both'rotatable pipe connections could have an adjustment as shown in Figs. :7 and 8 which can only beadjustedfronrinside.

A further feature ofthe invention =is the arrangement of the actual heat storage elements in the stationary regenerator chamber 15. As shown in Fig. l'l the-chamber isdivided into substantially sector form sections. By suitably sub-dividing the space in each -section-it can befilled with subsections-or units of only two different forms, namely, a rectangular form and a:triangular form. 'Desirably, these two unitary forms have a length half the mid radial length of'the sector form. :In Fig. 11 it isassumed that the chamber is internally and externally bounded by a regular dodecagon and that this is subdivided at half radius. The inner part is then made up of two triangular units and one rectangular unitand the outer part of two triangular units-and two rectangular units as shown in the figure. By this sub-division the production of the actual heat exchange bodies which are usually made up of thin waved or foldedsheet metal is substantially simplified. This arrangement also gives an unimpeded free flow area, close packing ofthe individual bodies without separate seals and it facilitates exchange.

The dividing walls between the elements run'radially so that an exact cutting off action by thesectorform apertures sweeping over them of the rotatable pipe con InFig. 12 is shown the securing of the waved sheets 80 :in boxes-81 by narrow bars 82, which are mounted for example at half height on the narrow sides of the rectangular boxes and of the short side and hypotenuse of the triangular boxes. The flow passage through the elements is in this way diminished very little. In order to obtain a thoroughly smooth surface of the regenerator chamber and the box form exchange bodies located therein, according to a further development of the invention, the shafts 25, 26, can be used as supports for a grinding A grinding carriage 83 runs on a radial support secured at one end to the shaft 26 and at the other end running, for example with aroller, on thetrackfor the rollers or the corresponding track on theunderside of thecylindrical chamber 15. A dished grinding disc driven by a compressed air motor 84 can be adjusted radially: over. the whole radius of the boxes inserted in the regenerator chamber by the aid of a screw spindle 86 manually or automatically while the arm can be rotated by theshat't 25 or 26, thusenabling the whole end surface'to be ground. The compressed air is drawn through the hollow shaft 26 after the air motor 84 has been connected tothe shaft in place of the cleansing tube 68.

The essential advantage which is obtained by the invention is that on one hand the moving parts are :of considerably smaller dimensions than the actual-heat exchanger and accordingly are also relatively light. -Further, the heat exchanger itself on account of its stationary mounting can now be rigidly constructed so that deformation through weight and sagging are longer to be feared. Further, the constructionzcan now be so arranged that deformation of the exchanger and the casing under the effect of varying heat action is no longer to be feared in the same measure as hitherto. For these reasonsthe problem of sealing hitherto found to be extremely difficult has been solved. The sealing of the two rotatable pipe connections to the stationary pipe bends presents no particular difiiculties as here uniform temperatures are met with so that these additional seals bring no special problems. The end :surfaces of the regenerator chamber will be made and erected as nearly as possible horizontal. Theshafts of the rotatable pipe connections can be set veryaccurately perpendicular to these surfaces without difliculty and the sealing frames of the rotating members 21, 22, can also be set strictly perpendicular to the shafts without'difiiculty. This applies in particular if, for example, the arcuate outer members and the radial members of the sealing frames are made of cast iron so that warping does not occur even at high temperatures. .By this very simple measure there is only a very small gap between thexend surfaces of the exchanger and the sealing frames of the rotating pipe connections. With the construction of 'Fig. 10 the size of this gap can also be regulated during operation, that is, after working tempera ture has been reached. The coupling 79 and the axial adjustment of the bearing 29 provide for this. It may be desirable to provide the arcuate members of the sealing frames with labyrinth combs which coact with corresponding combs on the exchanger. To obtain good sealing of the air in relation to the gas space it may be desirable to suck away the air passing through the gap. For this purpose, for example, the shaft 25 surrounded by the tube 27 can be used and for example a tube may be led from the radial members of the frames to this collecting tube 27. Further tubes can be connected from the inner seal to a collecting tube. From this collecting tube a pipe leads to a suction blower.

To seal the rotating pipe connections in relation to the gas inlet chamber 18 oroutlet chamber 19 and in relation to the air inlet bend 20 each of the rotating pipe connections may be provided with a flange which makes joint with a stationary flange by means of a labyrinth packing. This is all the more effective inthat the diameter is relatively small so that it can be-satisfactorily turned (machined) and is readily accessible for fitting.

The end surfaces of the regenerator chamber are formed by the edges of the sheet metal storage elements. In order to obtain statisfactory flat and horizontal end surfaces in the erection of the exchanger it is advantageous to provide an insert of small height in front of the storage element block. insertion is made of sector form pieces which are secured only to the casing and to the core wall and are slidably connected with the storage element block. Under the constantly varying temperatures the heat exchanger suffers constant changes of length which, however, are only slight- 1y noticeable in the construction according to the invention-because although the thin sheet metal elements react at once to temperature changes the stout sheet metal of the outer casing constituted by the inner tube 23 and the outer wall only varies about a mean temperature so that even during operation a substantially constant gap is to 'a great extent ensured. In this connection the position of the feet 16 on the casing is of importance. If these feet are secured as low down as possible to the casing 15 the changes in length of the exchanger only take place above this level so that a change in gap of the lower rotating pipe connection does not take place.

The journalling of the rotating pipe connections must also be considered from the point of view of varying the gap as little as possible under temperature changes. Thus, the axial location, that is to say, the position of the thrust hearing, may desirably be at the same hori- Zontal plane as thatat which the joint is'made. It may also be desirable to provide the bearings in the casing 15, preferably near the ends thereof so that the casing 15 constitutes the main bearing support for all the rotating parts.

It has already been proposed to make one part of the surfaces of a preheater from cast iron and it was intended that this should apply to the part which is most cooled because in consequence of this cooling danger of corrosion arises. This danger is all the greater the higher the sulphur content of the coal being burned. But a substantial increase in weight is bound up with the use of cast iron which is not tolerable for rotating heat exchangers. For this reason this prior proposal could not be used in practice. In a construction according to the invention, however, it is possible to make any desired part of the actual heat exchanger from heavy material such as cast iron because the actual exchanger is stationary.

We claim:

1. A heat exchange device comprising a cylindrical casing, regenerative material including flow paths for media undergoing heat exchange filling said casing, a first circular track around the edge of said casing at each end thereof said first track being flush with the surface of said regenerating material, a central tubular wall constituting an inner wall of said casing, a second circular track surrounding said tubular wall at each end thereof, at least one segment-shaped carriage at each end of said casing each said carriage comprising an annular wheelsupported plate mounted in contact with one of said second 'circular tracks, at least two radial members fastened to and extending from each said annular plate, an arcuate wheel-supported frame member mounted on the corresponding one of said first circular tracks and fastened at each end to one of said radial members, the fastenings of said radial members to said annular plates and to said arcuate frame members being such as to provide flexibility in said carriages, a shaft extending axially through said tubular wall, a rotatable pipe-connection mounted on said shaft at each end thereof the ends of said pipe-connections remote from said casing being circular and coaxial of said shaft, the ends of said pipeconnections adjacent said casing being segment-shaped to agree with the shape of said segmental frames, said pipe connections being secured to said carriages with axially slidable gas tight joints, gas tight sealing means between said annular plate, said arcuate frame member of said segmental carriage and said first and said second circular tracks, said sealing means comprising a plurality of flexible radially extending leaves mounted on said radial members to resiliently contact the surface of the regenerative material, and spring means mounted on said pipe connections to press said wheeled carriages against said first and said second circular tracks and to assure surfaces of said regenerative material.

2. A heat exchanger for flowing gaseous media such as combustion air and fiue gas, comprising a generally cylindrical chamber containing regenerative material having passages of substantially uniform size'therethrough, the surfaces of said regenerative material coinciding with the end surfaces of said chamber, rotatable supply and delivery conduits presenting segment-shaped portions toward the ends of said chamber, segment-shaped frames mounted for limited axial movement with respect to said supply and delivery conduits, packing means between said conduits and said segment-shaped frames, packing elements between said segment-shaped frames and the ends of said chamber, and packing means extending along the radial edges of said segment-shaped frames, said packing means between said segment shaped frame and said stationary chamber comprising a plurality of closely spaced parallel leaves of flexible material.

3. The heat exchanger of claim 2 including spring means between the said segment-shaped frames and the said conduits whereby spring pressure acting against said conduits holds said segment-shaped frames against the ends of said chamber.

4. The heat exchanger of claim 3 in which said segment-shaped frame is provided with adjustable wheels and said cylindrical chamber is provided with circular tracks to position said frame with respect to said chamber whereby uniform bearing of said packing means against the ends of said chamber and of said regenerative material is provided.

5. The heat exchanger of claim 4 in which said rotatable supply and delivery conduits extend from said segment-shaped portions to a circular pipe connection portion coaxial with the axis about which said conduits rotate, and in which a common driving shaft extending coaxially through said cylindrical chamber and its contained regenerative material, and means to rotate said shaft is provided.

6. The heat exchanger of claim 5 in which said common shaft comprises two coaxial parts extending beyond said conduits, the supply conduit at one end of said chamber and the delivery at the other end of said chamber being each secured to one of said coaxial parts of said shaft, and means operable from beyond one of said conduits to adjust the axial spacing of said conduits.

7. The heat exchanger of claim 4 in which said wheels arespring mounted with respect to said segment-shaped frames to resiliently suupport said segment-shaped frames with respect to said tracks.

8. The heat exchanger of claim 7 in which means are provided to adjust the springs in order to assure the desired degree of resiliency of said segmented frames.

9. The heat exchanger of claim 4 in which scrapers are mounted on said segment-shaped frames to contact said tracks to clean the said tracks for said wheels.

10. A heat exchange device as claimed in claim 1 including a hub carrying the end of each rotatable pipe connection adjacent the end surface of the regenerative casing, a shaft defining a driving means carrying the said hubs, adjustable tension members securing the concentric ends of the rotatable pipe connections to the driving means, the bores of the hubs being widened toward one end whereby the pipe connections may be rocked a small amount by adjustment of the tension means.

11. A heat exchange device as claimed in claim 1 including a duct and suction means for drawing cold air through the joints between the rotatable pipe connections and the regenerative casing.

. 12. The heat exchanger of claim 2, in which said packing means between said segment shaped frame and said stationary chamber present sealing surfaces, the breadth of which is a' small multiple of the dimensions of the passages of uniform dimension through said regenerative material.

(References on following page) References Cited in the file of this patent 2,650,074 UNITED STATES PATENTS 2,665,120

1,031,934 Hunter July 9, 1912 1,939,153 Villasuso Dec. 12, 1933 5 2,432,198 Karlsson et a1 Dec. 9, 1947 595,465 2,574,228 Lawyer Nov. 6, 1951 649,265 2,578,945 Rigby Dec. 18, 1951 639,522

10 Ballard Aug. 25, 1953 Blomquist Jan. 8, 1954 FOREIGN PATENTS Great Britain Dec. 5, 1947 Great Britain Jan. 24, 1951 Great Britain Apr. 1, 1953

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