US2414312A - Method of and means for bonding heat exchange cores - Google Patents

Description

3 Sheets-Sheet 1 AIIIQ.

Alm.

Jan. 14, 1947. L E FEVER M. LEE

METHOD OF AND MEANS FOR BONDING HEAT EXCHANGE CORES Filed March 1s, 1942 Jan. 14, 1947. LE FEVER M. LEE 2,414,312

METHOD 0F AND MEANS FOR BODING HEAT EXCHANGE CORES Filed March 16, 1942 3 Sheets-Sheet 2 INVENTOR .ZeF'everMLee ATTORNEY f Patented Jan. 14, Y1947 METHOD OF AND MEANS FOR BONDING HEAT EXCHANGE CORES Le Fever M. Lee, Buffalo, N. Y., assignor to Fedders-Quigan Corporation, Buffalo, N. Y.

Application March 1s, 1942', seriaI No. 434,874

6 Claims. 1

This invention relates to a method and means of bonding heat exchange cores of a type in which two fluids, such as air and water or air and air, respectively pass through and over a plurality of tubes to effect a temperature interchange .through the walls of the tubes. More particularly, the invention is concerned with the provision of means for integrating a tube and n or header assembly through localized fusion of bonding material at the joints.

For illustrative purposes, it may be recalled that heat interchangers of this class may be made by disposing a plurality of spaced parallel tubes between upper and lower header plates, and putting transverse or cross ns on the tubes if desired, as well as side plates and liquid receiving tanks on the headers. The metal of -which the core is made may be coated with solder, if the material of construction is copper or brass, or with a special alloy of aluminum and silicon if the material is aluminum, so that, upon heating to a suitable temperature, the coating metal will melt or fuse, run into the interstices existing at the joints, and thus bond and integrate the core elements. Such integration is desired to impart strength and durability to the unit.

It has heretofore been proposed to effect the bonding action by subjecting the core assembly to blasts or drafts of hot air or products of combustion, the manufacturing operation being conducted in an oven or furnace. It has also been proposed, in certain types of hot air furnaces not adapted to take heat exchange cores, to reverse the direction of hot air flow periodically as a means of expediting .the heat treatment. These prior art procedures and equipment are not satisfactory, however, for the integration of cores made of very thin metal, or of materials in which the fusion temperature is close to the melting point of the core metal.

Accordingly, it is among the objects of this invention to devise a method, or operating cycle, and apparatus, in which such cores may be subjected to a fusing temperature by hot air, delivered in such Way that a close control may be exercised over the heating air, the time of heat treatment may be reduced, 4and the required power input held to a minimum. It has now been discovered that such objects may be attained by dividing the hot air flow through the core in such manner that a por-tion of the air ows in one of the available paths while the remainder of the air flows in the other of the available paths through the core, the two available paths, of`

course, being those utilized for heat exchange purposes when .the core is placed in service.

When such procedure is employed, particularly if it be combined with the reverse flow effect referred to above, deviations in temperature differentials throughout the core are brought to very small values, the time cycle is greatly curtailed, and the horsepower input made a fraction of that heretofore required. Apart from the savings in production costs so effected, the invention also permits the manufacture of such cores Without the great loss heretofore encountered from burned or inadequately bonded assemblies, which, by reason of their imperfections, had to be rejected and scrapped.

The appended drawings show a hot air furnace in which the described method may be conducted, and for a fuller understanding of the invention, reference may be had to such drawings, in which:

Fig, 1 is a, view, partially in side elevation and partially in longitudinal section, through the furnace, and showing the divided air flow around the work;

Fig. 2 is a section taken on the line 2-2 of Fig. 1, or through the blower and heater end of the furnace; and

Fig. 3 is a section taken on the line 3-3 of Fig. 1, or through the work receiving end of the furnace.

In order to simplify the description, no discussion will be attempted of the electric circuits for controlling the motors, or supplying current to the electric heating elements, or regulating such circuits by control equipment, as these may be readily understood by those skilled in the electric furnace art. Similarly, the materials of construction are those commonly used, and need no specific description except to say this: when working with aluminum cores, fluoride fluxes may be specified. As these are somewhat corrosive against ordinary materialsthe erection engineer should therefore specify materials of construction adapted to withstand such action. Otherwise, the furnace may be subjected to an unnecessary maintenance cost.

As shown in the several figures, particularly Fig. 1, the furnace comprises a box-like hearth portion l0 which is contiguous with a domeshaped blower and heater portion Il. Both of these portions are framed on the exterior with sheets I2 and structural shapes I3, while the interior of the furnace is lined with heat-resistant ceramic material I4. 'Ihis lining may, if desired in 'connection with minimizing corrosion, be

faced oil with corrosion-resistant steel I5. The furnace, as thus far described, is formed internally with ducts and passageways through which the hot air may be circulated over and through the work.

The left hand end or blower portion of the furnace is formed with an internal pedestal I6 receiving a bearing |1, and with an external support I8 mounted on one of the columns |3 which receives another bearing I9. These bearings are aligned to receive a blower shaft 2|, driven by a motor 22 through suitable belts 23. A squirrel Icage type blower 24 is mounted on the shaft 2| within the portion I I to circulate the air.

In Figs. 1 and 2, the discharge side of the blower 24 is shown as delivering into a feed duct 26, while air is returned to the intake side of the blower through a duct 21, which is offset in order to supply returned air to both sides of the blower. To this end, the peripheral or disch-arge side of the blower 24 is shrouded by forming the liner I adjacent the inlet side 26 (which portion of the liner is here designated by the numeral 28) as a scroll which closely approaches the blower on its under side and diverges therefrom into the main portion of the duct 26. The duct 21 merges into a back duct 29 provided in the rear of the wall 28, which in turn terminates in a side chamber 3| disposed oppositely to the upper end of the duct 21. Air entering through the duct 21 therefore is divided by the back duct 29 and chamber 3| into two portions, and thus may enter the blower 24 from either side. As lthe air is driven by the blades of the blower, it emerges through the periphery into the chamber formed therebetween and the scroll 28, and so is directed into the feed duct 26.

The duct 26, adjacent the blower 24, is provided with a plurality of heating elements 33 which may conveniently be mounted on a panel section 34 which abuts the outer wall I 2 of the furnace, and which protrude into the duct 26 through a side opening 35. During operation, the panel 34 is covered with a removable wall section 36 to avoid unnecessary heat losses and protect the heating elements from damage. The elements 33 may be of any desired type, either electric resistors or gas-fired quartz tubes, but for present purposes the resistor type is preferred. Current is supplied thereto in the usual way, and temperature-responsive regulators should be included in the circuits so as to maintain the air at the desired temperature.

The blower and heater portion through the duct 26, merges into the hearth or work-receiving portion IU at the lower end of the duct 26, and the arrangement of-the portion I6 is such that the hot air is divided for dual flow through -t'he work, and also reverse flow, before returning through the duct 21 to the blower 24 for recirculation and reheating. Some of the constituents of the portion Ill are: a perforate work supporting platform or hearth 4|, upper and lower air passages 42 and 43 disposed in series through the platform 4 and means, such as a damper 44, for directing the hot air from the duct 26 through the passages and the platform and thence into the return duct 21.

It will be seen that the upper passage 42 is partially separated from the duct 26 by a depending wall 45, and is spaced from the return duct 21 by a bridge 46 formed with an overhanging portion 41 and a wall 48. The lower passage 43 is also separated from the return duct 21 by a bridge 49. Each passage, however, may be placed in communication with the ducts 26 or 21 through ter- ,4 minal portions 42a, 43a, respectively, in which are located curved baille plates 5|, 52. Similar baffles 53 are disposed at the lower end of the duct 26 to direct the hot air uniformly into the passageways as conditions permit.

The platform 4| is formed as a grid of intersecting bars, and extends from the edge of the bridge 49 to the back wall 54 of the passage 43, baflles 55 in the passage serving to direct and distribute the air over the platform. The left hand portion of the platform, as it will be noted, underlies the overhanging section 41 of the upper bridge 46. The upper passage 42 is offset to the right, as indicated by the reference numeral 56, and it also contains flow-directing ballles or plates 51.

The side walls of the portion I0, as best shown in Fig. 3, are provided with aligned openings 6| adjacent the platform 4|, and with sliding cover doors 62 guided between angle irons 63. The doors may be suspended by cables 64 passing over pulleys 65 mounted on an axle 66, which in turn is supported on posts 61 on top of the portion |Il. Roller tracks 68 are positioned at either side of the furnace, at the level of the platform 4I, so that the assembled cores C may be pushed in on one side, and withdrawn from the other.

It will be seen, particularly from Fig. l, that the core is so located in the furnace, on the platform 4|, as to abut the overhanging end 41 of the bridge 46, and be spaced from the back region 56 of the passage 42. This accordingly and automatically provides a split or divided passageway from passage 42 to passage 43-namely, in a vertical direction through the core C, and in a longitudnal direction. When cores 0f varying sizes are to be treated, shut-off plates or adapters may be laid against and on the portion 41 or platform 4| as desired, so as to maintain this dual path. The construction just described is preferred to additional duct work for dividing the air current, because of its simplicity and adaptability to most conditions.

The above noted damper 44, employed to effect reversal or short-circuiting of the air path between the inlet 26 and the return duct 21, `:onsists of a flat plate 1I mounted on a shaft 12 which is borne by an internal bushing 13 (Fig. 2) and a sleeve 14. Circular guards 15 are also positioned on the shaft adjacent the supported portions to reduce leakage along the sleeve and to protect the bearings from undue effects of the air current. The shaft 12 and the plate 1| are operated in unison by a small motor 16 driving a speed reduction gearing unit 11 to which the shaft is connected. This motor, depending upon the intended plan of operation, may be energized through automatically actuated controls to turn the damper 44 to one operative position, and then to the other by rotation, and again to a neutral position, in timed sequence. Or, in someinstances, such control may be dispensed with, and the positioning of the damper may be done manually.

'In either event, it will be clear from Fig. 1 that the damper 44 may be disposed in any desired angular position. Thus, it may extend from the lower left corner of the bridge 46 to the diagonally opposite corner of the duct 26. ln such case, flow will occur in the following circuit: From ductl 26 into passage 42 via throat 42a, thence over deflectors 51 down through the core C, and simultaneously from end region 56 longitudinally of the core to the region under overhanging bridge portion 41. through adjacent portions of the open-work of Both flows pass 90, then the plate 1I will extend from the lower edge of wall 45 to the diagonally opposite corner of lower bridge 49, and the air flow from the duct 26 to the return 21 will be just the reverse of that traced. The deflectors 55 will serve to divide the air stream, part of the air passing upwardly through the core, and the remainder passing through the apertures in the platform 4| for longitudinal flow. When the damper is placed midway between its terminal points, a short-circuit ing path is provided between ducts 26 and 21 as a path of least resistance, and will thus minimize heavy losses of heated air when the doors 62 are opened to insert or remove a core.

Alternatively, or in connection with the shortcircuiting of the ducts, the heat supplied to the elements 33 may be interrupted when the doors are opened, and the blower 24 may also be shut down. With heat exchange cores of the type hereinafter more specifically considered, one door 62 may be partially opened at the end of the heating period, and the work permitted to remain on the platform 4I. If the heat input to -the elements 33 is then interrupted, and the blower 24 continued in operation, a cooling draft of fresh air will enter the circuit, thus reducing the temperature of the work to a point where it may be handled with greater safety and convenience.

It has heretofore been noted that hot air furnaces, anddevices for effecting a reversal of air flow, have heretofore been made, but none of them has been adapted to the development of the divided iiow just described. In order to point out more clearly the significance of the new furnace, the steps or method of bonding a heat exchange core will be described.

For exemplary purposes, reference may be made to a tube and fin core assembly in which thin aluminum is used as the material of construction, the heat exchanger is formed with several hundred tubes, and it is desired to bond with aluminum-silicon alloy in order to integrate the structure. Since the alloy fuses at a temperature of say l1701180 Fahr., and the metal itself will melt at about 12201230, it is apparent that a maximum temperature dilerential of only about 50 Fahr. is available, thus making the control of temperature an extremely diflicult problem, even with modern precision instruments and regulators. It is, however, possible to hold the temperature of the air emerging from the duct 26to a fairly close and satisfactory value.

The problem therefore arises in limiting the temperature gradients through the core C itself, bringing al1 parts to temperature in a minimum of time, and avoiding such air velocities through the Work as will tend to distort, and therefore injure, its relatively fragile structure at the high temperatures.

It will be apparent that the hot air blown over the work will lose some of its heat thereto, and thus, under ordinary conditions, and to bring the entire core up to bonding temperature at its most inaccessible points, it is necessary to overheat the core at the points of initial contact. Thus, in s employing a single blast or air current, the possibility of burning cannot be eliminated. Similarly, it is now apparent that the customary reversal of air current, while serving to expose opposite surfaces to initial contact, still does not suffice to reach the remote parts of the work in a satisfactory manner. By dividing the air stream for dual flow in intersecting directions through the core, and by superimposing the reversing effect, however, the maximum thermal paths from initial contact points to remote points is reduced to a minimum. This avoids the burning condition heretofore encountered, and also curtails the time required to bring the core up to temperature.

Another factor pertaining to the split or dual circulation relates to the power consumed in supplying the air to the hearth. In one type of furnace, as a comparative example, it was found that a fifty horsepower motor was required to operate a blower delivering 10,000 c. f. m. of hot air passing through thework in one direction. According to the present invention, however, wherein the air is divided into two streams, it is sufficient, for the same size core, to supply '1,000 c. f. ml at the same temperature, using the input of a ten horsepower motor. The explanation of this surprising reduction in power consumption is in the circumstance that since the heating air has a much greater area through which to pass, it may pass through the core with less resistance or pressure drop. Since the power input rises as the cube of the resistance, the dual paths permit the accomplishment of the desired result with less air and less power.

In applying this method to heat interchangers as described, the work C is inserted into the furnace onto the platform 4I, the damper 44 being then at a neutral or short-circuiting position. The doors 62 are closed, and the damper is turned to one of its diagonal positions to direct the air flow through one or the other of the effective paths. Since the core C may be readily located on the platform, the dual paths are automatically determined, as heretofore described. Reversal of ow can be effected by the settings of the motor 16, and it may be any value found suitable by experience. Thus, if the core can be brought to temperature in six minutes, the damper 44 may be reversed every half minute, and for a nine minute heating cycle, reversals may be made every minute. As soon as the whole work has been brought to the bonding temperature, the damper should be returned to neutral, and the work removed, since prolonged heating may be actually detrimental and could serve no beneficial purpose.

For other types of work, it will be apparent that the cycles will be modified to suit the occasion, and it will also be apparent that under some conditions the reversal of flow may be omitted, since the savings incident to the provision of dual pathways may be obtained without resort to this step. The great advantage of reversing is, of course, to shorten the time cycle.

It will also be apparent to those skilled in the art that while the invention has been described with reference to one specific form of apparatus and the processing of a designated type of core, the principles may be otherwise embodied, and therefore it is intended that the foregoing description be considered as illustrative, and that the scope of the inventionY should not be restricted thereto, but should be deemed commensurate with the following claims.

I claim:

1. A hot gas furnace having a blower portion including a blower and heating means for circulating and heating air, inlet and return ducts respectively delivering the air from and inducting it to the blower, and a, hearth portion connec'ted to the blower portion through said ducts, said hearth portion including a pair of spaced passages, a perforate platform positioned between the passages, one of said passages having an olset portion and an overhanging portion member disposed in one of said passages and overhanging a portion of the platform thereby to provide, with respect to work positioned on the platform, dual paths between said passages, inlet and return ducts respectively connected to the passages, a blower portion communicating with the opposite ends of the ducts, and means in the blower portion for heating and recirculating the hot gas to said passages.

3. A hot gas blast heating furnace comprising a hearth portion and a iblower portion and ducts extending between and through said portions to form a cyclic ow path, said hearth portion having a pair of spaced passages forming parts of the path, a work-receiving platform positioned in the hearth portion and dividing the passages from each other, an inlet duct and a return duct spaced from said platform, each of said ducts being in open communication with said spaced passages, a damper movable to connect the inlet duct with one or the other of the passages and the return duct with the other or one of said passages, said inlet and return ducts extending to said blower portion, a blower mounted in the blower portion, said blower having a suction side and a discharge side, said return duct terminating in the blower portion at the suction side thereof, saidinlet duct connecting with the discharge side of the blower, and air heating means disposed in the inlet duct between the dist charge side of the blower and said damper.

4. A hot gas blast furnace comprising an elongated portion having an internal end wall provided with a horizontal section, a pair of bridges disposed transversely of the portion remote from the said end wall,- a perforate platform extending from said horizontal section to one of said bridges, flow passages formed in the portion above and below the platform and bridges, one of the bridges overhanging a portion of the platform, a work entry opening in the portion to permit the placement of work on the platform between the horizontal section and the overhanging bridge, a b lower and heater portion disposed contiguously to the elongated portion, ducts extending between said portions, and means for connecting the ducts and passages in a closed circuit extending through the platform.

5. Ahot gas furnace comprising a box-like structure having a blower portion and a hearth portion, means in the hearth portion to support work to be heated by the hot gas and passages adjacent said supporting means to receive hot gas from and return it to said blower portion, said blower portion including a dome, a rotary blower mounted in the dome, a scroll surrounding the periphery of the blower and terminating in an inlet duct, said inlet duct extending from said dome to the hearth portion and communicating with at least one of the passages therein, heating elements mounted in the duct to supply heat to the gas delivered by the blower, a back duct behind the scroll-and merging into side chambers at either side ofthe blower, and a return duct communicating with the black duct and side chambers and extending to the hearth portion and communicating with at least one of the passages therein.

6. A hot gas furnace comprising a blower and heater portion and a hearth portion, said blower portion being located at the end and partially to one side of the hearth portion, upper and lower passages formed in the hearth portion, said passages being divided by a Work-receiving platform and being separated by upper and lower bridges, a return 'duct extending from between the bridges to the blower portion, an inlet duct extending from the blower portion to the hearth portion, said inlet duct and passages being located in quadrantal positions to each other, a rotary damper mounted between the duct and passages adjacent the bridges, and means for rotating the damper to different angular positions to connect the inlet duct and the return duct successively to first one passage and then the other.

LE FEVER M. LEE.

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