US1571742A - Closed furnace and method of operating the same - Google Patents

Description

Feb. 2 1926. 1,571,742

0. STEENSTRUP CLOSED FURNACE AND METHOD OF OPERATING THE SAME .Filed Dec. 20, 1923 I ll/ Invesntor: Christian Steenstrup,

His Attorney.

Patented Feb. 2, 1926.

UNITED STATES A 1,571,742 PATENT o FicE.

CHRISTIAN STEENSTRUP, OF SCHENECTADY, NEW YORK, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK. O

CLOSED FURNACE AND METHOD OF OPERATING THE SAME.

To /7! 1 72 omit may concern lie itknown that I, CHRISTIAN STEEN- s'ri-iUr, a citizen of the United States, residing at Schenectady, in the county of Schenectady, State of New York, have invented certain new and useful Improvements in Closed Furnaces and Methods of Operating the Same, of which the following is a specification.

The present invention relates to closed furnaces of the type in which its operations are performed in the presence of a selected gas to prevent oxidation of the charge and especially to such furnaces when internally heated by electrical means. Briefly stated, such furnaces comprise a closed metal vessel or container heavily lined with heatresist-ing material, electrical heating units or resistors within its chamber, a conduit for supplying the selected gas, and usually a restricted outlet through which a small amount of the gas continually escapes to serve as an indicator that the proper gas conditions exist within the container. The temperature within the container is regulated by varying the amount of current admitted to the units or resistors, by varying the number of units or resistors in circuit, or their electrical connections, or by vary ing all of them. Such furnaces are entirely satisfactory for many classes or kinds of workbut are open to one serious defect for other classes or work because the temperature. ol" one or. more selected portions of the charge cannot be controlled or regulated imlcpcndently of another or other portions. As an illustration I refer to a class or classes of work in which the furnace charge is composed of two or more pieces or parts of metal which are to be united by fusion which pieces differ iii-mass or coefficient of expansion or heat conductivity. This can best be understood and appreciated by references to a particular kind or class of charge but without limitation thereto or to the particular type of furnace construction since my' invention is capable of wider application.

One application of my invention which I.

may use as an illustration is the uniting of the parts of a diaphragm or of a bucket wheel of a steam turbine by fusion, copper being the fusing metal, the operation being carried out in the presence of hydrogen gas. Briefly stated, a diaphragm comprises a Application filed December 20, 1923. Serial No. 681,864.

massive center member, a relatively thin annular rim, and thin, radially-extending nozzle partitions between the member and rim. A bucket wheel comprises a massive center member, a thin, annular cover and sharp edged radially-extending buckets located between the member and cover. To attain the best results the parts should be tightly fitted one to the other when cold so that there will be no appreciable spaces between parts at the joints. In other words, the spaces should be of a capillary nature. Upon heating up such a diaphragm or wheel in a closed hydrogen furnace the rim or cover, being less mas sive than the center member, reaches fusion temperature before the member and in so doing expands away from the partitions or buckets and causes objectionable looseness resulting in defective joints or in complete failure thereof.

In some cases I have found that the rim or cover does not heat up uniformly or if it does that one portion offers a greater resistance to movement than the remainder With the result that the part gets out of round. hen such a part shrinks in cooling it does not return to its original shape with the result in some instances that there is a decided bulge atone point. Under tioned objections can be overcome and uniformly good joints obtained by regulating the temperature of one or more of the component parts of the charge within the furnace and this independently of the'temperature of the furnace as a whole. To accomplish this I locate inside of the furnace one or more elements which for convenience may be termed coolers or cooling elements and which preferably conform rather closely in shape and size to thatselccted portion of.

the charge the temperature of which is to be regulated. These elements are made hollow and through themis caused to flow a suitable cooling fluid subject to the control of a regulating means such as a valve. The cooling elements may be made in different ways. For example :they may be closed at all points except the ends which extend outside of the furnace in which case the cooling fluid flows continuously from end to end absorbing heat from the walls of the element in so doing, or they may have one closed end and be provided with one or more perforations or orifices arranged to direct a stream or streams of cooling fluid against the part whose temperature is to be regulated.

The type of cooling element will be de-. termined by the character of the fluid employed. One simple effective way to accomplish the desired result is to use a perforated element having One closed end and supply to it from a suitable outside source the same kind of selected gas that is used in the furnace operation. By suitably varying the amount of fluid flowing through the cooler or coolers the heating of any particular or selected part or portion of the charge can be so retarded that it will reach the fusing temperature at approximately the same time as the other or more massive part. By the same neanssaid"selected part or portion an be cooled and therefore shrunk before another part and in this manner ensure uniformly good joints between those parts having different masses. Briefly stated my improvement permits of any selected part of the charge being retarded in its heating and advanced in its cooling without change of temperature in the furnace itself.

By Wayof example as applied to the manufacture of diaphragms or bucket wheels, I

locate in the furnace and in proximity to the rim or cover an annular chambered element which" has a narrow slot or one or more rows of small openings or orifices through which one or more small streams of gas escape with sufiicient velocity to strike the surface of the rim or cover. By admitting a regulated amount of gas in this. manner the heating of the rim or cover can be retarded so that it and the center member will reach. fusion temperature at the same time. This can be determined by the use of the usual sight openings in the furnace wall. On account of the difference in mass of the center member and rim or cover, the member cools more slowly and to ensure proper hardening of the copper between the rim or cover joints and the parts to be fused thereto the supply ofcooltemperature controlling gas directed against them may be increased to such an extent as to rapidly reduce the temperature of the rim or cover causing shrinking thereof and this before the temperature of the furnace as a Whole is reduced sufiiciently to cause the copper in the joints to solidify or set. The shrinking of the rim or cover in the manner described completes the joints between itand the partitions or buckets which joints are sufliciently strong so that when the center member cools it pulls the rim or cover inwardly with Instead of leaving an open space between the cooling element and the part to be controlled when a selected gas is used as the cooling fluid and directed against said part, I may in some cases separate the controlled part from the element by a small space which is filled with ordinary sand and through which the gas must pass before striking said part. resides in the fact that it prevents too sudden changes of temperature which might be occasioned by careless manipulation of the gas-controlling valve.

Reference has been made to causing one part to exert pressure on another by shrinking to ensure good joints, the cooling fluid absorbing heat from the member that is to be shrunk. This may be termed the direct method. The same result may also be accomplished in some instance by an indirect method. For example. take the simple case of two metal blocks which are to be fused. The blocks may be mounted between two heads and the latter connected by relatively long rods or bolts. After the blocks, heads and rods which in this case form the charge are heated to fusing temperature the rods or bolts are cooled which will cause them to shrink and thus exert heavy pressure at the joint between the blocks.

Since the o )erations in the furnace are carried out in the presence of a selected gas which must be continually supplied (luring the working period, it naturally follows that the best suited gas for controlling the temperature of the selected portion of the charge is the same kind of gas that is used for the main or fusing operation. lVhen this is done the main supply of gas can be cut down in proportion to the amountadmitted for cooling and therefore no extra gas is required. Fresh gas may be used for cooling or gas may be withdrawn from the furnace container and after being properly cooled discharged under pressure into the cooling element. It also follows where the same kind of gas is used for both purposes that small leakages fromrthe cooling-element duc to faulty joints, etc, may be disregarded.

In the accompanying drawing, which is illustrative of my invention, Fig. 1 is a view in vertical section of a closed furnace and its charge; Fig. 2 is a plan view illustrating a bucket wheel or diaphragm; Fig. 3 is a perspective view of a cooling element: Fig. 4.- is a View showing another form of charge and cooler; Fig. 5 illustrates another means for causing shrinkage in order to exert pressure at the joint between two parts, andFig. 6 shows a portion of a bucket wheel and cooler on an enlarged scale.

The furnace shown in Fig. l is of the same general type as that described and The advantage of this charge.

claimed in my prior application for patent, Serial No. 604,193, filed December 1, 1922. Briefly it comprises a foundation 7, on which is'a bed of sand 8 to support the 9 is a metal ring upon which is supported a metalcylinder 10. Inside the cylinder is a body of heat-insulating mate rial 11 which supports the resistors 11 which form the heaters, the latter being connected to a suitable source of current supply. The head 12 and ring 9 are united by bolts 13 which serve to hold the material 11 in position- '14 represents a labyrinth packing to prevent the escapeQof the selected gas and 15 indicates the flexible admiss on pipe therefor. Surrounding the packing is a gas burner 14 which causes ignition of any gas escaping from the furnace chamber through the packing. 16 indicates a small pipe through which a small amount of gas is permitted to escape and is burned at the point of exit to serve as an indicator of the gas conditions within the furnace. indicates valved sight tubes through which conditions within the furnace can be observed.-

On the sand bed are blocks which support a container 17 also containing sand in which the charge, in this case a bucket wheel 18, is located. The level of the sand approximately corresponds to the top surface of the charge. Surroundingthe charge and supported as by the sand bedfor example is a cooler 19 of annular form having a large number of perforations 20, Fig. 6, through which the'selectedgas is -directed in "regulated amount against the rim- 21 or part the temperature of which is to be controlledindependently of the center member 22 and buckets 23. A complete .bucket wheel is shown in Fig. 2 which may be taken also as illustrating a nozzle diaphragm.

Between the rim 21 and the cooler it is desirable to have'a-body of sand as shown in Fig. 1 so that careless manipulation of" the gas controlling valve will not cause sudden changes of temperature in the rim. It is also desirable to cover, this body of sand by a shield 10 to prevent. the gas fromflowing upwardly instead of horizontally against the rin I In Fig. 3 is shown a perforated cooler of ring shape which surrounds the charge, whatever it may be and to which a selected gas is admitted by the pipe 24 subject to the control of a regulating valve 25, 10

representing the shield. As shown in Fig. 1 .the sand container is slotted above the pipe so as to permit the furnace to be raised and lowered. I r

Fig. 4 illustrates a different kind of charge and a cooler of different shape. In this figure 30 indicates a block of steel and 31 a round steel pin or shaft that is to be fused expand more rapidly than the block and since the latter would not yield the forces exerted would cause the metal in the pin to flow slightly in an axial direction. If now the parts are cooled, it will be found that whereas the original fit was tight, it is now loose. To prevent this, a cooler 19 of appropriate shape and size is provided to which a cool, selected gas is admitted during the heating operation and caused to exert sufficient retardingeifect on the pin so that the parts will attain fusing temperature at practically the same time.

Fig. 5 shows a means for exerting pressure at the joint between two parts by an'indirect method. In this case the charge comprises the blocks 32 and 33 which are to be fused at the joint 34 between them, heads 35, the connecting rods 36 andthe fusing metal which should be placed over the joint. Be-

tween the heads and blocks are layers of asbestos 37 Or equivalent material to prevent accidental fusing between them. On one side of each rod is a cooler 19 to which a sup, ply of cool, selected gas is admitted inregulated amount. When the blocks and fusing metal are at fusing temperature, cool gas is directed against the rods which causes them to shrink and in so doing exert heavy pressure on the heads and through them similar pressure at the joint 34 after which the temperature of the furnace may be: reduced in the 'usual way as by reducing the supply of current to the resistors, or the charge may be transferred to a cooler for this purposes The principal distinction in this arrangemcnt over the other is that the means which are shrunk to exert pressure forin no part of .the finished article.

After the parts are snugly fitted together by suitable mechanical operations, the structure which is to be. fused, what ever may be its nature, is placed in the furnace which is preferably kept hot all the time and raised and-lowered at will by the rod 38 at the top. The structure is placed on the sand bed and covered with sand to about the top surface thereof. Copper or equivalent fusing metal -is then distributed over the structure where the joints are to be formed. This may be done by .wrapping copper wire about the the resistors to fusing temperature which for copper is about 1100 degrees C. and hydrogen gas admitted .to the chambers of the furnace by the, pipe 15 subject to the control of valve 15*.

To prevent the parts of lessermass from heating too rapidly a selected gas such as ,hydrogen is admitted to the cooler 19 by pgipe 24 subject to the control of valve 25.

y means of the sight, tubes 16 the conditions within the furnace can be observed and the amount of cooling gas increased or decreased as conditions require. The point is to admit sufficient gas to retard the heating of the parts'of lesser mass so that the whole charge will reach fusing temperature at practically the same time. As the supplies of selected gas are the same both for the normal fusing operation as well as the cooling, the main supply can be cut down in proportion to the increase of cooling gas. When fusing temperature is reached, the amount of cooling gas is increased so as to cause the parts of lesser mass to cool and thereby -shrink. This same action causes the copper or fusing metal to'harden and complete the p joints acted upon by the gas. The temperature of the furnace as a whole may. then be 4 reduced to finish the operation. or the furnace may be lifted and the charge moved to a separate container which may be water cooled \and in which a supply of selected gas is maintained during the cooling operation.

What I claim as new and desire to secure by Letters Patent of the United States is 1. In a furnace, the combination of a closed container adapted to contain the charge, means for maintaining a supply of selected gas within the container to prevent oxidation of the surfaces of the charge during the workingperiod, means for heating the container and its charge, and means acting independently of the heating means for controlling 'the temperature of a selected portion of the charge. c

2. In a furnace, the combination of a closed container adapted to contain the charge, means for maintaining a supply of selected gas within the containerto prevent oxidation of the surfaces of the charge dnring the working period, means for heating the container, and means acting independently of the heating means to retard the increase. in temperature of a selected portion of the charge with respect to another as the vtemperature of the furnaces rises due to the heating means and to cool said selected portion in'z ulvance of the cooling of another portion.

3. In a furnace. the combination of a closed container adapted .to contain the charge. means for maintaining a supply of selected gas within the container to prevent oxidation of the surfaces of the charge during the working period, means for heating the container, and a conduit entering the container and through which a selected non- .perature of that portion .of

oxidizing gas is directed against a selected portion of the charge to control its temperature independently of that due to the heating' means.

4:. In a furnace, the combination of a closed container adapted to contain the charge, means for maintaining a supply of selected gas within the container to prevent oxidation of the surfaces of the charge during the working period, means for heating the container, and an element independent of the charge which conforms generally in shape to a selected portion thereof, is perforatedyand through which a non-oxidizing gas flows for controlling the temperature of the selected portion of the charge.

5. In a furnace, the combination of a closed container which encloses the charge, means for maintaining an atmosphere of selected gas within the container during the working period, means for heating the container, a perforated element within the container which conforms generally in. shape to a selected portion of the charge and is independent thereof, a conduit for supplying a non-oxidizing gas to the element, and valve means for regulating the flow of gas through the conduit and element.

6. In a furnace, the combination of a closed container which encloses the charge, a conduit for supplying a selected gas to the container during the working period to prevent oxidation of the surfaces of the charge, means for heating the container, a chain'- bered means independent of the charge which is within the container, encloses a portion ofthe charge and is provided with a discharge orifice, and a conduit for supplying a selected gas under pressure to the chambered means for controlling the temthe charge enclosed by it.

7. In a furnace, the combination of a closed container adapted to contain the charge, comprising parts which are to be united by fusion and a fusing .metal, meansfor maintaining a supply of selected gas in the container during the working period to prevent oxidation, means forhe'ating the container and charge, -and means acting inde pendently of the heating means to cause shrinkage of a part of the charge with respect to another whereby pressure is exerted on the joint.

8-. In a furnace, the combination of a container comprising a closed casing lined with heat-resisting material and a chargesupporting platform, a conduit for supplying a selected gas to the container during the working period, electrical heating units for the container, a means supported by a part of the container which encloses a selected portion of the charge, and discharges a stream of selected gas against the adjacent portion of the charge to locally control its temperature, and a valve-controlled closed container, heating the container and conduit for supplying a selected gas under pressure to the means.

9. Ina furnace, the combination of a platform, a closed casing lined with heat-- ently control and a valve-controlled conduit for supplying a selected gas under pressure to the-chambered means.

10. In a furnace, the combination of a closed container adapted to contain acharge comprising pieces of metal of differ ng mass and a fusing metal of lower meltmg point for uniting them, means for heating the charge to fusing temperature, means for maintaining a supply of a selected gas in thecontainerduring the'working period to prevent oxidizing of the surfaces of the eharge,;and means for controlling the temperature of 'a piece of said charge having a lesser ma'ssirby directing a stream ofselected gas against it. u

11. lna.,.fu-rnace the combination of a closed container adapted to contain a charge 1 comprising pieces of metal which expand and contract by difierent amounts in the same period of time and a fusing metal of lower melting point for uniting them, means for heating the charge to fusing temperature, means for maintaining a supply of selected gas in the container during the working period to prevent oxidizing of the surfaces of the charge, means for directing a stream of selected gas against that piece of the -charge which has a tendency to expand more-rapidly than the other to retard said tendency, and a regulator for sald means.

12., In a furnace, the combination of a closed container adapted to contain a charge comprising separate pieces of metal which are to be joined by fusion'and a fusing metal, means for heating the container and charge to fusing temperature, a conduit for supplying a selected gas to the container during the working period to prevent oxidizing of the surfaces of the charge, and a controllable coolin means for causing pressure to be exerted at the joint between the pieces prior to reducing the temperature of the container.

13. The method of uniting separate pieces of metal by fusion which comprises placing charge above the melting point of the fussing metal, applying pressure to the pieces when hot through the medium of a cooling fluid to ensure good contact at the joint between them, and reducing the temperature of the charge to permitthe fusing metal to, harden.

let. The method of operating a closed furnace which comprises charging the furnace, heating the furnace and its charge to working ten'lperature, supplying a selected gas to the furnace to prevent oxidation of the charge, and supplying an additional amount selected gas to the furnace in such man- \ner as to control the temperature of a selected portion of the charge.

15. The method of operating a closed furnace which comprises charging the furnace,

heating the furnace to working temperature, maintaining a supply of selected gas in the furnace, regulating the temperature of a selected part of the charge by discharging a selected gas against it, and varying the main supply of selected gas approximately in proportion .to .the variations in the amount of gas supplied for temperatureregulating purposes. r

16. The method of uniting separate pieces of metal of differing mass by fusion which comprises placing the charge comprising said pieces and sufficient fusing metal having a lower melting point to fill the joints between them in a closed container, heating the charge .to a point above the melting temperature of the fusing metal, maintaining .a supply of selected gas within the coning of a selected portion of the charge as the temperature of the furnace increases,

and cooling said selected portion in advance of the remaining portlon.

18. In a furnace, the combination of a sealed container in which the charge is enclosed, conduit means for maintaining within the container an atmosphere of selected gas during the working period to prevent oxidation of the surfaces of the charge, means for heating the container and its charge, and conduit means for introducing a non-oxidizing'gas into the container in such manner as to control the changes of temperature of a selected part of the charge.

19. In a furnace, the combination of a sealed container which entirely encloses the charge, means for maintaining Within the' container an atmosphere of non-oxidizing gas during the Working period, means Within the container for heating it and the charge to operating temperature, and means for introducing an additional supply of the same selected gas into the container in such manner as to control the temperature of a selected part of the charge independently of the changes due to the heating means.

20. A furnace comprising a closed containcr, means for maintaining therein a supply of selected gas to prevent oxidation of the surfaces of the charge, a perforated "cooler located ithin the container which encloses a portion of the charge undergoing treatment, and conduit means for supplying to the cooler the same kind of selected gas which is supplied to the container by the 20

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