US2271091A - Method and apparatus for heat treating and sintering - Google Patents

Description

Jan. 27, "1942.

J. S. PECKER EI'AL METHOD AND APPARATUS FOR HEAT TREATING' AND SINTERING 5 Shee ts-Sheet V 1 Filed June 22, 1940 9 J. S. PECKER- ETAL METHOD AND APPARATUS FOR HEAT TREATING; AND SINTERING Filed June 22, 1940 5 $heetsh e et 2 SEPH S. E SR5: HENRY A.$IM P$ON ATTORN EY Jan. 27, 1942'. .1. s. PECKER EI'AL METHOD AND APPARATUS FOR HEAT TREATING AND SINTERING Filed June 22, 1940 5 Sheets-Sheet 3 C R 8r MPSON JOSEPH s. HENRY A. 5| W w A'I'TORNEY 5 Sheets-Sheet 4 J. 5. PECKER .ET AL Filed June 22, 1940 METHOD AND APPARATUS FOR HEAT TREATING AND SINTERING JOSEPH $.PECKER a: HENRY A. SIM

Jan- 7, 914 J. s. PECKER ETAL 2,271,091

METHOD AND APPARATUS FOR HEAT TREATING AND SINTERINU Filed June 22, 1940 5 Sheets-Sheet 5 INVENTORS JOSEPH S. PECKER 8r HENRY AISIMPSON BY W WATT URN EY Patented Jan. 27, 1942 i ivmrnon AND APPARATUS ron near ,zrnssrmc AND snvrnnme Joseph 'S. Pecker and Henry A. Simpson, Philadelphia, Pa., assignors to Machine and Tool Designing 00., Philadelphia, Pa., a corporation .0! Pennsylvania Application June 22, 1940, Serial No. 341,830

' 7 Claims.

This invention relates to a method and apparatus for a heat treating, sintering or welding system for the handling of metal objects or units especially those which have been formed from metallic powders, or incombination with chemicals and intended to be subjected to an atmos phere of inert gases, and has for a. purpose to provide compact, convenient and eflicient means for sintering, sintering and cooling, or sintering at varying temperature the materials during their continuous traverse through the system.

A further purpose is to provide a novel design for a sintering system wherein the total space occupied is of a greatly reduced area in comparison with plants and methods in use at the present time to accomplish similar purposes.

- A further purpose is to provide a continuous vertical helical trackway having a descending and an ascending path for the guidance of individual conveyors and a propelling means for controlling the movement of the conveyors both down and up the path of the trackway.

A further purpose is to provide two separate chambers,-one within the other, one for heating purposes and the other for cooling, and having a continuous vertical helical trackway passing through one chamber to provide an in-feed, and crossing to the other chamber to provide an outfeed.

A further purpose is to provide conveyors in the form of individual cars having wheel'trucks with separable container bodies supported there- 'on and adapted to roll freely over the tracks of the helical trackway, the bodies being formed of perforated material to permit of a free circulation of heat and/or cold, having provision for quick and eflicient mounting and demounting upon and from the wheel trucks, and trays of similar perforated material adapted to interlock in stack formation and to fit within the demountable bodies.

A further purpose is to provide a stationary insulated outer casing to form one of the chambers and an inner rotatable shell to form the other of said chambers, the rotatable shell carrying a propelling means for the individual conveyor cars and also acting to keep said cars in proper spaced relation during their traverse of the spirals.

' A further purpose is to provide sealed compartments with dual sets of doors for the intro-,

duction and ejection of the conveyor cars, whereby the escape of heat, gases, etc. are minimized.

A further purpose is to provide the introduction compartment with door controlling mechanism, operable from and in timed relation to the rotating propelling means and whereby both sets of doors cannot be opened at the same time.

A further purpose is to provide'one or both of the chambers with electric heating elements of helical or other formation so arranged as to follow the path of the conveyor cars and to re- 10 fiect heat thereon from above, below and from each side throughout the entire traverse of each car and to provide proper circuits for energizing the elements, either wholly or in part, in either one or both of the chambers and proper controls for same.

A further purpose is to provide one of said chambers with a controlled cooling means preferably in the form of circulated cooling medium which cooling is caused to function when but one of the chambers is used for heating.

A further purpose is to provide glazed openings ,at convenient points in the walls forming both chambers whereby visual inspection of the materials under treatment can be made.

A further purpose is to provide valve controlled means for the introduction of gases, and circulating means for retarding the escape of the gases through doors of entrance and exit compartments.

ture for the support of the respectiv casings forming the separate chambers, the helical trackway therein, the helical heating elements, and to further provide means for rotating the walls forming the inner chamber at variable speeds.

Other purposes and attendant advantages will become readily apparent from the accompanying specification and illustrated embodiment of one form of our invention, reference to which readily apparent.

It has been the practice in the past in the art of sintering objects formed of compressed powdered metals to introduce containers to and move them through insulated chambers of great length, as the sintering process is slow and requires much time. The cost of apparatus of this nature was necessarily high as well as the cost of maintenance, and the treating process comparatively slow. It is an object of the present invention to provide a compact device, wherein the necessary time for heating and time for cooling can be adequately provided within one'and the same housing and wherein economies of space and thereby initial costs can be effected.

A further purpose is to provide suitable strucwill make the' above and other purposes more The designof applicant's furnace lends itself admirably to mass production, due to its great,

stantially on the line 22 of Fig. 1.

Fig. 3 is an enlarged sectional detail taken on line 3-3 of Fig. 1, illustrating the doors leading from the entrance compartment to the heating chamber and showing mechanism for locking and unlocking. I

Fig. 4 is a sectional detail on the same scale as Fi .3 and taken on line 4-4 thereof, showing mechanism for preventing the opening of one set of doors when the second set is free to open.

Fig. 5 is a sectional plan taken on line 55 of Fig. 2 illustrating the crossing where the cars are inoved from the inner to the outer chamber, the end of the down helix and the beginning of the up helix.

Fig..6 is an enlarged detail showing in plan the section of track at the point of crossover from one chamber to the other and. illustrating in detail the switchinggof segments of track by the car propelling mechanism.

Fig. '7 is a sectional elevation of Fig. 6 taken on line 'l-l thereof, and

Fig. 8 is an enlargedsectional detail, taken-on line 8-8 of Fig. 6, illustrating a'spring tensioned pivot upon which the rail segments operate.

Fig. 9 is an enlarged detail of a vertical section' corresponding to a fragment of Fig. 2, and

showing'a conveyor car truck with a detachable "body mounted thereon and containing 'a nesting of trays for supporting articles to be sintered.

Fig. 10 is a view partly in side elevation and partly in section of one end of a conveyor car as shown in Fig. 9.

Fig. 11 is an enlarged sectional detail of one of the nesting trays used in supporting th articles to be sintered, one side of the view showing articles positioned at random.

Fig. 12 is a similar view to Fig. 11 showing two of the trays nested together and at one side articles uniformly positioned for sintering.

The cylindrical shell I8 is rotatable, being provided with a suitable rack H! at its base designed to mesh with a motor driven pinion connected with any suitable source of power (not shown). The base of the shell is also guided in a. suitable cylindrical guide 2| and its free movement is furthered by means such as a roller hearing or the like indicated at 22.

Aflixed to the inner face of the outer casing ill and within the chamber B is a plurality of supporting brackets 25. These brackets are so arranged as to support the trackway I 5 in a helical path, performing a similar function to that of arms M. It will be understood, however, and by reference to the drawings, that the arms 14 support the trackway in such manner as to'provide a downward helix within chamber A and the brackets 25 are so arranged as to provide an upward helix of the trackway within chamber B.

The trackway l5 comprises a continuous two rail track upon which conveyor cars 26. are propelled. Each of these cars is provided With suitable wheel trucks and have detachable body portions 21, the bottom and sides of which are formed of perforated metal, wire mesh or the like, to provide for a free circulation there-- through.

As the sizes and shapes of the articles to be sintered are of great variety and-the shapes infiuence the individual treatment, we further pro-. vide trays 21A for use in connection with the body portions 21. These trays are also made of perforated metal or thelike for the same reason the body is perforated, and are designed to nest one above another and fit within the confines of said bodies.

In some instances, the shapes of the articles are such that they may be loosely piled at random within a tray as shown in Fig. 11 and are best sintered in this formation; in others, the articles must be carefully placed and arranged ina uniform manner with free circulation entire about them, in order that'they be sintered to the best advantage, as shown in Fig. 12.

In still other treatments,. a preliminary subjection to a liquid bath is desirable, for, which purpose a conveyor having suspended hooked mem- Fig. 13 is an electric diagram illustrating the controls for the heating elements in both chambers, the cooling mechanism, and the driving mechanism; theheating elements being shown detached.

Referring now to the drawings, 10 indicates the outer stationary casing of a cylindrical housing, having a tightly closed top H and a tight for a vertical cylindrical shell l8. shell forms the wall for an inner chamber A and is so spaced in its relation to the outer-casing III as to provide an outer, chamber B entirely around the chamber A.

here can be utilized for engaging certain of the openings provided in the trays, as shown in Fig. 11; the trays being transported, immersed and stacked or nested by this means. In each case, however, thebody'portions either with or without the trays are mounted upon the conveyor cars 26 for transportation through the chambers.

The propelling means for these cars is provided in the form of a series of evenly spaced radially projecting fins 28, which project from both the inner and outer faces of the cylindrical shell l8 in such manner as to engage either the front .or rear of the cars 26 and cause them to move with the movement of cylindricalshell l8.

The cars are so constructed as to fit within the spaces created between fins 28 and'their front and rear ends are curved to cooperate with the action of said fins in their paths of rotation.

It will be observedthatdue to the smaller diameter of the trackway I 5 in chamber A, .the pitch thereof will be greater than that of the trackway within chamber B, the number of turns being equal, and that due to this difference a car fed into chamber A for travel down the helix, will be retarded by the speed of travel of fins 28 on the inner face of shell I8, while the same car when within chamber B and during itspathupfore, be seen that the initial feed to theinner chamber A is desirable, as the smaller diameter and the greater pitch of the trackway here, urges the cars in their downward path and tends to assist the movement of shell I 8, thereby acting to counterbalance the power required to lift the cars up the lesser pitched path of the trackway within outer chamber B of the greater diameter.

The cleaning unit in the present example is situated within the central compartment of the tank and comprises four rotary brushes 5, i, I, 8.

Arranged within chambers A and B in such helical formation as to follow closely the path of the cars in their respective travels are located aseries of electrical heating elements -3l-32 and 33. These elements are so positioned as to reflect heat upon the top, bottom, and sides respectively, of the car bodies as they travel the trackway i5. The elements 30-3! and 32 are stationary, fixedly supported by the arms l4 and brackets 25, while the elements 33 are attached to the inner and outer face of the rotatable shell 18 and move therewith, being provided with brush contacts for energizing same. Eachof the elements is interrupted at various points throughout their height to create separate zones of heat energy, and each part of the elements so divided can be separately energized and controlled from an electric switch board (see Fig. 13).

At the top I l of the outer casing Ill) and formed integral therewith is a compartment 35, provided at its outer end with a pair of inwardly swinging doors 36 and at its inner end with a second pair of inwardly swinging doors 31. This compartment-is of sufiicient size to house a car and is designed as a lock against the escapement of heat and gases. It is of such length as to permit a car to be pushed through and past the first set of doors permitting said doors to close before the second set of doors 3? can be opened. Both sets of doors are spring shut in their closed po-- sition and, are operated to open by the weight of a loaded car pushing against them and overcoming the tension of their springs, and are further provided with proper sealing means in the form of gaskets, etc. to efiiciently prevent the escape of gases...

To further minimize the escape of gas, locking means is provided whereby only one set of doors can be opened at the same time( see Figs. 3 and 4i) and as it is desirable to coordinate this time with the position of the fins during travel in their rotary path, the means for unlocking the doors' 3i and permitting the infeed of a car to chamber A is designed to be controlled from the rotating shell l8 carrying the fins 28. To this end a cam groove 38 is arranged about and close to the upper periphery, and on the inner face of the rotating shell l8, and a roller 39 is designed to follow the groove of the cam. This roller 39 is attached to the lower end of a vertically reciprocating plunger ill which is housed in apart of a fixed partition wall 4|, said partition being arranged in line with cylinder 18 and designed to separate chambers A and B above the rotating cylinder.

As cylinder 1 l8 rotates, carrying therewith groove cam 38, roller 39, attached to plunger 60 successively moves the latter down and up as it follows the path ofthe cam. This plunger is so positioned when up, as to lie in the path of and against the swinging doors 3'l thereby preventing their being forced open by, a car within compartment 35, In the down position, plunger is drawn clear of the doors and pressure of a car upon them will cause them to open permitting the car to roll down the incline of the track.

Cam 38 is so shaped as to cause the down movement of plunger 40 at such a time as to coordinate the in-feeding of a car in proper timed relation to the rotation of cylinder l8 and the subsequent positioning of that car between fins 28.

Attached to one face of plunger 40 is one arm of a bell crank 42, the fulcrum for which is attached to the fixed bottom of compartment 35. and its other arm is attached to a rod 43 interposed between one arm of a second bell crank 44. The bell crank 46 has a pivoted fulcrum attached the same as bell crank 52 and its second arm is pivotedly connected to a plunger 45 vertically operable within a guide opening in the. bottom of compartment 35. This second plunger is located directly in front of the swinging entrance doors 36 in such manner as to prevent their opening when the plunger is in its raised position and to permit the opening of the doors when the plunger is lowered.

It will thus be understood that, as cylinder l8 rotates, the cam 38 will continuously cause plunger 40 to rise and fall and, through the dual bell crank and rod connection just described, will also impart a like motion to plunger 45, the parts being so arranged that when plunger 40 is in the up position locking doors 31, the 'plunger 45 will be in the down position, permitting the opening of doors 36, and when the plunger 40 is lowered, to permit the opening of doors 31, plunger 45 will be raised to prevent the opening of doors 36.

To further oifset any possibility of a car contacting the top of a fin 28 as it descends its helix and assumes its proper relation to said iin, the

tops of each fin of the inner chamber are provided erlypositioned thereby and not derailed.

When the inner helicaltrackway reaches the bottom of chamber A, it is carried outward through openings 5! provided in the wall of cylindrical shell I8. These openings are of sufilcient height to allow a car to pass under and such passage is made by that ml which is following at the rear of the'car as it moves forward and into contact therewith, propelling the car across that section of angular track comprising the crossover (Fig. 5) and starting it on the upgrade of the helix in chamber B at which time it is engaged by that portion of fin 28 which extends from the outer face of the shell. In this position, the car is pushed up, the helix of the outer trackway by the engaging fin 28, the car tracking up the helix while its engaging face travels a vertical path against the face of that fin with which it happens to be engaged.

The tracks proper are broken as indicated at 52 (see Figures 5, 6 and 8) and short sections 54 are pivoted at 55in such manner as to be moved by supports 53 which are integral with the shell 88 as said shell is rotated.

These sections 54 are held normally in line with the rest of the track by springs 56 which surround the pivots 55 and act to retain them in contact at breaks 52 (see Fig. 6). As the shell [8 rotates, the supports 53 successively contact the track sections and swing them upon their pivots to the dot and dash positions indicated. When the supports pass beyond the sections 54, the action of the springs 56 return them to their normal (full line) positions, closing the tracks at points 52 to provide a continuous uninterrupted passage for the following car 26.

When a car has reached the upper limit of its travel in the outer chamber B under the influence of a fin 28, it-is moved over a crest as indicated at 60, Fig. 2, from which point the car moves by gravity over a downwardly inclined length of track 62 and away from engagement with its propelling fin. Arranged in line with this length of track 62 is a second compartment l (similar to and for a like purpose to compartment 35, and two sets of spring tensioned doors 66 and 68 are likewise respectively provided on entrance and exit ends. These doors are designed to swing with the pathof travel of the car and are opened thereby thesame as the doors 36 and 3! in compartment 35. However, no locking and unlocking mechanism is here required, as the spacing between cars has already been timed and there is no danger-of both sets of doors 66 and 68 being open at one and the same time.

At desirable and convenient points throughout the walls forming both chambers, there is provided glazed openings 58 for the visual inspection of the materials under treatment. This is essential as it enables the operators to properly control the electric heating elements, supplying heat of the required degree to cooperate with proper sintering requirements.

The outer chamber B is provided with suitable cooling means, in the present showing diagrammatically illustrated as a motor driven blower fan 16, supplying air through a duct or ducts I2 to desired points approximate the bottom of the chamber but above the bottom of cylinder l8 so as to prevent the cooling medium from entering the heating chamber A.

A valve controlled pipe for the introduction of gases is indicated at 14 leading from a suitable source (not shown) to the bottom of chamber A.

As stated, the entire structure is tightly closed to prevent the escape of introduced gases, but during the entrance and exit of the cars through compartments 35 and 64 respectively, there will be a tendency for a portion of the gases trapped in these compartments to escape out of the chambers. To minimize this loss, applicants provide the bottoms of said compartments with openings 13 forming connections with the top of cooling chamber B, and provide the tops of the compartments with other openings 15 communiating with ducts Tl which are in turn piped to I the convenient burners where the gases are disposed of ,by burning.

Gauges 16-46 are conveniently located to indicate temperature in either chamber, while at 18 a pressure gauge is shown connected with chamber A.

Referring now to Fig. 13, a diagrammatic view is shown to illustrate the electric elements of our invention and their various controls.

The heating elements 30, 3| and 32 comprising, together with element 33, the set'in outer chamber B are interrupted at various points 80 throughout their respective helical paths, whereby separate heating areas or zonesare formed, and a wiring connection 8| is supplied for each zone and leads to a switch board 82. Each connection in the present instance is controlled by a switch 83, whereby any one, or all, or any combinationof zones can be energized.

The element 33, which is attached to the moving shell I8 is furnished with a brush contact '84 and are shown as having separate wiring connections 85 and switch controls 86.

The elements 36-3l and 32 supplying heat to inner chamber A are similarly interrupted as in chamber B and wiring connections therefore are shown at 81 and lead to switches 88 on switchcontacts 89, with wires 90 leading to board 82.

Element 33in outer chamber B likewise attached to moving shell I8 is furnished with brush switches 9| on switch board 92. Each wire BI, 85, 81, and 96 where shown in heavy line indicates dual wires. It will thus be understood that either or both chambers can be heated in their entirety or the heat in different zones can be varied at will. Applicants recognizethe possibility of a further degree of variation by furnishing separate controls for each heating element in each zone, or

still further by providing varying degrees of heat to each element by such means asgrheostats or the like in' place of the switches shown.

A motor 92 is indicated for driving the inion I 26 through suitable gearing whereby the shell I8 is rotated. This motor is shown connected by wires 93 to a power source, one wire being subject to the control of a rheostat 94, whereby the speed of rotation of shell l8 can be controlled.

Themotor 16 (for driving the blower .fan) is shown connected through wires 95 to a power source, one wire being subject to'rheostat control shown at 96, whereby the speed of the fan can be varied and the amount of air supplied to chamber B controlled.

It will be understood that this showing is pure- 1y a diagrammatic illustration of one means of control, and the same may be varied to accomplish like purposes without departing from the spirit of this invention.

doors 36 closing behind each car, before the car itself opens the second set of doors 31. The dual plungers 40 and acting as looks at this time, prevent the opening of doors 3! if doors 36 are free to open and vice versa, under the control of the rotation of shell l8.

The opening of doors 3! is so timed by the cam 38 as to -allow the introduction of a car to the top of chamber A in such timed relation as to permit it to assume an initial position between any two inwardly projecting fins 28. As the pitch of the trackway of the inner helix is such as to cause the car to move at a greater. rate of speed than the movement of the fins, the car will engage the rear of one of the fins and be retarded thereby in its downward helical path.

Should the load within the car vary to the extent of changing the speed of the car following its introduction and thereby vary the timed relation of its engagement with a fin, the cam-like faces at the tops thereof act to either advance the car or retard it and thereby avoid derailing.

during operation, to the top, bottom and both sides of the car' The heating element located adjacent the paths of travel of the car are properly energized and heat therefrom is directed body, through the perforations, or orifices of the to create varying zones of difierent temperatures throughout the heating chamber in accordance with sintering requirements ascertained by visual inspection through glazed openings 58.

If it is found desirable to prolong the heat treatment for a duration greater than that provided within chamber A, then the heating elements within chamber B are energized and the total travel within both chambers is given to heating, the air flow from the cooling mechanism is discontinued, and the cooling is taken care of by conveying the cars over added lengths of trackway outward of the chambers or by dismounting the bodies 21 and/or trays 21A and stacking them, allowing the sintered objects to cool by contact with the normal atmosphere.

Ordinarily the cars and their contents are subjected to controlled, variable heat treatment throughout-the duration of their travel down the helical path of the trackway, and this time is dependent upon the speed of rotation of the cylindrical shell I8 and its connected fins 28,

which speed can be varied by any well-known mechanism, such, for example, as rheostat control for the driving motor.

When a car'reaches a point at the bottom of chamber A, it pauses on a level stretch of track, and the fin with which it has been in contact moves in advance of the car while the fin following, contacts the rear of the car urging it over the crossing to the outer helix through a registering opening Si in the bottom of cylinder i8 and starting it on the upgrade of the outer. helix.

As each car moves from the central chamber A to the outer chamber B, it passes from the heating to the cooling zone and is preferably subjected to cooling throughout its entire upward travel of the outer helix.

Upon reaching the top of the helical track, each car is moved over the crest 60 located at the beginning of the connected tangential length of downgrade track leading to the ejection chamber (it. At this point, the cars are switched away from the circular path of the propelling fins due to their following of the tangential track and again move by their own momentum down to and through doors 66, compartment 64 and in some processes and wherein the initial high heat treatment is given in one chamber and the subsequent lesser heat treatment in another.

Further attention is directed to the provision for both prolonged heat treatment and even longer time for cooling within a comparatively small structure. Assuming the diameter of the entire device to be 14 feet and its height 20 feet, and the diameter of the inner rotating shell 9 feet which are the proportions illustrated in Figs. 1-2 and 5 of the accompanying drawings, the travel of each conveyor would beapproximately 180 feet in the central chamber A and 325feet in the outer chamber B. Compare this with any continuous structure wherein over 500 lineal feet of space would be'required', plus space for loading and unloading. The condensing of the travel length within a greatly restricted area is also desirable as it is a great aid to the required visual inspection, attendants being able to closely observe the physical changes of the materials being sintered from a few difierent levels as compared with following the travel of the material over a comparatively excessive distance.

It will be evident that, if for any reason a reversal of the operation, 1. e. feeding down through theouter chamber and upward through the inner'one, becomes desirable, for other purposes, or reversing the positioningof the heating and cooling hambers or the gas inlet, such change can readily be made without greatly altering the design of mechanism here disclosed and without.

departing from the spirit of this invention.

Applicants also recognize the possibilities in employing a single heating chamber with spiral traverse and allowing the cooling to take place naturally in the open. The car bodies 2'! with the treated materials therein can be handled by doors '68 and on to a suitable stopping place (not shown) for unloading the car bodies 2i with the treated materials, and reloading them for another cycle of operation as just described.

It will be noted that the individual cars are free to travel through the two chambers controlled only by the fins 28, and that the cars may .be fed to the device as rapidly as the speed of rotation of'the cylindrical shell will permit.

It has been found that, in sintering certain alloys, 9. much more desirable product can be obtained in sintering by first subjecting the materials to a quick heat and then to a gradually reduced temperature. The present design lends itself admirably to this requirement as the initial heat subjection of the materials is at the top of the cylinder where the heat will naturally be the greatest due to it tendency to rise and the subsequent treatment will proceed through an area of gradually lessening temperature.

If it is found-advisable to suit certain conditions, the energizing of elements in given zones and the de-energizing of them in others, will enable the operator to control the application of heat at varying points throughout either chamber. v

This design will also eliminate the requirement for separate heating chambers as now employed special mechanisms and stacked for prolonged cooling, or the individual trays 21A in each body can be handled in like manner.

While the greater portion of this description has been directed to sintering, applicants are fully cognizant of the possibilities of the utilization of the same method and mechanism for other forms of heat treatment of metals, whether preformed from powder alloys or by other processes, such as for example, carbonization, galvanizing, various hardening treatments,

or, in fact, any treatment of metals requiring subjection to heat, controlled or otherwise, and/or subjected to the action of inert gases.

In view of ourinvention and disclosures, variations and modifications to meet individual whim or particular need, will doubtless become evident to others skilled in the art, to obtain all or part of the: benefits of our invention without copying the structure shown, and we, therefore, claim all such insofar as they fall within the reasonable spirit and scope of our invention in the following appended claims.

We claim:

1. In a device of the character described for heat treating metallic units, the combinationof means forming two elongated vertically extending closed chambers, one within the other, means for introducing the units into thetop of the inner chamber, and for discharging the units from the top of the outer chamber, helical trackways for carrying the units from top to bottom of the inner chamber, and from'the bottom to the top of the outer chamber, means for transferri'ng the units fromthe bottom of the inner chamber to the bottom of the outer chamber and heating elements associated withthe chambers,

said heating elements being so, disposed as to zones.

diroot the heat to the bottom, sides and top of the units moving in the inner chamber and whereby the heat-arising from said element may be accumulated at the top of said chamber.

2. In a device of the character described, for heat treating metallic units, the combination of means forming two elongated vertically extending closed chambers, one within the other, means for introducing the units into the top of the inner chamber, and for discharging the units from the top of the outer chamber, means for carrying the units from top to bottom of the inner chamber, and from the bottom to the top of the outer chamber, means for transferring the units from the bottom of the inner chamber to the bottom of the outer chamber, and heating means for creating arbitrarily controlledheating zones through which the units must travel, said heating means comprising a series of electric heating elements and means for connecting each element with a current source.

3. In a device of the character described, for heat treating metallic units, the combination of means forming two elongated vertically extending closed chambers, for introducing the units into the top of the inner chambenand for discharging the units from the top of the outer chamber, means for carrying the units from top to bottom of the inner chamber and from the bottom to the top of the outer chambe means for transferring the units from the bottom of the inner chamber to the bottom of the outer chamber, a plurality of electric heating elements following a path of travel parallel with that of the units, and arbitrarily actuated means for the independent control of the connections between said electric heating elements and a current source, whereby above-sintering temperature is created and maintained in the top of the inner chamber, de-

rived from the heat arising from the several 4. In a device of the character described, for heat treating metallic units, the combinationof means forming two elongated vertically extending closed chambers, one adapted to rotate within the other, means for introducing the units into the top of the inner chamber, and for discharging the units from the top of the outer chamber, means tor-carrying the units from top to bottom of the bottom to the top for transferring the units from the bottom of the inner chamber to the bottom of the outer chamber, a plurality of separately controlled electric heating elements following the courses of said trackways, and glazed windows in the walls of both chambers arranged to come into register one chamber wall rotates from time to time as relatively to the other.

5. In a device or the character described, the

one'within the other, means.

combination of an outer stationary casing closed at top and bottom, a plurality of track supporting' brackets projecting from the casing wall within the casing, a centrally positioned vertical stationary supporting column provided with radially projecting track-supporting arms, a vertical cylindrical shell supported to rotate between the outer casing and the central column, said shell provided with vertically extending fins projecting from its inner and outer sides in spaced relationship, an inner helical track supported on said radial arms, and an outer helical track supported on said brackets, material containers adapted to move upon said tracks, and adapted .to be actuated by the fins of the rotating shell, and electric heating elements carried by the shell and connected to a source by means of brush connections.

. relationship,

'6. In a device of the character described, the combinationof an outer stationary casing closed at top and bottom, a plurality of track/ supporting brackets projecting from the casing wall stationary supporting column provided with radially projecting track-supporting-arms, a vertical cylindrical shell supported to rotate between the outer casing and the central column,

" said shell provided with vertically extending fins projecting from its inner and outer sides in spaced an inner helical track supported on said radial arms, and an outer helical track supported on said brackets, material containers adapted to move upon said tracks, and adapted to be actuated by the fins of the rotating shell and suitable heating elements associated therewith, the heating elements being so disposed as to direct heat to the bottom, the sides and the top of the material introduced to and descending the inner chamber and from the of the outer chamber, means inner shell and so that the hottest zone will'be adjacent the point of introduction of the material to the inner shell.

7. The method of sintering metal powder units, which consists in the following steps, introducing the units into the top of an elongated vertically extending closed space, causing the downward movement of the units from the top to the bottom of said space, supplying heat to said space to form independently controlled zones of temperature, utilizing portions of the heat supplied to a plurality of zones, in maintaining a maximum temperature in the topmost part of the zone into which the material initially enters, then transferring the units into the bottom of a second enclosed space, causing the movement of the units from the bottom a centrally positioned vertical.

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