US2733912A

US2733912A - Vacuum furnace batch feeding method and apparatus

Info

Publication number: US2733912A
Authority: US
Publication date: 1956-02-07
Anticipated expiration: 1973-02-07

Description

Feb. 7, 1956 c. E. NEWCOMB ETAL 2,733,912

VACUUM FURNACE BATCH FEEDING METHOD AND APPARATUS Filed Aug. 30, 1954 2 Sheets-Sheet 1 w/iumwauxhwmm ATTORNEYS.

Feb. 7, 1956 c, EQNEWCOMB ET AL 2,733,912

VACUUM FURNACE BATCH FEEDING METHOD AND APPARATUS Filed Aug. 30, 1954 2 Sheets-Sheet 2 INVENTORS. CHARL 5 E. Nswcona.

JOHN A. Peers/e. y PA 01. E. Dnesn MMJMM ATTORNEY-5.

United States PatentO .VACUUM FURNACE BATCH FEEDING METHOD AND APPARATUS Charles E. Newcomb, Industry, Pa., John R. Porter, Chester, W. Va., and Paul F. Darby, Beaver, Pa., assignors to' Rem-Cm Titanium, Inc., Midland, Pa., a corporation of Pennsylvania Application August 30, 1954, Serial No. 452,965

8 Claims. (Cl. 266-27) This invention relates to means and methods for feeding charges of highly reactive metals, such as titanium sponge, and their alloying ingredients to a vacuum-tight ice * precise proportionate ratio of ingredients desired as the melting furnace in such manner as to produce a homo- 1 geneous ingot having the desired overall chemical analy- In the melting of titanium base alloys and alloys of other similar highly reactive metals, the chargeof material to be melted commonly consists of a mixture of the various desired ingredients in granular, comminuted or pulverulent form. Due to wide differences in the gravimetric densities of these various materials, gravitational separation of the samewill occur if an attempt is made to mix the entire charge in a single hopper. This gravitational separation will, of course, preclude homogeneous feed to the furnace from that single hopper, and such homogcneousfeed has been found necessary for the production of a structurallyhomogeneous ingot; the reason being that in the melting of such highly reactive metals, the ingots are built up bit by bitjas the charge is fed gradually into the 'furnace' with only a relatively small portion ofthat charge being in the molten state at any one time and therefore, unlessthat particular portion of the charg eiwhich is' molten is homogeneous, a non-homogeneous ingot willre'sult.

In'or dert'o provide suchari'ultim'ate homogeneous ingot structure' various homogeneous feed apparatus and methods are presently in use which call for individualiy but simultaneously feeding each particular ingredient of the charge from a'separate hopper while cont'rolli'rigthe rates of feed of these various ingredients in accordance with ultimateproportionaterequirements of the alloy melt. In such systems maintenance of the proper proportionate feed is a matter of constant concern to the-operators 'of the furnace: Moreover, such systems generally employ a plurality of rotating screw feed means or the likej each extending into the furnace through a wall thereof,and since these furnaces must be maintained vacuum-tight, vacuum-tight sealing means must be provided at the'e'ntry points'of these feed screws. Maintenance in operation offsuch' sealing means is quite dilficult'] p A Ourinvention herein eliminates the necessity of main raining a closely controlled proportionate feed, and provides a method and apparatus for feeding such charges to 'a-vacuum-tight furnace from a single hopper; Moreover, the invention largely eliminates the necessity of a multiplicity of difiicult tomaintain vacuum-tight seals for rotaryfeed'screws and the like, andrequires but a single'and simple vacuum-tight seal for a pulsating shaft. According to'the' invention "an incremental feeder is provided whichpermi'ts the use of blended charges of such small size that mechanical separation 'of the various ingredients thereof due to igravity is unimportant. in accordance with theincremental feed method'of the invention, the total charge necessary for the production of any ;given' size=ingot is made up --by individually; blending a plurality of small charge batches, each having the overall chemical analysis for the ingot to be produced, and then feeding said batches successively to the furnace without regard for homogeneous feed of each individual batch. The precise size of these batches will, of course, depend upon the particular operating conditions involved, such as the size of the furnace, and the size of ingot to be produced, but inany event each batch will be sized so as to be smaller than the portion of the charge which is in the molten state at any one time in the furnace. If, for example, itwere desired to produce a 4000 pound ingot containing 4% aluminum, 4% manganese and the balance titanium, the incremental feed apparatus and method of this invention would call for forty individual one-hundred pound charge batches to be made up, each precisely weighed and blended according to the desired ration of 92% Ti4% A14% Mn. and then fed successively into the furnace. Since the densities of these particular alloying ingredients vary widely, i. e., specific gravitiesTi, 4.5; A1, 2.7; Mn, 7.2, gravitational separation would probably occur in each of the forty small charges. Thus, as each of these charges is fed into the furnace the feed may not be homogeneous, that is, the composition of each hundred pound charge mayvary from pound to pound. Nevertheless, substantial homo geneityof the ingot produced is assured, since the overall composition of each 100 pounds is precisely correct, and since'the amount of metal in the molten state in the furnace crucible at any one time is by predetermined 'design substantially greater than 100 pounds, each incremental 100 pound batch will be further blended into a homogeneous mixture while within this molten bath of the furnace. I

The incremental feed apparatus according to. the invention comprises upper and lower interconnected feed hoppers with a charge restraining butterfly-type valve and a vacuum closur'e'ball-type valve disposed in that order in the line connecting the upper hopper with the lower hopper. Disposed beneath the lower hopper is a vacuum-tight enclosure which is in open communication both with said lower hopper and with the furnace, and in which there is positioned a reciprocating feed trough which is designed to receive the batch of charge from the lower hopper and deliver the same to the furnace itself. Suitable sealing means are provided tomaintain the aforedescribed system gas-tight. The reciprocating feed'trough is activated by a pulsating magnet assembly which is positioned exteriorly'of the aforementioned vac uum-tight system, its only connection therewith being a pulsating drive shaft which extends through a wall of the enclosure so asto be operatively connected. to the feed trough. The upper hopper is provided with both an inert gas inlet line and a vacuum line, the latter running to a suitable vacuum pump, with each of said, lines being provided with vacuum closure valves, While the furnace itself is of course suitably connected to vacuum pumppers are initially closed and the furnace, together with connecting feed trough enclosure and lower hopper, are pumped down to the desired vacuum. The first preweighed incremental batch of charge of a size and character as described above, is then delivered to the upper hopper. This upper hopper is then sealed and pumped down to the desired vacuum, generally corresponding to the pressure ofthefurnace. The vacuum closure ball valve and charge restraining butterfly valve are then opened 'in that order, thereby permitting the batch of charge in the upper hopper to' fall by gravity to the lower hopper from whence it is fed to the furnace by the feed trough. The rate of reciprocation of the trough and hence the ratefof feed to the furnace can, if desired,

be varied by providing a suitable rheostat control unit in the activating magnet assembly. As soon as theupper hopper is empty the butterflyfand vacuum closure valves in the line connecting the two hoppers are then closed, and the upper hopper is fiooded'with an inert gas, such as argon, until approximately atmospheric pressure is attained therein. The next incremental batch is then delivered to the upper hopper and as soon as the first batch has emptied fr om the lower hopper, the above described procedure is" repeated over and over until the entire charge has been fed to the furnace.

It will be observed that only the drive shaft of the pulsating magnet assembly passes through a wall of the aforedescribed vacuum-tight feed system'and since this shaft is limited to pulsating or reciprocating movement, it may be readily sealed in gas-tight fashion, according to conventional, well known means. Therefore the apparatus of the invention provides a system wherein the opportunity for, and chance of vacuum leaks is held to a minimum. Such a system moreover provides a relatively simple apparatus, which is subject to a minimum of mechanical failures. The present invention, moreover, provides better control of ingot homogeneity than has heretofore been possible undercomple x existing methods and moreover reduces the safety hazards involved, since the amount of highly active metals such as titanium sponge contained in the hopper at any given time is substantially reduced. The invention finds utility in all type furnaces for melting highly reactive metals, wherein the chargeis fed in granular or particle form to the furnace, and, even in the consumable electrode arc-melting type of furnace, which does not employ such a type of charge feed, theinvention can be employed to add lower melting point elements which are desired in the final ingot, but might prematurely melt out of the consumable electrode'if supplied in that fashion.

Other and more specific objects, features and advantages of the invention will appear from the detailed description given below, taken in connection with the accompanying drawings which form a part of this specification and illustrate by way of example the present preferred embodiment of the invention.

In the drawings:

Figure 1 is a vertical elevational view of the entire incremental feed apparatus of the invention. A

Figure 2 is an enlarged, fragmentary cross-sectional view of the upper portion ofthe apparatus of Figure 1, showing the butterfly and vacuum closure valves in the line connecting the upper and lower hoppers.

Figure 3 is an enlarged, fragmentary cross-sectional view of the lower portion of the apparatus of Figure 1, showing the feed trough with its activating magnet assembly. 1

Referring now in more detail to the drawings and partlcularly to Figure 1 the incremental feed apparatus of the invention, as shown, comprises an upper feed hopper having .a pivoted closure lid 11, which is provided with a resilient annular gasket 12 designed to render the hopper 10 vacuum-tight when the lid is pivoted to the closed position shown and pressure is applied thereto. heading into this upper feed hopper is an inert gas entry line 13 having a vacuum closure valve 14'of suitable known type, and a vacuum line 15 having a suitable vacuum closure valve 16 of known construction. Positioned beneath the upper feed hopper and connected therewith by means of a conduit or feed line 17 is a lower hopper 18, the lower endof which is open and continuous communication through a vacuum-tight enclosure 19 with a furnace 20, which latter may be of any conventional design for producing ingots of highly reactive materials such as titanium sponge. It shouldbe of course understood that the furnace 20 is provided with suitable connections leading to vacuum pump-down'means ,2,7as,912 p t (not shown) adapted to maintain the furnace at the desired low operating pressure. I

Referring now m'rigure 2 it will be seen that in the line 17 which interconnects hoppers 10 and 18 there is positioned, immediately beneath the upper hopper, a charge restraining butterfly-type valve 21 having an operating lever 22. Beneath this-charge restraining valve a ball-type vacuum closure valve 23 is located in the line 17. This valve is of standard construction and comprises a ball seat 24 having a gas-tight, sliding fit with a ball 25. The ball 25 is providedwith acentral passageway 26 and is adapted to be rotated by anoperating lever 2'7 from the closed position, as shown'in Fig. 2, to its open position wherein passageway 26 is aligned with the hopper interconnecting conduit 17; The hopper 18 has an open lower end 23 which extends, into enclosure 19, the hopper and enclosure being welded together as at 28a. This enclosure lt9, as mentioned above, is in open communication at one end 29 with the interior of furnace 20 and is provided at its other end with a vacuum-tight closure plate 30. Suitable resilient

annular gaskets

31, 31', 32,

' and 33 are provided at the juncture points of the feed line 17 and enclosure 19 so as to effectively seal the above described system in vacuum-tight fashion. Positioned beneath the open end 28 of the lower feed hopper 18 is a reciprocating or vibrating conveyor feed trough 34 which is designed to receive material from the hopper and deliver the same to the furnace. Vibratory conveyors employing such a trough are well'known and comprise in conjunction therewith a power driven vibratory mechanism connected to the trough at one end for delivering longitudinal vibrations to it, whereby material deposited on the trough at one end is caused to travel continuously thereover for discharge at the other end. Herein the necessary vibratingor reciprocating movement is delivered to the trough 34 by a pulsating magnet asembly 35 having a pulsating shaft 36 which is connected at 37 to one end of the feed trough. As is customary in such conveyor mechanisms, the feed trough 34 is resiliently mounted so as to have an nace.

upward component of motion as it moves forward toward the furnace and a downward component of motion as it returns rearwardly away from the furnace in order to therebypropel the charge material forwardly to the fur- As shown, this resilient mounting comprises a pair of elongated, rectilinear leaf springs 38 and 38', but it should be understood that any suitable resilient mounting could be employed. These mounting

springs

38 and 38 not only permit the desired vibratory or reciprocating movement of the feed trough delivered to the latter by the primer movermagnet assembly 35, but also the inherent regenerative force of those springs serves to aid the prime movers efforts.

The prime mover magnet assembly is of thepulsating type of well known design and comprises a winding 39 which is suitably connected to a source of energizing, alternating current, as indicated at 40, a core 41 which is attached to the shaft 36 via connector 42. Cylindrical guide means 43 holds the shaft 37 in proper alignment for passing through a vacuum-tight seal 44 which is provided in the closure plate 30 of the feed trough enclosure 19. This vacuum-tight seal 44 includes a semi-spherical resilient O-ring 45 which embraces the shaft 36 in gastight sealing relationship. Analternative means of providing this seal is by means of a section of rubber tubing surrounding and extending between shaft 36 and housing 44 andclamped at its opposite ends to these elements respectively. The pulsatingmagnet assembly is operatively positioned exteriorly of the aforedescribed vacuum-tight charge feeding system, being mounted on a rigid frame 45 which is attached by suitable means 46 to the closure plate 30 of enclosure 19. Only the pulsating shaft 36 extends, as described above'in gas-tight relationship through the closure plate 30 of the enclosure 19. Therefore the magnet assembly need not be sealed'fr'om the atmosphere and hence itssupporting frame 45 may be of the open hopper is then opened and the first incremental'batch of charge introduced thereinto. Lid 11 is then closed and, with valve 14 of the inert gas line in the closed position, valve 16 of the vacuum line is moved to its open position and the hopper 10 pumped down to the desired vacuum pressure as indicated on a suitable gauge 50, which pressure will ordinarily correspond to the operating pressure of the furnace. During this pump-down of hopper 10 the force of atmospheric pressure on the upper surface of the lid 11 will cause the sealing gasket 12 to be compressed thereby effectively sealing this upper hopper in gas-tight fashion from the ingress of harmful atmospheric gases. When the desired vacuum has been attained in hopper 10 the vacuum closure ball valve 23 is first moved to its open position with passageway 26 aligned with the hopper interconnecting line 17. As shown, at this point in the process, since the charge restraining butterfly valve 21 is still closed the titanium sponge or other material 51 contained in hopper 10 will be prevented by said butterfly valve from contacting the ball closure valve. This is most important since such charge material is generally highly abrasive, and if the same were permitted to be in contact with the valve seat 24 of the ball valve when that valve was being moved from its closed to its open position, the delicate surface of the seat would be marred by the particles of the charge thereby destroying the gastight sealing fit between the same and the ball 25. The action of the charge restraining valve 21, however, permits free movement of the vacuum closure valve without interference from or contact with the particles of the charge. The butterfly valve 21 is then moved to its open position thereby permitting the batch of titanium sponge or similar material 51 to fall by gravity into the lower hopper 18 from where it feeds gradually through the open end 28 on to the feed trough 34. The pulsating magnet assembly 38 is then energized thereby setting up a mag netic field of automatically reversing polarity in the winding 39 and causing core 41 and with it shaft 36 to pulsate thereby delivering reciprocating motion to the trough 34 which will result in a gradual delivery of the incremental batch of charge to the furnace as indicated at 52, with the actual rate of feed to the furnace depending on the rate of reciprocation of the feed trough.

As soon as all of the first batch of charge 51 has emptied from the upper hopper It) the

valves

21 and 23 will again be returned to their closed positions as shown in Fig. 2. The valve 16 of vacuum line is then closed and inert gas line valve 14 moved to its open position. Inert gas, such as argon, is then flooded into the hopper 10 until the same returns to approximate atmospheric pressure as indicated on gauge 50. At this point, since the pressures above and beneath lid 11 are approximately equalized, the lid may be opened and the second incremental batch of charge introduced to the hopper 10. When the furnace operator is convinced that the first charge has completely emptied from the lower hopper 18, the above procedure is then repeated thereby permitting the second batch to drop from the upper hopper 10 to the lower hopper and then into the furnace via feed trough 34 in the manner described aforesaid.

This procedure is repeated over and over until all of the incremental batches of the charge have been introduced into the furnace at which time the ingot will have been produced having the desired overall chemical analysis 6 and moreover a substantially homogeneous structure throughout.

Although certain particular embodiments of the invention are herein disclosed for purposes of explanation, various further modifications thereof, after study of this specification, will be apparent to those skilled in the art to which the invention pertains. Reference should accordingly be had to the appended claims in determining the scope of the invention.

What is claimed and desired to be secured by Letters Patent. is:

1. Apparatus for feeding incremental batches of charge of highly reactive metals and their alloying ingredients to a melting furnace, comprising a substantially gas-tight feed system having upper and lower feed receiving means interconnected by a feed conduit, vacuum closure means located in said feed conduit and adapted to seal off the upper feed receiving means, when desired, from the rest of the feed system and charge restraining valve means positioned in said conduit between the vacuum closure means and the upper feed receiving means and adapted, when closed, to prevent particles of the charge from contacting said vacuum closure means, means connecting said lower feed receiving means in open communication with the furnace, reciprocating feed delivery means positioned within said connecting means and adapted to receive particles of the batches of charge from the lower feed receiving means and deliver them to the furnace, and activating means located exteriorly of said gas-tight system and comprising a pulsating shaft extending through a gas-tight seal into said feed system and being connected to one end of the feed receiving means for imparting reciprocating movement thereto.

2. Apparatus for feeding batches of charge of highly reactive metals and their alloying ingredients to a melting furnace comprising substantially gas-tight upper and lower hoppers, a substantially gas-tight feed line interconnecting said hoppers, said feed line having a charge restraining valve and a vacuum closure valve positioned therein, a substantially gas-tight enclosure providing open communication between the lower hopper and the furnace, reciprocating feed means mounted in said enclosure beneath said lowerhopper and adapted to receive the charge from said lower hopper and deliver the same to the furnace, means for activating said feed means, said activating means being located exteriorly of the gas-tight enclosure and having a pulsating shaft extending in gas-tight sealing relationship into said enclosure and being operatively connected to the feed means.

3. Apparatus for feeding batches of charge of highly reactive metals and their alloying ingredients to a melting furnace comprising a substantially gas-tight feed system, having upper and lower feed receiving hoppers interconnected by a feed conduit and an enclosure connecting the lower hopper with the furnace, a reciprocating feed trough mounted in said enclosure of the feed system and adapted to receive the charge from said lower hopper and convey it to the furnace, and an activating magnet assembly positioned externally of said feed system and having a pulsating shaft extending through a gas-tight seal into the enclosure of said system, said shaft being connected to the feed trough for imparting reciprocatory movement thereto.

4. Apparatus for feeding batches of charge of highly reactive metals and their alloying ingredients to a melting furnace comprising a substantially gas-tight feed system, having upper and lower feed receiving hoppers interconnected by a feed conduit, a vacuum closure valve positioned in said feed conduit and a charge restraining valve positioned in said conduit between the vacuum closure valve and the upper hopper, and an enclosure connecting the lower hopper with the furnace, a reciprocating feed trough mounted in said enclosure of the feed system and adapted to receive the charge from said lower hopper and convey it to the furnace, and an activating magnet assembly positioned externally of said feed system and having a pulsating shaft extending through a gas-tight seal into the enclosure of said system, said shaft being-connected to one end of the feed trough for imparting reciproca'tor' 'mover'nentthe'reto.

5. A method of feeding a charge of particles of highly reactive metal, such as titanium sponge, and its alloying ingredients, said charge being characterized by the varying gravimetric densities of the individual ingredients thereof, in the desired proportions to a melting furnace so as to produce an ingot having the desired overall chemical analysis and having a substantially homogeneous structure throughout, which comprises individually weighing and blending according to the proportions desired a plurality of incremental batches of charge which together add up to the overall charge desired, delivering the first of said batches to a feed receiving means of a vacuumtight feed system Whilemaintaining said feed receiving means sealed off from the remainder of said feed system, pumping down said remainder of the feed system to the desired furnace operating pressure, then sealing ofi said hopper from the atmosphere, pumping said hopper down to the desired operating pressure, then opening said hopper into communication with the remainder of said feed system, then delivering said first batch of charge to the furnace then closing off said hopper from the remainder of the feed system and delivering the next batch of charge thereto so as to commence the cycle all over again.

6. A method of feeding a charge of particles of highly reactive metals to a furnace which comprises delivering a preweighed incremental batch of said charge to an upper feed receiving means of a substantially gas-tight feed system while maintaining that upper feed receiving means sealed oif from the remainder of said feed system, sealing off said upper feed receiving means from the atmosphere, pumping down said feed receiving means to a pressure corresponding to the operating pressure of the remainder of the feed system, then opening the feed receiving means into communication with the remainder of the system so as to deliver the first batch of charge to the furnace-and then sealing of? said-feed receiving means from the remainder of the furnace so as to permit introsmasher thenext batch of charge into thisfeedreceiving meanswithout eXposi-ngthe remaindenof the feed system to the atmosphere. i

7. A charge feeding system for'a furnace of the type wherein melting is' carried out under vacuum conditions comprising a substantially gas-tight feed system having upper and lower feed hoppers interconnected by a feed line and nieans'interconnecting said lower hopper with the furnace, vacuum c-losure means provided insaid feed conduit whereby said upper hopper can be sealed oil from the remainder of said feed system and charge restrainingmeans also located in said feed conduit betweenthe vacuum closure means and the upper hopper and adapted when in the closed'posit-ion to prevent particles of the charges from passing from the upper hopper into contact with the vacuum closure means, and reciprocating feed means positioned in' said feed system beneath the lower hopper thereof and adapted to receive the charge particles from said lower hopper arid deliver the same to the furnace.

8. Apparatus for feeding batches of charge of highly reactive metals and'their alloying ingredients to a melting furnace comprising a substantially gas-tight feed system, having feed. receiving means andan enclosure connecting said feed receiving means with the furnace, vibratory charge feeding means mounted in said enclosure and adapted to receive the charge from the feed receiving means and convey it to the furnace, and an activating magnet assembly positioned'externally of said feed system and having .a' pulsating shaft extending into the feed system through a gas-tight .seal providedin a wall of the enclosure of said-system,-.said shaft being connected to the feed trough for imparting reciprocatory movement thereto.

No references cited.

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