US3195873A - Vacuum degassing system - Google Patents

Description

Julyl 20, 1965 H. s. PHILBRICK, JR

VACUUM DEGASSING SYSTEM Filed March 27, 1961 3 Sheets-Sheet l July 20, 1965 H. s. PHlLBRlcK, JR

VACUUM DEGASSING SYSTEM 3 Sheets-Sheet 2 Filed March 27. 1961 July 20, 1965 H. s. PHILBRICK, JR 3,195,873

VACUUM DEGASSING SYSTEM Filled March 27. 1961 3 Sheets-Sheet 3 z. 93 uw mw nous,

United States Patent O 3,195,873 TVACUUh/.l DEGASSING SYSTEM Herbert S. Fhilhrick, Jr., Chicago, Ill., assigner to .lohn Mehr and Sons, Chicago, lll., a corporation of Iliinois Fiied Mar. 27, 1961, Ser. No. 98,381 S Claims. (Ci. 26d-3d) This invention relates generally to metallurgical vacuum degassing systems, and particularly to a vacuum tank and condenser system especially adapted for vacuum degassing of relatively small heats of molten metal.

It is now generally recognized that the quality of steel can be greatly improved by removing the included deleterious gases it contains when it leaves the melting furnace. The most deleterious gas is probably hydrogen although it is also desirable to reduce the nitrogen and oxygen content as much as possible. One of the best modes of reducing the included gas content is to subjec the molten metal to a high vacuum. The high vacuum enables the included gases, because of their greater internal gas pressure, to migrate to the surface where they may be drawn off through the vacuum system.

Various systems for vacuum degassing molten metal are known in the art. In order to obtain the high vacuums needed to effectively degas, steam ejector pumps are often used. A steam ejector system requires a cooling medium to condense the motive steam for the steam ejectors and the entrained gases drawn olf from the vacuum tank in order to function in the most etiicient manner and with a minimum consumption of motive steam.

The most commonly employed cooling systems are direct contact systems. Until the development of the present invention these systems utilized either a water column or a pump working on a column of water of a height less than atmospheric pressure. In each system there is generally direct physical contact between the vacuum circuit and the cooling water circuit, and as a result there are disadvantages to both systems. In the rst instance, exceedingly high head room was required.

Since a column of water requires a 34 foot head, a total of anywhere from 4050 feet is required. In the second instance, the head room is reduced but a mechanical pump must be used to keep the head below a level at which cooling water will enter the vacuum system, Should water enter the vacuum system, there is always the result that a very serious explosion can occur. Should the pump ever fail, the results can be disastrous Also, mechanical pumps frequently become a source of air leaks into the vacuum system and this serves to destroy or reduce the effectiveness of the process.

High head room and safety hazards are not the only drawbacks to the present systems. In many instances, vacuum degassing cannot be carried out because the time required to operate the system is so long that the permissible temperature drop of the metal to be degassed is exceeded. In addition, most present vacuum degassing systems are only capable of handling large heats of molten metal, on the order of l tons and above, and consequently they entail a relatively large physical installation, high equipment and installation costs, and are rather complicated to operate.

Accordingly, a primary object of this invention is to provide a vacuum degassing system capable of handling relatively small heats of molten metal on the order of the size found in foundries whereby included deleterious gases such as hydrogen, nitrogen, and oxygen can be removed.

Another object is to provide a vacuum degassing system especially adapted for small heats of molten metal in which the degassing can be carried out within permissible temperature drop limitations.

Q-Sq Patented July 20, i965 ICC Yet another object is to provide a vacuum degassing system for small heats of molten metal in which the cooling water system is physically separated from the vapor system whereby the danger of explosion due to backup of cooling water into the vacuum system is substantially eliminated.

Yet a further object is to provide a vacuum degassing system which is small, requires little head room, is low in equipment and installation costs, and extremely simple to operate.

Another object is to provide a vacuum tank and system for degassing relatively small ladles of molten metal at pressures on the order of about one-half millimeter of mercury.

Another object is to provide a vacuum tank which can be quickly opened and closed to receive and discharge a ladle of molten metal.

Yet another object is to provide a vacuum tank in which a ladle can be placed therein from either above or from the side thus eliminating the time required for ladle placement.

Yet a further object is to provide a vacuum tank in which lift and swing devices are eliminated thus speeding up the process by considerably reducing the equipment handling time.

Other objects and advantages will become apparent from a reading of the following description of the invention.

The invention is illustrated more or less diagrammatically in the accompanying drawings wherein:

FIGURE 1 is a side view of the system showing a ladle positioned within the vacuum tank;

FIGURE 2, which consists iof FIGURES 2a and 2b, is a front view illustrating particularly the steam, water, and vapor circuits; and

FIGURE 3 is a right side view taken substantially along the line 3 3 of FIGURE 2.

Like reference numerals will be used to describe like parts throughout the following description of the drawings.

rl`he vacuum tank and its opening and closing mechanism is illustrated best in FIGURES 1 and 2. The tank, which is indicated generally at 10, consists of a left and right half 1I, I2, which are pivoted about a horizontal pivot I3. The left half 1I is supported by a pair of braces or supports fabricated from plates 14, 15. The braces are welded to foot plates I6, 16 which in turn rests upon a pair of I-beams I7, I8. A framework consisting of longitudinal channels 19, 20 vand cross channels 21, 22 form an exterior framework for structure to be hereinafter described. A trapezoid shaped front plate is indicated at 23.

Left half Il of the tank is formed roughly in the shape of one-half of a clam shell. The circular edge of the tank half terminates in a flange 25 which mates with a corresponding iigure 26 on right half 12. When the halves are together as illustrated in FIGURE 2, a parting line is formed at 27. The abutting faces of flanges 25, 26 are recessed to receive an O-ring seal, or other suitable sealing means (not shown) to provide an air-tight joint when the tank is closed.

A pair of windows or ports 28, 29 open into the stationary tank half so that the condition of the molten metal in the ladle can be checked during the degassing operation.

Right half 12 is substantially complement-ary in general outlines to the left half I1. A pair of vertical brackets Si?, 3?. having collar-s 32, 35 at their lower ends respectively are welded along their upper edges to the exterior of tank half l2. A pair of side or wing brackets 34, 35 are welded along their inner edges to brackets 3i), 31 respectively and along their upper edges to the exterior of the tank to provide additional reinforcement.

is diverted through steam line 8115er the ir'st and second stages of the ejector system. This portion-of the steam passes through a steam-water separator 82 which removes the moisture from the steam. Separator 82 is connected by line 83 to .steam trap 84. Condensate from separator I S2 is collected in steam trap 84 and discharged at intervals opening cylinder. The framework consists essentially of a plurality of side L-'beatmstLV 41, 42 welded together asillustrated in -EIGU-RE 2 and a cross member 43. The Y inner end of` cross member 43 is welded by means of a short Ibrace'44 to the left or outside of support 14.

A hydraulic cylinder for opening and closing the vacuum tank is indicated generally at `41S. The 'cylinder is pivoted at its rear end to an ear 47 welded to the upper angey of the cross ybrace Extensible and retractible piston -rod'48 extends outwardly to a trunnion 49 on right Vacuum tank half 12. The piston rod is pivoted to the trunnion about an -axis 50i In FIGURE 1 the cylinder is shown inits completely open or extended position. The position of fthe cylinder when the tank is closed is indicated by the -line 51.l The parts are so proportioned that when the tank is closed the hydraulic cylinder will be'substantially perl pendicular to the parting line 27 and even during its most extended position the cylinder is still roughly perpendicuany other suitable molten metal container. In this instance a small ladle having a capacity on the order of from l-S tonslis illustrated.y The ladle includes a bale or hanger I 5,8 and a stopper rod rigging assembly 59 which extend considerably abovetletop ofthe closed ladle. When the tank Iis` closed, it will be seen from the dotted line position of right half 12 that there is ampleV clearance for any conventional'ladle .-st'r'ucture. The extrernities of the left half 11 are indicated in dotted lines .in FIGURE 1.

' The vacuum or vapor .system consists essentially of a circuit into which steam from a plurality of jets is injected. Thepath of gas removal from the chamber to atmosphere is substantially asgfollows. Y Stationary half- V11 of the tank is apertured at 6,0 and connected by a pair of short conduits 6,1, 62 to a jet chamber '63. The jet chamber is essentially tubular as'can be best .seen lby looking at the'left halfof FIGURE 1.

Vis the desired amount of superheat.

into condensate line .85. Y

From the separator the steam passes by line 87 to a Ajunction T 88. A portion 0f the Steam is diverted at T 88 through anV electric heater 89 which adds heat to the' steam to compensate for the temperature drop that occurs Abefore the steam enters the ejector. This portionof the steam then passes by line 90 over to the first-jet chamber 60 where it is admitted to the first stage 61 of the ejector system. It will be understood that the particular placement'of the nozzle of the steam jet willvary somewhat with the design of l any particular. plant, but usually the jet nozzle will open immediately upstream from the constriction 64a in thertirst stage.' Electric heater 89 .adds superheat to the steam going jto'the first stage ejector. This is necessary for the satisfactory operation of the ejector. Approximately 20 degrees F.l to 60 degrees F.

The balance of the steam which was not diverted to the first stage at the junction 88 passes upwardly through line 91 Ito the second jet chamber 68. Again, the exact loca.- tion of the steam jetV nozzle in the ejector will depend somewhat on the design of the lparticular plant.

- That portion of the steam which was not diverted to line 81 is diver-ted through line 92 to the third yjet chamber 76. In a three-stage system the third stage will often require a greater quantity of steam than the first and second stages combined, .and accordingly line 92 is larger than line 81. Y v

' Suitable valves for shutting oi any portion or all of the stea-m designed for eachof the three stages are provided. Since their function is well understood, they arev not further described.

The cooling water system is illustrated best in FIG- URES 2 and 3. Water enters the system from a suitable source (not shown) through pipe 95. The water passes to the inlet k96 of condenser 74 after passing through a main shut-oli lValve 97. The internal structureof the Condenser 74 is not material to this invention and accordingly is not further described in detail. Suice Vit to say that the arrangement is such that the cooling water will How counter-current .to the ow of vapor throughout at least condenser.

.The first stage of the vacuum cir-cuit is for-med by agradu- Y ally inwardly and then outwardly tapering pipe 64 which ils 'connected as at 65 to a short straight run 66. 'The Itapering portions of the pipe forma venturi aheadof which lis located a steam jet as will be explained hereafter. The withdrawn vapors then pass downwardly `through a Vshort connector 67. .into a second jet chamber 68. Run 6,6 opens into a dust lseparat-or vor dirt catcher '70 which is 4closed at its lower end by valve 71. In operation h eavy particles will continue Ion past connector 67 and collect in the bottom of separator 70 where they'can be subsequently blown outby manipulation of valve 71.

The second stage 72 of the steam ejector begins at jet chamber'68 and extends forwardlyto a connection 73 Y the third stage 77. The discharge end of third` stage 77,v

whichalso contains a venturi, may be connected by any suitable piping (not shown) to atmosphere at outlet.78.

The steam circuit is illustrated best in FIGURES 2 and 3. Steamv enters the syste-m from a suitable source (not l shown) Vthrough inlet header. 80.KV A portion of the steamy a portion of the path of-travelof the vapor through the Y VThe cooling water leaves the condenser through outlet 98 which may beconnected to any suitable discharge or return line, not shovtuji.

One of the most Yunique features of the invention is the provision for handling condensate from the vapor circuit. The vapor passing through the surface condenser has water vapor entrained in it. This water vapor is condensed in the condenser 74 and flows to discharge pipe 100. Pipe Y100 opens into a condensate tank 101 which injturn is'connected into a discharge line 102 and discharged to atmosphere through valve 104 at the end of cycle, and after atmospheric pressure lhas been restored t0 evacuating system. A valve'104 between clean-out'valve Y103 and valve 71 permits the condensate from the dirt separator 70 to be removed from the system without draining the condensate tank 101 `at the same time. By opening valves 71, 103 and 104 simultaneously,`the dirt from theseparator and condensate from the tankcan be d come in sideways, at least from about the mid-portion of the tank upwardly. This particular feature is of great advantage in installations in which head room is at a premium.

As soon as the ladle is placed on platform SS suitable conventional valve mechanisms associated with hydraulic closing cylinder 45 are actuated to close and seal the clam shell tank. As the right portion i2 of the chamber moves from its disengaged solid line position in FIGURE l to its engaged, dotted line position in FIGURE 1, it passes through its balance position. lt will also be obvious to those skilled in the art that the entire range of movement of right portion 12 is closely adjacent the balance position since the illustrated solid line positions of portions il and 12 are the positions of maximum displacement from one another. As soon as the two flanges 2S, 25 make contact and a seal is formed, the vacuum system is turned on and the interior of the tank evacuated. The atmosphere within the tank and, subsequently, the included gases drawn oli' from the molten metal leave the chamber through the vapor circuit which consists essentially of three stages, de, 72 and 77 of a steam ejector system. Steam for each of the individual stages is supplied through the steam circuit from header 30 to the venturies at the mid-portion of each stage.

The vapors in the vapor circuit, which includes both the gases withdrawn from the tank and the steam, passes into a surface condenser 74 after passing through two stages of the steam ejector. Since condenser 74 is a surface condenser and cooling water is separated from the vapors by suitable piping, there is no physical contact between condenser tubes and the vapors circulating around the outside of the tube. The vapor passes through the third stage 77 of the steam ejector system after leaving the surface condenser /t and is discharged to atmosphere through outlet 78.

The only water in the vacuum or vapor circuit is that which condenses from the steam jets ahead of the condenser. This is so small a quantity that it is feasible to collect it in the drain tank itil under vacuum during the cycle and then dump the condensate at the end of the cycle. The amount of condensate may be relatively small, say on the order of l gallon per minute. This quantity could be pumped out continuously but this would introduce a mechanical arrangement which is subject to failure. Drain tank lill can be made large enough to adequately take care of a number of degassing cycles and is foolproof as far as mechanical leakage is concerned. This particular set up is very practical for a short cycle, such as on the order of 5-15 minutes as would be employed in small ladle degassing.

By contrast, the amount of cooling water needed in this system may be on the order of gallons per minute. This large gallonage of course never comes in contact with the vapor and the vapor circuit. By arranging the condenser and drain tank as shown, the over-all height of the system is kept at a minimum and the condensing portion of the circuits, which in the prior art was the most contributing factor to high head room requirements, is entirely eliminated. In this system, any back-up of cooling water will merely cause a disruption in the cooling water circuit. Since the cooling water circuit is physically separated from the vapor circuit, no explosion can occur.

A typical example of the functioning of this system may be illustrated as follows.

ln actual operation, a ladle containing something over a ton of molten metal has been degassed in a total cycle time of about 5-6 minutes. Allowing approximately one minute of pump down-time leaves a total treatment period of around 3 4 minutes. During the degassing of the ladle above referred to, the absolute pressure in the tank and first stage was approximately 4-6 millimeters of mercury, the vacuum in the second stage was in the neighborhood of 25-35 millimeters of mercury and the discharge pressure in the third stage was 760 millimeters. The temperature of the cooling water in the surface condenser was on the order of about degrees F. The optimum pressures and temperatures of steam will vary from installation to installation. The amount of heat supplied and duration o time in which the heater 89 is turned on will also vary from installation to installation.

The two halves of the clam shell tank are so oriented that the maximum height of the tank is utilized. Thus, the tank is slightly tipped to one side so that the longest dimension of the ladle assembly, in this case the ladle rigging, will lie along a line passing through point A of right half 12 and point B of left half 1l. The distance between A and B is, of course, considerably greater than the barrel diameter of the tank. This feature is of considerable advantage in this type of installation because pump down-time is directly related to the size of the tank. By utilizing the smallest possible tank, it is possible to reduce the pump down-time to an absolute minimum.

It will be understood that the clam shell vacuum tank is utilizable with or without the particular condensing system illustrated. The main purpose of any condensing system is to increase the capacity of the vacuum system. The later ejector stages do require larger quantities of steam. By removing the steam from the earlier stages as condensate there is more capacity left to remove air and other vapors from the vacuum tank. This, however, may increase operating costs due to the cost of cooling water and it may be feasible on some small setups to dispense with the condenser.

When considering the invention as a combination of the vacuum tank with a low head room surface condensing system, it should also be understood that modifications may be made in the condensing system piping. In other words a single stage steam ejector or four or more stages might be utilized, depending upon the desired operating characteristics.

Suitable controls with gauges and other indicating instruments may be collected together at a convenient point such as a control panel indicated at in the right side of FIGURE 2. In view of the fact that the particular controls for the piping system shown are not considered to be essential to an understanding of the invention, they have been omitted for purposes of clarity.

While a preferred embodiment has been illustrated and described and several variations described, it should be understood that the scope of the invention is not to be so limited by the description. Instead it is the intent to limit the invention only by the scope of the following appended claims.

I claim:

l. A vacuum tank for use in degassing molten metal, said tank including a iirst and second tank half, said iirst and second halves forming, by themselves, a vacuum tank of a size suiicient to receive a container of molten metal, said halves being substantially symmetrically shaped and opening along a parting line formed approximately at the major dimension of the tank, at least one of said tank halves being pivotable about a generally horizontal axis into sealing engagement with the other tank half, means supporting the tank with its parting line disposed generally vertically to thereby form an upwardly, outwardly diverging opening for the reception of a container for molten metal when the tank halves are in an open position, a iiuid operated cylinder and piston means, said cylinder and piston means being pivotally connected to a stationary support structure and the movable half of the tank, said cylinder and piston means being so positioned as to lie substantially perpendicular to the parting line throughout the extension and retraction of the cylinder and piston means, a support structure for a container of molten metal within the tank, and a vacuum connection opening into the tank.

2. The vacuum tank of claim 1 further characterized in that the two halves of the vacuum tank are of substantially uniform diameter a substantial distance on "each Y side of the parting line, one of said halves being supported in a stationary Vsupport structure, theparting line of the tank being canted slightly from the vertical so that a container of molten metal, when placed on the support structure within the tank, will lie substantially along the longest dimension of the tank.

3. A vacuum chamber, said chamber including, in combination, Y

two portions, said portions being movableV relative to one another from a closed position in which they are in engagement to an open position in which they are disengaged, and means for supporting one of said portions, means for moving the other of said portions along a path, the ends of which correspond to engaged and disengaged positions of said other portions, all points of said path being at least adjacent the balance position of said other portion, said portions, when opened, forming a generally vertically axised'opening. Y 4. .The vacuum chamber of claim 3l further characterized in that the said other portion movesalong a path of travel which includes its balance position. l Y' 5. The vacuum chamber of c1aim3 further characterized in that the means for relativelymoving the portions from engaged to disengaged positions includes means for applying anV opening and closing force to the other por- Y tion which is substantially perpendicular to the partingV ing force to said other portion includes a fluid kcylinder assembly, Y

one end of said assembly being operatively connected to said other portion of the vacuum chamber,

t said fluidtcylinder assembly being substantially perpendicular to the parting surface of the said other portion throughout the entire path of travel of the said other portionas it moves from an engagedto a disengaged position.l

` 7. A vacuum system for degassing relatively small heats of molten metal, said system including a vapor circuit connected to a vacuum tank, said vapor circuit having at least a pair of steam ejector vacuum stages connectedin series, a surface condenser, the upstream end of the rst stage being constructed and arranged to be connected to Y '8 the. vacuum tank to be evacuated, the downstream end of one of the stages discharging into the surface condenser, said condenser havingV cooling water-,tubes therein so constructed and arranged that the vapor ow through the condenser runs counter to a substantial length of the Water tubes, said water tubes maintaining the vapor system physically separated from the cooling water system, acondensate tank and a connection betweenksaid surface condenser and condensate tank whereby condensate from the condenser may bedrained to the condensate tank, a vapor outlet from the condenser, and at least one additional vacuumv stage connectedrto the condenser outlet, said vacuum tank being composed of two halves which open about a generally vertically axised parting line slightlyv canted from theperpendicular, means supporting one of the tank. halves whereby the other tank half may move'with respect to it, the diameter at the parting line being substantially greater than the diameter perpendicular to saidsparting line whereby said halves, when in an openposition, form an upwardly, outwardly diverging -opening suitable for` reception of a container of molten metal from either l theside or above. .Y f i 8. The vacuum system of claim 7 further characterized in that one of the tank halves is stationary and the other is pivotable about a generally horizontal axis and further including fluid actuatedfmeans constructed and arranged to apply an opening force to the movable tank half yin a direction substantially perpendicular to vthe parting line throughout at least a portion of thefopening m-ovement of said movable tank half.

References` Cited bythe Examiner UNITED STATES PATENTS v 651,000V 6/00 Websterr 183-2.5 1,907,050 5/33 Elliott 1832.5 2,093,666* 9/37 Vogt 266--34 2,734,240 2/56 Southern V 266--34 2,852,246 9/58 flanco 266-34 y OTHER REFERENCES Bussard et al., German printed application, 1,041,216, Y 10/ 58.

MORRIS O. WOLK, Primary Examiner. R. K. WINDHAM, Examiner.

Claims (1)

1. A VACUUM TANK FOR USE IN DEGASSING MOLTEN METAL, SAID TANK INCLUDING A FIRST AND SECOND TANK HALF, SAID FIRST AND SECOND HALVES FORMING, BY THEMSELVES, A VACUUM TANK OF A SIZE SUFFICIENT TO RECEIVE A CONTAINER OF MOLTEN METAL, SAID HALVES BEING SUBSTANTIALLY SYMMETRICALLY SHAPED AND OPENING ALONG A PARTING LINE FORMED APPROXIMATELY AT THE MAJOR DIMENSION OF THE TANK, AT LEAST ONE OF SAID TANK HALVES BEING PIVOTABLE ABOUT A GENERALLY HORIZONTAL AXIS INTO SEALING ENGAGEMENT WITH THE OTHER TANK HALF, MEANS SUPPORTING THE TANK WITH ITS PARTING LINE DISPOSED GENERALLY VERTICALLY TO THEREBY FORM AN UPWARDLY, OUTWARDLY DIVERGING OPENING FOR THE RECEPTION OF A CONTAINER FOR MOLTEN METAL WHEN THE TANK HALVES ARE IN AN OPEN POSITION, A

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