US2261186A - Slug casting machine - Google Patents

Description

Nov. 4, 1941. R. SCHAFFERT 2,261,186

SLUG CASTING MACHINE Filed Aug. '7, 1940 4 Sheets-Sheet l /NVENTOR /w 4 BY l //MAW ma @my 7 ATTORNEY@ Nw. 4, wm. R, SCHAFERT mwa SLUG CASTING MACHINE Filed Aug. 7, 1 .940 4 Sheets-Sheet 2 [NVE R Nov. 4, 1941. R, SCHAFFERT 2,261,186

SLUG CASTING MACHINE Filed Aug. 7, 1940 4 Shets-Sheet 3 p m M j A TTORNE K5 Nov. 4, 1941. R. sHAFFl-:RT

SLUG' CASTING MACHINE Filled Aug. '7. 1940 4 Sheets-Sheet 4 Fig. 9

'NVENTOR ATTORNEYJ Patented Nov. 4, 1941 SLUG CASTING MACHINE Roland Schafert, Jamaica, N. Y., assignor to Mergenthaler Linotype Company, a corporation of New York Application August'l, 1940, YSerial No. 351,693

24 Claims. `(Cl. 199-47) The invention relates to slug casting machines of the character wherein a composed line of matrices is presented to the face of a slotted mold to close the same at the front, and the mold lled with molten metal which is forced, by the action of a pump plunger, from a crucible into the mold through the crucible throat, the outlet end or mouthpiece of which is moved into contact with the rear face of the mold, so as `to form a continuous path for the metal from the crucible to the mold during the slug casting operation.

The conditions which give riseA to the casting of a perfect slug in a line castingV machine are almost impossible of attainment since factors which correct or eliminate certainfmperfections introduce others which are, in many cases, equally as bad. The best that can be done under the circumstances is to seek a compromise which will give, for all practical purposes, a slug as near perfection as possible. With the present improvements, slugs having practically awless printing faces have been made, without however reducing the quality of the slug body beyond a point which would make the same unsuitable for printing. Indeed the slug bodies are good, i. e, their air content is sufficiently low to enable them to stand up under all ordinary conditions of use.

One imperfection frequently encountered in a cast slug is known as cold face, resulting from aslow build-up of pressure on the metal in the mold as distinguished from a cold face resulting from relatively cool metal or a cold crucible'mouthpiece. Where the pressure buildup is slow, the initial stream of metal flows slowly into the mold and up against the matrix line with very little impact, and by contact with the mold may become somewhat cooled before reaching the line of matrices. Under such conditions, the face of the slug has a ragged appearance, often with portions of the characters missing.

Another type of cold face is duev to what may be 'termed pre-cast dribbling, i. e., small amounts of metal dribbling out of the mouthpiece ahead of the main stream of metal. These small drops of metal become partially solidified in the mold and are washed up against Athe matrices as vthe main stream of metal is injected into the mold. These small prematurely solidied portions appear as cold spots here and there in the face of the slug. Pre-cast dribbling may be due to such causes as: -sludgy metal being lodged in the metal pot throat near the mouthpiece andA blown out ahead of the main stream; :55 end of the chamber is closed except fora nor-v the metal level being too high, permitting some metal to come through the mouthpiece during lookup; or a jerky or sticking plunger.

Another type of defect known as swirlsj is recognized by the presence, in the faces of the characters, of small irregular areas surrounded by creases which-give an-uneven appearance. Swirls are caused by the sludge and oxide which float on the surface of the metal in the pot throat. In the vstandard pot or Crucible, this sludge,` which is a mixture of metal and dross, is

forced out ahead of the metal during casting,

and strikes the matrices first. The sludge does not cast as Well as the pure metal, so that wherever it strikes, the quality of the cast is sacriced. Furthermore, since the sludge cast is mentary pump plunger `operating mechanism which operates on the plunger through a toggle,

the arrangement being such that a delayed second pressure impulse is given to the plunger during the casting of the slug so as thereby to improve its density. The special throat structure permits a quick build-up in pressure on the metal, causingit to impinge directly upon-the casting faces of the matrices and thereby eliminating the cold face due to slow pressure buildup. The advantages of Aa quick pressure builduphave been appreciated by those skilled in the art, the result usually being obtained by providing Va quick drop in'the cam from which the pump plunger -spring is controlled. Usually, however, trouble is encountered with a. quick pressure build-up due to the fact that? the air in the Crucible throat and the-mold is trapped by the metal as it rushes into the mold, thus giving a slug body which is structurally weak due to the large percentage of air contained therein.

In the improved arrangement, the Crucible throat, instead of continuing in an even curve directly up to the mold slot as is usually the case, is formed with a reverse bend, proceeding beyond the bend in a direction both upwardly and rearwardly, so as to present a chamber from which there branches a forwardly extending outlet passageway leading to the mouth of the crucible. The outlet passageway, while located above the bend, is va `substantial distancefrom the upper end of the chamber, and-theupper mally open air escape valve. During a casting operation, the metal, due to its velocity as it traverses the bend, passes up into the chamber, thereby expelling the air through the escape valve. When the chamber is filled with metal, the escape valve closes. The closing of the valve instantaneously builds up a substantial pressure in the metal, which thereupon is forced with considerable velocity through the outlet passageway leading to the mold. As a consequence, all of the advantages of a quick build-up pressure are obtained, without the accompanying disadvantages, since the only air trapped in the slug is that which was present in the mold itself and in the outlet passageway between.- the mold and the chamber. This volume of airis relatively small and its effect is minimized by maintaining a relatively high pressure in the metal while the latter cools in the mold. The ability to maintain the high pressure results from the toggle arrangement, which is so designed that, despite the decreasing force exerted by the spring which operates it,V the force exerted on the plunger is nevertheless increased.

The improved throat arrangement also eliminates the formation of swirls since, as the metal is initially forced up into the chamber, the sludge, being at the top, is carried up beyond the outlet passageway leading to the mold, with the result that the metal entering the outlet passageway, and consequently the mold, is pure type metal tapped from the main body below the sludge layer. Pre-cast dribbling is also prevented, since there will be no sludgy metal lodged in the throat to be blown out ahead of the metal stream, nor will the height of the metal in the pot make any difference during lock-up because of the reverse turn in the throat. Actually, with the improved arrangement, the metal normally does stand higher in the pot, so that there is less air to escape than would otherwise be the case.

The air escape valve preferably is adjustable to regulate the flow of escaping air, thus permitting regulation of the pressure build-up. This is desirable depending upon the type of slug being cast. The toggle spring arrangement is also adjustable so that the second or delayed impact may be properly timed.

,Referring to the drawings:

, Fig. 1 is a side elevation, partly in section, of a portion of a slug casting machine equipped with the present improvements, the parts being shown in their normal positions;

Fig. 2 is a similar view of a portion of the machine shown in Fig. 1, the pump plunger being shown at the commencementl of its active stroke;

Fig. 3 is a view similar to Fig. 2, but with the pump plunger shown near the bottom of its active stroke;

r Fig. 4 is a top plan view of the parts shown in Fig. 2;

Fig. 5 is a vertical sectional view taken on a fore-and-aft plane through the Crucible throat, the parts being shown in their normal positions;

Fig. 6 is a sectional view taken on line 6--6 of Fig. 1;

Fig. '7 is a sectional view taken on line 'l-'l of Fig. 5;

Fig. 8 is a vertical sectional view taken on a fore-and-aft plane through the Crucible throat and illustrating the position of the parts just prior to the entry of the metal into the passageway leading to the mold; and

Fig. 9 is a view similar to Fig. 8 after the metal has entered the mold.

The improvements have been illustrated in connection with a standard slug casting machine which includes, in part, a rst elevator A movable from a position wherein it receives a composed line B of matrices and spacebands to a position wherein the line is presented to the face of a, slotted mold C carried by a mold disc Cl which is rotatable to bring the mold into casting position, all as shown in Fig. l and as will be understood in the art. At the rear of the mold disc, there is a metal pot or Crucible D containing molten metal and which may be of standard construction except as hereinafter described. The ,Crucible D is supported in a housing D1 equipped Yat the front with a pair of legs D2 pivotally mounted at their lower ends on a transverse shaft (not shown) but which permits the crucible housing D1, and consequently the Crucible itself, to be rocked forwardly at the proper stage of the machine cycle to effect a lock-up between the mold and the composed line, on the one hand, and between the mold and the mouth of the Crucible, on the other hand.

The pressure for the lock-up is obtained from the main cam shaft M of the machine through the medium of an edge cam M1 mounted thereon and which rotates once during each machine cycle. The cam Ml engages a cam follower D3 journalled in a short rearwardly extending portion of a substantially vertical lever D4, somewhat above the center thereof. The lever D4, at its upper end, is pivotally connected to a lug D5 projecting from the rear face of the housing D1 and, at its lower end, is linked to another lug D6, projecting from the lower face of the housing D1 at the rear thereof, the latter connection being through the medium of a rod Drl passing through the lever and pivotally connected to` said lug. Normally, the relative locations of the crucible housing D1 and the lever D4 are maintained by a spring DB, reacting between the lever and a collar Dg with which the link D7 is provided, the proper compression in the spring being maintained by a pair of lock nuts D13 threaded on the end of the link and bearing against the rear face of the lever.

In the normal position of the parts, the metal pot stands with its mouthpiece spaced from the mold, but at the proper stage of the machine cycle, a high portion of the cam Ml engages the follower D3, thereby tilting the metal pot forward and through the spring D8 exerting the necessary pressure for the lock-up.

After the lock-up has been effected, the molten metal is forced into the mold by the action of a plunger E arranged for vertical reciprocation in a cylindrical chamber D1D formed in the crucible D and which communicates with the Crucible mouthpiece by way of a tapered passageway D11. When the plunger is in its topmost or normal position, metal enters the cylindrical chamber D1o through an aperture D12, but during the casting of the slug, the plunger E is Caused to move downwardly, thereby closing the aperture D12 and displacing the trapped metal upwardly through the throat and into the mold.

Ar vertical rod E1, connected at its lower end to the plunger E, extends upwardly through an opening formed in the cover plate of the housing D1, above which it is pivoted at the front end of a horizontal arm E2 forming part of a bellcrank lever arranged for rocking movement about a pivot rod E3 journalled in spaced vertical portions of a cantilever bracket F xed on the machine frame (Fig. 4). The bell-crank lever is movement, on an extension of the pivot rod E3. A

long powerful spring G, anchored at its lower end in the base of the machine, pulls down on the arm E6, at the front end of which the spring is connected, and through its engagement with the underlying arm E7, urges the cam follower E into engagement with the periphery of the cam M2, Which consequently controls the action of Ythe pump plunger E.

The cam M2 is concentric for the major portion of its circumference. However, at that phase in the machine cycle when the casting operation takes place, a depression M3 in the periphery of the cam permits the bell-crank which operates the plunger E to turn under the action of the spring G, in a direction to force the plunger downwardly (Fig. 2). The down--l ward movement of the plunger, of course, displaces metal which passes through the passageway D11 and thence into the mold to cast the slug. Y

The pump plunger mechanism thus far described is substantially the same as that used in the commercial machines. It presents several disadvantages, however, which arenot conducive to the formation of good slugs. For instance, when the spring G is allowed tov act, .it causes a quick descent of the plunger, thereby building up pressure in the trapped metal, which pressure reaches a maximum shortly after the plunger is arrested by the reaction of the metal as the mold becomes lled. The maximum pressure exertedk is usually substantially higher than what it would be were the spring reacting-merely between its bottom anchorage and the arm yE8 in a position of restas determined by the plunger in its lowermost position. In other words, the maximum pressure exerted on the metal results from impact due to the kinetic energy given up by the contracting spring, the moving parts of thepump plunger mechanism, and the molten metal which is in motion in the well and throat. After the maximum pressure has been reached, it falls off rapidly, fluctuating for a time below and above the pressure exerted by the spring when the same is in equilibrium with the plunger at the bottom of its stroke. In other words, if the pressure curve is plotted, over the period starting with the descent of the plunger until the spring reaches equilibrium at the bottom of the plunger stroke, it will be found that the curve has a damped oscillatory shape about the equlibrium pressure as an axis. The conditions are such that after the rst high impact pressure is reached, the pressure fallsv off rapidly, reaching momentarily a the subsequent application of the higher equilib` rum pressure.

' The conditions just described aresubstantially eliminated, according :to the present improve.` ments, by applying al secondV OrLdeIayed impact pressure tothe metal at or about the time the,-

reaction Vto the `rst impact pressure becomes eiective, i. e.,during ythe periodthe pressureA lordinarily would iirst'drop' below the equilibrium pressure. This second .delayed impact prevents the pressure from fallingbelow that which .will produce an excellent slug body.l Furthermore, the large pressure fluctuations are damped out more rapidly and the final equilibrium pressure is higher. The latter condition is augmented by the use of a mechanism capable ofexerting an increasing ,pressure as the plunger descends,v rather than a decreasing pressure, asA is the case with the ordinary spring arrangement. This in``v creasing pressure as the plunger descends is par; ticularly advantageous when casting large slugs' because of the greater distance the plunger descends in such cases., y

The supplemental Amechanism justl alluded to includes a toggle device (Fig. 1) having two links H and H1 hinged rtogether as at H2.` The upper link H is fulcrumedyat its center on a fixed pivot pin H 3 and when it is turnedin a counter-A clockwise directionV (looking at the parts` 'from the left) the toggle links are straightened out, the lower link H1 pushing down Wi-th substantial force on the bell-crank lever arm E2 which, as will be recalled, isconnected to the rod E1 of the plungerg(Fi g. 3). The connection betweenv the arm H1 andthe lever arm E2 is designed to absorb shock and determine the period of delay between the operation of the two plunger actuating devices. VIt includes a rod H4' forming part of the link H1 and extending-slidably through'a block H5 connected by means of a pivot pin H6 to the arm E2 (seeFig. 6). K A compressionspring H7 encircles the rod H4 and reacts between,v the block H5 and a shoulderpresented bythe link member H1, the normal length of the link H1 between thel pivots H2 and H6 being determined by a nut H8 threaded on the end of the rod H4 and banking against the block H5. However, when the toggle is straightened out to provide the delayed supplementary pressurel impact to the metal in the pot, the spring H7 will compress and absorb the shock occasioned thereby, the rod H1 merely sliding relatively to the block H5 (Fig.

3). The period of delay is determined by thel distance between the block H5 and the nut H8 and can be varied byadjusting the position of the nut H3;

The force for straightening out thetoggle member and for applying pressure therethrough is derived from a tension spring H9 anchored at the rear of the machine and connected at its front end to one arm of a shallow inverted U-shape'dy nected to the link Hat the .end thereof opposite v its pivotal connection with the link H1.

When the parts are in their normal position as shown in Fig. l, the link H is slightly 0E dead center Vin a clockwise or reverse direction as regards the pull of the spring H9, i. e., there is no tendency for the spring to rotate vthe link to straighten out they toggle. However, when the plunger descends under the inuence of the main spring G, the link H is rotated in a counterclockwise'direction and, lafter it moves through the dead center position, the spring H2 becomes active to continue straightening out the toggle. While the force exerted by the spring H2 decreases as litcontracts, the nature of the toggle construction is such that Ythe resultant force exerted on the plunger increases as the latter descends.

In order to prevent collapsing of the parts under the pull of the spring H9, a safetybanking screw H11 is provided, threaded through the U-shapecl member H1u and engaging the upper edge of the link H rearwardly of its central pivot point H3.

The improved type of crucible thoat structure by which a quick pressure build-up is obtained is shown in Fig. 5. Here, it will be observed, the tapered passageway D11, instead of leading directly up to the mouthpiece as usual, makes a reverse turn, as at J, terminating above the turn in a chamber J1 closed at the top by a plate J2. Centrally of the closing plate, is an air escape valve J3 consisting of a body portion J1 threaded into the chamber and which is formed at the bottom to retain a ball valve J 5. Just above the ball, the body portion is cut away to present two opposed apertures J6 through which air may escape from the chamber J1 out through a passageway J '1 communicating with the atmosphere via an aperture JB.

Now when the pump plunger E is depressed, metal is forced up through the tapered passageway D11, around the turn J and up into the chamber J1, the metal pushing the air before it and out through the apertures J1i to the atmosphere. When all the air has escaped, or in other words, when the chamber J1 is filled with metal, the ball valve J is forced upwardly into engagement with a valve seat Jg located above the air outlet apertures Js (Fig. 8). The closing of the ball valve prevents the escape of metal and, simultaneously with said closing, the pressure in the metal is instantaneously built up to a substantial degree.

The quick pressure build-up forces the metal out through a passageway J connecting the chamber J1, just above the bend J, with the mouthpiece of the crucible, and thence into the mold (Fig. 9). Because of the quick pressure build-up, the metal enters the mold with considerable velocity, with the result that it impinges directly upon the casting faces of the matrices, thereby eliminating the cold face due to the metal flowing slowly into the mold. The principle upon which the quick pressure build-up is obtained is somewhat on the order of a hydraulic ram. Itis quicker and more effective than that produced with a quick drop plunger action, and eliminates the pounding and strain on the crucible accompanying the quick drop.

It will also be apparent from Fig. `9 that the metal entering the mold is free from sludge since the latter is carried up into the chamber J1 past the passageway J10 which communicates with the mold. In other words, the metal forming the cast slug is tapped at a point beneath the level of the sludge, consequently eliminating the formation of swirls which occur when the sludge is allowed to enter the mold. At this point it might be stated that the initial velocity of the metal as it traverses the bend J is sufficient to force it up into the chamber J1. That is, the chamber is filled before the metal flows out of the passageway J10. The conditions ordinarily giving rise t0 pre-cast dribbling are also absent when the improved crucible throat structure is used.

Provision is also made for regulating the pressure build-up to suit the type of slug being cast. For this purpose, the valve body J1 is threaded at the'top to receive a cap J11 provided with an aperture J12 and which can be turned from a position wherein the air passageway J7 is com- 75 pletely open to a position wherein it is completely closed.

0f course, the quicker the air is allowed to escape, the quicker the pressure build-up will be. However, where the slug faces aer not diilicult to cast, advantage can be taken of the greater slug solidity obtainable with a slower pressure buildup.

In the accompanying drawings, the invention has been shown merely in preferred form and by way of example, but obviously many variations and modications may be made therein which will still be comprised within its spirit. It is to be understood, therefore, that the invention is not limited to any specific form or embodiment, except insofar as such limitations are specified in the appended claims.

Having thus described my invention, what I claim is:

1. In or for a slug casting machine, a pot crucible from which molten metal is pumped into a mold to form a slug and which has a throat terminating in an air chamber into which the metal passes prior to its entry into the mold, an air outlet for the chamber, and a passageway, through which the metal passes to the mold, connecting the mouth of the crucible with the chamber at a point below the air outlet thereof.

2. In or for a slug casting machine, a pot crucible from which molten metal is pumped into a mold to form a slug and which has a throat terminating in an air chamber into which the metal passes prior to its entry into the mold, said chamber being of a size to accommodate at least the layer of sludge floating on the surface of the metal in the throat, and a passageway, through which the metal passes to the mold, connecting the mouth of the crucible with the chamber at a point below the sludge layer.

3, In or for a slug casting machine, a pot crucible from which molten metal is pumped into a mold to form a slug and which has a throat terminating in an air chamber into which the metal passes prior to its entry into the mold, a passageway connecting the mouth of the crucible with the chamber, and an air relief valve for said chamber, said valve being automatically closable after the escape of air from the chamber.

4. In or for a slug casting machine, a pot crucible from which molten metal is pumped into a mold to form a slug and which has a throat terminating in an air chamber into which the metal passes prior to its entry into the mold, a passageway connecting the chamber with the mouth of the crucible, and an air relief valve adapted to be closed by the metal as it rises in the chamber, the closing of the valve acting to build up pressure in the metal to force the same through the passageway and into the mold.

5. In or for a slug casting machine, a pot crucible from which molten metal is pumped into a mold to form a slug and which has a throat terminating in an air chamber, an air relief valve for the chamber closable automatically by the rise of the metal in the chamber, and a passageway connecting the mouth of the crucible with the chamber at a point below the air outlet, the closing of said valve acting to build up pressure in the chamber to force the metal through the passageway and into the mold.

6. In or for a slug casting machine, a pot crucible from which molten metal is pumped into a mold to form a slug and which has a throat terminating in an air chamber. said chamberrbeingof a size 'to accommodate at least the-'layer ofy sludgefloating on the surface of the metal'in the throat, an air relief vvalve in the chamber closableV automatically by the rise of metal in the chamber, and a passageway connectingthemouth of the Crucible with the chamberY at a point below the sludge layer, the closing of'said Valve acting to build up pressure in the chamber to force sludge-free vmetal through the passageway andinto the mold.

' 7.' In or for a slug casting machine, a pot crucible from which molten metal is pumped intola mold'to form a slug *and which has a throat with a bend communicating with an air chamber located thereabove, and a passageway connecting the mouth of the crucible with the throat at a point between the chamber and the bend. v

I8. In or for a slug casting machine, a pot crucible from which molten metal is" pumped into a mold to form a slug and which hasl a throat with a reverse bend communicating with anl air -chamber extending upwardly and rearwardly from said bend, and a passageway connecting the mouth of the crucible with the throat at a point between the bend and the chamber.

.9. In. orfior,` a slug casting machine, a pot crucible from which 'molten metal 'is pumped into a mold to vform a slug Band which has a throat.`terminating in an air chamber into which the metal pass-es priorl to its entryv into the mold, a passageway 'connecting the mouth of the crucible with the chamber, an air relief valve for said chamber closable automatically after the escape of air from the chamber and .acting upon closing to build up pressure to force the metal through the passageway andinto the mold, and adjustable means for'regulating the escape of air through lsaid Valve.

10. In or for a slug casting machine, a pot crucible from which molten metal is pumped into a mold to form a slug and which has a throat formed with an upward bend terminating in an air chamber above the bend, a passageway connecting the mouth of the Crucible with the throat at a point between the chamber and the bend, and an adjustable air relief valve for said chamber.

11. In or for a slug casting machine, the combination of a pot crucible from which molten metal is pumped into a mold to form a cast slug, a plunger by which the pumping action is effected, and a plurality of devices each applying independently a pressure exerting force to the plunger as the slug is being cast.

l2. In or for a slug casting machine, the combination of a pot crucible from which molten metal is pumped into a mold to form a cast slug, a plunger by which the pumping action` is effected, and a plurality of devices each applying independently a pressure exerting force to the plunger as the slug is being castsaid forces acting at diferent times.

13. In or for a slug casting machine, the combination of a pot crucible from which molten metal is pumped into a mold to form a cast slug, a plunger by which the pumping action is effected, and a plurality of devices each applying independently a pressure exerting force to the plunger as the slug is being cast, said forces 4being timed so that one is applied substantially at the time the reaction of the metal to the other force becomes eiective.

14. In or for a slug casting machine, the

'theplungen anda device for applying a second pressure exerting-torce rto` the plunger to supplement theforce applied thereto by the spring, saidl device actingv subsequently to and independently vof'thesprin'g. f

16. Inor fora slug casting machine, the combination of a pct crucible from whi-ch molten metal is pumpedto form a c ast slug, a plunger by which the pumping action lis effected, a spring for `applying* apressure exerting force lto the plungerg a-device yfor applying a second 'pressure exerting Vforce to the plunger to supplement the forceiapplie'd thereto Vby the spring, and-means for delaying the action of-said device for a predetermined period vafter the commencement of the `plunger stroke'.v l l 17; In or for a slug'casting machine, the combination of apot crucible'from which molten metal is pumped to form a Cast slug, a plunger by which the pumping action is eiected, a spring for'applying a pressure exerting force to the plunger, a `device -for 4applying a second pressure exerting force'tothe plunger to supplement the force' applied thereto by the spring, means for delaying the action of said device for a predetermined period after the commencement of the plungerstroke, and adjustable means forvaryingV said period as desired; f Y

18. In or for a slug Casting machine, the combination of a pot crucible from which molten metal is pumped to form a cast slug, a plunger by Which the pumping action is effected, a spring for applying a pressure exerting force to the plunger, and means includingl a toggle device for applying a second pressure exerting force to the plunger to supplement the force applied thereto by the spring.

19. In or for a slug casting machine, the combination of a pot crucible from which molten metal is pumped to form a cast slug, a plunger by which the pumping action is effected, a spring for applying a pressure exerting force to the plunger, and means including a toggle device connected between the plunger and a xed part of the machine for applying a second pressure exerting force to the plunger to )supplement the force applied thereto ,by the spring, the toggle connections being such that the force exerted by said means increases in magnitude during the active plunger stroke.

20. In or for a slug casting machine, the combination of a pot Crucible from which molten metal is pumped to form a Cast slug, a plunger by which the pumping action is eiected, a spring for applying a pressure` exerting force to the plunger, and means including a toggle device connected between the plunger and a fixed part of the machine for applying a second pressure exerting force to the plunger to supplement the force applied thereto by the spring, the toggle connections being such that no force is exerted by said means during the initial portion of the plunger stroke, Whereas a force increasing in magnitude is exerted thereby during a subsequent portion of the plunger stroke.

2l. In or for a slug casting machine, the combination of a pot crucible from which molten metal is pumped to form a cast slug, a plunger by which the pumping action is effected, a spring for applying a pressure exerting force to the plunger, means including a toggle device connected between the plunger and a xed part of the machine for applying a second pressure exerting force to the plunger to supplement the force applied thereto by the spring, the toggle connections being such that no force is exerted by said means during the initial portion of the plunger stroke, whereas a force increasing in magnitude is exerted thereby during a subsequent portion of the plunger stroke, and adjustable means for varying the extent of that portion of the plunger stroke during which no force is exerted.

22. A slug casting mechanism including, in combination, a pot crucible from which molten metal is pumped into a mold to form a slug and which is provided with a throat terminating in an air chamber, an air outlet for the chamber, a passageway through which metal passes to the mold connecting the mouthpiece of the crucible with the chamber at a point below the air outlet, means acting automatically to close the air outlet when metal pumped from the crucible fills the air chamber and thereby build up pressure to force the metal through the passageway and into the mold, a plunger for effecting the pumping action, and a plurality of devices each applying independently a pressure exerting force to the plunger, the action of one of said devices being delayed until after the mold has been filled with molten metal.

23. A slug casting mechanism including, in combination, a pot crucible from which molten metal is pumped into a mold to form a slug and which is provided with a throat terminating in an air chamber, an air outlet for the chamber, a passageway through which metal passes to the mold connecting the mouthpiece of the crucible with the chamber at a point below the air outlet, means acting automatically to close the air outlet when metal pumped from the crucible fills the air chamber and thereby build up pressure to force the metal through the passageway and into the mold, a plunger for effecting the pumping action, a plurality of devices each applying independently a pressure exerting force to the plunger, the force exerted by one of said devices increasing in magnitude over the active plunger stroke, and means for delaying' the action of said device until after the mold has been lled with metal.

24. A slug casting mechanism including, in combination, a pot crucible from which molten metal is pumped into a mold to form a slug and which is provided with a throat terminating in an air chamber, an air outlet for the chamber, a passageway through which metal passes to the mold connecting the mouthpiece of the crucible with the chamber at a point below the air outlet, means acting automatically to close the air outlet when metal pumped from the Crucible lls the air chamber and thereby build up pressure to force the metal through the passageway and into the mold, a plunger Y for effecting the pumping action, a spring device for applying a pressure exerting force to the plunger, means including a toggle mechanism for independently applying a pressure exerting force to the plunger increasing in magnitude over the active plunger stroke, and means for delaying the action of the toggle mechanism until after the mold has been filled With metal.

ROLAND SCHAFFERT.

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