US2297973A - Centrifugal casting machine - Google Patents

Description

0a. 6, m2. E: O RE' 2,297,973

CENTRIFUGAL CASTING MACHINE .Filed Aug. 11, 1941 2 Sheets-Sheet 2 INVTOR.

Patented Oct. 6, 1942 iJNiTED STATES i t i'ihfi'i QFFICE CENTRIFUGAL CASTING MACHINE Emmett B. Moore, Evanston, Ill.

7 Application August 11, 1941, Serial No. 406,252

10 Claims.

This invention relates to casting machines of the centrifugal type employed in the casting of small articles of gold or other similar metals, as for example in making inlays or large fillings for dental work, or articles of jewelry.

One object of the invention is to provide a smoothly running mechanism with an articulated connection between the crucible and mold carrying parts and a rotatable driving member, together with means to control said crucible and mold in their response to centrifugal and inertia forces and to cause these parts to assume positions such as to avoid splashing or spilling of the molten metal during the initial portion of the rotary movement.

Another object is to provide means for holding the articulated parts against pivotal movement during preparation of the crucible and mold and mounting of these latter in the machine.

It is also an object of the invention to provide a plurality of control means to govern the initial movement of the articulated connection, such means to be employed selectively in accordance with the weight and other characteristics of the particular mold to be 'used in the machine.

Other objects and advantages will appear as the description proceeds. The invention consists in certain features and elements of construction in combination, as herein shown and-described and as indicated by the claims.

In the drawings:

Figure 1 is a side elevation of a centrifugal casting machine embodying this invention show- .ing the articulated connection at fully extended position.

Figure 2 is a topplan view of themachine with the parts in the same position as in Figure -1.

Figure 3 is a detail section taken substantially -as indicated at line 3-3 on Figure 1.

the action of centrifugal force.

Figure 7 is'a partial side elevation of the machine showing it fitted with amold ring of different size from that'shown'in Figure 1.

In the casting of gold or like metals in producing relatively small articles, such as dental fillings and inlays and small pieces of jewelry, the molten metalin the crucible-must beztransferred to the mold quickly and under some pressure to ensure accurately filling the mold and especially its narrower passages and more delicate features, and to ensure that no air shall be pocketed therein. In a centrifugal machine of this type .the crucible containing the molten metal and the mold to which it is to .be transferred are mounted in communicating relation and for rotation about an axis so positioned that the centrifugal force generated by the rotation shall act to transfer the metal from the crucible into the mold. The machine herein illustrated is in general similar to that shown .and described in my co-pending application .Serial No. 327,160 filed April 1, 1940, which includes a motor spring .to be wound up to the desired tension and then released suddenly for starting the rotation of the parts ,by which the mold and crucible are carried. A one-way clutch permits the parts to continue rotating after the spring has expended its force so that the centrifugal force may continue to act while the metal is cooling and hardening in the mold.

But in machines of this type it has been a difiicult problem to initiate the rotation of the gold suddenly and forcibly without causing the metal to splash or spill from the crucible before it has time to flow into the mold. The sudden application of :the force of the spring in starting the crucible from rest tends to accelerate the crucible at a rapid rate while the inertia of the molden gold causes the gold itself to lag,

so that the crucible is actually moved out from .under-thegold to someextent. This would cause a portion .of the fluid metal to spill over the ,edgesof .the crucible unless the latter were positioned in exactly correct relation to the forces acting on the gold. In order to take advantage of this inertia of the molten metal instead of allowing it thus to cause lossand possibledamage the present machine is designed to automatically change the position of the mold and .crucible with reference to their path of rotation during the initial portion of this move- ;ment in such a way as to .keep them adjusted .in substantial alignment with the resultant of inertia and centrifugal forces, so that the inertia tends to shift the gold toward and into the mold rather than over the sides of the crucible and is then supplemented by the centrifugal force as soon as sufficient speed is acquired in the movement.

As shown in the drawings, the machine in- :cludes a hollow base I which maybe understood as enclosing a motor springarranged to rotate a vertical shaft 2 journaled within the base and having a head 3 at its upper end in which there is secured a horizontally extending arm or crossbar 4. The longer end of the cross-bar 4 carries an adjustable weight 5 which may be shifted to approximately balance the rotatable elements of the machine, and the shorter end of the bar is provided with a projecting flat lug or plate 6 serving as one element of a. hinge to support a swinging or "floating arm I which carries the crucible and mold. A bolt 8 acting as the hinge pivot extends through the lug 6 and through cylindrical portions 9, 9 of a bifurcated bracket arm ID to which the arm I is attached. The arm I carries at its outer end a rigidly attached upstanding plate II which supports a holder I2 for the mold ring shown at I3, and the crucible I 4-is carried by a bracket I5 which includes a sleeve I5 adjustable along the arm I. A clutch or gripping device of any suitable construction such as that described in my co-pending application No. 327,160 may be enclosed within the arm I and sleeve I6 and provided with an operating member in the form of a knurled ring I! threaded on to the end of the sleeve I6 for clamping the sleeve and the bracket I5 at any desired position of adjustment along the arm I.

Just below the plane of rotation of the crossbar 4 the base I carries a cam plate which, as shown in the drawings, includes two spiral cams 2I and 22 respectively. The initial and terminal radii of the two cams are substantially the same but the cam 2I extends through a considerably greater angle than the cam 22. The terminal portion of each cam surface is spaced radially from the initial portion of the other cam surface so as to form notches or recesses 2Ia and 22a which are dimensioned to receive a cylindrical lug or follower 23 rigidly attached to thebracket I0 and depending therefrom as seen in Figure 1. When the spring within the base I has been tensioned by reverse rotation of the cross-bar 4 to the desired extent the floating arm I is swung about the pivot 8 to the position shown in Figure 3 so that the lug 23 can enter the notch 2 Ia (or 22a).

At this position one of the notches 24 in a locking disc 25 which is fixed to the shaft or spindle 2, as seen in Figure 3, is engaged with a locking dog 26 extending inside the upper portion of the base I so as to prevent rotation of the parts while the gold is being placed in the crucible I4 and melted therein and while the mold ring, which is heated in an electric furnace just prior to the casting operation, is being transferred to the casting machine and secured in its holder I2. The tension of the spring maintains engagement between the edge of the notch 24 and the locking dog 26 but the length of the notch 2Ia (or 22a) is enough to allow the crossbar 4 to be swung slightly against the tension of the spring so as to relieve this pressure, whereupon, the locking dog 26, being carried in a vertical slot 21 in the base housing, will drop by gravity out of engagement with the notched disc 25 so that upon manual release of the bar 4 the spring will start rotating the shaft 2 with the cross-bar and its hinged floating arm I. A button 28 is attached to the'locking dog 26 and is exposed outside the base housing I, for again lifting the locking dog 26 into active'position when required.

The gold is usually melted in the crucible I4 by means of a small blow torch and in order to determine when it is in proper molten condition for casting, it is desirable to jiggle or vibrate the crucible slightly in a horizontal plane. As indicated in Figure 3, the length of the notch 2Ia (or 2211) is suflicient to allow this to be done without releasing the follower 23, and the notch 24 is considerably wider than the dog 26, so that said dog 26 may be held up in its locking position without interfering with this shaking or jiggling procedure.

As shown in Figure 4 the hinged floating arm I at starting position extends at slightly less than degrees to the direction of the cross-bar 4. The crucible and the mold are in substantial alignment along the arm 'I with the crucible standing ahead of the mold with reference to the direction in which the parts are to rotate as indicated by the arrow R. Thus when the rotation starts the crucible and mold will trail from their pivotal connection with the cross bar at 8, and upon the sudden application of the force of the spring to initiate the rotation, the crucible and mold will move forward (in the direction of the arrow B) more quickly than the molten gold in the crucible, the inertia of the gold itself tending to hold it fixed in its original position in space. The quick forward motion of the crucible will thus act to slip it from under the gold forcing the gold or a portion of it to pass through the connecting passageway into the mold in the ring I3.

Meanwhile the rapid acceleration of the rotary movement of the cross-bar 4 generates centrifugal force tending to swing the floating arm 1 about the pivot 8 and carry the mold and crucible outwardly, that is, to positions farther from the axis of rotation. But experience has proven that the inertia of these parts delays their prompt response to the centrifugal force, whereas the molten gold in the crucible I4 will be affected by the centrifugal force more promptly than the connected group of parts carried by the floating arm I. As a result, if the arm 'I were merely allowed to adjust itself in response to centrifugal and inertia forces it would not move quickly enough to prevent some of the molten gold from spilling over the side of the crucible in the initial portion of the rotation--say, within the first twenty or thirty degrees thereof. Therefore I have provided the cam plate 20 with its spiral contour 2I extending from the notch 2Ia and its spiral contour 22 extending from the notch 22a so that as the follower lug 23 leaves one or the other of these notches at the commencement of rotation, the corresponding spiral edge of the cam plate will engage the lug 23 and force the arm 'I to swing outwardly at a rate controlled by the shape of the spiral. This rate is such as to maintain the crucible andmold in substantial alignment with the changing direction of combined inertia and centrifugal forces as the rotating parts pick up speed. In other words, the mold in the ring I3 is kept in line with the natural path which the gold tends to follow and is thus in position to receive the gold in the initial portion of the rotation of the device. Figure 5 indicates the change in angular relation between floating arm I and the cross-bar 4 which is effected by the travel of the follower 23 along the cam 2| in approximately of a revolution. As the follower 23 passes the end of the cam surface the centrifugal force will have become sufficient to swing the arm I farther outward into alignment with the cross-bar 4 as shown in Figure 6, and in this position it will continue to rotate under the momentum acquired from the force'of the spring, l.thus allowing time for the casting-to harden in the mold. A friction brake button at 29 may be employed if it-is desired to :check the rotation before the momentum-isexwork the ring l3 will accommodate most bridges and special dentures While a smaller ring i aas shown in Figure 7 will take care of the smaller castings such as inlays. While the holder or cradle l2 for the ring l3 is-securedclosely against the plate H at the end of the arm I, I ,prefer to provide the cradle 32 for the'ring 33 with a stem '31 by which it is spaced away from'the plate-ll by a distance equal to'the diiferencebetween the lengthof ring [3 and the length of ring-'33. Then with either ring in place, the crucible M will stand at the same position on the arm 'l and the samecam 2! will provide the correct control of the floating arm 1 to insure delivery'of all the gold to the mold without splashing or spilling over the side of the crucible.

When the machine is used in the manufacture or repair of jewelry a still longer ringmay be required as indicated in dotted outline atdt in Figure '7, in which case the crucible M inust be moved back to a position nearer the center-of rotation. At this shorter radius the centrifugal force Will be less effective on the molten gold-in the crucible at the beginning of rotative movement; but, on the other hand thegreater weight of the large mold and its ring 53 gives them more inertia and renders the floating assembly more sluggish in responding to centrifugal force as the device gains speed. Hence, to insure a sufficiently prompt outward swing of the arm 'i about its hinge pivot 8, when carrying this larger mold ring 43, the follower lug 23 is backed into the notch 22a, and the steeper cam 22 operates to control the movement for preventing splashing or spilling of the gold.

The extent to which the spring motor is ten sioned for any particular casting is within control of the operator, but in general, for castings, such as inlays, made in the small ring 33, the arm 4 will be turned backward to wind up the spring to the extent of two full turns; with the larger ring l3, it will begiven four turns; and for the largest ring 43, the spring will be wound up to six turns. Intermediate tensions may be chosen, if desired, since the looking disc 25 has four notches and the arm 4 can thus be locked at each quarter turn. The adjustment of initial tension is intended to compensate for the differences in weight of the different molds and the gold employed with them and to get the machine under way at about the same speed in each case.

While there is shown and described herein certain specific structure, it will be manifest that various changes and re-arrangements may be made without departing from the spirit and scope of the invention, and that it is not limited to the form herein disclosed, except in so far as indicated by the appended claims.

I claim as my invention:

1. In a centrifugal casting machine, a base, a cross-bar mounted for rotation thereon, a mold and crucible support with pivotal means connecting said support to the bar at a distance from the axis of rotation, the support being free to be swung inwardly about said pivotal connection before the rotation of the bar begins and to be swung outward by the centrifugal force generated by-the rotation, 'a substantially spiral cam onthe base anda fellower on the support positio'nedto engage the cam in the initial portion of said rotation, said cam acting to overcome the' in'ertia of the mold support and to positively swing the support outwardas the bar beginstotur'n.

2. In a centrifugal casting machine, a base a cross-bar'mounted for rotation thereon, a mold and crucible support with pivotal means connecting said support to the bar at a distance from the axis of rotation, the support being free 'to-be swung inwardly abcut said pivotal connection before'the rotation of the bar begins and tobe swung outward by the centrifugalforce generated by the rotation, and mechanical means acting positively to swing the-support outwardly-in the initial portion of the rotation of the bar.

3. In a centrifugal casting machine, a base, a cross-bar mounted for rotation thereon, a mold and crucible support with pivotal --means-conmeeting said support to the bar at a distance'from the axis of rotation, the support being freeto be swung inwardly about said pivotal connection'before the rotation of the bar begins and to be swung outward by the centrifugal force generated by the rotation, the inertia of the pivoted parts tending to'cause a lag in their response to centrifugal force as compared with the response of molten metal in the crucible, and means operative to forcibly overcome such lag and positively maintain the crucible and. mold in substantial alignment with the resultant of inertia and centrifugal forces acting on said metal in the crucible during the-initial portion of the rotation,

to insure delivery of the metal from the crucible to the mold.

4. In a centrifugal casting machine, a base, a cross-bar mounted for rotation thereon, a mold and crucible support with pivotal means connecting said support to the bar at a distance from the axis of rotation, the support being free to be swung inwardly about said pivotal connection before the rotation of the bar begins and to be swung outward by the centrifugal force generated by the rotation, and control means comprising a cam and a follower, one fixed on said base and the other carried by said support, positioned for mutual engagement during the initial portion of the rotation and formed to positively swing the support outward as the bar begins to turn.

5. In a centrifugal casting machine, a base, a cross-bar mounted for rotation thereon, a mold and crucible support with pivotal means connecting said support to the bar at a distance from the axis of rotation, the support being free to be swung inwardly about said pivotal connection before the rotation of the bar begins and to be swung outward by the centrifugal force generated by the rotation, said mold and crucible support including a carrier for the crucible adjustable along the support to accommodate molds of different sizes, such adjustment altering the initial distance of the crucible from the axis of rotation, and a plurality of substantially spiral cams on the base selectively engagea'ble with a follower on the support in the initial portion of the rotation, each cam being formed to positively swing the support outward as the bar begins to turn, said cams differing in pitch to adapt them for use with the crucible at its respectively different positions of adjustment accommodating the different sizes of molds.

6. In a centrifugal casting machine as defined in claim 1, said cam having a retaining notch at its inner end formed to receive the follower and hold the support against pivotal movement until said follower leaves the notch in the initial portion of its rotation.

'7. In a centrifugal casting machine as defined in claim 1, said cam having a retaining notch at its inner end formed to receive the follower and hold the support against pivotal movement until said follower leaves the notch in the initial portion of its rotation, together with detent means acting to hold the cross-bar against rotation under tension of a spring motor connected for rotating it, said detent means 'being positioned for efiecti-ve engagement when the follower is disposed in the notch at the end of the cam.

8. In a centrifugal casting machine as defined in claim 1, said cam having a notch at its inner end and of substantial extent in circumferential direction, formed to receive the follower and di-' mensioned to permit shaking or vibrating the crucible support through a limited angle about the axis of rotation without releasing the follower from said notch.

9. In a centrifugal casting machine as defined in claim 1, said cam having a retaining notch at its inner end formed to receive the follower and hold the support against pivotal movement until said follower leaves the notch in the initial portion of its rotation, together with detent means acting to hold the cross-bar against rotation under tension of a spring motor connected'for rotating it, said detent means comprising a notched disc connected to turn with the cross-bar and a locking dog on the base, adjustable to engage a notch of the disc, the notch being substantially wider than the dog, the dog being positioned to engaged in the notch of the disc when the follower is disposed in the notch at the end of the cam, said last-mentioned notch being dimensioned to permit shaking or vibrating the crossbar and the crucible through a limited angle about the axis of rotation without releasing the follower from said notch.

10. In a centrifugal casting machine, a base, a cross-bar mounted for rotation thereon, a mold and crucible support with pivotal means connecting said support to the bar at a distance from the axis of rotation, the support being free to be swung inwardly about said pivotal connection before the rotation of the bar begins and to be swung outward by the centrifugal force generated by the rotation, a substantially spiral cam on the base and a follower on the support positioned to engage the cam in the initial portion of said rotation, said cam acting to overcome the inertia of the. mold support and to positively swing the support outward as the bar begins to turn, said mold and crucible support including an arm with a fixed end plate and an upstanding bracket slidably adjustable on the arm, and supporting the crucible with space between the end plate and bracket to accommodate a mold ring, and a special cradle for a short mold ring, said cradle having a stem by which it is spaced from the end plate and secured thereto, whereby the short ring can be used with the crucible in the same position on the arm as it occupies when used with a longer ring.

EMMZE'IT B. MOORE.

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