Centrifugal casting furnace

A centrifugal ceramic casting furnace including a horizontal arm rotatably supported by the upper end of a vertical shaft driven by a motor and the arm having a casting ring cradle on one end, a muffle movable along said arm a limited distance toward and from the cradle and a counterweight device mounted upon the opposite end of the arm adjustably both longitudinally and upwardly in a manner to balance the opposite ends of the arm statically and also adjustably dispose the effective masses of the muffle and counterweight within a common horizontal plane to effect substantial freedom from vibration while the furnace is rotating at a centrifugal casting speed.

BACKGROUND OF THE INVENTION 
Centrifugal casting is a popular art that has been in existence for many 
years, especially in the jewelry industry, where, for example, by using 
the lost wax process, a simple mold can be made in plaster of Paris, or 
suitable gypsum products of industrial type. An ingot of precious metal or 
otherwise is placed in a muffle on one end of a horizontal rod mounted on 
the upper end of a vertical shaft which is rotated by any suitable motor. 
The muffle is usually electrically heated to melt the ingot and, when 
molten, it is introduced to the cavity in the mold and centrifical action 
insures full projection of the molten material into the mold and, when 
done expertly, no cavities or holes due to residual air occur in the 
finished product. The opposite end of the horizontal rod usually supports 
a counterweight to avoid the need of securely anchoring the rotatable 
shaft by suitably embedding the lower end thereof in a mass of heavy 
material such as Portland cement or otherwise. 
Centrifugal casting such as that broadly described above also is employed 
in the dental art for purposes of making crowns, inlays, and certain other 
related types of metal items employed in restorative dentistry, the lost 
wax process also frequently being used to make the necessary mold in which 
cavities of desired shapes are formed. One simple form of casting metallic 
dental material to form a molded object is the subject matter of prior 
U.S. Pat. No. 1,563,151 to Booth, dated Nov. 24, 1925 and a later, more 
sophisticated machine of this broad type comprises the subject matter of 
prior U.S. Pat. No. 2,235,443 to Steinbock et al, dated Mar. 18, 1941, 
both of the aforementioned patents revolving the muffles in a vertical 
plane about a horizontal shaft and in both of these counterweights are 
employed on the end the rotatable arm or bar which is opposite the muffle. 
Other forms of centrifugal casting machines for making cast dental objects 
and in which the arms that support the muffles and counter balances are 
disposed for operation about a vertical axis in a horizontal plane 
comprise the subject of prior U.S. Pat. Nos. 2,749,585 to Brosen, dated 
June 12, 1956; 4,077,060 to Halatek, dated Mar. 7, 1978; and 4,134,445 to 
Goodrich et al, dated Jan. 16, 1979, the examples of operation shown 
therein primarily employing counterweights in suitable arrangement so that 
vibration is minimized and comprise so called bench type centrifugal 
casting machines which do not require substantial anchoring because of the 
muffles and counterweights counterbalancing each other. 
Still another prior U.S. Pat. No. 4,280,551 to Ohara, dated July 28, 1981 
illustrates a somewhat more sophisticated type of centrifugal casting 
apparatus for dentistry in which the rotatable shaft for the transverse 
arm on one end thereof which carries the muffle and counterweight is 
disposed at an angle of substantially 45.degree. to the horizontal. 
The present invention also pertains to a centrifugal casting furnace, 
especially for dental purposes, which includes a transverse arm carried by 
the upper end of a vertical rotatable shaft and an electrically heated 
muffle is mounted adjacent one end of said arm, while a counterweight is 
carried by the opposite end of the arm, and is adjustable in certain ways 
that are distinct from the prior art and the invention also includes other 
beneficial and meritorious characteristics that likewise are not found in 
the prior art and especially the type of art referred to above. The 
present invention is especially directed to centrifugal ceramic casting 
furnaces for casting glass dental prosthetic parts. Details of such 
innovations and characteristics are set forth below. 
SUMMARY OF THE INVENTION 
It is among the principle objects of the invention to provide on one end of 
a rotatable transverse arm, a counterweight which is on the opposite end 
of the arm from that which supports the muffle and said counterweight is 
arranged to vertically adjust the mass of the same relative to the 
principle mass of the muffle in such manner that the counterweight and 
muffle are dynamically balanced in the static mode, as well as being 
balanced in the horizontal plane with respect to the upper end of the 
rotatable shaft, whereby substantial freedom from vibration is effected 
especially when the arm is rotated at casting speeds. 
Ancillary to the foregoing object, it is a further object to produce 
counterbalancing of the muffle by means of a pair of relatively heavy 
circular weights, one of which is centrally bored and threaded, while a 
second one has a bore which is substantially offset to the center thereof 
and is threaded, both of said weights being adapted to be adjustably 
positioned on the end of the rotatable arm which is opposite that which 
has the muffle thereon and said arm preferably is tubular and threaded in 
order that the weights may be adjustably positioned on the arm by 
threadably moving the same as required to effect static balancing and by 
threadably moving the two weights into firm contact with each other, so 
that a lock-nut function is produced to maintain the weights in the 
desired position and in which the mass of the eccentric weight is 
uppermost to effect dynamic balancing of the muffle which is mounted on 
the opposite end of the arm above the upper surface thereof for purposes 
to be described hereinbelow. 
A further object of the invention is to form the transverse arm from 
tubular stock for purposes of accomodating a longitudinally movable push 
rod which is slidable in the tubular arm, said arm also having 
longitudinally spaced slots respectively to accomodate a connection 
between one end of the push rod and the muffle and the other slot 
accomodates a manually operated handle connected to the opposite end of 
the push rod and extending through said other slot in the tubular arm in 
order that the muffle may be moved a limited extent longitudinally with 
respect to the end of the arm opposite the counterweights for purposes of 
positioning a casting ring on the rotatable arm outwardly from the outer 
end of the muffle and, to accomodate such casting ring, it is a further 
object of the invention to secure a substantially U-shaped cradle adjacent 
the terminal end of the arm on which the muffle is mounted and the 
sidewalls of the cradle being slotted upwardly for purposes of 
accomodating the ends of the tongs to facilitate positioning and removing 
casting rings within and from the cradle. 
Still another object of the invention is to facilitate at least static 
balancing of the arm with respect to the upper end of the rotatable shaft 
that supports it by providing said upper end of the shaft with a 
transverse opening of larger vertical dimension than the diameter of the 
arm and positioning a fulcrum-type transverse pin which extends through 
said shaft partially above the lower surface of the transverse opening and 
the arm having a notch in the lower surface thereof seated upon said pin 
for static balancing of the arm by adjustment of the counterweight thereon 
relative to the muffle, the shaft also being threaded on its upper end to 
accomodate a clamping cap suitably upon said upper end and having a lower 
end clampingly interengageable with the upper surface of the arm to clamp 
the same firmly upon the transverse pin after static balancing has been 
completed. 
Ancillary to the foregoing object, it is a still further object to employ a 
clamping cap which is cup-shaped and has a depending internal stud tapered 
at the lower end thereof and the upper surface of the arm having an 
opening therein complimentary to the tip of said stud and receiving said 
tip to effect a lock-type clamping of the arm relative to the upper end of 
the shaft, said clamping also employing a clamping ring surrounding the 
upper end portion of the shaft between the cap and upper surface of the 
arm, if desired, and also having transversly aligned notches in the lower 
surface of said ring disposed upon said arm to facilitate the clamping 
thereof relative to the rotatable shaft. 
One further important object of the invention is to provide a muffle which 
is suitably aligned and provided with heating means that surround a 
central axial opening that is open at opposite ends and is adapted to 
receive a crucible which contains materials such as pellets or small 
ingots of metal or ceramic material, glass and the like which is to be 
melted within the muffle and the opposite ends of the opening of the 
muffle are adapted to be closed by closure members preferably having 
projections of limited dimension on the faces thereof nearest the ends of 
the muffle and respectively mounted adjacent opposite ends of the muffle 
upon elongated members which are pivotly mounted upon shaft means carried 
by the muffle in parallel relationship to the axis thereof and coaxial 
with each other, whereby the elongated members may be pivoted upon said 
shafts between closure positions over the ends of the muffle and positions 
in which they are removed therefrom to permit access to the interior of 
the muffle. 
Ancillary to the foregoing object is another object of providing cam means 
on said shafts operable by manually engageable levers which initially 
effect limited axial movement of the closures relative to the ends of the 
muffle to first remove of the projections therefrom and then possibly 
either move the closures pivotly away from said opposite end or into 
engagement therewith, as required, the cams being actuated by the levers 
to achieve the axial movement of the closure members either toward or from 
the opposite ends of the muffle, as required. 
One additional object of the invention is to provide an adjustable mounting 
for the casting ring cradle relative to the end of the transverse arm upon 
which it is mounted in order to accomodate casting rings of different 
diameters within reasonable limits, the adjustment means comprising a 
rotatable disc-like cam operable about a pivot in the arm and disposed in 
a slot in the shaft which actually supports the cradle for movement 
transversly with respect to said arm, the arrangement also including 
releasable position-maintaining mechanism. 
Details of the foregoing objects and of the invention, as well as other 
objects thereof, are set forth in the following specifications and 
illustrated in the accompanying drawings comprising a part thereof.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION 
One of the objectives which gave rise to developing the present invention 
constituted the desire to provide a bench-type centrifugal casting furnace 
or machine which included structure by which substantial freedom from 
vibration is achieved and details of which are set forth below. Additional 
objectives also have been achieved as described hereinafter. 
Referring to FIGS. 1 and 2 in particular, it will be seen that the 
invention includes a housing 10 which actually includes adjoining 
compartments 12 and 14, both of which commonly extend upward from a base 
frame 16. The compartment 12 also has a hinged cover 18 which is rendered 
removeable by providing retractable hinge pins 20. Preferably, though not 
illustrated, the hinged cover 18 is L-shaped in cross section to provide a 
top panel and at least a partial front panel, the latter extending down to 
the upper portion of base frame 16. 
Compartment 14 includes an electric motor 22 of suitable horse power, the 
drive shaft 24 thereof depending therefrom as shown in FIG. 1 and 
including a sheave 26 around which an endless belt 28 extends and also 
encircles driven pulley or sheave 30 on the lower end of a rotatable shaft 
32 which extends through a suitable rugged bearing unit 34 which is afixed 
to a horizontal panel 36 comprising the upper wall of baseframe 16. The 
panel 36 also extends into compartment 14 for purposes of having the motor 
22 mounted thereon. A shield (not shown) protects the exposed end of 
rugged bearing unit 34 to prevent damage to the rugged bearing unit. 
The shaft 32 preferably is tubular, as best shown in FIG. 3, and 
accomodates electric conduits 38 which extend from a suitable source of 
electric power to a thermocoupled and the heating element within the 
furnace muffle 40, as shown in FIG. 3. 
In reality, the electric conduit 38 comprises several pairs of wires, one 
pair extending between a temperature indicator 44 on the front panel of 
housing 14 and a thermocouple 45 which is encased within a housing 
attached to the shell of muffle 40 to respond to the actual temperatures. 
A second pair comprises a power lead to the heating wire 46 within the 
muffle 40 as shown in FIG. 3, the opposite end of said pair being 
connected to said aforementioned source of power. Both sets of wires are 
connected to and extend from a mercury contact slip ring 42 which is of 
such nature as to enable a temperature within the muffle 40 to be visually 
seen on the temperature indicator 44 while the muffle 40 is being 
centrifuged as described hereinafter. At least some of the subject manner 
of said electrical arrangement described above comprises the subject 
manner of a separate invention covered by a copending application assigned 
to the assignee of the invention of the present application. 
Supported by the upper end of shaft 32 is a transverse arm 48 which 
preferably is tubular and one end 50 thereof is threaded externally. 
Slidably mounted within the arm 48 is a push rod 52 preferably supported 
within self-lubricating bearings 54 to facilitate the movement of said rod 
within the arm. The walls of the arm 48 also are provided with 
longitudinally spaced slots 56, the right-hand slot 56, as viewed in FIG. 
3, accommodating a manually operable, laterally extending handle 58 and 
the left-hand slots 56 as viewed in FIG. 3, actually being an opposed pair 
thereof to receive a transverse pin 60 which extends therethrough and also 
through a support sleeve 62 and on end of the push rod 52. Preferably, the 
sleeve 62 includes self-lubricated bearings 64 to facilitate movement of 
the muffle 40 in opposite longitudinal directions upon the arm 48. Muffle 
40 is secured to sleeve 62 by a vertical pin 65 which extends upward from 
sleeve 62 and the upper end is connected to the shell of muffle 40. 
The opposite end 66 of arm 48 from the threaded end 50 thereof adjustably 
supports a casting ring cradle 68 which is fixed to the upper end of a 
shaft 70 that is substantially perpendicular to the arm 48 and said arm is 
provided with a suitable aperture, complimentary in shape to that of the 
shaft 70 in order to guide the same for such perpendicular movement. Also, 
said end of arm 48 is provided with a slot 72 within which rotatable cam 
member 74, and preferably a relatively thin disc, is moveable, said disc 
also being fixed to a transverse shaft 76 which extends through suitable 
bearing openings, not shown, in opposite sides of the arm 48. Shaft 70 
also is formed with a narrow slot 78 which actually is coextensive with 
the slot 72, the length of slot 78 being equal to the diameter of the cam 
member 74. Said details are best shown in FIG. 7. The outer end of shaft 
76 has a manually operated knob 80 fixed thereto. 
As the shaft 76 is rotated in opposite directions, it will dispose the 
cradle 68 at different nearly horizontal axial positions relative to the 
axis of the central opening 82 in muffle 40 in order that casting rings 84 
of different diameters may be rendered coaxial with the opening 82. Said 
rings are employed to contain suitable mold-forming material 86 such as a 
gypsum material or the equivalent within which a mold cavity 88 may be 
formed, such as by the lost wax process, and adapted to receive molten 
material when same has been melted within the muffle 40. Further, in the 
preferred operation of the molding procedure in which the present 
invention mechanism is adapted, the casting rings 84 are preheated in a 
separate furnace so that there is no appreciable differential in 
temperatures between the cavity 88 and that of the molten material. 
To facilitate mounting the white hot casting ring 84 within cradle 68, said 
cradle is substantially U-shaped in cross section and the opposite 
sidewalls thereof are provided with slots 90 to receive and accomodate the 
ends of tongs which are used to handle the casting rings and the molds 
disposed therein. Also to facilitate positioning the casting rings in the 
cradle 68, the outermost end thereof is provided with a fixed end wall 92. 
To maintain the alignment position of the cradle 68 with the central 
opening 82 of muffle 40, the arm 48 is provided at one side with a boss 94 
within which a spring-loaded detent 96 is mounted for projection of the 
inner end thereof into one of a series of similar depressions 98, see 
FIGS. 3 and 7, formed in one side of the shaft 70, and to simplify the 
system, only a limited number of the depressions 98 are formed 
respectively according to a limited number of diameters of said casting 
rings to be positioned in the cradle 68. 
Arm 48 is supported within an opening 100 in shaft 32 which is larger than 
the diameter of the arm 48, at least in the vertical direction and, if 
desired, may be circular. Extending transversely through the upper end 
portion of shaft 32 is a pin 102 of which at least the upper portion 
extends above the lower surface of the opening 100 in order that the same 
may serve as a fulcrum used incident to statically balancing the arm 48. 
This is possible by virtue of the greater vertical dimension of the 
opening 100 than the vertical dimension of the arm 48 and the location of 
the pin 102 in said opening such as can be visualized when the cup-shaped 
cap 104 is relaxed from the clamping position illustrated in FIG. 3 and 
such relaxation also removes the tapered terminal end of the interior stud 
106 that is affixed within the cap 104 and is received within the 
complimentary opening 108 in arm 48. 
To firmly clamp the arm 48 in the position shown in FIG. 3 for example, 
after the arm has been balanced in a manner described hereinafter, the cap 
104 is threaded downwardly to laterally move the tapered end thereof into 
the complementary opening 108 in arm 48 and also force the lower surface 
of arm 48 into firm abutment with transverse pin 102 which, incidentally, 
preferably is received within a shallow notch 110 in the lower surface of 
arm 48 and at least somewhat serves as a safety means to prevent any 
appreciable longitudinal movement of the arm 48 in the event the cap 104 
has not been screwed tightly into clamping position. Further to aid in the 
clamping of the arm with respect to shaft 32, a clamping ring 112 is 
disclosed, the top of which is abutted by the lower face of the cap 104 
and the lower surface of ring 112 preferably is oppositely notched to 
receive the upper surface of the arm 48. 
When it is desired to statically and dynamically balance the opposite ends 
of the arm 48 with respect to each other, the muffle 40 is moved into 
abutment with the cradle 68 but only after first moving the rear closure 
114 to the inoperative phantom position shown in FIG. 5. This is done by 
means described hereinafter but it will be understood that the outermost 
end of the muffle 40 will firmly abut the mouth of the cavity 88 in the 
mold 86 disposed in the casting ring 84 and, to be even more precise, the 
muffle preferably is charged with a crucible 116 shown within the opening 
82 in the muffle and that is substantially the position it will occupy 
while the crucible is being heated to melting temperature. When 
centrifugal casting occurs, the nose of the crucible will be centrifugally 
forced against the inlet of the mold cavity 88. 
Balancing is achieved by means preferably comprising a mass of weight 
mounted on the threaded end 50 of arm 48 and longitudinally positioned 
thereon so as to statically balance of the weight of the muffle 40 and 
cradle 68 when in the abutting position described above and such balancing 
is achieved by relieving the cap 104 and preferably even removing the 
clamping ring 112 and also removing the tapered end of the stud 106 from 
the opening 108 in arm 48, whereby the arm 48 can teeter about the fulcrum 
pin 102. It is a relatively simple operation to statically balance the 
ends of the arm 48 with respect to each other by threadably moving the 
weights 118 and 120 on the shaft until balance is achieved. However, to 
dynamically balance the opposite ends in static mode, it is essential that 
the centers of gravity of the weights on opposite ends of arm are 
substantially in a common horizontal plane parallel to the axis of arm 38 
and this is achieved by employing, for example, a metal weight 118 which 
is centrally threaded and a similar weight 120 which is provided with an 
offset bore 122 that preferably is substantially off center as readily can 
be visualized from FIGS. 3 and 6 and, when the arm is dynamically balanced 
the greater mass of the weight 120 is disposed uppermost so as to 
counterbalance in a vertical direction the center of gravity of the mass 
of the elements on the opposite end of arm 48 which are positioned aboved 
the axis of said arm. When such dynamic balancing is not at least 
reasonably achieved, there is a tendency for the casting machine to 
vibrate and tend to generate circular motions at opposite ends of the arm 
that are out of phase with each other. Therefore, it is an important 
object of this invention to eliminate such vibration as far as possible 
and it has been found that the weight arrangement illustrated in FIGS. 3 
and 6 is at least one satisfactory means for achieving it. 
The dynamic balancing necessitates initially statically balancing opposite 
ends of the arm 48 and then operating the machine to determine whether 
static balancing has been achieved. If it is found not to be achieved to a 
desired extent, then further adjustment of the weights 118 and 120 is 
undertaken until the greatest possible elimination of vibration is 
achieved. This may require a number of trial operations and rebalancing of 
the arm. Another advantage of employing the weights 118 and 120 is that 
when final adjustment is achieved, the center of gravity of the assembled 
weights is uppermost and said weights may be coengaged in lock-nut manner 
to retain the desired adjustment and, having achieved such static as well 
as dynamic balancing, continual operation of the casting machine usually 
requires no further adjustment. A safty pin may be used at the end of the 
transverse arm 48 to prevent weights 118 and 120 from flying off if the 
weights should become dislodged. 
As shown especially in FIGS. 3 and 4, the muffle 40 has a rear closure 114 
and also a forward closure 124. When a casting is to be undertaken, a 
crucible containing metal, glass, or ceramic material such as represented 
by the ingot 126 within the crucible 116 which is placed on the interior 
of muffle 40 and both of the closures 114 and 124 are disposed in sealing 
relationship as illustrated, for example, in FIG. 3. It also will be seen 
that each closure comprises a metallic shell within which heat insulating 
plug-like projection 128 is formed, each of them having a nose extending 
partially into the central opening 82 of the muffle to effect firm sealing 
of the contents. Suitable switch means of conventional type are included, 
for example, in compartment 14 and provided with switch buttons 130, for 
example, for various purposes, including operating the motor 22 and 
directing current to the heater 46 in the muffle. After disposing the 
crucible 116 with its contents in the muffle 40, current is introduced to 
the heating member 46 and is continued until the contents of the crucible 
become molten. At that time, a pre-heated casting ring 84 with its mold 
configuration is placed in the cradle 68, the rear closure 114 is opened 
quickly and handle 58 is operated to move the muffle 40 rearwardly into 
abutment of the open rear end thereof with the mold 86 and, if desired, 
the closure 124 may be opened to effect pushing the crucible 116 to the 
rear end of the central opening of the muffle so as to abut the inlet end 
of the mold cavity 88, all of which is accomplished as quickly as 
possible. Then the motor 22 is activated to commence centrifugal casting 
of the material into the mold cavity 88. Such centrifugal casting is 
continued in accordance with known practice in order to insure faithful 
casting of the material in the cavity 88 and removal of any occluded air 
or otherwise which might result in a misfigured casting. At the conclusion 
of such casting operation, the crucible is moved toward the shaft 32 and 
the hot casting ring and molded item are removed from the cradle 68 and 
suitably processed by conventional means to remove the cast object from 
the mold-forming material. 
Operation of the closures 114 and 124 is performed by mechanism which 
specifically has been designed to take into consideration the projecting 
noses on the ceramic plug-like members 128 in the closures 114 and 124. 
The required operation of the closures includes moving the same from the 
full line illustration thereof in FIG. 5, wherein the plug-like members 
are disposed with the noses within the cavity of the muffle, and the 
phantom position shown thereof in FIG. 5 in which one or both ends of the 
central cavity of the muffle are fully exposed for either receiving or 
removing the crucible 116 or otherwise. Especially as shown in FIGS. 4 and 
5, the closures per se are mounted on one end of elongated members 132 
that are pivotly supported respectively on the outer ends of a pair 
coaxially aligned shafts 134 which are mounted for limited axial movement 
with respect to the bearings 136 which are affixed to one side of the 
housing of muffle 40. 
Attached to the inner end of each of the shafts 134 is an operating handle 
138 which may have a knob on the outer end thereof if desired. The members 
132 each have a bearing hole in the end thereof attached to the shaft 134 
and are freely suspended from such shaft so that, when desired, they may 
fall by gravity from the full line position shown in FIG. 5 to the phantom 
position shown therein and thereby render one or both ends of the muffle 
open. Affixed to each of said members adjacent to the pivot thereof is a 
pin 140 which extends into an arcuate slot 142 in each member 132. The pin 
is fixed to a cam member 144 which is provided with an angular cam face 
146 that is engageable with a suitable surface on fixed member 148 that is 
attached, for example, to bearing member 136. The cam member 144 may be 
secured to the shaft 134 for rotation therewith by any suitable means such 
as the set of screws clearly shown in FIG. 4. 
Referring to FIG. 4 at the right hand end, it will be seen that the closure 
member 124 is in full sealing relationship with the forward end of the 
muffle 40 and the projection thereon extends into the central opening of 
the muffle as shown in dotted lines. When it is desired to open that end 
of the muffle, the handle 138 interconnected to the closure 124 by 
elongated member 132 is moved in a direction initially to cause the cam 
face 146 to engage fixed member 148 at the right hand end of FIG. 4 and 
thereby axially move the closure member 124 so as to be disposed in a 
position similar to that illustrated at the left hand end of FIG. 4 with 
respect to closure member 114. When this has been accomplished, continued 
movement of the handle toward the uppermost phantom position shown in FIG. 
5 will permit the closure and elongated member 132 thereon to assume the 
phantom position by gravity and the innermost end of cam member 144 then 
will rest against fixed member 148 and maintain the open position. 
Conversely, when it is desired to close the ends of the muffle 40, the 
handle 138 is moved from said uppermost phantom position thereof shown in 
FIG. 5, for example, and at the initial part of such movement causes the 
cam face 146 to axially move the pivoted end of member 132 on closure 114 
to the full line position shown in FIG. 4 and continued movement will 
dispose the pin 140 on the cam member against the upper end of arcuate 
slot 142, as shown in FIG. 5, and thus positively effect clockwise 
movement of the elongated member 132 and closure member 114 to the sealing 
position and when this occurs, cam face 146 is in an idle position with 
respect to the fixed member 148 at the left side of FIG. 4 and tension 
spring 150, which extends between the adjacent ends of the shaft 134 
functions to firmly position the projecting inner surface of the closure 
member 114 within the end of the muffle it is to seal. A ceramic tube (not 
shown) is applied over spring 150 to insulate the spring from heat and the 
spring is attached to the doors 114 and 124 via a swivel (not shown) to 
prevent twisting. 
Looking at FIG. 1, it can be appreciated that the overall height of the 
centrifugal casting furnace of the present invention has been minimized 
while retaining excelent control parameters. The horizontally disposed 
casting arm 48 is horizontally disposed and carried at the upper end of 
the vertically disposed rotateable shaft 32. The driving motor 22 that 
powers the shaft 32 is mounted horizontally displaced and remote from the 
shaft 32 but on substantially the same horizontal level as the shaft 32. 
By this it is meant that the motor 22 and the shaft 32 are at 
substantially the same height or distance from the bottom of the housing 
10. The motor 22 is connected to the shaft 32 positively by the belt 28 
which is toothed to provide a positive driving connection therebetween. 
From the foregoing, it will be seen that the present invention provides a 
relatively simple yet highly effective centrifugal casting furnace or 
machine capable of easy operation and especially designed to be relatively 
free of vibration so as to be operated as a bench casting machine or 
furnace in view of the structure cited above. This is primarily due to the 
particular arrangement of counterweights and the adjustment thereof to 
effect not only static but likewise dynamic balancing of the arm 48 in the 
static mode. 
In one prefered operation sequence, of casting a ceramic dental prosthesis 
part, i.e. a dental crown, the muffle 40 is preheated to 1100.degree. C. A 
glass slug or ingot 126 is loaded into cruciable 116. Muffle door 124 is 
opened and the loaded cruciable is inserted into the muffle and the door 
is closed. The loaded muffle is then raised to a temperature of 
1360.degree. C. and this temperature is held typically for 6 minutes. The 
heating is by electrically heating the muffle by power supplied via the 
electrical conduits 38, which traverse the hollow shaft 32, the mercury 
wetted slip ring 42 and the electrical input conduits 38. This incubating 
or melting phase is preferably carried out with the crucible stationary, 
the shaft 32 being stationary. 
The casting ring 84 which has been preheated in an oven (not shown) to 
1650.degree. F. is then positioned in the casting ring cradle 68. The door 
114 is opened and the muffle 40 is moved into abutment with the casting 
ring 84. Next the cruciable 116 is manually pushed to seat against the 
mold-forming material 86. 
Then the hinged cover 18 of the casting machine is closed and the motor 22 
is powered to about 1790 rpm (motor rated at 1725 rpm) and rotates the 
shaft 32 at about 500 rpm via the endless belt 28. The belt 28 is 
preferable a toothed belt to assure accurate revolutions per minute 
corresponding to the motor speed and the sprocket ratios. The motor 22 is 
a constant speed motor. The shaft 32 is typically spun or rotated at a 
constant sustained speed for 4.5 minutes. The hinged cover 18 is then 
opened. At the end of the constant speed operation the rotation is 
terminated by internal frictional characteristics to stop promptly or 
abruptly, within 4 to 20 seconds, preferably 4 to 10 seconds and most 
preferably about 6 seconds. The casting ring and cruciable are then 
removed. The casting ring 84 and the cast material are set aside and 
allowed to cool at ambient. The door 114 is closed and the upper door 124 
is opened to receive a new loaded cruciable and the cycle is repeated. 
The foregoing description illustrates preferred embodiments of the 
invention. However, concepts employed may, based upon such description, be 
employed in other embodiments without departing from the scope of the 
invention. Accordingly, the following claims are intended to protect the 
invention broadly, as well as in the specific forms shown herein.