Dental centrifugal casting apparatus

A dental centrifugal casting apparatus includes a crucible for receiving a dental casting material, a crucible holding unit for holding the crucible, a heating furnace such as a high-frequency induction heating furnace for heating and melting the dental casting material in the crucible, a crucible forward and backward rotary driving unit for driving the crucible holding unit forward and backward so as to insert the crucible into the heating furnace to heat and melt the material in the crucible and remove the crucible from the furnace, and for rotationally driving the crucible holding unit so as to inject the melted material into a mold at a predetermined position, a bucket for holding the mold in which the molten material is injected by the forward and backward motion and the rotation of the crucible performed by the crucible forward and backward rotary driving unit, and a centrifuge unit for rotating a rotary arm swingably mounting the bucket on its end portion at high speed immediately after the material is injected to apply a centrifugal force to the mold and molten material, thereby performing casting.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a dental centrifugal casting apparatus for 
casting an artificial tooth such as an artificial crown by using, e.g., 
glass ceramic as a casting material. 
2. Description of the Related Art 
Conventionally, metal materials such as a gold alloy and a nickel-chromium 
alloy have been used as a material for casting an artificial tooth such as 
an artificial crown. Melting temperatures of these metal materials fall 
within the range of 1,000.degree. C. to 1,100.degree. C., i.e., 
comparatively low. Therefore, a resistant-heating electric furnace has 
been used as a material heating/melting means for use in a conventional 
dental centrifugal casting apparatus. In order to cast an artificial tooth 
such as an artificial crown, the above material heated/melted in the 
electric furnace is flowed into an investment preheated at 400.degree. C. 
to 500.degree. C., and then a manual centrifuge is operated to perform 
centrifugal casting. That is, casting has been conventionally performed by 
such a simple manual operation. 
In recent years, however, a glass ceramic material having good affinity to 
a living body is used as an artificial tooth material. A melting 
temperature of this glass ceramic material is about 1,300.degree. C. to 
1,500.degree. C., i.e., much higher than that of the conventional metal 
materials. When a material having such a high melting temperature is used, 
cast products having uniform characteristics cannot be stably manufactured 
by the conventional manufacturing process since casting must be performed 
under strict casting conditions. 
In order to solve this problem, various types of artificial tooth casting 
apparatuses improving the conventional manufacturing process have been 
proposed. For example, Published Unexamined Japanese Utility Model 
Application No. 60-166460 discloses an apparatus of this type. Such an 
apparatus, however, is generally large in size. In addition, a highly 
skilled operator is required to operate the apparatus of this type in 
order to cast a metal into an artificial tooth. That is this apparatus 
cannot be easily used for dental casting apparatus. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a dental centrifugal 
casting apparatus which allows an unskilled operator to easily perform 
casting, can finish casting before cooling/solidification of a casting 
material progress, can protect a material from being overflowed from a 
mold due to a shock upon start of rotation of a centrifuge or a 
centrifugal force during high-speed rotation, can easily obtain a cast 
product such as a high-quality artificial crown, and can heat/melt a 
casting material with high efficiency. 
In order to achieve the above object, the present invention provides the 
following basic means. 
That is, there is provided a dental centrifugal casting apparatus 
comprising a crucible for receiving a dental casting material, a crucible 
holding unit for holding the crucible, a heating furnace composed of, 
e.g., a high-frequency induction heating device and provided to heat/melt 
the dental casting material in the crucible, a crucible forward/backward 
rotary driving unit for driving forward/backward the crucible holding unit 
so as to insert/remove the crucible into/from the heating furnace to 
heat/melt the material in the crucible, and for rotationally driving the 
crucible holding unit so as to inject the heated/melted material into a 
mold at a predetermined position, a bucket for holding the mold in which 
the molten material is injected by the forward/backward motion and the 
rotation of the crucible performed by the crucible forward/backward rotary 
driving unit, and a centrifuge unit for rotating a rotary arm swingably 
mounting the bucket on its end portion at high speed immediately after the 
material is injected to apply a centrifugal force to the mold and molten 
material, thereby performing casting. 
The above means provides the following effects. 
(1) A series of processes such as heating/melting of a material, injection 
of the material into the mold, and rotation and stop of the centrifuge can 
be performed substantially automatically. Therefore, even an unskilled 
operator can easily operate the casting apparatus to perform casting. 
(2) Since the centrifuge rotates at high speed at the same time the 
heated/melted material is injected in the mold, casting can be finished 
before cooling/solidification of the casting material progresses. 
(3) Since the position of the mold changes in accordance with the rotation 
of the centrifuge unit, the molten material is protected from being 
overflown from the mold due to a shock upon start of rotation of the 
centrifuge unit or a centrifugal force during high speed rotation. 
(4) A heating furnace such as a high-frequency induction heating device is 
used as a heating/melting means. Therefore, the casting material can be 
heated/melted with high efficiency, and the apparatus can be made compact. 
It is another object of the present invention to provide a dental 
centrifugal casting apparatus for facilitating practically smooth use, the 
apparatus, including measuring means for correctly measuring a crucible 
temperature means for preventing, e.g., a furnace member, a crucible 
holding member and a coupling flange from being adversely thermally 
affected, means for easily replacing a crucible holding unit at an 
arbitrary timing, and means for rapidly and correctly driving the crucible 
holding unit forward/backward and rotationally. 
Additional objects and advantages of the invention will be set forth in the 
description which follows, and in part will be obvious from the 
description, or may be learned by practice of the invention. The objects 
and advantages of the invention may be realized and obtained by means of 
the instrumentalities and combinations particularly pointed out in the 
appended claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
(1st Embodiment) 
FIG. 1 is a front view showing an installation state of a dental 
centrifugal casting apparatus according to the first embodiment of the 
present invention. Referring to FIG. 1, reference numeral 10 denotes a 
casting apparatus installation table. A power supply/control unit 20, a 
cooling unit (not shown) and the like are placed on a floor 11 below the 
table 10. A casting apparatus main body 30 is placed on the table 10. 
Although not shown, the power supply/control unit 20 includes a 
high-frequency power supply, a sequence control circuit and the like. A 
main switch 21, an ON/OFF indication lamp 22, an ammeter 23 and the like 
are arranged on a front surface of a box member of the unit 20. Note that 
the main switch 21 has a circuit breaker function. 
A high-frequency power cable 24 for supplying high-frequency power to the 
casting apparatus main body 30 and a control signal cable 25 for supplying 
a control signal to the main body 30 are extracted from the power 
supply/control unit 20. The other end of each of the cables 24 and 25 is 
connected to the casting apparatus main body 30. Therefore, when the main 
switch 21 is turned on, the ON/OFF indication lamp 22 is turned on, and 
the main body 30 is set in a standby state before a main operation. The 
ammeter 23 indicates a value of a high-frequency current to be supplied to 
the main body 30. 
The casting apparatus main body 30 has four legs 30a to 30d on its box 
member bottom surface. The length of at least three out of the four legs 
can be adjusted. By adjusting the lengths of these legs, therefore, the 
main body 30 can be horizontally placed on the table 10. A chimney 30e for 
exhausting heat generated by a high-frequency induction heating furnace 
(to be described later) outside the casting apparatus main body 30 is 
provided on the upper surface of the box member of the main body 30. 
A start button 31, a reset button 32, a stop button 33, a crucible 
temperature indicator 34, a mold-preheating furnace temperature indicator 
35, progression lamps 36, an alarm lamp 37 and the like are arranged on a 
panel on the front surface of the box member of the main body 30. 
The start button 31 is used to supply a command to a sequence control 
circuit included in the power supply/control unit 20 to start a sequential 
operation. The stop button 33 is used to simultaneously stop all the 
operations including the sequence of the overall apparatus. The crucible 
temperature indicator 34 is used to receive a signal from a thermocouple 
mounted on a material melting crucible (to be described later) to indicate 
the temperature of the crucible. The mold-preheating furnace temperature 
indicator 35 is used to receive a signal from a thermocouple placed in a 
mold-preheating furnace (to be described later) to indicate the 
temperature of the mold-preheating furnace. The progression lamps 36 are 
used to indicate a progression state of a casting operation and 
sequentially turned on one after another in accordance with the 
progression state of the operation sequence in the casting apparatus main 
body 30. The alarm lamp 37 is turned on when an abnormal phenomenon as 
described in the following item (1) or (2) occurs while the casting 
apparatus main body 30 is in operation. 
(1) An amount of water flowing through a work coil becomes smaller than a 
predetermined amount. 
(2) An excessive current flows through a high-frequency power supply 
circuit. 
When the alarm lamp 37 is turned on, the operation of the overall apparatus 
is stopped. When an operation is stopped by the stop button 33 or when the 
alarm lamp 37 is turned on to stop an operation, the reset button 32 is 
used to execute an operation for returning the crucible or the 
mold-preheating furnace from the stop position to its initial position. 
Various constituting parts (to be described later) are included in the 
casting apparatus main body 30. One feature of this embodiment is that a 
material of a coupling flange indicated by a broken line portion A in FIG. 
1, a material of a furnace member indicated by a broken line portion B 
therein, a material of a crucible holding member indicated by a broken 
line portion C therein, a crucible temperature measuring means indicated 
by a broken line portion D therein and the like are specified. 
In order to clarify the above feature and a detailed structure of each 
part, an internal arrangement of the casting apparatus main body 30 will 
be described below. 
FIG. 2 is a sectional view taken along a line 2--2 in FIG. 1. As shown in 
FIG. 2, the interior of the casting apparatus main body 30 is partitioned 
by two base plates B1 and B2 to form a 3-stage structure with upper, 
middle and lower stages. The upper stage serves as a casting material 
melting section 100 for heating/melting a casting material. The middle 
stage serves as a centrifugal casting section 200 for rotating a mold 
containing a molten material to mold the molten material in the mold by 
using a centrifugal force. The lower stage serves as a rotary driving 
section 300 for rotationally driving the centrifugal casting section 200 
and a mold preheating section 400 for preheating a mold before a molten 
material is injected in the mold. 
The casting material melting section 100 shown in the upper stage in FIG. 2 
comprises a high-frequency induction heating furnace 110, a crucible 
holding unit 120, and a crucible forward/backward rotary driving unit 130 
as will be described later. Reference numeral 136 denotes a driving motor 
for the unit 130. 
The centrifugal casting section 200 shown in the middle stage in FIG. 2 
comprises a bearing 201, a rotary shaft 202 rotatably supported by the 
bearing 201, a rotary arm 203 supported by the rotary shaft 202, bucket 
holders 204 and 205 mounted on two ends of the rotary arm 203, a first 
bucket 206 swingably held at the distal end of the bucket holder 204, and 
a second bucket 207 swingably held at the distal end of the bucket holder 
205. 
The rotary driving section 300 shown in the lower stage in FIG. 2 comprises 
a shaft member 301 for rotationally driving the rotary shaft 202 of the 
centrifugal casting section 200, a slit plate 302 fitted in the shaft 
member 301 and having slits (not shown) formed in part thereof, a 
photosensor 303 having a light-emitting portion and a light-receiving 
portion sandwiching the slit formation portion of the slit plate 302 in a 
non-contact state, a pulley 304 fitted on the shaft member 301, a motor 
306 (not shown in FIG. 2) for applying power to the pulley 304 via a belt 
305, a disc 307 which consists of a ferromagnetic substance and rotates 
together with the shaft member 301, and an electromagnetic chuck 308 which 
is arranged close to one surface of the disc 307 and attracts the disc 307 
as needed to stop free rotation of the shaft member 301 and therefore free 
rotation of the overall rotary section including, e.g., the centrifugal 
casting section 200, thereby positioning the first and second buckets 206 
and 207. 
Note that the slits of the slit plate 302 are formed in a position 
corresponding to an angular position of the bucket 206 (207). The 
electromagnetic chuck 308 operates in accordance with a control signal 
from the power supply/control unit 20. 
The mold preheating section 400 shown in the lower stage in FIG. 2 
comprises a mold-preheating furnace 401, a pulley 402 to be rotationally 
driven by a preheating furnace-elevating motor 406 (not shown in FIG. 2), 
a change nut 403 which rotates together with the pulley 402, a nut 
receiver 404 which meshes with a threaded portion of the change nut 403 
and vertically moves upon rotation of the nut 403, and a support member 
405 having a proximal end portion mounted on the nut receiver 404 and a 
distal end portion for supporting the mold-preheating furnace 401. 
During an operation period of the casting apparatus main body 30, an upper 
cover 38 is locked so as not to be opened by a lock solenoid 39. Even if 
the upper cover 38 is open during the operation period, a high-frequency 
current supplied to the casting material melting section 100 is cut off by 
a door interlock switch (not shown), and the operations of the centrifugal 
casting section 200 and the like are stopped. 
FIG. 3 is a plan view showing an arrangement of the casting material 
melting section 100 of the casting apparatus main body 30 shown in FIG. 2. 
As shown in FIG. 3, the section 100 is constituted by the high-frequency 
induction heating furnace 110, the crucible holding unit 120 and the 
crucible forward/backward rotary driving unit 130. 
The high-frequency induction heating furnace 110 comprises a 
heat-insulating cylinder 111, a bottom wall heat-insulating plate 112 
which consists of the same material as the cylinder 111 and closes one 
open end (at the left side in FIG. 3), a work coil 113 made of, e.g., a 
copper pipe wound around the outer circumferential surface of the cylinder 
111 and covered with an insulating coating, and pipes 114a and 114b for 
circulating cooling water between the work coil 113 and a cooling unit 
(not shown) and supplying a high-frequency current from the power 
supply/control unit 20 to the work coil 113. 
The heat-insulating cylinder 111 and the bottom wall heat-insulating plate 
112 are made of an alumina fiber board having a high thermal shock 
resistance and a high heat resistance. The alumina fiber board is obtained 
by mixing a filler and an organic or inorganic binder in a fiber material 
mainly consisting of an alumina fiber and forming the resultant material 
into a board. Examples of the material is "RF BOARD 17HD" and "RF BOARD 
18HD" (tradenames) available from NICHIAS CORP and "FIBER MAX 16-R BOARD" 
and "FIBER MAX 17-D BOARD" (tradenames) available from Toshiba Monoflux 
Co., Ltd. 
When a casting material is melted in the crucible of the high-frequency 
induction heating furnace 110, the other open end (at the right side in 
FIG. 3) of the heat-insulating cylinder 111 is closed by a cover member 
heat-insulating plate 124 (to be described later) consisting of the same 
material as the heat-insulating plate 112. As a result, the interior and 
exterior of the furnace 110 are thermally insulated. 
Terminals 115a and 115b are mounted on the pipes 114a and 114b, 
respectively. A high-frequency current of about 27 kHz and several tens to 
several hundreds mA is supplied from the power supply/control unit 20 to 
the terminals 115a and 115b. In this manner, the work coil 113 is powered 
via the pipes 114a and 114b. As shown in FIG. 3, in order to electrically 
insulate the work coil 113 from the cooling unit, an insulating Tetron 
hoses 116a and 116b are inserted between the pipes 114a and 114b and water 
supply and drainage ports 118a and 118b at the cooling unit side, 
respectively. A flow amount switch 117 is mounted on the hose 116b. When a 
cooling water flow rate becomes lower than a predetermined level, the 
switch 117 outputs an ON (or OFF) signal to turn on the alarm lamp 37 and 
to step the sequence in the casting apparatus main body 30. As a result, 
abnormal overheating of the work coil 113 due to an insufficient cooling 
water flow rate can be prevented. 
The crucible holding unit 120 comprises a platinum based crucible (to be 
referred to as a "platinum crucible" hereinafter) 121, a crucible holding 
member 122 for stably holding the platinum crucible 121, a platinum pin 
123 for pressing the crucible, a cover member heat-insulating plate 124 
for closing the other open end of the heat-insulating cylinder 111, and a 
coupling flange 125 for coupling the crucible holding member 122 to an 
operation shaft 131 of the crucible forward/backward rotary driving unit 
130 to satisfy a predetermined positional relationship. 
FIGS. 4 and 5 are views showing the crucible holding unit 120 in detail. As 
shown in FIGS. 4 and 5, a recess having substantially the same dimensions 
as the outer dimensions of the crucible 121 is formed in the crucible 
holding member 122 to stably hold the crucible 121. Note that when the 
crucible holding member 122 is tilted upon injection of a molten material, 
the crucible 121 may be dropped from the member 122. Therefore, the 
locking platinum pin 123 is inserted in the member 122. That is, the pin 
123 presses an opening portion of the crucible 123 from outside (above). 
The crucible holding member 122 consists of an alumina fiber board similar 
to the heat-insulating cylinder 111, the bottom wall heat-insulating plate 
112, and the cover member heat-insulating plate 124. As shown in FIG. 4, a 
recessed notched portion 122a is formed in a portion of the crucible 
holding member 122 immediately below a crucible molten material injection 
port. When a molten material such as a glass material in the crucible 121 
is injected into a mold (to be described later), this notched portion 
prevents the molten material from being adhered or stacked on the portion 
of the member 122 immediately below the molten material injection port. 
One end of each of alumina pipes 126a and 126b as support members is 
inserted in the crucible holding member 122. The other end of each of the 
pipes 126a and 126b projecting from the member 122 extends through the 
cover member heat-insulating plate 124 made of a alumina fiber board 
consisting of the same material as the button wall heat-insulating plate 
112. The end portions of the pipes 126a and 126b are inserted in a 
coupling flange 125 and fixed by machine screws (not shown). 
As shown in FIGS. 6 and 7, a scald contact portion 127a of a platinum-based 
thermocouple (R-Type) 127, which is covered with a platinum piece 127b, is 
connected to the outer surface of the platinum crucible 121 by means of, 
e.g., "scalding" at a comparatively low temperature. Both the end portions 
of the thermocouple 127 are extracted outside the crucible holding unit 
120 through the inside of an alumina protecting ring 128a and through an 
alumina protecting tube extending through the cover member heat-insulating 
plate 124 and the coupling flange 125. 
Referring back to FIG. 4, both the end portions of the thermocouple 127 
extracted outside the unit 120 through the inside of the tube 128 are 
fixed on the outer circumferential surface of the flange 125 together with 
two end portions at one end of extension lead wires 129 of the 
thermocouple 127, respectively, by machine screws. Two end portions at the 
other end of the wire 129 are guided to and connected to the crucible 
temperature indicator 34 described above. 
The crucible temperature measuring means provided as described above can 
obtain correct temperature information following only a heating 
temperature of the crucible 121 without being adversely affected by 
electromagnetic induction caused by an induction heating means. In 
addition, both the end portions of the thermocouple 127 are fixed on the 
outer circumferential surface of the coupling flange 125 as a part of the 
crucible holding unit 120 and then connected to the extension lead wire 
129 of the thermocouple 127. Therefore, even when the unit 120 rotates 
about the operation shaft 131, a bending or twisting stress produced by 
the rotation does not act on the thermocouple 127. Therefore, the crucible 
heating temperature can be constantly, stably and correctly measured, and 
correct temperature control based on the measurement can be performed. 
A shown in FIG. 3, the coupling flange 125 couples the crucible holding 
member 122 to the operation shaft 131 of the crucible forward/backward 
rotary driving unit 130 to satisfy a predetermined positional relationship 
as will be described later. The flange 125 consists of heat-resistant 
nonconductive ceramic. A suitable example of this nonconductive ceramic is 
"MACOR" (registered trademark) available from Cornings Glass Works. 
Therefore, the flange 125 is not induction-heated even in a magnetic field 
generated by the high-frequency induction heating furnace 110. Therefore, 
the flange 25 does not thermally, adversely affect the unit 130. 
FIGS. 8 and 9 are views showing the shape of the crucible 121. FIG. 10 is a 
sectional view taken along a line 10--10 in FIG. 9. 
The crucible 121 is used to heat/melt a dental casting material and to 
inject the molten material into a mold. Therefore, the crucible 121 has a 
molten material injection port 121b in a part of an open end of a cup-like 
crucible main body 121a. The port 121b of the crucible 121 has a sectional 
shape as shown in FIG. 10. That is, the vertical section of the port 121b 
is arcuated so that the molten material stayed in the port 121b is 
separately flowed inside and outside the crucible while the crucible 121 
is horizontally held. The crucible 121 preferably consists of platinum 
containing, e.g., 0.16% of zirconium as an oxide so as not to deform even 
if it is repeatedly exposed to an environment in which a temperature 
rapidly rises or falls. 
Referring back to FIG. 3, the crucible forward/backward rotary driving unit 
130 comprises the operation shaft 131 having the distal end coupled to the 
coupling flange 125, a shaft guide 132 for guiding the shaft 131, another 
guide 133, a straight-moving collar 134, a driving force transmitting 
portion 135, and a crucible-moving motor 136. 
The flange 125 and the shaft 131 are coupled to satisfy a predetermined 
positional relationship so as to position the distal end of the molten 
material injection port 121b of the crucible 121 on a virtual extended 
line of the axis of the shaft 131. Therefore, when the crucible is tilted 
to inject a molten material, almost no variation is produced in distal end 
position of the port 121b. Therefore, the molten metal can be accurately 
injected with respect to a mold center. 
A groove as indicated by a broken line is formed inside the shaft guide 
132. A pin (not shown) extending from the shaft 131 engages with the 
groove. As shown in FIG. 3, an inclined groove 133a is formed in the guide 
133 coupled to the right end of the shaft 131. A pin projecting from the 
inner surface of the straight-moving collar engages with the groove 133a. 
The driving force transmitting portion 135 converts a rotational force of 
the crucible-moving motor 136 into a linear driving force via a cam 137, a 
crank 138 and a ball bush 139 and transmits the converted force to the 
straight-moving collar 134. 
Therefore, when the motor 136 rotates to move the collar 134 straight, this 
linear driving force is transmitted to the operation shaft 131. During 
transmission of this linear driving force, the shaft 131 is allowed to be 
rotated due to the relationship between the pin of the collar 134 and the 
inclined groove 133a. As the pin of the shaft 131 is guided by the groove 
of the guide 132, the shaft 131 is moved forward/backward and rotated. As 
a result, the crucible 121 can be inserted/removed with respect to the 
heating furnace 110 to heat/melt the material, and the molten material can 
be injected in the mold. 
FIG. 11 is a view showing a mounting state of bucket 206 (207) with respect 
to a bucket holder 204 (205) and a positional relationship between the 
bucket 206 (207) and the base plates B1 and B2 which partition the box 
member of the casting apparatus main body 30. 
When the centrifugal casting section 200 starts rapid rotation about the 
rotary shaft 202, the bucket 206 (207) is pivoted upward about a support 
axis P of the bucket 206 (207). In this case, the bucket 206 (207) must be 
protected from being collided against the lower surface of the first base 
plate B1 supporting the casting material melting section or the upper 
surface of the second base plate B2 supporting the centrifugal casting 
section 200. Therefore, the dimensions of the bucket is considered as 
follows. That is, assuming that a distance from the support shaft of the 
bucket 206 (207) to the circumferential edge of a bottom portion of the 
bucket 206 (207) located at the farthest position is l and a distance 
between the first and second base plates B1 and B2 is H, a relation 
EQU H&gt;2 l (1) 
is satisfied, and the support axis P of the bucket 206 (207) lies midway 
between the plates B1 and B2. In this manner, the bucket 206 (207) can be 
protected from collision against the plate B1 or B2. 
FIG. 12 is a perspective view showing an outer appearance of the bucket 206 
(207) described above. As shown in FIG. 12, projecting portions 210a and 
210b to be inserted in support holes of the bucket holder 204 (205) extend 
from the outer circumferential surface near the open end of the bucket 206 
(207). A line connecting the portions 210a and 210b is a pivot axis of the 
bucket 206 (207). 
FIGS. 13 and 14 are views showing a detailed structure of a mold to be held 
in the bucket 206 (207), in which FIG. 13 is a perspective view and FIG. 
14 is a sectional view taken along a line 14--14 of FIG. 13. A mold 211 
consists of, e.g., an orthophosphate-based investment. A molten material 
receiving portion 212 for receiving an injected molten material is formed 
in the center of the upper surface of the mold 211. A cavity 213 having 
the same shape as a product to be cast such as a crown is formed below the 
portion 212. The portion 212 is substantially formed into an inverted 
conical trapezoid as a whole, and its bottom portion 214 is substantially 
semispherical. 
FIG. 15 is a perspective view schematically showing a portion from the 
bottom portion 214 in order to clarify the shape of the bottom portion 
214. It was experimentally confirmed that when the inverted conical 
trapezoidal molten material receiving portion 212 with the bottom portion 
214 having the shape as shown in FIG. 15 was formed, a molten material 
injected in the mold 211 was not overflown outside the mold 211 even if a 
shock was applied on the mold 211 upon start of rotation of the 
centrifugal casting section 200. It was confirmed that a funnel-shaped 
bottom portion 215 as shown in FIG. 16 could be used instead of the 
semispherical bottom portion 214 as shown in FIG. 15 to achieve the same 
effect. 
FIGS. 17 and 18 are perspective views showing an arrangement of the casting 
preheating furnace 401 in the casting preheating section 400 shown in FIG. 
2. The mold-preheating furnace 401 is obtained by forming a strainless 
steel cylindrical member 410 with a bottom as shown in FIG. 17 and winding 
a sheath heater 411 on the outer circumferential surface and the bottom 
surface of the cylindrical member 410 as shown in FIG. 18. In an actual 
operation, the sheath heater 411 is covered with a heat-insulating member. 
FIG. 19 shows a positional relationship between the centrifugal casting 
section 200, a part of the rotary driving section 300, and a part of the 
mold preheating section 400. Referring to FIG. 19, reference numeral 306 
denotes a centrifuge-driving motor, and a belt 305 is looped between a 
rotary shaft of the motor 306 and a pulley 304 coupled to the rotary shaft 
202 of the centrifugal casting section 200. 
In order to preheat the mold 211 in the mold-preheating furnace 401, a 
preheating furnace-elevating motor 406 is rotated to move a mold support 
member 405 upward. As a result, the bucket 206 is received in the 
mold-preheating furnace 401, and the mold 211 is heated together with the 
bucket 206. In order to rotate the centrifugal casting section 200 after a 
molten metal is injected into the mold 211, the motor 406 is rotated in a 
reverse direction to move the support member 405 downward. As a result, 
the preheating furnace is removed from the bucket 206. 
FIGS. 20A and 20B are block diagrams showing an arrangement of an electric 
system. 
The power supply/control unit 20 receives power of AC 200 V. This power is 
supplied to the respective portions in the unit 20 via the main switch 21. 
The power transformed from 200 V to 100 V by a transformer 500 is supplied 
to a rectifier circuit 521 via a fuse 501 and a make contact of a relay 
511. A rectified output from the circuit 521 is supplied to the 
centrifuge-driving motor 306. 
The transformed 100-V power is also supplied to a rotating 
direction-controlling circuit 522 via a fuse 502 and a make contact of a 
relay 512. Similarly, the above 100-V power is supplied to a rotating 
direction-controlling circuit 523 via a fuse 503 and a make contact of a 
relay 523. An output from the circuit 522 is supplied to the 
crucible-moving motor 136, and an output from the circuit 523 is supplied 
to the mold-preheating furnace-elevating motor 406. 
The 100-V power transformed by the transformer 500 is also supplied to the 
electromagnetic chuck 308 in the casting apparatus main body 30 via a fuse 
504 and a make contact of a relay 514. In addition, this power is supplied 
to the crucible temperature indicator 34 in the main body 30 via a fuse 
505. 
The 200-V power supplied from the main switch 21 via a fuse 506 is 
transformed to 24-V power by the transformer 530 and rectified by a 
rectifier circuit 531. A rectified output from the circuit 531 is supplied 
to a sequence control circuit 532. The circuit 532 ON/OFF-controls the 
relays 511 to 514 at predetermined timings. A high-frequency power supply 
540 obtains a high-frequency current of about 27 kHz and several tens to 
several hundreds ampere from the 200-V power supplied from the main switch 
21 and supplies the current to the work coil 113 of the high-frequency 
induction heating furnace 110. 
The 200-V power from the main switch 21 is also supplied to a temperature 
controller 550 for the mold-preheating furnace via a fuse 507. The 
controller 550 receives a temperature information signal S concerning mold 
preheating from a thermocouple 401a provided in the mold-preheating 
furnace 401 and performs temperature control for the furnace 401 on the 
basis of the signal S. The temperature of the furnace 401 is indicated by 
the temperature indicator 35. 
A series of operations of the casting apparatus according to the present 
invention will be described below with reference to a timing chart in FIG. 
21. 
(1) Water is supplied from the cooling unit to the casting apparatus main 
body 30, and the main switch 21 of the power supply/control unit 20 is 
turned on. The upper cover 38 of the main body 30 is opened, and a 
predetermined amount of a glass material as a dental casting material is 
put in the platinum crucible 121. The form of this glass material may be 
any of a rod, a pellet and a powder. 
(2) The mold 211 is housed in the bucket 206 held by the bucket holder 204. 
In order to obtain a good balance, an aluminum cylinder or the like having 
substantially the same weight as the total weight of the mold 211 and the 
glass material is housed in the other bucket 207. 
(3) The rotary shaft 202 of the centrifugal casting section 200 is manually 
pivoted to move the mold 211 in the bucket 206 to a predetermined 
position, i.e., a position in the casting material melting section 100 to 
receive a molten material dropped from the crucible 121. When the mold 211 
is moved to this position, the slits formed in the slit plate 302 are 
detected by the photosensor 303, and an LED (not shown) is flashed. 
Therefore, the arrival of the mold 211 to the predetermined position can 
be checked. 
(4) While the LED is flashing, an electromagnetic chuck biasing switch (not 
shown) is turned on. As a result, the electromagnetic chuck 308 is 
activated to fix a rotational position of the centrifugal rotary shaft 
202. At this time, the LED is set in a continuous ON state. 
(5) The upper cover 38 of the main body 30 is closed, and the start button 
31 is depressed. As a result, all of heating/melting of the glass material 
by the casting material melting section 100, injection of the molten glass 
into the mold 211, casting of the molten glass by the centrifugal casting 
section 200 and the like are automatically performed as will be described 
in detail below. 
(6) That is, as shown in FIG. 21, when the start button 31 is depressed at 
time 0, the crucible-moving motor 136 rotates in a normal direction to 
move the operation shaft 131 straight. Therefore, the crucible 121 is 
inserted in the high-frequency induction heating furnace 110. In this 
case, positioning of the crucible 121 is accurately controlled by a 
photosensor or the like (not shown). At the same time the crucible 121 is 
inserted in the heating furnace 110, a high-frequency induced current is 
supplied to the work coil 113. As a result, heating of the crucible 121 is 
started, and the crucible temperature rises to start melting of the 
casting material in the crucible 121. 
At the same time the start button 131 is depressed, preheating 
furnace-elevating motor 406 rotates in a normal direction, and the 
mold-preheating furnace 401 is moved upward by the support member 405. The 
preheating furnace 401 rises and stops at a position to cover the bucket 
206. This positioning is also accurately controlled by a photosensor or 
the like (not shown). Immediately after positioning, the preheating 
furnace 401 is powered. As a result, the mold 211 is heated together with 
the bucket 206 to start preheating. Therefore, the mold-preheating 
temperature rises. 
(7) The high-frequency induced current is maintained constant for about 
first six minutes and then maintained at a lower value than the above 
value for the next four minutes. Therefore, the temperature of the 
crucible 121 rises to 1,450.degree. C. six minutes after activation and 
then falls to 1,250.degree. C. ten minutes after activation. 
The mold-preheating furnace 401 is set to reach a temperature of 
600.degree. C. in about first six minutes. Therefore, the glass material 
is melted about ten minutes after the start button 31 is depressed, and 
the mold 211 in the bucket 206 is maintained at substantially 600.degree. 
C. 
(8) When 10 minutes has elapsed after the start button 31 is depressed, the 
high-frequency induced current is cut off. At the same time (or 
immediately before) the current is cut off, the crucible 121 containing 
the molten glass is extracted from the high-frequency induction heating 
furnace 110 and tilted by about 90.degree. to 150.degree. at a 
predetermined position, and the molten glass in the crucible 12 is 
naturally dropped accordingly. As shown in FIG. 2, the hole 150 is formed 
in the base plate B1. Therefore, the molten material naturally dropped as 
described above is injected in the mold 211 in the bucket 206 set 
immediately below the hole 150 through the hole 150. The crucible 121 is 
returned to a horizontal state about two seconds after injection. 
(9) At the same time the crucible 121 is returned to the horizontal state, 
the mold-preheating furnace 401 moves downward from the position to heat 
the bucket 206 to a position below the second base plate B2. At the same 
time the furnace 401 falls to the predetermined position, the 
centrifuge-driving motor 306 is released from a locked state by the 
electromagnetic chuck 308 and rotates for a predetermined time T1 (about 
one minute). By a centrifugal force generated upon rotation, the molten 
glass as a casting material is sufficiently cast in the mold 211. 
Thereafter, a chime is sounded, and one sequence of operations is 
finished. 
According to the first embodiment as described above, since the coupling 
flange 125 is formed of a heat-resistant nonconductive ceramic, it is not 
induction-heated by the work coil 113 even if it is located near the 
high-frequency induction heating furnace 110. Therefore, the crucible 
forward/backward rotary driving unit 130 and the like are not adversely 
affected. 
In addition, since the heat-insulating cylindrical member 111, the 
heat-insulating plate 112, and the crucible holding member 122 
constituting the high-frequency induction heating furnace 110 are made of 
an alumina fiber board, these members have a high heat resistance and a 
high heat shock resistance. Therefore, even if a temperature is rapidly 
and repeatedly increased and decreased by induction heating, neither crack 
nor damage are produced. Therefore, a service life of the high-frequency 
induction heating furnace 110 can be prolonged, and the material melting 
crucible 121 can be stably held for a long time period. 
Furthermore, the platinum crucible is used as the material melting crucible 
121, the scald contact side of the platinum-based thermocouple 127 for 
temperature measurement is connected to the outer surface of the crucible 
121 by means of, e.g., scalding at a comparatively low temperature, and 
the other end portion of the thermocouple 127 is fixed to the flange 125 
of the crucible holding member 122 for holding the crucible 121 by machine 
screws and then externally extracted by the extension lead wire 129 of the 
thermocouple. Therefore, temperature measurement can be accurately 
performed following only changes in crucible heating temperature without 
being adversely affected by induction heating. In addition, the 
thermocouple 127 is not twisted upon rotation of the crucible holding unit 
120. 
(2nd Embodiment) 
The second embodiment of the present invention will be described below with 
reference to FIGS. 22 to 29. The second embodiment is the same as the 
above first embodiment except that the mold-preheating furnace 401 and the 
arm positioning electromagnetic chuck 308 are omitted and a detachable 
crucible holding unit and an improved crucible forward/backward rotary 
driving unit are additionally used. 
FIG. 22 is a front view showing an installation state of a dental 
centrifugal casting apparatus according to the second embodiment of the 
present invention. A power supply unit 70 is placed below a casting 
apparatus installation table 60, and a casting apparatus main body 80 is 
placed on the table 60. That is, this apparatus is of a separation type, 
and the two separate parts are connected by cables 91 such as a signal 
line cable, an extension lead wire cable for a platinum thermocouple and a 
motor driving cable, and a high-frequency power supply feeder 92 for 
supplying high-frequency power to a work coil of a high-frequency 
induction heating furnace. A commercial AC power supply cable 93 with a 
plug is connected to the power supply unit 70. 
A main switch 71 and a crucible current temperature indicator 72 are 
mounted on a case upper surface of the unit 70. A temperature adjuster 73 
also serving as a temperature indicator for program-controlling a crucible 
temperature is provided in the unit 70 so that its indication surface is 
exposed on the case front surface. Although not shown, the unit 70 also 
houses a high-frequency power supply unit using an inverter circuit, a 
capacitor for forming a series oscillation circuit with the work coil, a 
matching transformer for obtaining impedance matching, and a sequence 
control circuit for controlling the overall apparatus to perform a 
sequence operation. 
Although not shown, the casting apparatus main body 80 has a water 
supply/drainage port for supplying/draining work coil cooling water at a 
case rear surface side. The water supply/drainage port can be arbitrarily 
connected to a water plug by a flexible hoses. 
An operation panel 81 is provided at the left side of the upper surface of 
the casting apparatus main body 80. The panel 81 includes a "start/cast" 
button 82 having a first function of starting the sequence operation and a 
second function of injecting a molten casting material (glass) into a mold 
and applying a centrifugal force to perform casting, a "stop" button 83 
for interrupting all operations in an emergency, and a "reset" button 84 
for moving a crucible to an initial position. The operation panel 81 also 
includes a temperature pattern indication lamp 85 and an abnormality 
indication lamp 86. The temperature pattern indication lamp 85 indicates a 
temperature pattern of the crucible. The abnormality indication lamp 86 
indicates abnormality when an abnormal excess current flows through the 
power supply unit 70 or the crucible temperature is much higher or lower 
than a programmed temperature. 
A cove 87 is provided at the right side of the case upper surface of the 
main body 80 so as to be freely opened/closed. The cover 87 is open when a 
dental casting material such as glass is set in the crucible, a mold 
preheated outside is set in a bucket, or the mold after casting is 
extracted outside 
FIG. 23 is a side view showing the interior of the casting apparatus main 
body 80, and FIG. 24 is a plan view showing the interior of the main body 
80. 
As shown in FIGS. 23 and 24, a high-frequency induction heating furnace 810 
including a furnace member 811 (constituted by a heat-insulating cylinder 
and a heat-insulating plate as in the first embodiment) is located above a 
partition 800 of the main body 80, and about ten turns of a work coil 813 
consisting of a copper pipe having an outer diameter of .phi. 5 to 6 and 
an inner diameter of .phi. 3 to 4 and covered with an insulating coating 
are wound around the outer circumferential surface of the furnace member 
811. The work coil 813 has an inner diameter of .phi.60 and a length of 60 
mm. Right and left central portions of the coil 813 are brazed with silver 
to the distal ends of L-shaped support metal pieces 812 and 814. The 
proximal ends of the metal pieces 812 and 814 are fixed to a holding plate 
815 consisting of a ceramic material having a high heat resistance by 
bolts 816 and 817. Both the end portions of the coil 813 are extracted to 
the rear side through the holding plate 815. Both the extracted extended 
end portions of the coil 813 are bent downward at a right angle and 
connected to the water supply/drainage port (not shown) via a hose having 
a high insulation property. Although not shown, a check valve is mounted 
on a water supply path of the two extended end portions of the coil 813, 
and a flow meter for measuring a flow rate of a cooling water is mounted 
on a drainage path. Terminals 818 and 819 are brazed with silver to the 
two extended end portions of the coil 813 extracted to the rear side 
through the holding plate 815. The end portion of the feeder 92 is 
connected to the terminal 818 and 819 by machine screws. 
A crucible holding unit 820, an attaching/detaching means 830, a crucible 
forward/backward rotary driving unit 840 and the like are arranged in a 
position opposing the heating furnace 810 located on the partition 800. As 
will be described in detail later, reference numeral 821 denotes a 
crucible; 822, a crucible holding member; 858, a driving motor; and 860, a 
timing belt. 
A centrifuge unit 870 is placed below the partition 800 of the casting 
apparatus main body 80. In the unit 870, a rotational force of a 
centrifuge-driving motor 871 is transmitted to a rotary main shaft 873 by 
a belt 872, and a centrifugal force is applied to a mold and a molten 
material by rotation of the shaft 873, thereby performing casting. 
FIG. 25 is a side view of the crucible holding unit 820, and FIG. 26 is a 
plan view showing only the crucible 821 in the unit 820. 
As shown in FIG. 25, in the crucible holding unit 820, the platinum 
crucible 821 is held by a crucible holding member 822, and a coupling 
flange 825 is provided for the member 822 via a heat-insulating plate 824 
consisting of a heat-insulating material. The unit 820 is detachably 
connected to a coupling flange 845 of the crucible forward/backward rotary 
driving unit 840 (to be described latter) via the attaching/detaching 
means 830. Reference numeral 823 denotes a crucible urging pin made of 
platinum; 826 and 827, crucible holding member mounting machine screws 
made of alumina; 828, a platinum-based thermocouple; and 829, a terminal 
of the thermocouple. Although only one terminal 829 is shown in FIG. 25, 
the terminal 829 is actually a pair of columnar terminals connected to the 
two end portions of the thermocouple 828. The terminals 829 are embedded 
with a predetermined interval therebetween in an eccentric position of the 
right end face (in FIG. 25) of the flange 825 so that one end face of each 
terminal is exposed on the flange surface. 
As shown in FIG. 26, the crucible holding member 822 is constituted by a 
member 822A which consists of, e.g., an alumina fiber having high 
heat-insulating properties, heat resistance and heat shock resistance and 
holds the platinum crucible 821, and a member 822B which consists of, 
e.g., aluminum titanate having high physical strength, heat resistance and 
heat shock resistance and holds the member 822A. A notched portion 822C is 
formed to smoothly perform a molten material injection operation and has 
the same meaning as that of the notched portion 122a in the first 
embodiment. Note that the notched portion 822C is formed by cutting the 
left half of the crucible holding member 822 as shown in FIG. 26. Since 
the notched portion 822C is formed in this manner, a part of the crucible 
holding member 822 does not interfere with a tightening operation of the 
machine screws 827 or the like. Therefore, the tightening operation of the 
machine screws 827 or the like can be smoothly performed. In addition, the 
above shape can be easily manufactured. 
The attaching/detaching means 830 has the following arrangement. A first 
engaging portion 831 consisting of a pulley-like columnar projecting 
portion is formed at the central portion of the right end face (in FIG. 
25) of the coupling flange 825 provided for the crucible holding member 
822. A second engaging portion 832 consisting of a cylindrical recess 
portion to be engaged with the first engaging portion 831 is formed at the 
central portion of the left end face (FIG. 25) of the coupling flange 845 
provided at the distal end of the crucible forward/backward rotary driving 
unit 840. By engaging the first and second engaging portions 831 and 832, 
the unit 820 can be detachably connected to the unit 840. 
A hole 833 is formed in a position far from the central position of the 
right end face (FIG. 25) of the flange 825 of the crucible holding unit 
820. A projection 834 to be fitted in the hole 833 is formed in a position 
far from the central position of the left end face (FIG. 25) of the flange 
845 of the crucible forward/backward rotary driving unit 840. By fitting 
the projection 834 in the hole 833, positioning in the rotational 
direction of the units 820 and 840 is performed. A pair of pin terminals 
835 (although only one terminal is shown in FIG. 25) are formed in a 
position opposing the pair of embedded terminals 829 in the left end face 
(FIG. 25) of the flange 845. Each terminal 835 is inserted in a 
corresponding one of a pair of terminal holding holes 845a so as to 
project from the surface of the flange 845 or to be pushed below the 
surface within a predetermined depth range. A pair of coil springs 845b is 
placed in a compression state between the proximal end portion of each pin 
terminal 835 and the bottom portion of a corresponding one of the hole 
845a. Each terminal 835 is normally biased by the each of spring 845b to 
project from the surface of the flange 845 by a predetermined length. When 
the flanges 825 and 845 engage with each other, the distal end portion of 
each terminal 835 is pressed by the exposed surface of a corresponding one 
of the pair of embedded terminals 829 and pushed inside the each hole 
845a. The terminals 835 are pushed while compressing the coil springs 
845b. Therefore, the distal end portion of the pin terminals 835 and the 
exposed surface of the embedded terminals 829 are brought into contact 
with each other by a high pressure. As a result, the pair of terminals 829 
and the pair of terminals 835 are electrically connected to each other. 
The pin terminals 835 are connected to end portions of a pair of extension 
lead wires 836 guided from the rear surface side of the coupling flange 
845. 
A locking means is provided between the first and second engaging portions 
831 and 832 to prevent the first engaging portion 831 from being 
disengaged from the second engaging portion 832. This locking means is 
constituted by a V-shaped annular groove 831a formed in the outer 
circumferential surface of the first engaging portion 831 consisting of 
the columnar projecting portion at the flange 825 side, and a locking 
screw 837 having a distal end portion facing the inner circumferential 
surface of the second engaging portion 832 consisting of the cylindrical 
recess portion at the flange 845 side. The screw 837 is threadably engaged 
with the flange 845 so a to be freely inserted in/removed from the flange 
845. That is, the distal end of the screw 837 of the locking means is 
inserted in the groove 831a of the first engaging portion 831 engaged with 
the second engaging portion 832 to prevent the first engaging portion 831 
from being disengaged from the second engaging portion 832. 
Note that a platinum alloy-based crucible which can be repeatedly used is 
used as the crucible 821 and prepared for each crucible holding unit 820. 
In this manner, the entire crucible holding unit 820 can be arbitrarily 
attached to/detached from the crucible forward/backward rotary driving 
unit 840 while the crucible 821 is held. Therefore, when the crucible 821 
must be replaced with another to perform casting in order to use a casting 
material of another type, the locking screw 837 is loosened to remove the 
currently used crucible holding unit 820 from the driving unit 840. 
Thereafter, another crucible holding unit 820 holding a predetermined 
crucible prepared beforehand is mounted on the driving unit 840 by 
tightening the screw 837. That is, the first engaging portion 831 is 
engaged with the second engaging portion 832, and the screw 837 is 
tightened. As a result, the distal end of the screw 837 is inserted in the 
V-shaped groove formed in the outer circumferential surface of the 
columnar projecting portion. Therefore, removal of the first engaging 
portion 831 can be prevented. 
Since the crucible holding unit 820 can be simply attached/detached to/from 
the crucible forward/backward rotary driving unit 840, a material having a 
different glass composition or glass having a different content of a 
coloring agent can be used as a casting material by simply replacing the 
unit 820. Therefore, working efficiency of a dental technician can be 
increased. 
Note that an operation may be simplified by using, instead of the locking 
screw 837, a locking pin mechanism (not shown) comprising a locking pin 
and a coil spring for constantly biasing the locking pin to displace it in 
an axial direction. 
FIGS. 27 and 28 are exploded perspective views showing an arrangement of 
the crucible forward/backward rotary driving unit 840. 
Referring to FIG. 27, reference numeral 841 denotes a columnar operation 
shaft. The coupling flange 845 is fitted on and fixed to one end of the 
shaft 841. A pin screw hole 842 is formed in the outer circumferential 
surface close to the other end of the shaft 841. A guide pin 843 is 
threadably engaged with the hole 842 via a groove formed in the 
circumferential wall of a guide cylinder and a driving cylinder (to be 
described later). In order to reduce a sliding friction between the guide 
pin 843 and the groove, a pair of rollers 844a and 844b and a spacer 844c 
are fitted on the pin 843. 
The guide cylinder 846 has a shaft hole 847 for slidably and pivotally 
holding the operation shaft 841 along its axis. A first guide groove 848a 
for guiding the pin 843 in a direction parallel to the axis of the 
cylinder 846 and a second guide groove 848b continuous with the first 
guide groove 848a, for guiding the pin 843 about the axis of the cylinder 
846 are formed in the circumferential wall of the cylinder 846. The two 
ends of the guide cylinder 846 are sandwiched between support plates 849 
and 850. The two end faces of the guide cylinder 846 and the plates 849 
and 850 are fixed by a plurality of machine screws 851 to 854. 
A driving cylinder 855 is rotatably fitted on the outer circumferential 
surface of the guide cylinder 846. A spiral groove 856 to be engaged with 
the guide pin 843 is formed in the circumferential wall of the driving 
cylinder 855. A gear portion 857 is formed on the outer circumferential 
surface at one end of the cylinder 855. 
FIG. 28 is a perspective view showing a coupling relationship between the 
driving cylinder 855 and driving control system located near one end of 
the cylinder 855. The driving control system has the following 
arrangement. That is, a timing belt 860 is looped between a driving gear 
859 mounted on a shaft of a driving motor 858 rotatable in both normal and 
reverse directions and the gear portion 857 of the driving cylinder 855. 
An arcuated index piece 864 is mounted on one end face of the cylinder 
855. The index piece 864 can pass through gap portions formed in three 
photointerrupters 861, 862 and 863. The photointerrupters 861, 862 and 863 
sense passing of the index piece 864, thereby sensing a pivoting angle of 
the driving cylinder 855. The driving motor 858 is controlled on the basis 
of information obtained by this sensing, thereby positioning the operation 
shaft 841. 
When the driving motor 858 is rotated in a normal direction, this 
rotational force is transmitted to the driving cylinder 855 by the timing 
belt 860. Therefore, the cylinder 855 is rotated in a normal direction 
indicated by an arrow in FIG. 27. Therefore, the spiral groove 856 applies 
a moving force toward the upper left side in FIG. 27 to the guide pin 843. 
The movement of the pin 843 is limited such that the pin 843 can move only 
long the guide grooves 848a and 848b of the guide cylinder 846. Therefore, 
when the moving force is applied, the pin 843 located at a point b 
circumferentially moves (toward the upper side in FIG. 27) along the 
second guide groove 848b to a connection point c between the first and 
second guide grooves 848a and 848b. The pin 843 then moves along the axial 
direction (toward the left side in FIG. 27) along the first guide groove 
848a to a point a. 
When the driving motor 858 is rotated in a reverse direction, the above 
operation is performed in a reverse direction. As a result, the guide pin 
843 moves from the point a in the axial direction along the first guide 
groove 848a to the connection point c. The pin 843 then circumferentially 
moves along the second guide groove 848b to a point b. 
The above movement of the pin 843 directly represents those of the 
operation shaft 841 and the crucible 821. That is, when the guide pin 843 
is located at the point c, the crucible 821 is in its initial position. 
When the pin 843 moves to the point a, the crucible 821 moves forward to a 
melting position in the furnace member 811. In this state, when the pin 
843 moves to the point b via the point c, the crucible 821 is extracted to 
a predetermined position outside the furnace member and pivoted through 
about 120.degree., thereby injecting a molten material into a mold. 
Positioning of the above three points a, b and c is performed by the 
sensing operation by the index piece 864 and the photointerrupters 861 to 
863. 
FIG. 29 is a perspective view showing only a main part of the casting 
apparatus main body 80. As shown in FIG. 29, the centrifuge unit 870 has a 
pair of arms 874a and 874b perpendicular to the axis of a rotary spindle 
873. A mold holding bucket 876a (876b) is swingably mounted on the distal 
end of the arm 874a (874b) via a bucket holder 875a (875b) consisting of a 
U-shaped frame. The bucket 876a (876b) has the same structure as shown in 
FIG. 12. A mold (not shown) is held by the bucket 876a (876b). A knob 878 
is connected to the upper end portion of the rotary spindle 873 via a 
shaft 877. 
Upon injection of a molten metal, a molten metal in the crucible 821 is 
injected into a mold (not shown) held in each bucket positioned by the 
knob 878 through a through hole 801 formed in the partition 800. 
Subsequently, the shaft 873 is rotated to rotate the buckets 876a and 
876b. As a result, a centrifugal force is applied to the mold and the 
molten metal in each of the buckets 876a and 876b, thereby casting the 
molten material. 
An overall operation of the second embodiment will be described below. 
First, cooling water is flowed. The main switch of the power supply unit 
70 is turned on. The cover 87 of the casting apparatus main body 80 is 
opened. A dental casting material such as a glass material is put into the 
crucible 821. The cover 87 is closed. The "start/cast" button 82 is 
depressed. As a result, the crucible 821 is inserted in the furnace member 
811. The high-frequency power supply is switched on, and a high-frequency 
current is flowed to the work coil 813 via the feeder 92. The temperature 
of the platinum crucible 821 rises to 1,450.degree. C. in about 5 to 10 
minutes, and the material is melted. Thereafter, when the temperature is 
decreased to 1,250.degree. C., a buzzer is sounded to alarm that a standby 
state capable of casting is set. 
In order to obtain a predetermined set crucible temperature, the 
high-frequency current to be supplied to the work coil 813 is 
program-controlled by the temperature adjuster 73. An actual crucible 
temperature is measured by the platinum-based thermocouple 828. 
Information about the measured temperature is fed back to the temperature 
adjuster 73. 
The cover 87 is opened, and a mold preheated up to 600.degree. C. is placed 
in one of the buckets, e.g., the bucket 876b. An aluminum balancer having 
the same weight as the mold is placed in the other bucket 876a. The knob 
878 is rotated to position the mold immediately below the hole 801 of the 
partition 800. This positioning is performed by a sensing operation by a 
sensor (not shown) having the same arrangement as the index piece 864 and 
the interrupters 861 to 863. The cover 87 is closed. The "start/cast" 
button 82 is depressed again. As a result, the crucible 821 is extracted 
from the furnace member 811 and pivoted through 120.degree. above the 
through hole 801. Therefore, the molten material is injected into the 
mold. The crucible 821 is returned to the initial state in about two 
seconds. At the same time, the centrifuge-driving motor 871 is turned on 
to rotate the rotary spindle 873 at high speed, thereby performing an 
centrifugal operation for about one minute. The molten material is cast 
inside the mold by a centrifugal force generated by the centrifugal 
operation. Thereafter, when the buzzer is sounded, the cover 87 is opened 
to extract the mold after casting. 
According to the above embodiment, a series of processes of, e.g., 
heating/melting of a material, injection of the material into a mold, and 
rotation and stop of the centrifuge unit 870 can be substantially 
automatically performed. Therefore, even an unskilled operator can easily 
operate the casting apparatus to perform casting. 
Since the high-frequency induced heating furnace 810 is used as a 
heating/melting means, the casting material can be heated/melted with high 
efficiency, and the apparatus can be made compact. 
The apparatus is arranged such that the centrifuge unit 870 rotates at high 
speed at the same time the heated/melted material is dropped into the 
mold. Therefore, the casting operation can be finished before 
cooling/solidification of the casting material progresses. 
In addition, the position of the mold changes together with the bucket 876a 
or 876b in accordance with rotation of the centrifuge unit 870. Therefore, 
the molten material can be protected from being overflown from the mold 
due to a shock upon start of rotation of the centrifuge unit or a 
centrifugal force during a high-speed rotation. 
Additional advantages and modifications will readily occur to those skilled 
in the art. Therefore, the invention in its broader aspects is not limited 
to the specific details, and representative devices, shown and described 
herein. Accordingly, various modifications may be made without departing 
from the spirit or scope of the general inventive concept as defined by 
the appended claims and their equivalents.