Information
-
Patent Grant
-
6637496
-
Patent Number
6,637,496
-
Date Filed
Friday, November 30, 200122 years ago
-
Date Issued
Tuesday, October 28, 200320 years ago
-
Inventors
-
Original Assignees
-
Examiners
- Elve; M. Alexandra
- Kerns; Kevin P.
Agents
- MacMillan, Sobanski & Todd, LLC
-
CPC
-
US Classifications
Field of Search
US
- 164 133
- 164 134
- 164 135
- 164 136
- 164 335
- 164 336
- 164 337
- 164 129
- 164 130
- 164 322
- 164 323
- 164 324
- 164 325
- 164 326
- 164 329
- 164 119
- 164 306
-
International Classifications
- B22D1804
- B22D502
- B22D3900
-
Abstract
Apparatus for making a cast article includes a rotary table with a drive for indexing the rotary table to a plurality of rotational positions. A molten metal supply apparatus is placed at a first fixed location adjacent to said rotary table. A plurality of casting machines are supported at predetermined spacings on the rotary table, each respective casting machine having a respective holding furnace feeding a respective stalk tube and having a molten metal inlet port for receiving molten metal from the molten metal supply apparatus when the respective casting machine is indexed to a fill position adjacent the first fixed location. Each respective casting machine is adapted to receive one or more molds and has an open mold configuration and a closed mold configuration. A cast article removal apparatus is placed at a second fixed location adjacent the rotary table for removing the cast article from a respective casting machine when the respective casting machine is at an unload position adjacent the second fixed location and is in the open mold configuration.
Description
BACKGROUND OF THE INVENTION
The present invention relates, in general, to the layout and use of a plurality of low-pressure permanent mold (LPPM) casting machines, and more specifically to deployment of modified LPPM casting machines on a rotary table.
It is known to use a low pressure countergravity casting apparatus to cast molten metal into a mold. One example of such an apparatus is described in U.S. Pat. No. 5,215,141, which is incorporated herein by reference. Basically, in a low pressure countergravity casting apparatus, metal (e.g., aluminum) is melted in a melt furnace and then supplied to a holding furnace. The holding furnace includes a supply conduit for introducing a gas under pressure into the holding furnace. As the gas is introduced, the molten metal is forced through a submerged feed tube into the mold. The feed tube is commonly referred to as a stalk tube. The mold receives the molten metal through holes in the bottom of the mold.
The holding furnace located beneath the mold in a prior art LPPM casting machine has been constructed to operate in a fixed location near a supply of molten metal. A human operator monitors machine operation, such as removing cast parts and operating molten metal refill equipment. Due to the structure and operation of prior art LPPM machines, one human operator could tend at most two or perhaps three machines simultaneously. It would be desirable to reduce the manufacturing floor space required for LPPM machines and to reduce the need for human operators.
SUMMARY OF THE INVENTION
The present invention has the advantage of successfully molding articles in low pressure permanent mold casting machines while reducing floor space, capital expense, and labor costs.
In one preferred aspect of the invention, apparatus for making a cast article comprises a rotary table with a drive for indexing the rotary table to a plurality of rotational positions. Molten metal supply apparatus is placed at a first fixed location adjacent to said rotary table. A plurality of casting machines are supported at predetermined spacings on the rotary table, each respective casting machine having a respective holding furnace feeding a respective stalk tube and having a molten metal inlet port for receiving molten metal from the molten metal supply apparatus when the respective casting machine is indexed to a fill position adjacent the first fixed location. Each respective casting machine is adapted to receive a mold and having an open mold configuration and a closed mold configuration. A cast article removal apparatus is placed at a second fixed location adjacent the rotary table for removing the cast article from a respective casting machine when the respective casting machine is at an unload position adjacent the second fixed location and is in the open mold configuration.
Further advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1
is a front elevational view of a low pressure permanent mold casting machine used in the present invention.
FIG. 2
is a partially cross-sectioned side view of a holding furnace of the casting machine of FIG.
1
.
FIG. 3
is a plan view of a rotary casting system according to the invention.
FIG. 4
is an elevational view of the rotary casting system of FIG.
3
.
FIG. 5
is cross-sectional view of a holding furnace showing a side wall and a level sensor.
FIG. 6
is a plan view of two rotary casting systems integrated side by side for additional efficiency.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
FIGS. 1 and 2
illustrate a low pressure permanent mold casting machine
10
. The general structure and operation of such casting machines are conventional in the art. Thus, only those portions of the casting machine
10
which are necessary for a full understanding of this invention will be explained and illustrated in detail. The preferred embodiment of deploying casting machine
10
in the rotary casting system is illustrated in
FIGS. 3
,
4
and
6
.
Referring now to
FIG. 1
, casting machine
10
includes a frame with lower portion
11
and an upper portion
12
. Lower portion
11
is operative to support a machine holding furnace
14
and a mold bottom section
13
. Upper portion
12
is operative to support a mold top section
15
. One or more molds can be fitted into the machine at any one time. The casting machine frame registers a fixed location of casting machine
10
on the rotary table, as will be described below. Casting machine
10
is shown in
FIG. 1
is in an open mold configuration which allows for removal of a finished cast article and for inspection of the mold or molds prior to the next casting cycle. Casting machine
10
also has a closed mold configuration as shown in dashed lines.
A sliding frame portion
16
includes a cylindrical sleeve
17
for guiding frame portion
16
between raised and lowered positions and clamps
18
that can be engaged to hold frame portion
16
in one position. Linear drive means
19
can be controlled automatically or manually to obtain the open and closed mold configurations.
Holding furnace
14
is shown in greater detail in
FIG. 2. A
chamber or crucible
20
retains a supply of molten metal
21
. Heat to maintain the liquid state of molten metal
21
can be provided, for example by a gas-fired radiant heat tube
22
supplied with natural gas via an inlet
23
. An outlet for exhaust is not shown. Other means of heating such as electric radiant heaters or electric immersion heaters can also be employed. Crucible
20
is insulated by a refractory liner
25
.
Stalk tubes
24
penetrate near the bottom of crucible
20
and extend upwards to feed molten metal to the mold or molds. Pressurized gas is introduced into crucible
20
above molten metal
21
to force molten metal into stalk tubes
24
by a pump and gas injection valve (not shown).
Refills of molten metal are provided to holding furnace
14
through a metal fill port
26
. Optionally, the molten metal newly transferred into holding furnace
14
may pass through a filter
27
for removing impurities as is known in the art. Fill port
26
preferably includes a closing device (not shown) to facilitate pressurization of crucible
20
.
Holding furnace
14
can be provided with wheel assemblies
28
to facilitate removal of holding furnace
14
from the casting machine frame (i.e., off of the rotary table) for maintenance.
Referring now to
FIGS. 3
,
4
and
6
, a plurality of casting machines
10
are mounted on a rotary table
30
. Rotary table
30
includes structural support beams
31
to reduce deflection. A table drive
32
provides motive power for indexing rotary table
30
to predetermined rotational positions. Programmable system controllers
33
are coupled to drive
32
and coordinate its movement. Controllers
33
are mounted in a raised control station
34
preferably located at the center of rotary table
30
and accessible by a ladder
35
. Controllers
33
regulate operation of the molds and operation of the holding furnaces. Control station
34
may also include gas couplings, air couplings, electrical couplings, electric motors, and pumps to support operation of the rotary casting system. Rotary table
30
and table drive
32
are preferably positioned in a pit
38
below a work floor
36
such that rotary table
30
is about flush with work floor
36
.
The illustrated rotary casting system includes six casting machines
10
on one rotary table
30
, although the rotary casting system may include any suitable number of casting machines. The casting machines are supported at predetermined spacings and are preferably equally spaced at a predetermined interval (e.g., having their centers spaced at 60° intervals for six casting machines on a table).
Table drive
32
can comprise a hydrostatic drive or any other suitable power means. Rotary table
30
rotates in a direction illustrated by an arrow
37
. Casting machines
10
revolve in the direction of arrow
37
and may be brought into any predetermined rotational position.
A molten metal supply apparatus
40
is located at a first fixed location adjacent to rotary table
30
. Metal supply apparatus
40
delivers a selected volume of molten metal to holding furnace
14
through metal fill port
26
of a casting machine
10
that has been indexed to a fill position aligned with metal supply apparatus
40
. In a preferred embodiment, metal supply apparatus
40
is retractable and may move in a trajectory to a fill position shown at
41
. As shown in
FIG. 6
, molten metal supply apparatus obtains molten metal from a melt furnace
42
and a hold furnace
43
, both of which are stationary. A de-gasser
44
may be interposed between furnaces
42
and
43
.
A cast article removal apparatus
45
is located at a second fixed location adjacent to rotary table
30
. Removal apparatus
45
is preferably comprised of a robotic arm for lifting a finished cast article out of a mold when a casting machine
10
is in its open mold configuration and has been indexed to an unload position aligned with removal apparatus
45
. The robotic arm or other casting unloading device swings through a controlled trajectory to a position shown at
47
to deliver the finished casting to a transport (e.g., a conveyor belt
46
as shown in FIG.
6
). Removal apparatus
45
may also present the finished casting (such as a cast aluminum wheel for a motor vehicle) to a human operator at an inspection position, such as is indicated generally at
48
. Inspection position
48
allows inspection of a cast article
50
prior to delivery to conveyor
46
. Inspection may be done by any suitable means, including visual, manual, scanning, or the like. Inspection position
48
is also conveniently located to permit inspection of an open mold from which cast article
50
was just removed so that if any debris remains in the mold, it can be removed prior to the next use of the mold.
In a preferred embodiment the fill position of a casting machine is coincident with the unload position so that the filling of molten metal and the removal of a cast article can occur simultaneously and at the same position of rotary table
30
.
In operation, rotary table
30
positions each casting machine
10
in turn into alignment with molten metal supply apparatus
40
and cast article removal apparatus
45
. After filling of the holding furnace and removal of the cast article, rotary table
30
is indexed to the position where the next casting machine
10
is in the fill/unload position. The first casting machine which has now moved on, moves into its closed mold configuration and pressurized gas is introduced to force molten metal into the closed mold. The mold is then cooled as rotary table is further indexed until the first casting machine returns to the fill/unload position and the cast article has hardened for removal from the mold. The molds preferably include integral cooling passages for receiving a cooling fluid under control of cooling controllers
51
. The entire process is preferably engineered so that the time of one full revolution of table
30
is sufficient for solidification of the article.
More specifically, an operational sequence for making a cast article is as follows. Molten metal is transferred into a first holding furnace of a first casting machine with the rotary table positioned such that the first casting machine is in the fill position. As used herein, the transfer of molten metal can be obtained by pressure filling, pouring, or injection, for example. The rotary table is indexed such that a second casting machine is in the fill position. Molten metal is transferred into a second holding furnace of the second casting machine. The first casting machine is closed to the closed mold configuration. The first holding furnace is pressurized to fill the mold with molten metal. The rotary table is further indexed and molten metal is transferred into a least one more casting machine mounted on the rotary table. The second casting machine is closed to the closed mold configuration. The second holding furnace is pressurized to fill the second mold with molten metal. The molds cool in the first and second casting machines during filling of other casting machines with molten metal. The first casting machine is opened to the open mold configuration either before or after the first casting machine is indexed to the unload position. A cast article is removed from the first casting machine. Molten metal is transferred into the first holding furnace of the first casting machine. The second casting machine is indexed to the unload position. A cast article is removed from the second casting machine. Molten metal is transferred into the second holding furnace of the second casting machine. The first casting machine is closed to the closed mold configuration. The first holding furnace is pressurized to fill the mold with molten metal for the next cast article.
Depending upon the capacity of a holding furnace in a casting machine, it may not be necessary to refill it after each cast article produced. However, it is preferable to refill each time since a greater depth of molten metal helps ensure the least amount of gas or impurities in the metal moving up through the stalk tubes. Furthermore, it can be advantageous to reduce the overall size, weight, and capacity of the holding furnaces to reduce the cost of the rotary table.
To maintain an optimum level of molten metal in a holding furnace, a level sensor
53
is provided within the furnace in contact with molten metal
21
as shown in FIG.
5
. Level sensor
53
may be comprised of a known electrical probe, for example. A level signal is provided to molten metal supply apparatus
40
to control the amount of molten metal being charged into the respective holding furnace in order to maintain a full crucible.
Due to rotation of rotary table
30
, molten metal
21
may slosh up the sides of crucible
20
. Cooling of the metal could occur as it contacts the crucible side walls above the nominal level of the molten metal. A freeze-out
52
of metal might thus occur. To prevent freeze-out, a freeze-out prevention means
55
is provided in a side wall
56
. Prevention means
55
can comprise a heat-conductive layer for keeping sloshing metal at the same temperature as the main body of molten metal, for example. Special shaping of the side walls or deflectors may also be employed. To reduce sloshing of molten metal both in the furnace and in a filled mold, other measures are also preferably taken. These measures include 1) designing table acceleration and deceleration profiles during indexing to minimize the amount of slosh, and 2) controlling the molten metal fill process for the mold(s) using a proportional fill method as described in copending application U.S. Ser. No. 10/045,659, entitled “Method for Filling a Casting Apparatus”, which is incorporated herein by reference.
One or more optional workstations or change-out stations
57
may be placed around the periphery of rotary table
30
. Change-out stations
57
are employed to permit changing of tools, perform casting machine maintenance (e.g., removing a holding furnace for cleaning), or perform additional manufacturing operations on the cast articles while in an open mold configuration.
FIG. 6
shows a second rotary casting system, in dotted lines, which is substantially identical to the first rotary casting system. The two rotary casting systems share melt furnace
42
, hold furnace
43
, and conveyor belt
46
to optimize manufacturing productivity.
The principle and mode of operation of this invention have been described in its preferred embodiments. However, it should be noted that this invention may be practiced otherwise than as specifically illustrated and described without departing from its scope.
Claims
- 1. Apparatus for making a cast article comprising:a rotary table with a drive for indexing said rotary table to a plurality of rotational positions; molten metal supply apparatus at a first fixed location adjacent to said rotary table; a plurality of casting machines supported at predetermined spacings on said rotary table, each respective casting machine having a respective holding furnace feeding at least one respective stalk tube and having a molten metal inlet port for receiving molten metal from said molten metal supply apparatus when said respective casting machine is indexed to a fill position adjacent said first fixed location, each respective casting machine further adapted to receive at least one mold and having an open mold configuration and a closed mold configuration; and a cast article removal apparatus at a second fixed location adjacent said rotary table for removing said cast article from a respective casting machine when said respective casting machine is at an unload position adjacent said second fixed location and is in said open mold configuration; wherein said fill position and said unload position are coincident such that a respective casting machine is refilled with molten while a completed cast article formed prior to reaching said unload position is removed from said respective casting machine.
- 2. The apparatus of claim 1 wherein each of said casting machines closes to its closed mold configuration and dispenses molten metal from its respective holding furnace through its respective stalk tube and then cools a resulting cast article while said respective casting machine indexes away from said fill position.
- 3. The apparatus of claim 1 wherein said holding furnace is refilled for each cast article made.
- 4. The apparatus of claim 1 further comprising: a change-out station at a third fixed location adjacent said rotary table, said change-out station including a maintenance apparatus for servicing said casting machines.5.The apparatus of claim 1 wherein each of said casting machines further comprises a respective level sensor for sensing a molten metal level in each respective holding furnace, and wherein said casting machines communicate said sensed molten metal levels to said molten metal supply apparatus, said molten metal supply apparatus adjusting a molten metal pour to each respective holding furnace in response to said respective sensed molten metal level.
- 6. The apparatus of claim 1 wherein each of said holding furnaces further comprises side walls and freeze-out prevention means for avoiding buildup of solidified metal on said side walls.
- 7. A method of making cast articles in pressurized casting machines mounted on a rotary table at predetermined spacings, wherein said rotary table includes a drive for indexing to a plurality of rotational positions, wherein a molten metal supply apparatus is at a first fixed location adjacent to said rotary table, wherein each respective casting machine has a respective holding furnace feeding a respective stalk tube and having a molten metal inlet port for receiving molten metal from said molten metal supply apparatus when said respective casting machine is indexed to a fill position adjacent said first fixed location, wherein each respective casting machine is adapted to receive at least one mold and having an open mold configuration and a closed mold configuration, and wherein a cast article removal apparatus is at a second fixed location adjacent said rotary table for removing said cast article from a respective casting machine when said respective casting machine is at an unload position adjacent said second fixed location and is in said open mold configuration, said method comprising the steps of:(a) transferring molten metal into a first holding furnace of a first casting machine with said rotary table such that said first casting machine is in said fill position; (b) indexing said rotary table such that a second casting machine is in said fill position; (c) transferring molten metal into a second holding furnace of said second casting machine; (d) closing said first casting machine to said closed mold configuration; (e) pressurizing said first holding furnace to fill said mold with molten metal; (f) indexing said rotary table and transferring molten metal into at least one more casting machine mounted on said rotary table; (g) closing said second casting machine to said closed mold configuration; (h) pressurizing said second holding furnace to fill said second mold with molten metal; (i) cooling said molds in said first and second casting machines during filling of other casting machines with molten metal; (j) opening said first casting machine to said open mold configuration; (k) indexing said first casting machine to said unload position; (l) removing a cast article from said first casting machine; (m) transferring molten metal into said first holding furnace of said first casting machine; (n) indexing said second casting machine to said unload position; (o) removing a cast article from said second casting machine; (p) transferring molten metal into said second holding furnace of said second casting machine; (q) closing said first casting machine to said closed mold configuration; and (r) pressurizing said first holding furnace to fill said mold with molten metal.
- 8. The method of claim 7 further comprising the steps of:(s) sensing a molten metal level in said first holding furnace; (t) communicating said sensed molten metal level to said molten metal supply apparatus; and (u) adjusting an amount of molten metal to be transferred into said first holding furnace.
- 9. The method of claim 7 wherein said fill positions in steps (a) and (b) and said unload positions in steps (k) and (n) are coincident.
US Referenced Citations (4)
Foreign Referenced Citations (2)
Number |
Date |
Country |
34 22 121 |
Dec 1985 |
DE |
57-64466 |
Apr 1982 |
JP |