Note: Descriptions are shown in the official language in which they were submitted.
CA 02592792 2007-07-23
A SYSTEM FOR PROVIDING CONSISTENT FLOW THROUGH MULTIPLE
PERMEABLE PERIMETER WALLS IN A CASTING MOLD
This is a divisional application of Canadian Patent Application No.
2,295,839 filed July 9, 1998.
Technical Field
s This invention pertains to a system for providing consistent lubricant
and/or gas flow through multiple permeable perimeter walls in a metal casting
mold table.
Backeround Art
Metal ingots and billets are typically formed by a casting process, which
io utilizes a vertically oriented mold situated above a large casting pit
beneath
the floor level of the metal casting facility. The lower component of the
vertical casting mold is a starting block mounted on starting block pedestals.
When the casting process begins, the starting blocks are in their upward-most
position and in the molds. As molten non-ferrous metal is poured into the
15 mold and cooled, the starting block is slowly lowered at a pre-determined
rate by a hydraulic cylinder or other device. As the starting block is
lowered,
solidified non-ferrous metal or aluminum emerges from the bottom of the
mold and ingots or billets are formed.
While the invention applies to casting of metals in general, including
20 without limitations aluminum, brass, lead, zinc, magnesium, copper, steel,
etc.,
the examples given and preferred embodiment disclosed are for aluminum,
and therefore the term aluminum will be used throughout for consistency
even though the invention applies more generally to metals.
There are numerous mold and pour technologies that fit into these
25 mold tables. Some are generally referred to as "hot top" technology, while
others are more conventional casting technologies that use floats and
downspouts, both of which are known to those of ordinary skill in the art.
The hot top technology generally includes a refractory system and molten
metal trough system located on top of the mold table, whereas the
3o conventional pour technology involves suspending or supporting the source
of
molten metal above the mold table and the utilization of down spouts or
CA 02592792 2007-07-23
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tubes and floats to maintain the level of molten metal in the molds while
also providing molten metal to the molds.
These different casting technologies have different advantages and
disadvantages and produce various billet qualities, but no one of which is
required to practice this invention.
The metal distribution system is also an important part of the casting
system. In the two technology examples given, the hot top distribution
trough sits atop the mold table while the conventional pouring trough is
suspended above the mold table to distribute the molten metal to the molds.
Mold tables come in all sizes and configurations because there are
numerous and differently sized and configured casting pits over which mold
table are placed. The needs and requirements for a mold table to fit a
particular application therefore depends on numerous factors, some of which
include the dimensions of the casting pit, the location(s) of the sources of
!s water and the practices of the entity operating the pit.
The upper side of the typical mold table operatively connects to, or
interacts with, the metal distribution system. The typical mold table also
operatively connects to the molds which it houses.
The use of a permeable or porous perimeter wall has proven to be an
2o effective and efficient way to distribute lubricant and gas to the inside
surface
of a continuous casting mold, such as is described in U.S. Patent No.
4,598,763 to Wagstaff.
In the typical use of a permeable perimeter wall, lubricant and gas are
delivered to the perimeter wall under pressure through grooves or delivery
25 conduits around the perimeter wall, typically using one delivery conduit
(if
grooves are used for the delivery of lubricant) and one or two delivery
conduits (grooves) for the delivery of gas. The preferred lubricants are
synthetic oils, whereas the current preferred gas is air. The lubricant and
gas
then permeate through the perimeter wall and are delivered to the interior
30 of the mold as part of the casting process.
The perimeter walls on existing mold tables each have delivery conduits
to deliver the lubricant and/or gas, and the delivery conduits may be
CA 02592792 2007-07-23
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circumferential groove-shaped delivery conduits with the same depth and
width, or they may be holes partially drilled through the perimeter walls, or
any other delivery means for that matter. The typical perimeter wall has a
separate lubricant delivery conduit and a gas conduit.
s Graphite has proven to be the preferred permeable material for use
as the perimeter wall material or media. However, graphite has proven to
be expensive in consistently producing high quality individual products which
have very similar permeability to other graphite perimeter walls.
One of the significant factors causing the high cost incurred in
jo providing consistent permeability or lubricant/gas flow rates through the
perimeter walls is the variability in the relevant properties of the perimeter
wall material. The properties related to the lubricant and gas flow rates can
vary significantly from batch to batch of graphite for instance, and even
within the same batch and within a given perimeter wall. Variations in
is properties such as porosity, permeability and density, impact the rate of
delivery of lubricant and or gas through the perimeter wall. Furthermore, the
viscosity of a particular lubricant or gas as well as the pressure at which
the
lubricant or gas is supplied to the perimeter wall, are factors affecting the
respective flow rates through the permeable perimeter walls.
20 Experience has taught that graphite from a particular supplier or
source will tend to have more similar properties than graphite from two
different sources or suppliers, however, there may still be unacceptable
variations in the properties of the graphite from a single source and even
from a single batch. This is the case even though a particular density is
25 typically specified when ordering.
In a typical application, one perimeter wall is used for each mold, and
there are typically numerous molds on a single mold table, each mold having
a perimeter wall. It is preferred to supply gas from one source line at one
pressure and to supply lubricant from one source line at one pressure, to all
30 perimeter walls in molds of a particular mold table.
The variations of most concern in the lubricant and/or gas flow rates
through the graphite are therefore based on the variability in the properties
CA 02592792 2007-07-23
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of the graphite related to the respective flow rates, which becomes the
critical
factor in accomplishing the goal of the equal or predictable flow rates of
lubricant and gas through the perimeter walls in each of the molds on the
same mold table, or even in the same manufacturing facility.
s Prior to this invention, achieving the same flow rate or delivery rate
of lubricant and/or gas flow through multiple perimeter walls on the same
mold table, was very time consuming and expensive, and resulted in
significant waste. Each individual perimeter wall was extensively tested to
determine its properties relevant to flow rate and an unnecessarily large
ro percentage were rejected due to the flow rate variations.
With numerous molds on the same table simultaneously casting metal,
it becomes critical to achieving a reliable process for producing high quality
molded products (billet, ingot or special shapes) that the lubricant and/or
gas
delivered to the perimeter walls during casting is very closely the same from
15 perimeter wall to perimeter wall in the same mold table.
In order to achieve consistent lubricant and/or gas flow rates through
the perimeter walls in each of the molds in a given mold table, a high rate
of rejection of graphite rings has been experienced. Typically, graphite
perimeter walls with similar properties may be grouped together to achieve
zo closely similar lubricant and/or gas flow rates. However, while grouping
perimeter walls together may work for new construction, managing the
selective replacement of perimeter walls in place in a facility can be very
difficult.
From a practical and expense perspective, lubricant and/or gas are
25 supplied at a constant pressure, and the perimeter walls are manufactured
at
a constant or fixed thickness and general size to fit within the molds. The
inner and outer diameters of the perimeter walls, as well as their overall
height also is generally fixed.
It is an objective of this invention to achieve a sufficiently consistent
3o lubricant and/or gas flow rate through multiple perimeter walls on a mold
table or in a casting facility, even though the perimeter walls generally have
CA 02592792 2007-07-23
variations in their individual properties related to the flow rate of
lubricant
and/or gas through the perimeter wall body.
It is also an objective of this invention to reduce the significant
expense of a high rejection rate for perimeter walls to achieve the
sufficiently
s consistent lubricant and/or gas flow rate.
This invention accomplishes these objectives by providing a system for
providing consistent lubricant and/or gas flow through multiple permeable
perimeter walls. The system involves ascertaining one or more of the
relevant properties, or the actual flow rate, of the perimeter walls, and then
lo determining and creating the appropriate surface area of the delivery
conduit
which provides the lubricant and/or gas to the exterior of the perimeter wall,
and/or the appropriate delivery distance.
The system provided by this invention has the significant advantage of
allowing the use of multiple perimeter walls with different flow related
rs properties, or with different lubricant and/or gas flow rates, to be used
in the
same mold table, while achieving consistent flow rates through each perimeter
wall.
The system provided by this invention has the significant advantage of
providing a significantly similar flow rate of lubricant or gas in a plurality
of
2o perimeter walls in molds on the same mold table.
In accomplishing these objectives, this invention provides a system
which is simpler and less expensive than all prior systems.
Brief Description of the Drawioes
Preferred embodiments of the invention are described below with
21 reference to the accompanying drawings, which are briefly described below.
Figure 1 is an elevation view of a typical casting pit, caisson and
aluminum casting apparatus;
Figure 2 is a cross sectional elevation view of a typical mold casting
assembly, illustrating the perimeter wall in place;
3o Figure 3 is a cross sectional view of a perimeter wall seated in a mold
housing, illustrating the flow of lubricant or gas through its
body;
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Figure 4 is a cross sectional view of a perimeter wall seated in a mold
housing, illustrating the flow of lubricant or gas through its
body, only wherein the delivery conduits are in the mold
housing;
s Figure 5 is a perspective of one embodiment of a perimeter wall which
is contemplated for use by this invention;
Figure 6 is a top view of the perimeter wall illustrated in Figure 5;
Figure 7 is an elevation view of the perimeter wall illustrated in Figure
5;
io Figure 8 is Section 8 - 8 from the perimeter wall illustrated in Figure 6;
Figure 9 is a top view of an alternative embodiment of a perimeter wall
contemplated by this invention, wherein lubricant and/or gas are
delivered to the perimeter wall through holes drilled from the
top of the perimeter wall;
Is Figure 10 is a top view of an alternative embodiment in which lubricant
and/or gas are delivered to the perimeter wall through holes
drilled from the top of the perimeter wall, and wherein the
holes through which lubricant and/or gas are delivered are not
equally spaced;
2o Figure 11 is a top view of an alternative embodiment in which lubricant
and/or gas are delivered to the perimeter wall through holes
drilled from the top of the perimeter wall, and wherein shape
of the perimeter wall is not circular; and
Figure 12 is a top partial view of a perimeter wall which illustrates the
25 movement of the location of the delivery holes to affect the flow
rates.
Best Modes for Carrying Out the Invention and Disclosure of Invention
While there are numerous ways to achieve and configure a vertical
casting arrangement, Figure 1 illustrates one example. In Figure 1, the
3o vertical casting of aluminum generally occurs beneath the elevation level
of
the factory floor in a casting pit. Directly beneath the casting pit floor la
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is a caisson 3, in which the hydraulic cylinder barrel 2 for the hydraulic
cylinder is placed.
As shown in Figure 1, the components of the lower portion of a
typical vertical aluminum casting apparatus, shown within a casting pit 1 and
s a caisson 3, are a hydraulic cylinder barrel 2, a ram 6, a mounting base
housing 5, a platen 7 and a starting block base 8, all shown at elevations
below the casting facility floor 4.
The mounting base housing 5 is mounted to the floor la of the casting
pit 1, below which is the caisson 3. The caisson 3 is defined by its side
walls
io 3b and its floor 3a.
A typical mold table assembly 10 is also shown in Figure 1, which can
be tilted as shown by hydraulic cylinder 11 pushing mold table tilt arm l0a
such that it pivots about point 12 and thereby raises and rotates the main
casting frame assembly, as shown in Figure 1. There are also mold table
is carriages which allow the mold table assemblies to be moved to and from the
casting position above the casting pit.
Figure 1 further shows the platen 7 and starting block base 8 partially
descended into the casting pit 1 with billet 13 being partially formed. Billet
13 is on starting block 14, which is mounted on pedestal 15. While the term
20 starting block is used for item 14, it should be noted that the terms
bottom
block and starting head are also used in the industry to refer to item 14,
bottom block typically used when an ingot is being cast and starting head
when a billet is being cast.
While the starting block base 8 in Figure 1 only shows one starting
21 block 14 and pedestal 15, there are typically several of each mounted on
each
starting block base, which simultaneously cast billets or ingots as the
starting
block is lowered during the casting process.
When hydraulic fluid is introduced into the hydraulic cylinder at
sufficient pressure, the ram 6, and consequently the starting block base 8,
are
3o raised to the desired elevation start level for the casting process, which
is
when the starting blocks are within the mold table assembly 10.
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The lowering of the starting block base 8 is accomplished by metering
the hydraulic fluid from the cylinder at a pre-determined rate, thereby
lowering the ram 6 and consequently the starting blocks at a pre-determined
and controlled rate. The mold is controllably cooled during the process to
assist in the solidification of the emerging ingots or billets, typically
using
water cooling means.
As noted earlier, Fig. 2 is a cross-sectional elevation view of a typical
mold casting assembly, illustrating the perimeter wall 30 in place in mold
housing 31. The entrance of the mold is indicated by reference numeral 34.
Fig. 3 shows a perimeter wall 30 contemplated by this invention seated
in a mold housing 31. A gas inlet line 45 and a lubricant inlet line 44 are
also
shown, and illustrate how lubricant and gas may be provided to a lubricant
delivery conduit 40 and gas delivery conduits 41.
Fig. 4 is also a cross sectional view of an embodiment of a perimeter
wall 30 contemplated by this invention, seated in a mold housing 31, and
further illustrating an embodiment wherein a lubricant delivery conduit 42 and
gas delivery conduits 43 are within the mold housing 31. A gas inlet line 45
and a lubricant inlet line 44 are also shown, and illustrate how lubricant and
gas may be provided to the lubricant delivery conduit 42 and the gas delivery
conduits 43.
Fig. 5 is a perspective of one embodiment of a perimeter wall 30 which
is contemplated for use by this invention, and illustrates an inner surface
50,
an outer surface 51, gas delivery conduits 52 and a lubricant delivery conduit
53. The two gas delivery conduits 52 are shown in operative connection to one
another.
Fig. 6 is a top view of the perimeter wall 30 illustrated in Fig. 5, also
illustrating the inner surface 50 and the outer surface 51.
Fig. 7 is an elevation view of the perimeter wall 30 illustrated in Fig. 5,
and illustrates the outer surface 51, gas delivery conduits 52 and lubricant
delivery conduit 53.
FIG. 8 is section 8-8 of the perimeter wall illustrated in Fig. 6, and
shows a cross section of one embodiment of the invention. Fig. 8 illustrates
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perimeter wall 30, perimeter wall body 56, lubricant delivery conduit 53,
lubricant delivery conduit height 61, lubricant delivery conduit depth 60, gas
delivery conduits 52, gas delivery conduit height 62, and gas delivery conduit
depth 63. Fig. 8 further illustrates a delivery distance 66 from the
termination
of a delivery conduit to the inner surface 50 of the perimeter wa1130.
Fig. 9 shows an alternative embodiment of the invention wherein the
gas and/or lubricant are delivered to a perimeter wall 70 through delivery
holes 71 drilled from the top of the perimeter wall 70. An outer surface 73
and an inner surface 72 of the perimeter wa1170 are also shown.
Fig. 10 is a top view of an alternative embodiment in which lubricant
and/or gas are delivered to the perimeter wall through delivery holes 71
drilled
from the top of the perimeter wall 70, only wherein the delivery holes 71
through which lubricant and/or gas are delivered are not equally spaced. The
holes in region 74 are spaced closer together to achieve a higher flow of gas
and/or lubricant in that region.
Fig. 11 is a top view of an alternative embodiment in which lubricant
and/or gas are delivered to a perimeter wall 80 through delivery holes 81
drilled from the top of the perimeter wall 80, and wherein the shape of the
perimeter wa1180 is not circular.
Fig. 12 shows a section of a perimeter wall 90 within the
contemplation of this invention, with an inner surface 93, an outer surface 94
and delivery holes 91. Delivery holes 91 are shown a distance 95 from the
inner surface 93 of the perimeter wall 90. The distance 95 would be the
delivery distance for those particular delivery holes 91. The dotted lines
comprising a circle illustrate a second possible location for relocated
delivery
holes 92, which are a lesser second distance 96 from the outer surface of the
perimeter wall 90. The second distance 96 would be the delivery distance for
the relocated delivery holes 92.
