U.S. patent application number 12/128242 was filed with the patent office on 2008-11-20 for gas lubricant and delivery apparatus.
This patent application is currently assigned to CAST CENTRE PTY LTD. Invention is credited to Ian Frank BAINBRIDGE, John Francis GRANDFIELD, John Andrew TAYLOR.
Application Number | 20080283212 12/128242 |
Document ID | / |
Family ID | 38091805 |
Filed Date | 2008-11-20 |
United States Patent
Application |
20080283212 |
Kind Code |
A1 |
GRANDFIELD; John Francis ;
et al. |
November 20, 2008 |
GAS LUBRICANT AND DELIVERY APPARATUS
Abstract
A lubricant delivery element for delivering lubricant into a
cavity, the lubricant distribution element comprising a thin
element of porous material for delivering lubricant into the cavity
through the element.
Inventors: |
GRANDFIELD; John Francis;
(Victoria, AU) ; TAYLOR; John Andrew; (Queensland,
AU) ; BAINBRIDGE; Ian Frank; (Queensland,
AU) |
Correspondence
Address: |
RODMAN RODMAN
10 STEWART PLACE, SUITE 2CE
WHITE PLAINS
NY
10603
US
|
Assignee: |
CAST CENTRE PTY LTD
ST. LUCIA
AU
|
Family ID: |
38091805 |
Appl. No.: |
12/128242 |
Filed: |
May 28, 2008 |
Current U.S.
Class: |
164/149 |
Current CPC
Class: |
B22D 11/0401 20130101;
B22D 11/07 20130101; B22D 11/049 20130101 |
Class at
Publication: |
164/149 |
International
Class: |
B22D 11/07 20060101
B22D011/07 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 30, 2005 |
AU |
2005906692 |
Nov 30, 2006 |
AU |
PCT/AU2006/001820 |
Claims
1. A lubricant delivery element for delivering lubricant into a
cavity, the lubricant distribution element comprising a thin
element of porous material for delivering lubricant into the cavity
through the element.
2-32. (canceled)
33. A lubricant delivery element as claimed in claim 1, wherein the
lubricant distribution element has a thickness of less than
approximately 5 mm.
34. A lubricant delivery element as claimed in claim 1, wherein the
porous material has a porosity of 10 to 70%.
35. A lubricant delivery element as claimed in claim 1 wherein the
porous material is selected from sintered metal, ceramic or porous
plastic.
36. A gas and lubricant delivery apparatus for delivering gas and
lubricant into a cavity, the apparatus comprising a lubricant
distribution element as claimed in claim 1, and a gas distribution
element for delivering gas into the cavity.
37. A gas and lubricant delivery apparatus as claimed in claim 36,
wherein the gas distribution element is integrally formed with the
lubricant distribution element.
38. A gas and lubricant delivery apparatus as claimed in claim 36,
wherein the gas distribution element comprises radial grooves and
at least one circumferential groove formed in the upper surface of
the lubricant distribution element.
39. A gas and lubricant delivery apparatus as claimed in claim 36,
wherein the gas distribution element is in the form of a
distribution plate, the distribution plate having a first set of
grooves formed in the top surface of the plate for delivery of gas
into the cavity.
40. A gas and lubricant delivery apparatus as claimed in claim 39,
wherein, the distribution plate also has a second set of grooves
formed in the top surface to connect the first set of grooves to
one another for distribution of the gas to all the grooves in the
first set.
41. A gas and lubricant delivery apparatus as claimed in claim 36,
wherein the gas distribution element has a cut away portion in its
lower surface into which the lubricant distribution element is
adapted to fit snugly.
42. A gas and lubricant delivery apparatus as claimed in claim 36,
wherein the apparatus further comprises sealant for sealing the
lubricant distribution element from the gas distribution
element.
43. A hot top mould for direct chill continuous casting of metal
ingots comprising a mould having a mould body and a cavity defined
in the mould body and a gas and lubricant delivery apparatus for
delivering gas and lubricant to the mould cavity as claimed in
claim 36.
44. A hot top mould as claimed in claim 43, wherein the gas and
lubricant delivery apparatus is located proximate the molten metal
entry end of the mould.
45. A hot top mould as claimed in claim 43, wherein the mould body
has a space therein for the flow of coolant through the mould body,
wherein the space for the flow of coolant is shaped to flow the
coolant close to the gas and lubricant delivery apparatus.
46. A hot top mould for direct chill continuous casting of metal
ingots comprising a mould having a mould body and a cavity defined
in the mould body, and a lubricant delivery element for delivering
lubricant to the mould cavity according to claim 1.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a gas and lubricant
delivery apparatus and more particularly to a lubricant delivery
element, in particular for direct chill continuous casting hot top
moulds.
BACKGROUND OF THE INVENTION
[0002] One known method of casting metal ingots is that of direct
chill continuous casting using a hot top mould. In this method, a
bath of molten metal is located directly above or next to the mould
cavity, through which the molten metal is either drawn horizontally
or flows vertically under gravity. The mould body is continuously
cooled using a coolant in a chamber around the mould, thus chilling
the molten metal to form the ingots. The mould body also acts as an
outlet for the direct chill water spray.
[0003] A lubricant is introduced into the mould cavity to improve
the surface quality of the ingots by preventing the sticking of the
metal to the inside wall of the mould.
[0004] In U.S. Pat. No. 4,157,728 it was found that the surface
quality of non-ferrous metal ingots cast using this method is known
to be improved by the introduction of gas into the mould cavity
just below the hot top containing the molten metal bath. This was
done using an array of small holes which delivered oil to the
molten metal entry end of the mould cavity (ie. the top in the
vertical case), with radial slots used to deliver the air.
[0005] Subsequently, various means of delivering the lubricant and
gas into the mould cavity have been disclosed. In one version,
disclosed in U.S. Pat. No. 4,598,763, air and oil are introduced
into the mould cavity through a porous graphite ring whose primary
function is to act as a mould liner to form the casting surface.
This arrangement involves the introduction of the air and oil in
contact with the molten metal at the point where the molten metal
solidifies in the mould. This results in one significant problem,
being that tar-like deposits build up within the graphite due to
the vaporisation of the oil, thus restricting the flow of both air
and oil. A further problem with this arrangement is that high
delivery pressures are required to force the oil through the
graphite ring, increasing the manufacturing and operating costs of
the hot top mould.
[0006] In another version, disclosed in U.S. Pat. No. 5,320,159,
oil and air are introduced into the mould cavity via grooves in the
top and bottom of a distribution plate. Circumferential channels in
the mould body are provided to deliver oil and air to the radial
grooves in the distribution plate. However, the grooves in the
distribution plate may suffer from molten metal entry. After
entering the grooves the metal solidifies, resulting in tearing of
the billet surface and damage to the distribution plate. This
problem may be minimised by reducing the diameter of the grooves
(to as little as 100-200 micron), however, the manufacturing
required is costly and ultimately it is not sufficient to
completely prevent metal entry should the gas pressure in the mould
cavity be insufficient.
[0007] A further problem with using a distribution plate, is that
because oil is introduced to the distribution plate at one point
from the circumferential channel, this results in a region of low
oil flow directly opposite the feed point and hence an uneven
distribution of oil occurs in the mould cavity. Similar problems
may also occur with the air distribution.
SUMMARY OF THE INVENTION
[0008] According to a first aspect of the present invention there
is provided a lubricant delivery element for delivering lubricant
into a cavity, the lubricant distribution element comprising a thin
element of porous material for delivering lubricant into the cavity
through the element.
[0009] Preferably, the lubricant distribution element has a
thickness of less than approximately 5 mm.
[0010] Preferably, the lubricant distribution element has a
thickness of 0.1 to 5 mm, more preferably, 1-5 mm, more preferably
2-3 mm.
[0011] Preferably, the lubricant distribution element has a
thickness of approximately 1.5 mm.
[0012] The lubricant distribution element may however, have a
thickness of less than 0.1 mm.
[0013] The lubricant distribution element may have at least one
groove formed in the surface of the element. When present, the
groove may assist in the circumferential distribution of lubricant
through the element for even flow of lubricant from the
circumference or sides of the distribution element.
[0014] Preferably, the groove extends substantially around the
circumference or the sides of the element.
[0015] Preferably, the groove is approximately 0.5 mm deep.
[0016] Preferably, the porous material comprises an agglomerate of
particles.
[0017] Preferably, the particles have an average diameter of less
than approximately 0.25 mm.
[0018] Preferably, the particles have an average diameter of 10 to
100 micron.
[0019] More preferably, the particles have an average diameter of
40 to 70 micron.
[0020] The average diameter of the particles may be less than 10
microns.
[0021] Preferably, the average diameter of the pores in the porous
material is less than the size of the particles.
[0022] Preferably, the porous material has a porosity of 10 to 70%,
more preferably 20 to 40%.
[0023] The porosity of the material may change across the width of
the lubricant distribution element.
[0024] Preferably, the porous material is of the kind commonly used
in powder metallurgy applications.
[0025] Preferably, the porous material is aluminium, iron, copper
or sintered bronze, more preferably, sintered bronze. In this
embodiment, the thin element of porous material is manufactured by
sintering bronze powder in a steel die at high temperature.
[0026] The porous material may be a porous ceramic.
[0027] The porous material may also be graphite. However, if the
porous material is graphite, then the lubricant distribution
element is preferably provided with a strengthening means. The
strengthening means may be, for example, a thin element of metal
laminated to the graphite.
[0028] The porous material may be a porous plastic, such as
polytetrafluoroethylene.
[0029] Preferably, the lubricant distribution element is shaped so
that in use, it extends around the perimeter of the cavity.
[0030] Typically, the lubricant distribution element is in the
shape of an annular disc. The annulus of the annular disc may be
round or non-round in shape.
[0031] The lubricant distribution element may comprise a single
element or a number of parts which, in use, abut one another to
form the lubricant distribution element.
[0032] Preferably, the lubricant delivery element further comprises
a sealant for sealing the lubricant distribution element.
[0033] Preferably, the sealant seals at least portions of the
horizontal surfaces of the element. This forces the lubricant to
flow through the element as opposed to over the surface.
[0034] Preferably, the sealant seals at least a portion of the
surface of the lubricant distribution element which is not arranged
to be exposed to the cavity.
[0035] Preferably, the sealant comprises a layer of varnish on at
least a portion of the surface of the lubricant distribution
element.
[0036] Alternatively, the sealant may comprise a layer of
impermeable foil on at least a portion of the surface of the
lubricant distribution element.
[0037] Alternatively, the sealant may comprise a layer of settable
rubber. The settable rubber is applied as a paste which sets after
application.
[0038] The sealant may comprise a combination of layers of any two
or more of varnish, impermeable foil and a settable rubber.
[0039] Alternatively, the sealant comprises a fibre gasket(s).
[0040] Alternatively, the sealant comprises an O-ring.
[0041] Alternatively, the sealant comprises a flat surface.
[0042] Preferably, the flat surface is provided by a metal plate.
The flat surface may, alternatively, be provided by the top of the
mould body.
[0043] According to a second aspect of the present invention there
is provided a gas delivery element for delivering gas into a
cavity, the element comprising a thin element of porous material
for delivering gas into the cavity through the element.
[0044] Preferably, the gas distribution element has one or more of
the features of the lubricant distribution element according to the
first aspect.
[0045] According to a third aspect of the present invention there
is provided a gas and lubricant delivery apparatus for delivering
gas and lubricant into a cavity, the apparatus comprising a
lubricant distribution element according to the first aspect of the
present invention, and a gas distribution element for delivering
gas into the cavity.
[0046] Preferably, the gas distribution element is substantially
similar to the lubricant distribution element. In this embodiment
gas is delivered into the cavity through the gas distribution
element.
[0047] The gas distribution element may be integrally formed with
the lubricant distribution element.
[0048] In this embodiment, the gas distribution element preferably
comprises radial grooves and at least one circumferential groove
formed in the upper surface of the lubricant distribution
element.
[0049] Alternatively, the gas distribution element may take the
form of a distribution plate, which may be part of the top of the
cavity wall or be a separate plate.
[0050] In this embodiment, preferably, the distribution plate has a
first set of grooves formed in the top surface of the plate for
delivery of gas into the cavity.
[0051] Preferably, the distribution plate also has a second set of
grooves formed in the top surface to connect the first set of
grooves to one another for distribution of the gas to all the
grooves in the first set.
[0052] Preferably, the distribution plate is manufactured from a
metal, such as, for example steel or aluminium.
[0053] Alternatively, the distribution plate is manufactured from a
ceramic.
[0054] Alternatively, the distribution plate is manufactured from a
plastic, such as polytetrafluoro-ethylene.
[0055] Preferably, the gas distribution element is shaped to extend
around the perimeter of the cavity.
[0056] Preferably, the gas distribution element is of a similar
shape to the lubricant distribution element.
[0057] Typically, the gas distribution element is in the shape of
an annular disc. The annulus of the annular disc may be round or
non-round in shape.
[0058] Preferably, the gas distribution element is arranged, in
use, to be located above the lubricant distribution element.
[0059] Preferably, the gas distribution element has a cut away
portion in its lower surface into which the lubricant distribution
element is adapted to fit snugly.
[0060] The gas distribution element may comprise a single element
or a number of parts which, in use, abut one another to form the
gas distribution element.
[0061] Preferably, the apparatus for delivering gas and lubricant
further comprises a sealant for sealing the lubricant distribution
element and the gas distribution element.
[0062] Preferably, the sealant seals the gas distribution element
from the lubricant distribution element.
[0063] Preferably, the sealant seals at least a portion of the
surface of the gas and lubricant distribution elements.
[0064] Preferably, the sealant comprises a layer of varnish and/or
impermeable foil and/or settable rubber and/or a fibre gasket(s) on
at least some of the surface of the gas and lubricant elements.
[0065] Alternatively, the sealant may comprise an O-ring.
[0066] Alternatively, the sealant may comprise a flat surface.
[0067] Preferably, the sealant further comprises a sealing plate
overlaying the gas distribution element for sealing the top of the
gas distribution element.
[0068] According to a fourth aspect of the present invention, there
is provided a hot top mould for direct chill continuous casting of
metal ingots comprising a mould having a mould body and a cavity
defined in the mould body and a gas and lubricant delivery
apparatus for delivering gas and lubricant to the mould cavity
according to any one or more features of the third aspect of the
invention.
[0069] Preferably, the gas and lubricant delivery apparatus is
located proximate the molten metal entry end of the mould.
[0070] Preferably, the gas and lubricant delivery apparatus is
located above the level of the mould body at which the molten metal
solidifies.
[0071] Preferably, the gas and lubricant delivery apparatus is
located on top of the mould body.
[0072] Preferably, the mould body has a space therein for the flow
of coolant through the mould body.
[0073] Preferably, the space for the flow of coolant is shaped to
flow the coolant close to the gas and lubricant delivery
apparatus.
[0074] Preferably, the hot top mould further comprises a supply
mechanism for supplying gas and lubricant to the gas and lubricant
delivery apparatus.
[0075] Preferably, the supply mechanism comprises gas and lubricant
supply channels formed separately in the top of the mould, the
supply channels being in fluid connection with the gas and
lubricant delivery apparatus.
[0076] Alternatively, the supply mechanism may comprise pipe
fittings through the mould body and connected directly to the gas
and lubricant delivery apparatus.
[0077] Preferably, the hot top mould further comprises a molten
metal bath for feeding molten metal to the mould cavity.
[0078] Preferably, the hot top mould further comprises an orifice
plate, which spaces the molten metal bath from the mould.
[0079] The mould body may or may not have a graphite insert located
just below the gas and lubricant delivery apparatus.
[0080] Preferably, the metal is a non-ferrous metal such as
aluminium, magnesium, copper or zinc and their alloys.
[0081] According to a fifth aspect of the present invention, there
is provided a hot top mould for direct chill continuous casting of
metal ingots-comprising a mould having a mould body and a cavity
defined in the mould body, and a lubricant delivery element for
delivering lubricant to the mould cavity according to the first
aspect of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0082] A preferred embodiment of the present invention will now be
described, by way of example only, with reference to the
accompanying drawings, in which:
[0083] FIG. 1 is a schematic view of a gas and lubricant delivery
apparatus for delivering gas and lubricant according to one
embodiment of the present invention located in a hot top mould;
[0084] FIG. 2 is a top plan view of a gas distribution element of
the apparatus of FIG. 1;
[0085] FIG. 3 is a view of the gas distribution element of FIG. 2
through axis A-A;
[0086] FIG. 4 is a schematic view of a gas and lubricant delivery
apparatus for delivering gas and lubricant according to an
alternative embodiment of the present invention located in a hot
top mould;
[0087] FIG. 5 is a schematic view of a gas and lubricant delivery
apparatus for delivering gas and lubricant according to another
alternative embodiment of the present invention located in a hot
top mould;
[0088] FIG. 6A is a top plan view of a hot top mould incorporating
a gas and lubricant delivery apparatus for delivering gas and
lubricant according to another embodiment of the present
invention;
[0089] FIGS. 6C, 6D and 6E are schematic views of the hot top mould
of FIG. 6A through sections A-A, B-B, C-C and D-D,
respectively;
[0090] FIG. 7 is an image of the surface of a metal ingot cast
using a hot top mould comprising a gas and lubricant delivery
apparatus for delivering gas and lubricant according to preferred
embodiments of the present invention;
DETAILED DESCRIPTION OF THE DRAWINGS
[0091] Referring firstly to FIG. 1, a section of a hot top mould 10
for use in direct chill continuous casting of non-ferrous metals
such as aluminium, magnesium, copper, zinc and their alloys, for
example, is shown. The hot top mould 10 comprises a molten metal
bath 11 located above a mould 12 in a vertical arrangement, ie, so
molten metal will flow substantially vertically through the mould
12. The mould 12 and molten metal bath 11 may be arranged so that
flow through the mould 12 is substantially horizontal.
[0092] The hot top mould 10 also comprises a gas and lubricant
delivery apparatus 13 according to preferred embodiments of the
present invention located at the top of the mould body 14 (ie.
proximate the molten metal entry end of the mould 12 and above the
level of the mould body 14 at which the molten metal contacts the
mould body 14) for the delivery of gas (typically air) and
lubricant (typically oil) to the mould cavity 15.
[0093] The mould body 14 in use is cooled using a coolant
(typically water) flowing through a space 17 in the mould body 14
in order to solidify the molten metal. The mould body 14
preferably, but not necessarily, has an insert 27 manufactured of
graphite.
[0094] The gas and lubricant delivery apparatus 13 comprises a
lubricant distribution element 20 and a gas distribution element
21. The lubricant distribution element 20 is an annular disc of
porous material through which lubricant is delivered to the mould
cavity 15. Although the annulus of the annular disc is shown as
being round, it may be non-round. Furthermore, the lubricant
distribution element 20 may comprise a single element or a number
of parts which, in use, abut one another to form the lubricant
distribution element 20. The porous annular disc is thin, having a
thickness of approximately 1 to 5 mm. This range represents a
balance between the disc being as thin as practical to fit into the
hot top mould 10 and the pressure required to force the oil through
the disc into the mould cavity 15. However, it may be possible to
use a much thinner disc of, for example, less than 0.1 mm. In an
alternative embodiment (not shown here) the disc has a thickness of
at least approximately 1.5 mm with a 0.5 mm groove formed in the
top surface of the disc to further improve the distribution of oil
around the circumference of the disc for even circumferential flow
of lubricant and gas from the apparatus 13.
[0095] The space 17 in the mould body 14 for the coolant is shaped
to flow the coolant close to the gas and lubricant delivery
apparatus 13. Because the lubricant distribution element 20 is so
thin it is readily cooled by the coolant cooling the mould body 14.
This substantially prevents the lubricant, while it is inside the
distribution element 20, from reaching a temperature where it will
vaporise and decompose into tar-like deposits and thus restrict its
flow through the lubricant distribution element 20.
[0096] The lubricant distribution element 20 in the form of a
porous annular disc may be manufactured from any materials commonly
used in powder metallurgy applications; such as aluminium, iron,
copper or sintered bronze. Sintered bronze is a preferable material
as it provides the required strength and flexibility and is readily
and cost effectively manufactured into any shape, including thin
annular discs by sintering bronze powder in a steel die at high
temperatures. In addition, sintered bronze allows for good control
over the porosity and pore size, particularly compared to graphite.
Use of porous ceramic materials to form the disc may also be
possible. Another alternative material which could be used is a
porous plastic such as polytetrafluoroethylene. Furthermore, it may
also be possible to form the thin disc of graphite of adequate
porosity. In this case, the graphite would need to be strengthened
by, for example, lamination to a thin metal support disc as of
itself, graphite would not have the required strength.
[0097] In forming the disc, it has been found that as the particle
size of the material forming the porous disc increases, the
uniformity of circumferential oil distribution throughout the disc,
in use, decreases. The diameter of the particles used to form the
disc is therefore less than approximately 0.25 mm. Particles
smaller than approximately 10-20 micron in diameter may be used to
form a disc, however, at smaller particle sizes, the pressure
required to force the oil through the porous disc may become too
high for effective operation of the lubricant and gas delivery
apparatus 13. The diameter of the pores is generally approximately
20-40 micron. However, for discs manufactured of smaller particles,
this diameter may be reduced. The porosity of the thin disc is 10
to 70%, preferably, 20 to 40%. In an alternative embodiment, the
disc has a gradient of changing porosity across its width.
[0098] Because the diameter of the pores/porosity is so small the
surface tension of the molten metal acts to prevent it from
entering the pores and damaging the lubricant distribution element
20.
[0099] Referring now also to FIGS. 2 and 3, in one embodiment of
the gas and lubricant delivery apparatus 13 of the present
invention, the gas distribution element 21 is in the form of an
annular distribution plate, shown in detail in FIGS. 2 and 3. The
gas distribution element 21 may comprise a single element or a
number of parts which, in use, abut one another to form the gas
distribution element 21. The distribution plate has radial grooves
40 on its top surface 41 for delivering the gas to the mould cavity
15. The distribution plate also has at least one circumferential
groove 42 connecting the radial grooves 40 for distribution of the
gas to all the grooves 40. The distribution plate is preferably
manufactured from a metal such as, for example, steel or aluminium.
The gas distribution element 21 in the form of an annular
distribution plate also has a cut away portion 43 in its lower
surface 44 into which the lubricant distribution element 20 in the
form of the annular porous disc is adapted to fit snugly.
[0100] In an alternative embodiment (not shown), the gas
distribution element 21 is integrally formed with the lubricant
distribution element 20 by forming radial grooves and at least one
circumferential groove on the upper surface of the lubricant
distribution element 20 which is in the form of an annular disc of
porous material.
[0101] Referring more specifically again to FIG. 1, as described
above, the gas and lubricant delivery apparatus 13 comprising the
lubricant distribution element 20 and the gas distribution element
21 is located on top of the mould body 14. In use, an orifice plate
25 spaces the top of the gas distribution element 21 from the
bottom of the molten metal bath 11, with the entire arrangement
fixed into position by a locking plate 26. Part of the mould body
14 comprises a graphite liner 27, located immediately beneath the
gas distribution element 21. The purpose of the graphite liner 27
is to provide a casting surface upon which the molten metal
initially begins to solidify. In the embodiment shown in FIG. 1,
the orifice plate 25 has an overhang portion 28 extending into the
mould cavity 15 past the lubricant and gas distribution elements
20,21. The overhang portion 28 creates a space 29 between the
orifice plate 25 and the mould body 14, which is the entry point to
the mould cavity 15 for the gas and lubricant delivered by the gas
and lubricant delivery apparatus 13.
[0102] Thus, the gas and lubricant delivery apparatus 13 is
arranged so that it is highly unlikely to be contacted by molten
metal. Instead, the molten metal meniscus will contact the graphite
liner 27 which is below the gas and lubricant delivery apparatus
13. This means that the apparatus 13 is not directly heated by the
molten metal and hence the likelihood of lubricant vaporisation is
further reduced. In use, the lubricant is allowed to enter the
mould cavity 15 as a liquid and flow down a part of the mould body
15 before reaching the solidifying molten metal.
[0103] The supply of gas and lubricant to the gas and lubricant
delivery apparatus 13 is provided by gas and lubricant supply
channels 30,31 respectively formed in the top of the mould body 14.
Alternatively, pipe fittings through the mould body 14 may be used
to supply lubricant and/or gas directly to the gas and lubricant
delivery apparatus 13. A first O-ring 32 seals the lubricant and
gas supply channels 30,31 from one another. A second O-ring 33
seals the entire gas and lubricant delivery apparatus 13 at the
boundary between the locking plate 26 and the top of the mould body
14.
[0104] Further sealing of the lubricant and gas distribution
elements 20,21 may be provided. In FIG. 1, sealing of the top
surface 41 of the gas distribution element 21 in the form of an
annular distribution plate is provided by a sealing ring 34
overlaying the plate. The bottom surface of the lubricant
distribution element 20, in the form of the annular porous disc, is
sealed by a thin coat of varnish. Alternatively, a layer of thin,
impermeable foil or an O-ring or a layer of settable rubber,
applied as a paste, or a flat surface in the form of a metal plate
or the top of the mould body 14 could be used. Sealing of the
lubricant and gas distribution elements 20,21 guards against loss
of lubricant and/or gas into other parts of the mould 12 providing
controlled flow both radially and circumferentially.
[0105] Referring now to FIG. 4, an alternative embodiment of the
gas and lubricant delivery apparatus 113 is shown. Similar features
to those described in the previous embodiment have been referenced
with the same numbers, but are prefixed with the numeral 1.
[0106] In the embodiment shown in FIG. 4, the gas distribution
element 121 is in the form of an annular porous disc similar to the
lubricant distribution element 120. The disc forming the gas
distribution element 121 is sandwiched between the lubricant
distribution element 120 and the orifice plate 125. A layer 135 of
either impermeable foil or varnish separates and seals the discs
forming the lubricant and gas distribution elements 120,121 from
one another. The, gas is therefore delivered to the mould cavity
115 through the porous disc forming the gas distribution element
121 without substantial mixing with the lubricant being delivered
to the mould cavity 115, through the porous disc forming the
lubricant distribution element 120.
[0107] Rear surfaces 136 of both the lubricant and gas distribution
elements 120,121 are sealed selectively using an impermeable foil,
varnish layer, or a thin fibre gasket. The lower surface 132 of the
lubricant distribution element 120 is similarly sealed. Notably,
the lower surface 137 is not sealed where it is located above the
lubricant supply channel 132 so that lubricant can be fed to the
lubricant distribution element 120 from the channel 132.
[0108] FIG. 4 also discloses an alternative supply mechanism of
supplying gas to the gas distribution element 121, whereby an air
supply line 145 through an air supply plate 136 located behind the
delivery apparatus 113 (ie. away from the mould cavity 115) on top
of the mould body 114 supplies the gas from the gas supply channel
131.
[0109] FIG. 4 also shows the molten metal meniscus 150 where it
contacts the graphite liner 127.
[0110] Referring now to FIG. 5, another alternative embodiment of
the gas and lubricant delivery apparatus 213 of the present
invention is shown. Similar features to those described in the
previous embodiments have been referenced with the same numbers,
but are prefixed with the numeral 2.
[0111] In this embodiment of the gas and lubricant delivery
apparatus 213, the gas and lubricant distribution elements 220,221
are shown extending beyond the mould body 214 defined by the
graphite liner 227 into the mould cavity 215. Furthermore, the gas
distribution element 221 overhangs the lubricant distribution
element 220. This assists in directing the flow of gas
perpendicular to the mould bodies 214. The gas distribution element
221 in FIG. 5 may be in the form of either an annular distribution
plate or an annular porous disc.
[0112] FIG. 5 also shows the gas and lubricant delivery apparatus
213 in use with an orifice plate 225 which does not have an
overhang extending into the mould cavity 215 past the lubricant and
gas delivery apparatus 213.
[0113] Referring now to FIGS. 6A to 6E, a further alternative
embodiment of the gas and lubricant delivery apparatus 313 of the
present invention is shown. Similar features to those described in
the previous embodiments have been referenced with the same
numbers, but are prefixed with the numeral 3.
[0114] The delivery apparatus 313 comprises lubricant and gas
distribution elements 320 and 321, respectively. The top and bottom
surfaces of the lubricant distribution element 320 are sealed by
thin fibre gaskets 355, 356.
[0115] The gas distribution element 321 is different from
previously described embodiments in that the radial and
circumferential grooves 340, 342 for delivering the gas to the
mould cavity 315 are formed in the lower surface 344 of the gas
distribution element 321 as opposed to the top surface. As shown
specifically in FIG. 6E, the gas distribution element 321 comprises
two circumferential grooves 342 in the form of chambers, connected
by a plurality of radial grooves 340, also in the form of chambers.
One of the circumferential chambers 342 is located on the inside
wall of the mould cavity 315, slightly vertically spaced away from
the other such that the radial channels 340 are slightly angled
with respect to the horizontal. The gas supply channels 330 are
provided through the locking plate 326 as opposed to through the
mould body 314 as shown in FIG. 6B in particular.
[0116] The delivery apparatus 313 is also shown comprising a
locating pin 357 for correctly positioning the gas and lubricant
distribution elements 320, 321 within the hot top mould 310.
EXAMPLES
Example 1
[0117] A hot top mould 10 according to preferred embodiments of the
invention was used to cast a billet of aluminium alloy 6063. The
lubricant distribution element 20 in the form of an annular disc
was formed from particles of sintered bronze of between 45 and 63
micron in diameter. The resulting disc had a porosity of 45-50%.
The disc had a thickness of approximately 1.5 mm. The gas
distribution element 21 comprised a metal disc having radial
grooves machined on one surface. Air was used as the gas and oil as
the lubricant.
[0118] A single billet with a diameter of 152 mm was cast under the
following conditions:
[0119] Casting Speed: 150 mm/min
[0120] Coolant Water Flowrate: 75 L/min
[0121] Metal Head: 75 mm
[0122] Air Pressure: 2.5 kPa
[0123] Melt Temperature: 670-710.degree. C.
[0124] Oil Flowrate: 5 mL/min
[0125] The resulting casting had a surface which was free of any
defects as shown in FIG. 7.
Example 2
[0126] A test mould was set up in the lab to test a gas and
lubricant delivery apparatus 13 according to embodiments of the
present invention, in which the lubricant distribution element 20
and the gas distribution element 21 are formed of a porous plastic
material, specifically polytetrafluoroethylene ("PTFE"). FIG. 13
shows a schematic view of the test mould used. Notably, the steps
machined into the top of the mould body 14 in which the gas and
lubricant distribution elements sit are of a depth which is 0.1 mm
less than the thickness of the distribution elements so as to
provide a compressive force to the horizontal surfaces of the
distribution elements 20, 21 by the sealing ring 34. The
distribution elements 20, 21 were formed by cutting annular rings
from 1.5 mm thick sheets of a porous PTFE plastic (having pores of
50 micron) supplied by Porex. The diameters of the elements 20, 21
were such as to provide a 5 and 10 mm radial section through which
the lubricant and gas, respectively, would flow to the inner
surface of the mould 12. The inner surface diameter of the mould
was 150 mm. The two distribution elements 20, 21 were stuck
together using Dow-Corning Silastic 732, which is a silicon
adhesive/sealant. The top surface of the gas distribution element
21 and the lower surface of the lubricant distribution element 20
were also coated with silicon prior to assembly into the mould. The
gas supplied to the gas distribution element 21 was dry air from a
cylinder, through a regulator to a needle valve for accurately
controlling the flow. The gas flow rate was measured using an
Aalborg digital gas flow meter. The gas flow meter was kept in the
gas delivery line and the flow around the circumference of the
mould was detected using a soap solution. The lubricant supplied to
the lubricant distribution element 20 was Exa145 as supplied by ODT
Engineering. The circumferential flow of the lubricant in the mould
was observed through the test mould which was formed from
transparent Perspex for the purposes of this test.
[0127] A very uniform circumferential distribution of gas was
obtained at a flow rate of 2.0 litres per minute. The gas pressure
required to achieve this flow was low, approximately 20-30 mbar,
High gas flows did not change the distribution which remained
uniform around the circumference of the mould.
[0128] On initial connection of the lubricant supplied to the
mould, gas was found to be bubbling back through the lubricant
supply. This was traced to the gas supply and was due to a portion
of the surface of the gas distribution element 21 not being coated
with silicon. This portion of the surface was subsequently coated
and as a result no bypass of gas to the oil supply line occurred.
At a head height of 1000 mm, a flow rate of 1 ml/min of lubricant
to the lubricant distribution element 21 was obtained. Even
circumferential flow was obtained after about 10 minutes.
Example 3
[0129] A hot top mould 10 according to a preferred embodiment of
the invention was used to cast a billet of magnesium alloy AZ80.
The mould diameter was 203 mm. The nominal composition for AZ80 is
8.5% Aluminium and 0.5% Zinc, with the balance magnesium. Table 1
below provides details of the operating conditions usd for the
casting of the AZ80 billet.
TABLE-US-00001 TABLE 1 Conditions for AZ80 alloy cast Parameter
Unit Setting/Actual Furnace set point .degree. C. 740 Metal
temperature in hot top box .degree. C. 720-730 Pump start power %
120 Pump start power hold time seconds 25 Pump run power % 38 Cast
speed mm/minute 90 Water flow litres/minute 160 Mould gas flow rate
litres/minute 3 Metal level-hot top box mm 60 Orifice plate
material & coating N17 + graphite
[0130] The alloy was successfully cast to a length of approximately
1380 mm. FIG. 14 shows the surface of the cast billets which have a
satisfactory cast surface and are not cracked.
[0131] In the claims which follow and in the preceding description
of the invention, except where the context requires otherwise due
to express language or necessary implication, the word "comprise"
or variations such as "comprises" or "comprising" is used in an
inclusive sense, ie. to specify the presence of the stated features
but not to preclude the presence or addition of further features in
various embodiments of the invention.
[0132] It is to be clearly understood that although prior art
publications are referred to herein, this reference does not
constitute an admission that any of these documents forms part of
the common general knowledge in the art in Australia or in any
other country.
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