Note: Descriptions are shown in the official language in which they were submitted.
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IMPROVED FEEDER ELEMENT FOR METAL CASTING
The present invention relates to an improved feeder element for use in metal
casting operations utilising casting moulds, especially but not exclusively in
medium-pressure sand moulding systems.
In a typical casting process, molten metal is poured into a pre-formed mould
cavity which defines the shape of the casting. However, as the metal
solidifies
it shrinks, resulting in shrinkage cavities which in turn result in
unacceptable
imperfections in the final casting. This is a well known problem in the
casting
industry and is addressed by the use of feeder sleeves or risers which are
integrated into the mould during mould formation. Each feeder sleeve provides
an additional (usually enclosed) volume or cavity which is in communication
with the mould cavity, so that molten metal also enters into the feeder
sleeve.
During solidification, molten metal within the feeder sleeve flows back into
the
mould cavity to compensate for the shrinkage of the casting. It is important
that metal in the feeder sleeve cavity remains molten longer than the metal in
the mould cavity, so feeder sleeves are made to be highly insulating or more
usually exothermic, so that upon contact with the molten metal additional heat
is generated to delay solidification.
After solidification and removal of the mould material, unwanted residual
metal from within the feeder sleeve cavity remains attached to the casting and
must be removed. In order to facilitate removal of the residual metal, the
feeder sleeve cavity may be tapered towards its base (i.e. the end of the
feeder
sleeve which will be closest to the mould cavity) in a design commonly
referred to as a neck down sleeve. When a sharp blow is applied to the
residual
metal it separates at the weakest point which will be near to the mould (the
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process commonly known as "knock off'). A small footprint on the casting is
also desirable to allow the positioning of feeder sleeves in areas of the
casting
where access may be restricted by adjacent features.
Although feeder sleeves may be applied directly onto the surface of the mould
cavity, they are often used in conjunction with a breaker core. A breaker core
is simply a disc of refractory material (typically a resin bonded sand core or
a
ceramic core or a core of feeder sleeve material) with a hole in its centre
which
sits between the mould cavity and the feeder sleeve. The diameter of the hole
through the breaker core is designed to be smaller than the diameter of the
interior cavity of the feeder sleeve (which need not necessarily be tapered)
so
that knock off occurs at the breaker core close to the mould.
Breaker cores may also be manufactured out of metal. DE 196 42 838 Al
discloses a modified feeding system in which the traditional ceramic breaker
core is replaced by a rigid flat annulus and DE 201 12 425 Ul discloses a
modified feeding system utilising a rigid "hat-shaped" annulus.
Casting moulds are commonly formed using a moulding pattern which defmes
the mould cavity. Pins are provided on the pattern plate at predetermined
locations as mounting points for the feeder sleeves. Once the required sleeves
are mounted on the pattern plate, the mould is formed by pouring moulding
sand onto the pattern plate and around the feeder sleeves until the feeder
sleeves are covered and the mould box is filled. The mould must have
sufficient strength to resist erosion during the pouring of molten metal, to
withstand the ferrostatic pressure exerted on the mould when full and to
resist
the expansion/compression forces when the metal solidifies.
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Moulding sand can be classified into two main categories. Chemical bonded
(based on either organic or inorganic binders) or clay-bonded. Chemically
bonded moulding binders are typically self-hardening systems where a binder
and a chemical hardener are mixed with the sand and the binder and hardener
start to react immediately, but sufficiently slowly enough to allow the sand
to
be shaped around the pattern plate and then allowed to harden enough for
removal and casting.
Clay-bonded moulding uses clay and water as the binder and can be used in the
"green" or undried state and is commonly referred to as greensand. Greensand
mixtures do not flow readily or move easily under compression forces alone
and therefore to compact the greensand around the pattern and give the mould
sufficient strength properties as detailed previously, a variety of
combinations
of jolting, vibrating, squeezing and ramming are applied to produce uniform
strength moulds at high productivity. The sand is typically compressed
(compacted) at high pressure, usually using a hydraulic ram (the process being
referred to as "ranuning up"). With increasing casting complexity and
productivity requirements, there is a need for more dimensionally stable
moulds and the tendency is towards higher ramming pressures which can result
in breakage of the feeder sleeve and/or breaker core when present, especially
if
the breaker core or the feeder sleeve is in direct contact with the pattern
plate
prior to ram up.
The above problem is partly alleviated by the use of spring pins. The feeder
sleeve and optional locator core (similar in composition and overall
dimensions
to breaker cores) is initially spaced from the pattern plate and moves towards
the pattern plate on ram up. The spring pin and feeder sleeve may be designed
such that after ramming, the final position of the sleeve is such that it is
not in
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direct contact with the pattern plate and may be typically 5 to 25mm distant
from the pattern surface. The knock off point is often unpredictable because
it
is dependent upon the dimensions and profile of the base of the spring pins
and
therefore results in additional cleaning costs. The solution offered in EP-A-
1184104 is a two-part feeder sleeve. Under compression during mould
formation, one mould (sleeve) part telescopes into the other. One of the mould
(sleeve) parts is always in contact with the pattern plate and there is no
requirement for a spring pin. However, there are problems associated with the
telescoping arrangement of EP-A-1184104. For example, due to the
telescoping action, the volume of the feeder sleeve after moulding is variable
and dependent on a range of factors including moulding machine pressure,
casting geometry and sand properties. This unpredictability can have a
detrimental effect on feed performance. In addition, the arrangement is not
ideally suited where exothermic sleeves are required. When exothermic
sleeves are used, direct contact of exothermic material with the casting
surface
is undesirable and can result in poor surface finish, localised contamination
of
the casting surface and even sub-surface gas defects.
Yet a further disadvantage of the telescoping arrangement of EP-A-1184104
arises from the tabs or flanges which are required to maintain the initial
spacing
of the two mould (sleeve) parts. During moulding, these small tabs break off
(thereby permitting the telescoping action to take place) and simply fall into
the
moulding sand. Over a period of time, these pieces will build up in the
moulding sand. The problem is particularly acute when the pieces are made
from exothermic material. Moisture from the sand can potentially react with
the exothermic material (e.g. metallic aluminium) creating the potential for
small explosive defects.
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An attempt to mitigate the effect of sleeve breakage is made in DE 201 12 425
U1 by
providing the mounting surface that bears the weight of the sleeve with a pair
of
spaced apart lips that with the mounting surface form a channel or groove
within
which the sleeve sits. The inner lip prevents broken pieces of the sleeve
falling into
the mould and the outer lip prevents broken pieces from falling into the
moulding
sand.
W02005/051568 discloses a feeder element (a collapsible breaker core) that is
especially useful in high-pressure sand moulding systems. The feeder element
has a
first end for mounting on a mould pattern, an opposite second end for
receiving a
feeder sleeve and a bore between the first and second ends defined by a
stepped
sidewall. The stepped sidewall is designed to deform irreversibly under a
predetermined load (corresponding to the crush strength). The feeder element
offers
numerous advantages over traditional breaker cores including:-
(i) a smaller feeder element contact area (aperture to the casting);
(ii) a small footprint (external profile contact) on the casting surface;
(iii) reduced likelihood of feeder sleeve breakage under high pressures during
mould formation; and
(iv) consistent knock off with significantly reduced cleaning requirements.
The feeder element of W02005/051568 is exemplified in a high-pressure sand
moulding system. The high ramming pressures involved necessitate the use of
high
strength (and high cost) feeder sleeves. This high strength is achieved by a
combination of the design of the feeder sleeve (i.e. shape, thickness etc.)
and the
material (i.e. refractory materials, binder type and addition, manufacturing
process
etc.). The examples demonstrate the use of the feeder elernent with a FEEDEX
HD-
VS 159 feeder sleeve, which is designed to be pressure resistant
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(i.e. high strength) and for spot feeding (high density, highly exothermic,
thick
walled, not high volume feed demand). The feeder sleeve is secured to the
feeder element via a mounting surface which bears the weight of the feeder
sleeve and which is perpendicular to the bore axis. For medium pressure
moulding there is the potential opportunity of using lower strength sleeves
i.e.
different designs (shapes and wall thicknesses etc.) and/or different
composition (i.e. lower strength). Irrespective of the sleeve design and
composition, in use there would still be the issues associated with knock off
from the casting (variability and size of footprint on the casting) and need
for
good sand compaction beneath the feeder element. If the feeder element of
W02005/051568 were to be employed in medium-pressure moulding lines it
would be necessary to design the element so that it collapses sufficiently at
the
lower moulding pressure (as compared to high pressure moulding) i.e. to have a
lower initial crush strength. It would also be highly advantageous to use
lower
strength feeder sleeves (typically lower density sleeves), which would allow
for
a greater range of sleeve designs and compositions to be used successfully and
optimally for a greater range of casting types and correspondingly lower cost
feeder sleeves. However, when this was attempted the inventors surprisingly
discovered that the feeder sleeve suffered damage and breakages on moulding
which if used for casting would have resulted in the casting suffering from
defects.
It is an object of the present invention in a first aspect to provide an
improved
feeder element which can be used in a cast moulding operation. In particular,
it
is an object of the present invention in its first aspect to extend the
utility of
collapsible feeder elements into medium pressure moulding systems while
allowing the use of relatively weak feeder sleeves without introducing casting
defects.
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According to a first aspect of the present invention, there is provided a
feeder
element for use in metal casting, said feeder element comprising:
(i) a first end for mounting on a mould pattern;
(ii) an opposite second end for receiving a feeder sleeve; and
(iii) a bore between the first and second ends defined by a stepped sidewall;
said feeder element being compressible in use whereby to reduce the distance
between the first and second ends, wherein the stepped sidewall has a first
sidewall region defining the second end of the element and a mounting surface
for a feeder sleeve in use, said first sidewall region being inclined to the
bore
axis by less than 90 and a second sidewall region contiguous with the first
sidewall region, said second sidewall region being parallel to or inclined to
the
bore axis at a different angle to the first sidewall region whereby to define
a
step in the sidewall.
The feeder element may comprise additional sidewall regions, whereby
multiple steps in the sidewall are defined, in which case at least one of the
additional sidewall regions is preferably inclined at a greater angle to the
axis
than the first sidewall region.
It will be noted upon reading W02005/051568 that, although the orientation of
the sidewall region defining the mounting surface for the feeder sleeve and
bearing the weight of the feeder sleeve is not particularly limited, it is
said to be
preferably perpendicular to the bore axis as is shown in all of the examples.
The only significance placed on the orientation of this surface is that the
perpendicular arrangement is the most convenient for mounting the sleeve.
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Preferably the first sidewall region is inclined to the bore axis at an angle
of
between 5 and 85 , more preferably at an angle of between 15 and 80 , even
more preferably at an angle of between 25 and 75 , and most preferably at an
angle of between 30 and 70 . For example, the first sidewall region may be
inclined to the bore axis at an angle of 60 .
It will be understood that the amount of compression and the force required to
induce compression will be influenced by a number of factors including the
material of manufacture of the feeder element and the shape and thickness of
the sidewall. It will be equally understood that individual feeder elements
will
be designed according to the intended application, the anticipated pressures
involved and the feeder size requirements.
Preferably, the initial crush strength (i.e. the force required to initiate
compression and irreversibly deform the feeder element over and above the
natural flexibility that it has in its unused and uncrushed state) is no more
than
5000 N, and more preferably no more than 3000 N. If the initial crush strength
is too high, then moulding pressure may cause the feeder sleeve to fail before
compression is initiated. Preferably, the initial crush strength is at least
250 N.
If the crush strength is too low, then compression of the element may be
initiated accidentally, for example if a plurality of elements is stacked for
storage or during transport.
The feeder element of the present invention may be regarded as a collapsible
breaker core as this term suitably describes some of the functions of the
element in use. Traditionally, breaker cores comprise resin bonded sand or are
a ceramic material or a core of feeder sleeve material. However, the feeder
element of the current invention can be manufactured from a variety of other
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suitable materials including metal. In certain configurations it may be more
appropriate to consider the feeder element to be a feeder neck.
As used herein, the term "compressible" is used in its broadest sense and is
intended only to convey that the length of the feeder element between its
first
and second ends is shorter after compression than before compression.
Preferably, said compression is non-reversible i.e. after removal of the
compression inducing force the feeder element does not revert to its original
shape.
In a particularly preferred embodiment, the stepped sidewall of the feeder
element comprises a first series of sidewall regions (said series having at
least
one member) in the form of rings (which are not necessarily planar) of
increasing diameter (when said series has more than one member)
interconnected and integrally formed with a second series of sidewall regions
(said second series having at least one member). Preferably, the sidewall
regions are of substantially uniform thickness, so that the diameter of the
bore
of the feeder element increases from the first end to the second end of the
feeder element. Conveniently, the second series of sidewall regions are
cylindrical (i.e. parallel to the bore axis), although they may be
frustoconical
(i.e. inclined to the bore axis). Both series of sidewall regions may be of
non-
circular shape (e.g. oval, square, rectangular, or star shaped). The second
sidewall region constitutes the sidewall region of the second series closest
to
the second end of the feeder element.
The compression behaviour of the feeder element can be altered by adjusting
the dimensions of each sidewall region. In one embodiment, all of the first
series of sidewall regions have the same length and all of the second series
of
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sidewall regions have the same length (which may be the same as or different
from the first series of sidewall regions and which may be the same as or
different from the first sidewall region). In a preferred embodiment however,
the length of the first series of sidewall regions and/or the second series of
sidewall regions incrementally increases towards the first end of the feeder
element.
The feeder element may be defined by the first sidewall region and one each of
the first and second series of sidewall regions. However, the feeder element
may have as many as six or more of each of the first and the second series of
sidewall regions. In a particularly preferred embodiment, four of the first
series
and five of the second series are provided.
Preferably, the thickness of the sidewall regions is from about 4 to 24%,
preferably from about 6 to 20%, more preferably from about 8 to 16% of the
distance between the inner and outer diameters of the first sidewall regions
(i.e.
the annular thickness in the case of planar rings (annuli)).
Preferably, the distance between the inner and outer diameters of the first
series
of sidewall regions is 4 to 10 mm and most preferably 5 to 7.5 mm. Preferably,
the thickness of the sidewall regions is 0.2 to 1.5 mm and most preferably 0.3
to 1.2 mm. The ideal thickness of the sidewall regions will vary from element
to element and be influenced by the size, shape and material of the feeder
element, and by the process used for its manufacture.
In a convenient embodiment, only an edge contact is formed between the
feeder element and casting, the first end (base) of the feeder element being
defined by a sidewall region of the first or second series which is non-
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perpendicular to the bore axis. It will be appreciated from the foregoing
discussion that such an arrangement is advantageous in minimising the
footprint and contact area of the feeder element. In such embodiments, the
sidewall region which defines the first end of the feeder element may have a
different length and/or orientation to the other sidewall regions of that
series.
For example, the sidewall region defming the base may be inclined to the bore
axis at an angle of 5 to 300, preferably 5 to 15 . Preferably, the free edge
of the
sidewall region defming the first end of the feeder element has an inwardly
directed annular flange or bead.
It will be understood from the foregoing discussion that the feeder element is
intended to be used in conjunction with a feeder sleeve. Thus, the invention
provides in a second aspect a feeder system for metal casting comprising a
feeder element in accordance with the first aspect and a feeder sleeve secured
thereto.
A standard feeder sleeve has an annular base for mounting onto a breaker core
(collapsible or otherwise). In the feeder system of the second aspect the base
of the feeder sleeve is profiled at the same angle as the first sidewall
region of
the feeder element.
The nature of the feeder sleeve is not particularly limited and it may be for
example insulating, exothermic or a combination of both. Neither is its mode
of
manufacture particularly limited, it may be manufactured for example using
either the slurry or core-shot method. Typically a feeder sleeve is made from
a
mixture of refractory fillers (e.g. fibres, hollow microspheres and/or
particulate
materials) and binders. An exothermic sleeve further requires a fuel (usually
aluminium or aluminium alloy) and usually initiators/sensitisers. Suitable
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feeder sleeves include for example those sold by Foseco under the trade name
KALMIN, KALMINEX or FEEDEX. Feeder sleeves are available in a number
of shapes including closed and open cylinders, ovals, neckdowns and domes.
Preferably the feeder element is used in conjunction with any conventional
insert sleeve design which consists of a closed (capped) sleeve that may be
flat
topped, domed, flat topped dome, or any other insert sleeve design. The feeder
sleeve may be conveniently secured to the feeder element by adhesive but may
also be push fit or have the sleeve moulded around part of the feeder element.
Preferably the feeder sleeve is adhered to the feeder element.
The invention allows the use of lower strength sleeves to be used down to a
value of 3.5kN. Preferably, the sleeve strength is at least 5kN. Preferably,
the
sleeve strength is less than 20kN. For ease of comparison the strength of a
feeder sleeve is defmed as the compressive strength of a 50x50mm cylindrical
test body made from the feeder sleeve material. A 201/70 EM compressive
testing machine (Form & Test Seidner, Germany) is used and operated in
accordance with the manufacturer's instructions. The test body is placed
centrally on the lower of the steel plates and loaded to destruction as the
lower
plate is moved towards the upper plate at a rate of 20mm/minute. The effective
strength of the feeder sleeve will not only be dependent upon the exact
composition, binder used and manufacturing method, but also on the size and
design of the sleeve, which is illustrated by the fact that the strength of a
test
body is usually higher than that measured for a standard flat topped 6/9K
sleeve. The potential availability of a greater range of sleeve compositions
and
designs that can be used together with the invention enables the most
appropriate (technically and economically) sleeve to be specified for each
individual casting, which is not possible with the existing prior art.
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Embodiments of the invention will now be described by way of example only
with reference to the accompanying drawings in which:-
Figure 1 is a cross section of a test piece containing features of the feeder
element in accordance with invention.
Figures 2a and 2b are a cross section and a top view respectively of a known
feeder element.
Figure 3a is a known VSK feeder sleeve design.
Figure 3b is a known 6/9K feeder sleeve design.
Figure 3c is a flat topped dome feeder sleeve design.
Figure 4 is a cross section of another known feeder element.
Figures 5a to 5c are computer simulations of the known feeder element of
Figure 4 in use.
Figure 6 is a cross section of a feeder element in accordance with the
invention.
Figures 7a and 7b are computer simulations of the feeder element of figure 6
in
use.
Figure 8 is a cross section of another feeder element in accordance with the
invention.
Figure 9 is a flat topped dome feeder sleeve with modified base together with
a
feeder element in accordance with the invention.
Figure l0a is a plot of force applied against displacement for a KALMINEX
2000ZP 6/9K feeder sleeve under compression
Figures l Ob to l0i are plots of force applied against displacement for the
test
pieces of Figure 1 together with a KALMINEX 2000ZP 6/9K feeder sleeve
with varying angle a.
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METHODOLOGY
In the subsequent examples standard feeder systems comprising standard
feeder elements with standard feeder sleeves were tested as well as feeder
systems in accordance with the present invention. Both the standard and
inventive feeder elements are manufactured by pressing sheet steel. The
profiling of the base of the inventive feeder sleeves was achieved either by
manufacturing the sleeves with the profile already in place (flat topped dome
shaped sleeves) or by the use of abrasive paper on standard sleeves (6/9K
shaped sleeves). When manufacturing the profiled 6/9K shaped feeder sleeves
commercially it will be understood that it would be more practical to produce
the feeder sleeves with the profile already in place.
Moulding Test
Testing was conducted on a commercial Herman moulding machine using a
clay-bonded greensand system. A wooden pattern plate was bolted to a steel
plate. Four feeder elements and corresponding feeder sleeves were then
mounted onto the pattern plate using locating pins, spaced 150 mm and 114mm
from the centre lines of the pattern plate. A moulding flask was placed on the
pattern plate to give a mould of approximate dimensions 576mm x 432mm x
192 mm (length x width x height). Sand was added to the flask such that its
level was approximately 50mm above the height of the flask. The weight of
sand was approximately 112 kg. A 576 x 432mm ram plate was positioned
144mm above the height of the flask (approximately 94mm above the surface
of the non-compressed sand) and the mould compressed by downward
movement of the ram plate to the prescribed pressure, taking between 3 and 6
seconds to compact the sand to the level of the moulding flask. The mould was
then excavated and the condition of the feeder elements and feeder sleeves was
observed.
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Compression Test
Feeder element test pieces and feeder sleeves were tested by sitting them
between the two parallel plates of a Hounsfield compression strength tester.
The bottom plate was fixed, whereas the top plate traversed downwards via a
mechanical screw thread mechanism at a constant rate of 30mm per minute and
graphs of force applied against plate displacement were plotted.
The feeding element test pieces that were compression tested had the basic
configuration shown in Figure 1. Briefly, the feeder element test piece 10
consists of a circular base 12 (of diameter D) with a cylindrical sidewall
region
14 (of height h) extending upwardly therefrom. Contiguous with the cylindrical
sidewall region 14 is an outwardly tapering sidewall region 16 (with a
maximum diameter d) which is inclined toward the cylindrical sidewall region
14 by an angle a. The tapering sidewall region 16 serves as a mounting surface
for a feeder sleeve in use. It will be noted that these test pieces used for
compression testing are not provided with an opening in the base since they
will not be used for casting.
Various feeder elements were prepared where a = 90 (standard), 80 , 70 ,
60 , 50 , 40 , 30 or 20 . The test pieces were manufactured from mild steel
with a thickness of 0.5mm. In the case of the standard feeder element test
piece
(a = 90 ) D was 53.5mm, h was 7.5mm and d was 80.0mm. The test pieces
were designed such that the height (h) of the cylindrical sidewall region 14,
the
maximum diameter (d) of the outwardly tapering sidewall region 16 and the
area of the mounting surface provided by the first sidewall region 16 remained
constant whilst a was varied (i.e. as a decreases, the diameter (D) of the
circular base 12 increases). The feeder elements were tested with a
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KALMINEX 2000ZP 6/9K exothermic feeder sleeve as supplied by Foseco
having a density of 0.55-0.65 g/cm2 and a compression strength of the order
4kN.
COMPARATIVE EXAMPLE 1- Moulding Test
A feeder element (a metal collapsible breaker core sold under the nomenclature
MH/33 as described in W02005/051568 and shown in Figures 2a and 2b) was
tested in combination with the following feeder sleeves listed in Table 1:
Table 1
FEEDEX KALMINEX KALMINEX KALNIINEX
HD 95 2000XP 2000XP
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Shape VSK (thick 6/9K (parallel 6/9K (parallel Flat topped
walled mini- conical capped conical capped dome (flat-
sleeve as insert sleeve insert sleeve topped closed
shown in with Williams with Williams dome sleeve
figure 3a) wedge as wedge as with variable
shown in figure shown in figure wall section as
3b) 3b) shown in figure
3c)
Manufacturing Core shot Slurry formed Core shot Core shot
Process
Density (gcni ) 1.35-1.45 0.85-0.95 0.55-0.65 0.55-0.65
Strength (kN)a High (>25) Medium (10- Medium (11- Medium (11-
11) 12) 12)
Strength (kN) n/a Medium (8-9) Medium (9-10) n/a
a) strength of standard cylindrical test body b) strength of actual 6/9K
sleeve
The sleeve formulations vary according to the required product properties,
however, all have the general formulation: 20-25% aluminium fuel; 10-20%
oxidants and sensitisers; 5-10% organic binders; and 35-55% refractory
fillers.
The type of refractory fillers used has the most direct influence on both
density
and strength of the sleeves.
Referring to Figures 2a and 2b, the feeder element 20 comprises a first end
(base) 22 for mounting on a mould pattern; an opposite second end (top) 24 for
receiving a feeder sleeve; and a bore 26 between the first and second ends 22,
24 defined by a stepped sidewall 28. The second end 24 of the feeder element
20 is defined by a first sidewall region 25, said first sidewall region 25
being
perpendicular to the bore axis A. A second sidewall region 30 is contiguous
with the first sidewall region 25 and parallel to the bore axis A. The stepped
sidewall 28 additionally comprises an alternating series of first 28a and
second
28b sidewall regions of approximately equal length. The second sidewall
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region 30 constitutes the first sidewall region of the second series 28b
closest to
the second end 24 of the feeder element 20. The first series of sidewall
regions
28a consists of three sidewall regions that are perpendicular to the bore axis
A.
The second series of sidewall regions 28b consists of four sidewall regions.
The first three sidewall regions of the second series 28b are parallel to the
bore
axis A. The fourth sidewall region 32 is inclined to the bore axis A at an
angle
of 15 and has an inwardly directed annular flange in order to minimise its
footprint and thus improve knock off. The fourth sidewall region 32 is also
approximately twice the length of the other sidewalls of the second series
28b.
The feeder elements and feeder sleeves were moulded as described above using
a moulding pressure of 380PSI (2620kN). The feeder elements collapsed as
expected and there was no visible damage to the FEEDEX HD VSK feeder
sleeve, however, there was cracking and some breakages at the base of the
KALMINEX 95 6/9K sleeve and KALMINEX 2000XP dome sleeve as well as
some slumping (compression of the sleeve). The KALMINEX 2000XP 6/9K
sleeve showed severe damage and the sleeve base was broken into several
pieces. A KALMINEX 2000ZP feeder sleeve was not tested with the feeder
element 20 because it is weaker than the KALMINEX XP and KALMINEX 95
feeder sleeves which suffered from damage at 380PSI (2620kN).
The series of tests were then repeated at the higher moulding pressure of
620PSI (4275kN). Again, all of the feeder elements collapsed, however this
time there was visible damage to all of the sleeves. At the base of the FEEDEX
HD VSK sleeve there were some small internal cracks and in one instance a
chip close to the feeder element. For the KALMINEX 95 6/9K sleeve, there
was more extensive cracking at the base of the sleeve and some buckling and
slumping of the sleeve (the height of the sleeve was reduced by up to 10mm
CA 02597109 2007-08-06
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after moulding). The KALMINEX 2000XP flat topped dome shaped sleeve
showed severe damage and the sleeve base was broken into several pieces. The
KALMINEX 2000XP 6/9K sleeve was not tested.
In all instances, it was noticeable that after moulding, the first sidewall
region
of the collapsed feeder element was bent down past the horizontal i.e. was at
an
angle >90 to the bore axis.
COMPARATIVE EXAMPLE 2 - Computer Simulation
A computer simulation (ABAQUS, manufactured by Abaqus Inc.) was
conducted to evaluate the stresses imposed on a feeder system comprising a
standard feeder sleeve with similar dimensions to a FEEDEX HD VSK sleeve
and the feeder element 40 of figure 4. The advanced finite element analysis
software includes a static and dynamic stress-strain resolver which was used
for the simulations. The simulation was conducted by fixing the feeder element
in the z-axis and then putting the model under a level of strain such that it
compresses in the z-axis by a certain distance in a certain time. This puts
various parts of the model under different stresses. The model was programmed
with the mechanical properties of the sleeve and the feeder element, such that
the stresses within the feeder sleeve can be simulated and the metal feeder
element compresses.
Referring to figure 4, the feeder element 40 comprises a first end (base) 42
for
mounting on a mould pattern; an opposite second end (top) 43 for receiving a
feeder sleeve; and a bore 44 between the first and second ends 42, 43 defined
by a stepped sidewall 45. The second end 43 is defined by a first sidewall
region 46, said first sidewall region 46 being perpendicular to the bore axis
A.
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A second sidewall region 47 is contiguous with the first sidewall region 46
and
parallel to the bore axis A. The stepped sidewall 45 additionally comprises an
alternating series of first 45a and second 45b sidewall regions. The second
sidewall region 47 constitutes the first sidewall region of the second series
45b.
The first series of sidewall regions 45a consists of two sidewall regions that
are
perpendicular to the bore axis A. The second series of sidewall regions 45b
consists of three sidewall regions that are parallel to the bore axis A.
Figure 5a shows part of the a feeder sleeve 50 mounted on the feeder element
40 of figure 4 before moulding. Figure 5b is an enlarged view of the base of
the
feeder element 50 mounted on feeder element 40. Figure 5c shows an enlarged
view of the same feeder sleeve 50 and feeder element 40 during moulding. The
feeder sleeve cavity is indicated by arrow A. The shading, as shown in the
key,
represents the magnitude of the force imposed on the feeder sleeve 50.
Referring to figure 5c, it can be seen that the feeder element 40 deforms
under
pressure as expected. Surprisingly, its mounting surface 46 is forced
incrementally downward at its peripheral edge. This leads to an uneven
distribution of forces with a concentration on the inner wall of the feeder
sleeve
50 (point loading) as indicated by arrow B.
EXAMPLE 1- Computer Simulation
The computer simulation of comparative example 2 suggests that the cracking
observed in comparative example 1 may be caused by point loading on the
inner wall of the feeder sleeve. The inventors attempted to alleviate this by
changing the shape of the feeder element. The simulation was run again using
the feeder element 52 of figure 6 in place of the feeder element 40 of figure
4.
The inventive feeder element 52 is the same in all respects to that shown in
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figure 4 except that the mounting surface 54 of the feeder element 52 is
inclined relative to the bore axis A at an angle of 60 . The base of the
feeder
sleeve 56 (figure 7a) was profiled to the same angle.
Figures 7a and 7b show the feeder element 52 and the base of the
corresponding feeder sleeve 56 before and during moulding respectively.
Figure 7b shows that the force is no longer concentrated on the inner wall of
the feeder sleeve 56 during moulding. It is more evenly distributed along the
base of the feeder sleeve 56 so that no part of the base suffers from an
excessive force. It will be noted that the area of maximum force (arrow B) is
in
a region of the sleeve remote from the feeder sleeve cavity (arrow A). Failure
in this region will not cause fragments of feeder sleeve material to enter the
casting and thereby cause defects.
EXAMPLE 1- Moulding Test
A feeder element 60 as shown in Figure 8 was tested in combination with the
flat topped dome shaped feeder sleeves listed in Table 2 below (as shown in
figure 9):
Table 2
KALMINEX KALMINEX KALMINEX
2000ZP 95 2000XP
Manufacturing Slurry formed Slurry formed Core shot
Process
Density cm" 0.55-0.65 0.85-0.95 0.55-0.65
Strength (kN)* Low (4-5) Medium (10- Medium (1-12)
11)
a) strength of standard cylindrical test body
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The sleeve formulations vary according to the required product properties,
however, all have the general formulation: 20-25% aluminium fuel; 10-20%
oxidants and sensitisers; 5-10% organic binders; and 35-55% refractory
fillers.
The type of refractory fillers used has the most direct influence on both
density
and strength of the sleeves.
Referring to figure 8, the feeder element 60 is identical to the feeder
element 20
shown in figures 2a and 2b except that the first sidewall region 62 is
inclined to
the bore axis at an angle of 60 . The feeder element was manufactured from
mild steel and has a thickness of 0.5mm. The maximum diameter d is 92.9mm
and the height h is 35.4mm. The diameter of the bore 26 at the base of the
feeder element is 22.9mm.
The feeder element 60 and feeder sleeve combinations were moulded as
described above at various pressures between 420PSI (2896kPa) and 700PSI
(4826kPa). The results are summarised in Table 3 below.
Table 3
Pressure KALMINEX KALMINEX KALMINEX 95
2000ZP 2000XP
420PSI Sleeve buckled No failure No failure
(2896kPa)
460PSI Sleeve buckled No failure No failure
(3172kPa)
520PSI Sleeve buckled No failure No failure
(3585kPa)
580PSI Sleeve buckled No failure No failure
(3999kPa)
600PSI Sleeve buckled No failure No failure
(4137kPa)
700PSI Sleeve buckled Cracked at dome No failure
(4826kPa)
700PSI Collapsed Cracked at dome Buckled on one side of
4826kPa sleeve
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Re eat test
Feeder element 60 and KALMINEX 2000ZP feeder sleeve
This combination was the weakest of those tested and showed signs of failure
from low moulding pressure (420PSI; 2896kPa). The feeder element did not
compress fully and the feeder sleeve buckled. Despite this, there were no
signs
of cracking or breaking of the base of the feeder sleeve adjacent to the
feeder
element.
Feeder element 60 and KALMINEX 2000XP feeder sleeve
This combination was successful to moderately high pressure (700PSI;
4826kPa). The feeder sleeve eventually suffered from horizontal cracking
along the dome portion of the sleeve. This was attributed to the sleeve
composition (binder) and the influence of the sleeve shape and method of
manufacture (core-shot). The failure was not immediately obvious, only being
noticed when the sleeve was excavated from the sand mould after ram up. As
expected, the level of compression of the feeder element increased with the
moulding pressure until the feeder element was almost completely compressed.
No sleeve debris was discovered inside the feeder sleeve therefore this mode
of
failure would not necessarily lead to debris falling into the casting and
causing
casting defects.
The flat topped dome shaped KALMINEX 2000XP feeder sleeve was
employed with a conventional feeder element 20 in Comparative Example 1
where it failed at much lower pressures. At just 380PSI (2620kPa), the feeder
sleeve slumped and cracked along its base and at 620PSI (4275kPa) it suffered
severe damage.
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Feeder element 60 and KALMINEX 95 feeder sleeve
This combination was also very successful. The feeder element 60 compressed
and the first failure of the feeder sleeve occurred only at moderately high
pressure (700PSI; 4826kPa). No feeder sleeve debris was discovered inside the
feeder sleeve after it buckled therefore the failure would not necessarily
have
led to casting defects if the mould had been poured.
The KALMINEX 95 6/9K feeder sleeve was employed with a conventional
feeder element 20 in Comparative Example 1 with very different results. The
feeder sleeve suffered from cracking along its base at just 380PSI (2620kPa).
At 620PSI (4275kPa) it suffered from more extensive cracking along its base
and significant slumping. Cracking along the base is particularly problematic
because chips of feeder sleeve may enter the casting.
It can be clearly seen that feeder element 60 of the present invention
provides
advantages over conventional feeder elements such as feeder element 20 shown
in Comparative Example 1. When used in combination with feeder element 52
the medium strength feeder sleeves KALMINEX 2000XP and KALMINEX 95
are successful to much higher pressures. Further, when the feeder sleeves do
eventually fail their mode of failure is less likely to lead to casting
defects.
EXAMPLE 2 - Compression Test
Referring to Figure 10a, force is plotted against plate displacement for a
KALMINEX 2000ZP 6/9K feeder sleeve (as shown in figure 3b) without a
feeder element test piece. It will be noted that as force is increased, there
is
compression of the feeder sleeve associated with the natural flexibility
(compressibility) of the feeder sleeve until a critical force is applied
(point Z),
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referred to herein as the sleeve crush strength (approximately 4.5kN) after
which point the compression of the sleeve proceeds steadily under a reducing
loading.
Referring to Figure lOc, force is plotted against plate displacement for a
feeder
element test piece 10 with oc=80 and a KALMINEX 2000ZP 6/9K feeder
sleeve, the base of which was profiled at an angle of 80 . It will be noted
that
as force is increased, there is minimal compression of the feeder element and
sleeve, until a critical force is applied (point A), referred to herein as the
initial
feeder element crush strength, after which compression proceeds rapidly under
a lower loading, with point B marking the minimum force measurement after
the initial feeder element test piece crush strength occurs. Further
compression
occurs and the force increases to a maximum (maximum feeder element crush
strength, point C). When the feeder element test piece has reached or is close
to
its maximum displacement (point D) the force increases rapidly until the
sleeve
body begins to fracture. Visual inspection of the sleeve shows that at point A
there is some fracturing of the bottom corner (internal base and wall) of the
feeder sleeve.
Figure l Ob shows the plot of force against plate displacement for a feeder
element test piece 10 with a=90 and a KALMINEX 2000ZP 6/9K feeder
sleeve that had a flat base.. This shows a similar but smoother curve compared
to that in figure lOc (a=80 ) and the initial displacement occurs at a lower
applied force and continues for a long period. This is due to the initial
feeder
element test piece crush strength being lower but also, more significantly, it
is
due to damage of the feeder sleeve at the base due to the applied force from
the
feeder element test piece (damaging) breaking the feeder sleeve such that the
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feeder element is pushed up into the feeder sleeve and causes the measured
displacement.
Figures l Od and l0e show the plots of force against plate displacement for
feeder element test pieces 10 with a=70 and oc=60 respectively when tested
together with KALMINEX 2000ZP 6/9K feeder sleeves, the bases of which
were profiled at an angle of 70 and 60 respectively. Comparing these plots
with figure lOc ((x=80 ) it can be seen that the initial feeder element test
piece
crush strength (A) increases with decreasing a. It was also noted that the
amount of visible damage to the base of the sleeve was significantly reduced
and was minimal for a=70 with no fracture of the sleeve being visible.
Figures l Of and l Og show plots of force against plate displacement for
feeder
element test pieces with a=50 and a=40 respectively when tested together
with KALMINEX 2000ZP 6/9K feeder sleeves, the bases of which were
profiled at an angle of 50 and 40 respectively. For both of these, the
initial
feeder element test piece crush strength (point A) is comparable with the
previously measured feeder sleeve crush strength (Z, approximately 4.5kN).
However for both, there is greater displacement at point A compared to the
typical sleeve crush point (point Z) due to the collapsing of the feeder
element.
No damage to the base of the feeder sleeve caused by the feeder element test
piece was observed.
Figures l Oh and l0i show plots of force against plate displacement for feeder
element test pieces 10 with oc=30 and oc=20 respectively when tested
together
with KALMINEX 2000ZP 6/9K feeder sleeves, the bases of which were
profiled at an angle of 30 and 20 respectively. Comparing these plots with
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figure l Og (a=40 ) it can be seen that the initial feeder element crush
strength
(A) now decreases with decreasing a and the amount of displacement before
the initial feeder element crush strength is increased. This is thought to be
partly due to the distance travelled during the crushing of the feeder element
test piece and partly due to a small amount of compression of the feeder
sleeve
into the feeder element test piece itself at the base of the feeder sleeve.
The ideal initial crush strength of the feeder element will be dependent upon
the feeder sleeve (compression strength) and the moulding pressures employed.
The initial feeder element crush strength should clearly be lower than the
sleeve crush (compression) strength and ideally, the initial crush strength
should be lower than 3000 N. If the initial crush strength is too high then
moulding pressure may cause failure of the feeder sleeve before the feeder
element has a chance to compress. The ideal maximum crush strength is very
much dependent on the application for which the feeder element core is
intended i.e. the moulding pressure employed and the sleeve composition
(strength). If the maximum crush strength were too high for the moulding
pressures employed, then there would be insufficient collapsing of the feeder
element and subsequently insufficient sand compaction. In addition, it would
limit the type (strength) of sleeves that could be successfully employed.
