U.S. patent application number 11/883419 was filed with the patent office on 2009-01-15 for feeder element for metal casting.
Invention is credited to Philip Robert Dahlstrom, Anthony Cosmo Midea, Colin Powell, Trevor Leonard Tackaberry.
Application Number | 20090014482 11/883419 |
Document ID | / |
Family ID | 36745596 |
Filed Date | 2009-01-15 |
United States Patent
Application |
20090014482 |
Kind Code |
A1 |
Tackaberry; Trevor Leonard ;
et al. |
January 15, 2009 |
Feeder Element for Metal Casting
Abstract
The present invention discloses 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 (54) for a feeder sleeve in use, said first
sidewall region being inclined to the bore axis by less than
90.degree. 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 offers improvements over the element disclosed in
WO2005/051568.
Inventors: |
Tackaberry; Trevor Leonard;
(Strongville, OH) ; Dahlstrom; Philip Robert;
(Cleveland, OH) ; Midea; Anthony Cosmo;
(Brunswick, OH) ; Powell; Colin; (Birmingham,
GB) |
Correspondence
Address: |
NIXON & VANDERHYE, PC
901 NORTH GLEBE ROAD, 11TH FLOOR
ARLINGTON
VA
22203
US
|
Family ID: |
36745596 |
Appl. No.: |
11/883419 |
Filed: |
April 30, 2007 |
PCT Filed: |
April 30, 2007 |
PCT NO: |
PCT/GB2007/001572 |
371 Date: |
November 28, 2007 |
Current U.S.
Class: |
222/591 |
Current CPC
Class: |
B22C 9/088 20130101;
B22C 9/084 20130101 |
Class at
Publication: |
222/591 |
International
Class: |
B22D 35/04 20060101
B22D035/04 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 9, 2006 |
GB |
0611430.0 |
Claims
1. A feeder element for use in metal casting, said feeder element
comprising: (iv) a first end for mounting on a mould pattern; (v)
an opposite second end for receiving a feeder sleeve; and (vi) 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.degree. 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.
2. The feeder element of claim 1 comprising additional sidewall
regions, whereby multiple steps in the sidewall are defined.
3. The feeder element of claim 2, wherein at least one of the
additional sidewall regions is inclined at a greater angle to the
axis than the first sidewall region.
4. The feeder element of any preceding claim, wherein the first
sidewall region is inclined to the bore axis at an angle of between
5.degree. and 85.degree..
5. The feeder element of any preceding claim, wherein the first
sidewall is inclined to the bore axis at an angle of between
30.degree. and 70.degree..
6. The feeder element of any preceding claim, wherein the initial
crush strength is no more than 5000 N.
7. The feeder element of any preceding claim, wherein the initial
crush strength is at least 250 N.
8. The feeder element of any preceding claim, wherein said
compression in use is non-reversible.
9. The feeder element of any preceding claim, wherein the stepped
sidewall of the feeder element comprises a first series of sidewall
regions in the form of rings interconnected and integrally formed
with a second series of sidewall regions.
10. The feeder element of claim 9, which is defined by the first
sidewall region and one each of the first and second series of
sidewall regions.
11. The feeder element of claim 9 or 10, wherein the thickness of
the sidewall regions is 0.2 to 1.5 mm.
12. The feeder element as claimed in any one of claims 9 to 11,
wherein said rings are circular.
13. The feeder element of any one of claims 9 to 12, wherein said
rings are planar.
14. The feeder element of any one of claims 9 to 13, wherein 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.
15. The feeder element of any one of claims 9 to 14, wherein the
second series of sidewall regions are annular.
16. The feeder element of any one of claims 9 to 15, wherein the
first end of the feeder element is defined by a sidewall region
having a greater length than the other sidewall regions of the
corresponding series.
17. The feeder element of any one of claims 9 to 16, wherein the
sidewall region defining the first end of the feeder element is
inclined to the bore axis by an angle of 5 to 30.degree..
18. The feeder element of any one of claims 9 to 17, wherein the
thickness of the sidewall regions is from 4 to 24% of the distance
between the inner and outer diameters of the first sidewall
region(s).
19. The feeder element of claim 18, wherein a free edge of the
sidewall region defining the first end of the feeder element has an
inwardly directed annular flange or bead.
20. A feeder system for metal casting comprising a feeder element
in accordance with any one of claims 1 to 19 and a feeder sleeve
secured thereto.
21. A feeder system in accordance with claim 20, in which the
feeder sleeve is secured to the feeder element by adhesive or by
being a push fit with the feeder element or by moulding the sleeve
around part of the feeder element.
22. A feeder system in accordance with claim 20 or 21, wherein the
base of the feeder sleeve is profiled at the same angle as the
first sidewall region of the feeder element of any one of claims 1
to 20.
23. A feeder system in accordance with any one of claims 20 to 22,
wherein the sleeve strength is at least 5 kN and less than 20 kN.
Description
[0001] 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.
[0002] 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 tmm 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.
[0003] 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 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.
[0004] 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.
[0005] Breaker cores may also be manufactured out of metal. DE 196
42 838 A1 discloses a modified feeding system in which the
traditional ceramic breaker core is replaced by a rigid flat
annulus and DE 201 12 425 U1 discloses a modified feeding system
utilising a rigid "hat-shaped" annulus.
[0006] Casting moulds are commonly formed using a moulding pattern
which defines 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.
[0007] 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.
[0008] 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
"ramming 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.
[0009] 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 direct contact with the pattern plate and may be
typically 5 to 25 mm 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.
[0010] 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.
[0011] 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.
[0012] WO2005/051568 (the entire disclosure of which is
incorporated herein by reference) 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.
[0013] The feeder element of WO2005/051568 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 element with a FEEDEX HD-VS159 feeder sleeve, which is
designed to be pressure resistant (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 WO20051051568 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.
[0014] 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.
[0015] 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.degree. 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.
[0016] 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.
[0017] It will be noted upon reading WO2005/051568 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.
[0018] Preferably the first sidewall region is inclined to the bore
axis at an angle of between 50 and 85.degree., more preferably at
an angle of between 15.degree. and 80.degree., even more preferably
at an angle of between 25.degree. and 75.degree., and most
preferably at an angle of between 30.degree. and 70.degree.. For
example, the first sidewall region may be inclined to the bore axis
at an angle of 60.degree..
[0019] 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.
[0020] 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.
[0021] 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
suitable materials including metal. In certain configurations it
may be more appropriate to consider the feeder element to be a
feeder neck.
[0022] 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.
[0023] 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.
[0024] 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 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.
[0025] 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.
[0026] 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)).
[0027] Preferably, the distance between the inner and outer
diameters of the first series of sidewall regions is 4 to 10 ml 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.
[0028] 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-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 defining the base
may be inclined to the bore axis at an angle of 5 to 30.degree.,
preferably 5 to 15.degree.. Preferably, the free edge of the
sidewall region defining the first end of the feeder element has an
inwardly directed annular flange or bead.
[0029] 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.
[0030] 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.
[0031] 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 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.
[0032] The invention allows the use of lower strength sleeves to be
used down to a value of 3.5 kN. Preferably, the sleeve strength is
at least 5 kN. Preferably, the sleeve strength is less than 20 kN.
For ease of comparison the strength of a feeder sleeve is defined
as the compressive strength of a 50.times.50 mm 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 20 mm/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.
[0033] Embodiments of the invention will now be described by way of
example only with reference to the accompanying drawings in
which:--
[0034] FIG. 1 is a cross section of a test piece containing
features of the feeder element in accordance with invention.
[0035] FIGS. 2a and 2b are a cross section and a top view
respectively of a known feeder element.
[0036] FIG. 3a is a known VSK feeder sleeve design.
[0037] FIG. 3b is a known 6/9K feeder sleeve design.
[0038] FIG. 3c is a flat topped dome feeder sleeve design.
[0039] FIG. 4 is a cross section of another known feeder
element.
[0040] FIGS. 5a to 5c are computer simulations of the known feeder
element of FIG. 4 in use.
[0041] FIG. 6 is a cross section of a feeder element in accordance
with the invention.
[0042] FIGS. 7a and 7b are computer simulations of the feeder
element of FIG. 6 in use.
[0043] FIG. 8 is a cross section of another feeder element in
accordance with the invention.
[0044] FIG. 9 is a flat topped dome feeder sleeve with modified
base together with a feeder element in accordance with the
invention.
[0045] FIG. 10a is a plot of force applied against displacement for
a KALMINEX 2000ZP 6/9K feeder sleeve under compression
[0046] FIGS. 10b to 10i are plots of force applied against
displacement for the test pieces of FIG. 1 together with a KALMINEX
2000ZP 6/9K feeder sleeve with varying angle .alpha..
METHODOLOGY
[0047] 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
[0048] 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 114 mm from the centre
lines of the pattern plate. A moulding flask was placed on the
pattern plate to give a mould of approximate dimensions 576
mm.times.432 mm.times.192 mm (length.times.width.times.height).
Sand was added to the flask such that its level was approximately
50 mm above the height of the flask. The weight of sand was
approximately 112 kg. A 576.times.432 mm ram plate was positioned
144 mm above the height of the flask (approximately 94 mm 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.
Compression Test
[0049] Feeder element test pieces and feeder sleeves were tested by
sitting them between the two parallel plates of a Hounsfield
compression strength tester.
[0050] The bottom plate was fixed, whereas the top plate traversed
downwards via a mechanical screw thread mechanism at a constant
rate of 30 mm per minute and graphs of force applied against plate
displacement were plotted.
[0051] The feeding element test pieces that were compression tested
had the basic configuration shown in FIG. 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 .alpha.. 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.
[0052] Various feeder elements were prepared where
.alpha.=90.degree. (standard), 80.degree., 70.degree., 60.degree.,
50.degree., 40.degree., 30.degree. or 20.degree.. The test pieces
were manufactured from mild steel with a thickness of 0.5 mm. In
the case of the standard feeder element test piece
(.alpha.=90.degree.) D was 53.5 mm, h was 7.5 mm and d was 80.0 mm.
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
KALMINEX 2000ZP 6/9K exothermic feeder sleeve as supplied by Foseco
having a density of 0.55-0.65 g/cm.sup.2 and a compression strength
of the order 4 kN.
COMPARATIVE EXAMPLE 1
Moulding Test
[0053] A feeder element (a metal collapsible breaker core sold
under the nomenclature MH/33 as described in WO2005/051568 and
shown in FIGS. 2a and 2b) was tested in combination with the
following feeder sleeves listed in Table 1:
TABLE-US-00001 TABLE 1 FEEDEX KALMINEX KALMINEX KALMINEX HD 95
2000XP 2000XP 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 FIG. 3a) wedge as wedge as with
variable shown in shown in wall section as FIG. 3b) FIG. 3b) shown
in FIG. 3c) Manufacturing Core shot Slurry formed Core shot Core
shot Process Density (gcm.sup.-3) 1.35-1.45 0.85-0.95 0.55-0.65
0.55-0.65 Strength (kN).sup.a High (>25) Medium (10-11) Medium
(11-12) Medium (11-12) Strength (kN).sup.b n/a Medium (8-9) Medium
(9-10) n/a .sup.astrength of standard cylindrical test body
.sup.bstrength of actual 6/9K sleeve
[0054] 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.
[0055] Referring to FIGS. 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 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.degree. 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.
[0056] The feeder elements and feeder sleeves were moulded as
described above using a moulding pressure of 380 PSI (2620 kN). 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 380 PSI (2620
kN).
[0057] The series of tests were then repeated at the higher
moulding pressure of 620 PSI (4275 kN). 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 10 mm 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.
[0058] 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
[0059] 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 FIG. 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.
[0060] Referring to FIG. 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. 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.
[0061] FIG. 5a shows part of the a feeder sleeve 50 mounted on the
feeder element 40 of FIG. 4 before moulding. FIG. 5b is an enlarged
view of the base of the feeder element 50 mounted on feeder element
40 . . . FIG. 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 FIG. 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
[0062] 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 FIG. 6 in place of the feeder element 40 of FIG. 4.
The inventive feeder element 52 is the same in all respects to that
shown in FIG. 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.degree.. The base of the feeder sleeve 56 (FIG. 7a) was profiled
to the same angle.
[0063] FIGS. 7a and 7b show the feeder element 52 and the base of
the corresponding feeder sleeve 56 before and during moulding
respectively. FIG. 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
[0064] A feeder element 60 as shown in FIG. 8 was tested in
combination with the flat topped dome shaped feeder sleeves listed
in Table 2 below (as shown in FIG. 9):
TABLE-US-00002 TABLE 2 KALMINEX KALMINEX KALMINEX 2000ZP 95 2000XP
Manufacturing Slurry formed Slurry formed Core shot Process Density
(gcm.sup.-3) 0.55-0.65 0.85-0.95 0.55-0.65 Strength (kN).sup.a Low
(4-5) Medium (10-11) Medium (1-12) .sup.astrength of standard
cylindrical test body
[0065] 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.
[0066] Referring to FIG. 8, the feeder element 60 is identical to
the feeder element 20 shown in FIGS. 2a and 2b except that the
first sidewall region 62 is inclined to the bore axis at an angle
of 60.degree.. The feeder element was manufactured from mild steel
and has a thickness of 0.5 mm. The maximum diameter d is 92.9 mm
and the height h is 35.4 mm. The diameter of the bore 26 at the
base of the feeder element is 22.9 mm.
[0067] The feeder element 60 and feeder sleeve combinations were
moulded as described above at various pressures between 420 PSI
(2896 kPa) and 700 PSI (4826 kPa). The results are summarised in
Table 3 below.
TABLE-US-00003 TABLE 3 KALMINEX KALMINEX KALMINEX Pressure 2000ZP
2000XP 95 420 PSI Sleeve buckled No failure No failure (2896 kPa)
460 PSI Sleeve buckled No failure No failure (3172 kPa) 520 PSI
Sleeve buckled No failure No failure (3585 kPa) 580 PSI Sleeve
buckled No failure No failure (3999 kPa) 600 PSI Sleeve buckled No
failure No failure (4137 kPa) 700 PSI Sleeve buckled Cracked at
dome No failure (4826 kPa) 700 PSI Collapsed Cracked at dome
Buckled on (4826 kPa) one side of Repeat test sleeve
Feeder Element 60 and KALMINEX 2000ZP Feeder Sleeve
[0068] This combination was the weakest of those tested and showed
signs of failure from low moulding pressure (420 PSI; 2896 kPa).
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 KALMIEX 2000XP Feeder Sleeve
[0069] This combination was successful to moderately high pressure
(700 PSI; 4826 kPa). 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.
[0070] 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 380 PSI
(2620 kPa), the feeder sleeve slumped and cracked along its base
and at 620 PSI (4275 kPa) it suffered severe damage.
Feeder Element 60 and KALMIEX 95 Feeder Sleeve
[0071] 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 (700 PSI; 4826 kPa). 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.
[0072] 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 380 PSI (2620 kPa). At 620 PSI (4275 kPa) 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.
[0073] 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
[0074] Referring to FIG. 10a, force is plotted against plate
displacement for a KALMINEX 2000ZP 6/9K feeder sleeve (as shown in
FIG. 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), referred
to herein as the sleeve crush strength (approximately 4.5 kN) after
which point the compression of the sleeve proceeds steadily under a
reducing loading.
[0075] Referring to FIG. 10c, force is plotted against plate
displacement for a feeder element test piece 10 with
.alpha.=80.degree. and a KALMINEX 2000ZP 6/9K feeder sleeve, the
base of which was profiled at an angle of 80.degree.. 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.
[0076] FIG. 10b shows the plot of force against plate displacement
for a feeder element test piece 10 with .alpha.=90.degree. and a
KALMINEX 2000ZP 6/9K feeder sleeve that had a flat base. This shows
a similar but smoother curve compared to that in FIG. 10c
(.alpha.=80.degree.) 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 feeder
element is pushed up into the feeder sleeve and causes the measured
displacement.
[0077] FIGS. 10d and 10e show the plots of force against plate
displacement for feeder element test pieces 10 with
.alpha.=70.degree. and .alpha.=60.degree. respectively when tested
together with KALMINEX 2000ZP 6/9K feeder sleeves, the bases of
which were profiled at an angle of 70.degree. and 60.degree.
respectively. Comparing these plots with FIG. 10c
(.alpha.=80.degree.) it can be seen that the initial feeder element
test piece crush strength (A) increases with decreasing .alpha.. It
was also noted that the amount of visible damage to the base of the
sleeve was significantly reduced and was minimal for
.alpha.=70.degree. with no fracture of the sleeve being
visible.
[0078] FIGS. 10f and 10g show plots of force against plate
displacement for feeder element test pieces with .alpha.=50.degree.
and .alpha.=40.degree. respectively when tested together with
KALMINEX 2000ZP 6/9K feeder sleeves, the bases of which were
profiled at an angle of 50.degree. and 40.degree. 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 4.5 kN). 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.
[0079] FIGS. 10h and 10i show plots of force against plate
displacement for feeder element test pieces 10 with
.alpha.=30.degree. and .alpha.=20.degree. respectively when tested
together with KALMINEX 2000ZP 6/9K feeder sleeves, the bases of
which were profiled at an angle of 30.degree. and 20.degree.
respectively. Comparing these plots with FIG. 10g
(.alpha.=40.degree.) it can be seen that the initial feeder element
crush strength (A) now decreases with decreasing .alpha. and the
amount of displacement before the initial feeder element crush
strength is increased. This is thought to be partly due to the
distance traveled 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.
[0080] 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.
* * * * *