Note: Descriptions are shown in the official language in which they were submitted.
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METHOD FOR THE PRODUCTION OF A METAL CASTING MOULD HAVING A
RISER AND A CAVITY FORMER AND R~ISER SLEEVE FOR USE THEREIN
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The present invention is concerned with a method for
the production of a metal casting mould having a riser, and a
cavity fonmer and riser for use therein.
The use of riser sleeves in metal casting moulds is
well known. Up to now, they have been located either by moulding
directly on the pattern used to make the mould or subsequently
by insertion into the top or cope part of the mould into a cavity
formed by a loose pattern piece which has been removed from the
top of the mould.
It has also been proposed to insert riser sleeves into
open half moulds where the mould has a vertical parting line.
3ecause of the increasing automation of methods used
for the production of casting moulds from moulding material such
as sand, there is less access to the pattern plates at the moulding
station, especially in the production of repetition castings. As
a result, it is no longer possible to apply riser sleeves directly
on the pattern plate, nor is it possible to locate a loose piece
on the pattern plate to rorm a cavity into which is later inserted
a riser sleeve.
When it is no longer possible to obtain accsss to the
pattern plate an alternative procedure may be possible with
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automatic moulding plants which are squipped with a cope mould
line which is synchronised with a drag line where cores are set
into the drag. 0n the moving cope line, inverted cope moulds
are accessible for additional work, so riser sleeves may be
inserted in the inverted cope mould.
With riser sleeves which have been used hitherto
this is either impossible or only partially successful. Known
riser sleeves have a cylindrical or almost cylindrical outer
surface for reasons partly concerned with their production
technique and partly concerned with their function. Because of
dimensional variations inherent in their method of production
such riser sleeves cannot be inserted into a preformed cavity
with sufficient confidence that they will remain in place securely.
Another group of riser sleeves, especially those
which are closed by means of a cap at one end, have a positive
taper from their base going up towards the cap, i.e, the outside
diameter becomes larger from bottom to top,and therefore they
cannot be used for the subsequent insertion into ths inverted
cope mould.
One object of this invention is the creation of a new
method for the production of a metal casting mould made of finely
dividsd mouiding material such as moulding sand which makes it
possible to insert a riser sleeve readily and so that the sleeve
remains securzly in a prefonmed cavity.
According to the invention there is provided a method
for the production of a metal casting mould having a riser, in
which method a riser sleeve is inserted in a cavity in the mould,
the cavity being fonmed by locating a cavity fonmer in a body
of particulate moulding material, compacting the material abou~
the fonmer, and removing the fonmer, characterised in that thz
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former is made oversize relative to the sleeve to be received
in the cavity and has one or more recesses therein whereby the
cavity is fonmed with at least one inwardly projecting rib-like
formation of moulded material for gripping the sleeve when
received thsrein and the former has a negative taper from bottom
to top.
When objects such as riser sleeves are made in
quantity to a predetenmined nominal size i.e. height and diametsr,
in practice the slseves deviate from that nominal size. Such
sleeves can still be used provided that they can be inssrtsd in
ths mould cavitiss which ars to rsceivs them, and that oncs
inserted they will remain in place.
By checking and recording the actual height and
diameter of a particular nominal size of slesve during the courss
of production it is possibls to calculats ths standard deviation
in height and diameter from the mean values for those parameters
for that slseve.
The invention also includes for carrying out ths
method a former whose exterior has a plurality of radially spaced
apart grooves extending between the top and towards the bottom
of the former and whose outside diameters are larger than the
corresponding mean outside diameters plus three times ths
standard deviation of the riser sleeves which are to be used.
In this way the outside diameter of the former is larger than
the outside diameter of ths riser slesvss which are to be
inserted in the cavities. Retention of the sleeves in the
cavities results from the grip on the outside of
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the riser sleeve of the sand ribs which are moulded from the recesses
in the former. This results in a clamping effect because according
t:o the invention the circles which can be geometrically incribed
inside the base of the recesses have diameters which are smaller than
the corresponding mean outside diameters less three times the
standard deviation of the riser sleeves which are to be used.
According to a preferred feature of the invention the
former has at its top end a raised rim which is so dimensioned that
the total height of the former thus constituted is greater than the
1û mean height plus three times the standard deviation of the actual
riser sleeves which are to be used. Thus there remains after the
insertion of the riser sleeve an annular cavity into which any
sand, which has been loosened during the insertion of the riser sleeve,
may fall, without in any way hindering the desired depth of location
of the riser sleeve.
According to another preferred feature of the invention
the former has at its top end an annular depression which is so
dimensioned that the height of the former up to the base of the
annular depression is smaller than the mean height less three times
the standard deviation of the actual riser sleeves which are to be
used.
By using such a former there is formed after moulding an
annular rib of moulding material. This rib is of such depth that
it touches even the lowest or shortest inserted sleeve at its top
end and when longer riser sleeves are inserted the pad becomes
partially compressed. A sealing means is achieved with this arrange-
ment.
A further example of a former according to the invention
is characterised in that the annular depression adjoins a surface
lying above the level of the annular depression whereby the height
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of the former up to this surface is greater than the mean height
plus three times the standard deviation of the actual riser sleeves
which are to be ussd. By this means, using riser sleeves which
are open at the top, an additional riser volume is achieved, while
when using a riser sleeve with a closed top an air gap remains
between the surface and the top of the cap of the riser sleeve.
The invention also includes a riser sleeve of sxothermic,
exothermic and heat-insulating or heat-insulating material.
According to the invention such a riser sleeve is characterised
1û in that its outer surface exhibits from its base to its top a
negative taper having an angle from 2 to 2û with respect to
the vertical. Preferably, the inner and outer surface of the
tapered riser sleeve are parallel one with another. In another
embodiment the sleeve also has a height to diameter ratio (with
respect to the lowermost internal diameter~ in the range 1 : 1 to
1.6 : 1.
According to a further embodiment a riser sleeve according
to the invention is characterised in that it has a closed top in
which a blind recess is provided which reduces the thickness of the
top and which permits the controlled venting of the riser.
Because the cavity is oversize by a predetenmined amount,
when a riser sleeve is inserted, several air cavities are formed
which are separated from each other by the vertical sand ribs and
which are connected one with another by the gap at the bottom of the
cavity. This has several advantages. Firstly, heat transfer to
surrounding moulding material or moulding sand is reduced, and the
modulus extension factor of the riser sleeve is increased. Secondly,
the atmospheric oxygen contained in the air cavities can lead to a
reduction in the necessary quantity of oxidising agents in the sleeve
material or by retaining the same amount of oxidising agents the
ignition and burning rates of the exothermic sleeves can be increased.
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Further, in the case of green sand moulds the transfer of moisture
to the riser sleeve is reduced. Thereby the ignition and burning
characteristics in the case of exothermic sleeves will become more
consistent.
Preferably a breaker core is present at the lower end of
the riser sleeve and the core has an outside diameter larger than
that of the riser sleeve so that the cavity formed by the former
can be sealed by the projecting edge of the breaker core. 3y choosing
suitable dimensions for the breaker core the breaker core can be
made to seal the cavity fo~med by the former.
The former of the invention may be made from any suitable
material which will retain its shape during mould production.
The invention is illustrated with reference to the
drawings in which
Figure 1 is a cross section through a closed tapered riser
sleeve fitted with a breaker core.
Figure 2 is a section through a tapered open riser sleeve
fitted with a breaker core.
Figure 3 is a top plan view of a fonmer.
Figure 4 is a section along the line A-F of Figure 3.
Figure 5 shows schematically a riser sleeve fitted with
a breaker core inserted into a casting mould,
Figure 6 shows schematically a riser slseve without a
breaker core inserted into a casting mould.
Figure 7 shows a cavity in a sand mould for the later
insertion of a riser sleeve the cavity being formed by a former
according to the invention.
Figure 2 is analogous to Figure 7 but shows a riser
sleeve fitted with a breaker core inserted into the cavity in the
sand mould.
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In Figure 1 a riser sleeve 1 has a closed top 2 and a
brsaksr cors 4 fitted by glueing, whose outside diameter i5 larger
than the outside diameter of the riser sleeve 1. As a result the
breaker core 4 exhibits with respect to the riser sleeve 1 a pro-
jecting rim 4'.
In Figure 2 a riser sleeve 1a is shown which is open atthe top and to which a breaker core 4 can be fitted as is indicated
in the reprssentation of Figure 2.
The riser sleeve 1 or 1a is made from exothermic, exothenmic
and heat-insulating or heat-insulating material. The breaker cores
4 are made of refractory material.
As can be seen from Figures 1 and 2 the outer surface of
the respectiv~ riser sleeve has a negative taper from bottom to top
having an angle of from 2 to 20 with respect to the vertical.
Moreover the inner and outer surfaces of the tapered riser sleeve
are parallel one to another.
The ratio of height to diameter of the riser sleeve l or
1a lies in the range of 1 : 1 to 1,6 : 1 with respect to the lower-
most inside diameter.
In the exampls according to Figure 1 the riser slseve 1
has a closed top 2 and in this closed top at least one blind recess
11 which reduces the thickness of the top 2 is provided. ~y means
of one or more of such blank recessss a controlled venting of the
riser i5 possible.
In Figures 3 and 4 a fonmer 5 is shown whereby the left
half of Figure 4 represents a sectioned view of lins A-B in Figure
3 and the right half of Figure 4 represents the external view.
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The former of Figures 3 and 4 has a tapered form
corresponding to that of the riser sleeves 1 and 1a according to
Figures 1 and 2, but, the Outside diameters of lhe fonmer 5 are
larger than the respective mean outside diameters plus three
times the standard deviation of the ris?r sleeves which are to
be used. Oy this means it is ensured that the former 5 has at
any point on its height or length an outside diameter which is
larger than the outside diameter of the riser sleeve which after
moulding will be inserted or pushed into the cavity formed by
the use of the former 5.
The outer surface of the former 5 has distributed around
its circumference, severalrecesses 6 which extend from the top of
the former towards the bottom. The recesses6 form ribs from the
moulding sand. The depth of the recesses 6 is chosen such that the
circles which can be geometrically inscribed inside the base of the
recesseshave diameters smaller than the corresponding mean outside
diameters less three times the standard deviation of the riser
sleeves which are to used. In this way the height of the sand
ribs formed in the cavity by the recesses6 is always such that a
riser sleeve inserted into the cavity is gripped by the ribs. The
riser sleeve is held fast by the sand ribs with sufficient force
to withstand rough treatment likely to separate the sleeve from the
cavity.
A raised rim 7 is present on top of the former 5 and is
dimensioned so that the total height of the former 5 so formed is
larger than the mean height plus three times the standard deviation
of the riser sleeves which are to be used. 3y "mean height" of the
riser sleeve the mean height of a particular type of riser sleeva
is to be understood. Therefore the former 5 has an added length
or is oversize with respect to the length or height of the riser
sleeve which is to be inserted. As a result there remains after the
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insertion of the riser sleeve an empty annular cavity into which
sand which is loosened during the insertion of the riser sleeve
may fall. This ensures that the riser sleeve is always fixed
at the desired depth.
An annular depression 7a is present within the rim 7 and
is so dimensioned that the height of the fonmer 5 up to the base
of the annular depression 7a is smaller than the mean height less
three times the standard deviation of the riser sleeves 1, 1a which
are to be used. As a result an annul2r sand pad is fonmed in the
cavity produced by the fonmer 5 and the height of the pad is suff-
icient for the pad to contact the top of even the shortest or
lowest riser sleeve. With this arrangement a seal is achieved
especially in the case of open riser sleeves, or when using capped
sleeves which have been vented in the foundry, so that when the
15 sleeves are used and filled with metal, metal cannot flow from -~
above, behind the sleeves.
The annular depression 7a on its inside adjoins a
surface 5 which lies above the level of the annular depression,'he
height of the former to this surface 3 being larger than the mean
height plus three times the standard deviation of the riser sleeves
1, 1a which are to be used. By "mean height" here again the mean
height of a particular type of riser sleeve is to be understood.
As a result, after a riser sleeve 1 or 1a has been inserted into the
preformed cavity an air gap or a volume of air remains between the
top end of the riser sleeve and the surface of the cavity opposite
to the sleeve.
Figure 5 is a schematic representation showing a pre-
formed cavity 9 fonmed by means of a former 5 according to the
invention and in which cavity 9 has been inserted a riser sleeve 1.
It is to be understood that the riser sleeve 1 is in close contact
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on its outer surface with the ribs which are formed on the
inner surface of the prefonmed cavity 3 by means of therecesses 6
in the former. In addition the cap 2 of the riser sleeve 1 is in
contact with the annular pad which has been formed by the annular
S depression 7a in the fonmer 5. Between the outside of the insert-
ed riser sleeve 1 and the wall of the preformed cavity 9 there are
several air cavities separated from one another by the vertical
ribs but which are all connected one with another by means of the
annular air cavity which is formed in the prefonmed cavity 9 by
the rim 7 on the former 5. In addition, an air cavity exists
between the cap 2 of the riser sleeve 1 and the opposite end wall
of the preformed cavity 9 and is also to be seen in Figure 5.
In the example according to Figure 5 a riser sleeve 1
with breaker core 4 is used. Since the diameter of the breaker
core 4, already described above, is larger than the lowenmost
outside diameter of the riser sleeve 1 a seal is formed between
the projecting rim 4' of the breaker core 4 and, according to
Figure 5, the lower end of the wall of the preformed cavity 9
when the riser sleeve 1 is inserted into the preformed cavity 9.
Figure 6 is an analogous view to Figure 5 but where a riser
sleeve 1, which has no breaker core, is inserted. In order to
achieve a seal between the outside of the riser sleeve 1 and the
lower end of the wall of the preformed cavity 9 by the use of such
a riser sleeve the outside diameter at the lower end of the former
5 is so narrowly shapbd that when a riser sleeve 1 is inserted a
sealing contact results between the outside of the riser sleeve and
the wall of the preformed cavity 9.
Figure 7 is a schematic view of a section of a sand mould
with a preformed cavity 9 in compacted moulding sand 10 and having
sand ribs 11 formed by the recesses6 in the fonmer 5. An annular rib
30 12 is formed by the rim 7, the cavity 7a and the surface 8 in the
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shape of the former 5.
Figure 8 is an analogous view to Figure 7 in which a rissr
sleeve 1 has been inserted into the preformed cavity 9~. It may be
seen that to a certain extent during insertion of the riser sleeve
1 the sand ribs 11 have been compressed or pinched together so
that a secure fit is ensured between the outside of the riser sleeve
1 and the ribs 11. 13 indicates that part of the sand ribs 11 with
which the riser sleeve does not come into contact. Sand 14 loosened
during the insertion of the riser sleeve 1 has fallen into the des-
cribed annular cavity where it does no harm.
Figure 8 shows once again the seal at the wall of thepreformed cavity 9 between the breaker core 4 and the compacted
moulding sand 10.
As has been said, the riser sleeves may consist of exothermic,
15 exothermic and heat-insulating or heat-insulating material.
Examples of such materials are given below:-
EXAMPLE 1
Exothermic riser sleeves wers made having the following
composition by weight:-
Silica sand 51.5%
Aluminium grindings 26.0%
Sodium cryolite5.0%
Clay binder 2.0%
Resin binder 3.5%
Sodium nitrate12.0%
The materials were mixed with 3-4% by weight water and compacted in
core boxes by ramming by hand or using a core shooting machine. The
"green" sleeves were stripped from the core boxes and dried at 180C.
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The sleeves had a density of 1.3 g/cm3.
EXAMPLE 2
Exothermic and heat-insulating riser sleeves were made
having the following composition by weight:-
Aluminium powder and grindings 24.0%
Ooric acid 1.0%
Sodium cryolite 7.0%
Resin binder 6.9%
Iron oxide 11.0%
Silica sand 17.0%
Alumina 1~.5%
Organic fibres 3.6%
Lightweight silica 11.0%
A slurry of the matsrials was produced in water. Formers for the
sleeves were im~ersed in the slurry and the solid materials in theslurry were sucked on to the formers by means of pressure. The
formers were removed and the "green" riser sleeves were dewatered.
The sleeves were then stripped from the formers and dried at 120 C.
The sleeves had a density of 0.~5 g/cm .
EXAMPLE 3
Heat-insulating riser sleeves were made having the
following composition by weight:-
Aluminium 5.5%
Alumina 13.0~
Resin binder 9.0%
Aluminium sulphate 1.0%
Colloidal silica sol 6.5%
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Aluminium silicate fibres 6.0%
Silica fibres 55.0%
Organic fibres 4.0%
Ths sleeves were produced using the method descri;oed in
Exam,ole 2.
The sleeves had a density of 0.45 g/cm .
