Note: Descriptions are shown in the official language in which they were submitted.
CA 02498240 2005-03-08
1
SLEEVE, PROCEDURE FOR THE MANUFACTURE THEREOF AND
MIXTURE FOR THE PRODUCTION OF SAID SLEEVE
FIELD OF THE INVENTION
This invention refers to exothermic sleeves for obtaining mini-
deadheads applicable in the obtaining of cast pieces, especially in ductile
iron, in the procedure for its production by blowing and curing and in the
mixture which constitutes said sleeve.
BACKGROUND OF THE INVENTION
The production of cast metallic pieces comprises the pouring of the
molten metal into a mould, the solidification of the metal by cooling and the
de-moulding or extraction of the piece formed by means of the removal or
destruction of the mould.
The moulds can be metallic or they can be formed by aggregates of
different materials (ceramics, graphite and, mainly, sand). These moulds
need to have some sprues or runners for communication between the
internal cavity and the exterior, through which the molten metal is poured in
the moulding or casting phase. Due to the contraction of the metal during the
cooling process, some overflows have to be foreseen in the mould which are
filled with reserve molten metal with the object of forming a deadhead
intended to offset the contractions or cavities in the metal. The purpose of
the
deadhead is to feed the piece when the melt contracts in this, for which
reason the metal has to remain in the deadhead in a liquid state for a longer
period of time than the piece. For this reason, the deadheads are usually
covered with some sleeves, consisting of insulating and/or exothermic
materials, which slow the cooling of the metal contained in the deadheads in
order to guarantee the fluidity thereof when cavity voids are produced in the
cast metal.
The use of exothermic sleeves around the deadheads allows
contraction problems to be reduced and the quality of the cast pieces to be
CA 02498240 2005-03-08
2
improved, which allows smaller deadheads (mini-deadheads) to be employed
which improve production and reduce the contact surface of the deadhead
with the cast piece, the elimination of which costs money.
Exothermic sleeves are known based on fibres manufactured in a wet
process starting with a fibrous refractory material combined with a mixture of
materials capable of producing an exothermic reaction constituted by an
oxidizable metal, in which aluminium is habitually the most used, an oxidizing
agent and a fusing agent or initiator of the exothermic reaction which,
habitually, is a fluorinated compound. The oxidizable metal, when mixed with
the oxidizing agent and the fusing agent and exposed to extreme heat, is
oxidized liberating heat in proportion to the advancing reaction.
Exothermic sleeves are also known based on sand, highly appreciated
in ductile iron foundries. The composition of these high-density sand-based
sleeves contains a greater quantity of aluminium very high so that the
amount of heat produced is very high. This heat is necessary to raise the
temperature of the sand-based sleeve before favourably influencing the
temperature of the metal in the deadhead.
In 1997 a fibre-free sleeve technology was introduced, furnishing a
new alternative to the exothermic sleeves. The patent application WO
97/00172 discloses a procedure for blowing and cold box curing to
manufacture dimensionally accurate, exothermic and/or insulating sleeves,
based on a mixture blowable into a mould, said mixture consisting of
microspheres of aluminium silicate with an alumina content of less than 38%
by weight, a binding agent for cold box curing and, optionally, some non-
fibrous loads. A typical composition for the production of exothermic sleeves
comprises hollow microspheres with an alumina content of less than 38% by
weight, aluminium powder, iron oxide and cryolite as fluorinated flux.
At the present time sleeves exist in the foundry industry for obtaining
the so-called mini-deadheads, the function of which is also to feed liquid
metal to the piece while the latter contracts during solidification.
CA 02498240 2005-03-08
3
The fundamental difference with the conventional exothermic sleeves
is that the latter maintain the metal liquid for a longer time, whereby the
volume of metal necessary, this is, the mini-deadhead, is smaller for a same
feeding operation.
This result is achieved by increasing the exothermic load of the
sleeve, but this increased exothermicity gives rise to undesired collateral
problems, such as:
1. The excess of residual aluminium in the deadhead, which is later
recast, gives rise to problems with pores in the molten pieces.
The defect known as "fish-eye" is a surface flaw in the cast piece,
originated by the accumulation of materials produced in the
recovery of contaminated sand, fundamentally by the aluminium
which is found in high proportions in exothermic sleeves.
This defect can be overcome by the use of, for example, hollow
microspheres of aluminium silicate with a low content of alumina,
such as that described in WO 97/00172.
2. Degradation of the nodules in the area of contact of the sleeve
with the piece which results in the rejection of pieces through non-
compliance with the specifications for nodulation required by the
client.
This second problem is originated by the excess of fluorine
proceeding from the fluorinated materials which are habitually
used as initiating charge in the exothermic reaction.
To avoid this problem, either the sleeve is not put in contact with
the piece, which makes it necessary to use more metal, or an
intermediate, fluoride-free biscuit is used, stuck to the mouth of the
sleeve and having an equivalent central hole, which prevents
contact of the actual sleeve with the piece. This biscuit, its
CA 02498240 2005-03-08
4
production and securing to the sleeve, signify a substantial
additional expense.
SUMMARY OF THE INVENTION
The invention arises from the challenge of furnishing a sleeve for
obtaining mini-deadheads which does not require the use of a fluoride-free
biscuit, nor of any other element to avoid contact of the sleeve with the
piece
and which, moreover, produces in the deadhead a notch to facilitate its later
separation from the cast piece and all this based on a blowable mixture,
without fluorine, capable of producing an exothermic reaction for the
provision of the heat required.
The starting point for this is, in the first place, blowing the mixture
which will constitute the fluoride-free sleeve, into a mould which has two
cores which, on one hand, will make possible the extraction of the sleeve
once cured and, on the other hand, the obtaining of two orifices: one of them
in the actual mouth of the sleeve, the orifice of which has a double interior
circumferential chamfer, capable of producing an equivalent notch in the
deadhead when the sleeve performs its function at the time of the casting.
Another orifice in the base opposite the mouth, which will be closed, after
the
sleeve is cured, with a cheap material, because that area of the sleeve has
no operational function in the casting process and only needs to be closed for
the purpose of preventing sand or other undesirable materials from falling
inside the deadhead.
This exothermic sleeve for obtaining mini-deadheads, is obtained by cold box
blowing and subsequent curing of a fluoride-free mixture which comprises (a)
hollow spheres of alumina silicate; (b) an exothermic material which
comprises:
a) An insulating/ refractory material.
b) An oxidizable metal.
c) An oxidizing agent.
d) Magnesium as the reaction initiator element.
CA 02498240 2008-09-19
27395-168
e) A catalyst purified in cold box.
Hollow microspheres of aluminium silicate are basically used as
insulating material. Mixtures of these aluminium silicate spheres with sand
5 can also be used, when it is necessary to improve the mechanical properties
of the sleeve, to the detriment of the insulating properties.
As oxidizable metals aluminium, silicon and others can be used.
Preferably aluminium in a combination of fine and coarse powder.
As oxidizing agents, nitrates, chlorates, permanganates and metallic
oxides such as iron and magnesium oxide can be used and, of course,
combinations of these compounds.
As initiator of the exothermic reaction, magnesium is used.
Once this mixture is blown into the mould, the sleeve extracted and
cured, the orifice opposite the mouth is closed with a plug which can be
made of plastic, wood, sawdust, sand, etc. and even of the same material as
the sleeve.
The use of these sieeves allows the manufacture of high quality
pieces, without degradation of the graphite nodules in the deadhead-piece
contact zone, at reduced cost, comparatively less than that of other
conventional procedures which deliver pieces of similar quality based on
contact between the deadhead and the piece through an intermediate biscuit.
CA 02498240 2008-09-19
27395-168
5a
In one process aspect, the invention provides a
process for the production, by blowing and cold box curing,
of an exothermic sleeve for a foundry mould, which
comprises: (A) introducing, by blowing, in a space defined
between the foundry mould and two cores, a mixture for the
production of the exothermic sleeve, obtaining an uncured
sleeve, open at both ends thereof, with one opening being
the mouth and having an internal double chamfer, wherein the
double chamfer is formed by means of the area of the union
of the two cores, whilst the other opening is flat, wherein
said mixture for the production of the exothermic sleeve
comprises: (a) a fluoride-free composition for the
production of the sleeve, which comprises: (a.1) an
insulating/refractory material, (a.2) an exothermic mixture
based on an oxidizable metal, an oxidizing agent capable of
producing an exothermic reaction and magnesium as an
initiator element of the reaction, and (b) a binding agent
for the cold box curing; (B) curing the uncured sleeve
prepared in (A) with a catalyst for curing said uncured
sleeve; (C) removing the cured sleeve from the mould; and
(D) locating a plug in the other opening which is in the
base of the sleeve and opposite the mouth of the sleeve.
In one product aspect, the invention provides a
sleeve produced according to the above process, which when
moulded, de-moulded and cured, has a mouth with an internal
peripheral chamfer for the entrance of a melt which forms a
deadhead, which chamfer produces in a deadhead a rut or slot
of equivalent geometry, whilst an orifice opposite the mouth
is closed with a plug of plastic, wood, sawdust, sand or the
material which constitutes the sleeve.
CA 02498240 2008-09-19
27395-168
5b
BRIEF DESCRIPTION OF THE FIGURES
Figure 1 illustrates the steps for the production
of a sleeve by means of a conventional procedure of blowing
and cold box curing pertaining to the state of the art. In
this case, the mixture for the production of sleeves is
blown into a mould (3) with the collaboration of a core (2)
[Figure 1A]; next, the sleeve (1) is cured and de-moulded
leaving the void intended for the deadhead (4) [Figure 1B];
and, finally, an intermediate biscuit (5) is applied
CA 02498240 2005-03-08
6
which has an orifice (6) for the melt to pass [Figure 1 C].
Figure 2 illustrates the steps for production of an exothermic sleeve
according to the procedure of blowing and cold box curing disclosed by the
present invention.
DETAILED DESCRIPTION OF THE INVENTION
In one aspect, the invention is related with a procedure for the
production by blowing and cold box curing of an exothermic sleeve for
obtaining mini-deadheads which comprises:
(A) Introducing, by blowing, in a cold box curing mould, in the space
defined between the mould and two cores which configure a
double chamfer in the mouth of the sleeve, a blowable mixture, to
obtain an uncured sleeve, open at both its ends, in which said
mixture comprises:
a) a fluoride-free composition for the production of sleeves based
on:
a.1) an insulating/refractory material.
a.2) an exothermic mixture which comprises an oxidizable
metal and an oxidizing agent capable of producing an
exothermic reaction, and magnesium as initiator material of the
reaction.
b) a binding agent for cold box curing;
(B) Putting the uncured sleeve prepared in (A) in contact with a cold
box curing catalyst;
(C) Leaving the sleeve resulting from (B) to cure;
CA 02498240 2005-03-08
7
(D) Removing the cured sleeve from the mould; and
(E) Locating a plug in the orifice opposite the mouth of the sleeve.
As can be appreciated in Figure 2, contrary to the conventional
procedures pertaining to the state of the art (see Figure 1), in the procedure
disclosed by this invention, the fluoride-free mixture for the production of
exothermic sleeves is blown inside a mould, in the space defined between
the mould (3) and the cores (2,2') [Figure 2A]. The cores (2,2') as well as
allowing the subsequent extraction of the sleeve, produce a double chamfer
(8) in the mouth thereof. When the sleeve (1) is cured, it is de-moulded
leaving the void intended for the deadhead (4) [Figure 2B]; and, finally, a
plug
(9) is located in an open end of the sleeve (1) for the purpose of preventing
sand or of any other undesirable element from entering inside the cavity
intended for the deadhead during the casting operation [Figure 2C].
The double chamfer (8) of the sleeve, will produce in the deadhead a
rut or slot equivalent in form which defines and facilitates the cutting line
for
the separation of the deadhead from the piece.
The insulating/refractory material (a.1) present in the fluoride-free
composition for the production of sleeves is a material which basically
comprises hollow microspheres of aluminium silicate, although it could also
contain a certain quantity of sand, on the assumption that, by sacrificing
insulating capacity, it is desired to improve the mechanical properties of the
sleeve.
In general, the quantity of insulating/refractory material (a.1) will be
between 30 and 70% by weight with respect to the total of the fluoride-free
composition.
The exothermic material (a.2) present in the fluoride-free composition
for the production of sleeves comprises an oxidizable metal and an oxidizing
agent capable of producing an exothermic reaction, wherein said exothermic
material comprises:
CA 02498240 2005-03-08
8
(i) magnesium as initiator element of the exothermic reaction,
together with one or more oxidizable metals, preferably a mixture of
powdered and granulated aluminium.
(ii) an oxidizing agent capable of reacting with the oxidizable metal
and producing an exothermic reaction at the pouring temperature of the
metal, said oxidizing agent being selected from the group formed by (a) salts
of alkaline metals or alkaline earths, for example, nitrates, chlorates and
permanganates of alkaline metals or alkaline earths; (b) metallic oxides, for
example, iron and manganese oxides, preferably iron oxide; and (c) mixtures
of (a) and (b). Said exothermic material (a.2) is in non-fibrous form, to be
capable of being blown.
A property of the composition for the production of the exothermic
sleeves according to the present invention resides in that said composition
comes without the inorganic fluorinated flux habitually utilized as initiators
of
the exothermic reaction. Magnesium is used in place thereof, which reacts at
a lower temperature whereby the exothermic reaction produced between the
oxidizable metal and the oxidizing agent begins earlier.
The reaction between the oxidizable metal and the oxidizing agent is
an exothermic reaction which produces heat thereby enhancing the heating
properties of the exothermic sleeves. Thus, the loss of temperature is
reduced of the molten material in the sprue, which is kept hotter and liquid
for
a longer time.
Depending on the level of exothermic properties it is desired to attain
in the sleeve, the quantity of oxidizable metal present in the exothermic
material (a.2) will be between 20 and 30% by weight with respect to the total
of the fluoride-free composition for the production of the sleeve.
The procedure disclosed by this invention allows exothermic sleeves
to be obtained with the desired balance of insulating and exothermic
properties merely by using the quantities of insulating material (a.1) and of
material exothermic (a.2) present in component A in the appropriate ratios by
weight.
CA 02498240 2005-03-08
9
The cold box curing binding agents which can be used in the mixture
for the production of sleeves according to the sleeve manufacturing
procedure disclosed by this invention are known. In principle, any cold box
curing binding agent can be used which is capable of maintaining the
fluoride-free composition for the production of sleeves in the form of a
sleeve
and polymerise in presence of a curing catalyst. By way of example, use can
be made of phenol resins, phenol-urethane resins, epoxy acrylic resins,
alkaline phenol resins, resins of silicates, etc. activated by an appropriate
catalyst in the gaseous phase. In a particular embodiment, this cold box
curing binding agent is selected from among the epoxy acrylic resins
activated by SO2 (gas) and the phenol-urethane resins activated by amine
(gas) known as cold box curing binding agents EXACTCAST (Ashland).
The necessary quantity of cold box curing binding agent is the
effective quantity to maintain the form of the sleeve and to permit its
effective
curing, that is, a quantity such as allows a sleeve to be produced which can
be handled after the curing process. By way of example, the quantity of cold
box curing binding agent will be between 1 and 10% with respect to the total
of the composition for the production of the sleeve.
The catalyst for cold box curing is applied in gas form and is made to
pass through the sleeve until the latter reaches a manageable consistency.
The catalyst in the gaseous phase can be an amine, carbon dioxide, methyl
formate, sulphur dioxide, etc. depending on the cold box curing binder
utilized.
Operating appropriately and selecting the components of the
composition for the production of sleeves, exothermic sleeves can be
obtained with both internal and external dimensional accuracy, which can be
coupled easily to the moulding assembly in the foundry after being
manufactured with no need to carry out additional manipulations.
The exothermic sleeve obtainable according to the procedure
disclosed by this invention constitutes an additional aspect of the present
invention.
CA 02498240 2005-03-08
As can be appreciated in Figure 2, the sleeve (1) provided by this
invention comprises:
(i) a body which surrounds the void intended to contain the
5 deadhead (4) and which has a double chamfer (8) on the mouth
thereof, and
(ii) a plug (9) in the base opposite the mouth.
10 The double chamfer (8) present in the sleeve provided by this
invention is due to the combined action of 2 cores (2,2') during the blowing
of
the mixture. The double chamfer (8) will define in the deadhead a rut or slot
which facilitates the separation of the same from the cast piece.
Due to the manufacturing procedure of the sleeve provided by this
invention, which comprises the combined action of 2 cores, 2 open ends are
produced. One of said ends contains a double chamfer (8) whilst the other
open end is closed with a plug (9) for the purpose of preventing sand or any
other undesirable element from passing into the interior of the sleeve during
the mounting of the same on the mould and, of course, during the casting
operation. Thus, said plug (9) has no structural purpose nor does it intervene
in the formation or action of the deadhead, and, for this reason, the material
used in the production of the plug can be practically any material,
advantageously, a cheap material, such as plastic, wood, sawdust, paper,
sand, etc., or even the actual material constituting the sleeve.
By way of comparison a table is provided below of blowable mixtures
for obtaining exothermic sleeves with fluorinated and fluoride-free flux,
according to the invention, for the same exothermal capacity.
CA 02498240 2005-03-08
11
COST OF THE MIXTURES FOR THE SAME DEGREE DE
EXOTHERMICITY
MINI- MINI- MINI-
DEADHEADS DEADHEADS DEADHEADS
WITH FLUORINE WITHOUT MADE OF SAND
FLUORINE
Microspheres 56.0% 54.0%
Microspheres
Aluminium, fine
22.0% 22.0% 22.0%
Aluminium,
coarse 6.0% 6.0% 6.0%
Fe304-Magnetite 4.0% 4.0% 4.0%
Cryolite 4.0% 4.0%
KNO3-
Potassium 8.0% 10.0% 8.0%
nitrate
Magnesium 4.0%
Sand 60/70 56.0%
COST PER
KILOGRAM OF 100.0% 100.0% 100.0%
MIXTURE
