WO2004022262A1

WO2004022262A1 - Sleeve, production method thereof and mixture for production of same

Info

Publication number: WO2004022262A1
Application number: PCT/ES2002/000422
Authority: WO
Inventors: Jaime Prat Urreiztieta
Original assignee: Iberia Ashland Chemical, S.A.
Priority date: 2002-09-09
Filing date: 2002-09-09
Publication date: 2004-03-18
Also published as: PT1543897E; ATE365086T1; BR0215879A; DK1543897T3; DE60220841D1; AU2002336110B2; CA2498240C; CN1668402A; US20050247424A1; EP1543897A1; EP1543897B1; JP2005537935A; DE60220841T2; BR0215879B1; ES2288560T3; CN1305601C; CA2498240A1; SI1543897T1; US20080121363A1; AU2002336110A1

Abstract

The invention relates to a method of producing sleeves for mini-feeders. According to the invention, a fluorine-free mixture, which contains aluminium silicate microspheres, an oxidizable metal, such as aluminium powder, an oxidizable agent and magnesium by way of an exothermic reaction initiator, is introduced by means of blowing into a mould comprising two male parts in order to produce a sleeve having two openings, one of which is sealed with a plug before use.

Description

SLEEVE, PROCESS FOR ITS MANUFACTURE AND MIXTURE FOR THE PRODUCTION OF SUCH SLEEVE

FIELD OF THE INVENTION

This invention relates to exothermic sleeves for obtaining minimazarotas applicable to obtaining castings, especially ductile iron, to the process for their production by blowing and cold box curing and to the mixture that constitutes said sleeve.

BACKGROUND OF THE INVENTION

The production of cast metal parts includes pouring the molten metal into a mold, solidifying the metal by cooling, and removing or removing the part formed by removing or destroying the mold.

The molds can be metallic or can be formed by aggregates of different materials (ceramic, graphite and, above all, sand). These molds must have drinkers or communication holes between the internal and external cavity, through which the molten metal is poured in the molding or casting phase. Due to the contraction of the metal during cooling, overflows must be provided in the mold, which are filled with reserve molten metal in order to form a riser intended to compensate for the contractions or cracks in the metal. The riser is intended to feed the piece when the broth contracts in it, so the metal must remain in the riser in a liquid state for a longer period of time than the piece. For this reason, the risers are usually covered with sleeves, Composed of insulating and / or exothermic materials, which retard the cooling of the metal contained in the risers to guarantee their fluidity when chinks occur in the cast metal.

The use of exothermic sleeves around the risers reduces shrinkage problems and improves the quality of the castings, which allows the use of smaller risers (miniature risers) that improve production and reduce the contact area of the riser with the piece casting, the removal of which costs money.

Exothermic fiber-based sleeves are known made in the wet route from a fibrous refractory material combined with a mixture of materials capable of producing an exothermic reaction consisting of an oxidizable metal, in which aluminum is the most commonly used, an agent oxidant and a flux or initiator of the exothermic reaction, which is usually a fluorinated compound. The oxidizable metal, when mixed with the oxidizing agent and flux and exposed to extreme heat, oxidizes releasing heat as the reaction progresses.

Exothermic sand-based sleeves are also known, highly appreciated in ductile iron foundries. The composition of these high-density sand-based sleeves contain a greater amount of very high aluminum so that the amount of heat generated is very high. This heat is necessary to raise the temperature of the sand-based sleeve before favorably influencing the temperature of the metal in the riser.

In 1997 a sleeve technology was introduced without fibers, providing a new alternative to exothermic sleeves. Patent application WO 97/00172 describes a cold box curing and blow molding process for manufacturing dimensionally accurate, exothermic and / or insulating sleeves from a blown-in-mold mix consisting of aluminum silicate microspheres containing in alumina less than 38% by weight, a cold box curing binder and, optionally, non-fibrous fillers. A typical composition for the production of exothermic sleeves comprises hollow microspheres with an alumina content of less than 38% by weight, powdered aluminum, iron oxide and cryolite as fluorinated flux.

Currently there are in the foundry industry sleeves to obtain the so-called mini-risers, whose function is also to feed liquid to the piece while it contracts during solidification.

The fundamental difference with conventional exothermic sleeves is that they keep the liquid metal for a longer time, with which the necessary volume of metal, that is, the minimazarota, for the same feeding function is less.

This result is achieved by increasing the exothermic load of the cuff, but this increase in exothermicity leads to unwanted collateral problems, such as:

1. Excess residual aluminum in the riser, which is then remelted, leads to pore problems in the castings.

The defect known as "fisheye" is a superficial defect in the casting, originating by the accumulation of materials from the recovery of polluted sands, mainly by aluminum, which is found in high proportions in exothermic sleeves.

This defect can be overcome by using, for example, hollow aluminum silicate microspheres with a low alumina content, as described in WO 97/00172.

2. Degradation of the nodules in the area of contact of the sleeve with the part that leads to the rejection of parts for not meeting the nodulation specifications required by the client.

This second problem is caused by the excess of fluorine from fluorinated materials that are usually used as a starting charge for the exothermic reaction.

To avoid this problem, either the sleeve does not contact the part, which requires more metal, or an intermediate biscuit, free of fluorine, adhered to the mouth of the sleeve and is provided with an equivalent central hole , that avoids the contact of the sleeve itself with the piece. This cookie, its production and fastening to the sleeve, represents a not inconsiderable additional cost.

SUMMARY OF THE INVENTION

The invention faces the challenge of providing a sleeve for obtaining mini-risers that does not require the use of the "biscuit" free of fluorine, or any other element to avoid the contact of the sleeve with the piece and that, on the other hand, produces a notch in the riser to facilitate its later separation from the cast piece and all this from a blown, fluorine-free mixture capable of producing an exothermic reaction to supply the required heat.

To do this, first of all, by blowing the mixture that will constitute the fluorine-free sleeve, in a mold equipped with two males that, on the one hand, will make it possible to extract the sleeve once cured and, on the other hand, obtaining two holes: one of them in the mouth of the sleeve itself, whose hole has a double internal circumferential chamfer, capable of producing an equivalent notch in the riser when the sleeve performs its function at the time of casting . Another hole in the base opposite the mouth, which will be closed, once the sleeve cures, with a low-cost material, since that area of the sleeve has no operation in the casting process and should only be closed in order to avoid falling inside the lingo from sand or other undesirable materials.

Said exothermic sleeve for obtaining minimazarotas, is obtained by blowing and subsequent cold box curing of a fluorine-free mixture comprising (a) hollow spheres of alumina silicate; (b) an exothermic material comprising:

a) An insulating / refractory material. b) An oxidizable metal. c) An oxidizing agent. d) Magnesium as an initiating element of the reaction. e) A cold box purified catalyst. Hollow microspheres of aluminum silicate are basically used as the insulating material. Mixtures of these aluminum silicate spheres with sand can also be used, when it is necessary to improve the mechanical characteristics of the sleeve, to the detriment of the insulating characteristics.

Aluminum, silicon and others can be used as oxidizable metals. Preferably aluminum in a combination of fine and coarse powder.

As oxidizing agents, nitrates, glorates, permanganates and metal oxides such as iron and magnesium oxide and, of course, combinations of these compounds can be used.

Magnesium is used as the initiating agent for the exothermic reaction.

Once this mixture is blown into the mold, the sleeve is removed and cured, the hole opposite the mouth is closed with a plug that can be made of plastic, wood, sawdust, sand, etc. and even the same material as the cuff.

The use of these sleeves allows the manufacture of high quality parts, without degradation of the graphite nodules in the riser-part contact area, at a reduced cost, lower compared to other conventional procedures that yield parts of similar qualities based on contact between the riser and the piece through an intermediate cookie.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 illustrates the steps for the production of a sleeve using a conventional cold box curing and blowing process belonging to the state of the art. In this case, the mix for the production of sleeves is blown into a mold (3) with the collaboration of a male (2) [Figure 1A]; then, the sleeve (1) is cured and it is removed from the mold leaving the hole destined for the riser (4) [Figure IB]; and, finally, an intermediate biscuit (5) is applied that has a hole (6) for the passage of the broth [Figure 1C].

Figure 2 illustrates the steps for the production of an exothermic sleeve according to the cold box cure and blow method provided by the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In one aspect, the invention relates to a process for the production by blow molding and cold box curing of an exothermic sleeve for obtaining mini-taps, comprising:

(A) introduce, by blowing, into a cold box curing mold, in the space defined between the mold and two males that make up a double chamfer at the mouth of the sleeve, a blowable mixture, to obtain an open, uncured sleeve at its two ends, in which said mixture comprises:

a) a fluorine-free composition for the production of sleeves based on:

a.l) an insulating / refractory material.

a.2) an exothermic mixture comprising a oxidizable metal and an oxidizing agent capable of generating an exothermic reaction, and magnesium as a starting material for the reaction.

b) a cold box curing binder;

(B) contacting the uncured sleeve prepared in (A) with a cold box cure catalyst;

(C) allowing the cuff resulting from (B) to cure;

(D) removing the cured sleeve from the mold; Y

(E) place a plug in the hole opposite the mouth of the sleeve.

As can be seen in Figure 2, unlike the conventional procedures belonging to the state of the art (see Figure 1), in the process provided by this invention, the fluorine-free mixture for the production of exothermic sleeves is blown into a mold, in the space defined between the mold (3) and the males (2,2 ') [Figure 2A]. The males (2,2 ') in addition to allowing the subsequent extraction of the sleeve, produce a double chamfer in the mouth of the sleeve (8) .Once the sleeve (1) has cured, it is removed from the mold leaving the hole destined for the riser (4 ) [Figure 2B]; and finally a cap is placed

(9) at an open end of the sleeve (1) in order to prevent the entry of sand or any other undesirable element into the cavity intended for riser during the casting operation [Figure 2C].

The double chamfer (8) of the sleeve will produce a formally equivalent fingerprint or notch in the riser that defines and facilitates the line of cut for the separation of the lingo of the piece.

The insulating / refractory material (al) present in the fluorine-free composition for the production of sleeves is a material that basically comprises hollow microspheres of aluminum silicate, although it could also contain a certain amount of sand, on the assumption that, sacrificing Insulating capacity, want to improve the mechanical characteristics of the sleeve.

In general, the amount of insulating / refractory material (a.l) will be between 30 and 70% by weight with respect to the total fluorine-free composition.

The exothermic material (a.2) present in the fluorine-free composition for the production of sleeves comprises an oxidizable metal and an oxidizing agent capable of generating an exothermic reaction, wherein said exothermic material comprises:

(i) magnesium as an initiator of the ixothermal reaction, together with one or more oxidizable metals, preferably a mixture of aluminum powder and granules.

(ii) an oxidizing agent capable of reacting with the oxidizable metal and generating an exothermic reaction at the metal pouring temperature, said oxidizing agent being selected from the group consisting of (a) alkali or alkaline earth metal salts, for example, nitrates, chlorates and alkali or alkaline earth metal permanganates; (b) metal 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 blown. A characteristic of the composition for the production of exothermic sleeves according to the present invention is that said composition lacks the inorganic fluorinated fluxes commonly used as initiators of the exothermic reaction. Instead, magnesium is used which reacts at a lower temperature whereby the exothermic reaction generated between the oxidizable metal and the oxidizing agent begins earlier.

The reaction between the oxidizable metal and the oxidizing agent is an exothermic reaction that generates heat thereby enhancing the thermal properties of the exothermic sleeves. In this way, the temperature loss of the molten material in the sprue is reduced, which keeps it hotter and more liquid for a longer time.

Depending on the degree of exothermic properties to be achieved in the sleeve, the amount of oxidizable metal present in the exothermic material (a.2) will be between 20 and 30% by weight with respect to the total fluorine-free composition for production of the cuff.

The procedure provided by this invention allows exothermic sleeves to be obtained with the desired balance of insulating and exothermic properties by simply using the amounts of insulating material (al) and exothermic material (a.2) present in component A in the appropriate weight ratios .

Cold box curing binders that can be used in the mix for the production of sleeves according to the sleeve manufacturing process provided by this invention are known. In principle, any cold box curing binder that be able to maintain the fluorine-free composition for the production of sleeves in the form of a sleeve and polymerize in the presence of a curing catalyst can be used. By way of illustration, phenolic resins, phenol-urethane resins, epoxy acrylic resins, alkaline phenolic resins, silicate resins, etc. can be used. activated by an appropriate gas phase catalyst. In a particular embodiment, said cold box curing binder is selected from S0 ₂ (gas) activated epoxy-acrylic resins and amine (gas) activated phenol-urethane resins known as EXACTCAST ^® cold box curing binders. (Ashland).

The required amount of cold box curing binder is the effective amount to maintain the shape of the sleeve and allow for its effective cure, ie, such an amount as to produce a sleeve that can be handled after curing. By way of illustration, the amount of cold box curing binder will be between 1 and 10% of the total composition for the production of the sleeve.

The cold box cure catalyst is applied as a gas by passing it through the sleeve, until the sleeve reaches a manageable consistency. The gas phase catalyst can be an amine, carbon dioxide, methyl formate, sulfur dioxide, etc. depending on the cold box curing binder used.

By operating properly and selecting the components of the composition for the production of sleeves, exothermic sleeves can be obtained with dimensional accuracy, both internal and external, which can be coupled easily to the cast molding assembly after being manufactured without the need for additional manipulations.

The exothermic sleeve obtainable according to the procedure provided by this invention constitutes a further aspect of the present invention.

As can be seen in Figure 2, the sleeve (1) provided by this invention comprises

(i) a body that surrounds the hole intended to contain the riser (4) and contains a double chamfer (8) in its mouth, and

(ii) a plug (9) at the base opposite the mouth.

The double chamfer (8) present in the sleeve provided by this invention is due to the combined action of 2 males (2,2 ') during the blowing of the mixture. The double chamfer (8) will define a lug or notch in the riser that facilitates its separation from the casting.

Due to the sleeve manufacturing process provided by this invention, which comprises the combined action of 2 males, 2 open ends are generated. One of these ends contains a double chamfer (8) while the other of the open ends is closed with a plug (9) in order to prevent the passage of sand or any other undesirable element into the sleeve during placement thereof in the mold and, of course, during the casting operation. Therefore, said plug (9) does not have any structural mission or intervene in the formation or performance of the riser, and, due to Thus, the material used in the manufacture of the stopper can be practically any material, advantageously a cheap material, such as plastic, wood, sawdust, paper, sand, etc., or even the constituent material of the sleeve itself.

By way of comparison, a table of blowable mixtures for obtaining fluorine-free and fluorinated flux-free exothermic sleeves according to the invention for the same exothermic capacity is illustrated below.

COST OF MIXTURES FOR THE SAME EXOTHERMAL CAPACITY

Claims

1. A process for the production by blowing and curing in a cold box of an exothermic sleeve for foundry molds, comprising:

(A) introduce, by blowing, into the mold in the space defined between the mold and two males, a mixture for the production of an exothermic sleeve, obtaining an uncured sleeve, open at its two ends, presenting the opening of the mouth an internal double chamfer, while the other opening is normally smooth, wherein said mixture for the production of exothermic sleeves comprises:

a) a fluorine-free composition for the production of sleeves comprising:

a.l) an insulating / refractory material

a.2) an exothermic material based on an oxidizable metal, an oxidizing agent capable of generating an exothermic reaction and magnesium as the reaction initiating element.

a) a cold box curing binder;

(B) contacting the uncured sleeve prepared in (A) with a catalyst to cure said uncured sleeve;

(C) let the cuff resulting from (B) be cured;

(D) remove the cured cuff from the mold; and (E) place a plug in the hole in the base opposite the mouth of the sleeve.

2. The method according to claim 1, wherein said insulating material with refractory properties (a.l) is aluminum silicate in the form of hollow microspheres.

3. The method according to claim 1, wherein said oxidizable metal is aluminum, preferably a fine and coarse powder mixture of this metal.

4. The method according to claim 1, wherein said oxidizing agent is selected from the group consisting of alkali metal or alkaline earth metal salts, metal oxides, and mixtures thereof.

5. A process according to claim 1 and 4, wherein said oxidizing agent is selected from the group consisting of nitrates, chlorates and permanganates of alkali or alkaline earth metals, iron oxide, manganese oxide, and mixtures thereof.

6. The method according to claim 1, wherein said exothermic material (a.2) is in a non-fibrous form, that is, in a blowable form.

7. The method according to claim 1, wherein said cold box curing binder is selected from the group consisting of phenolic resins, phenol-urethane resins, epoxy-acrylic resins, alkaline phenolic resins and silicate resins.

8. The method according to claim 12, wherein said cold box curing binder is selected from group formed by epoxy-acrylic resins activated by S0 ₂ (gas) and phenol-urethane resins activated by amine (gas).

9. The method of claim 1, wherein, in step (B), the uncured sleeve prepared in step (A) is contacted with a gas phase catalyst suitable for curing said sleeve.

10. The method according to claim 1, wherein said catalyst for curing the uncured sleeve is a gas phase catalyst selected from a gas amine to activate phenol-urethane resins; S0 ₂ (gas) to activate epoxy-acrylic resins; C0 ₂ (gas) or methyl formate (gas) to activate alkaline phenolic resins; and C0 ₂ (gas) to activate sodium silicate resins.

11. Sleeve according to claim 1, characterized in that once molded, unmoulded and cured, it has a mouth for the entrance of the broth that must form the mazarota equipped with a double internal perimeter chamfer, which will produce a footprint or notch of equivalent geometry, while the hole opposite the mouth is closed with a plug made of plastic, wood, sawdust, sand or even the material that constitutes the sleeve.