JPS6146345A - Combustion preventive treatment for heat insulating sleeve in riser part for casting mg alloy - Google Patents

Abstract

PURPOSE:To prevent the burning of a molten metal by treating the heat insulating sleeve in a riser part with a soln. of boric acid or borofluoride alone or a soln. mixture composed thereof and blowing an inert gas into a casting mold if necessary. CONSTITUTION:The riser part 6 is provided on a mold 5 and a pouring basin 4 and the product mold 5 are connected by a runner 9. The heat insulating sleeve 7 made of ceramic fibers in the riser part is chemically treated with the soln. of >=2wt% boric acid or borofluoride alone or the soln. mixture composed thereof. Such sleeve 7 is installed in the casting mold and if the riser capacity is large, the inert gas such as sulfar dioxide is blown into the mold; thereafter the molten Mg alloy is poured into the mold. The burning of the molten alloy in the riser part 6 is prevented by the above-mentioned method.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for flameproofing a heat insulating sleeve for a feeder part for Mg alloy casting, and in particular to a method for flameproofing a heat insulating sleeve for a feeder part by chemically treating the heat insulating sleeve for a feeder part. The present invention relates to a flameproof treatment method for preventing combustion of molten Mg alloy for casting filled in a riser.

[Prior Art] As a method of obtaining a sufficient feeder effect to compensate for the solidification shrinkage of castings, there is a method of insulating the wall of the feeder section. In recent years, cast iron,
A heat insulating sleeve made of ceramic fiber, which has a good thermal insulation effect at high temperatures, is used in the riser part of a mold used for casting steel, A1 alloy, etc. It has been found that this ceramic fiber heat insulating sleeve is even more suitable as a feeder heat insulating sleeve for Mg alloy casting, which targets molten Mg alloy having a small heat capacity.

[Problems to be Solved by the Invention] However, when casting Mg alloys, there is a problem that the Mg alloy for casting filled in the feeder section burns due to the heat insulation of the molten metal.To prevent this, there is a problem. It is necessary to apply flameproofing treatment to the ceramic fiber.

The present invention has been made in view of the above circumstances, and is an Mg alloy casting method in which a heat insulating sleeve of a feeder part is chemically treated to prevent combustion of molten Mg alloy for castings filled into the feeder part. A method for flame-retardant treatment of a heat-insulating sleeve for a feeder part and a method for casting after blowing a nonflammable gas into a mold in order to further enhance the flame-retardant effect of the chemically treated heat-insulating sleeve for a feeder part.
The purpose of this invention is to provide a flameproof treatment method for a feeder heat insulating sleeve for g-alloy casting.

[Means for Solving the Problems] The structure of the present invention that achieves the above object is as follows: First, the heat insulating sleeve for the feeder part for Mg alloy casting is prepared by using a boric acid or boric fluoride solution with a concentration of 2% by weight or more. The gist is to treat the heat insulating sleeve for the riser part for Mg alloy casting either singly or with a mixture of these solutions. The gist of this method is to process the mold with a liquid and blow one or more nonflammable gases such as carbon dioxide gas, sulfur dioxide gas, or sulfur fluoride into the mold before casting.

[Function] That is, 2% by weight of the heat insulating sleeve for the feeder part for Mg alloy casting.
If the above concentration of boric acid or boric fluoride solution is treated alone or with a mixture thereof and then attached to the mold and used to insulate the feeder section, it is possible to is small), it is possible to prevent the combustion of the molten Mg for casting that is poured into the feeder and fill the feeder, and to maintain the heat insulation of the molten metal, thereby reducing the solidification shrinkage of the Mg alloy casting. A sufficient riser effect can be obtained to compensate. Also, when the molten metal capacity increases (in other words, when the feeder capacity increases), a nonflammable gas such as carbon dioxide gas, sulfur dioxide gas, or sulfur fluoride is blown into the mold in addition to the flameproofing treatment of the heat insulation sleeve of the feeder section. By doing so, the desired flame-proofing effect can be obtained.

[Example] FIG. 1 is an explanatory cross-sectional view showing a heat insulating sleeve for a riser part for Mg alloy casting, which has been subjected to the flameproof treatment method according to the present invention. A sprue 3 into which molten Mg alloy is poured is provided above a sump 4 provided between an upper mold 1 and a lower mold 2. (1) The Mg
A feeder section is installed along with the sprue 3 for the two purposes of replenishing the molten metal to compensate for shrinkage during solidification of alloy castings, and (2) using its height and weight to apply pressure to the castings to make the material denser. 6 is provided on the product mold 5. Furthermore, a runner 9 is provided between the trough 4 and the product mold 5 to communicate with each other. Reference numeral 8 indicates the filled and solidified sand material.By the way, as a practical method for controlling the solidification of the molten metal for the feeder poured into the feeder part 6, a heat insulating sleeve 7 is placed around the feeder part 6. is installed and used. Conventionally, heat insulating materials such as plate-like asbestos have been used to insulate feeders for Mg alloys, but as mentioned above, it is becoming more and more preferable to use ceramic fibers, which have excellent heat-retaining and heat-insulating properties. However, if the ceramic fiber heat-insulating sleeve is attached to the feeder part 6 as it is, the heat-retaining effect is high, so the heat-retaining sleeve is
There is a problem in that the molten Mg alloy poured into the tank is maintained at a high temperature and as a result burns (oxidation reaction). In order to avoid this, it was necessary to subject the heat insulating sleeve 7 to anti-flame treatment in advance. That is, a heat insulating sleeve made of ceramic fiber with a diameter of 200 mm, a height of 300 mm, and a thickness of 10 m1+ was placed in each of boric acid aqueous solutions of 1%, 2%, and 3% (all percentages by weight; the same applies hereinafter) at saturated and moderate concentrations. Soaked for an hour. In addition, in a 2% solution of tetrafluoroboric acid (HBF4),
or sodium tetrafluoroborate (NaBF4)2
% solution is also shown. and 25
After drying at 0°C for 2 hours, it was attached to the feeder section 6, and magnesium AZ91C alloy was poured at 750°C. All molds were pre-filled with 1.0% sulfur and 0 potassium borofluoride.
．． 5% was added to prevent combustion inside the mold. Moreover, S02 was used as a nonflammable gas for flame prevention inside the mold. Table 1 is a table showing the influence of the heat-retaining sleeve subjected to the flameproofing treatment on the combustion of molten Mg alloy.

In the column of flame-proof status of Mg alloys in Table 1, O indicates that the alloy did not burn, and X indicates that it burned.

In other words, according to the results shown in Table 1, when the insulation sleeve is immersed in 1% boric acid, combustion of the Mg alloy occurs even in the presence of nonflammable gas, but when it is immersed in 2% boric acid, combustion of the Mg alloy occurs. Combustion of the Mg alloy will not occur if a non-flammable gas is used in combination, and furthermore, combustion of the Mg alloy will not occur if a non-flammable gas is used in combination when immersed in a 3% aqueous solution, a saturated aqueous solution, or a supersaturated aqueous solution of boric acid. ,or,
Even when immersed in a 2% KBFt solution or a 22% NaBF solution, the Mg alloy will not burn if a nonflammable gas is used in combination.

Next, Table 2 shows that HBFa is present in 1% and 2% boric acid aqueous solutions.
Table 1 shows the results when a heat insulating sleeve made of ceramic fiber was immersed in a mixed solution to which a flame retardant such as , NHa, BFa, or NaBF4 was added.The conditions other than the mixed solution were exactly the same as those in Table 1. Furthermore, the results when using a mixed gas of SFc and CO2 are also shown.

In Table 2, in the column of flame-proof status of the Mg alloy, 0 indicates that it did not burn, and X indicates that it burned.

As a result, no flame-retardant effect of the molten Mg alloy was observed in thermal sleeves immersed in a mixture of 1% boric acid and 41% HBF, 1% boric acid and 1% NH4BFa, and 1% boric acid and 42% NaBF; % and HBF42%
, 2% boric acid and 42% NH4BF, 2% boric acid and Na
BF42% and NaBF42% and HBF42%, HBF
The flame-proofing effect of the molten Mg alloy was confirmed in the thermal sleeves immersed in the mixed solutions of 42% NH48F and 42% NH48F when nonflammable gas was used in combination.

Next, Table 3 shows the results of spraying or dipping two types of thermal sleeves with different outer diameters and heights using a mixed solution of 2% HBF and 42% HBF.Other conditions were The conditions are the same as those in Table 1.

In Table 3, in the column of flame-proof status of the Mg alloy, 0 indicates that the alloy did not burn, and X indicates that it burned.

According to Table 3, the larger the shape of the thermal sleeve (
(If the feeder capacity increases), even if flameproofing treatment is performed by immersing the mold in the above solution, combustion of the Mg alloy will occur if nonflammable gas is not blown into the mold. In addition, when the shape of the heat insulation sleeve is small (in other words, when the feeder capacity is small), a flame retardant effect can be obtained by simply spraying a flame retardant or using a nonflammable gas, or by immersing it in the above solution. A heat-retaining sleeve can provide a flame-retardant effect without using nonflammable gas.

By summarizing the results in Tables 1 to 3 above, the following conclusions can be drawn. That is, (1) If the feeder capacity is relatively small (diameter 100a+x or less), the Mg alloy will not burn if the heat insulating sleeve is immersed in a flame retardant without blowing nonflammable gas into the mold.

When the feeder capacity is large (diameter 200+o+++ or more), the Mg alloy will burn if nonflammable gas is not blown into the J4 type, even if the heat insulating sleeve is immersed in a flame retardant.

■Boric acid or HBF4゜NH4BF as a flame retardant
4. NaBFt alone at a concentration of 2% or more or boric acid or H
BFa, NHa BFa.

A mixture of at least two solutions of boron fluoride such as NaBFa having a concentration of 2% or more can provide a flame-proofing effect.

It should be noted that there is no noticeable difference in the flame retardant effect between a solution containing boric acid or boric fluoride added and a mixture of these alone, and there is no significant difference in the flame retardant effect observed due to the difference in the flame retardant treatment (spraying or dipping). It is presumed that the difference is due to the difference in the amount of flame retardant attached to the heat insulating sleeve.

On the other hand, the lower the flame retardant concentration is, the better in terms of the amount used, and generally a 2% relaxing concentration is used, but 2% to 2%
The range of 5% is particularly preferable, and the nonflammable gases blown into the mold in Tables 1 to 3 include 302, SF6, and C, which are generally used as nonflammable gases for Mg alloy casting.
Nonflammable gases such as O2 can be used alone or in combination.

[Effects of the Invention] Since the present invention is configured as described above, it is possible to apply chemical treatment to the heat insulating sleeve of the riser part for Mg alloy casting, or to blow nonflammable gas into the mold. By post-casting, it became possible to prevent the molten Mg alloy for casting in the riser from burning.

[Brief explanation of the drawing]

FIG. 1 is an explanatory sectional view showing a feeder heat insulating sleeve for Mg alloy casting according to the present invention. 1...! - Upper mold 2... Lower mold 3... Sprue 4... Reservoir 5... Product mold 6
...Riser part 7...Heat insulation sleeve 8...Sand material 9
・・・N11) Road

Claims (2)

[Claims] (1) 2% by weight heat insulating sleeve for feeder part for Mg alloy casting
Mg characterized in that it is treated with a boric acid or boric fluoride solution of a concentration above or with a mixture thereof.
Flameproof treatment method for heat insulating sleeves for feeder parts for alloy casting. (2) 2% by weight heat insulating sleeve for feeder part for Mg alloy casting
Casting is carried out after treatment with boric acid or boric fluoride solution of the above concentration alone or with a mixture thereof, and at least one nonflammable gas such as carbon dioxide, sulfur dioxide, or sulfur fluoride is blown into the mold. A flameproof treatment method for a heat insulating sleeve for a riser part for Mg alloy casting, characterized by the following.