JP2005040860A - Core for light alloy casting - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a core for casting a light alloy casting that does not corrode the apparatus and the obtained casting at all and is extremely soluble in water.
SOLUTION: Chemically stable refractory particles such as silica sand, zircon sand, and alumina are used as an aggregate, and as a binder, it is selected from sodium nitrate, potassium nitrate, barium nitrate, strontium nitrate, sodium nitrite, and potassium nitrite. A core for casting a light alloy casting characterized by containing one or more of the above.
[Selected drawing] None

Description

  The present invention is a core in which a sandy material that is fire-resistant and chemically stable is bonded with a water-soluble salt that does not have corrosive properties, and can be easily obtained by immersing the casting in water or hot water after casting the metal. The present invention relates to a core for casting a light alloy casting that can be rapidly collapsed.

Conventionally, as cores for casting used in light alloy castings made of aluminum alloys, shell cores using phenol resin as a binder for fire-resistant sand, and cold box cores using urethane resin as a binder are used. Has been widely adopted. However, the core using these binders has a problem in disintegration. That is, in a portion where the casting is thin and the heat capacity is small, these binders are not completely thermally decomposed, so that the core is not completely collapsed. For this reason, to remove the core after pouring, vibration is applied or a great number of man-hours are required. In order to solve such a problem, a casting core using barium chloride, calcium chloride, or sodium aluminate that is easily dissolved in water, warm water or dilute acid as a binder is disclosed (for example, see Patent Document 1).
JP-A-51-81726 (pages 1 to 4)

  However, chlorides such as barium chloride and calcium chloride disclosed here have the property of corroding metals (even stainless steel, which is generally said to be “resistant to corrosion”, is “corroded by chlorine ions”). Are well known.) In addition, strong alkaline materials such as sodium aluminate have the property of easily corroding the obtained casting when it is a light alloy such as an aluminum alloy. This produces visible damaging scars. That is, in the former case, when an attempt is made to make an apparatus, a great deal of study is required to prevent corrosion of the apparatus. Further, in the latter case, even a slight amount is not allowed to remain in the casting after washing, and extremely careful washing is required.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a core for casting a light alloy casting that does not corrode the apparatus or the obtained casting at all and is extremely soluble in water.

In order to achieve the above object, the core for casting a light alloy casting according to the present invention is composed of chemically stable refractory grains such as silica sand, zircon sand, alumina and the like, and as a binder, sodium nitrate, potassium nitrate, One or more kinds selected from barium nitrate, strontium nitrate, sodium nitrite and potassium nitrite are contained.
Furthermore, it is composed of chemically stable refractory grains such as silica sand, zircon sand, alumina, etc., and as a binder, it is a kind selected from sodium nitrate, potassium nitrate, barium nitrate, strontium nitrate, sodium nitrite, potassium nitrite or It is characterized by containing plural kinds and further an inorganic binding aid.
In forming the casting core, the casting core is heated at a temperature equal to or higher than the melting point of the binder.
In forming a casting core, moisture is allowed to act on the binder contained in the aggregate to dissolve all or part of the binder, and then the moisture is removed in the mold.
Further, when forming a casting core, an appropriate amount of water is added to the aggregate coated with the binder and kneaded, or an appropriate amount of moisture is added to the mixture of the aggregate and the binder, and the aggregate is mixed. A mixture obtained by adding and kneading an appropriate amount of an aqueous solution in which a binder is dissolved is filled in a mold, and then moisture is removed in the mold.

  The present invention provides a core for casting a light alloy casting that does not corrode the apparatus and the obtained casting at all by simply using the above-described solution, and can be easily disintegrated by just immersing it in water or warm water. It becomes possible to do.

  As is apparent from the above description, the present invention does not corrode the apparatus or the obtained casting at all, and uses nitrate or nitrite, which is a compound that is extremely soluble in water, as a binder. Since the core that is easily disintegrated by hot water is provided, the core can be removed very easily without applying external force such as vibration, and the benefit to the industry is significant.

The present invention comprises chemically stable refractory grains as an aggregate, and contains, as a binder, one or more selected from sodium nitrate, potassium nitrate, barium nitrate, strontium nitrate, sodium nitrite and potassium nitrite. And forming a casting core. Examples of the aggregate include silica sand, zircon sand, and alumina.

When molding, the casting is performed by heating at a temperature equal to or higher than the melting point of the binder or by allowing moisture to act on the binder to dissolve all or part of the binder and then removing the moisture in the mold. A core can also be formed.

Hereinafter, the present invention will be described with reference to specific examples. Prepare quartz sand as chemically stable refractory grain aggregate, and one or more kinds of nitrates and nitrites selected from sodium nitrate, potassium nitrate, barium nitrate, strontium nitrate, sodium nitrite and potassium nitrite as binders .
One or more kinds of nitrates selected from the binder, nitrite is heated to its melting point or higher to be in a molten state, and then silica sand is added as an aggregate to this and mixed well, on the surface of the silica sand as an aggregate, Coated sand in which the binder is uniformly attached in a thin film is obtained. After the coated sand is sufficiently cooled, the particle size is adjusted by a sieve.
In the present invention, the melting point of the salt refers to the solidus temperature of the salt.

  The coated sand is filled into a core mold heated to a melting point or higher of the binder by a method such as blowing, and then held for several minutes. After the binder on the surface of the coated sand is in a semi-molten state, the mold is cooled below the melting point of the binder, and the casting core formed by the coated sand is taken out from the mold. The obtained casting core has a size of 10φ × 70 L.

This was placed in a casting mold, and an aluminum alloy melted at 740 ° C. was poured. After cooling and solidifying, it was immersed in a hot water bath at 80 ° C.
The casting core collapsed in about 2 minutes and could be removed from the casting. Subsequently, it was taken out from the hot water tank and washed easily with clean water to obtain a casting made of an aluminum alloy.
The obtained casting had a thickness of 2 mm and no defects were observed on the surface. Moreover, when left untreated, no spots were formed, and no harmful corrosion was observed.
Nitrate used as a binder is oxidizable at high temperatures, and the aggregate is quite fine, so the aggregate used here must be chemically stable and not easily oxidized. is there.

In the above embodiment, the salt is heated and melted and then coated to uniformly adhere the salt to the surface of the aggregate. However, the aggregate is immersed in an aqueous solution of salt and the surface of the aggregate is subjected to salt water. It is also possible to deposit the salt on the surface of the aggregate after drying. Furthermore, when a large amount of salt is desired, a recrystallization method may be employed in which aggregate is immersed in a saturated aqueous solution of salt to increase the concentration of the aqueous solution and precipitate the salt.
Furthermore, in the above embodiment, salt is uniformly attached to the surface of the aggregate, but when segregation of the aggregate and the salt does not become a problem, the coated sand is not formed, and the aggregate and It is also possible to use a mixture with a salt.
Furthermore, in the said Example, although immersed in a 80 degreeC warm water tank, you may make it soak in normal temperature water. In this case, however, the time to reach collapse increases slightly.

  Another embodiment will be described. Alumina as the chemically stable refractory grain aggregate, one or more nitrates and nitrites selected from sodium nitrate, potassium nitrate, barium nitrate, strontium nitrate, sodium nitrite, potassium nitrite as binders, and A primary binder such as colloidal silica is prepared as an inorganic binding aid.

  One or more kinds of nitrates and nitrites selected from the binder are sufficiently mixed with the aggregate, and then a primary binder such as colloidal silica is further added to obtain a slurry sample. The slurry-like sample is filled into a casting core molding die, and the mold is released after the primary binder is solidified. After drying, this is heated above the melting point of the binder to bring the binder into a semi-molten state and then cooled to obtain a casting core.

After releasing from the mold, the binder is brought into a semi-molten state, but the core for casting was not deformed due to the strength of the primary binder. The obtained casting core has a size of 10φ × 70 L.
This was placed in a casting mold, and an aluminum alloy melted at 740 ° C. was poured. After cooling and solidifying, it was immersed in a hot water bath at 80 ° C.
The casting core collapsed in about 2 minutes and could be removed from the casting. Subsequently, it was taken out from the hot water tank and washed easily with clean water to obtain a casting made of an aluminum alloy.

The obtained casting had a thickness of 5 mm, and no defects were observed on the surface. Moreover, when left untreated, no spots were formed, and no harmful corrosion was observed.
In addition, since the nitrate used as a binder has a strong property of oxidizing organic substances at high temperatures, the primary binder used here is preferably an inorganic one.
The hot water tank was made of stainless steel (SUS304) generally used in water systems, but no harmful corrosion was observed at all even when used for one month.

Next, preferable blending ratios of the materials used in the present invention are as shown below. However, it is not limited to this.
The ratio of the binder to the aggregate is preferably 3 to 40%. If it is less than 3%, the strength is weak, and if it exceeds 40%, the air permeability becomes poor and gas defects increase. It is also economically disadvantageous.
However, if the casting method can deal with gas defects and degassing through the core is not important, and if an extremely strong core is required, the proportion of the binder should be increased. It is also possible to implement. That is, it is possible to implement a mode in which the majority of the whole core is made into salt and aggregate is added thereto. In this case, a mixture obtained by adding the necessary amount of aggregate to the heat-melted salt may be poured into a casting core molding die in a molten state, and the core may be taken out of the die after cooling and solidification.
Further, the ratio of the primary binder to the aggregate is preferably 2 to 30%. If it is less than 2%, the green strength is low, which is a problem in handling. In addition, the fluidity is low and it is difficult to fill the mold. If it exceeds 30%, the air permeability becomes poor and gas defects increase. Further, the fluidity is too high, and aggregates and the like are easily segregated by the slurry.
Table 1 illustrates the formulation of the binder used in the present invention and its melting point. However, it is not limited to this.

In addition, when the thickness of the casting is thin and the heat capacity is small, a compound salt having a relatively low melting point can be used. However, when the casting is thick and has a large heat capacity, it is preferable to use a blended salt having a relatively high melting point.

In the above two embodiments, in order to bond the aggregates to each other, a method of bonding the binder by heating it to a semi-molten state or a molten state and cooling and solidifying it again is described. Before or after filling, an appropriate amount of moisture is allowed to act on the aggregate and binder, or on the aggregate and binder, and the inorganic binding aid, and once or part of the binder is dissolved with this moisture, Then, moisture can be removed and the aggregates can be combined with a binder and solidified to obtain a casting core.
Specifically, an appropriate amount of water is added to the aggregate coated with the binder and kneaded, or an appropriate amount of moisture is added to the mixture of the aggregate and the binder and kneaded, or the binder is dissolved in the aggregate. After filling the mixture obtained by adding an appropriate amount of aqueous solution and kneading into the mold, remove the moisture in the mold, or mix the aggregate coated with the binder or the aggregate and the binder After filling into the mold, moisture can be added to the mold or allowed to flow through and allowed to stand for a while, after which the moisture in the mold is removed. The appropriate amount of water is determined as appropriate depending on the molding method, type of aggregate, and the like because it relates to the fluidity, moldability, and fillability of the mixture into the mold.
The water can be removed by heating and / or normal temperature by suction pressure reduction, suction flow, pressurized flow, or the like.
In this way, the binder does not need to be in a semi-molten state, and therefore the mold does not need to be heated to a high temperature, so an expensive mold is not required and a relatively inexpensive resin mold can be used. .

Claims (5)

One or more materials selected from sodium nitrate, potassium nitrate, barium nitrate, strontium nitrate, sodium nitrite, and potassium nitrite are used as a binder with chemically stable refractory particles such as silica sand, zircon sand, and alumina as aggregates. A core for casting light alloy castings characterized by containing seeds. One or more materials selected from sodium nitrate, potassium nitrate, barium nitrate, strontium nitrate, sodium nitrite, and potassium nitrite are used as a binder with chemically stable refractory particles such as silica sand, zircon sand, and alumina as aggregates. A core for casting a light alloy casting characterized by containing a seed and an inorganic binding aid. 3. The light alloy casting core according to claim 1, wherein the core for casting is heated at a temperature equal to or higher than a melting point of the binder. 4. In forming a casting core, water is applied to the binder contained in the aggregate to dissolve all or part of the binder, and then the moisture is removed in a mold. The core for casting a light alloy casting according to claim 1 or 2. When forming a casting core, an appropriate amount of moisture is added to the aggregate coated with the binder and kneaded, or an appropriate amount of moisture is added to the mixture of the aggregate and binder, and the binder is added to the aggregate. 3. A light alloy cast casting according to claim 1 or 2, wherein after the mixture obtained by adding an appropriate amount of an aqueous solution in which kneading is added and kneaded is filled in the mold, moisture is removed in the mold. For core.