JPS60196245A - Composition for molding sand - Google Patents

Abstract

PURPOSE:To improve the collapsing property of a core by mixing specific wt%, by the sand component of molding sand, quicklime or/and calcined dolomite with the molding sand. CONSTITUTION:Quicklime or/and calcined dolomite is mixed with molding sand at 1-30% by the weight of the sand component therein and a casting mold is manufactured of said sand. The mold can be easily broken when the mold is immersed in water or water is sprayed thereto after casting and therefore the mold including a core can be easily broken by immersion into water, etc. after casting according to the above-mentioned method.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a foundry sand composition used in the production of foundry molds, and more particularly to a foundry sand composition that allows easy destruction of subsequent casting molds. It is.

In the present invention, foundry sand refers to resin-coated sand or sand mixed with a small amount of a molding binder. Examples of the above binders include organic binders such as drying oil, phenolic resin, urea resin, furan copolymer resin, unsaturated polyester resin, polyvinyl alcohol, and urethane resin, bentonite, clay cement, water glass, and ceramics. There are inorganic binders.

The binder is used to impart moldability to the sand. When a mold made by mixing sand with an organic binder is applied to a casting with a high casting temperature (1300 to 1400°C), such as cast iron casting, the organic binder will thermally decompose and reduce the mechanical strength of the mold. decreases significantly. As a result, the mold can be easily destroyed with a small external force. However, when applied to manufacturing at a casting temperature of 650~B, such as in aluminum casting, even though the outer mold of the mold can be destroyed by vibration or other relatively small external forces, the core cannot be easily destroyed. cannot be destroyed.

This is because oxygen is not supplied to the core because it is surrounded by molten metal, and the organic binder is not sufficiently decomposed and carbonized, resulting in insufficient reduction in the mechanical strength of the core.

For this reason, the extra step of reducing the mechanical strength of the core is usually required by performing so-called sand firing at a temperature of 400 to 500° C. for 4 to 10 hours.

For these reasons, various attempts have been made to create cores that are easily broken after casting. For example, a method that uses potassium nitrate or sodium nitrate in combination with a phenolic resin binder and thermally decomposes these substances at the casting temperature to generate oxygen to help the combustion of the phenolic resin, and a method that uses modified phenolic resin instead of phenolic resin. or the Ashland method using incyanate. However, none of these methods achieves sufficient effects and has not yet been put into practical use.

Furthermore, when an inorganic binder is used, it has the advantage of not emitting bad odor or toxic gas during casting operations, but has the disadvantage that the mold is less likely to be destroyed after casting.

Accordingly, an object of the present invention is to provide a foundry sand composition that improves the breaking properties of casting molds, especially cores, after casting.

As a result of extensive research in line with the above objectives, the present inventors have found that molds made by mixing 1 to 30% by weight of quicklime and/or calcined dolomite with respect to the sand content of foundry sand can be submerged in water after casting. It was discovered that it could be easily destroyed by immersing it in water or spraying it with water, and based on this knowledge, the present invention was achieved.

That is, in the present invention, the sand content of foundry sand is 1 to 30% by weight.
This is a foundry sand composition made by mixing quicklime and/or calcined dolomite.

If the mixed amount of quicklime and/or calcined dolomite is less than 1%, the effect will not be sufficiently exhibited, and even if it exceeds 30%, the effect will hardly change.

A mold made using the foundry sand composition of the present invention, including the core, can be easily destroyed by a small external force by simply immersing it in casting drainage water or spraying water on it.

Next, the present invention will be explained in more detail with reference to Examples.

Example: Quicklime and calcined dolomite with adjusted particle size were added to and mixed with commercially available foundry sand 2) used for manufacturing mold cores (the amount added was 1% each based on the sand content of the foundry sand).
5, 10, 15, 20 and weighted amount %) foundry sand compositions were prepared.

This was cut into a length of 10 (7), and one of the openings of the schedule 40-25 A carbon copper steel pipe for pressure piping (hereinafter simply referred to as "steel pipe") was covered with aluminum foil, and then vibration was applied. while pouring the foundry sand composition from the other side,
Furthermore, the entire steel pipe was wrapped in aluminum foil and held in an electric furnace kept at a temperature of 500° C. for 1 minute to harden the foundry sand composition and create a test piece. For comparison, a test piece was similarly prepared using foundry sand to which quicklime and calcined dolomite were not added.

After removing the aluminum foil and immersing the test piece together with the steel pipe in water for 2 hours, the steel pipe was subjected to vibration for 1 minute, and the amount of disintegration of the test piece was measured. The test results are shown in Figures 1 and 2 (C1).

In these figures, Figures 1 and 2 are each 3
When quicklime and calcined dolomite with adjusted particle size are added to 5-65 mesh and 65-150 mesh,
(A), fB) and (C1) show the cases where the temperature of the water in which the test piece was immersed was 30°C, 50°C and 70°C, respectively.

In the figure, the "disintegration rate" is expressed as the proportion (% by weight) of the foundry sand composition that collapsed under vibration and was extracted from the steel pipe, relative to the weight of the test piece after subtracting the weight of the steel pipe.

In the figure, the ○ mark indicates quicklime, and the * mark indicates calcined magnesia.

Note 1) Tochu Foundry Sand Co., Ltd. R8-30 Resin coated sand (resin content 3% by weight) Sand grain size
35 mesh remaining 1.2% by weight 48 // 18.4
tt 65 # 34.2 /1 ioo pao, o # 150 # 12.4 7' 200 F 1.6 lI 270 II O, 17/ 2) Calcined dolomite composition Ca0 65% by weight Mg0 30 tt F2033〃 SiO2 Others Residue

[Brief explanation of the drawing]

The figure shows the results of the disintegration rate test of the foundry sand composition test piece prepared in the example. Figures 1 and 2 show the results when quicklime and calcined dolomite whose particle sizes were adjusted to 35-65 mesh and 65-150 mesh were added, respectively.
(Support), (Bl and (C) show the cases where the temperature of the water in which the test piece was immersed was 30℃, 50℃ and 70℃, respectively. In the figure, ○ mark is quicklime, ・ mark is calcined dolomite. Patent applicant Sumitomo Cement Co., Ltd. and one other person Oni 1 Ward (A) (13) 4 forces...1 (weight 2) Amount of retained calories (weight Z) (C) Amount added (weight meth) Hikari 2 diagram ( A) (8) Addition amount (weight'/-) Addition amount (weight Z) (G)

Claims (1)

[Claims] 1 to 30% by weight of quicklime or
and a foundry sand composition formed by mixing calcined dolomite.