JPH0429451B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for producing a sand core for die casting, which is suitable for high pressure casting such as die casting.

[Prior art] Generally, when manufacturing various products by casting,
Die casting is widely used as a pressure casting method due to its advantages in terms of improved productivity and the like.
However, when manufacturing a casting in which a part of the product has a complicated cavity or undercut by die casting, a drawn core cannot be used as the core. Therefore, the use of a sand core with good collapsibility has been considered as an alternative, but this has the completely contradictory functions of being able to withstand the high casting pressures used in die-casting methods and having good disintegration properties after casting. It must be equipped at the same time.

[Problems to be Solved by the Invention] By the way, regarding the casting of a product with a clean casting surface and good dimensional accuracy by the die casting method using a sand core, it is necessary to There are problems such as breakage of the sand core, penetration of molten metal between the sand particles of the sand core, and disintegration of the sand core after die casting, and various methods have been tried, but none have yet been perfected. The current situation is that there is no such thing.

[Means and effects for solving the problem] Therefore, we used a sand core molded with an organic binder to produce castings with complex cavities or undercuts by high-pressure casting methods such as die casting. In order to make it suitable for manufacturing, the surface of the sand core is coated to give it enough strength to withstand high casting pressure, and the cast product has excellent surface and dimensional accuracy. To prevent defects such as penetration of molten metal or cracks into the contact surface between the cast metal and the sand core, and to have good collapsibility of the sand core after die casting, and to be able to produce the core at a low cost. As a result of intensive research and development with these objectives in mind, we have come to the following conclusions.

That is, the surface of a sand core molded using an organic binder is first coated with one or more kinds of refractories made of finely powdered zircon flour, silica flour, or alumina flour in a binder made of colloidal silica, ethyl silicate, or water glass. The mixed slurry is coated to close the gaps between particles on the surface of the sand core, and the surface of the sand core is then coated with mica in a water-soluble organic binder containing phenolic resin, methyl cellulose, and polyethylene oxide. Alternatively, we have provided a method for manufacturing sand cores for die-casting, which is characterized in that the sand core is coated again with a slurry made by adding fine powder with lubricating properties such as frogstone.

[Example] Examples of the present invention will be described below.

First, the process of molding a sand core using an organic binder will be described.

As the aggregate for the sand core, silica sand, zircon sand, chromite sand, high alumina sand, or Cerabis is used, and as the organic binder, a binder for fermold such as thermosetting phenol resin or unsaturated polyester resin, Alternatively, a cold box binder such as a chemical reaction-curable phenolic resin may be used and mixed with these components to achieve a resistance of 30Kg/cm2 to 70Kg/ ^cm2 .
Make a cm ² coated sand and use it to mold the core.

Next, on the surface of the sand core, one or more kinds of refractory fine powders such as silica flour, zircon flour, or alumina flour crushed to 300 mesh or less are dispersed and mixed in a binder such as colloidal silica, ethyl silicate, or water glass. The obtained slurry is immersed in the atmosphere to allow the slurry to penetrate.
After that, the slurry layer that has permeated the surface of the sand core is dried to evaporate the moisture, closing the gaps between particles on the surface of the sand core, and ensuring that the molten metal is able to withstand the casting pressure during die casting. It serves to prevent it from being inserted into the child's body. The thickness of the permeable layer having sufficient pressure resistance is preferably in the range of 0.2 to 0.5 mm, and if it is thicker or thinner than this, the disintegration of the sand core after die casting tends to deteriorate.

After sealing the surface gaps of the sand core in this way and imparting pressure resistance during die-casting, it is necessary to provide this surface with lubricating properties, no affinity with molten metal, and thermal resistance. A slurry made by dispersing and mixing powder of mica or frogstone, which are chemically stable substances, in a water-soluble organic binder containing phenol resin, methyl cellulose, polyethylene oxide, etc. is applied again and dried.

By coating the surface of the sand core molded using an organic binder as described above, damage to the core due to casting pressure during die casting and insertion of molten metal into the sand core are eliminated, and molten metal Seizure is eliminated, and castings with excellent surface roughness and dimensional accuracy can be manufactured, and the disintegration of the sand core after die casting is also good.

Next, a specific experimental example will be described below.

Experimental example Using sand for shell molding consisting of 100 parts of JIS No. 7 silica sand as aggregate, 2.0 parts of thermosetting phenolic resin as organic binder, and 0.1 part of calcium stearate as lubricant, A sand core was molded. The molding conditions were a mold temperature of 270°C and a firing time of 20 seconds.

Next, add 300 c.c. of colloidal silica (SiO ₂ 30%) as a binder, 10 g of sodium dodecylbenzenesulfonate as a wetting agent, and 1 g of octyl alcohol as an antifoaming agent to the water in step 1, and mix well. To this solution, 300 g of zircon flour ground to 300 mesh or less was added and thoroughly mixed and stirred to prepare a slurry solution. Then, after immersing the shell core in this slurry liquid for 1 minute to close the gaps on the surface of the sand core, immediately
The surface was cured by drying in a hot air dryer at 120°C for 30 minutes.

In addition, a 3% aqueous solution of water-soluble phenolic resin 1
Inside, 500g of mica crushed to less than 300mesh,
10 g of sodium dodecylbenzenesulfonate as a wetting agent, 1 g of octyl alcohol as an antifoaming agent
Mix well and stir to prepare a slurry solution, and apply this again to the surface of the sand core using a brush.
It was dried for 1 hour in a dryer heated to 120°C.

Set the sand core obtained in this way into a mold and
Pouring temperature of JIS ADC-12 aluminum alloy is 750℃.
Die casting was carried out under conditions of casting pressure of 200 to 400 Kg/cm ² . After casting, the sprue was cut and sand blasted to remove the sand from the sand core. However, when the sand was removed from the sand core by sandblasting, a plug layer formed by the aluminum mixed between the sand particles and the sand particles was generated, and a layer was formed due to the high casting pressure. There was no damage to the core, there was no seizure due to the molten metal, the disintegration was easy, and the sand core could be completely removed. Furthermore, after cutting the sprue mentioned above, if sand baking is performed in a furnace for a predetermined period of time, the resin in the sand core will be thermally decomposed, and if sandblasting is performed in the same manner as above, the removal of the sand core will be even easier, resulting in an extremely smooth surface. We were able to obtain die castings with good dimensional accuracy.

[Effects of the Invention] As is clear from the above description, according to the method for manufacturing a sand core according to the present invention, a sand core is molded using an organic binder, and the surface of the sand core is coated with colloidal silica, colloidal silica, A slurry made by mixing a binder such as ethyl silicate or water glass with a refractory material such as finely powdered silica flour, zircon flour, or alumina flour to completely close the gaps between particles and create a surface that can withstand the casting pressure during die casting. Gives strength.

Furthermore, when this sand core is coated with a slurry containing mica or frogstone, mica or frogstone has lubricating properties and is not compatible with molten aluminum alloy, so the above-mentioned precautions are taken during die casting. The synergistic effect with the stopping action also completely prevents the molten aluminum from penetrating between the surface particles of the sand core, eliminating seizure by the molten metal, and preventing the molten aluminum from penetrating between the surface particles of the sand core. Facilitates the disintegration of children. In other words, by simply tapping the cast product or giving it a slight vibration, the sand core inside the casting can be made to come out smoothly, and the sand core inside the casting can be easily removed. Sand particles can be easily and sufficiently removed from every corner of the sand.

As a result, a die cast product can have a clean casting surface, and a cast product with excellent dimensional accuracy and surface roughness can be manufactured.

Claims (1)

[Claims] 1. First, the surface of the sand core formed using an organic binder is coated with a slurry made of a binder made of colloidal silica, ethyl silicate, or water glass, and a refractory material made of finely powdered silica flour, zircon flour, or alumina flour added. The surface of the sand core is then coated with a water-soluble organic binder containing phenolic resin, methyl cellulose or polyethylene oxide, and lubricated with mica or frogstone. 1. A method for producing a sand core for die-casting, characterized by coating the sand core with a slurry to which a fine powder having properties is added.