JPS622898B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a hardening material for casting hardening that can form a good surface hardening layer even in thin castings.

BACKGROUND ART Conventionally, casting molds for hardening casting are known as shown in FIG. 1 and FIG. 2, which is a sectional view taken along the line -2 in FIG.

In FIGS. 1 and 2, 1 is a mold molded by a CO ₂ process or furan process, etc., 2 is a hardening material layer provided on a part (desired location) of the inner surface of the mold 1,
The hardening material layer 2 is coated with a hardening material which is mainly a mixture of high carbon ferrochrome powder, phenolic resin, colloidal silica and alcohol solvent;
It is dried. Reference numeral 3 denotes a mold cavity formed into a desired shape by the inner surface of the mold 1 and the two surfaces of the hardened material layer.

When molten metal (for example, low carbon steel) is injected into the mold cavity 3 from above the mold 1, the high carbon ferrochromium in the hardening material layer 2 melts, forms an alloy with the low carbon steel, and solidifies. Since a large amount of carbide is generated in this alloy layer, it is possible to cast a casting that is hard only in the surface layer.

FIG. 3 is a cross-sectional plan view of this casting, where 4 is the casting, 5 is the hardened layer, D is the thickness of the hardened layer 5, and T is the wall thickness of the casting 4.

However, the above mold has the following drawbacks. The hardening material layer 2 is melted by the heat of the molten metal at the time of injection, and the amount of the melted material is determined by the amount of heat of the molten metal, that is, the temperature of the molten metal and the thickness of that portion. Therefore, in a casting 4 having a thin wall thickness T, the amount of the hardened material layer 2 that is melted is small, so the thickness D of the hardened layer 5 is small. In general, when pouring temperature of low carbon steel to 1600℃ or higher, it is difficult to produce a sound casting using a normal mold due to mold reaction and gas absorption. According to the experience of the inventors,
When the pouring temperature is 1600°C for low carbon steel, the minimum wall thickness T of the casting 4 where the thickness D of the hardened layer 5 with a Bitkers hardness (Hv) of 200 or more is 1 mm or more is approximately 14 mm, and if it is less than that, hardening will occur. Since the thickness D of layer 5 is 1 mm or less, it is often unsuitable for use as general mechanical parts.

The present invention provides a hardening material for casting hardening that can eliminate the above-mentioned drawbacks.

That is, the present invention uses the conventional hardening materials such as high carbon ferrochromium powder, phenolic resin,
A hardening material for casting hardening characterized by adding aluminum powder and an oxidizing agent in addition to colloidal silica and alcohol such that the total amount of the aluminum powder and oxidizing agent is 12 to 27 wt% of the total amount. It is related to.

As the oxidizing agent, iron oxides such as manganese dioxide, ferrous oxide, and ferric oxide, sodium nitrate, and the like can be used.

The hardening material of the present invention combines the oxidizing agent and aluminum powder with the conventional hardening material components of high carbon ferrochromium powder, phenol resin, colloidal silica, and alcohol as its solvent. They may be mixed so that the total amount is 12 to 27 wt % based on the total amount of hardening material. For example, as shown in FIGS. 1 and 2, this hardening material is applied to a desired portion of a mold 1 and then dried to form a hardening material layer 2.

Casting can be carried out in the casting mold using the hardening material of the present invention as shown in FIGS. 1 and 2, for example, in the same manner as when using the conventional hardening material. You can get castings.

Since the hardening material of the present invention contains aluminum powder and an oxidizing agent, it generates heat with the help of the heat of the molten metal after pouring, slowing down the solidification of the molten metal and at the same time alloying the high carbon ferrochromium with the molten metal. It has the effect of promoting Therefore, it is possible to form a desired hardened layer 5 even in a casting 4 having a thin wall thickness T, which is difficult to achieve using conventional hardening materials.

As a result of numerous experiments, the present inventors have found that when the proportion of aluminum powder and oxidizing agent is less than 12 wt%, the heat generation effect is low and there is no difference from conventional hardening materials, and when the proportion of aluminum powder and oxidizing agent is less than 25 wt%, the hardened layer 5
As the thickness D becomes thinner, the hardness of the hardened layer 5 also decreases.
It has been confirmed that this is not desirable as it is less than 200Hv.

The hardening material of the present invention is used as a hardening material for casting hardening of steel materials. However, since it is pointless to apply this method to materials whose hardness is 200Hv or more throughout the casting, it is meaningless to apply this method to materials whose internal hardness is 200Hv or less, such as ordinary cast steel or low alloy castings. It is desirable to apply it to cast steel and various types of cast iron when performing sand mold casting. As a product, it is applied to the casting of parts that require wear resistance, such as cutter tips for excavation.

Example High carbon ferrochromium powder (7.6wt%C, 3.7wt
%Si, 61.0wt%Cr) -250 mesh 37wt%, phenolic resin 5.0wt%, methyl alcohol 35wt%,
Colloidal silica 2wt%, aluminum powder 9wt
%, and 12 wt% of ferric oxide was applied as a hardening agent to the inner surface of molds (furan molds) of various thicknesses, and molten low carbon steel was poured at a casting temperature of 1600°C.

As a result, even in a thin casting with a wall thickness of 7 mm, a hardened layer with a hardness of 200 Hv or more was obtained with a thickness of 1.2 mm.
The hardness of the unhardened part (base material) of this casting is 140~
It was 160Hv.

As described above, the casting mold for hardening using the hardening material of the present invention can provide a good surface hardening layer even in thin-walled castings, and is very useful for manufacturing various mechanical parts.

[Brief explanation of the drawing]

Figure 1 is an example of a vertical side view of a casting mold for hardening.
FIG. 2 is a sectional view taken along the - line in FIG. 1, and FIG. 3 is a cross-sectional plan view of a casting obtained using the mold shown in FIGS. 1 and 2.

Claims (1)

[Claims] 1 A hardening material for casting hardening that is attached to a part of the inner surface of the mold in order to harden only the surface part of the casting, the ingredients of which are high carbon ferrochromium powder, phenolic resin, colloidal silica, alcohol, and aluminum powder. and an oxidizing agent, and the total amount of the aluminum powder and oxidizing agent is 12% of the total amount.
A hardening material for casting hardening of steel materials, characterized by accounting for ~25wt%.