JPH01289539A - Exothermic pad - Google Patents

Abstract

PURPOSE:To improve the quality of a product by containing the specific ration with wt. of nickel oxide into powder mixing material for pad. CONSTITUTION:A flask 11 is set on a base plate 10, and molding sand 7 is stamped and also the exothermic pad 4 is set in the feeder head sleeve 3. Then, NiO powder (<=10mu grain size) in the powder mixing material for the exothermic pad 4 is contained at >=0.3wt.% and <15%. At the time of pouring molten cast steel having the prescribed temp. from a sprue 1 in the mold, the NiO powder in the exothermic pad 4 generates reduction reaction with Al in the molten metal in the pad 4, and diffusion of Al into the molten steel is prevented. By this method, the original exothermic reaction of the exothermic pad 4 is not obstructed but the formation of hardened layer on the casting surface containing with the pad 4 is prevented. Therefore, the development of defect in the product caused by Al is prevented and the quality of the product is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an improvement in a heating pad applied to a mold for steel casting, and more particularly to a heating pad that causes hardening of the surface of the casting.

[Conventional technology]

In the manufacturing of castings, in steel castings that have thin wall areas, wall thickness intersections, or wall thickness variation areas, casting defects such as cavities occur in center drawing due to insufficient hot water supply to the center of wall thickness during solidification, resulting in poor quality. .

To prevent this, a heating pad is used in the mold in that area to control the solidification rate. As an example of measures to prevent internal defects in this casting, a general casting method in which a heating pad is applied to a thin-walled L-shaped test piece is shown in Figure 2 (A) and a cross-sectional view of the same figure. Figure 2 (Blk shown).

Figure 2 (4), (In the process, a mold with a sprue 1, a runner 2, and a riser 9 is made from foundry sand 7, surrounded by a surface plate 10 and a casting flask 11, and then a molten steel 5 When you cast the heating pad 4
The molten steel 5 generates heat, suppressing premature solidification of thin-walled parts, etc., and center drawing allows the production of cavity-free castings.

[Problem to be solved by the invention]

However, on the casting surface in contact with the heating pad 4, a hardened surface layer is generally formed with a thickness of about 2 mm, although it varies depending on the thickness of the casting.

This hardened layer has reduced ductility (cracks occur at a bending angle of 500 degrees), so it remains like a cast surface! cannot be used. Therefore, in the past, attempts have been made to prevent the formation of the above-mentioned hardened layer by applying a zircon type coating agent to the four surfaces of the pad that come into contact with molten steel, but in reality, almost no effect could be expected.

The inventors of the present invention conducted repeated research to prevent surface hardening of the casting surface in contact with the heating pad in the production of castings using the heating pad, and as a result, they discovered that the hardening factor is due to the hardening. In other words, quantitative analysis of the hardened layer revealed that it contained about 70 times more mucus than the cast surface without padding.
In addition, needle-like crystals of A4 AtN were observed in the microstructure of the hardened layer.

Therefore, the present inventors believe that the AL of and is caused by kl, which is a component of the heating pad, and that the above-mentioned curing reaction can be suppressed by preventing the diffusion of At in the pad at the mold interface (pad surface). reached the conclusion.

An object of the present invention is to provide a heating pad that does not cause this curing reaction.

[Means to solve the problem]

In order to achieve the above object, the present invention provides a heating pad powder mixture containing nickel oxide on an α3 heavy weight plate and 15
It is characterized by containing less than - by weight.

[Effect]

In the present invention, nickel oxide, which easily causes a reduction reaction with At, is added in advance to the heating pad powder, and this nickel oxide prevents At from diffusing into the molten steel.

For example, in the pad, At and nickel oxide are 2At+
3NiO=3Ni+MutzO.

The reduction reaction shown by occurs, and the diffusion of At into the molten steel is prevented.

If the nickel oxide is less than α3% by weight of the heating pad powder mixture, it is too small to prevent the diffusion of Mut into the molten steel by the above reduction reaction, and the reverse ICl3 weight -
If the amount is too much, the heat generating effect of the heat generating pad is inhibited, and casting defects such as cavities occur.

〔Example〕

Example 1 P290-N manufactured by Meiso Kagaku Kogyo Co., Ltd. as heating pad powder
NiO powder (particle size of 10 μm or less) was added to the powder at various ratios shown in Table 1. These I/c48 Baume silicate sodas are 81. (weight) was added and kneaded, and after molding a flat plate, a heating pad was prototyped using the curing reaction caused by carbon dioxide gas.

The components of the above P290-H are shown below.

kt: 24.5To, Mutgo: 5 & 5%, 810.
:&9chi, F'eO: 14%%F0201: 1
6%, K, 0:1.3chi (weight%) Next, in order to evaluate the heating pad prototyped as described above, FIG. A casting test was carried out using the casting method shown in FIG. 1 (Bl).The mold making procedure at this time was as follows.

In Figure 1 (A) and (B), (1) Place the casting flask 11 on the surface plate 10, and use the furan process as bed sand (1 to 1.5 inches of furan resin is added to the foundry sand).
Freeman Torsil sand (Australian foundry sand that has a spherical grain shape and contains 99.5% or more of 10E) (2) Insert the heating pad 4 of the present invention into a predetermined position in the casting feeder sleeve 3, and arrange the gas vent 6 and runner 2 above and below the sleeve 3, A sprue 1 is disposed in the runner, and Freeman silica sand 7 is further introduced, pounded and hardened to complete mold formation.

The mold described above is a mold in which the periphery of the heating pad 4 of the present invention comes into contact with molten steel, and the evaluation was conducted under severe conditions.

Cast steel (SC!46) was built in the above mold at 1560°C and tested. After the casting test, a test piece 8 was taken from the center of the casting 5 in contact with the heating pad 4 of the present invention, and the depth of surface hardening was observed using an optical microscope. The results are shown in Table 1.

In Table 1, Comparative Example &9 uses a heating pad (conventional material) to which no oxide is added, and the surface hardening depth was α38+im. On the other hand, in the A1-90 example using a heating pad containing nickel oxide, NiO
begins to show its effect significantly at 0.3% (weight i) (
'42), it was confirmed that the formation of a surface hardening layer could be prevented at 0.5 inches (weight) or more (43-8).

Table 1 Relationship between the amount of nickel oxide added and the depth of surface hardening However, for the NiO 15 inch (weight) (A8), a casting test was conducted using the casting method shown in Figure 2 above, and the optical Observed with a microscope. As a result, no surface hardening layer was formed, but as a result of cutting the center cross section of the thin casting (plate thickness: 50 corners), a centerline hole was formed inside.

This phenomenon suggests that if the amount of NiO added is excessive, it inhibits the heating effect inherent to the heating pad.

Example 2 In place of P290-H manufactured by Meiso Kagaku Kogyo Co., Ltd. in Example 1, heat-generating roses made by the same company with the components shown in Table 2)'P290-■,
P-290-■, P290-2F were used, and the casting test and optical test after the test were performed in the same manner as in Example 1, except that NiO powder (particle size 10μ or less) was added at the ratio shown in Table 3. Microscopic observation was performed. The results are also shown in Table 3.

Table 3 Relationship between the amount of nickel oxide added and the depth of surface hardening The above results show that the amount of NiO added to the heating pad material is
When the thickness is 1 inch (weight) or more, especially 15 inch (weight) or more, the formation of a surface hardening layer is almost prevented;
Since the original exothermic effect is inhibited if more than 10% is added, in the present invention, the amount of NiO added is 15% by weight or more.
(weight). It was confirmed from Table 1 that the most preferable addition amount is 5 to 10 cL (by weight).

It has been confirmed that adding an oxide other than NiO as the nickel oxide is effective in preventing surface hardening.

〔Effect of the invention〕

By applying the heating pad of the present invention, it is possible to prevent the formation of a hardened layer on the surface of the casting, and as a result, even in the case of a casting whose wall thickness is not uniform, casting defects such as shrinkage cavities will occur in the thick part. You can get a high quality product without any hassle.

[Brief explanation of the drawing]

Figure 1 (Al, (Bl) is a diagram showing a casting method evaluated as an example of the present invention, Figure 1 (B) is Figure 1 (A)
Figures 2 (A) and 2 (B) are diagrams showing conventional casting methods and an embodiment of the present invention, and Figure 2 (B) is a view taken along the line I-1 of Figure 2 (A). It is a view taken along the line ■-■.

Claims (1)

[Claims] A heating pad for preventing surface hardening of castings, characterized in that a heating pad powder mixture contains nickel oxide in a weight percentage of 0.3% or more and less than 15%.