JPS588935B2 - Manufacturing method of heat-generating self-hardening water-soluble mold - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a heat-generating self-hardening water-soluble mold used for casting aluminum alloys, copper alloys, cast steel, etc.

Currently, foundries use green molds made of silica sand as aggregate,
Inorganic self-hardening molds, organic self-hardening molds and cement molds have been used.

Green molds are used for producing relatively small castings, while other molds are used for producing medium and large castings due to their high strength.

These conventional molds are not easy to disassemble;
There are problems in that noise, vibration, dust, odor, etc. are generated, deteriorating the working environment and causing pollution.

In order to solve this problem, the present inventors first developed a heat-generating self-hardening water-soluble mold that can be easily disassembled using water after casting.

This mold is a heat-generating self-hardening water-soluble mold made by mixing and molding 100 parts by weight of alumina sand, 3 to 10 parts by weight of sodium aluminate as a binder, and 0.3 to 1 part by weight of aluminum powder.

That is, it uses alumina sand as an aggregate and sodium aluminate and aluminum powder as a binder, and the alkaline content of sodium aluminate and aluminum powder react to generate heat and harden to form sodium aluminate. It is something.

This mold can withstand the casting of cast steel, cast iron, and copper alloys with high melting points, and the binder is dissolved by water after casting, so it can be easily disassembled and the alumina sand can be easily recovered. It has special features.

However, the hardening reaction of sodium aluminate and aluminum powder starts immediately after kneading, and there is a drawback that sufficient time is not available for forming a mold, that is, the pot life is short.

The purpose of the present invention is to solve this problem of short pot life, and when making a mold, alumina sand is mixed with liquid nitrogen and cooled, and sodium aluminate and aluminum powder are mixed with this. The problem could be solved by molding.

By mixing alumina sand with liquid nitrogen, the alumina sand can be cooled very easily, and the curing reaction between the sodium aluminate and aluminum powder that is mixed in this sand is at a low temperature, so the reaction rate is slow and it takes time to make the mold. can be extended.

Furthermore, since liquid nitrogen is used, (1) the alumina sand is brought into direct contact with the liquid nitrogen, and the temperature is low, so cooling can be performed efficiently and in a short time.

(2) No special equipment for cooling is required.

(3) Since it is easy to adjust the temperature to the appropriate temperature by changing the amount of mixture, molding can be done efficiently.

(4) Since it is liquid nitrogen, it has excellent effects such as not deteriorating the working environment, not becoming a source of pollution, and not causing a fire.

The aggregate alumina sand used in the present invention is 60 to 15
0 mesh high purity alumina is suitable.

Also, sodium aluminate is Na20/A l20
It is preferable that the molar ratio of 3 to 3 is 1.5 to 3.0 and the water content is 60% by weight or more.

When the molar ratio is less than 1.5, the alkali content is too small and curing becomes poor, and when it is more than 3.0, the sodium aluminate aqueous solution deteriorates and becomes difficult to store.

Further, if the water content is less than 60% by weight, sufficient reaction cannot be obtained and curing becomes difficult.

The amount of liquid nitrogen mixed with the alumina sand is the amount that will keep the temperature of the alumina sand at least below 0℃.The lower limit of the amount of sodium aluminate and aluminum powder mixed with the alumina sand is determined by the effective strength of the mold. is the limit amount indicating
The upper limit value needs to be the limit amount, since molding becomes difficult when the amount of the binder increases.

Therefore, for 100 parts by weight of alumina sand, 3 to 10 parts by weight of sodium aluminate and 0.3 to 1 part by weight of aluminum powder.
Parts by weight.

These binders may also be blended after cooling.

Example 70-150 mesh high purity alumina sand 3 kg (10
0 parts by weight) was kneaded with 210 g (7 parts by weight) of liquid nitrogen and cooled to -10°C.

To this, the molar ratio of Na2O/A1203 is 1.7.
, 90P (3 parts by weight) of sodium aluminate with a moisture content of 65% was mixed and kneaded, and further 23g (0
．． 75 parts by weight) were mixed and kneaded.

For comparison, we made a similar device that was not cooled with liquid nitrogen.

A block of 80xl20x140mm was molded using these prepared sands, and the temperature at the center was measured.

The results were as shown in Figure 1.

In the figure, 1 is a relationship curve between elapsed time and exothermic temperature in the case of cooling with liquid nitrogen, and 2 is a similar curve in the case of no cooling.

As shown in the results, without cooling, the heat generation start time is very short, and the temperature rises rapidly, reaching the maximum temperature of 100° C. in just 7 minutes, making it difficult to mold the product because the pot life is too short.

On the other hand, when cooling with liquid nitrogen, the gradient of increase in heat generation was gradual until 15 minutes had elapsed, after which it rose sharply, but the pot life was extended to 15 minutes and molding became easier.

Using the same raw materials as above, 50mm according to JIS standard
A standard test piece with a diameter of 50 m and 11 L was prepared, and the compressive strength of the mold was examined. The results are shown in Table 1.

As shown by this result, in the case of the present invention, the compressive strength is the same as that without cooling after 1 hour elapsed time, but after 24 hours, the compressive strength becomes weaker by 2 to 3 kg/cm2, but at a minimum of 15 kg/cm2. cm2, and there is no problem in terms of strength.

A mold is made from this raw material, cast iron equivalent to FC20 is cast, and after the casting has cooled, the water pressure is 1 kg/cfi2 and the water amount is 10.
As a result of dissolving in water at 1/min, the mold easily collapsed.

Moreover, a sound casting was obtained.

[Brief explanation of the drawing]

The drawing is a diagram showing the relationship between elapsed time and exothermic temperature in the curing reaction in the case of the present invention and in the case of no cooling. 1: In the case of the present invention, 2: In the case of no cooling.

Claims (1)

[Claims] 1 When molding a mold using 100 parts by weight of alumina sand, 3 to 10 parts by weight of sodium aluminate and 0.3 to 1 part by weight of aluminum powder as a binder, the alumina sand is mixed with liquid nitrogen and cooled. , a method for producing a heat-generating self-hardening water-soluble mold, characterized by blending and molding sodium aluminate and aluminum powder.