SU1468638A1 - Sand for making water-soluble cores - Google Patents

Description

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The invention relates to a foundry, namely, mixture compositions for the manufacture of water-soluble rods weighing from 0.05 to 10 kg and having a wall thickness of less than 2 mm used in the casting of aluminum alloys.

A mixture containing dehydrated magnesium sulphate and its saturated solution is known.

The disadvantage of the mixture is low solubility, since to remove it from the cavity, it is necessary to use shock or vibration, which is inadmissible in the manufacture of thin-walled casting from aluminum alloys.

Mixtures based on water-soluble salts are also known, the removal of which from castings does not require the use of mechanical effects.

The known dry water soluble inorganic salt (NaCl or KCl), having a residual moisture less than

one%. From this mixture, cores are prepared by pressing 1.5-4 tf / m. Pressed rods are calcined at 100- ...

Pressed rods are calcined at 100-300 C. The compressive strength of the obtained rods is more than 1000 kgf / cm. The cores are used to produce castings from aluminum and zinc alloys. Full 1-e. The extension of the rods occurs after 1 when washing with a cooled casting with water.

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The disadvantage of this mixture is the low quality of the surface of the rods due to their hygroscopicity and the impossibility of obtaining rods of complex configuration, which in many cases is decisive.

The known mixture for the manufacture of water-soluble rods, containing a water-soluble mineral salt (Nad, NaCO, NaNOj), a fast-hardening paint coating (GF-02 glyphtha or partaphthalic primer) and a refractory filler (firestone, magnet oxide, quartz, magnet oxide, quartz, silica gel, zinc oxide, magnet oxide, quartz, magnet oxide, quartz, magnesium oxide, magnesium oxide, GF-02 primer; ).

The rods made from this mixture are of low hygroscopicity (hygroscopicity can reach zero), are freely washed out of the cavities of the castings with a stream of water and can be spontaneously or heat-treated.

However, the curing rate of this mixture is very low, which causes a high degree of deformation of the rods in the cf state. Partially distorted during transport. rods geometry that does not provide for obtaining castings with high dimensional and weight accuracy. Particularly high deformation is observed with rods having a large mass and height. In addition, the mixture is toxic due to the content of paint and varnish primer in it.

A known mixture for making water-soluble rods containing alumina, stearin, paraffin, and sodium chloride. Sodium chloride with a particle size up to 100 microns and anhydrous alumina are used to obtain the core mixture of the indicated composition. These powder materials in the indicated amounts are biased with the organic components at 70-80 ° C. The resulting suspension is pressed into the mold at a pressure of 1.5-3.0 kgf / C1. Then the raw rods are burned in the layer of adsorbent at 700-.

The obtained rods are characterized by a decrease in fire shrinkage during the drying process. The ultimate strength of compression is 180-210 kgf / cm. The rods are removed from the casting with cold water in 4-5 minutes.

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The use of a known mixture for the manufacture of water-soluble cores makes it possible to obtain complex cavities of castings with a surface purity of 6-7 class.

The disadvantages of these water-soluble rods are their low mechanical strength, the low rate of removal from the casting, and the presence of insoluble residue in the rod, which can remain in the casting cavity after the rod is dissolved.

Closest to the invention is a mixture for the manufacture of water-soluble rods, including May. %:

Chloride

sodium 60-90

Partially dehydrated sulfate

aluminum 10-40

Partially dehydrated aluminum sulphate is different in composition and properties from aluminum sulphate, which makes it possible to use it as a binder in the composition of a water-soluble rod.

From the proposed mixture, the rods are made as follows. Powdered materials in the specified amounts are mixed and filled with water at the rate of obtaining a semi-dry, plastic or durable consistency mass and molded by pressing or pouring into a mold. Then the raw rods are baked at 550-65 O with for 2-4 hours.

The rods obtained from a known mixture have the following characteristics:

ultimate compressive strength, kgf / cm 215-290 speed of core removal,

g / min 3-5

water solubility,% 100

rod strength, MPa15-20 Water-soluble rods made from a known mixture have high mechanical strength, full water solubility, and have a high rate of leaching from the casting.

The disadvantage of these water-soluble rods is their high; the degree of deformation in the wet state, since the curing rate of this mixture is low, which distorts the geometry of the rods and produces castings with a low size-weight accuracy.

The production of rods from a known mixture requires energy consumption in connection with the need to roast raw rods during heating for many hours to BSO C.

In addition, the known mixture as a binder contains partially dehydrated aluminum sulphate, which is highly toxic, which worsens the working conditions of workers and requires the creation of a powerful ventilation system, as well as special measures for the production of waste water, as soluble aluminum salts Toxin and for plants. Thus, the use of aluminum sulfate in the foundry industry entails additional material costs for enterprises.

The purpose of the invention is to increase the raw strength of the rods and prevent their deformation due to the fact that the mixture for the manufacture of water-soluble rods, including sodium chloride and inorganic binder, contains, as an inorganic binder, a valuable calcium chloride aqueous solution and additionally magnesium sulfate in the following ratio ingredients, wt.%: Sulfate

magnesium 2.0-20.0

Calcium chloride saturated aqueous solution 5.0-20.0 Chloride

sodium Remapt To obtain a core mixture of the indicated composition, sodium chloride is used, which is a white crystalline powder, m.p. about 800 ° С, solubility in water at 20 ° С 36 g / 100 HZ O magnesium sulfate - powder of white color, t. pl. , solubility in water at 107 g / 100 g HjOi saturated solution hl0

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calcium calcium - concentration at ZO c is 44 wt.%, so pl. Chalice Alcium 772 C.

In this composition of the core mixture, sodium chloride is the main refractory substance, which ensures the solubility of the rods after casting, magnesium sulphate is not toxic, and in these quantities, it is an additive that provides the heat resistance of the rods and stabilizes their degree of deformation in the raw state. Nii, a valuable calcium chloride aqueous solution is a binder that provides strength to the rods.

The hardening of the rods is due to the additional chemical interaction between the solid and liquid phases of the mixture, according to the equation

MgS04 + CaClj MgCli2 + CaS04.

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As a result of this exchange reaction, gypsum is released, which strengthens the core.

The ratio of components in the mixture is optimal. When the content of a saturated calcium chloride aqueous solution is less than 5 wt.%, The mixture is not mobile, which complicates the formation of the rods, while its content is more than 20 wt.%, The strength of the rods decreases, and the degree of deformation increases.

When the content of magnesium sulfate is less than 2 wt.%, The strength of the rods is not ensured during manufacture and when they are removed from the mold, they are destroyed, and if it is more than 20%, the solubility of the rods decreases (the dissolution rate is halved).

In tab. 1 shows the compositions of the mixtures according to the invention (1,2,3) and the prototype (A).

From the proposed mixture, the rods are made as follows.

The powdered materials are mixed in the indicated amounts and a previously prepared saturated aqueous solution of calcium chloride is added at the rate of obtaining a semi-dry or plastic mass. The resulting suspension is pressed into a mold heated to 70-80 and maintained at this temperature714

re for 3-5 min, after which the rods are removed and dried in a layer of silica gel at 70-150 ° C for 3-6 hours

Comparative tests were performed on dry rods and rods in the wet state, made from the proposed and known mixtures.

The test results are shown in Table. 2 (for dry rods) and 3 (for rods when wet).

From the table. 2, it follows that the performance of the matched mixtures in the dry state does not differ significantly.

From the table. 3, it follows that the strength of the rods in the raw state, made from comparable mixtures, is significantly different. When lashing in a heated mold for 5 minutes, the strength of the mixture according to the invention is 200 times higher than the strength of the known mixture (the rods were practically not removed from the mold). The latter circumstance leads to a significant increase in the rate of solidification of the mixture and, accordingly, a decrease in the degree of deformation of the rods in the wet state, and consequently, an improved quality of the surface of the rods and an increase in their accuracy.

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The rods of the mixture according to the invention are hardened to form gypsum by the reaction of magnesium sulfate with a saturated aqueous solution of calcium chloride. After the mixture is pressed into the equipment, it self-hardens without the occurrence of primary shrinkage and does not require additional heating for many hours, which ensures a reduction in the energy consumption to get older. The rods can withstand heating up to 750 s for 10 hours without breaking and resizing.

Replacing the partial dehydrated aluminum sulphate with magnesium sulphate reduces toxicity while maintaining the technological properties of the rods.

PeajAi3auHH mixtures according to the invention for the manufacture of water-soluble rods compared to the known mixture (5) allow: dramatically shorten the time for the production of casting rods without distorting their geometry while maintaining high mechanical strength, full water solubility and high removal rate from the casting to obtain hollows of stable geometric castings sizes with a surface finish of 6-7 cells. improve working conditions by reducing toxicity while maintaining the technological properties of the rods.

Table 1

table 2

Claims (1)

MIXTURE FOR THE PRODUCTION OF WATER-SOLUBLE RODS, Including Sodium Chloride and Inorganic