SU555966A1 - Mixture for making water soluble rods - Google Patents

Description

one

The invention relates to the field of foundry, in particular, to mixture compositions for the manufacture of water-soluble rods.

Known compounds based on carbamide, containing, in addition to carbamide, boric acid up to 2% (composition QBcc 98-2), potassium nitrate up to 20% (composition Kbcn 80-20); polyvinyl alcohol 1-5%, water 2-20%, calcium chloride 1.5-4%.

Along with acceptable characteristics - low melting point, high quality of the surface of the model or rod, the compositions used have a significant drawback associated with the decomposition of urea. The decomposition of liquid carbamnd sotavov leads to the release of toxic ammonia.

Especially dangerous in this respect is the overheating of carbamide mixtures, since the amount of ammonia formed increases dramatically with temperature. The gassing of ammonia from carbamide mixtures depends not only on the temperature regime, but also on the chemical composition of the mixtures used.

The presence of a hygroscopic salt enhances the ability of finished models (rods) to absorb moisture from the environment. As a result, along with toxicity, the quality of the surface deteriorates, the technological regime of the foundry itself is disrupted.

(storage of finished products and rods). This disadvantage is particularly noticeable in the manufacture of large batches. In order to eliminate it, it is necessary to provide for special storage measures.

The closest to the described invention to the technical essence and the achieved effect is a mixture based on technical urea with the addition of soluble salt.

As a salt, the lime composition contains potassium and sodium nitrate salts or aluminum and ammonium sulfate salts.

However, this mixture has a lower heat resistance, which leads to a significant release of ammonia when the mixture is heated, resulting in the formation of gas pockets in the rods and its increased melting point. The rods (models) obtained from the mixture have an increased hygroscopicity due to the content of oxygen-containing acids in the salt salts.

In order to reduce toxicity and hygroscopicity, the mixture as ammonium salt contains ammonium halide, namely ammonium chloride or ammonium bromide, with the following ratio of ingredients, weight. %; Ammopi halide 10-50

Urea Technical 50-90

The effect of the proposed additives is based on a change in the equilibrium of carbamide hydrolysis. Upon contact with the water contained in the urea, the reaction occurs.

NH2CONH2 + 2H20: (NH4) 2C03, (1)

as a result of which ammonium carbonate is formed. This compound, at relatively low temperatures (70 ° C), is capable of decomposing with the release of ammonia, water, and carbon dioxide.

(LH4) 2CO3: 2MNz + C02 + H20 (2)

The lung ammonia is then released to the atmosphere and the balance is shifted to the right. Thus, continuous decomposition of urea occurs, and water plays the role of a catalyst

decomposition. Increasing the temperature facilitates the removal of ammonia and increases the rate of decomposition of the urea. If the carbamide contains ammonium salts, then the equilibrium of reaction (1) is shifted to the left, the stronger

the higher the concentration of ammonium halide.

The table shows the composition of the mixture.

The physicomechanical properties of the mixture are given below:

Mechanical strength, kg / cm

Thermal expansion, 1 / degree

Linear shrinkage, 96 Heat resistance, С ° Ash content,% Specific weight, g / cm Melting point, ° С Allocation of ammonia, ml / min

The composition of the mixture with an ammonium halide content of 10-50% is optimal, since in the indicated temperature range, ammonia emission is practically not observed, increasing the amount of halide more than 50% leads to an increase in ammonia emission, while reducing the halide content less than 10%, the hygroscopicity of the mixture increases.

Hygroscopicity tests were carried out by comparative weighing of carbamyl, halide containing compounds, their water-soluble compositions by isobutane, and known composition. For testing, cylindrical rod samples were made from the indicated soils. Samples were placed in boxes with a known constant humidity of 75%. The weight gain was determined 30 minutes after pouring into the mold and 48 hours later. In known mixtures, a noticeable increase in weight is observed, which characterizes their higher hygroscopicity.

The weight on the known mixtures was, weight. %:

30 min0,1

48 hours3,6

120

80 No

160 No No

In the proposed mixture, the weight gain was, weight. %:

After 30 min0.05-0.06

48 hours1,2

The removal time is reduced by a factor of 1.5 compared with known mixtures. The reason for the reduction in the removal time can be the following: in known carbamide-containing mixtures, accumulation of thermal decomposition products (biuret, melamine, etc.) occurs, whose solubility is much lower than both urea and ammonium halides.

In the mixture according to the invention, the accumulation of these substances does not occur, since their temperature range increases the chemical stability of urea, i.e. its decomposition is suppressed.

Claims (1)

Invention Formula A mixture for the manufacture of urea-based water-soluble rods, comprising an ammonium salt, characterized in that, with the aim of reducing toxicity and hygroscopicity, it contains ammonium halogen, ammonium chloride 6 or ammonium bromide as the ammonium salt in the following ratio of ingredients , weight. %: Ammonium halide Jn nA Technical urea 50-90.