FI95445B - Procedure for producing alkali-silicate binders to be used for making cores and moulds - Google Patents

Description

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The invention relates to a process for the preparation of an alkali silicate binder for the manufacture of chemochemicals and molds. The invention relates to a process for the preparation of an alkali silicate binder for the manufacture of chemicals and molds.

Inorganic binders are commonly used in the manufacture of chemicals and molds. Several different methods are already known for the preparation of these binders, the best known and still commonly used of which are the so-called water glass method. Water glass (NajO x n SiO where n is greater than 1) is prepared by melting a mixture of soda ash (sodium carbonate; Na 2 CO 3) and quartz sand (silica; SiO 2) at high temperature. The result is an amorphous glass. The resulting amorphous glass is dissolved under pressure, generally by heating, to about 5 to 10 times the amount of water, resulting in a partially hydrolyzed rigid water glass solution. This water glass solution is generally known to be used as a binder and the molar ratio of water glass can generally vary between 1.7 and 3.3. The viscosity of the water glass solution can also be varied according to the application.

25 Water glass reaction equation:

1400 ° C

Step 1 n SiO 2 + Na 2 CO 3 -------------> NajO x nSiO 2 + CO 2 silica soda amorphous glass carbon dioxide 30

6 bar / 160 ° C

Step 2 NajO x n SiO 2 + H 2 O ------------------> Water glass solution amorphous glass 2 95 ^ 46

The manufacture and use of water glass have been described in detail e.g. in the book: "Foundry Technology 2"; E. Autere, Y. Ingman, P. Tennilä, starting on page 152.

As can be seen from the water glass reaction equation described above, the preparation of a water glass-5 solution is a complex large-scale industrial process requiring a large amount of energy and pressure. A high temperature of 1400 ° C has to be used for smelting soda and quartz sand, and a pressure of the order of 6 bar and a temperature of 160 ° C have to be used for dissolving amorphous glass in water. Implementing such a process in a plant using cores, for example, is completely economically unprofitable.

It is an object of the present invention to provide a novel process for the preparation of an alkali silicate binder 15 for use in the manufacture of cores and molds, which process represents a substantial improvement over currently used processes. To achieve this object, the process according to the invention is mainly characterized in that alkali hydroxide, water and amorphous finely divided silica ash are used as raw materials, first dissolving the required amount of alkali hydroxide in water to give a strongly alkaline and exothermic reaction fine silica ash with constant stirring and reacting the silica ash with an alkali hydroxide solution to form an alkali silicate binder.

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The invention provides several significant features of the prior art; advantages, the following of which can be highlighted in this context. The manufacturing process according to the invention makes it possible to prepare an alkali silicate binder from generally known raw materials and industrial waste in an economically viable manner. The binder can simply be produced in small or large quantities, in which case the manufacturing process according to the invention is also suitable for use in a production plant using cores as an economically viable process.

I! 3 95 £ 4b

Although even industrial waste is used as the raw material for the alkali silicate binder, the end product is nevertheless a sufficiently pure alkali silicate binder for the manufacture of cores and molds. The manufacturing process is easy to control and the equipment required is simple, as the 5 devices required in the process are just a mixing vessel and a mixer. Manufacturing also does not require increased pressure, and no heat needs to be introduced into the process from outside the process. From the point of view of energy economy, the manufacturing process according to the invention is thus significantly better than the previously used water glass manufacturing method. Other advantages and features of the invention will become more apparent from the following detailed description of the invention.

In the process according to the invention for the preparation of the alkali silicate binder, alkali hydroxide, water and finely divided amorphous silica ash are used as raw materials. The alkali hydroxide used in the process is most preferably sodium or potassium hydroxide. Silica ash, in turn, can be ash generated as waste in the ferrosilicon process, such as fly ash, or other impure amorphous and finely divided silica.

The preparation process according to the invention proceeds by first dissolving the desired amount of alkali hydroxide in the required amount of water. This reaction is strongly exothermic and results in a hot alkali hydroxide solution. To this hot solution is added amorphous and finely divided silica ash with constant stirring. The solution is strongly alkaline and due to the exothermic reaction, the temperature of the solution is generally above 80 ° C, whereby due to this strong alkalinity of the solution and the temperature of the solution, the silica ash reacts with the above-mentioned alkali hydroxide solution. The silica ash reacts with the alkali hydroxide solution to form an alkali silicate, and when the reaction is complete, i.e., when all the ash added to the solution has reacted to alkali silicate, an alkali silicate binder is obtained as the reaction product.

In the composition of the resulting alkali silicate binder, the molar ratio of silica to alkali metal oxide can be determined as desired, and depending on the application, this molar ratio is preferably between 0.5 and 4.0. Viscosity and concentration in the reaction product resulting from the alkali silicate binder production process can also be determined as desired. Thus, the properties of the binder can be modified as desired for different uses.

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The alkali silicate binder generated in the manufacturing process can be used as a binder in the manufacture of cores and molds in a manner similar to generally known inorganic binders. The manufacturing process itself as well as the equipment required in the process are simple, as no equipment other than a mixing vessel and a mixer is required. There is also no need to use elevated pressure in the manufacturing process, and there is no need to bring heat to the manufacturing process from outside the process. The process pressure is normal ambient pressure and the process temperature is usually above 80 ° C. This temperature is also due to the exotherm of the reaction itself.

The invention has been described above by way of example with reference to one preferred embodiment thereof. However, the invention is not limited to the described embodiment only, but the invention may vary within the scope of the inventive idea defined in the appended claims.

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Claims (5)

Process for the production of alkali silicate adhesives for use in the manufacture of cores and molds, characterized in that the process 5 uses as raw material alkali hydroxide, water and amorphous atomized silica ash, in order to first dissolve an required amount of alkali hydroxide in water of a strongly alkaline and due to exothermic reaction hot alkali hydroxide solution and in the alkali hydroxide solution formed amorphous silica ash mixture is constantly mixed with the mixture and the silica ash is allowed to react with the alkali hydroxide solution to an alkali silicate solution. Process according to Claim 1, characterized in that the silica ash used in the process is produced as waste in a silicon iron process or other similar impure amorphous and finely divided silica ash. 3. A process according to claim 1, characterized in that the alkali hydroxide used in the process is sodium or potassium hydroxide. 20 4. Process according to any of the preceding claims, characterized in that the mole ratio of silica to alkali metal oxide is adjusted to the desired in the reaction product formed by the process, advantageously in such a way that the mole ratio is between 0.5 and 4.0. 25 5. A process according to any one of the preceding claims, characterized in that the viscosity and concentration of the reaction product formed in the process are determined according to the purpose of use. A process according to any of the preceding claims, characterized in -30, that the process is carried out in ambient pressure and in the reaction heat generated in the process.