In recent years, in order to solve the problem that the water glass can be used for a short period of time, the low-modulus water glass is often used to extend the usable time of the water-glass sand. Each factory has developed its own factory standard according to specific conditions and measures.
At present, many medium and small-sized water glass factories supplying foundries usually purchase bulk or powdery solid sodium silicate raw materials from large-scale sodium silicate production plants, and then heat-dissolve and process solid sodium silicate raw materials. Production of foundry water glass.
It should be especially noted that the foundry industry also advocates the use of high quality water glass. In general, the use of high-quality water glass and high-quality raw sand can greatly reduce the amount of water glass added, not only will not increase the manufacturing cost of castings, but also solve the problem of poor water glass sand collapsibility. Effect.
2. Performance parameters of sodium water glass
(1) Modulus Is the molar ratio of SiO2 to Na2O
M = amount of SiO2 mass / amount of Na2O substance
M=(SiO2 mass fraction/Na2O mass fraction)*1.033R#xkhks# silicate ratio #xkhjs#= SiO2 mass fraction / Na2O mass fraction
The modulus is determined by the composition of the solid sodium silicate, which has a major impact on the properties of the water glass
(2) DensityIt can indirectly indicate the concentration of sodium silicate in the water glass or the content of solid sodium silicate. The higher the density, the higher the content of solid sodium silicate.The above indicates that the density is positively correlated with the Baume degree, that is, the greater the density, the greater the Baume degree. In fact, the relationship between modulus and density shows a reverse change, but there is no fixed relationship
(3) Impurity content
The pure sodium water glass has a colorless viscous liquid and contains gray, green or even black when it contains impurities such as ferric oxide, aluminum oxide and calcium oxide. In addition, the sodium water glass also contains an impurity salt, sodium chloride, sodium sulfate, sodium carbonate, and the like. The impurities of the water glass have obvious adverse effects on the density, viscosity, hardening speed, bonding strength, aging speed and surface
tension of the water glass. Therefore, the impurity content in the water glass should be minimized, which reduces the water glass. The amount of addition, the improvement of the bond strength of the water glass and the collapsibility of the molding sand are of great significance
(4) Properties of sodium water glass
Sodium water glass is a complex dispersion system that has both the properties of an ionic solution and the nature of a colloidal solution. The nature of the solution is determined by the modulus of the water glass: when M is less than 2, it is a simple ionic solution, and there is almost no colloidal ion; when M is greater than 2, silica colloidal particles begin to appear in the solution, and The increase in the proportion of the number of colloidal particles increases; when M = 4, the sodium water glass is substantially silica sol. Therefore, the high modulus water glass is easy to coagulate and unstable, and has both weak electrophoresis phenomenon and the Dingzel effect, and the characteristics of the colloidal solution. In the water glass solution, the phenomenon of spontaneously forming colloidal polymerization is called "aging".
3. Method for adjusting the modulus and density of sodium water glass
(1) Reduce the modulus: add sodium hydroxide (caustic soda);
(2) increasing the modulus: adding hydrochloric acid or ammonium chloride;
(3) Modular adjustment: Two high and low modulus water glass are used to adjust the modulus.
The modulus requirements for commercial sodium water glass are set by the manufacturer according to the requirements of the foundry. When the density is not suitable, it can be adjusted by adding pure water or by heating and concentrating.
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