The chemical resistance of refractory materials is understood as their ability to withstand the destruction from the chemical and physical effects of products formed in the furnace – metal, slag , dust, ash, vapors and gases. The greatest effect on refractories in smelting furnaces is provided by slags. With respect to the action of slags refractories can be divided into three groups – acidic, basic and neutral. Acid refractories are resistant to acid slags containing a large amount of Si 0 2 , but are corroded by the main slags.
An https://refractoriesmaterials.com/acidic-refractory/ is dinas. Dinas is resistant to the action of oxidizing and reducing gases.
The main refractories are resistant to the action of the main slag , but are corroded by acid ones. These include refractories containing lime, magnesia and alkaline oxides (dolomite, magnesite , etc.).
Neutral (intermediate) refractories, in a composition which comprises amorphous oxides react with both the acidic and the basic slags , newly much lesser extent than the acidic and basic. These include chromium iron ore containing FeO – Cr 2 O 3 as the main constituent.
Production of Precision Castings
For precision casting, the same material was used for mold production as for dismountable sand and clay molds in conventional cast iron and steel foundries. It is silicon dioxide (silica) in the form of finely ground quartz flour (P-quartz). With increasing demands on the properties and quality of precision castings, the use of silicic acid is limited and is currently used where no special requirements are placed on the dimensional dimensions of castings, the quality of their surfaces, dimensional tolerances. However, silica is also used where it is the only cheap starting material, and so far there is no way to buy another, more suitable refractory material.
The use of silica is undesirable from the point of view of occupational health. Dusty silica, inhaled by humans, causes a dangerous occupational disease – goose gland among workers in foundries. Molding compounds for investment casting also contain strong inorganic acids, which increase the activity of the fine part of the powdered quartz.
The development of precision casting is aimed at the production of precision castings from high melting point materials, very often from the latest heat resistant alloys, which are melted and vacuum cast. The use of such alloys and vacuum techniques involves the use of molding mixtures from which ceramic molds of high strength and high temperature resistance can be made.
The mold should not interfere with fillable alloys, change its volume during manufacture, and should also be sufficiently gas permeable. Only molds with such properties can guarantee that castings with large masses and overall dimensions are of high quality.
Shapes with low strength and high temperature resistance can be used to make only small and light castings. With a large volume of cast metal, the ceramic mold is heated to high temperatures by the heat of the metal, softened and deformed, thereby deforming the casting. In addition, the metal penetrates into the pores of the ceramic mold with a large casting compound, which partially determines the metallostatic head, and the casting is defective due to poor surface quality. Low strength ceramic molds are easily eroded by the metal being cast and erosion products (ceramic particles) can cause clogging in the castings. When the ceramic material reacts with the metal to be cast and with its oxides. Read more on this page:RefractoriesMaterials.com