1. Refractory powder
Commonly used refractory powders include zircon powder, brown steel jade powder, bauxite powder, quartz powder, mullite powder, chromite powder, magnesia powder, etc. zircon powder is an excellent refractory powder for cast steel.
Zircon powder, namely zirconium decanoate powder, becomes zro267.2%, sio232.8%, melting point 2430 ± 20 ℃, ZrO2 ≥ 63%, and contains impurities such as Fe2O3, Cao, TiO2 and Al2O3. Its melting point is only 1600-1800 ℃, while zirconium silicate in zircon powder begins to decompose into single ZrO2 and amorphous SiO2 at 540 ℃, the latter will react with FeO and alkaline substances to produce low melting point compounds, even when the temperature is lower than 1400 ℃, zircon powder The coating is beneficial to prevent sand sticking of castings. In addition, zircon powder has low thermal expansion (only 1 / 3-1 / 6 of quartz), high thermal conductivity and heat storage coefficient (which makes the coating have a greater chilling ability to metal), and large chemical inertia, so the castings with fairly smooth surface can be obtained. If it is used for thick castings and many kinds of steels, it is suggested to control ZrO2 content ≥ 65%, while the content of impurities (TiO2, Al2O3, Fe2O3, Na2O, P2O5, free SiO2) should not be more than 2%; for general iron carbon alloy castings without complexity, zircon powder with ZrO2 ≥ 63% can be used. Zircon powder density is 4.0-4.8g/cm3, so the suspension system of coating is required to be high.
Zircon powder from Guangdong, Yulin and Australia. The first three kinds of ZrO2 content are 63% – 65%, the imported ZrO2 ≥ 65%, and the fire resistance ≥ 1700 ℃.
2. Carrier liquids
The molding line must have drying station, alcohol based chloride, and soft water is suitable for water-based coating.
3. Suspending agent
The common suspending agent of water-based coating is bentonite, organic polymer compound, bentonite polymer compound thickening system. The suspending agent for HB type coating is one of the better ones. At present, Zhangjiakou bentonite and Xinyang bentonite are commonly used.
The ideal suspension agent for alcohol based coating is organobentonite, which has good suspension, coating and leveling properties. However, the carrier ethanol penetrates into the sand core quickly and deeply. On the one hand, it causes great damage to the working surface strength of the sand mold (core); on the other hand, the coating on the working surface of the sand mold (core) is not even enough. On the other hand, it is filled with other suitable suspension agents and binders to make B The second is to develop a new type of suspension agent with good performance, low price and suitable for flow coating. Hb-i type suspension agent for flow coating based on alcohol is one with better application effect.
The binder is to make the refractory powder in the coating stick together with each other.
For water-based coatings, they belong to low temperature type: sodium carboxymethyl cellulose (CMC), sodium alginate, water-soluble synthetic resin, polyvinyl alcohol (PVA), polyvinyl acetate emulsion (Bai Rujiao), starch, syrup, sulfite pulp waste liquid, water tar, dry vegetable oil, etc., which belong to high temperature binder, such as sodium silicate, silica sol, bentonite, ordinary clay, and poly Polyphosphate, etc.
The common binders for alcohol based coatings are thermoplastic phenolic resin, ethyl decanoate, polyvinyl butyral (PVB), rosin, paint chips, etc.
5. Other additives
In order to improve the infiltration and permeability of flow coating on the surface of sand mold (core) and improve the bonding strength between the coating and the surface of sand mold (core), anionic and non-ionic surfactants are better.
When the alcohol based coating is ignited and dried, bubbles or pits may also be produced. The former is often dripped with small amount of alcohol, such as n-butanol, n-pentanol, or n-octanol, etc.; the latter is often achieved by adding a low melting point of an evil substance, such as a hard acid salt or other substance that is helpful to destroy the continuity of the adhesive film during drying.
In order to improve the high temperature strength of coatings, the oxides, fluorides, hydroxides and salts of alkali metals and alkaline earth metals.
5.4 Water reducing agent
The water reducing agent used is methylnesulfonate formaldehyde condensate.
Cellulose derivatives, syrup, starch and other polysaccharide organics can be prevented by adding some formaldehyde, phenols and their derivatives.
It is to keep the individual particles dispersed in an isolated state without agglomeration.
6. Coating preparation process
In this book, the water-based zircon powder coating for cast steel is taken as an example for systematic discussion. There are 7 process properties, such as suspension property, coating thickness, penetration depth, leveling property, coating homogeneity, low mark resistance and fluidity.