1. Water based lost foam casting coating test materials
Bauxite: the main mineral composition is mullite, which has the advantages of small thermal expansion coefficient, high fire resistance, good chemical stability and low price. The particle size is 325 mesh;
Kaolin: the main mineral composition is SiO2 and Al2O3. It has excellent physical and chemical properties such as good acid solubility resistance, chemical stability, sintering, low cation exchange capacity and good fire resistance. The fire resistance is 1700 ℃;
Wollastonite: a calcium containing metasilicate mineral, acicular and fine-grained, bright color, melting point 1 540 ℃, particle size 200 mesh;
Talc powder: the main component is aqueous magnesium silicate. The fire resistance is 1200 ~ 1300 ℃. It has excellent physical and chemical properties such as lubricity, fire resistance, acid resistance, insulation, high melting point and strong adsorption, with a particle size of 325 mesh;
Sepiolite (325 mesh); CMC (200 mesh);
Silica sol: SiO2 content 24% ~ 30%, Na2O ≤ 0.05%; Polyvinyl alcohol (PVA);
Surfactant: sodium dodecylbenzene sulfonate; Defoamer: n-octanol; Additive: Fe2O3.
2. Raw material pretreatment and coating preparation method
Raw material pretreatment: ① in order to facilitate the preparation of water-based lost foam casting coating, the binder silica sol and polyvinyl alcohol (PVA) need to be activated. Firstly, the aqueous solutions of the two need to be stirred evenly at high speed (1200 R / min), then sodium dodecylbenzene sulfonate is added for activation, and stand for 24 hours; ② CMC: first disperse CMC and ethanol according to the mass ratio of 1 ∶ 1, then add water according to the mass ratio of CMC ∶ water = 1 ∶ 50, stir evenly, and stand for 24 hours; ③ Sepiolite: stir sepiolite and water evenly at a mass ratio of 1:50 at a high speed (1200 R / min) to prepare sepiolite slurry, which shall stand for 24 hours. Preparation method of water-based lost foam casting coating: firstly, mix the weighed refractory aggregate (bauxite, kaolin, wollastonite and talc powder) and Fe2O3 powder in a roller mixer, and then slowly add activated silica sol, polyvinyl alcohol (PVA) aqueous solution, CMC aqueous solution, sepiolite slurry, n-octanol defoamer and an appropriate amount of water for 2 hours, Grind with colloid mill for 2 times and leave the mill for use.
3. Main performance test methods of coatings
(1) Coating strength. Firstly, the water-based lost foam casting coating is coated on the glass plate. After the coating is dried, the glass plate is inclined to a 45 ° angle with the horizontal plane. At a distance of 1000 mm from the glass plate, use a coated 4 viscosity cup to drop sand on the glass plate until the coating is scraped to expose the glass plate. Use a balance to weigh the total mass of sand falling as a quantitative index to judge the strength of the coating surface.
(2) Gas generation. Firstly, the water-based lost foam casting coating is dried in a 101-2 drying oven and ground evenly with a ceramic mortar. Then, five samples with a mass of 1G ± 0.01g are weighed by a precision balance, and the gas evolution is measured on the stz-a direct reading gas evolution tester (produced by Handan Huayu Instrument Co., Ltd.). After removing the highest and lowest values, take the average value of the remaining three test data, that is, the gas evolution of water-based lost foam casting coating.
(3) Conditional viscosity. Lnd-1 coated 4 viscosity cup was used for determination.
(4) Coating resistance. The preparation specification is 120 mm × 60 mm × The 30 mm EPS pattern is ready for use. First weigh the mass M1 of the pattern, then dip it in the prepared water-based lost foam casting coating for three times, put it into a constant temperature drying oven (the set temperature is 40 ℃) and dry it for 2 ~ 4 hours. After the coating is completely dry, weigh the total mass m2. The difference between the two masses m (M = m2-m1) is the adhesion, And observe the flow condition of the coating surface to judge whether the coating is good or bad. The coating is uniform and smooth without cracks and no peeling from the pattern, which is class I; If there are dendritic or reticular fine cracks less than 1 mm, and there is no obvious peeling between the coating and the pattern, it is grade II; There are dendritic or reticular fine cracks greater than 1 mm, or penetrating cracks, and peeling between the coating and the pattern is grade III.
(5) Peelability. The ability of the coating to separate from the surface of the lost foam casting after pouring. After the lost foam casting casting is poured and formed, the coating on the surface of the lost foam casting casting can be flaked and peeled automatically by naked eye is class I; The surface coating of lost foam castings that needs to be knocked to peel off is grade II; The surface coating of lost foam casting is tightly adhered to the lost foam casting, and the coating that cannot be stripped is grade III.