The development process of cast stainless steel is introduced in detail
Mold coating is the main component of refractory aggregate is, its ability to resist adhering sand on coating plays a decisive role, and the binder, suspending agent, thickening agent, defoaming agent, surfactant and other additives is the auxiliary material coating, decides the suspension stability of coatings, thixotropy, and intensity of flowing property, such as performance, is the key to the development of coatings.
Refractory aggregate, anti - sticky sand of refractory aggregate, is the basic composition of the coating, thermal chemical stability requirements, high degree of fire resistance.
1. Zirconium is a mineral mainly composed of zirconium silicate. At about 1540 ℃ can decompose the ZrO2 and SiO2, melting point is 2420 ℃ or so, softening point is 1600 ~ 1860 ℃, has high refractoriness, also has a smaller than quartz sand with high thermal conductivity and thermal expansion. Generally, ZrO2 content is used as the acceptance criterion for the fire resistance of zircon powder.
The technical conditions of zirconium powder are as follows: zirconium silicate content should be greater than 98%, of which ZrO2>65%, SiO2<33%, TiO2<0.4%, Fe2O3<0.2%,P2O5<0.15%, AL2O3<0.3%. The particle size is required to be 95% over 270 mesh and the rest over 200 mesh.
Zircon powder in composition is relatively simple, so the calcination reduction generally are low, which is favorable for stable performance of coating, but there are a small amount of impurity in zircon powder, it will fall to about 2200 ℃, melting point and, if the zircon powder containing impurities, is lower decomposition temperature, decomposition of SiO2 coating has great activity, make the casting surface form "pitting", and zircon powder acidic, adverse to the production containing Cr stainless steel, easy to cause the adhering sand.
2, kaolin powder, its mainly contains kaolinite clay minerals, the water after the volume expansion of small, pure kaolin powder is white and the melting point is 1750 ~ 1780 ℃, with yunnan.
Second, auxiliary materials
1, bentonite, white or light yellow, fine, shiny, is not only a binder, but also a suspension stabilizer, which mainly contains montmorillonite clay minerals, montmorillonite is a kind of clay minerals with small particle size and large bond strength.
Influence the crackle resistance of coating and intensity, add quantity more, the intensity of coating layer is bigger, but crackle tendency also is bigger. It can be divided into calcium-bentonite and natrium-bentonite, almost all of which are mined in China belong to calcium-bentonite, so it needs alkali treatment to show a large yield value to activate, improve its bond performance and sand inclusion resistance.
Na2CO3 is commonly used, the general amount of 5 ~ 7%, in the preparation of coating should be made into bentonite paste, bentonite paste treatment should be placed 24 hours reserve.
2, clay, binder, which mainly contains kaolinite clay minerals, small volume expansion in water, affect the stability and strength of the coating.
3. Diatomaceous earth is a kind of biochemical sedimentary rock composed of the siliceous cell wall of diatom broken and formed. It is light yellow or light gray, soft, porous and light. In the case of water-soluble phenolic resin as binder in water-based coating, 0.5% diatomite powder was added, and the coating performance was good. I use 104 diatomaceous earth, produced in zhejiang.
4, CMC(sodium carboxymethyl cellulose) organic polymer compound. It is a suspension stabilizer and can be used in combination with clay and bentonite. In alkaline solution, it is conducive to the stretching of the chain molecules, improving the flocculation efficiency and getting good results.
5, polyacrylamide, selected anion type, usually in the form of powder supply, made of powder high viscosity of the working solution, in the paint to add a few parts in ten thousand, the concentration of 0.01 ~ 0.1%.
6, water-soluble phenolic resin, room temperature strength binder, produced by chengdu resin factory.
7, alcohol soluble phenolic resin, room temperature strength binder, produced by chengdu resin factory.
8, rosin, yellow or brown solid, after smashing was yellow-white, reversible sclerosing, melting point is 75 ~ 135 ℃, the proportion of 1.01 ~ 1.09%, the normal temperature strength adhesive, soluble in organic solvents commonly, generally as binder in the quick drying coating materials.
9, Na2CO3 powder, adjust PH value and make bentonite, clay and CMC hydrolytic.
10, PVB, increase the sedimentation stability and thixotropy of the coating, powder, is the alcohol based coating suspension agent, can not be added, to produce coating layer surface bubbles and film layer.
11. Organobentonite that can be dissolved in alcohol by lithium bentonite, produced in henan province.
12. Low-foam laundry pulp and surfactant.
13, antifoaming agent, n-butanol.
14. Preservative and formaldehyde solution.
Iron oxide powder, fine red powder.
16. Industrial mixed alcohol essence.
17, phosphate binder, such as sodium hexametaphosphate, white powder, in the coating amount of 0.25 ~ 1%.
Three, coating equipment
I designed and made the coating equipment by myself. I bought a high-power two-phase motor directly from chengdu micro electric machine factory, which was driven by pulley, welded two blades for stirring and loaded with 25KG aggregate.
Fourthly, mixing process
1. Pre-soaking materials: clay, bentonite, CMC, polyacrylamide, rosin, PVB, lithium bentonite, etc. For PVB must first stir, sieving particles, to rosin first crushed before soaking.
2. Feeding process: add auxiliary materials and solvent first, and then add aggregate. For equipment with a rotating speed of 60 ~ 100 RPM, the water-based coating is stirred for 1 hour and the alcohol-based coating is stirred for 0.6 hours.
Five, paint formula
1, water-based zirconium powder stainless steel coating
Zirconium powder 80 ~ 100%, kaolin powder 20 ~ 0%, water-soluble phenolic resin 2 ~ 2.5%, shuang-flow bentonite 1.5%, leshan clay 1%, CMC0.6%, with addition of trace additives, water accounts for 25 ~ 35% of the total weight.
2, alcohol based zirconium powder stainless steel coating
Zirconium powder 80%, kaolin powder 20%, alcohol soluble phenolic resin 2%, double bentonite 2%, leshan clay 0.5%, rosin 1%, PVB0.15%, add low bubble laundry pulp a little bit, then add trace additives, industrial alcohol accounts for 20 ~ 30% of the total weight.
In the actual process of mixing coating, first add auxiliary materials, stir evenly and then add refractory aggregate. Stirring process at the end of the room to measure the strength of the coating, simply said, the coating is hung up, with resistance furnace baking, and then feel the coating is not easy to fall off the final.
In addition, but also test the coating brush and leveling. After the coating is prepared, its suspension should be observed and adjusted according to the situation. According to oneself design, coating cost reduces greatly, agitate coating time is shorter, use the effect is good, achieve the requirement of commodity coating completely.
What should explain is, coating binder affects to coating intensity: organic binder can improve the normal temperature intensity of coating commonly, but the high temperature intensity that can destroy coating. Water glass and silica sol can not improve the high temperature strength of the coating, while phosphate can effectively improve the room temperature and high temperature strength of the coating.
Still have wet dot: average moisture is equivalent to pink weight 15 ~ 25%.
Cream point: the general moisture equivalent to powder weight 25 ~ 35%.
Dilution point of use: the general moisture equivalent to 50-70% powder weight.