In order to give full play to the advantages of the silica sol water glass shell making process produce high-quality castings, in the specific production of artistic casting, the silica sol water glass composite shell making process is used to reduce production costs. , Can effectively improve the surface quality of artistic castings the yield of castings.

1 Advantages disadvantages of silica sol water glass shell making process

1.1 Shell making process of silica sol

Silica sol is easy to be formulated into a coating with a high powder-to-liquid ratio, the coating has good stability. The shell made of silica sol does need to be chemically hardened, there is no air pollution during the shell making process. The artistic castings prepared by the silica sol shell process have clear surface decoration good finish. The disadvantage is that the shell making time is long, the shell strength is lower, the coating layer is more, the material cost is higher.

1.2 Water glass shell making process

The production cost of the water glass shell making process is lower. Coatings prepared by water glass are stable easy to use. Using ammonium chloride aluminum chloride, magnesium chloride for chemical hardening, the hardening is rapid the strength is greater. The disadvantage is that the casting surface is prone to defects, such as falling sand, sticking sand, bulging burrs.

2Silica sol water glass composite shell making process

The silica sol water glass composite shell making process is to make the surface layer the transition layer the silica sol, the transition layer the strengthening layer the water glass. After the silica sol shell making process is completed, the water glass shell making process is performed.

2.1 Production of silica sol shell

Silica sol process flow: the molding wax module prepares a silica sol surface layer coating, dips slurry, sands, naturally air-drys, prepares silica sol transition layer coating, dips, scatters sand, naturally air-dried, enters the water glass shell making process.

2.1.1 Fabrication of silica sol surface layer

(1) Workshop temperature humidity

Temperature: 24~25oC; Humidity: 60%~70%.

(2) Paint preparation

Coating ratio: silica sol 100Kg; mullite powder (320 mesh) 400Kg; wetting agent 180ml; defoamer 110ml. Flow cup viscosity: 35～4OS.

Preparation: First add the wetting agent defoamer to the paint bucket, then add the silica sol to stir, add mullite powder during the stirring process, stir well for 4-10h, measure the viscosity of the paint until it is suitable.

(3) Surface coating

1) Clean the floats on the wax mold.

2) Rosin for wax mold degreasing industrial alcohol (ratio: alcohol 80Kg: rosin 20Kg). Clean the wax mold with the mixed rosin alcohol solution. After the drying is controlled, it is convenient for the wax mold the paint to be combined, so that the paint can evenly stick to the wax mold.

3) Put the wax mold in the mixed silica sol paint, make the wax mold evenly covered with the paint inside outside, slowly take it out, so that the coating layer on the wax mold can reach 75 microns thickness, remove the excess paint, finally sprinkle Upper moss sand (40~70 mesh).

4) Insert a ventilated drying rack let it dry naturally for about 12 hours.

2.1.2 Fabrication of silica sol transition layer

(1) Workshop temperature humidity

Temperature: 20~25oC; Humidity: 3O%~40%.

(2) Paint preparation

Coating ratio: silica sol 100kg; mullite powder (270 mesh) 140kg. Flow cup viscosity: l6～l8S.

Preparation: the preparation of the same surface coating.

(3) Coating of transition layer

1) Put the air-dried shell into the transition layer paint, take it out after hanging the paint, remove the excess paint sprinkle with mullite sand (30-60 mesh).

2) Insert it into a ventilated drying rack let it dry naturally for about 12 hours.

2.2 Production of water glass shell

2.2.1 Production of water glass transition layer

(1) Paint preparation

Pour the water glass with a specific gravity of 1.30 into the paint tank, add 270 mesh mullite powder stir.

Flow velocity viscosity: adjust to 18～20S in summer; adjust to 25～35S in winter.

(2) Coating of transition layer

1) The transition layer adopts sand (30~60 mesh). The coating method is the same as silica sol coating.

2) Put it in the prepared hardening solution (75Kg water: 25kg ammonium chloride) for hardening, harden for 15-20 minutes, take it out dry it with water, reinforce with 18 iron wire winding. For larger shells, 8 steel bars are needed for welding reinforcement.

2.2.2 Production of water glass reinforcement layer

(1) Preparation of the back layer paint. Extract the water glass stock solution, adjust its specific gravity to between 1.32 1.34, pour it into the paint tank add 3n2oo mesh mullite powder for mixing.

Flow velocity viscosity: 65S in summer 70S in winter.

(2) Back coating

Mullite sand (10-20 mesh) is used, the coating operation method is the same as above, generally between five a half to seven a half layers.

After careful selection of raw materials careful operation, the phenomenon of sand inclusion, scarring, burrs, bulging of the castings will be greatly reduced, the current yield of castings has reached more than 95%.

3Silica sol water glass composite shell dewaxing

Dewaxing is also an important process of shell making. The quality of dewaxing also affects the quality of artistic castings. Dewaxing operating procedures:

(1) Check whether the power supply steam circuit of the automatic dewaxing kettle are safe.

(2) Turn on the steam generator to generate steam pressure up to 0.4Mpa, preheat the electrothermal dewaxing kettle, open the wax discharge valve drain valve at the right time to ensure that the cooling wax discharge valve in the valve is unblocked.

(3) Put the cleaned shell in the dewaxing frame, discharge it steadily without floating, etc., to prevent damage to the shell during the pushing process.

(4) Open the door of the dewaxing kettle, push the dewaxing frame steadily into the dewaxing kettle, close the kettle door, open the steam inlet valve to pass steam into the dewaxing kettle, make the pressure in the chamber reach No. 1 quickly. 4Mpa.

(5) Observe the pressure in the silo, wait 13 to 18 minutes, close the inlet valve, open the exhaust valve to discharge the steam out of the dewaxing kettle, when the pressure reaches a certain pressure, open the drain valve, then reduce the pressure to about a certain pressure, close Drain the valve then open the wax drain valve. After the liquid wax is drained, close the wax drain valve. Then open the safety interlock device exhaust for 1 minute, then slowly open the kettle door to avoid excessive wax overflow the front door, finally take out the dewaxing shell.

(6) For shells with more complex shapes, a second dewaxing should be performed. Put the sprue cup of the shell upwards, then pour the prepared hydrochloric acid solution (1000g of water at a temperature of 80～l00℃ + 1g of hydrochloric acid water) into the shell slowly until it is full. Push the shell into the dewaxing kettle for a second dewaxing, the time is 3~5min, after taking it out, put the shell pouring cup down to let the wax residue flow out.

4 Conclusion

The silica sol water glass composite shell effectively ensures the surface quality of artistic castings, reduces production costs, improves the yield of artistic castings. It is a practically valuable precision casting shell making process