Application of silica sol in precision casting

Precision casting is the development direction of modern industrial forging, no cutting, high surface finish, high precision other complex parts assemblies that are difficult to process

The manufacturing technology has created a broad application prospect;The military aerospace products have high requirements on the surface quality dimensions of the casting parts, ethyl silicate hydrolyzes

Liquid because of greater pollution, preparation process is complex, high cost reasons, silica sol is prepared diluted sodium silicate solution by a specific process

A colloidal dispersion system with discontinuous amorphous silica particles as the dispersing phase water as the dispersing medium is alkalized stable, in which SiO2 particles are shown

After the surface is modified by alkalization, acidification silicon dissolution, it can be used as an adhesive by dissolving with organic polymers.

At present, silica sol adhesive is used to manufacture ceramic shell. The process has many advantages: the preparation process is simple, the coating is easy to store, the coating has been dipped coated

The slurry can be continued to be used after adjusting the composition of the slurry, reducing the material consumption, the dip coating process performance is stable, easy to operate, the use of ethyl silicate hydrolysate is canceled

Ammonia dry, the working environment is improved, the use of humidity controlled hot air drying, high shell type strength, ensure the quality of ceramic shell type precision casting parts,

At the same time, water-based silicon solvent is used to ensure good safety.Its disadvantages: the wettability is as good as ethyl silicate, the paint flow is poor, the bubble should be eliminated;with

Water evaporates faster than alcohol, is greatly affected by the humidity temperature of the operating environment, resulting in a relatively long production cycle.

1, The characteristics of silica sol silicon

Sol is milky white transparent colloid.Like liquid sodium silicate ethyl silicate hydrolysate, it is bonded by silicate colloid in the manufacture of ceramic shell

The basic component is amorphous SiO2. The particles have a large specific surface area a negative charge. The hydrated silicon alcohol layer provides wet strength during the drying process.

During shell roasting, most of the free structural moisture evaporates, the maximum strength can be obtained to withstand the impact of the casting molten alloy.

One of the important properties of silica sol is its stability.The stability is related to the PH value, the pH range is 8.5 ~ 10.Stable at PH 2 ~ 4,

The most unstable PH is around 7.The dielectric in the silica sol affects the charge distribution of the double-layer structure reduces the stability of the silica sol.Preparation of silica sol formula

There are many methods, such as acidification method, dialysis method, ion exchange method, gel gel solution method, hydrolysis method, etc.

2, The choice of silica sol

The performance indicators of silica sol include SiO2 content, density, content of stabilizer, PH value, SiO2 particle size, etc., special silica sol needs surface modification

Sex additive active agent.

3, The preparation of silica sol

For high temperature alloy, steel, titanium alloy, aluminum alloy copper alloy castings, due to the casting temperature of the alloy to different ceramic shell lithofacies composition

It’s also different.But the selection of refractory powder must be able to be bonded by silica sol, the preparation of paint at room temperature will cause slurry gelation.Often makes

With particle size of 0.075mm so of alumina, zirconia, mullite, aluminum ore quartz glass powder, in order to improve the coating dip-coating, often also

To add suspending agent, mineralizing agent, penetrant, leveling agent other auxiliary materials.Diluents are often deionized water alcohol.The addition of powder must be edge addition

Stir into the edge to prevent excessive water absorption of local powder resulting in silica gel.After the formulation is selected, the properties of the coating are determined by its viscosity density.As the

The properties of coatings are bound to change when they are impregnated.Water evaporation is reduced viscosity is increased, so a little silicon sol deionized water need to be added according to the calculated amount.

To ensure the original coating SiO2 content viscosity.

4, Silica sol coating process of drying

The drying condition in the coating process is an important factor to ensure the quality. Shell drying is the transfer of moisture the inside of the shell through capillary action to the coating

The surface then it evaporates outward.Therefore by the air relative humidity, ambient temperature, airflow speed, drying time, shell material a series of reasons

The influence of element.

In the drying process, the moisture the shell surface evaporation absorption of heat, which will make the wax mold temperature drop, size reduction, easy to produce surface defects.

The drying process should be as fast as possible to prevent the effects of changes in temperature on the inner surface of the shell.The ideal drying system should be able to take advantage of the temperature drop during the drying process

A large amount of moving air is required to balance the wet bulb temperature with the room temperature in the dipping chamber.

Weighing method measuring resistance method can be used to monitor the drying of each layer during the drying process of the shell, until the shell is fully dried then coated with the next layer.

After dewaxing roasting, the mold shell becomes the shell shape of castable liquid metal. The performance of each batch of mold shell can be checked with the furnace sample.Made of different silica sol

The strength deformation resistance of the ceramic shell can be seen the data analysis of the strength level the high temperature self-weight deformation performance of the domestic silica sol shell

It is close to the advanced type of silicon sol abroad.