In the process of ensuring casting quality, in addition to the formulation of reasonable scientific manufacturing technology, it is more important to strictly control the quality of silica sol coating, so as to ensure the quality of casting.Through the strict control of coating parameters, coating quality drying quality, the quality of precision castings can be further improved to ensure that enterprises can produce qualified products.

1. The related characteristics of silica sol

Silica sol is a kind of appearance is milky white translucent colloidal solution, most of the stable alkaline, a few cases appear acidic.Silica sol has low viscosity, good dispersion performance, can fully enter the need to fill the solid material, can guarantee the smooth surface of the solid material.Silicol hydroxyl group adsorbed water are on the surface of silica sol particles, which can effectively improve the wettability of silica sol.In addition, the silica sol also has good bonding reactivity, in the use of silica sol after drying sintering can form a layer of solid film, this film once formed will again dissolve in water other substances.Silica sol can effectively improve the mechanical chemical properties of the mixture after homogeneous mixing with organic resin.At the same time, the silica sol also has good stability, once solidified will be dissolved in water metamorphism.

2. Silica sol coating its preparation

In the process of precision casting, the preparation method of silica sol coating should be selected according to the actual situation.Silica-sol coating is divided into surface coating back coating in the manufacture of shell. Surface coating will be in direct contact with metal liquid, which is also an important factor in determining the surface quality of castings. This coating needs to have good heat resistance, viscosity lubrication.The main components of this coating are: refractory material, wetting agent, binder defoaming agent. the back layer coating does need direct contact with the metal liquid, it is mainly to ensure the strength of shell, rigidity other comprehensive mechanical properties, the composition of this coating surface coating composition is basically the same, but the adhesive viscosity is smaller, can avoid the accumulation of paint.In addition, there is a transition layer coating between the surface layer coating the back layer coating, which is mainly to make the surface layer the back layer well bonded together, then protect the quality of the transition layer coating the quality of the whole shell type.The composition of this coating is basically the same as the composition of the above two coatings, but the adhesive viscosity is larger, so as to ensure that the surface layer the back layer are closely bonded together.In the preparation of silica sol coating, first add a certain amount of silica sol to the mixing pool, then add a certain proportion of lubricant, stir, in the process of mixing need to add refractory powder, finally add defoaming agent.

3.Quality control of silica sol coatings

There are many factors affecting the quality of investment precision castings, such as shell manufacturing process equipment.However, among the factors affecting the quality of investment precision castings, the quality of silica sol coating is the main one.Therefore, it is very important to control the quality of silica sol coating to ensure the quality of casting.In the process of quality control of silica sol coating, it is necessary to understand that the quality control process is prone to problems, take corresponding measures to solve the problem, mainly the following aspects of control.

1. Control of silica sol coating parameters

The control of silica sol coating parameters mainly includes SiO2 content, PH value, viscosity other parameters.It is difficult to control the SiO2 content, because the water of the binder in the silica sol coating is evaporating all the time, which will lead to the change of the composition of the coating binder, then lead to the increase of SiO2 content in the coating.

2. Coating hanging quality control

In order to ensure the coating quality, before coating, it is necessary to clean the module slightly etch the surface of the module, so as to ensure that the coating is tightly bonded to the module.In addition, it is necessary to carry out a comprehensive inspection of the module when painting hanging, to ensure that there is no quality problem of the module before painting hanging.

3. Coating drying quality control

The drying of silica sol coatings requires different forms of drying according to its type.The drying of the surface coating should be carried out without wind, the drying time should be about 8 hours.The drying of the excessive layer the back layer is ventilated dried, but the wind speed needs to be controlled at 8m/s, the humidity needs to be controlled at about 50%, the drying time generally needs to be controlled at about 6 hours.In addition, it is necessary to ensure that the next layer of coating is completely dry before the next layer of coating hanging drying.