Testing method of casting coating

Generally, for a qualified casting coating product, in order to ensure the normal realization of the function of the casting coating product, the foundry needs to inspect at least the following indicators in the use process [4-5]:

PH value: the pH value of casting coating reflects the pH value of casting coating. It is an important method to detect whether the quality of casting coating changes during the use and storage of casting coating. If the pH value is beyond the range of casting coating, the quality of casting coating has changed.

Measurement method of pH value: colorimetry and potentiometer are generally used for measurement.

Concentration: the concentration of casting coating is the primary process parameter in the use of casting coating. The concentration of casting coating is generally reflected by the Baume degree or density of casting coating.

Coating concentration measurement method: Baume degree is measured by Baume meter; density is generally measured by measuring cylinder weighing method.

Coating thickness: coating thickness is an important factor affecting the performance of casting coating. For the selected casting coating and the selected casting, it is necessary to realize the function of casting coating, corresponding to a suitable coating thickness.

Coating thickness measurement method: wet coating thickness measurement plate is generally used for wet coating, and micrometer is generally used for dry coating.

In addition to the above indicators, in order to better understand and use the casting coating, the foundry can also choose to measure the following indicators:

Viscosity: generally, the apparent viscosity of casting coating indicates the rheological properties of casting coating system. The viscosity of casting coating affects its brushing performance. The brushing performance is measured by the brushing index, which can be expressed by the ratio of apparent viscosity measured at low speed (6R / min) and high speed (60R / min) of rotary viscometer.

Viscosity measurement method: use rotary viscometer for measurement.

Leveling property: the leveling property of casting coating is related to the brush mark of casting coating. The leveling property of casting coating is not good, and the coating is easy to form brush marks.

Leveling measurement method: generally, the time when the brush mark of casting coating on the glass plate disappears and becomes a uniform and smooth surface is used to determine.

Moisture absorption of casting coating: if the core coated with water-based casting coating reabsorbs moisture from the air after drying, it will not only reduce the strength of the casting coating, but also increase the air flow rapidly, which will cause defects such as sand sticking and air holes in the casting. The hygroscopicity of casting coating is related to the binder used in casting coating.

Hygroscopicity measurement method: generally, weighing method is used. That is to say, the moisture absorption rate of the cast coating coating is w = (m1-m) / m when the weight of the weighed cast coating sample is kept in the constant humidity box until the sample mass reaches the constant value M1.

Coating permeability: the permeability of casting coating refers to the ability of casting coating to penetrate into the void of sand mold. The permeability has an important influence on the adhesion, sand control and drying temperature and time of casting coating.

Measuring method of coating permeability: for the casting coating with small permeability, the glass bead method is used to measure the device; for the casting coating with large permeability, the standard sand test block is used to measure the permeability of the casting coating.

Permeability of coating: the coating forms an isolation layer between the liquid metal and the core. In order to prevent the gas in the core from entering the liquid metal to form pores and other defects during solidification, the isolation layer is generally required to be dense and low permeability.

Measurement method of coating air permeability: use electric air permeability meter to measure.

Gas evolution of coating: the casting coating contains organic matter and decomposable inorganic salts, so gas will be produced at high temperature. When the gas content of casting coating is too large, the casting defects such as porosity, scab and orange peel will be formed on the casting.

Measurement method of coating gas evolution: use recording gas evolution meter to measure.