Testing methods for casting coatings

Generally, for a qualified casting coating product, in order to ensure the normal realization of the function of the casting coating product, the foundry shall at least inspect the following indicators during the use process:

(1) PH value

The pH value of casting coating reflects the pH value of casting coating, which 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 exceeds the specified range of casting coating, the quality of casting coating has changed. PH value measurement method: generally, colorimetric method and potentiometer method are used for measurement.

(2) Concentration

The concentration of casting coating is the primary process parameter in the process of using casting coating. The concentration of casting coating is generally reflected by measuring the Baume degree or density of casting coating. Measurement method of coating concentration: Baume meter is used to detect Baume degree; The density is generally measured by measuring cylinder weighing method.

(3) Coating thickness

Coating thickness is an important factor affecting the performance of casting coatings. For the selected casting coating and the selected castings, to realize the function of casting coating, a suitable coating thickness should be corresponding. Coating thickness measurement method: wet coating thickness measurement plate is generally used for wet coating; The dry coating is generally measured with a micrometer. In addition to the above indicators, the foundry can also choose to measure the following indicators in order to better understand and use the casting coating.

(4) Viscosity

The rheological properties of casting coatings are generally described by the apparent viscosity of casting coatings. The viscosity of casting coating affects its brushing performance. Brushing performance is measured by 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.

(5) Leveling property

The leveling property of casting coating is related to the brush marks of casting coating. The leveling property of the casting coating is not good, and the casting coating is easy to form brush marks. Leveling measurement method: it is generally determined by observing the time when the brush mark of casting paint on the glass plate disappears and becomes a uniform and smooth surface.

(6) Hygroscopicity of casting coating

If the core coated with water-based casting coating reabsorbs water from the air after drying, it will not only reduce the strength of the casting coating, but also sharply increase the air generation, and in serious cases, 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. Moisture absorption measurement method: weighing method is generally used for measurement. That is to say, put the weighed casting coating sample with mass m in a constant humidity box until the sample mass reaches the constant value M1, then the moisture absorption rate of the casting coating is w= (m1-m) /m.

(7) Coating permeability

The permeability of casting coating refers to the ability of casting coating to penetrate into the gap of sand mold. The permeability has an important influence on the adhesion, sand resistance and the drying temperature and time of the casting coating. Measurement method of coating permeability: for the casting coating with low permeability, the glass bead method measurement device is used; For the casting coating with high permeability, the permeability of casting coating was measured by dipping standard molding sand test block.

(8) Permeability of coating

The coating forms an isolation layer between the molten metal and the core. In order to prevent the gas in the core from entering the molten metal during solidification to form pores and other defects, the isolation layer is generally required to be dense and low in permeability. Measurement method of coating permeability: use an electric permeability meter to measure.

(9) Coating gas evolution

The casting coating contains organic matter and decomposable inorganic salts, so it will produce gas at high temperature. When the air evolution of casting coating is too large, the casting defects such as pores, scabs and orange peel will be formed on the casting. Measurement method of coating gas evolution: use a recording gas evolution meter for measurement.

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