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What Are the Precautions for Salt Spray Test?

The purpose of the salt spray test is to examine the salt spray corrosion resistance quality of the product or metal material. The judgment of the salt spray test results is the judgment of the product quality. Whether its judgment result is correct and reasonable is the key to correctly measure the anti-salt spray corrosion quality of a product or metal. The judgment methods of the salt spray test results include: rating judgment method, weighing judgment method, corrosive substance appearance judgment method and corrosion data statistical analysis method. For more ort reliability testing, please contact us.

Ⅰ. Precautions for salt spray test

(1) The sample substrate for the test must be thoroughly cleaned of rust and lubricating grease. Whether it is sandblasted, sanded or phosphated substrates, beware of exposure to moist air to prevent the formation of a water film on the surface of the substrate causing re-rusting or reducing the adhesion between the coating and the substrate. It is particularly emphasized that it is strictly forbidden to touch the effective part of the substrate with fingers. Finger grease and perspiration stains the board surface, which will cause local blistering and rusting of the coating.

(2) The key to the salt spray corrosion test is to prepare the concentration of the electrolyte solution. The solutes of various components should be strictly weighed in proportion to ensure the accuracy of the pH value. Otherwise, it will directly affect the test results.

(3) When preparing the coated samples and parts, it is necessary to seal the edges with paint and cover the exposed parts of the substrate. Otherwise, rust marks will sag and contaminate the surface of the board, which will bring difficulties to the grading work.

(4) When checking the board regularly, the board surface should be kept wet. Minimize the time the board is exposed to the air.

(5)When the test is completed, an objective evaluation should be made on the surface of the board immediatly, including: blistering, discoloration, rust and peeling. The detection and evaluation of adhesion and unilateral rust distance of scratches can also be added according to customer requirements.

(6) If the board surface needs to be scratched, it should be scratched through the coating film at one time and the substrate should be exposed. The knife should not be applied repeatedly to avoid flanging the coating at the scratch and widening the rust distance on one side. According to experience, the scratches on the board surface are usually cross-shaped X, while the cylindrical workpiece can be divided into parallel lines II. However, the scratches should be more than 20 mm from the edge of the plate and a single-edged cutter should be used according to the method recommended by the standard.

(7) It must be noted that the plate parts in the salt spray test chamber should be regularly adjusted and placed. Regularly measure the amount of salt spray deposition to ensure that the salt spray is evenly distributed in all parts of the box.

Ⅱ. Determination method of unilateral corrosion distance at the scratch of salt spray test

According to the author's many years of work experience, during the test process, the periodic inspection plate should keep the original rusted state and record the single-item rating results. When the comprehensive rating is carried out after the test, select the most severely rusted part of the scratched side for measurement first, and then use a tool to carefully peel off the rust. Try not to damage the coating, rinse with water and then measure the rust distance. The measurement results may have the following three situations:

① The coating bubbles along the edge of the scratch, the substrate is corroded and the coating is incomplete, so the unilateral corrosion distance is greater than the specified requirement. In this case, the adhesion of the coating is not ideal, which will result in blistering and rusting.

② It seems that the rust spots are large during the measurement. When the rust is cleaned, the coating is complete, the adhesion is good and the substrate has no rust spread. The result should be based on the unilateral rust distance measured after rust removal. The rust spots are larger, which may be caused by the local accumulation of rust due to the wider scratches.

③ After the rust is cleaned, the coating is peeled off from the substrate and the substrate has been corroded in a large area. This situation often occurs in multi-coat thick films, indicating that the coating has poor wettability and adhesion.

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