Painted metal parts are important parts and play a very important role in products of various industries. In the process of metal painting, due to materials, equipment, tools, environment and other reasons, the finished products of painted metal parts (as shown in Figure 1) will have color difference. For enterprises with high requirements, it is necessary to abandon the previous method of judging color difference with naked eyes, Instead, seek accurate measurement methods to monitor the quality of painted metal parts.

Figure 1 - painted metal parts

A company is a manufacturer of painted metal parts and needs to accurately measure the color difference value of finished products to ensure the quality of products. Therefore, it seeks to use the spectrophotometer cs-580 (as shown in Figure 2) of Hangzhou CHNSpec technology to test painted metal parts.

Figure 2 - Hangzhou CHNSpec technology spectrophotometer cs-580

Due to the particularity of painted metal parts, CIELab color difference formula widely used in general industry is used as the evaluation standard of color difference, which is lack of certain accuracy. Therefore, we recommend using color difference formula to evaluate the color difference of painted metal parts.

The color difference formula was proposed by f.j.j.clark, R. McDonald and B. rig in 1984 on the basis of modifying the jpc79 formula. It overcomes the defect that the calculated value of jpc79 in the dark neutral color area deviates greatly from the visual evaluation results, and further introduces the lightness weight factor and chromaticity weight factor to meet the needs of different applications. The formula is recommended by the CMC (color measurement Committee) of the society of Dyers and colorists, and its color difference expression is

Where, and are the chromaticity parameters of standard color samples. These values and,,, in the above formula are calculated by CIELab color difference formula; Lightness weight factor and chroma weight factor are used to adjust the influence of lightness and chroma on the total color difference, so different ratios should be taken in different applications. A large number of experiments show that CMC (1:1) formula is recommended for the observability parity of color difference, such as chromaticity correction of digital system and coating or plastic industry; For example, CMC (2:1) formula is mostly used for product quality control in the textile industry.

Because CMC color difference formula has better visual consistency than CIELAB formula, the "single number tolerance" independent of the color region of the sample can be used for the quality control of different color products, which brings great convenience to the user for color measurement and instrument evaluation of color difference. Therefore, the color difference formula has been widely used since its introduction. Many countries and organizations have adopted the formula to replace CIELAB formula. Therefore, the formula will be widely used in industry as a general and authoritative color difference formula.

The spectrophotometer of Hangzhou CHNSpec technology is an earlier spectrophotometer in China. It integrates a number of technical features and extends the boundary of on-site color quality control in production. The built-in color difference formula includes CMC (1:1) formula and CMC (2:1) formula. Therefore, it can meet the color difference measurement requirements of painted metal parts and accurately measure the color difference of painted metal parts, Get the color difference data tested according to different formulas.

The following is how to use the spectrophotometer cs-580 of CHNSpec technology to test the color difference of painted metal parts.
Step 1: open the instrument, set various parameters and formulas according to the instructions, and conduct black-and-white calibration (as shown in Figure 3 and Figure 4);

Figure 3 - Black calibration

Figure 4 - white calibration

Step 2: after the black-and-white calibration is completed, press the "print" key, first locate the measurement area with the image, align the standard sample to be measured with the test hole, be careful not to leak light, so as not to affect the test results, then press the "test" key, complete the measurement after "dripping" sound, and view the test results (as shown in Figure 5);

Figure 5 - sample measurement

Step 3: after the above standard sample measurement is completed and saved, press the "menu" key to enter the "sample measurement" interface under the standard sample. Align the sample with the test hole according to the standard sample measurement method, press the "test" key for measurement, and complete the color difference measurement after "dripping" sound, and then the measurement result can be obtained (as shown in Figure 6).

Figure 6 - sample measurement

After the measurement, the specific color difference data of the test can be clearly seen from the instrument screen. The customer is very satisfied with the test results. He bought the spectrophotometer cs-580 of CHNSpec technology on the spot. He believes that the company can continuously improve the product quality and provide better services for customers. He also believes that it can reach more in-depth cooperation with Hangzhou CHNSpec technology Co., Ltd. in the future, Mutual benefit and win-win!