Coating appearance quality inspection methods and problems
The appearance of the coating quality requirements include: the color of the coating, the flatness of the film, the impurity content of the coating gloss and coating
1.Coating color test
The color is light on the object surface colored light absorption and reflection, feeling again the role of the visual organ formation. The coating of the color test is divided into visual comparison method and instrument measurements. The visual comparison method, you must first preparation of standard colors and darker, lighter maximum tolerance of 3 swatches, and then try a model with which to compare, compare the test model with the standard plate overlap area, the eye with its distance of 500mm, the observed line of sight with the model surface close to the vertical, test a model of color within the color range of three standard board can determine the coating color qualified; otherwise unqualified.
Instrument measurement colorimeter, spectrophotometer, and other special instruments were used to measure the standard color and the color of the test model, and automatically calculates the outstanding difference ΔE, depending on the size of its ΔE is more than the agreed value of the supply and demand sides, in order to as judged by the qualified basis of coating color. 0 kinds of test methods have advantages and disadvantages, the visual comparison method is simple, intuitive input and low cost, but due to the visual comparison method is to use the resolution of human eye color to distinguish between the coating color, so the only is a qualitative test methods, human error is inevitable due to the constraints of color, memory capacity and a variety of natural conditions and other factors. Measurement instruments to measure the coating color measurement values are accurate and reliable, reproducible, and can objectively reflect the actual situation of the coating color, scientific, supply and demand sides have the same types of measuring instruments, can be long-distance exchange value to determine the eigenvalues of the color, and agreed that the coating color without having to go to the paint manufacturers face, so that will help improve the work efficiency. Colorimeter, spectrophotometer, measuring instruments and more expensive, currently only used in scientific research units are more rarely used in the coating manufacturer.
2.film flatness test
The flatness refers to the distance between the coating of the highest and the lowest point, the degree of characterization of the coating surface of the punch, but also indirectly reflects the uniformity of the coating. Coating flatness inspection of the visual method, the normal process conditions, the film flatness can meet user requirements.
The reason for this is based on the following two reasons:
- Spraying the same batch of products of the line speed of the workpiece, covering the number, take the gun speed, spraying distance, the spray gun parameters, the amount of dusting and workpiece processing status and other process parameters constant;
- local area powder uneven thickness in the spraying process, the use of powder curing leveling, but also make the original loose deposits on the surface of solid particles melt plasticized into a uniform continuous, smooth the coating.
3 gloss coating test
Gloss, the ability of the coating surface is projected on the light reflected off the other direction, the higher the reflectivity, the higher gloss. Coating gloss inspection is also divided into the visual comparison method and instrument measurements. Using the visual comparison method, the supply and demand sides in the same light, the same distance and the same point of view to observe the comparative standards board and the gloss of the test model, in order to determine whether the test model coating gloss qualified basis . Although this method has simple features, but there is human error. Instrument measuring the gloss of the coating, and general gloss meter, the result is a positive amount of reflected light from the film surface is expressed with the percentage of the ratio of the amount of light under the same conditions from the standard plate surface to a positive reflection. Therefore, the gloss of the coating generally refers to the relatively standard plate gloss value. Gloss measurements and the angle of incidence of the light source, the light incident angle 20 ° In general, measurement of high-gloss coating is appropriate; measurement of low-gloss coating, the light incident angle 85 ° is appropriate, so that allows more accurate measurement results. Higher on the product surface coating gloss, you can use this method.
4.coating impurity content inspection
The coating surface impurities include particles, pits, color point, pinhole defects. The new industry standards promulgated by this not be clearly defined, but in the actual painting work, it is precisely this most likely caused by supply and demand sides of controversy over the film surface quality problems and disputes. General product demand side is generally agreed that the product after coating, the surface should be perfect, no flaws, in particular, exports and even more so, when the coating surface contains a number of impurities, and often will be used as the basis for rejection; and product supplier, raw material procurement, production, transportation, powder coating powder and curing of powder coatings in numerous aspects to completely eradicate the impurities defects of the coating surface is difficult or even impossible. Both supply and demand due to the position in which there are different views on the same issue is understandable. In order to avoid the emergence of products due to the coating impurity defects in the delivery of the coating product rejection of the situation, the common solution is to: batch coating of the product, the first spray trial sample or specimen, wait until the curing after observation of the coating surface, depending on its ability to meet the technological requirements of the demand side, the quality of the coating surface, and then decide whether the surface coating of the bulk product.
This approach has three shortcomings:
① Because the test model of the area generally does not do much, the shape is also very simple and therefore can not truly reflect the appearance of the coating defects in the product after coating, it may appear to test model for the appearance of the coating of acceptable quality, the product coating After the appearance of the coating of substandard quality;
② If the product directly (in particular, is bulky, complex structured products) sample coating, if the product appearance of the coating quality of less than demand-side technology, both supply and demand in terms of manpower, resources, time will be a certain degree of loss;
③ this method is the coating impurity content of the product after the test, rather than pre-control, so the work has a certain degree of passivity. In order to fundamentally solve this problem, change the passive checks for active control, the best way is the only way for different coating requirements, the establishment of more detailed, clear, objective and has a workable new coating film appearance quality of the national standard.