Coating standard: quality inspection related to anti-corrosion coating

Core tip: anticorrosive coating is a kind of coating material which is applied to the surface of the coating for the purpose of coating service and plays its protective function for different corrosive environment Its application value is reflected by the formation of the film on the surface of the coating The quality of coating is finally reflected in the quality of the coating Therefore, the quality inspection after coating is mainly to inspect the performance of the coating, including the mechanical properties (such as adhesion, impact strength, hardness, gloss, etc.) and other special properties (weather resistance, acid and alkali resistance, oil resistance, solvent resistance, etc.) Different corrosion systems for coating services, corrosion protection Paint knowledge | precautions for wall paint color selection Recommended introduction: when painting the wall, the owner sometimes has difficulty in choosing what color of the wall paint to paint In fact, there is no ugly color in the wall paint, only the disharmonious color matching The use of wall color contains the knowledge of health Too strong color will stimulate people's perception, make people have a sense of fidgety, affect people's mental health Grasp the basic principles of wall color and paint a colorful space 1、 Wall paint color selection notice 1 Light color is generally used for the top surface Light colors make people feel light, dark colors make people feel heavy Usually, the treatment of rooms is from top to bottom, from shallow to deep For example, the ceiling and walls of rooms are white and Coating home news: anti-corrosion coating is for coating service, applied to the surface of the coating, for different corrosion environment and play its protective function of coating materials Its application value is reflected by the formation of the film on the surface of the coating The quality of coating is finally reflected in the quality of the coating Therefore, the quality inspection after coating is mainly to inspect the performance of the coating, including the mechanical properties (such as adhesion, impact strength, hardness, gloss, etc.) and other special properties (weather resistance, acid and alkali resistance, oil resistance, solvent resistance, etc.) According to the different corrosion systems served by the coating, the performance and testing methods of each technical index of the anti-corrosion coating are different, and different testing methods and standards are issued in different anti-corrosion industries But the above conventional performance is common in different industries For the inspection of large-scale project anti-corrosion coating, a professional testing agency with national testing qualification can be entrusted to conduct the performance inspection of coating in accordance with national standards or industry specifications The owner may also entrust a third-party professional institution to carry out the test There are also owners with their own qualified coating inspectors in charge of routine inspection on site Requirements for coating inspectors vary from industry to industry For example, in ship industry, inspectors are generally required to have NACE inspector Level 2, frosio inspector III qualification or equivalent qualification recognized by competent authority This paper introduces the detection of coating adhesion and coating thickness Although the detection of coating thickness does not belong to the range of coating mechanical properties, it is often an indispensable inspection item in the field inspection, because this item is directly related to the service life of the coating The above mentioned tests are carried out after the standard test plate is prepared under the operation of the general preparation method of the paint film 1 Test method for film adhesion: film adhesion refers to the firmness of the combination of the film and the surface of the object to be coated Adhesion is one of the important indexes of physical and mechanical properties of coatings Through this inspection, the composition of coatings, especially the use of resins, can be inspected The adhesion of paint film not only depends on the selected paint base material, but also has a very important relationship with the surface pretreatment of the substrate, the construction method and the maintenance of the paint film For example, in the wet, rusty, greasy metal surface coating, the adhesion is poor There are several methods to determine the adhesion: circle method, grid method, pull out method, twist open method and the X-cut method in American ASTM The national standard gb1720-89 (79) specifies the circle method to determine the adhesion of paint film, while gb9286-88 specifies the grid method to determine the adhesion, and gb5210-85 specifies the pull out method to determine the adhesion of coating Among them, the most convenient method is to determine the adhesion of paint film by circle drawing, and the most commonly used method on site is grid drawing (1) The adhesion tester used for the determination of adhesion by the method of scribe circle is evaluated according to the integrity of the paint film within the scratch range, expressed by grade It is fixed on the tester according to the prepared tinplate In order to make sure that the paint film is completely scratched, weight shall be added as appropriate Shake the handle evenly at 80-100r / min in a clockwise direction, and scratch with a round rolling line The standard round length is 7.5cm Take out the sample and grade it The following points should be paid attention to in the experiment: (a) the needle of the tester must be sharp, otherwise it is impossible to distinguish grade 1 and grade 2 Before measuring, you should first touch with your finger to see if it is sharp, or change it after measuring several test plates (b) Try to carve a few circles first, and the scratch should just scratch through the paint film If the base plate is not exposed, add weight as appropriate; but do not add too much to avoid increasing resistance and wearing the needle (c) When rating, it can be rated from Grade 7 (the innermost layer) or grade 1 (the outer ring) Check the integrity of the paint film of each part in sequence If the lattice of a part is more than 705 intact, it is considered that the part is intact, otherwise it is considered as damaged For example, if the film of Part 1 is intact and the adhesion is the best, it is determined as grade 1; if the film of Part 1 is damaged and Part 2 is intact, the adhesion is determined as grade 2 According to analogy, level 7 adhesion is the worst Generally, it is required that the adhesion of primer should reach level 1, and that of topcoat can be around Level 2 (2) The main standards for the determination of adhesion by the cross cut method are ASTM d3359, iso-2409 and gb9286-98 The test method is basically the same as the description, but the order of the description of the adhesion level is just the opposite Astmd3359 is a 5b-ob level from good to bad, while iso-2409 is a 0-5 level from good to bad The experimental tool is a grid tester It is a multi blade cutter with six cutting surfaces The cutter clearance is 1mm, 2mm and 3mm (the cutter head can be replaced) After the sample is coated on the sample plate and dried for 16 hours, pull 3-4cm in parallel with a scriber, and there are six cuts, which should cut through the paint film to the substrate; then use the same method to be vertical with the former, and the same six cuts; in this way, many small squares are formed For the soft substrate, use a soft bristle brush to form each diagonal along the grid diagram, and then gently sweep forward and backward for several times to assess the grade; for the hard substrate, first sweep, then stick on the tape (3m tape is generally used), and ensure that the tape is in full contact with the experimental area, so that it can be well contacted by rubbing back and forth with fingers, and then quickly pull out, use visual or magnifying glass Compare and grade the standards with the attached drawings The standard description of its classification is: level description 0, the cutting edge is completely smooth, there is no grid falling off, 1, there is a little coating falling off at the intersection, the affected area cannot be significantly greater than 5%, 2, there is coating falling off at the intersection of the incision or along the edge of the incision, the affected area is 5% - 15%, 3, the cross cutting area affected by coating falling off partially or completely along the cutting edge is 15% - 35% 5 The whole strip falls off along the edge, some or all of the lattices fall off, and 35% - 65% of the affected area 6 The degree of peeling off is more than grade 4 When the adhesion is measured by the cross cut method, the film thickness of 250 μ M can be measured at most According to the coating thickness, different grid spacing can be selected, generally, the coating is less than 60 μ m, the hard substrate spacing is 1mm, and the soft substrate spacing is 2mm; the coating thickness is 60-120 μ m, and the soft and hard substrate spacing is 2mm; the coating thickness is greater than 120 μ m, and the soft and hard substrate spacing is 3mm According to iso12944, the adhesion needs to reach level 1 to be qualified; in GB, the adhesion needs to reach level 1-2 to be qualified The difference between the delimitation method and the delimitation method is that the area of the parts formed by the intersection of the delimitation is increasing, and the rating is to examine the location of the undamaged area, while each delimitation area of the delimitation method is fixed, and the rate of the damaged area is used for the rating (3) The adhesion measured by pull apart method refers to the vertical and uniform tensile force applied on the cemented surface of the sample at the specified speed to measure the force required for the adhesion failure between the coating or coating and the substrate, expressed in MPa This method can not only test the adhesion degree between the coating and the substrate, but also the adhesion between the coatings It can also check whether the compatibility of the coating is reasonable, and comprehensively evaluate the overall adhesion effect of the coating The relevant standards of pull off test are iso4624-2004 (latest version), astmd-4514, gb5210, etc Elcometer adhesion tester is commonly used to measure pull off method in foreign countries This instrument is small and can be used for field test However, in some cases, the accuracy of the test results is affected by the instability of manual operation of the elcometer-106 manual pull tester, which is no longer used in some countries The Elcometer test is to stick an aluminum test pull head on the coating, pull the pull head off with a calibrated mechanical tensile tester, and read the pull force of the aluminum head off the scale Generally, three failure types may be found in the pull off test on the metal matrix: (a) adhesion failure, that is, the adhesive layer breaks from the coating or the test pull head or its own internal pull off after tensile force, which is considered as the failure of the adhesive The adhesion between the coating and the substrate or between the coating and the coating exceeds some values (b) Adhesion failure, that is, the separation of coating and substrate under tension, this value is the adhesion of coating and substrate (c) Cohesion failure, that is, the coating itself is pulled off, this value is taken as the value of interlayer adhesion, and the adhesion between the coating and the substrate exceeds this value For each kind of coating, there is a specified pull off method to determine the value, which is generally required to be greater than 2MPa, and the epoxy two-component coating is required to be greater than 4MPa It should be noted that there is a certain gap between the pull off adhesion data measured by Elcometer tester and that measured by national standard tensile tester According to the experience of many experiments, the data of Elcometer tester multiplied by 3-3.5 times is close to the value measured by tensile machine Therefore, the test data of each test method can only be compared in the same kind, with a certain degree of accuracy When filling in the test report, it is also necessary to indicate the test instruments and methods used For the requirements of adhesion, the adhesion of coating system (dry film thickness greater than 250 μ m) in iso12944-6 shall be tested according to iso4624 pull off method, at least 5MPa For the old coating, the reference value is 2 MPa If it is lower than 2 MPa, the old coating shall be removed 1、 Detection of film thickness: one of the important indexes for the quality inspection of anti-corrosion coating of the thickness of the coating The thickness of the anti-corrosion coating is different from that of the ordinary decorative coating The thickness of the anti-corrosion coating often determines the service life of the anti-corrosion system and is an important index for the detection of the anti-corrosion coating It has been proved by experiments that in a certain corrosion environment, the coating thickness has a linear relationship with the protection life after the matching of the coating is determined Therefore, it has become a trend to thicken the coating (200-1000 μ m) as much as possible, so it is not difficult to see the importance of coating thickness detection （1） Detection of film thickness: in the process of coating, when it is difficult to measure the dry film thickness, the wet film thickness shall be detected to ensure the dry film thickness of coating The wet film thickness must be measured immediately after the film is prepared