Common knowledge of coating: common misunderstandings and Countermeasures of heavy anticorrosive coating spraying construction

Core tip: the spraying process of heavy-duty anticorrosive coating is usually applied to products with high anticorrosive life and harsh service environment, such as wind power generator, marine ship parts, etc the heavy-duty anticorrosive coating materials and spraying process of these products have meticulous and strict requirements After spraying, the main characteristics of the coating are as follows: ① thick film, the dry film thickness of the heavy-duty coating is usually more than 200 μ m, or even up to 2mm; ② the heavy-duty coating needs to have the ability of long-term corrosion protection under harsh conditions, which can be used for 10 or 15 years in the chemical atmosphere and marine environment Application scope and advantages of roller ceramic coating Recommended introduction: the surface of ceramic rubber plate used for roller ceramic coating is cast into durable rubber plate by hundreds of independent small ceramic pieces Each ceramic piece has raised characteristics Under general conveyor belt pressure, thousands of unique cast bumps can produce positive traction, prevent slipping and extend the service life of conveyor belt roller At the same time, the bottom layer adopts high-quality rubber, which has strong elasticity and can play a good impact resistance role The scope of application of roller ceramic coating is one three six 83857180 (the same as V) 1 Roller coating in extremely harsh working environment 2 The belt joint is not suitable for fixing with iron buckle; 3 It is suitable for leather Coating home news: heavy anti-corrosion coating spraying process is usually applied to products with high anti-corrosion life requirements and harsh use environment, such as wind power generators, marine ship parts, etc., and the heavy anti-corrosion coating materials and spraying implementation process of these products have strict requirements After spraying, the main characteristics of the coating are as follows: ① thick film, the dry film thickness of the heavy-duty coating is usually more than 200 μ m, or even up to 2mm; ② the heavy-duty coating needs to have the ability of long-term anti-corrosion under harsh conditions, which can be used for more than 10 or 15 years in the chemical atmosphere and marine environment; ③ the coating has good adhesion, physical properties and Mechanical properties, strong adhesion to steel matrix or other coating The special use environment of wind power and marine ship parts, high maintenance cost and particularity of spray construction determine the economic importance of spray quality Spray enterprises must ensure the construction quality of anti-corrosion spray to avoid economic losses to themselves and customers 1 Key control points of heavy-duty anticorrosive paint spraying process: strict coating construction management: three parts of products, seven parts of construction; emphasis on key process control, continuous optimization On the contrary, if the process is found to be inconsistent, regardless of the product measurement results, it is necessary to consider re spraying to eliminate the hidden quality risks 1.1 strict pre-treatment of coating Incomplete oil removal and excessive corrosion may cause the surface treatment not up to standard during sand blasting, especially for the coating with high surface requirements, such as inorganic zinc rich paint, which will usually lead to peeling off of subsequent coating The appearance and cleaning quality of the blank are not up to the standard, because the operator is not clear about the control standard and does not understand the causal relationship between the quality of the blank and the quality of the paint For the initial construction of the spraying workshop, this kind of phenomenon is relatively common and can be solved by standardized construction scheme First of all, technicians are required to be able to prepare construction plans for different parts according to the characteristics of different products, so as to avoid one construction plan guiding the construction of all products and avoiding the special points of each product The construction scheme shall point out how to achieve: leveling the base material, avoiding concavity and sand hole; polishing the free edge (generally r = 2mm); defining the porous casting, ensuring enough time in the process, thoroughly removing oil and water, if necessary, using heating method to evaporate oil and water In addition, it shall be ensured that the compressed air pipeline is equipped with oil-water separator 1.1.2 there may be improper selection of abrasives in the surface treatment of blasting, such as steel sand and steel shot without distinction; only look at the roughness value, and simply think that the greater the roughness is, the higher the coating adhesion will be; spray is still arranged after the sandblasting stays for more than the specified time (such as 6h); after sandblasting, lifting, treading, touching the sandblasting surface, local pollution, can not be effectively treated in place To correct this problem, the essence of roughness should be clarified Roughness can be recognized from several aspects: ① shape (micro profile of roughness), depending on whether angular sand or shot material; ② depth (distance between micro wave crest and wave trough); ③ density (number of wave crest and wave trough), as shown in Figure 1 Fig 1 improper depth and density of different abrasives, different depths and different densities affect adhesion, paint coverage (causing pitting) and cleaning ability The hardness of the abrasive determines whether it can form a chain like appearance If the shape and size of abrasives are improper, even if the roughness value reaches, it will not reach the corrosion prevention intention expected by the corrosion protection design When the roughness value is greater than or equal to the coating thickness value, it is easy to lead to uneven paint film, premature pitting of wave crest and bubble interception at valley bottom For example, when constructing zinc rich paint, water curing is required to be dry When the roughness is greater than the film thickness, the possibility of corrosion will be enlarged This example also shows that the surface with high roughness is not suitable for painting thin film The selection of abrasives shall be completed in the spraying process design stage Select the type and size of abrasive strictly according to the requirements of customers, and inspect the hardness, chemical composition and size of each batch of incoming abrasive to ensure the quality of abrasive Combined with the actual equipment and personnel of the factory, the experimental adjustment is carried out to determine the air pressure and other parameters 1.2 the metal thermal spraying thermal spraying coating is directly sprayed on the casting surface Once it is repaired, it will face the protection difficulties brought by the reverse process spraying During the repair process, the roughness treatment and thermal spraying are likely to cause damage and pollution to the non repaired parts, resulting in the secondary repair Therefore, first of all, the construction scheme shall ensure that the spraying is done in place at one time, and if necessary, the chamfering, small holes and narrow parts shall be protected by the spraying production process to assist in spraying Secondly, ensure that the operator is in place according to the construction scheme, such as: avoid re spraying after stagnation for a long time to form 2 layers of skin or steps; chamfer is not in place, etc 1.3 before painting construction, the technician must determine whether the operator is clear about the construction scheme of specific paint, such as wet film thickness, coating method (airless spraying, air spraying, brush coating, roll coating), drying time, humidity requirements, curing conditions, etc It is necessary to provide operators with intuitive operation instructions and training The training of operators and inspectors shall be completed before construction The first piece shall be tracked and implemented, the process shall be improved, and the construction errors and omissions shall be corrected As for the construction scheme of specific paint, this paper takes the relative humidity as an example to illustrate its importance Common three-layer (bottom, middle and surface) anti-corrosion paint for wind power products The relative humidity requirement of the paint instruction is no more than 80% However, the relative humidity of polyurethane finish is required to be no more than 85% As for the inorganic zinc rich paint, taking the international brand interzinc22 as an example, the instruction clearly points out that "when the relative humidity is lower than 50%, the curing will be seriously delayed, and it is necessary to use steam or water spray to improve the humidity..." When the humidity is lower than 50%, the curing will be affected The film is hard and easy to crack Taking our company as an example, more than 60 groups of relative humidity values were collected between July and August 2011, with an average of 40% But in this period of time, 60% of the parts without curing by water cracked Through investigation and test, the main reason is that humidity is not up to standard and the film thickness is too thick In addition, the non-standard use of diluent leads to the misuse of paint, which reminds production managers to pay attention to and standardize the management of warehouses at all levels The basic construction conditions of the paint material shall be fully considered in the spraying process: wet film thickness, coating method (airless spraying, air spraying, brush coating, roll coating), drying time, humidity requirements, curing conditions, and the planning and guarantee of process control shall be fully realized to ensure that it is implemented to the operators and inspectors and the process capability is stable 2 The inspection and experiment scheme of each link shall be clear and detailed in painting process design and quality planning Pay attention to the mistakes that are easy to get into (1) Insufficient time line for self inspection and inspection In particular, the sand blasting process may result in missed spraying and complicated repair after the procedure When the light is insufficient, the inspector and the operator can use a light meter to measure and check whether the brightness requirements of the spraying area are met Generally, it is better to be able to read ordinary printed matter clearly (2) Improper selection of roughness detection method The commonly used methods are roughness control board iso8503, needle type measuring instrument and brand tape method When choosing to use, the measurement accuracy, measurement principle, compliance with customer requirements and applicability of each measurement method are not evaluated When using the comparison sample block, pay attention to whether the roughness value is RA or RZ or other, which should be consistent with the measurement unit of roughness value required by the customer Roughness samples include shot peening roughness comparison, sanding roughness comparison, machining surface roughness comparison, casting surface roughness comparison and anti-corrosion surface treatment Sa2.5 First of all, different kinds of samples are suitable for different occasions When the customer requires to determine the roughness value with small value or tolerance range, it is suggested to abandon the use of samples and use other methods to measure the roughness in view of the large visual judgment error The characteristic of the method is that it can measure plane and curved surface accurately But the cost of measurement is high Generally, needle type and tape method are used together, and the latter is used to correct the former (3) No holiday detection as required If the specification is not understood or the test method is not understood, the construction unit may not carry out the holiday detection in the spray inspection scheme Leakage point will lead to electrolytic penetration of the barrier and accelerate the formation of corrosion The detection of holiday spots can determine the continuity and stable thickness of the film, help to find out the parts where the anti-corrosion coating is too thin, leaking metal or pinholes, and is also an effective auxiliary means to measure the film thickness of complex products The instrument used is spark detector (4) After cleaning, the salt content on the surface of the casting was not detected, and the casting was mistakenly considered to be clean after cleaning, and the input factors that may cause salt residue in the cleaning process were not analyzed The surface of steel sand, cleaned and sandblasted castings shall be subject to salt inspection or spot check, and appropriate cleaning agent and cleaning water shall be selected to monitor the possible salt pollution from the process (5) It is mistaken that the cross cut method can only be used for coating with film thickness no more than 250 μ M For the cross cut method, there is often such a description: "the cross cut method can be used for coatings with film thickness less than 250 μ m", but for coatings with film thickness less than 250 μ m, the pull-out method can also be used to measure the adhesion, but the cross cut method is not suitable for the adhesion test of coatings with film thickness greater than 250 μ M Special paint materials such as inorganic zinc rich paint, whose typical thickness is less than 125 μ m, but cross grid method is not recommended When using cross grid method, it is necessary to distinguish the grid spacing according to the film thickness If the gear is blunt, it should be grinded in time (6) Judge whether the paint is dry and solidified, press the nail to pick, and observe whether there is any indentation (if the paint is not hard dry, the indentation will be displayed) Taking inorganic zinc rich primer as an example, the paint is characterized by thin film (generally less than 120 μ m) and high hardness, so the nail picking method can not be used to judge the curing degree of the coating The common method is to scratch the paint film with coins or hard objects, and only a small amount of paint powder is dropped through visual inspection