Test board preparation method for ship paint performance test

1. Foreword
ships, especially military vessels, have always been in the harsh environment of sea water and ocean atmosphere during their service. Therefore, in the ship's anti-corrosion coating, the quality of the coating has a high demand. When selecting a coating, it is necessary to test to assess the performance of the chinese
the
. Whether the test test board preparation method is appropriate or not will seriously affect the test results. The surface treatment of steel before the ship is coated is usually cleaned with jet abrasives, which contain metal abrasives and non-metallic abrasives. Different abrasives and different abrasive particle sizes also have different surface effects, including surface cleanliness and surface roughness, resulting in different test results. In order to evaluate the performance of the coating reasonably and ensure the quality of the ship's coating, it is necessary to compile a standard for the preparation of the ship's coating performance test plate.
2 Surface treatment quality and coating protection performance
2.1 various factors affect coating protection life
coating protection life of ships and steel structures is related to a variety of factors, such as the quality of steel surface treatment prior to coating, the type of coating used, coating thickness, coating process conditions, etc. Figure 1 shows a statistical analysis of the effects of various factors on coating protection life.
2.2 Effect of surface cleanliness rating on coating protection performance
The rust removal quality of steel surfaces is closely related to coating protection performance, as shown in Figure 2, which is an example of the effect of surface cleanliness grade on coating protection performance.
Figure 2, performance evaluation from poor to good divided into 0 to 10 levels, coating paint before the steel surface rust removal work is not complete, steel surface residual part of oxidizing skin, rust and other dirt, will certainly affect the protection effect of anti-corrosion coating, surface cleanliness rating in Sa1 performance evaluation is poor. Therefore, when spray cleaning should be completely removed oxidizing skin, rust and other dirt, surface cleanliness level in Sa2.5, anti-corrosion coating protection performance evaluation is better, Sa3 performance evaluation is the best.
2.3 surface roughness on coating protection performance
Surface roughness affects the adhesion between the coating film and the substrate and the distribution of coating thickness. Sand blasting, especially the injection of abrasives with angular angles, not only increases the surface area of the steel, but also provides a suitable surface geometry for coating attachment. In such a surface coating, in addition to molecular gravity between the coating film and the metal surface, there is also a mechanical bite cooperation, which is very beneficial to the attachment of the coating. With the roughness of the coating surface, the attachment performance of the coating film is improved, and the protective ability of the coating film is improved to a certain extent. However, if the roughness is too large, it is also detrimental to the protective performance of the coating film. In order to ensure the protective properties of the coating film, there should also be restrictions on the roughness of the steel surface before coating.
3 Sample material and size, thickness selection
3.1 test plate material selection
national standard GB/T1727-1992 "paint film general preparation method", GB/T 1763-1979 "paint film chemical resistance testing method" provisions, for paint film general preparation test plate thickness of 0.45 to 0.55mm. GB/T 9271-1988 Color and Varnish Standard Test Plate (eqv ISO1514:1984), GB/T 1765-1979 Measured wet heat, salt spray resistance, weather resistance (artificial acceleration) The paint film preparation method, ASTM D609:1973 "Test paint varnish and related products with steel plate preparation" requirements of the test plate is a thickness of 0.8 to 1.5mm of ordinary carbon steel sheet or cold-rolled steel plate. This kind of thin steel plate is only suitable for manual polishing or chemical treatment, and the actual construction of ships used in the steel plate is mostly thick hot-rolled steel plate, in order to be consistent with the actual process requirements of the construction of the ship, the test plate selected for hot-rolled steel plate.
3.2 test plate size selection
the above standard requirements, unless otherwise specified, the test plate area used in general coating testing environmental testing is (50 to 70) mm×150mm, the test board size selected in this study is 70mm×150mm.
3.3 test plate thickness selection
the use of jet cleaning metal and non-metallic abrasives for different thickness hot-rolled steel plate for a large number of injection cleaning treatment and testing, analysis of the thickness of different test plate after sand blasting, see Table 1.
from Table 1, the test plate thickness of <2.0mm, in the use of metal and non-metallic abrasive injection cleaning conditions (compressed air pressure 0.3 to 0.7MPa) are deformation, and thickness >2.0mm is no deformation occurred. Therefore, the test plate thickness selected in the test is 2.5mm.
4 The selection of surface treatment quality and the assessment and selection of
4.1 surface cleanliness
for ships, The Sa2.5 class is fully enough to meet the requirements, compared to the Sa3 grade, the cleaning costs required can be greatly reduced. In accordance with the above principles, the test plate blast surface cleanliness level in this study reached Sa2.5. It is comparable to the surface treatment requirements of steel before coating in the actual shipbuilding process. Sa2.5 level is expressed in words, very thorough injection or ejection rust removal, steel surface should be free of visible grease, dirt, oxide skin, rust and paint coating and other attachments, any residual traces should be only point or striped slight spots. After the test plate has been blasted surface treatment, the surface cleanliness rating is GB/T8923-1988 "Pre-coating steel surface corrosion grade and rust removal grade".
4.2 surface roughness selection and evaluation
usually ship anti-corrosion coating, steel surface maximum roughness value generally does not exceed 100 m, the more appropriate range is 40 to 75 m. The surface roughness of this test is controlled at 40 to 75 m. It is comparable to the surface treatment requirements of steel before coating in the actual shipbuilding process. Steel surface roughness refers to the formation of a microscopic unevenness of the steel surface after blasting or blasting. The roughness of steel surface is assessed using the standard GB/T17850.1-2002 "The roughness classification of steel surface after injection cleaning - comparative block method".
5 Test and Results
5.1 Test Plate Preparation
5.1.1 Test Plate Surface Treatment Method and Brief Symbol
A: Test Plate Surfaces are de-oiled, sandpaper polished to remove impurities such as oil and oxidizing skins.
B: The test plate surface is de-oiled and 10% HCl pickled surface treatment.
C: The test plate surface has been de-oiled, copper refining slag (copper ore) blasting treatment, spray distance of 15cm.
D: The test plate surface has been de-oiled, steel sand blasting treatment, spray distance of 15cm.
5.1.2 Test plate surface roughness preparation backup blasting abrasives and conditions
(1) copper refining slag (copper ore), abrasive particle size 0.6 to 1.6mm;
(2) steel sand, particle size 0.7 to 1.0mm, spray distance of 15cm, blasting compressed air pressure of 0.2 to 0.7MPa for blasting treatment.
5.1.3 Test plate spray coating
spray coatings are used in 1 s (aluminum pink), 2 s (epoxy), 3 s (chlorinated rubber), 4 s (water inorganic zinc-rich) anti-rust and anti-corrosion paint.
5.2 corrosion test conditions
5.2.1 salt spray test
test standards using GB/T 1771-1991 "color paint and varnish resistance to neutral salt spray performance."
test conditions. 5% NaCl, 35 degrees C, continuous spray, salt mist subsidm 1 to 2 ml / h .80cm2, time 96h.
5.2.2 immersion test
test standards using GB/T 1763-1979 "paint film chemical resistance reagent performance measurement method."
test conditions. 3% NaCl, 25 degrees C for immersion test 96h.
5.3 Results and discussion
5.3.1 Roughness of the test plate surface for blasting at different compressed air pressures
The size of the surface roughness depends on the particle size, shape, material, compressed air pressure, action time and other process parameters of the abrasive. Different compressed air pressure blasting was selected in the test, and the test plate surface was blasted with metal and non-metallic abrasives, namely copper refining slag (copper ore sand) and steel sand, and the results were shown in Figure 3.
from Figure 3, the roughness of the test plate surface increases with the blast pressure and increases with the sand blast particle size. The surface of the test plate treated with copper ore sand blasting is slightly darker than that of the test plate treated with steel sand blasting. When spraying steel sand abrasives, the diameter of steel sand abrasives is 0.7 to 1.0mm in order to achieve the roughness of the steel surface in the range of 40 to 70 m. The compressed air pressure should be greater than 0.3MPa, otherwise the injection processing speed will be affected.
5.3.2 Different surface treatment methods on the corrosion resistance of the coating
Table 2, A, B test plate sprayed 1 , 2 , two anti-rust coatings, the same thickness of the coating is 45 m, salt water resistance (3% NaCl) test 96h, A, B plate sample surface rust-free, in line with GB/T6748-1986 technical indicators, and the use of sand blasting treatment test plate surface roughness in 40 to 75 m. See table 2 C or D test plate, the same spray 1 , 2 , anti-rust coating, coating film thickness of the same 45 m, after resistance to 3% NaCl (salt water) test 96h, C or D plate test surface appeared different degrees of corrosion, are not up to GB / T 6748-1986 requirements, and the same results were carried out in the salt spray test. Table 3 The surface of the test plate is sand blasted, the roughness is 40 to 75 m, and then sprayed with 3 x anti-rust coating, the thickness of the paint film is 45 m. As can be seen from Table 3, the corrosion resistance of the coating decreases with the increase of roughness. Table 4 and Table 5 of the
show that when testing anti-rust and anti-corrosion coatings, such as test plate surface roughness reached 40 to 75 m, the thickness of its plate coating film should reach about 80 m, in order to achieve the corresponding technical indicators.
in summary, the ship coating performance test plate coating preparation should be different from GB/T 1727-1992 "paint film general preparation" standard, the original requirement coating thickness of 45±5 m, according to the test data, taking into account After sand blasting treatment, roughness and coating film thickness measurement deviation, it is recommended that the anti-rust anti-corrosion coating single paint film acid-resistant alkaline and salt-resistant water-resistant film thickness should be 80±10 m. When the ship is coated, the total thickness of the matching coating film used is generally more than 200 m. At the same time, with reference to GB/T 10834-1989 "ship paint salt resistance determination" requirements, in doing the supporting coating corrosion resistance test, it is recommended that the coating thickness of the supporting coating salt water resistance determination should be the primer two coating film thickness of 100±15 m, paint two coating film thickness of 100±10 m, the total coating thickness of 200±25 m.
6 Coating film thickness measurement method
6.1 coating film thickness measurement points
In view of the local changes in coating film thickness and instrument repetition problems, each point is required to be measured multiple times and averaged, especially on the rougher coating surface, it is necessary to select a few more points for repeated measurement, if the individual reading is particularly high. According to GB/T1764-1979 Paint Film Thickness Determination Method 3-point average method, ASTM D 1186-1973 "Non-magnetic organic coating dry film thickness determination on magnetic substrates" 5-point average method and our experiment with 9-point averaging method for measurement, measurement values and deviations can be seen in Table 6. From Table 6, it can be seen that the three membrane thickness measurement methods are basically similar. Therefore, it is stated that the original standard method of thickness measurement GB/T1764-1979 "paint film thickness determination method" is also suitable for film thickness determination on blasting board.
6.2 Different pre-treatment methods of the surface coating film thickness measurement value and deviation
rough surface will make the coating film once measured incorrectly, but the average of multiple measurements can more reliably represent the thickness of the entire coating film. Rough surfaces can cause some instruments to have high measurement results because the instrument's probe touches the top of the particles on the coating film, so the accuracy of the measurement is related to the thickness gauge used and the specific use. From Table 6, it can be seen that A, D, that is, two different surface-treated test plates with 0 x sandpaper and sand blasting, spray the same thickness coating, but the results obtained at the time of measurement have a large deviation; There is also a certain deviation in the thickness measurement of the coating film. Measuring the standard deviation < 50 m when the thickness of the coating film is <5 m, and the standard deviation < 50 m< and the thickness < 100 m, the measurement standard deviation < 10 m. Therefore, the thickness of the coating film should be considered when designing the deviation of the coating film measurement results caused by surface roughness and measurement itself.
7. References
1. Wang Guoping, Hong Donghuang. Coating and corrosion prevention technology of ship and steel structure. Beijing: National Defense Industry Press, 1993.
2 GB /T1727-92 Paint Film General Preparation Law.
3 GB/T 1763-1979 Paint Film Chemical Resistance Reagent Performance Measurement Method.
4 GB/T 1765-1979 Paint film preparation method for determining moisture, salt spray and weather resistance (artificial acceleration).
5 ASTM D609:1973 Test Color Paint Varnish and Preparation of Steel Plates for Related Products.
6 GB/T 9271-88 Color paint and varnish standard test plate (eqv ISO 1514:1984).
7 GB/T 8923-88 "Pre-coating steel surface corrosion grade and rust removal grade" (eqv ISO8501-1).
8 GB/T 6748-86 General Technical Conditions for Marine Rust-proof Paint.
9 GB/T 1771-1991 "Color paint and varnish resistance to neutral salt spray performance determination."
1 0 ASTM D 1186:1973 Determination of the thickness of the dry film of a non-magnetic organic coating applied to a magnetic substrate.
1 1 ASTM D4417 B: 2003 Standar