Fluorocarbon Sprayed Aluminum Panel Testing

Fluorocarbon sprayed aluminum panel inspection mainly conducts scientific testing and analysis on the coating thickness, coating adhesion, color and gloss, hardness, impact resistance and chemical corrosion resistance, objectively assessing the product quality grade and issuing a detailed test report, providing a basis for manufacturers' quality control and downstream users' product acceptance.

Testing Items

Coating thickness: Referring to the total dry film thickness of the fluorocarbon coatings (usually the primer, topcoat and clear coat), it is the basis of ensuring the coating durability, corrosion resistance and decorative effects. Testing whether the thickness is uniform and meets the design requirements (usually ≥30μm or ≥40μm) is the primary link of the quality control.

Coating adhesion: The key indicator of measuring the bonding firmness between the coatings and aluminum substrates. The insufficient adhesion will lead to the coating blistering and peeling. The cross-cut method or cross-hatch method is commonly used for the testing, and the rating grades are usually required to reach the grade 0 or grade 1 (the highest grades).

Color and gloss: Evaluating whether the product appearances meet the design color plate requirements. The color difference meters are used to measure the color difference values (ΔE), usually requiring ΔE ≤ 1.0 or less. The gloss meters are used to measure the gloss intensities of the coating surfaces, which need to be compared with the standard samples at the specified angles (such as 60°), and the deviations should be within the allowable ranges.

Hardness: The physical property reflecting the capability of the coating surfaces to resist the mechanical scratches or indentations. The pencil hardness method is commonly used for the testing. According to the different coating types, the hardness grades from H to 3H are required, to ensure that they are not easy to be scratched during the transportation, installation and use.

Impact resistance: Simulating the capability of the coatings to resist the impact of the external objects without the cracking or peeling. The falling weight impact testing is usually adopted. A weight of a certain mass free-falls from the specified height to impact the front or back sides of the coatings, checking whether the coatings are cracked or peeled.

Chemical corrosion resistance: Testing the capability of the coatings to resist the erosion of the common chemical substances. The acids (such as the hydrochloric acid), alkalis (such as the sodium hydroxide) and solvents (such as the methyl ethyl ketone) of the specific concentrations are dripped on the coating surfaces and observed for the specified time. The coatings are required to have no blistering, discoloration, gloss loss or peeling.

Artificial weathering resistance: Evaluating the long-term weatherability of the coatings through the accelerated aging testing. The specimens are placed in the xenon lamp aging test chambers or UV fluorescent aging chambers, simulating the conditions such as the sunlight, rain and condensation. After the specified periods (such as 1000 hours and 4000 hours), the property changes such as the color, gloss and chalking are tested.

Testing Scope

Raw material inspection: The testing items begin with the aluminum substrates, including their alloy designations, states, thickness tolerances, mechanical properties and the quality of the surface pretreatments (such as the chromate or chromate-free conversion coatings). These are the foundations of ensuring the subsequent coating properties.

Production process monitoring: The online monitoring is carried out at the key processes such as the pre-treatment before the spraying (degreasing and conversion), spraying (electrostatic spraying or roll coating) and baking and curing, such as measuring the pretreatment film weights, wet film thicknesses and oven temperature curves, to prevent the batch quality problems.

Finished product factory delivery inspection: The comprehensive testing is carried out on the finished fluorocarbon sprayed aluminum panels after the forming and processing, covering all the above coating property items, as well as the panel dimensions, hemming angles, stiffener settings and packaging, ensuring that each batch of products meets the standards and contract requirements.

Engineering site re-inspection: After the products arrive at the construction sites, the sampling re-inspection needs to be carried out, with the key checks of the appearance quality, coating thicknesses and color consistency, to prevent the transportation damages or batch mixing, ensuring the wall-mounting effects.

Dispute arbitration inspection: When the disputes over the product qualities occur between the suppliers and purchasers, or the construction parties and owners, the third-party testing institutions recognized by both parties are entrusted to carry out the arbitration inspection according to the relevant standards, issuing the legally effective test reports.

Standard conformity verification: The testing scope must cover the domestic and foreign standards that the products claim to comply with, such as the Chinese national standard GB/T 23443, American Architectural Manufacturers Association standard AAMA 2605 and Qualicoat specifications, verifying their comprehensive compliance.

Specific environment adaptability testing: For the aluminum panels used in the special environments such as the coastal areas, chemical plants and high-UV areas, the corresponding salt spray corrosion testing, SO2 pollution gas resistance testing and heat and humidity resistance testing need to be added, evaluating their performance under the extreme conditions.

Testing Methods

Magnetic thickness measurement method: Used to measure the thicknesses of the non-magnetic coatings (fluorocarbon coatings) on the magnetic substrates (the aluminum panels are usually equipped with the galvanized steel backings or use the thickness gauges based on the magnetic induction principle). The coating thickness gauges conforming to the GB/T 4956 or ISO 2808 standards are used, taking the multi-point measurements on the panel surfaces and calculating the averages and minimum values.

Cross-cut method adhesion testing: According to the GB/T 9286 or ISO 2409 standards, the dedicated cross-cut testers are used to scratch the grids with the 1mm or 2mm spacings on the coating surfaces, with the cuts reaching the substrates. The dedicated adhesive tapes are applied and quickly torn off. According to the ratios of the coating peeling areas, the adhesion grades are rated (0-5 grades, with the grade 0 being the best).

Accelerated aging testing: Mainly according to the xenon lamp aging method of GB/T 1865 (equivalent to ISO 11341) or the UV fluorescent aging method of GB/T 23987 (equivalent to ISO 16474). Through the precise control of the irradiation intensities, black panel temperatures, chamber temperatures, spraying and condensation cycles, the natural aging processes are accelerated and simulated.

Neutral salt spray testing: According to the GB/T 10125 (equivalent to ISO 9227) standard, the specimens are placed in the salt spray test chambers, and the 5% neutral sodium chloride solution is continuously sprayed. The long-time testing (such as 1000 hours and 3000 hours) is carried out at 35°C, evaluating the corrosion resistance and blistering capability of the coatings.

Pencil hardness testing: According to the GB/T 6739 (equivalent to ISO 15184) standard, the drawing pencils of the different hardnesses from 6B to 9H are used to push and scratch on the coating surfaces at the 45° angle, finding out the hardness of the hardest pencil that does not scratch the coatings, which is the coating pencil hardness.

Color difference and gloss measurement: The spectrophotometers or color difference meters (such as according to the CIE Lab color space) are used to measure the color parameters, calculating the ΔE values compared with the standard color plates. The gloss meters with the 60° incident angles (according to GB/T 9754 or ISO 2813) are used to measure the gloss, taking the multi-point averages.

Chemical reagent resistance testing: According to the GB/T 9274 (equivalent to ISO 2812) standard, the filter papers soaked with the specified chemical reagents are placed on the coating surfaces, covered with the glass covers, and removed after the specified time (such as 24 hours). After the cleaning, the coating changes are checked.

Testing Standards

Domestic Standards:

1. GB/T 23443, Aluminum panels for building decoration

2. GB/T 9286, Paints and varnishes — Cross-cut test

3. GB/T 10125-2021, Corrosion tests in artificial atmospheres — Salt spray tests

4. GB/T 9754, Paints and varnishes — Determination of specular gloss of non-metallic paint films at 20°, 60° and 85°

5. GB/T 4956, Coating thickness measurement of non-magnetic coatings on magnetic substrates — Magnetic method

6. GB/T 1865, Paints and varnishes — Artificial weathering and exposure to artificial radiation — Filtered xenon-arc radiation

7. GB/T 23987, Paints and varnishes — Exposure of coatings to artificial weathering — Exposure to fluorescent UV lamps and water

8. GB/T 6739, Paints and varnishes — Determination of film hardness by pencil test

9. GB/T 9274, Paints and varnishes — Determination of resistance to liquids

International Standards:

1. ISO 9227, Corrosion tests in artificial atmospheres — Salt spray tests

2. ISO 2808, Paints and varnishes — Determination of film thickness

3. ISO 2409, Paints and varnishes — Cross-cut test

4. ISO 11341, Paints and varnishes — Artificial weathering and exposure to artificial radiation — Exposure to filtered xenon-arc radiation

5. ISO 16474, Paints and varnishes — Methods of exposure to laboratory light sources

6. ISO 15184, Paints and varnishes — Determination of film hardness by pencil test

7. ISO 2813, Paints and varnishes — Determination of gloss value at 20°, 60° and 85°

8. ISO 2812, Paints and varnishes — Determination of resistance to liquids

9. AAMA 2605, Voluntary specification, performance requirements and test procedures for high performance organic coatings on architectural extrusions and panels

Note: The applicable standard can be selected according to the product use and customer trade requirements; standards agreed in the contract take precedence over general standards.

Testing Instruments and Equipment

Coating thickness gauge: Divided into the magnetic induction type and eddy current type. The eddy current type is usually used for the coating testing of the aluminum panels. The instruments need to be regularly calibrated with the standard sheets, ensuring the measurement precision (usually ±(1-3)%). The portable equipment is often used for the fast on-site testing.

Color difference meter/spectrophotometer: The precision optical instrument used to quantify the color differences. The high-precision equipment can measure the spectral reflectances, provide the color data such as the L*, a* and b*, and calculate the multiple color difference formulas. Equipped with the integrating spheres, the effects of the surface textures on the measurement can be eliminated.

Gloss meter: By emitting a beam of light at the specific angles (such as 20°, 60° and 85°) to the coating surfaces, the ratios of the reflected light intensities to the standard plate reflected light intensities are measured. For the medium-gloss fluorocarbon coatings, the 60° angle is the commonly used measurement angle.

Artificial weathering aging test chamber: The core equipment is the xenon lamp aging chambers or UV fluorescent aging chambers. The xenon lamp chambers have the spectra closer to the sunlight, equipped with the irradiation control, temperature and humidity control and spraying systems. The fluorescent UV chambers mainly use the UV-A or UV-B lamps, with the lower costs, often used for the screening testing.

Salt spray corrosion test chamber: Consisting of the chambers, spraying systems, heating systems and saturated air barrels. It can simulate the marine or industrial atmospheric environments and carry out the accelerated corrosion testing on the coatings. The salt solution concentrations, pH values and sedimentation amounts need to be regularly checked to meet the standard requirements.

Adhesion tester/cross-cut tester: The cross-cut testers are usually the multi-blade cutting tools with the fixed blade spacings. The more precise adhesion testers (such as the pull-off method) use the hydraulic or mechanical devices to pull the specific specification dollies off the coatings, directly measuring the pull-off strengths (MPa).

Precision balance and drying oven: Used for the auxiliary testing, such as weighing the specimen mass changes to calculate the chalking rates, or carrying out the condition adjustment of the specimens under the standard temperature and humidity conditions before the testing. The drying ovens are used to cure the test coatings or process the specimens.