What Coated Aluminum Coil Test Results Actually Measure.
A coated coil data sheet can list more than ten tests. Each one isolates a single way a coating can fail, and none of them predicts total performance on its own. Knowing what each test measures is what makes the numbers usable.
Key takeaways
- Each test isolates one failure mode: corrosion protection, weathering, forming, impact, adhesion, appearance, wear or cure.
- Test methods leave variables open, such as duration, solvent, rub count and bend direction, so a result only means something with its conditions attached.
- Several standards carry cautions in their own text: salt spray results used alone have seldom been correlated with outdoor performance, and impact results should stay within one laboratory.
- Orbit checks coated coil on salt spray, UV weathering, T-bend, impact, adhesion, gloss retention, abrasion, MEK rub, pencil hardness, delta E and paint thickness, to ASTM or EN references by market.
- This post gives no Orbit result values. Values are confirmed against your specification.
Why does a data sheet list so many tests?
Because a coating fails in more than one way. It can let corrosion reach the metal, fade in sunlight, crack when the coil is formed, chip on impact, lose adhesion, wear through, or never cure fully. Each test is built to expose one of those failures under controlled conditions.
Reading a data sheet well means asking which failure each line addresses and whether that failure matters for your application. The methods come from ASTM International and, in Europe, from the EN 13523 series on test methods for coil coated metals: part 1 covers film thickness, part 3 color difference, part 4 pencil hardness, part 5 impact, part 7 the T-bend test, part 8 salt spray, part 10 fluorescent UV and condensation, and part 11 solvent rubbing. The table below summarizes the tests.
| Test | What it measures | What it does not show | What to report |
|---|---|---|---|
| Salt spray (ASTM B117) | Specimen condition after exposure to a controlled salt fog | Outdoor performance, when used alone | Specimen and exposure duration |
| UV weathering (ASTM D4587) | Accelerated weathering under fluorescent UV and condensation | Performance, until the property measured afterward is stated | That property (gloss retention, color change, chalking) and the hours |
| T-bend (ASTM D4145) | Cracking and loss of adhesion on a bent panel | A result that holds for every bend direction and temperature | T rating, bend direction, specimen temperature |
| Impact (ASTM D2794, EN 13523-5) | Cracking after rapid deformation | A number that compares across laboratories | Laboratory and method |
| Adhesion (ASTM D3359) | Coating loss after cuts and a tape pull | Higher levels of adhesion | Method (A or B) and rating with its letter suffix |
| Gloss retention (ASTM D523) | Gloss after exposure against the starting value | Comparability when angle or exposure differs | Measurement angle and exposure |
| Delta E (ASTM D2244) | Color difference calculated from measured color coordinates | Anything without its reference color, formula, instrument conditions and exposure | Reference color, formula, instrument conditions, exposure |
| Abrasion (ASTM D4060) | Resistance to wear from abrasive wheels | Corrosion, fade, cracking or other failure modes | Conditions and pass criterion |
| MEK rub (ASTM D5402) | Whether the coating reaches the solvent resistance of a cured film | Cure itself, which it only indicates | Solvent and number of double rubs |
| Pencil hardness (ASTM D3363) | Hardest pencil lead that does not cut or gouge the film | Differences between coatings close in hardness | Lead manufacturer and batch |
| Film thickness (ASTM D7091) | Thickness by magnetic or eddy current gauge, without cutting | Performance alone, since thickness changes how other results behave | Gauge calibration, verification, adjustment |
What do salt spray and UV weathering results tell a buyer?
Salt spray (ASTM B117) exposes a coated specimen to a controlled salt fog in a chamber. The standard itself notes that performance in natural environments has seldom been correlated with salt spray results used as stand-alone data, and it leaves specimen type and exposure duration to the product specification. UV weathering (ASTM D4587) uses fluorescent UV light and condensation to accelerate weathering, so a result needs the property measured afterward and the hours stated.
What do T-bend, impact and adhesion results say about forming?
T-bend (ASTM D4145, coating flexibility of prepainted sheet) bends a coated panel and checks the coating for cracking and loss of adhesion. Results are written 0T, 1T, 2T and so on, and a lower number is a tighter bend. The standard notes that bend direction and specimen temperature can change the result. For impact (ASTM D2794, or EN 13523-5 in Europe), see the question below on laboratory differences.
Adhesion (ASTM D3359) has two methods, X-cut (Method A) and cross-cut (Method B). Each rates the result from 0 to 5 with a letter suffix, so a datasheet should state which method it used, and results from the two methods should not be compared directly. The standard states that it measures only lower levels of adhesion, and one of its two methods is limited to thinner films.
What do gloss retention and delta E measure?
Gloss (ASTM D523) compares the specular reflectance of the surface with that of a black glass standard. ASTM D523 provides 20, 60 and 85 degree geometries, so a datasheet should state the angle and the exposure behind any gloss retention figure.
Delta E is the calculated difference between two colors from measured color coordinates, as described in ASTM D2244. The PE vs PVDF comparison shows how color fade is tracked in practice.
What do abrasion, MEK rub and pencil hardness tell you?
MEK rub is the common name for a solvent rub test, described by ASTM D5402. It checks whether the coating reaches the solvent resistance expected of a cured film, which is used as an indicator of cure. The practice leaves the solvent and the number of double rubs to the coating supplier, and temperature and film thickness change the result. Abrasion (ASTM D4060, Taber Abraser) and pencil hardness (ASTM D3363) are in the table.
How do I read a data sheet line so it is useful?
Beyond the table, look for the method and its edition, the substrate (alloy, temper and gauge), the coating system and film thickness, the test conditions and the criterion for a pass. Ask for any that is missing before comparing two suppliers, because the same test name can describe different conditions.
What does Orbit test, and how do I ask for results?
Orbit checks coated coil on salt spray, UV weathering, T-bend, impact, coating adhesion, gloss retention, abrasion, MEK rub, pencil hardness, color difference (delta E) and paint thickness, to ASTM or EN references by market. Test reports and the references are available on request, and the methods are confirmed for your specification. Name the tests and standards your project requires in the RFQ. The quality page lists the testing program.
Common questions
Does a longer salt spray time mean a longer service life?
Not by itself. The salt spray standard notes that performance in natural environments has seldom been correlated with salt spray results used as stand-alone data. Use the figure to compare coatings tested the same way.
Why do impact results differ between laboratories?
ASTM D2794 states that the method has poor reproducibility between laboratories and that numerical results should be limited to one laboratory, or ranked. Ask which laboratory and method produced a number.
Can Orbit share test results for my order?
Test reports and ASTM or EN references are available on request. Tell us the tests and standards you need in the RFQ and we will confirm what is provided for your specification.
Are test result values published in this article?
No. Result values depend on the coating system, substrate and specification, and are confirmed per specification.
References
- ASTM International: B117, Standard Practice for Operating Salt Spray (Fog) Apparatus: the salt fog practice discussed above.
- BSI: BS EN 13523, Coil coated metals, Test methods: the BSI listing for the European series of coil coating test methods.
Need test results for a specification?
Send your alloy, gauge, coating system and the tests your project requires. We respond to RFQs within one business day.