A technical datasheet and a test report are two different documents with different purposes. Many problems start when one is treated as the other.
Datasheet: typical values
A datasheet describes a product in general. The values are averages from laboratory test pieces cured under stated conditions. Unless the sheet gives minimum and maximum limits, the numbers are not guaranteed for each batch.
Check:
- Does the sheet say "typical" and give the cure and post-cure used to make the test pieces? Properties of a moulded part may differ.
- Are minimum and maximum limits shown for release? Limits make a datasheet a specification.
- Are test methods and conditions stated, such as compression set method, time and temperature?
- Are units clear (MPa or psi, Shore A or IRHD)?
- Is there a revision date and a version?
Test report: specific results
A test report describes one set of tests on identified samples. It should say who ran the tests, when, how and on what.
Check:
- Sample identity. Compound name, lot number and how the samples were prepared and cured.
- Methods and editions. Standards with year, and any deviations.
- Conditions. Time, temperature, specimen type and size, fluids and their make-up.
- Results with units, and the number of specimens. Averages and spread, not a single value.
- Acceptance criteria and whether each result meets them.
- Laboratory details. Name, accreditation scope if any, signatory and date.
- Statement of what the report does not cover.
Warning signs
- A single compression-set number with no method, time, temperature or specimen.
- A claim of approval with no certificate number, scope or expiry.
- "Meets" a standard, with no edition and no list of which tests were run.
- Mixed units, or rounded values with no spread.
- A report on a different compound with a similar name.
- Tests run on test plaques and described as if they were on finished parts.
Making your own comparison fair
If you compare two suppliers, ask both to test the same method, the same conditions and the same samples. Otherwise you are comparing documents and not materials.
Sources and further reading
- ISO/IEC 17025 for the requirements of testing laboratories. ASTM and ISO methods named on the Testing page.
About this guide. It is an original summary written from public sources and standards. It is not a copy of any standard or book, and it is not engineering advice. Confirm values against the current edition of the standard and test in your own application.