Blocking
Thermal FOR: Insulation $1,350This test evaluates if a finished wire/cable specimen will block (stick to itself) when subjected to the specimen's rated temperature. While on an aircraft, wires may be exposed to high temperatures and it is important to check if the finished wire specimens are prone to blocking (in other words, the test examines whether the wire will melt and adhere to itself at the rated temperature).
The test's pass/fail criteria is based on the sample's post-elevated temperature exposure visual examination. If the specimen shows no adhesion between layers of the wire spooled on itself, then the specimen has passed. If adhesion is observed, the specimen will have failed the test (this may mean that a lower temperature rating is necessary for the specimen).
Parameters that can be changed with this test include:
- Mandrel diameter
- Exposure duration
- Post-test assessment
For the combined Blocking and Lamination testing as outlined in EN3475, please refer to the Delamination and Blocking page
Procedure
- Visually examine the specimen for any defects. Record any anomalies.
- Wrap the specimen around a mandrel of specified diameter ensuring the specimen is kept taught.
- Place the specimen in an air circulating oven at rated temperature of the specimen for the specified duration.
- Remove the specimen from oven and allow sufficient time to return to ambient temperature.
- Slowly uncoil the specimen from the mandrel, recording any observed adhesion between layers.
- Report elevated temperature exposure duration, elevated temperature, and results of the post-exposure examination.
Covered specifications
- ANSI/NEMA WC 27500 Section 4.3.15
- AS22759 Paragraph 5.3.11
- AS4373 Method 808
- AS5382 Method 5.4.9
- AS6070 Method 5.3.4
- AS81044 Method 4.7.5.11
- AS85485 Method 4.7.4
- BSS7324 Method 7.7
- BSS7324 Method 7.07