Checking control cables for corrosion is a critical maintenance task, primarily involving a detailed visual and tactile inspection to identify early signs of degradation.
The most effective way to detect corrosion on control cables involves a two-pronged approach: observing the cable's surface for tell-tale signs and performing a tactile test using a soft cloth.
1. Visual Inspection for Corrosion Signs
Corrosion often manifests visually before it severely compromises the cable's integrity. When inspecting control cables, look for the following indicators:
- Broken Wires: Even a single broken strand can be a precursor to more significant corrosion or fatigue. These often appear as individual wires fraying from the main cable body.
- Powdered Metal: A powdery residue on the cable's surface, typically white, gray, or reddish, indicates oxidation of the metal. This is a direct sign of corrosion.
- Oxidized Metal: Discoloration or a dull, non-metallic appearance on the cable's surface, distinct from its original shiny or lubricated finish, suggests oxidation. This can range from light discoloration to significant pitting.
- Swelling or Distortion: In severe cases, corrosion can cause the cable to swell or strands to bulge, indicating internal degradation.
2. Tactile Inspection with a Soft White Cotton Cloth
A practical and highly effective method for identifying both corrosion and broken wires, especially those not immediately visible, involves using a soft white cotton cloth.
Here's how to perform this check:
- Prepare the Cable: Ensure the section of the control cable you are inspecting is clean from heavy grease or dirt, though a light film might reveal more if the corrosion is embedded.
- Rubbing Technique: Gently, but firmly, rub a soft white cotton cloth along the length of the cable. Pay close attention to areas that pass through fairleads, pulleys, or bends, as these are often high-stress points prone to wear and corrosion.
- Interpreting Results:
- Cloth Snags: If the cloth snags as you rub it along the cable, this is a clear indication that broken wires are present. The snags are caused by the loose ends of broken strands catching on the fabric.
- Discoloration on Cloth: If the cloth picks up a fine, powdery residue or shows discoloration (e.g., rust color, white powder), it confirms the presence of powdered, oxidized metal—a definitive sign of corrosion.
- Smooth Passage: A cable is likely free from significant surface corrosion or broken wires if the cloth glides smoothly without snagging and remains clean.
Table: Signs of Control Cable Corrosion
| Sign of Corrosion | Description | Method of Detection |
|---|---|---|
| Broken Wires | Individual strands frayed or broken from the main cable. | Visual inspection, Cloth snagging |
| Powdered Metal | Fine, powdery residue on the cable surface (e.g., white, gray, red). | Visual inspection, Cloth discoloration |
| Oxidized Metal | Dull appearance, discoloration, or pitting on the cable surface. | Visual inspection |
| Cable Swelling/Distortion | Bulges or abnormal shape indicating internal degradation. | Visual inspection |
Regular and thorough inspection using these methods is crucial for maintaining the operational safety and longevity of control cable systems in various applications, from aircraft to industrial machinery. For comprehensive guidelines on cable inspection and maintenance, refer to specific maintenance manuals and standards provided by regulatory bodies or original equipment manufacturers, such as those detailed by organizations like the Federal Aviation Administration (FAA).
