Solving the Problem of Oil Seepage in Gel Seals for Optical Cable Closure Junction Boxes

1. Characteristics of Gel Sealant Materials

 

 

Wide Temperature Adaptability:​ It maintains its gel state and sealing performance across a wide temperature range (e.g., -40°C to +60°C), preventing melting at high temperatures or becoming brittle and cracking in the cold.

Chemical Stability:​ It exhibits good compatibility with cable jackets, metals, and plastics, minimizing the risk of chemical reactions.

In essence, an ideal gel functions like an "intelligent, flexible putty"​ that perfectly fills gaps and adapts to shape changes.

 

2. Root Causes of Oil Seepage

 

Oil seepage occurs when the physical and chemical stability of the gel is compromised under specific conditions, causing internal oily components (plasticizers or low-molecular-weight siloxanes) to separate and migrate. The primary causes are:

 

1. Material Quality Issues (The Most Common Cause)

 

Formula Defects:​ To reduce costs, manufacturers may use excessive amounts of low-quality plasticizers or mineral oils. These components have weak bonding with the gel matrix and easily separate under temperature changes or pressure.

Insufficient Cross-Linking:​ The gel's three-dimensional network structure is formed by chemical cross-linking. An incomplete cross-linking reaction results in a loose network that fails to "lock in" small molecules, leading to seepage.

 

2. Extreme Environmental Conditions

 

Sustained High Temperatures:​ If a junction box is exposed to direct sunlight, internal temperatures can far exceed ambient air temperatures. Heat accelerates the movement of small molecules within the gel, making it easier for them to escape. High temperatures also make the gel thinner and more fluid.

Significant Temperature Cycling:​ In areas with large day-night temperature swings, the gel repeatedly expands and contracts. This continuous "breathing" effect acts like a pump, gradually squeezing the oily components out.

 

3. Improper Mechanical Pressure

 

Over-Compression:​ Applying excessive force when tightening the closure subjects the gel to extreme pressure, forcibly "squeezing" the oil out.

Uneven Pressure:​ Improper cable routing inside the box can cause uneven stress on the gel seal, leading to localized high pressure and seepage.

 

4. Material Compatibility Issues

 

Prolonged contact between the gel and specific materials (e.g., certain types of PE/PVC cable jackets or plastic closure materials) can cause slow interaction, degrading the gel's performance and indirectly causing seepage.

Testing often reveals significant differences in the performance of gel materials from various suppliers. The following image illustrates a typical 7-day test result comparing different materials:

 

3. Comprehensive Solutions

 

A systematic approach involving both prevention​ and remediation​ is required to address this issue.

 

A. Preventive Measures (For New Projects and Installations)

 

1. Select High-Quality Products:

Brand and Certification:​ Prioritize products from reputable brands. Request material certification reports (e.g., UL, RoHS) and specific test data for oil separation or exudation under high temperatures.

On-Site Testing:​ For critical projects, conduct a simple test: place a sample of the gel on white paper and leave it in an oven at 60-70°C (or under direct sunlight) for 24-48 hours. Check for visible oil stains on the paper.

 

2. Follow Standardized Installation Procedures:

Adhere to Instructions:​ Tighten closure screws strictly according to the manufacturer's specified torque to avoid over-tightening.

Proper Cable Routing:​ Ensure cables enter smoothly without sharp bends to prevent uneven compression of the gel seal.

Surface Cleaning:​ Before installation, ensure the cable surface and closure channels are clean, dry, and free of oil and dust to allow optimal gel adhesion.

 

B. Remediation Measures (For Affected Junction Boxes)

 

1. Assess the Severity:

Minor Seepage:​ If only a slight surface oil film is present, wipe it clean with a lint-free cloth and monitor. If it does not recur and the closure passes a seal integrity test (e.g., air pressure test), it may be monitored with increased inspection frequency.

Severe Seepage:​ If oil appears continuously, forms droplets, or if moisture is detected inside the box with increased fiber attenuation, immediate action is necessary.

 

2. Replace the Seal (The Most Fundamental and Reliable Solution):

Steps:

Schedule a maintenance window to power down and interrupt optical service.

Open the closure and carefully document the fiber splice tray layout.

Thoroughly remove all old, compromised gel.​ Clean the closure body and cables meticulously using lint-free wipes and a compatible cleaner (e.g., alcohol).

Install a new, high-quality gel sealant unit.

Reassemble the closure, ensuring it is tightened to the correct specification.

Perform a seal integrity test​ (e.g., air pressure or immersion test) post-installation to confirm the issue is resolved.

 

3. Apply Auxiliary Sealing (Temporary or Supplemental Measure):

 

As a temporary reinforcement, wrap several layers of waterproof sealing tape (e.g., Butyl tape) around the cable entry point outside the primary gel seal. This adds an extra defensive layer but does not cure the underlying gel seepage problem.

 

4. Conclusion

 

The core cause of oil seepage in optical closure gel seals is substandard material quality, exacerbated by environmental temperature and mechanical pressure. Therefore, the fundamental solution lies in prevention-selecting proven, high-quality products and adhering to standardized installation practices. For existing problems, prompt replacement with a qualified sealant​ is the only permanent solution to ensure the long-term stability and reliability of the optical cable network.