Production of Optical Cable Loose Tubes

Loose tube optical cables are produced by extruding protective plastic tubes around optical fibers, often using co-extrusion and gel-filling techniques to ensure flexibility, protection, and performance.

Overview of Loose Tube Construction

Loose tube cables are designed for harsh outdoor environments, where optical fibers are enclosed within semi-rigid protective tubes that allow the fibers to move freely and absorb mechanical stress, temperature variations, and bending forces. Each tube can contain multiple fibers, and the fibers are often surrounded by a gel or water-blocking material to prevent moisture ingress and provide additional protection.

Materials and Tube Formation

The tubes are typically made from polypropylene (PP) or a mixture of PP and low-density linear polyethylene (PE-LLD). In modern production, double-layer co-extrusion is used: the inner layer is soft PP to protect the fibers, while the outer layer is a PP/PE-LLD blend for mechanical strength and environmental resistance. This co-extrusion process allows simultaneous extrusion of two materials through a single die, optimizing tube stability, excess fiber length, and mechanical properties.

Extrusion and Cooling Process

The production begins with a resin extruder, which coats the optical fiber bundle with molten plastic. The extruded tube is then cooled in a water tank with a sizing die to maintain the tube's shape and dimensions. Air pumps and cooling water suction mechanisms are often integrated to ensure uniform tube formation and prevent deformation during cooling.

Fiber Launching and Process Efficiency

To improve production efficiency, Fiber Launching Systems (FLS) are used. These systems feed fiber bundles into the extrusion line at production speed, reducing manual handling, minimizing scrap, and allowing continuous operation. This is particularly important during start-up or when switching production batches.

Gel-

Filling and ProtectionFor outdoor applications, the loose tubes are often filled with a gel or water-blocking compound using specialized jelly dies or needle-like dispensing nozzles. This step ensures moisture protection and stabilizes the fibers within the tube. Advanced jelly die systems improve gel flow, reduce turbulence, and enhance process stability, resulting in better quality and reliability.

Advantages of Modern Loose Tube Production

Flexibility and fiber protection: Tubes allow fibers to move and absorb bending stresses. Enhanced mechanical properties: Co-extrusion and optimized materials improve tensile strength and durability. Process efficiency: Fiber launching systems and advanced jelly dies reduce downtime and scrap.

Environmental resistance: Gel-filling and material selection protect against moisture, temperature extremes, and mechanical damage. Modern loose tube production combines material science, extrusion technology, and automation to produce high-quality optical cables suitable for demanding outdoor installations.