High-temperature Resistance Of Pre-insulated Bushings: Material And Temperature Analysis

In the field of electrical connections and line protection, the high-temperature resistance of pre insulated sleeve directly determines its service life under harsh operating conditions. Unlike ordinary insulating sleeves, pre insulated junction sleeve combines conductor crimping and insulation protection through a composite structure design. Its temperature resistance rating is not a single value, but a performance range determined by the metal tube body, insulation material, and environmental stress. Understanding this parameter correctly is fundamental for selection, from conventional power distribution to high-temperature industrial scenarios.

How does the insulating substrate define the temperature resistance "ceiling"?

The heat resistance of insulated joint sleeve bushings primarily depends on the physicochemical properties of its insulation layer. For standard applications, pre-insulated bushings made of polypropylene (PP) or nylon typically withstand long-term operating temperatures of 105°C to 120°C, commonly found in building electrical and general equipment wiring. However, in automotive engine compartments or near high-temperature pipelines, radiation-crosslinked polyolefins or modified fluoroplastics are required. After cross-linking modification, the molecular structure of these materials changes from linear to network, increasing their temperature resistance to 150°C or even 175°C, and they also possess excellent aging resistance.

Material and Performance Relationship:

• Polyolefins: Commonly found in heat-shrinkable pre-insulating sleeves. The higher the degree of cross-linking (e.g., ≥75%), the stronger their long-term temperature resistance and resistance to thermal aging.

• Fluoropolymers: Such as PVDF, with long-term temperature resistance up to 150°C-175°C, while possessing extremely high insulation resistance and chemical inertness, suitable for use inside precision instruments.

• Inorganic Fiber Composite Layers: Used for extreme high-temperature protection, mainly utilizing their low thermal conductivity to prevent heat transfer inwards, protecting the internal cable structure.

Temperature Limits and Structural Design under Special Operating Conditions

When the application involves extreme heat sources, the high-temperature resistance of the pre-insulating sleeve needs to be comprehensively considered in conjunction with the composite structure. For aerospace or rail transportation fields, some pre-insulating sleeves adopt a "double-layer composite" or "with sealant layer" design. The inner layer uses a high-temperature resistant thermoplastic material to ensure insulation stability, while the outer layer is physically insulated using a fiberglass braided layer or a heat-resistant coating. For example, some specialized pre-insulated sleeves, through this structure, can withstand a long-term operating temperature of 204°C while also withstanding an instantaneous thermal shock of 649°C, thanks to the synergistic effect of inorganic and polymer materials.