The physical properties of fiberglass material fundamentally distinguish its braiding process from ordinary textile fibers. Glass fiber monofilament diameter is typically between 5-25 microns, with tensile strength of up to 1500-2500MPa, but it is highly brittle and has poor abrasion resistance, easily breaking when the bending radius is less than 3mm. Glass fiber yarn used for braiding sleeving typically employs E-glass (alkali-free glass) or C-glass (medium-alkali glass), with yarn counts ranging from 300tex to 1200tex. E-glass has a softening point of about 850°C and a long-term service temperature of up to 550°C, making it the preferred material for motor insulation and high-temperature protection applications. Due to the low surface friction coefficient of glass fiber (about 0.15-0.25) and its tendency to generate static electricity, yarn must undergo sizing treatment before braiding. Common sizing agents include silane coupling agents (such as A-1100, A-187) and paraffin emulsions; after treatment, the yarn surface friction coefficient can be increased to 0.35-0.45, while improving bundle cohesion and abrasion resistance. Sizing agent solid content is typically controlled at 1.5%-3.0%, with drying temperature of 80-100°C and time of 15-20 minutes. Unsized glass fiber yarn will generate large amounts of flyings during braiding, not only polluting the environment but also accelerating wear of guide wheels and spindle eyes.
The braiding process parameter settings for fiberglass sleeving require particular care. The braiding angle is a key parameter affecting sleeving performance; for standard insulation sleeving, the braiding angle is typically controlled between 38°-42°, at which point the longitudinal expansion rate of the sleeving is minimal (about 2%-4%) and the radial expansion rate is moderate (about 15%-25%). The relationship between braiding pitch and sleeving diameter follows the formula: Pitch = π × Sleeving Diameter × cot(Braiding Angle). For a sleeving with 10mm diameter, when the braiding angle is 40°, the pitch is approximately 37.5mm. Due to the brittle nature of glass fiber, braiding tension must be strictly controlled at a low level, typically 0.3-0.8N per yarn, and tension variation between spindles must not exceed 3%. Excessive tension will cause fiber breakage and uneven sleeving wall thickness; insufficient tension will result in loose braiding structure, affecting the sleeving's crush resistance. Spindle speed is recommended at 120-180rpm; excessively high speeds will cause yarn tension fluctuations due to increased centrifugal force. For heavy-duty sleeving with high wall thickness requirements (over 1.5mm), a double-layer braiding process can be used—the inner layer is braided with finer count yarn (300-450tex) at a smaller angle (35°-38°), and the outer layer is braided with coarser count yarn (600-900tex) at a larger angle (42°-45°), with opposite braiding directions for the two layers, which can significantly improve the sleeving's crush resistance and abrasion resistance.
After braiding is complete, fiberglass sleeving must undergo a series of post-processing procedures to meet application requirements. First is heat treatment setting, where the braided sleeving passes through a high-temperature oven (temperature 380-420°C, time 30-60 seconds), allowing the glass fiber molecular structure to rearrange, eliminating braiding internal stress and stabilizing sleeving dimensions. After heat treatment, sleeving shrinkage can be controlled within 1%. Next is surface coating treatment; different coating materials are selected according to insulation class requirements: Class F insulation (155°C) uses polyurethane coating, Class H insulation (180°C) uses silicone coating, and Class C insulation (above 220°C) uses PTFE coating. Coating thickness is typically 0.05-0.15mm, applied by dipping or spraying process, then cured at 150-200°C for 20-40 minutes. For quality inspection, fiberglass sleeving must pass the following standard tests: voltage withstand test (per IEC 60684, 1kV class sleeving must withstand 2kV AC voltage for 1 minute without breakdown), insulation resistance test (≥10^12 Ω·cm under normal conditions, ≥10^10 Ω·cm after damp heat treatment), tensile strength test (axial tensile strength ≥200N/10mm width), abrasion resistance test (Taber abraser, CS-17 wheel, 1000g load, mass loss ≤5% after 1000 revolutions), and flame retardancy test (UL VW-1 vertical burning standard). Only sleeving products that pass these rigorous tests can be applied in fields with extremely high safety requirements such as aerospace, rail transit, and nuclear power.