UL 94 V-0 Flame Retardant Cooling Hose – for EV / Energy Storage / Data Center Fire Safety Requireme
Inverters and frequency converters are core power conversion devices in industrial drives, new energy power generation, electric vehicles, and uninterruptible power supply systems. With the continuous increase in power density, the heat generation of their internal power modules, such as Insulated Gate Bipolar Transistors (IGBTs) and Integrated Gate Commutated Thyristors (IGCTs), has increased significantly. Water-cooling systems, due to their high heat conduction efficiency, have become the mainstream heat dissipation solution for high-power inverters and frequency converters. Cooling hoses, as flexible channels connecting radiators, water pumps, and heat exchangers in the water-cooling circuit, play a crucial role in reliably delivering the cooling medium to the power modules and removing heat.
This product must operate stably for extended periods in complex electrical environments and limited spaces, placing specific requirements on temperature resistance, pressure resistance, aging resistance, electrical insulation, and flexibility. Unlike general industrial cooling hoses, inverter cooling hoses typically operate in environments with strong electromagnetic fields, frequent temperature cycles, and limited installation space, thus requiring unique technical focuses in material selection and structural design.
II. Operating Conditions and Performance Requirements The operating conditions of water-cooled systems for frequency converters and inverters have the following significant characteristics:
Frequent Temperature Cycling: Power modules experience drastic and frequent temperature fluctuations under varying loads, causing corresponding changes in coolant temperature. The hoses are subjected to cyclic thermal expansion and contraction stress. Long-term temperature cycling can lead to fatigue of rubber materials and a decrease in interlayer adhesion strength.
Complex Electromagnetic Environment: The high-speed switching of power switching devices generates strong electromagnetic fields. While these do not directly affect rubber materials, attention must be paid to the grounding and induced eddy current issues of the metal reinforcement layer in the hoses.
Compact Space: The internal space of the frequency converter cabinet is limited, requiring the hoses to bend in multiple directions within a confined space, placing high demands on bending radius and flexibility.
Long-Term Continuous Operation: Industrial frequency converters often operate continuously without interruption. The hoses must possess long-term reliability, with a design life typically consistent with the equipment body, reaching over 10 years.
Diverse Cooling Media: Commonly used cooling media include deionized water, water-glycol mixtures, and specialized coolants. Deionized water is extremely sensitive to leaching from rubber materials. The leached ions reduce the resistivity of the water, affecting the insulation performance of the power module. Therefore, the inner layer material must possess extremely low ion leaching characteristics.
III. Structural Design and Material Selection
Inner Layer (Inner Rubber Layer): For the specific requirements of the inverter's water-cooling system, the inner layer typically uses peroxide-cured EPDM material. Compared to sulfur-cured systems, peroxide-cured EPDM has significant advantages in terms of uniform cross-linked network structure and low extractable content, reducing the amount of organic matter and ions leached into the coolant and maintaining the coolant's insulation performance. For systems using specialized coolants (such as glycol-based coolants), the inner layer material also needs to have its long-term swelling performance in that coolant verified.
Reinforcement Layer: The internal piping of the inverter experiences frequent bends and has limited space, requiring high flexibility in the flexible hoses. Fiber braided reinforcement has become the mainstream choice due to its small bending radius and good flexibility. Operating pressures can generally cover 1.0–2.5 MPa, which is sufficient to meet the needs of conventional water-cooling systems. For centralized cooling systems with higher pressure, a steel wire winding reinforcement scheme can be used. However, attention must be paid to the grounding treatment of the metal reinforcement layer to avoid induced current in high-frequency electromagnetic fields.
Outer Layer (Outer Rubber Layer): A synthetic rubber formula with excellent ozone resistance, oil resistance, and flame retardancy should be selected. Oil mist or chemical gases may exist inside the inverter cabinet, and the outer rubber layer must have corresponding resistance capabilities. Flame retardancy is a basic requirement for materials used inside electrical cabinets. Simultaneously, the outer layer should have good resistance to mechanical wear to withstand friction during installation and use.
IV. Performance Parameters
Operating Pressure: The operating pressure of a conventional inverter water-cooled system is generally 0.3–0.6 MPa, while centralized cooling systems may reach above 1.0 MPa. The rated operating pressure of the hoses is usually designed to be 2–3 times the system operating pressure to ensure sufficient safety margin.
Temperature Range: The coolant temperature is generally between 5 and 60℃, but sections near the power modules may be subject to heat radiation, and the surface temperature may be higher. Standard EPDM flexible hoses operate within a temperature range of -40℃ to +100℃, covering the entire temperature range for normal inverter operation.
Electrical Insulation Performance: The insulation resistance of the hose assembly should meet the requirements of relevant electrical safety standards. For systems using deionized water, the ion expulsion rate of the inner layer material is an important indicator of its quality.
Bending Radius: To accommodate the compact space within the cabinet, the bending radius is typically required to be no more than 3 to 4 times the outer diameter of the hose. Fiber-braided reinforced products have a significant advantage in this regard, allowing for more compact wiring.
Flame Retardancy Rating: Materials used inside the cabinet must meet the corresponding flame retardancy requirements. The outer adhesive layer material can be formulated to achieve UL94 V-0 or V-1 ratings.
