Published: 2025-08-11 09:29:10
When the cable outer sheath is made of polyurethane (PU), to further improve its oil resistance, it is necessary to consider multiple dimensions such as material selection, structural design, and process optimization, and to develop solutions for the swelling and erosion effects of oils (mineral oil, hydraulic oil, animal and vegetable oils, etc.) on the sheath. The following are specific optimization directions:
1. Precisely select oil-resistant polyurethane materials
The oil resistance of polyurethane is closely related to its molecular structure. Different types of PU have significant differences in oil resistance, and it is necessary to prioritize selecting models suitable for oil environments:
Prefer to choose polyether-based polyurethane (PEU). Polyether-based PU is produced by the reaction of polyether polyols with isocyanates, and its molecular chain contains ether bonds (-O-), giving it higher chemical stability and better resistance to non-polar oils such as mineral oil, hydraulic oil, and lubricating oil compared to polyester-based PU. Its molecular structure is not easily swollen by oils, and the volume change rate in oily environments is low (usually
Choose a PU formulation with a high crosslinking density by adjusting the isocyanate ratio or adding crosslinking agents (such as trifunctional polyols) to increase the crosslinking density of PU molecules. A high-density crosslinked structure can enhance intermolecular forces and reduce the likelihood of oil molecules penetrating inside the sheath, thereby decreasing swelling and performance degradation (for example, with a 20% increase in crosslinking density, oil resistance can improve by 15%-30%).
Adding oil-resistant additives and modifiers to PU raw materials by mixing in oil-resistant additives (such as fluorides, chloroprene rubber micropowder) or conducting copolymer modification (such as blending with oil-resistant materials like polytetrafluoroethylene PTFE or chlorinated rubber) can further enhance the sheath's resistance to oils. For example, fluorine-modified PU can improve resistance to swelling in non-polar oils by more than 30%.
2. Optimize the sheath structure design
Apart from the material itself, a reasonable sheath structure can reduce the contact area between oils and the cable or slow down the penetration rate, helping to improve oil resistance:
Increasing sheath thickness and density: Without compromising cable flexibility, appropriately increasing the thickness of the polyurethane sheath (for example, increasing from the conventional 0.8mm to 1.2mm) can extend the path for oil molecules to penetrate inside; At the same time, by optimizing the extrusion process (such as increasing extrusion pressure and reducing cooling speed), the sheath structure becomes denser, free of bubbles or pinholes, and reduces the passage through which oil enters.
If a single PU sheath is still insufficient to handle strong oil contamination environments using a multi-layer composite sheath structure, a composite structure with a "PU oil-resistant inner layer" can be designed:
Outer layer: Polyurethane (provides wear resistance, weather resistance, and mechanical protection);
Inner layer: Materials with stronger oil resistance, such as nitrile rubber (NBR) or chlorosulfonated polyethylene (CSM), which prevent further oil penetration. This structure combines the overall performance of PU with the strong oil resistance of the inner layer, suitable for scenarios with high oil concentration and long-term immersion (such as oil depots and ship engine rooms).
Surface smoothing treatment is optimized through extrusion molds or post-grinding to make the PU sheath surface smoother. A smooth surface reduces oil adhesion and retention time, lowers the risk of corrosion from long-term soaking, and facilitates daily oil cleaning.
3. Process control and quality inspection
Process details during production directly affect the oil resistance of PU sheaths and must be strictly controlled:
Precise control of vulcanization/curing parameters The curing reaction of polyurethane (especially cross-linking of thermoplastic PU) must be carried out at appropriate temperatures (typically 100-120°C) and for 30-60 minutes to ensure sufficient molecular crosslinking. Insufficient curing leads to loose sheath structures and reduced oil resistance; Over-curing may make the sheath brittle and lose elasticity.
Strict raw material purity and formulation must prevent the inclusion of moisture, impurities, or inferior additives (such as low molecular weight plasticizers, which are easily extracted by oils), as this may cause micro-defects inside the sheath, becoming weak points for oil molecule penetration. For example, the moisture content of raw materials should be controlled below 0.05%.
The pre-delivery oil resistance test involves immersing the finished cable in oil: the sample is soaked in the target oil (such as IRM 903 mineral oil according to ISO 1817 standard) at a specified temperature (e.g., 70°C) for a set period of time (usually 7 days), and indicators such as the volume change rate of the sheath (requirement ≤10%), hardness change (≤15 Shore A), and tensile strength retention (≥80%) are measured to ensure they meet the standards before delivery.
4. Adaptation and maintenance of usage scenarios
Even with excellent oil resistance, the cable's lifespan is still related to how it is used. Please note:
Avoid prolonged exposure to high temperatures and oil contamination: Polyurethane becomes more reactive at high temperatures (such as above 80°C), and the penetration rate of oils will accelerate. Therefore, it is necessary to control the operating temperature of the cable environment or choose high-temperature and oil-resistant PU (such as special PU that can withstand 120°C).
Regular cleaning and inspection: In oily environments, regularly use a neutral cleaner to remove oil and grime from the surface of the sheath to prevent slow corrosion caused by long-term oil adhesion; at the same time, check whether the sheath has cracks, swelling, or discoloration, and promptly replace damaged cables.
Summary
To make cables with a polyurethane outer sheath 'more oil-resistant,' the key is to select the right materials (polyether type, highly cross-linked PU), optimize the structure (thicker, composite, densified), strictly control the process (curing, purity), and combine this with maintenance according to the usage scenario. Through this series of measures, the service life of PU sheaths in oily environments can be extended by more than 50%, meeting the needs of oil-heavy scenarios such as machine tools, automotive production lines, and oilfield equipment.