1. Technical Principles: Direct Correlation Between Viscosity and Performance

1. Insufficient film-forming ability

   The film-forming ability of dimethyl silicone oil is positively correlated with its viscosity. 5 cSt belongs to the extremely low viscosity grade, with short molecular chains and extremely strong fluidity. After coating, it is difficult to form a continuous and dense lubricating film. During the high-speed winding process of enameled wires (e.g., 12,000–15,000 rpm), the surface needs to withstand severe friction. The weak film formed by low-viscosity silicone oil is easily peeled off, leading to lubrication failure and even mechanical damage to the insulation layer.
2. Defects in lubrication performance

   The lubrication requirements of enameled wires focus on two aspects: reducing the coefficient of friction and anti-wear performance. Although 5 cSt silicone oil has low surface tension (approximately 15.9 mN/m), the intermolecular forces are weak, which cannot provide sufficient boundary lubrication protection. Compared with 500–1000 cSt silicone oil commonly used in the industry, its longer molecular chains can form a more stable adsorption layer on the metal surface, significantly reducing direct contact between the wire and winding equipment (e.g., guide wheels, molds).
3. Thermal stability risks

   Enameled wires may experience high-temperature environments (e.g., baking processes) during production. However, low-viscosity silicone oil has a low flash point (usually below 300°C), which is prone to volatilization or oxidation. This causes the lubricating film to fail and may produce carbon deposits, affecting the electrical performance of the wire.

2. Industry Practices: Insights from Standards and Patents

1. Recommendations from industry standards

   The authoritative standard for insulating silicone oil (e.g., ASTM D4652-20) clearly stipulates that the minimum viscosity of silicone oil used in electrical equipment is 50 cSt. Although this standard mainly targets transformer oil, its viscosity requirements reflect the basic stability needs of materials in the electrical field. As a core category of magnet wires, enameled wires have similar performance requirements for lubricating materials to insulating media, and 5 cSt silicone oil obviously cannot meet the basic standards.
2. Evidence from patent technologies

   Numerous patents on enameled wire lubricants show that the concentration of methyl silicone oil used is usually 1–3%, but none of them adopt extremely low-viscosity models of 5 cSt. For example, in a patented formula, methyl silicone oil is compounded with paraffin and aromatic solvent oil to improve lubricity through a synergistic effect, and the viscosity of the methyl silicone oil used is not lower than 50 cSt. Another patent uses 3GS refrigerating oil compounded with silicone oil, emphasizing the key role of high-viscosity base oil in high-temperature resistance and anti-wear performance.
3. Differences in application scenarios

   5 cSt silicone oil is more suitable for scenarios requiring extremely high fluidity, such as short-term lubrication of precision instruments or defoamers. However, the surface treatment of enameled wires needs to balance multiple properties such as lubrication, wear resistance, and heat resistance, and low-viscosity silicone oil performs poorly in such long-term, high-intensity applications.

3. Practical Applications: Alternative Solutions and Optimization Suggestions

1. Viscosity selection

• Conventional scenarios: Prioritize 500–1000 cSt dimethyl silicone oil. Its viscosity can ensure film-forming ability while maintaining stable lubrication performance during high-speed winding.
• High-temperature environments: If high-temperature processes are involved, 2000–10000 cSt high-viscosity silicone oil or modified products such as methylphenyl silicone oil can be selected, as they have better thermal stability.

2. Formula optimization

• Compound system: Compound silicone oil with waxy substances such as paraffin and beeswax (e.g., 1–3% silicone oil and 8–20% waxes) to significantly improve the strength and adhesion of the lubricating film.
• Functional additives: Add phosphate-based flame retardants (e.g., tris(hydroxymethyl)aminomethane hydrochloride) or antibacterial additives (e.g., triadimenol) to endow the wire with additional properties such as flame retardancy and stain resistance on the basis of lubrication.

3. Process adaptation

• Coating method: When using dipping or roller coating processes, adjust the coating speed and temperature according to the viscosity of the silicone oil to ensure uniform film thickness (usually controlled at 0.1–0.5 μm).
• Quality testing: Focus on testing the coefficient of friction (should be ≤0.2), wear resistance times (≥1000 times), and volatilization rate (≤5%) at high temperatures of the lubricated wire to verify the effectiveness of the formula.

4. Risk Tips

• Compatibility issues: The compatibility between silicone oil and the enameled wire insulation paint needs to be confirmed through small sample tests to avoid coating peeling or degradation of insulation performance.
• Environmental requirements: If the product involves export or high-end applications, select silicone oil products that comply with regulations such as REACH and RoHS, and ensure that the content of solvents (e.g., aromatics) meets the standards.

In conclusion, due to its extremely low viscosity, 5 cSt dimethyl silicone oil cannot meet the core requirements for enameled wire surface treatment. It is recommended to follow industry practices, select 500–1000 cSt silicone oil, and optimize the formula to achieve the best lubrication, wear resistance, and thermal stability performance.