Detailed Description
Silicone — The High-Temperature Answer
Every cable jacket material has a temperature ceiling. PVC softens at 70°C. PUR at 90°C. TPE at 100–120°C. Beyond these limits, the jacket loses mechanical integrity — it deforms, melts, or embrittles — and the cable fails regardless of how well the conductor is engineered.
Silicone (VMQ — vinyl methyl polysiloxane) raises that ceiling to 180°C continuous, with short-term capability to 220°C. At the other end, silicone remains flexible at -60°C — a temperature range span of 240°C that no other flexible cable jacket material approaches.
This is not an incremental improvement over PVC or PUR. It is a fundamentally different material class — silicone is an inorganic-organic hybrid polymer with a silicon-oxygen backbone rather than the carbon-carbon backbone of organic polymers like PVC, PUR, and TPE. The Si-O bond energy (452 kJ/mol) is significantly higher than C-C (348 kJ/mol), which is why silicone survives temperatures that destroy organic polymers.
Where Silicone Cables Are Essential
| Application | Operating Temperature | Why Silicone Is Required |
|---|---|---|
| Industrial oven internal wiring | 150–180°C continuous | PVC/PUR melt; silicone survives |
| Foundry ladle preheater power | 120–160°C with radiant heat | Radiant heat raises cable surface above PUR limit |
| Medical autoclave / sterilizer | 121–134°C saturated steam | Steam + heat; silicone is steam-resistant and non-toxic |
| Stage lighting (halogen/HMI) | 120–180°C at fixture | PVC jacket would melt onto hot fixture housing |
| Automotive engine compartment | 100–150°C ambient near exhaust | PUR softens at 90°C; silicone is stable |
| Heat trace power connections | 150–200°C at connection point | Connection point temperature can exceed 200°C locally |
| Cryogenic / freezer (-60°C) | -60°C to -40°C | PVC cracks at -5°C; PUR at -30°C; silicone flexes at -60°C |
| Laboratory environmental chamber | -70°C to +180°C cycling | Temperature cycling degrades organic polymers; silicone is stable |
Tinned Copper — Not an Option, a Requirement
At temperatures above 100°C, bare copper oxidizes rapidly in air — forming a dark copper oxide layer that increases contact resistance at terminations and can eventually cause the conductor to thin and fail.
Tinned copper is mandatory for silicone cables. The tin coating prevents oxidation at sustained high temperatures. Every silicone cable from Yichi uses tinned copper as standard — not an option, not an upcharge. It is the correct engineering choice for a cable designed to operate above 100°C.The Silicone Trade-off — Mechanical Strength
Silicone's mechanical properties differ from PUR and PVC. Understanding these differences prevents misapplication:
| Property | PVC | PUR | Silicone |
|---|---|---|---|
| Tensile strength | 10–20 MPa | 30–50 MPa | 5–10 MPa |
| Tear strength | Good | Excellent | Moderate |
| Abrasion resistance | Moderate | Excellent | Low — silicone tears easily |
| Cut resistance | Good | Excellent | Low |
| Compression set | Moderate | Good | Excellent — fully recovers |
| Coefficient of friction | 0.35–0.45 | 0.25–0.30 | ~0.5 (higher — "grippy" surface) |
For applications where both high temperature AND mechanical robustness are required, a silicone-insulated cable with an E-glass fiber braid over-jacket provides partial mechanical protection. The glass braid resists cutting and abrasion while remaining stable at the same temperatures as the silicone jacket beneath it. This is the standard construction for furnace and oven cables.
Electrical Properties at Temperature
Silicone's electrical insulation properties remain stable across its entire temperature range — an important advantage for applications where the cable is heated:
| Temperature | PVC Insulation Resistance | Silicone Insulation Resistance |
|---|---|---|
| 20°C | ~20 MΩ·km | ~200 MΩ·km |
| 70°C | ~1 MΩ·km (PVC limit) | ~50 MΩ·km |
| 150°C | Failed (melted) | ~10 MΩ·km |
| 180°C | Failed | ~5 MΩ·km |
The key data point: at 180°C, silicone still provides 5 MΩ·km of insulation resistance — adequate for most industrial control and power applications. PVC cannot physically exist at this temperature.
Fluorosilicone — When Oil and Heat Coexist
Standard silicone swells significantly when exposed to mineral oils and hydrocarbon solvents. This limits silicone cable in applications where hot oil is present — such as engine compartments and hydraulic equipment.
Fluorosilicone (FVMQ) is a modified silicone with trifluoropropyl groups that provide oil resistance comparable to PUR while maintaining the high-temperature capability of silicone (up to +175°C continuous). Fluorosilicone cables are available on request for applications requiring both thermal and chemical resistance.Why Choose Yichi Cable Silicone?
- Tinned copper as standard: Every silicone cable uses tinned copper conductors — no risk of ordering the wrong conductor and discovering oxidation at temperature
- Peroxide-cured silicone: Our silicone is peroxide (platinum) cured — no acid-cure byproducts that can corrode copper over time at high temperature. The more common acid-cure (acetoxy) silicone releases acetic acid during curing — acceptable for sealants, unacceptable for cable in contact with copper
- E-glass over-jacket expertise: We advise when an over-jacket is needed and specify the right type — E-glass for general mechanical protection, stainless steel for armor, aramid for cut resistance
- Medical and food-grade documentation: FDA 21 CFR 177.2600 and USP Class VI compliance certificates available with every shipment for medical and food contact applications
- Custom core configurations: Single core, multi-core, shielded, twisted pairs — silicone cables built to your specification