Why mica for strip heaters and barriers?
Mica strips combine exceptional electrical insulation with thermal stability:
- High dielectric strength: Mica withstands tens of kilovolts per millimeter (e.g.,>20 kV/mm).
- Thermal stability: Muscovite mica tolerates ~500 °C continuously (800 °C peak) and phlogopite ~700 °C (1000 °C peak). This allows heaters to run very hot without breaking down.
- Heat transfer & uniformity: Mica’s thermal conductivity is relatively high for an insulator, enabling strip heaters to deliver uniform heat. In band heaters, the mica layers transfer heat from the NiCr ribbon windings into the sheath.
- Chemical and flame resistance: Mica is inert and flame-resistant, making it a good asbestos substitute in high-temperature gaskets and barriers.
- Flexibility & machinability: Thin mica strips are flexible and can wrap around curves. They cut cleanly and can include slots or holes for custom profiles.
- Reliability: Mica-insulated heaters withstand thermal cycling and mechanical stress.
Common industrial uses
Mica strips and plates are used throughout industrial heating:
- Strip heaters: Flat mica strip heaters use mica insulation to heat hot plates, sealing bars, molds, and other surfaces. They appear in packaging lines and food warmers.
- Band heaters: Mica band heaters wrap around barrels of injection-molding and extrusion machines. The mica layers insulate NiCr heating ribbons, providing uniform barrel heat for plastics processing.
- Furnace linings: Mica laminates and mica rolls serve as thermal-barrier liners in kilns and furnaces. They protect refractory linings by acting as high-temperature slip-planes and vapor barriers.
- Insulation barriers & gaskets: Mica sheets insulate electrical parts (arc chutes, busbars) and serve as high-temperature gaskets due to their low thermal conductivity and flame resistance.
Muscovite vs Phlogopite mica
Mica used in heaters comes in two varieties:
- Muscovite: White mica with very high dielectric strength. Good to ~500 °C continuously (800 °C peak).
- Phlogopite: Brown mica with a higher temperature rating. Good to ~700 °C continuously (1000 °C peak).
Most heater mica sheets are roughly 0.1–3 mm thick. Choose muscovite for moderate temperatures and phlogopite for extreme heat.
Specifying and sourcing mica strips
Match the mica type to the application temperature: use muscovite for ≤500 °C or phlogopite above that. Specify the sheet thickness (mica sheets range from ~0.1 mm to 100 mm) and strip dimensions (width, length, any slots or holes). Also specify the electrical termination (lead wires, terminals, etc.) needed for the heater. Work with suppliers who offer custom-cut mica strips. High-grade, silicone-impregnated mica is standard for reliable performance.