Muscovite Mica Sheets

What the slip plane actually does. The refractory lining expands when the furnace heats and contracts when it cools. If it is rigidly restrained against the coil, that movement turns into stress, and the lining cracks. The mica layer is compressible and slides, so the lining moves without failing. It is a low-cost part that prevents a very expensive failure - a cracked lining means an unplanned reline.

 

Muscovite or Phlogopite? Choose on the Working Temperature

 

	Muscovite (white mica)	Phlogopite (gold mica)
Dielectric strength	Higher	Slightly lower
Continuous temperature	500 °C	700 °C
Intermittent temperature	800 °C	1000 °C
Colour	White / translucent	Amber / gold
Choose it when	Electrical insulation is the primary requirement and the continuous temperature stays within 500 °C	The working temperature is the constraint - the hottest zones of the furnace

Straight guidance: if the mica will sit continuously above 500 °C, specify phlogopite, not muscovite - even though muscovite has better dielectric strength. Above 500 °C muscovite degrades and the insulation you paid for is gone. Also note that the figures differ between grades: rigid muscovite is rated 500 °C continuous / 700 °C intermittent, while flexible muscovite is 500 °C / 800 °C. Tell us the construction and we will confirm.

Grade	Construction	Temperature
FOIL MGMG	Mica + glass fabric + mica + glass fabric	~ 800 – 1200 °C
FOIL MGGM	Mica + glass fabric + mica	~ 800 – 1200 °C
FOIL GMMG	Glass fabric + mica + glass fabric	~ 800 – 1200 °C
FOIL GMMF	Glass fabric + mica + PET film	-
COMBI MGC	Mica + glass fabric + ceramic fibre	~ 1000 – 1200 °C
COMBI GMC	Glass fabric + mica + ceramic fibre	~ 1000 – 1200 °C

Ceramic-fibre grades (COMBI) are asbestos-free and are the choice for the hottest positions and for slip planes that must survive the full service campaign. Tell us the furnace, the position and the temperature, and we will specify the construction - including the reinforcement.

For flexible muscovite these are 500 °C continuous and 800 °C intermittent. The single figure of 800 °C often quoted for mica is the intermittent value. Specifying a slip plane for continuous 800 °C service on that basis will lead to premature failure.

How to use this correctly: give us the temperature at the mica's actual position in the furnace - not the melt temperature. In an induction furnace the mica sits behind the lining, so it sees a lower temperature than the molten metal, and that number decides both the material and the grade. If you do not know it, tell us the lining thickness and the melt temperature and we will help you estimate.

 

Why the Slip Plane Reduces Lining Cracking

The mica slip plane is a low-cost component that protects a very expensive one. Its function is mechanical as much as electrical:

It decouples the lining from the coil. The refractory lining expands on heat-up and contracts on cool-down. Restrained rigidly, that movement becomes stress, and stress cracks the lining.

It provides a sliding interface. The lining can move against the mica instead of against the coil.

It accommodates manufacturing tolerance. Lining installation is not dimensionally perfect; the mica layer compresses and takes up the variation.

It insulates electrically. It separates the lining from the coil, protecting the coil from the electrical environment of the melt.

It acts as a barrier during sintering. When the lining is sintered in place, the mica protects the components behind it.

The practical payoff: a lining that cracks prematurely costs an unplanned reline - lost production, refractory cost and labour. The mica slip plane is what prevents that, which is why the industry treats it as insurance rather than as a consumable.

Installation note: slip planes are installed as overlapping wraps around the coil, with the reinforcement orientation and overlap specified by the furnace builder. Give us the furnace make and model, or the coil diameter and lining height, and we will supply the roll width accordingly to minimise cutting on site.

 

How We Test

Check	Method	Why it matters
Mica content	IEC 60371-2	Sets the temperature and dielectric performance
Bond (resin) content	IEC 60371-2	Excess binder softens the sheet at temperature
Density	IEC 60371-2	Detects porosity and pressing variation
Thickness and tolerance	Micrometer	Fits the lining gap; drives the slip-plane function
Dielectric strength	IEC 60243 / IEC 243	The core electrical specification
Volume resistivity at 23 °C and at 500 °C	IEC 60093 / IEC 93	Confirms the material still insulates when hot - the number that matters here
Heat loss at temperature	IEC 60371-2 / IEC 371	Measures degradation under thermal load
Flexural strength (rigid)	GB/T 5019	Structural performance
Water absorption	GB/T 5019	Moisture pickup during storage
Visual	Black spots, impurities, delamination	Crystal size and purity - visible quality
Sheet dimensions and squareness	Gauge	Cutting yield

Documents available: MSDS · TDS · test report · certificate of origin (Form A, Form E) · SGS test report. Third-party inspection welcome.

Important storage condition (from our own technical notes): mica sheet is not waterproof. Moisture degrades its performance. Store in a dry, moisture-proof indoor area at room temperature. We pack in polythene and carton, palletised, but the storage condition is on the user - so plan for it on site.

 

 

 

 

FAQ

What temperature can muscovite mica sheet withstand? 500 °C continuous and 800 °C intermittent for the flexible grade; 500 °C continuous and 700 °C intermittent for rigid. Always quote which one you mean - the 800 °C figure commonly seen is the intermittent value, and specifying it as a continuous rating causes premature failure.

 

Should I use muscovite or phlogopite in my furnace? Choose on the temperature at the mica's position. Above 500 °C continuous, use phlogopite (700 °C continuous, 1000 °C intermittent), even though muscovite has higher dielectric strength. Below 500 °C continuous, muscovite gives better electrical insulation and is the more economical choice. See Phlogopite Mica Sheet.

 

Is mica sheet used in induction furnaces? Yes - the slip plane between the working lining and the induction coil, as coil insulation, as crucible-form wrapping, and as a barrier during lining sintering. It allows the lining to expand and contract without cracking and insulates it from the coil.

 

Which form should I use for a slip plane? A reinforced slip-plane roll rather than a plain sheet. Glass-fibre and ceramic-fibre reinforced rolls (our FOIL and COMBI constructions) are cold-formable, tear resistant and rated 800 – 1200 °C, so they can be wrapped around the coil on site.

 

Do you supply ceramic-fibre reinforced slip planes? Yes - COMBI MGC and GMC, reinforced with ceramic (calcium-silicate) fibre, asbestos-free, rated approximately 1000 – 1200 °C, for the hottest positions and for long service campaigns.

 

What is the dielectric strength? Greater than 20 kV/mm at ambient. At elevated temperature the value is lower - our technical notes quote 15 kV/mm in the 500 – 1000 °C range. Both are true on their own basis; tell us your working temperature and we will quote the value that applies to your duty.

 

Is mica sheet waterproof? No. Moisture affects its performance. Store in a dry, moisture-proof indoor area at room temperature. We pack it in polythene and carton on pallets, but the storage condition on site is your responsibility - please plan for it.

 

Can you cut, die-cut or machine mica to size? Yes - full sheets, cut strips, die-cut washers, spacers and gaskets, and CNC-machined mica components to drawing. We also slit slip-plane rolls to coil width.

 

What documents can you provide? MSDS, TDS, test report, certificate of origin (Form A, Form E) and SGS test report.

Hot Tags: muscovite mica sheets, China, suppliers, wholesale, buy, price