Mica gaskets for high temperatures
Mica is used in gaskets and parts exposed to high temperatures, both for insulation and in certain sealing applications. Its thermal stability and electrical properties make it a material worth considering for furnaces, exhausts, heating elements and industrial equipment where other materials may fall short.
At Manufactures Cusell we manufacture custom mica gaskets, washers and parts as part of our range of electrical and thermal insulating materials. The choice between muscovite mica, phlogopite and the different formats depends on the function of the part and its operating conditions.
What is a mica gasket?
Mica is a mineral with a laminar structure that can be split into very thin sheets. To produce industrial sheets, mica flakes or mica paper are bonded with a binder, often a silicone resin. Bonded mica materials are also known as micanite.
There are flexible and rigid formats, as well as grades with stainless steel reinforcement to improve mechanical strength and make handling easier. Their composition determines the final performance of the part.
It is important to distinguish between grades intended for sealing gaskets and sheets used mainly for insulation. A rigid insulating sheet does not necessarily offer the same compressibility or sealing capability as a material developed for gaskets.
The properties valued in these materials include:
- Heat resistance: suitability for high-temperature applications, within the limits of the selected grade.
- Electrical insulation: particularly relevant in formats without metal reinforcement, depending on the technical data sheet and the assembly.
- Fire behaviour: the mineral base is non-combustible; the classifications of the finished material must be checked in its documentation.
- Chemical resistance: to many agents, depending on composition, concentration and exposure temperature.
- Asbestos-free: in the industrial grades used for these parts.
- Conformability to the seating surface: grades designed specifically for sealing have a compressibility that must be assessed according to thickness and bolt load.
Muscovite or phlogopite mica: which should you choose?
Muscovite and phlogopite are the two most common types of mica in these industrial materials. Phlogopite is usually considered when thermal demands are higher, while muscovite is widely used in electrical insulation parts.
| Criterion | Muscovite mica | Phlogopite mica |
|---|---|---|
| Typical use | Electrical insulation and thermal applications within the limits of each grade | Applications with higher thermal demands |
| Thermal behaviour | Generally lower heat resistance than phlogopite | Generally higher heat resistance than muscovite |
| Formats | Flexible or rigid sheets and parts, depending on the product | Flexible or rigid sheets and parts, depending on the product |
| Selection criteria | Electrical properties, temperature, geometry and function | Temperature, function, composition and service conditions |
The type of mineral alone does not determine the operating temperature of a gasket. The binder, the reinforcement and the construction of the material also play a part. Operating limits should be checked in the technical data sheet for the specific grade.
What temperature and pressure can a mica gasket withstand?
Temperature: distinguish between continuous service and peaks
Continuous service temperature and maximum short-term temperature are different figures. As well as the maximum value, what matters is how long the exposure lasts, how often thermal cycles occur and the operating environment.
For this reason, there is no single temperature that applies to all mica gaskets. To compare material families, see our guide to temperature ranges of gasket materials.
Pressure: check the grade and the assembly conditions
Mica gaskets for hot gases are usually considered for high-temperature, limited-pressure applications. As a reference, KLINGER® Milam PSS, a mica material with stainless steel reinforcement, publishes values of up to 900 °C and 5 bar. These figures relate to that product and must be interpreted in line with its documentation; they are not universal limits for every mica, nor a guarantee that both values can be reached simultaneously in any joint.
The permissible pressure depends on the material, temperature, thickness, geometry and assembly. The load applied to the gasket must also be considered: we explain this in our guide to sealing pressure and bolt load.
A cold test does not guarantee hot performance
A leak test at room temperature does not guarantee the same behaviour at the actual service temperature. Thermal cycling can alter the bolt load and the response of the material, so it must be taken into account when selecting and validating the gasket.
Mica or graphite: when to consider each
Graphite is a common choice for gaskets that need to combine heat resistance and sealing capability. In the presence of oxygen, oxidation limits its use at high temperatures; the limit depends on the grade and the exposure conditions.
Mica may be considered for certain applications involving hot gases and limited pressure. However, it does not automatically replace graphite above a fixed temperature.
| Situation | Options worth considering |
|---|---|
| High temperature and need for sealing under pressure | Reinforced graphite or metal and semi-metallic gaskets, depending on the service |
| Hot gases, oxidising atmosphere and limited pressure | Mica grades designed specifically for sealing |
| High temperature and demanding pressure | Metal or semi-metallic solutions with a filler suited to the conditions |
| Conditions requiring greater oxidation resistance | Specific high-temperature materials, such as certain Thermiculite® grades |
This comparison is for guidance only. Selection requires knowledge of the fluid, atmosphere, temperature, pressure and joint characteristics. You can find out more about graphite gaskets, spiral wound gaskets and Thermiculite®, or see our gasket material selection guide.
Mica gaskets and parts as electrical insulators
Mica is used in heating elements, electrical equipment and supports where heat and the need for insulation come together. In these cases, the part may be a washer, a spacer or a plate, and its main function is not necessarily to seal a fluid.
Electrical properties must be checked for the selected grade and the operating conditions. If the material includes metal reinforcement, its construction and the contacts in the assembly must be assessed before it can be considered an insulation solution.
We manufacture micanite washers and other electrical insulators for fixings, housings and supports. See also our solutions for the electrical and electronics sector.
Common applications of mica parts
Depending on the format and grade, these materials are used in:
- Exhausts and hot-gas equipment: gaskets in ducts and joints, where the grade and service conditions allow.
- Furnaces and thermal equipment: spacers, shields, shims and certain gaskets for heat-exposed areas.
- Heating elements and household appliances: support plates, washers and insulating parts.
- Electrical and railway equipment: insulating components and thermal barriers, subject to the requirements of each application.
- Industrial installations: insulating or sealing parts selected according to temperature, pressure and chemical compatibility.
See our solutions for infrastructure and transport and for energy, chemicals and petrochemicals.
How we manufacture custom mica gaskets
The laminar structure of mica means the manufacturing process must be adapted to limit delamination and produce a part fit for its function. We select the cutting process according to rigidity, thickness, the presence of metal reinforcement and geometry.
Die-cutting may be suitable for materials and runs compatible with this process. For other geometries and quantities, we consider waterjet or plotter cutting, depending on the material; where applicable, these processes allow production without dedicated tooling.
At Manufactures Cusell we manufacture to drawing, using the format and grade defined for each order. Thicknesses, reinforcements and quantities are confirmed according to the selected material and manufacturing feasibility.
To prepare a quote we need:
- A dimensioned drawing, with the required dimensions, thickness and tolerances.
- The specified material or grade, if already defined.
- Continuous and maximum operating temperature, indicating the duration of any peaks if applicable.
- Pressure and the fluid or gas in contact.
- Function of the part: sealing, electrical insulation, separation or thermal protection.
- Quantity required.
Frequently asked questions
Is a mica gasket suitable for pressurised steam?
It should not be chosen on the basis of heat resistance alone. You need to check that the specific grade is suitable for steam and for the service pressure. Depending on the conditions, reinforced graphite or metal and semi-metallic gaskets may be considered as alternatives.
What is the difference between mica and micanite?
Mica is the mineral. Micanite is a material made from mica bonded with a binder, which allows sheets and parts to be produced with different degrees of rigidity and performance. You can see the options available on our electrical and thermal insulating materials page.
Do mica gaskets contain asbestos?
The current mica materials we use for these parts are asbestos-free. If you need specific documentation, please mention it when requesting a quote.
Can a mica gasket be used as an electrical insulator?
Suitable grades can be used for electrical insulation. The technical data sheet and the assembly must be checked, especially if the part includes metal reinforcement.
What thicknesses do you manufacture?
The available thickness depends on the grade, the format and whether there is reinforcement. Indicate the required thickness on the drawing so that we can confirm availability and manufacturing feasibility.
Do you need custom mica gaskets?
Send us a dimensioned drawing, the quantity and the operating conditions. At Manufactures Cusell we can advise you on material options and confirm manufacturing feasibility; validation of the part in the equipment is the responsibility of the person in charge of the application.
Contact us or browse our range of electrical and thermal insulating materials.
