Mica gasket material has excellent high temperature resistance. At temperatures above 900 F, ideal sealing materials Grafoil® or flexible graphite cannot be used. Flexible graphite or Grafoill® will coke at high temperatures when oxygen is present, whereas mica gasket materials will not (900 - 1850 F).
Mica gasket material is an excellent alternative for these high temperature (to 1800 F) applications. Some of the basics of Mica are shown below. As a gasket material, mica can be very effective in sealing those high temperature critical applications without failure due to the presence of oxygen.
Mica comes in many forms. (1) Laminated (2) Flexible and rigid. The mica image above is a combination of laminated mica and shank stainless steel, a premium grade for higher pressures. Mica is also combined with polymers by heat treatment to make flexible mica sheets. Mica is also available as a rigid product. The best mica for you depends on your application.
Mica Gasket
Mica is a mineral with a wide range of special properties.
You may find that certain properties of mica can improve different products in your range.
Mica in flake form is completely harmless and has very high thermal and mechanical properties, making it a successful replacement for asbestos gasket materials in many applications.
Mica Thermal Properties - Withstands temperatures up to 1850oF (1000oC). - Fire resistant without burning. - Low thermal conductivity.
Mica Electrical Properties - Dielectric strength better than 25 kV/mm. - Good resistance to arcing and arc erosion. - Permeability to microwaves.
Mica chemistry - very good compression resistance. - Good tensile and flexural strength. - High modulus of elasticity.
Mica Thermal Properties -
Withstands temperatures up to 1850oF (1000oC).
Fire resistant without burning.
Low thermal conductivity.
Mica Electrical Properties-
Dielectric strength is better than 25 kV/mm.
Good resistance to arcing and arc erosion.
Permeability to microwaves.
Mica Properties-
Very good pressure resistance.
Good tensile and flexural strength.
The elastic modulus is large.
Mica cut gasket
Fills the space between two objects, usually to prevent leakage between the two objects when they are under pressure. Cut spacers save money by allowing less precise mating surfaces on machine parts that can use mica cut spacers to fill in irregularities. Mica gaskets are usually cut from mica sheets. Mica has two basic forms: Phlogopite and Muscovite.
Phlogopite or muscovite mica impregnated with excellent high temperature resistant silicone provides a softer, more snug gasket.
It is generally desirable that the gasket be made of a compressible material so as to tightly fill the space for which it is designed, including any slight irregularities. The most common misconception when choosing a cutting shim thickness is choosing a cutting shim that is too thick. The thicker the material, the more likely the contained material will seep through the pores of the cutting pad itself. This is a bigger problem for some materials than others. The rule of thumb is to make the material thick enough to compensate for any surface irregularities and allow for some compression. The amount of compression required to cut a gasket depends on many factors, including:
1) Surface area of mica gasket
2) Mica sealing pressure.
3) Bolt size (assuming bolts are used)
4) Number of bolts
5) Bolt condition
6) Bolt lubrication
All factors must be considered when determining torque. Torque data must be determined using all of the above methods and should be provided by the engineer using the M&Y data we can provide.
In most cases, unless your gasket is a standard ANSI or API flange, torque data using ring or full gaskets will be difficult to obtain (due to staffing and fear of legal action). In most cases the old ones will be tightened enough to stop any leaks, but usually not so tight as to completely crush the gasket.
Excessive compression of cut gaskets is a common problem with metal gaskets, which have mechanically designed recovery built into the gasket. This applies to mica filled spiral wound gaskets. Excessive compression will eliminate the resiliency of the cut gasket.
The common strategy of "the more compressive load you put on the gasket, the longer it lasts" generally applies to elastomeric materials because elastomers (rubber) are incompressible but deflect compression. Many materials, such as non-asbestos compression cutting gaskets and agitator added (i.e. Armstrong) materials, have elastomers in the material mixture they produce that make it difficult to overcompress.
In industrial applications, one of the more desirable properties of an effective mica gasket is the ability to withstand high compressive loads. Most industrial gasket applications involve applying pressure well to bolts in the 14 MPa (2000 psi) range or higher. This is why mica cutting gaskets are so widely used in industrial cutting gasket applications.
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