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Engineer Talk

Design With Mica in Mind

by Roland Morales

Mica

Mica is a superb insulating material which is versatile and cost effective for heater design.

At Tutco-Farnam the majority of our custom designed heaters use mica board machined to meet the customer’s specifications.  A variety of types and thicknesses of mica are available and are selected for use based on the parameters required.  Design variations using mica are virtually endless and can be customized to fit most applications.

Two different types of mica are used in Tutco-Farnam heaters; muscovite and phlogopite. Muscovite, the most common mica, is referred to as ‘light’ mica due to its aluminium and potassium composition – KAl2;(AlSi3;O10)(F,OH)2.  Phlogopite, with its higher iron and magnesium content, is referred to as ‘dark’ mica - KMg3AlSi3O10(F,OH)2.  Both micas have great dielectric strength and can be easily machined to fit any proposed design.  Muscovite is used in most of our mica heaters since the maximum operating temperature of 500-600°C is adequate for the majority of applications.  When a heater requires higher temperatures phlogopite is preferred.  Its maximum operating temperature of 800-1000°C allows it to handle much higher temperatures.  The primary advantage of using mica for heater design is its machinability as well as the wide range of thicknesses that are available.  Mica sheets ranging from 0.004” thick to 0.120” thick are used at Tutco-Farnam – enabling us to make our mica designs as precise as possible for the best fit to any application.

Mica boards function in a number of ways in heating units.  The most common use is as a winder for a resistance coil.  The coil is wound around the board (usually in slots that have been cut to fit the specific coil) and then terminated on the board with eyelets or hardware.  Boards may also be utilized simply as an insulator between (or around) other parts that will be electrified.  Finally, mica boards are also used as covers for heating elements – making them safer to handle and providing attachments for lead wires or other heater features. 

Mica is versatile, relatively inexpensive and has insulating characteristics which allow Tutco-Farnam to design and produce quality heaters to meet a vast array of customer applications.   The range of mica thicknesses available enables us to provide best fit products when limited space is a factor.  Attention to careful handling and low-moisture operating conditions will ensure long life and durability of these popular heaters.  



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