Characteristics of Micarta sheet
Phenolic plastics or Micarta sheet makes use of phenolic as a binder to impregnate layers of a substrate to form an extremely versatile material that can be used for a wide range of applications. The resins used in the Micarta sheet is usually phenolic, silicone, melamine or epoxies while the substrates can either be paper, cloth or glass. Micarta sheet is often referred to as phenolic laminates with impressive resistance to shock, heat, stress and corrosive chemicals. The phenolic laminates can be punched, machined, drilled, sanded, tapped, turned, milled, sheared and cut. The dielectric properties of phenolic laminates make them highly suitable for electrical applications that include electric transformers and circuit boards.
The most commonly used NEMA thermoset laminate grades
Unlike other groups of plastic materials, thermoset plastic industrial laminates have NEMA standards with the most commonly used grades as:
NEMA Grades C, CE (Canvas Cotton-cloth Reinforced Phenolic) – these grades of phenolic are composed of continuous cotton weave cloth that has been impregnated with a phenolic resin binder. Phenolic sheets are generally acceptable for a fair percentage of electrical applications and they are among the lowest in cost and easiest to prepare. However, phenolic resins are not as strong as epoxies when it comes to moisture resistance, humidity-resistance, dimensional stability, shrinkage and retention of electrical properties when exposed to extreme environments. NEMA Grades C and CE contain medium weave canvas which is known for its mechanical properties. However, it is not suggested for primary electrical insulation.
NEMA Grades X, XX and XXX Paper Reinforced Phenolic – a paper base is impregnated with a phenolic resin binder to create a paper-reinforced phenolic that has good electrical properties with fair mechanical strength. The paper-reinforced phenolic can be used as a template material or a backup material for most applications. It is important to take note that when selecting a paper grade the more X’s means better electrical properties while those with fewer X’s means superior mechanical properties.
NEMA Grades L and LE Linen Cotton Cloth Reinforced Phenolic – contains a fine weave of linen that is also well known for its mechanical properties. However, the finer weave of linen cloth allows machining of intricate details such as gear teeth. While NEMA Grade LE has superior moisture resistance to NEMA Grade L, C and CE it is not recommended for primary electrical insulations.
NEMA GPO-1, GPO-2and GPO-3 Glass-mat Reinforced Phenolic – are known for its extremely low moisture absorption, high heat resistance with excellent mechanical and electrical properties. The most common grades in different applications are G-10 and G-11.
There are other grades available that include glass with silicone, glass with melamine, nylon and phenolic which are offered in sheets, rods, film and tube.