Mica Shields are widely used in visual liquid level gages to protect the glass surface from the corrosive effects of hot alkaline or acidic solutions. Mica is commonly used in steam water applications to prevent etching and the weakening of the glass.
Mica Selection: The quality of mica used in visual liquid level applications continues to be determined by visual examination where the suitability is assessed on the basis of appearance. In this process of quality evaluation undue emphasis is placed on clarity, color, flatness, hardness, stains, visible inclusions and structural imperfections.
The clarity, color, flatness, hardness, stains, visible inclusions and structural imperfections determine the quality of the Mica Shields. The most common Mica grades used in liquid level gage applications are V1, V2 and V4.
V1 Green or Ruby (Clear)
Highest grade quality of clear and nearly flat, of uniform colors, free from cracks, buckles, air inclusions foreign inclusions. Mostly used in single piece construction.
V2 Green or Ruby (Slightly Stained)
Navy grade quality, of uniform color, may contain slight crystallographic discoloration, cracks, buckles, and other similar defects and foreign inclusions except for a few tiny air inclusions in no more than one-fourth of the usable area. Used in single piece or in a two-piece construction.Suitable for saturated steam service from 600 to 1500 PSIG – Conforms to ASTM D351 specifications – Government spec. number: MILG-18498A – Thickness from .009 to .012 in single piece or in two pieces (the thinnest not less than .0045).
V4 Green or Ruby (Stained)
Commercial grade quality, may contain crystallographic discoloration, cracks, and other similar defects and foreign inclusions, except somewhat wavy but not rippled, may contain air inclusions in not more than two-thirds of the usable area. Used in single piece or in a two-piece construction.Suitable for saturated steam service from 300 to 600 PSIG. – Conforms to ASTM D351 specifications and the Government spec. number: MILG-18498A – Thickness from .009 to .012 in single piece or in two pieces (the thinnest not less than .0045).
As a result of this procedure, Mica is classified according to grades. The most common grades used in liquid level gage applications are
Green Color Quality.