ASTM D710-97 pdf free.Standard Specification for Vulcanized Fibre Sheets,Rods, and Tubes Used forElectrical Insulation.
Vulcanized fibre adjusts its moisture content tocorrespond with the atmospheric humidity to which it isexposed.The moisture content of vulcanized fibre is determined by the procedure given in Test Methods D 619 and isexpressed as a percentage of the dry weight of the testspecimen employed.
The approximate amount of moisture which vulca-nized fibre will hold at equilibrium under various relativehumidity conditions at approximately 23°C is indicated by thecurve shown in Fig.X1.1.This curve applies to the variousgrades of vulcanized fibre in normal use, although the rate ofabsorption tends to vary, with the lower density grades absorbing moisture faster than the higher density grades.In the winter season vulcanized fibre is often stored in aheated room after the fibre has reached moisture equilibrium in the coldatmosphere. Unless moisture is added to the storage room, the vulcanizedfibre will tend to reach a new lower moisture equilibrium.For general uses，vulcanized fibre should be storedwhere it will maintain its normal moisture content of approximately 5 to 8 %.If subjected to extremely damp conditions,it willpick up moisture and tend to warp out of shape and to increaseits dimensions slightly.
If subjected to extremely dry conditions, such as thelow humidity that develops in heated rooms during the winterseason, it will tend to dry out. This tends to cause warpage andslight shrinkage in all dimensions as well as some increase instiffness and hardness.Avoid storing fibre under extremely damp or ex-tremely dry conditions. Approximately 50 % relative humidityis recommended.
Vulcanized fibrepossessesexcellent arcextinguishing and nontracking characteristics which make itparticularly suitable in many kinds of equipment where theseproperties are required,for example,arc chutes for smallcircuit breakers, lightning arrestors, both high and low voltagefuses of many types and expulsion type high voltage cutouts.An increase in moisture content usually improves the arcextinguishing and nontracking characteristics.
Moisture Content influences the voltage breakdown,dc resistivity and ac permittivity and dissipation factor of hardfibre to an extent that makes it difficult to evaluate theseproperties in a standardized manner. Under relatively wetconditions, these characteristics will be negatively affected ascompared to dry conditions.This characteristic could possiblylimit certain applications unless previously approved bytesting.ASTM D710 pdf download.