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Timber which are slow and difficult to season free from defects, are classified as based upon their behaviour to cracking and splitting during normal air-seasoning practice.
High refractory
Null refractory
Low refractory
Moderate refractory
High refractory
Timber is classified into three categories based on its susceptibility to cracking and splitting during the seasoning process: High Refractory, Moderate Refractory, and Low Refractory. High refractory timbers are difficult to season because they possess high moisture content and complex cellular structures that lead to severe surface and end checking if dried rapidly.
IS 1141:1993
Timber is classified into three categories based on its susceptibility to cracking and splitting during the seasoning process: High Refractory, Moderate Refractory, and Low Refractory. High refractory timbers are difficult to season because they possess high moisture content and complex cellular structures that lead to severe surface and end checking if dried rapidly.
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The principle relies on the rate of moisture diffusion versus the rate of surface drying. In high refractory woods, the permeability of moisture from the core to the surface is low, creating a high moisture gradient. This causes the surface to shrink faster than the core, leading to stresses that exceed the ultimate strength of the wood, resulting in defects like splitting and warping.
High refractory timbers require slow and controlled seasoning, often using steam or high humidity kilns.
Low refractory timbers can be air-seasoned rapidly with minimal risk of defects.
Refractoriness is a measure of how prone the timber is to seasoning degrade.
Examples of high refractory timber include Sal and Toon, which require very careful management.
Preventing structural degrade during kiln drying
Optimizing moisture content to reach the Equilibrium Moisture Content (EMC)
Reduction in material waste due to rejects
High refractory timbers increase production time significantly
High energy consumption in kiln seasoning for slow-drying species
Structural timber members
Furniture manufacturing requiring high-dimensional stability
Low Refractory: Easy to season, can be air-dried quickly (e.g., Pine, Deodar).
Moderate Refractory: Requires moderate caution (e.g., Teak, Rosewood).
High Refractory: Slow to season, prone to cracking (e.g., Sal, Sissoo).
A is correct тАФ Timber classified as High Refractory is slow to season and highly prone to surface checking, end splitting, and warping if dried rapidly.
Always remember that 'refractory' in wood technology is inversely proportional to the ease of seasoning; the higher the rating, the more complex the seasoning schedule.
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