Unshaped refractories, better known as monolithic refractories, are special mixes or blends of dry granular or cohesive plastic materials without definite form.
Monolithic refractories are used to form virtually joint free linings and are only given shape upon application. They are installed as some form of suspension that ultimately harden to form a solid mass. Most monolithic formulations consist of large refractory particulates, fine filler materials and a binder phase. Monolithic refractories can be divided into plastic refractories, patching refractories, ramming mixes, castables, gunning mixes, fettling mixes, mortars, etc..
Monolithic refractories have advantages over refractory bricks in different type of furnaces. Their use promotes quick installation, avoid delays for the manufacture of special brick shapes. Use of monolithic refractories frequently eliminates difficult brick laying tasks and joints, which may be accompanied with weakness in construction.
Monolithic refractories represent a wide range of mineral compositions and vary greatly in their physical and chemical properties. Some are low in refractoriness while others approach high purity brick compositions in their ability to withstand severe environments. Under certain conditions, monolithic linings of the same composition as refractory bricks provide better insulation, lower permeability and improved resistance to the spalling effects of thermal shock. It has better volume stability and improved mechanical resistance to vibration and impact. Another advantage is that shrinkage and expansion can be matched to the application.
With little or no preparation, monolithic refractories can be applied to form monolithic or joint free furnace linings in new constructions or to repair existing refractory lining. Transportation and handling are simple. It offers considerable scope to reduce inventory and eliminate special shapes. It has ability to install in hot standby mode.
Monolithic refractories are of major importance in the maintenance of furnaces because substantial repairs can be made with a minimum loss of time and, in some cases, even during operations. They are replacing the traditional refractories at a much faster rate in many applications.
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