Monolithic refractory, the name generally given to all unshaped refractory products, are materials installed as some form of suspension that ultimately harden to form a solid mass.
Castable refractories
Castable refractories, also known as refractory concretes, is a dry, granular material designed to be mixed on site with water and capable of curing to a stable dimensional form through hydraulic or chemical setting. These are the materials that contain cement binder, which imparts hydraulic setting properties when mixed with water. Castable refractories have the advantage of being readily usable at the operating temperature of the equipment after hydraulic or chemical setting and removal of all moisture has taken place.
Castable refractories can be used to create the monolithic linings within all types of furnaces and kilns. Castable refractories are particularly suited to the molding of special shapes and parts at the installation site. The can be applied by pouring, pumping, troweling, funning, and shotcreting.
Plastic refractories
Plastic refractories are mixtures of refractory aggregates and cohesive clays which is prepared in stiff, unfired and formable plastic condition at the proper consistency for use without further preparation. Plastic refractories has high refractoriness and wide range of compositions, and can easily be rammed into place. They are often highly resistant to destructive spalling. Plastic refractories are used to form refractory monolithic linings in various kinds of furnaces, and are especially adaptable for making quick, economical emergency repairs.
Ramming Mixes
Ramming mixes consist essentially of ground refractory aggregates, with a semi-plastic bonding matrix which can be purchased ready-to-use or prepared by adding water in the mixer at the construction site. Ramming mixes are very similar to plastic refractories, but ramming mixes supply a denser, stronger refractory body than plastic refractories. They need some sort of form to restrain them when rammed. Ramming mixes is characterized by thermal stability, corrosion resistance and wear resistance because it contains less binders, fire clay and moisture compared to plastic refractories.
The ramming mixes are used in constructing the internal refractory lining of the stack for filling the gaps between the refractory elements and the walls or other metal elements forming the blast furnace stack. Ramming mixes are used mostly in cold applications where proper consolidation of the material is a concern.
Gunning mixes
Gunning mixes are granular refractory materials sprayed on application area using a variety of air placement guns. Gunning mixes consist of graded refractory aggregate and a bonding compound, and may contain plasticizing agent to increase their stickiness when pneumatically placed onto a furnace wall. Dense, homogeneous monolithic linings can be gunned without the use of forms to save time. More than a third of all monolithic refractories are installed by gunning.
These are heat setting and are used for patching and maintenance works for kilns and furnaces. In some industrial furnaces, turnaround time and installation costs are the major factors when choosing a refractory lining. In other cases, repairs need to be made with little or no downtime. In both circumstances, pneumatic convey-ing of material, or gunning, is often the method of choice.
Mortars
Mortars are generally neither classified under refractory brick nor monolithic refractories. These are finely ground refractory materials, which become plastic when mixed with water. Mortars must have good water retention properties and must not sediment. The composition and characteristics of the mortar materials, grain size and consistency are the important properties of the mortars.
These are used to bond the brickwork into solid unit, to provide cushion between the slightly irregular surfaces of the brick, to fill up spaces created by a deformed shell, and to make a wall gas-tight to prevent penetration of slag into the joints. Refractory mortars can be with ceramic bonding, chemical bonding or hydraulic bonding.
Patching refractories
Patching Refractories are similar to plastic refractories though have a very soft plasticity allowing them to be pounded into place. They have been widely used for steel industry, chemical furnaces, boilers, nonferrous furnaces and the other high temperature furnaces.
Coating refractories
Refractory coatings designed to protect the bricks, steel, monolithics, castables, refractory and steel shells in furnaces, kilns, boilers and various high temperature vessels usually against chemical attack. Coating refractories are normally intended to cover just the working surface of a lining. They tend to be fairly thin layers.
Fettling mixes
Fettling mixes are also granular refractory materials, with function similar to gunning mixes, but are applied by shoveling into the furnace needing patching.
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