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How To Choose Refractory Bricks And Its Basic Property

when choosing refractory materials, you must consider not only the cost but also its performance in a particular situation. The selection of the refractory should be done on the basis of careful analysis of service conditions, availability of refractory materials, thickness requirements, anchorage, ease of installation and future repair and maintenance. 
For different applications and service conditions, different types of refractories are used. You can choose refractory based on its properties.You need to evaluate the thermal performance, physical properties, chemical characteristics of the service conditions. You must take into consideration the specific raw materials you will process, the temperature you will reach, the length of your melt, how long you will be holding the raw materials in the furnaces,etc.. 
If the refractory material is destined for heating or cooking, you may choose a normal refractory such as the fire brick. Some applications may require special refractory materials. Zircon is used when the material must withstand extremely high temperatures. Silicon carbide and carbon are two other refractory materials used in some very severe temperature conditions, but they cannot be used in contact with oxygen, as they will oxidize and burn. 
The quality of a refractory and its suitability of a particular application primarily depends on its properties. There are three general, acidic refractories, neutral refractories, and basic refractories. Be sure to select the corresponding chemical properties of refractories, otherwise chemical changes occur at high temperatures. Acid refractories are used in areas where slag and atmosphere are acidic. Neutral refractories are used in areas where slags and atmosphere are either acidic or basic. Basic refractories are used on areas where slags and atmosphere are basic.
Below simply introduce Some basic property of refractory for your reference: 
Melting Point: The temperature at which the material changes state from solid to liquid at atmospheric pressure. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depends on pressure and is usually specified at standard pressure. When considered as the temperature of the reverse change from liquid to solid, it is referred to as the freezing point or crystallization point.  Below chart shows the melting point of some pure compounds used as Refractory.
Size And Shape: The size and shape of the Refractory is a part of the design feature. It is an important feature in design since it affects the stability of any structure. Accuracy of size is extremely important to enable proper fitting of the refractory shape which can minimize the thickness and joints in construction. 
Bulk density: Bulk density is an indicator of Weight of a unit volume of a loose material (such as a powder or soil) to the same volume of water. Expressed in kilograms per cubic meter (kg/m3) or pounds per cubic foot (lb/ft3), it is a type of relative density and is used mainly in quality control, shipping, and soil analysis. Bulk density is a useful property of Refractory, which defines the material present in a given volume. An increase in bulk density of a given refractory increases its volume stability, its heat capacity, as well as resistance to slag penetration. 
Porosity: Porosity is a term which is used to describe an important physical property of refractory. The porosity of refractory is determined by measuring the amount of void space inside, and determining what percentage of the total volume of the material is made up of void space. Porosity measurements can vary considerably, depending on the material, and high or low porosity will impact the way in which the material performs. This is an important property in cases where the refractory is in contact with molten charge and slags. A low apparent porosity is desirable since it would prevent easy penetration of the refractory size and continuity of pores will have important influences on refractory behaviour.
Cold Crushing Strength: The Cold Crushing Strength represents the ability of a product to resist failure under compressive load at room temperature. It has an indirect relevance to refractory performance, and is used as one of the indicators of abrasion resistance. The higher the Cold Crushing Strength of a material is the greater should be the resistance to abrasion. Refractory with high Cold Crushing Strength are also expected to have higher resistance to slag attack. The determination of cold crushing strength is also highly important in case of refractory insulating bricks where bricks have to be porous as well as strong.
Refractoriness Under Load: Refractoriness under load is a measure of the deformation behavior of refractory products subjected to a constant load and increasing temperature. The temperature range in which the softening of refractory products occurs is not identical with the melting range of the pure raw material; therefore it must be reliably determined. 
Permanent Linear Change: Permanent Linear Change is a factor used to judge the suitability of Refractory in ranges of temperature limits. Refractory materials can undergo mineral formation, phase transformation or shrinkage when heated.
Thermal conductivity: Thermal conductivity is the intrinsic property of a material which relates its ability to conduct heat. Heat transfer by conduction involves transfer of energy within a material without any motion of the material as a whole. Conduction takes place when a temperature gradient exists in a solid medium. Conductive heat flow occurs in the direction of decreasing temperature because higher temperature equates to higher molecular energy or more molecular movement. Energy is transferred from the more energetic to the less energetic molecules when neighboring molecules collide. 

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