Refractory Castables for Cement Kiln Various Parts Construction
Refractory castable in storage may absorb moisture and partially hydrate, resulting in insufficient hydration during construction and reduced bonding strength, so the castable must be stored in a dry place. The high strength castables are usually used for 6 months, and the alkali-resistant castables are for 12 months. If the castables are found to be agglomerated, they should be discarded and not used normally. Refractory castable can be used in a degraded manner, or the proportion can be modified as appropriate, or the aggregate can be preserved to discard the powder.
Refractory Castables Suitable Range and General Requirements
1.As an amorphous refractory material, refractory castables are often used in places with complicated shapes and surfaces, because these parts are not suitable for refractory bricks for masonry, and refractory castable is difficult to ensure stability under working conditions.
2.Fireproof castable is combined with the shell by means of a nail fixed to the steel shell. In the cement industry, the commonly used heat-resistant steel nails are V-shaped and Y-shaped. The commonly used materials are 1Cr18Ni19Ti and Cr25Ni20.
3.For general parts, steel rivets can be made of steel with 1Cr18Ni19Ti. In addition to considering the high temperature strength of the refractory material, the material should also be considered for destructive expansion due to oxidative corrosion under high temperature conditions. Although some ordinary low temperature parts can meet the strength requirements of working temperature, the oxidized and corroded scale may generate huge expansion stress and swell the refractory castable. Especially in high temperature areas, such as coal injection pipes and kiln mouth parts, the nails should be made of Cr25Ni20 brand heat resistant steel with high temperature strength.
4.In order to avoid the damage of the refractory castable due to the shrinkage during the solidification process and the expansion during the heating process, for large area castables, the masonry should be carried out in a row with a certain length and width (the area of each plot should be Within 1.5 m2), these plots are separated from each other by application of joints, and refractory fibers are packed therein to form de facto expansion joints and crack control joints. Expansion joints and crack control joints should avoid important or weak areas, or areas of major stress.
5.Refractory castables of each plot are to be cast once, castable refractory is difficult to ensure the joint strength between the two castables by two castings.
6.The surface of the lining is intended to be smooth and flat, the uneven surface causes undesired build up and thus causes large chunks and blockages. Special attention should be paid to the portion of the cone that is prone to blockage. The masonry formwork should have sufficient strength, the support should be firm and the surface should be clean. The steel formwork shall be coated with a release agent, the wood formwork shall be coated with a waterproof paint or directly coated with a thin film.
Refractory Castable Construction
1.Mixers and other equipment must be cleaned before use. Other types of debris can have a significant impact on the performance of the refractory castable.
2.The mixing water must be clean. In the case of normal temperature conditions, in order to reduce excessive evaporation of water and excessive temperature rise, excessive ventilation, heating and direct sunlight must be avoided during the mixing process. In the case of low temperature, proper temperature should be paid to prevent the refractory material temperature from being too low. Concrete mixing must use a forced mixer to reduce mixing moisture and improve mixing quality. Refractory castable is not allowed to improve the pourability of the partially coagulated mixture by adding water, which will be the most important indicator of the loss of the refractory castable in cement klin.
3.In order to ensure uniform mixing and minimize mixing water to ensure higher strength and uniformity of the castable, the castable must be mixed in the dry state for 1 min, add 50% water and continue to stir for 1 min, then the remaining as needed the water is slowly added to seek a suitable value between 80% and 100% of the required water addition. The mixing time should be according to the manufacturer's requirements. The mixing time after adding water is about 5 minutes. The amount of water should be reduced as much as possible. Excessive mixing water will cause segregation of water and slurry and aggregate, resulting in loss of slurry and a significant drop in masonry strength. The amount of material to be poured per mixing should be an integral multiple of the minimum packaging batch, that is, 100 to 300 kg.
4.The appropriate degree of water addition can be verified by the following method. After adding water and stirring, refractory castable can reach a certain viscosity in about 4 minutes. At this time, you can pinch a concrete ball with one hand. When you squeeze it with your fingers for 5-6 times, then open the palm of your hand, it loses its shape and slowly hands. Spread out in the heart, the amount of water added will not flow from the open fingers.
5.Pour the mixed refractory castable into the formwork, the bottom will start to vibrate until all the air is discharged, the refractory castable is evenly integrated. However, the above operations should not be excessive, so that surface bleeding and slurry separation occur. Excessive vibration will also cause the ordering of the fire resistant steel fibers in the castable (the film is disorderly), which will cause the flaking resistance of the refractory fiber to be reduced in the refractory castable.
6.Refractory castable in the cell divided by the expansion joint must be completed in one continuous casting. The refractory casting material should be added continuously and vibrated until the template is fully filled. The pouring work must not be stopped before the completion of the delineated plot. The pouring and vibrating operations must be completed before any part of the castable in the plot begins to condense.
7.Try not to layer the refractory casting. If no part of the layer is to be poured, the casting of the second layer must be completed before the first layer of castable is condensed. Applying the castable to the solidified castable is meaningless and will fall off during the low temperature phase.
8.During the vibration process, the surface of the castable will tend to be horizontal. If a special shape is required, the vibrator can be moved in parallel according to the surface to be processed, and the material is pushed in the required direction.
Refractory Castables Hardening Curing
1.After the castable begins to coagulate, the hardening time must be not less than 24 hours under normal temperature conditions, and to some extent, prolonging the hardening time to 48 hours or more is advantageous for enhancing the strength of the concrete. For less cement castables, the setting time tends to be longer. For parts that use high-strength castables, such as coal injection pipes, kiln mouths, etc., the curing and demoulding time should be extended appropriately.
2.Before the hardening, the water should be prevented from evaporating. For example, the surface of the lining should be covered with a thin plastic or herb mat, or it can be cured by applying muddy water. During this period, due to the low strength of the concrete, excessive mechanical forces should be prevented to cause damage to the concrete.
3.After hardening, the castable should be dried at an ambient temperature of 15 to 30 ° C for a period of time (24 to 48 h). The lower the temperature, the longer the hardening time. If the temperature is below 10 °C, warming measures should be considered to improve the curing conditions.
4.For water glass and phosphate castables, it should be cured in a dry environment, using the dehydration strength of water glass, and not watering.
Refractoryt Cement Demold Time Properly Selected
The non-load-bearing formwork shall be demolded when the strength of the castable does not cause cold sensation.
The load-bearing castable should be considered to be demolded at a strength of 70%.
The core mold with higher strength should be demolded in time without causing concrete damage, so as to avoid the difficulty of demoulding due to the high strength of the castable.
Refractory Castables Maintenance
Refractory material should be inspected after the kiln and the first kiln stop. This inspection can be considered as the first inspection of the lining material after the first high temperature burning. Refractory castable should be comprehensive and detailed, the repaired parts should be strictly followed. Quality requirements are carried out. In addition, the lining should be inspected regularly, and the inspection cycle should be shortened for some key parts. When it is confirmed that the lining has fallen off, it should be repaired immediately until it is replaced, so as to prevent the insulation layer and the carcass from being exposed to high temperatures. If it is found that the steel nail has leaked out or the lining has worn to 65% of the original length, the lining should be repaired immediately. When repairing the lining, it is usually necessary to insert a new dowel and appropriately increase the density of the dowel (10%) while leaving an expansion joint between the new and old lining.
Refractory Castable Pouring Area Dividing Retention Control Joint
1.Refractory Castables Shrinkage Expansion
In the first heating process, the refractory castable will undergo two volume shrinkage when dehydrated at 50 ° C ~ 200 ° C and sintered at 900 ° C ~ 1000 ° C. In other temperature ranges, heating will expand the castable. After the first heating, the castable generally does not shrink.
In order to prevent the stress caused by the volume change from causing damage to the castable, the lining material must be cut into a cell having a diagonal size of not more than 1.5 m, and the zone is poured and a gap of expansion and contraction is left at the boundary line of each casting zone.
2.Refractory Castable Expansion Joint Expansion Range
The size of the gap should ensure that the castable in each cell is free to expand, and the expansion joint with the proper position can also become the control joint. In the high temperature section (>600 ° C), the width of the expansion joint should be controlled to 3 to 4 mm according to the spacing of the expansion joints. The expansion joint and the control slit are placed on a plane above and below the bulge of 200 mm, and the shed is placed in the lobes and the sharp cone. The expansion joints on both sides of the expansion joint and the control joint have a large tendency to crack, and the density of the nail can be appropriately increased.
3.Refractory Castable Expansion Joint Width Control
The width of the expansion joint is related to the operating temperature and the length of the wire being controlled. The temperature is higher, the length of the control is longer, and the expansion joint can be appropriately widened. In areas with relatively low temperatures (<400 ° C), castables can be used directly in the equipment enclosure, and insulation is not allowed. Under such conditions, a 2 mm thick cardboard or plastic film can be inserted every 1.5 m to meet the expansion space requirements.
4.Refractory Castable Optimization Expansion Joint Position
When determining the expansion position, the reasonable arrangement of the vibrating process should be considered together. The vibration of the casting material on the side of the gap should not affect the castable that has been cast and started to harden. The position of the expansion joint avoids the force part, the furnace body skeleton and the hole of the lining. In areas with complex shapes, such as corners, protrusions, etc., the expansion joints corresponding to their surfaces shall be provided at the surface of the convex angle and the radius of curvature. When the two casting surfaces intersect at a concave angle, they shall be at the concave corner. Set a type of expansion joint.
The lining diagram should show the position and size of the expansion joint at the main part. If the working temperature of the castable exceeds 1200 °C, an expansion joint with a width of more than 3 mm is set and the fiber mat is inserted therein.
5.Refractory Castable Control Seam Setting
If the castable causes cracking due to shrinkage, it is necessary to provide a control joint at about 200 mm of the corner portion, so that the shrinkage crack can occur in a predetermined, relatively safe portion. The control seam is set up by inserting paper, paraffin or thin wood board at a predetermined gap, and pouring the flammable or lost material under high temperature conditions. After burning or losing the combustible material, the control seam is left.
The control seam must be placed in the middle of the adjacent dowels, which are approximately equal to the dowels on either side. Set on continuous surfaces, conical surfaces and tubes, and should be placed on planes and surfaces that do not control the risk of shrinkage. Avoid setting in areas where expansion joints are not possible, such as setting expansion joints at small casting faces and lobes.
