The service life of the rotary kiln lining depends to a large extent on the quality of bricks and masonry, as well as on the composition of raw materials, the properties of fuel, the adjustment of flame and the stability of the thermal system of the kiln. Because the kiln lining body rotates with the rotary kiln at high temperature, it is in a vibrating state for a long time, and it also bears the wear and impact of the charge, which not only requires the kiln lining brick to have high strength and thermal shock stability at high temperature At the same time, it also puts forward higher requirements for the construction quality of the rotary kiln furnace. This article introduces the construction essentials and quality control of rotary kiln furnace construction, as well as the construction of key points such as expansion joints, brick retaining rings and locking bricks.
Construction principles: ensure quality, ensure safety, and shorten the masonry time as much as possible.
Construction method
There are two types of masonry methods commonly used in rotary kilns: wet masonry and dry masonry. The following is a brief introduction to the construction essentials of the two construction methods.
3.1 Wet masonry
Wet masonry is generally used for anti-stripping high alumina bricks, silicon molybdenum bricks, and silicon molybdenum red bricks. The following matters must be paid attention to in the wet masonry process:
1) The refractory bricks require that the joints be full of grout, and the width of the brick joints should meet the design requirements of the drawings.
2) After each refractory brick is placed, it should be hit with a wooden hammer or a rubber hammer in order to squeeze out the excess fire mud. It is necessary to ensure that the brick seam is completely close to the shell, and the fire bricks should be in surface contact and firmly combined. When knocking refractory bricks, inappropriate knocking or squeezing should prevent damage to refractory bricks or damage to the refractory clay that begins to solidify.
3) The excess fire mud should be scraped off before the fire mud in the brick joints is completely hardened. If the fire mud needs to be filled in some places, the scraper plug should be used to fill the new fire mud, that is, the masonry joints.
4) The ash joint should be horizontal and vertical, the arc surface should be flat, and the joints should be tight. It should be ensured that the masonry is consistent with the dimensions indicated by each equipment.
5) The straight walls are built with staggered joints, and the vaults and kilns should be built with straight joints in the direction of the circumferential ring. The masonry should strive for a straight and smooth arc surface of the brick joints. The geometry of the masonry shall comply with the drawing requirements to ensure quality.
6) During the process from construction to production, the masonry should be prevented from being damp and frozen, and also prevent the premature occurrence of excessively high temperature, so that the refractory mud cannot reach its due strength.
3.2 Dry masonry
Dry masonry is generally suitable for magnesia brick systems, such as straight magnesia bricks, magnesia-aluminum spinel bricks and magnesia-iron spinel bricks.
Arch ring refractory bricks built by dry method have similar requirements to wet method, and should be wedged with 2mm thick steel plates at the end. The steel plate should be flat, no bumps, no burrs, no rust, and the head should be ground with a grinding wheel to a wedge angle less than 60 for wedging. A brick joint can only be wedged into one steel plate, and it is forbidden to wedge two steel plates into a brick joint. The steel plate should not be wedged into the brick joints of the lock joint bricks, and should be separated by 1 to 2 brick joints.
construction
First of all, before laying the lining, carefully check whether the convexity of the weld in the kiln shell meets the welding technical requirements of the kiln shell, and use a portable grinding wheel to grind the weld that exceeds the specified limit. Before masonry, the rotary kiln should be thoroughly cleaned, kept clean and dry, so as to be free of ash, rust, oil and water, and wire brushes must be used to remove metal rust. To ensure a good combination between the refractory bricks and the kiln shell.
Secondly, the refractory bricks of the rotary kiln must be laid out before the masonry is laid, and the accurate positioning line is used as the benchmark to check and inspect the masonry in stages. The axial reference line of the rotary kiln is about 1.5m long along the circumference, and the axial direction should be parallel to the axis of the rotary kiln. Rotary kiln circumferential reference line is placed every 10m, and circumferential control line is placed every 1m. The planes formed by the closed loop lines should be parallel to each other and perpendicular to the axis of the rotary kiln. These positioning lines will be the standard for routine inspection during the masonry process. Multiple inspections, and timely adjustment and correction will effectively prevent the accumulation of large deviations in the masonry process. The axis line of the rotary kiln should be carried out by professional measuring personnel, and the approved measuring instrument should be used to measure the line.
The masonry of the rotary kiln can only be carried out on the premise of ensuring that the rotary kiln cylinder is clean and dry, truly free of ash, rust, oil and water, and the positioning line is accurate. In the masonry process of the rotary kiln, the following matters should be paid attention to:
1) Brick laying shall be laid sequentially from the outlet end of the kiln to the inlet end, and shall be carried out in sections according to the length given in the drawings;
2) At the beginning of masonry, first lay a row of bricks along the kiln length reference line, and then take turns to lay bricks on both sides until it is slightly larger than a semicircle;
3) When axially staggered bricks are laid, every 4~6 rows must be checked whether the brick rows are flat and whether the arc lengths of the masonry are equal, and the problems should be corrected in time;
4) The lining of the bricks must be close to the shell, the bricks must be tightly attached to the bricks, the brick seams should be straight, the circles should be accurate, the bricks should be locked firmly, not in place, and not sagging and falling off. In short, it is necessary to ensure that the brick lining and the kiln body are reliably concentric during the operation of the kiln, and the stress in the brick lining should be evenly distributed on the entire lining and each brick lining;
5) When masonry, pay attention to the big and small heads of the bricks, and never turn them upside down; the bricks must be close to the cylinder, and the bricks must be close to each other;
6) When building the kiln lining, it should be built according to the design proportion, and there should be no “steps or climbing”. In case of unevenness of the cylinder, use thick glue to level it, and do not use cardboard or other pads;
7) When locking the opening, the selection of lock bricks should be appropriate. After the lock bricks are pushed in from the side, the gaps in all aspects should be consistent, and then wedge them with steel plates. The lock bricks cannot be connected together, and the wedge brick steel plate should not be hit on both sides of the lock brick;
8) For the places where processed bricks are required, the processed bricks should be machined as much as possible. The size of the processed bricks should not be less than 1/2 of the original bricks in both the length and width directions, and the processing must be flat;
9) After the brick lining of the whole kiln is completed, the brick lining of the whole kiln should be checked and tightened as necessary.
The masonry quality of the cement rotary kiln lining bricks determines the service life of the refractory bricks to a large extent. High-quality masonry is an essential prerequisite to ensure the efficient and stable operation of the rotary kiln.
