How are bricks made

It is said that the process of firing bricks goes as follows: select high-quality loam → add crushed cinder to form clay blanks → after the blanks are dried, they are placed in the kiln in an orderly manner → the kiln door is sealed, and a large amount of coal is added on top of the kiln to be ignited → after being fired for a certain period of time, the bricks or tiles are ready.

The brick carving materials used for constructing screen walls differ from those used in stone and wood carving; the latter can be obtained directly from nature, whereas bricks are formed from clay through the interaction of water and fire. The main steps in brick manufacturing are: 1. Collecting soil. The soil used for firing bricks is taken from ancient soil at a depth of two feet beneath the surface; this layer of soil is slightly darker in color than the surface soil, and it was formed approximately 80,000 to 120,000 years ago. At that time, the Earth’s climate was warm and humid, and the intense biological activity resulted in soils that were soft and sticky during that period, making them excellent materials for firing bricks and tiles. 2. The excavated clay is left to lie exposed to the sun, snow, rain, and freezing conditions for about half a year; this process causes it to decompose and loosen up from within. It is then manually crushed and screened to leave only fine, pure soil. 3. Moisten the pure soil with water, then knead it repeatedly or have oxen trample on it to turn it into a thick mud; manual kneading and mixing are required about 5 to 6 times. This process plays a crucial role in the quality of the bricks produced in the end. 4. Fill the wooden shaping mold with soil, compact it, and then use an iron wire brush to remove excess soil, thus forming the shape of the object. Before shaping the blank, a layer of fine sand should be spread under the wooden mold to prevent the mud from sticking to the ground. 5. After demolding, the brick blanks should be placed in a shaded area to dry slowly, to prevent cracking and deformation caused by exposure to direct sunlight. 6. Once the brick blanks are completely dry (after about one to two months), they are sent to the kiln for firing. This process is the most important step in the entire brick-making process. For ordinary bricks, coal is used as fuel, while bricks with higher density, such as filter bricks, are fired slowly using materials like straw and pine branches. 7. After more than a dozen days of firing, the green bricks have essentially been sintered. If the fire is extinguished slowly at this point, external air will enter the kiln, and once the bricks cool down, they will take on a red color – this is what we commonly refer to as red bricks. Blue bricks, on the other hand, require a different process: during high-temperature firing, the ventilation holes in the top of the kiln are sealed with soil to reduce air intake, thereby creating a reducing atmosphere inside the kiln. As a result, the red iron oxides in the bricks are reduced to blue-gray iron oxides of lower valence. To prevent these lower-valence iron compounds from being oxidized again, water is poured on the sealed part of the kiln’s roof; the water turns into steam when heated by the high temperature, absorbing heat from within the kiln. In this way, the bricks remain in a reducing atmosphere throughout the cooling process, until they are completely cooled and removed from the kiln. The process of turning loess into blue bricks is now complete. Today, history has entered the modern mechanical era, and scientific methods have become increasingly sophisticated; the quality of bricks and tiles could therefore be even better. Yet in reality, the quality of bricks and tiles used for restoring cultural relics today is inferior to that of the Ming and Qing dynasties. There is only one reason for this: brick factories focus solely on making profits, reducing the processes of mixing clay and firing bricks during production.

A newcomer in brick firing – the suspended kiln. The suspended kiln is a highly advanced device for burning bricks; it incorporates the principles of various brick-firing kilns and has been improved through numerous tests. It features a rational structure, an attractive appearance, and precise internal design, boasting a very high level of technological sophistication. In summary, it has eight key characteristics and nine advantages. Eight key features: 1. Easy to construct: To build a suspended kiln capable of producing 10,000 bricks per day, 10 people are sufficient; from the start of construction to its operation, only one week is required, and bricks can be fired after just 10 days. 2. Easy to load: Only two people are needed to load the kiln, and one board can be loaded in 20 minutes. 3. Easy to burn: Brick firing relies on natural heating; no mechanical or electrical means for blowing air or extracting it are required. Bricks placed in the kiln can be turned into finished bricks after about ten hours. 4. Easy to remove: A hydraulic pump is used for removing bricks; two people can take ten minutes to remove one brick slab. 5. Easy to assemble: Place the racing car on the track, and pull it gently to secure it in place. Each board holds around 600 bricks, and two people can arrange them neatly in half an hour. 6. Fuel savings: In kilns that operate in a suspended manner, the interior of the kiln remains at a high temperature of around 900 degrees. Once the bricks are baked, the residual heat from them is transferred to the unbaked bricks above, enabling the recycling of heat; as a result, a significant amount of fuel can be saved. 7. Durability: All parts exposed to high temperatures are constructed using refractory bricks, so major repairs are not required for one or two years generally. 8. Easy to operate: The process of firing bricks involves only three steps – loading, unloading, and removing the bricks – and this is repeated daily. The technique is very simple; many women and children here are able to carry out this task, and no accidents have ever occurred. Nine major advantages: 1. Easy to start a business: To establish a brick factory that can produce ten thousand bricks per day, only an investment of over 30,000 yuan is needed for building the kilns, with another amount of over 30,000 yuan as working capital to get the business up and running. (Excludes shaping equipment.) ) 2. Simple technology: Brick firing is carried out using a top-loading and bottom-unloading method with natural burning, and only three to four people are required for the entire process. 3. It requires very little space: To build a suspended kiln capable of producing 10,000 bricks per day, the kiln itself occupies less than 30 square meters; including the area for preparing the brick blanks and the area for taking out the finished bricks, the total area does not exceed three mu. A regular residential house can be used to house such a kiln for brick production. 4. Energy conservation: Coal cinders or coal ash are added as fuel during the production of brick blanks, which results in significant savings in coal usage during firing. Under normal circumstances, the amount of coal required per brick does not exceed half an ounce. 5. Land conservation: Since the internal combustion material used is also a raw material, coal slag or coal ash can be turned from waste into a valuable resource, replacing part of the clay; generally, one truckload of coal slag or coal ash can yield over 10,000 more brick blanks. 6. No environmental pollution: Since this kiln uses only a very small amount of anthracite to burn bricks, and it relies on natural heating, no dust is emitted. So there is basically no pollution at all. 7. Extremely fast results: Starting from the stage of creating brick blanks for kiln construction, finished bricks can generally be seen within 15 days, and the total cost can be recovered in just over a month. 8. High-quality bricks: Bricks fired in suspended kilns are red on the outside and brown on the inside, with a steel core; brown spots appear at the points where bricks touch each other, and sparks are generated when cutting them with a brick cutter. The compressive strength standard is above MU10. 9. Significant benefits: The cost of these bricks is about 30% lower than that of bricks produced in rotary kilns. A suspended kiln capable of producing 10,000 bricks per day can generate 300,000 bricks in one month. At a profit of 0.1 yuan per brick, the monthly profit amounts to 30,000 yuan, while the annual profit exceeds 300,000 yuan. Because one brick-making machine can serve two kilns, if two kilns are built, the annual profit can exceed 600,000 yuan. This kiln is particularly suitable for development zones, reconstruction areas, and highway construction sites; it is also the best choice for those who strive to achieve prosperity through hard work.

Slag brick making involves mixing half slag with half soil, mixing it with water to form a paste, using it to create brick blanks, and then firing them in a simple kiln using firewood. Main raw materials: 1. Furnace ash. In various types of boilers, there is unburned ash, which generally contains 20% to 50% unburned coal fragments and furnace ash. 2. Yellow clay or yellow sandy soil. 3. Water, well water, or river water; it is best to use water that is free of alkalis. Equipment and tools 1. Coarse sieve ； 2. Fine sieve (sieve pores not exceeding 3 millimeters) ； 3. Brick blanks (manual or mechanical) ； 4. Simple kiln: On flat ground with good soil and a level surface, dig a pit that is 2 meters deep, with a diameter of 5 meters at the top and 1.5 meters at the bottom, forming an iron pot shape. At the bottom of the kiln, along the surrounding walls, 5–7 air outlet grooves are dug at equal intervals. Each groove is 30 centimeters wide and 15 centimeters deep, extending all the way to the top of the kiln; above these grooves, a structure made of bricks is built up to a height of 30–35 centimeters. Dig another air intake and ignition passage as well as an ignition door. First, dig an open-sided sloping passage starting 15–2 meters away from the inner wall of the kiln, with a width of 1.5 meters. At the end of this sloping passage that is close to the kiln, dig downward until it reaches the same level as the kiln, while at the other end it should slope upward gradually toward the ground, to facilitate ignition in the next stage. At the bottom of the end where the air inlet flue is at the same level as the bottom of the kiln, a horizontal tunnel 70–80 centimeters high and 50–60 centimeters wide is dug vertically in the direction of the kiln chamber, until the kiln wall is penetrated; this constitutes the air inlet and ignition door. Construct a ventilation and ignition archway: starting from the ignition door, build a passage using stones or bricks that is 70–80 centimeters high and 50–60 centimeters wide, running 75 centimeters long toward the center of the kiln. 5 to 6 circular ventilation and ignition holes with a diameter of 5 cm are evenly drilled in the arch ； 5. Soft hay, short branches, coal, used diesel. Method of production: First, use a coarse sieve to screen the slag; place the larger pieces of slag and coal fragments that are filtered out in one pile. Then use a fine sieve to screen again, collecting the slightly larger pieces of slag and coal fragments in another pile. The diameter of the remaining ash particles should not exceed 3 millimeters – the finer, the better. The ash and soil are mixed in a certain ratio; if unburned coal particles and furnace ash make up 20% to 50% of the ash, then the ratio of furnace ash to soil is 1:2. Mix the ash and soil evenly, soak them in water, let them absorb moisture for half a day, and form them into soft clumps; their hardness is similar to that of ordinary clay bricks. Then, the brick blanks can be made manually or mechanically. The prepared brick blanks are placed on a flat surface to dry for half a day; once they are semi-dry, they are stacked into piles with ventilation openings. The dried brick blanks are placed in layers inside the kiln cave. Press the brick blanks tightly together. At the bottom of the kiln, including the ignition arch, 50 kilograms of soft dry straw are laid from bottom to top, 25 kilograms of dry short branches (10–20 cm long), and 200–250 kilograms of high-quality coal. Finally, spread a layer 5 cm thick of slag and coal cinders sifted through a fine sieve. Every 7 to 8 layers of brick blanks, a layer 2 cm thick of soft straw, along with 2 cm thick of screened slag and coal cinders, is evenly spread. After the brick blanks are raised above the ground level, they are surrounded by large clay bricks that are 60 centimeters long and 10 centimeters thick (made of loam). Leave a gap of 10–15 cm between the adobe bricks and the brick blanks, fill it with large slag and a small amount of large coal cores, and tamp it slightly until all 20,000 brick blanks have been filled. The top of the kiln is covered with 20–30 cm thick layers of slag and coal cinders, without the need to use a core. During ignition, dry wood soaked in used diesel, or soft grass and straw, is used to start the fire at the flame hole; after 15 to 20 days of burning, furnace ash bricks can be produced. Process flow http://www.cnncn.net/img/img/028.jpg

Key points of brick-making using rice husks As a method of using rice husks instead of coal for brick production, it is one of the feasible technical approaches in rural areas to explore and utilize new energy sources, thereby replacing fossil fuels in brick-making. Rural experience has shown that rice husks have a high calorific value of 3,137 kilocalories per kilogram, a low ignition point, and fast burning speed; they can be used not only for firing bricks but also to produce high-quality bricks. Of course, burning bricks with rice husks as fuel is similar in procedure to using raw coal for brick firing, but it differs technically. 　　I. The natural moisture content of the soil used as raw material for brick manufacturing should be kept between 17–18%, while the residual moisture in the brick blanks before they are fed into the kiln should generally not exceed 10%. With a high moisture content, the brick blanks release large amounts of water vapor during preheating in the kiln; if this vapor cannot be removed quickly, it can pose a risk of backdraft. 　　II. The amount of internal fuel to be incorporated during brick manufacturing should be 750 kilocalories per brick. If the amount varies frequently, it will cause large fluctuations in the temperature of the firing zone; an increase in the amount of shells added, along with blockages in the fire pathways at the bottom of the pit, can lead to the formation of bricks with insufficient firing or black spots. 　　III. The encrypted Fire Eye Bridge has been upgraded from four bridge bricks to six, allowing the poured rice husks to spread evenly both above and below. If the packing gap at the fire-eye furnace bridge is too large, combined with factors such as slow combustion, once the rice husks reach the bottom they burn up immediately, resulting in over-ignition in the bottom and middle parts of the kiln, while under-ignition occurs in the top part of the kiln. 　　IV. The gates should be of the bridge-type design; until the stacking method is improved, the maximum height of these gates shall not exceed 5 inches. V. It is advisable to use the “81” brick-assembly method in the kilns, with a density of around 250 bricks per cubic meter inside the kiln. For the insulation and firing zones, 3.4–4 kiln chambers are appropriate, while 5–6 airlocks are suitable for the roof zone. 　　When using rice husk to burn bricks, the following points should also be taken into account: When the brick blanks are in good drying conditions, the proportion of additives used can be increased appropriately (by incorporating half rice husk ash into the brick mixture). By employing super-combustion techniques for brick production, it is possible to significantly increase the output ； During periods of continuous rain, the moisture content of the brick blanks in the kiln is high; in such cases, it is necessary to use raw coal for firing, as raw coal burns more slowly and helps to maintain a stable flame ； Using rice husks to burn bricks requires higher standards in processes such as kiln stacking and firing compared to using raw coal. However, bricks made from clay mixed with 1/4 rice husk ash are first dried in the shade for a day and then exposed to the sun for 5–7 days. A layer of rice husk 30 centimeters thick is placed at the bottom of the kiln, after which a second layer is added, and this process is continued. Approximately 1200 bricks can be baked per kiln. The firing is started using fire from an external source, and after about a week of baking, the bricks are cooled; the method is not difficult to follow.

Baking bricks requires skills and experience! Bricks fired with poor technique will have cracks or be yellow in color! In the north, it’s more common; I used to go to brick kilns to play there as a child.

Baking bricks is a technique, while firing porcelain is an art. Tile is a combination of technology and art.

Not all bricks are fired; environmentally friendly products such as slag-based bricks that do not require firing are being increasingly used, and energy-saving and environmentally sustainable brick types made from power plant fly ash are gradually replacing ordinary clay bricks.

The setting process of cement involves mixing cement with water, after which the clinker minerals rapidly hydrate to produce a large amount of C-S-H gel as a hydration product, as well as Ca(OH)2 and afthite (AFt) crystals； After a certain period of time, C-S-H also grows as long-fiber crystals from the clinker particles, while struvite crystals gradually enlarge and interconnect with each other within the cement paste to form a network structure, thereby generating strength.

Clay bricks are becoming increasingly rare these days; more factories close down, and it is no longer allowed to open new clay brick factories, as they turn large amounts of high-quality soil into bricks, causing severe damage to arable land. The soil used in ordinary clay brick factories is usually dug from farmland, turning what was originally flat land into a landscape full of trenches and ravines.

I see that some bricks these days have many holes in them; I think they’re called porous bricks. Such bricks do not affect the strength of the bricks, but they help save some raw materials and reduce the weight of the walls.

The traditional method of brick manufacturing is very poor, as it destroys a large amount of arable land. It is better to use industrial waste such as slag for brick production, as this enables sustainable and harmonious development!