We first need to introduce the concept of selecting raw materials for brick making. As is well known, the main raw materials for brick making nowadays are coal gangue, shale, silt, fly ash, slag, etc., and coal gangue accounts for a large proportion in many raw material choices. So what is coal gangue? Coal gangue is a product of the sedimentation process of coal seams in coal accumulating basins. It is a combustible ore formed by the combination of coal forming materials and other sediments. It is actually a mixture of carbonaceous mudstone, carbonaceous sandstone, and other rocks mixed in.
However, due to the different geological ages, mineralization structures, mining methods, and stacking states of coal gangue, its composition, structure, and characteristics vary greatly. Therefore, not all coal gangue can be used to produce sintered products. The raw materials suitable for making bricks must meet the characteristics of their mineral composition, chemical composition, and process performance requirements. The above is just an example of using coal gangue, which accounts for a large proportion of raw materials, and so on. The selection of all brick making raw materials should be determined during the research period, which also lays the foundation for the selection of brick making processes in brick factories.
As people in the brick sintering factory or industry know, there are two production processes for producing sintered products using tunnel kilns, namely primary code firing and secondary code firing. So what is the difference between the two, and which process condition is more advantageous? Through the following explanation, everyone can see at a glance.
1. Product output
The overall output of a single code burn is lower than that of a second code burn. The reason is that the height (number of brick layers) of the first brick firing is lower than that of the second brick firing (mainly limited by the extrusion process of the first brick firing), and the amount of bricks loaded on the same specification kiln car is less.
2. Product Guidelines
A single firing process is suitable for producing solid bricks and load-bearing porous bricks, but not very suitable for producing hollow brick products and decorative brick products with large holes, because thin-walled products with large holes are prone to deformation of the brick body after extrusion under the conditions of a single firing process. Therefore, the product scope of the secondary code burning process is different from that of the primary code burning process.
3. Raw materials
The first batch of code burning has strict requirements for raw materials, and materials with high plasticity and high drying sensitivity are not suitable for this process, while the second batch of code burning process is relatively different. At the same time, one-time code firing is suitable for raw materials with a drying sensitivity coefficient<0.9 and a drying shrinkage rate<50-/0. Through sampling and analysis of raw materials in many regions, from the perspective of raw material drying performance, sintered solid bricks and load-bearing porous bricks mainly made of coal gangue should adopt one-time code firing technology. However, sintered hollow bricks and thin-walled products mainly made of clay (yellow) soil and shale are often produced using secondary code firing technology.
4. Forming
In order to meet the strength requirements of wet billet kiln firing, a one-time code firing requires hard plastic extrusion molding or semi hard plastic extrusion molding to avoid deformation of wet billets under pressure. Therefore, one-time code firing is suitable for high vacuum and high-pressure extrusion molding; And the secondary code burning is to re load the dried brick body into the kiln, greatly improving the strength of the body, so there is no such limitation, and soft plastic extrusion molding can be used.
5. Power consumption
In terms of power consumption, the author believes that the entire process of both processes should be fully considered. Firstly, starting from the processing of raw materials, a one-time code burning has high requirements for the processing of raw materials, so relatively more raw material processing equipment is used. In terms of brick forming, the first batch of brick firing adopts hard plastic or semi hard plastic extrusion technology. Due to the different extrusion pressures, the extrusion power consumption of the first batch of brick firing is greater than that of the second batch of brick firing (soft plastic extrusion), but it reduces the grouping up and down frame system in the second batch of brick firing technology. Overall, the unit manufacturing cost of this area is comparable to that of the second batch of brick firing technology. In terms of kilns, the one-time code burning process reduces the number of drying car steps compared to the second code burning process, thereby reducing damage to the bricks during the second transportation process. Other kiln operating equipment also requires less equipment for the one-time code burning process compared to the second code burning process.
6. Production volume
The output of hard plastic and semi hard plastic extrusion molding is lower than that of soft plastic extrusion molding. Because the basic moisture content for a single molding process is generally 14% -16%, it must not exceed 16%, because when the natural moisture content of the billet is greater than 16%, the strength of the wet billet is difficult to meet the requirements of manual or mechanical molding, and it also increases the drying shrinkage of the billet. And the second time
The natural moisture content of the billet can be relaxed to around 20% by code burning.
7. Production process
The basic process of a code burning process is: extrusion molding - cutting strips and billets - transporting the billet belt - automatic coding machine/or manual coding - drying kiln - roasting kiln - product.
The basic process of secondary code burning technology is: extruding and forming all strips and cutting blanks, transporting the raw materials with a belt, grouping them and putting them on the rack/or manual code drying car, placing them on the rack in the drying room, automatic code machine/or manual code kiln car, and baking kiln. Product.
It can be seen that the secondary code burning process has three additional steps compared to the primary code burning process: ① grouping and shelving/or manual code drying car; ② Take down; ③ Automatic coding machine/or manual coding kiln car, the process is more complex than one-time coding burning, and there are more operators than one-time coding burning. Under the premise of an annual output of 50-60 million pieces (standard bricks), there are 6-8 more people per shift.
8. Total investment
The investment for the 4.6rn large section tunnel kiln scheme is relatively high, reaching over 20 million yuan. This is mainly due to the complex structure and high cost of the large section tunnel kiln, as well as the high price of the kiln car. Moreover, due to the large size of the kiln car, corresponding operating systems must be set up to smoothly move these large objects, resulting in a high price for the entire operating system.
9. Operating costs
A single code burn consumes a lot of power, but there are few process steps involved; There are many steps in the secondary code burning process, but the output is high; The first batch of code burning requires less labor but has a lower output, while the second batch requires more labor but has a higher output; There are also differences in the pass rate, with a slightly lower pass rate for first pass code burning compared to second pass code burning. Tunnel kiln
After the above analysis, the author has made a rough summary as follows
The advantages of one-time code burning: it simplifies the production process and reduces the total investment in building a factory by 10% -15% compared to second time code burning; Reduced labor quota, facilitated production management, and improved labor productivity; Omitting the grouping loading and unloading system in the secondary code burning process reduces the loss of the billet. The disadvantages are also very clear: a one-time code burning requires high requirements for raw material preparation and process, generally using hard plastic and semi hard plastic extrusion processes, which are difficult to form, high extrusion pressure, and high energy consumption.
The characteristics of secondary code burning: there are no special requirements for raw material preparation, and there are relatively few equipment during the crushing and mixing processes; In terms of brick forming, soft plastic extrusion technology is often used, which has relatively low requirements for parameters such as moisture content, drying sensitivity, and particle size distribution of raw materials; In terms of brick forming, the addition of a drying car as a small kiln operating equipment in the secondary firing process undoubtedly increases the operating costs of the enterprise, although it is an auxiliary equipment.