We first need to introduce the concept of brick-making raw material selection. As we all know, the main raw materials for brick making today are coal gangue, shale, silt, fly ash, slag, etc., and coal gangue accounts for a large proportion of many raw material choices, so what is coal gangue? Coal gangue is the product of the coal seam deposition process in the coal accumulation basin. 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 mixed rocks.

However, due to the different geological age, metallogenic structure, mining method and stacking state of coal gangue, its composition structure and characteristics are very different. 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 technological performance requirements. The above is just an example of coal gangue, a raw material that accounts for a large proportion. By analogy, the selection of all brick-making raw materials should be determined during the project investigation period, which will pave the way for the brick-making process selection of the brick factory. .

Everyone in the sintered brick factory or the industry knows that there are two production processes for producing sintered products using tunnel kilns, namely primary firing and secondary firing. What is the difference between the two, and which process conditions are more advantageous? ? You can see at a glance through the following description.

1. Product output

The overall yield of one-time code burning is lower than that of second code-burning. The reason is that the height of the bricks (layers of bricks) in the first sintering is lower than that in the second sintering (this is mainly limited by the extrusion process of the primary sintering), and the amount of bricks loaded on a kiln car of the same specification is less.

2. Product outline

One-time sintering is suitable for producing solid bricks and load-bearing porous bricks, but not suitable for producing large-hole hollow brick products and decorative brick products, because large-hole, thin-walled products are easily deformed after extrusion under the one-time sintering process. Therefore, the product program scope of the second code burning process is different from that of the first code burning.

3. Raw materials  

The primary sintering has strict requirements on the raw materials, and the raw materials with high plasticity and high drying sensitivity are not suitable for this process, while the secondary sintering process is relatively different. At the same time, one-time sintering is suitable for raw materials with drying sensitivity coefficient < 0.9 and drying shrinkage rate < 50-/0. Through sampling and analysis of raw materials in many areas, from the perspective of raw material drying performance, coal gangue is used as the main raw material. The sintered solid bricks and load-bearing porous bricks should adopt a one-time sintering process. The sintered hollow bricks and thin-walled products with clay (loess) and shale as the main raw materials mostly use the secondary sintering process.

4. Forming

In order to meet the strength requirements of kiln roasting of wet blanks, one-time sintering requires hard plastic extrusion or semi-hard plastic extrusion to avoid deformation of wet blanks under compression, so one-time sintering is suitable for high vacuum and high pressure extrusion; The second sintering is to reload the dried brick into the kiln, and the strength of the brick is greatly improved, so there is no such restriction, and soft plastic extrusion can be used.

5. Power consumption

In terms of power consumption, the author believes that the entire process of the two processes should be fully considered. First of all, starting from the processing of raw materials, one-time sintering has high requirements on the processing of raw materials, so relatively more raw material processing equipment is used. In terms of brick molding, the one-time code burning adopts the hard plastic or semi-hard plastic extrusion process. Due to the different extrusion pressure, the extrusion power consumption of the first code burning is greater than that of the second code burning (soft plastic extrusion), but it reduces the The grouping and racking system in the secondary code burning process, comprehensive comparison, the unit manufacturing cost of this piece is equivalent to the secondary code burning process. In terms of kilns, the primary sintering process reduces the process of the drying car compared with the secondary sintering, thereby reducing the damage to the bricks during the second re-transportation. Burning process to reduce some equipment.

6. Output

The output of hard plastic and semi-hard plastic extrusion is lower than that of soft plastic extrusion. Because the basic molding moisture of one sintering is generally 14%-16%, it must not exceed 16%, because when the natural moisture content of the green body is greater than 16%, the strength of the wet billet is difficult to meet the requirements of manual or mechanical billet, and It also increases the drying shrinkage of the green body. while the second

The natural moisture content of the green body can be relaxed to about 20% by the code burning.

7. Production process

The basic process of the one-time coding process is: extrusion molding - cutting and cutting blanks - blank conveying belt - automatic blank blanking machine/or manual blanking - drying kiln - roasting kiln - product.

The basic process of the secondary coding process is: extrusion molding of all strips and cutting blanks - billet conveying belt - grouping and racking/or manual coding drying car - drying chamber down frame - automatic blank coding machine/or manual coding kiln car _ roasting kiln . product.

It can be seen that the secondary coding process has three more steps than the primary coding process: ① marshalling on the shelf/or manual coding drying car; ② unloading; ③ automatic blank coding machine/or manual coding kiln car, the process is more than the one The code burning is complicated, and the corresponding operators are more than one code burning. Under the premise of the annual output of 50-60 million pieces (standard bricks), there are 6-8 more people per shift.

8. Total investment

4.6rn The investment of the large-section tunnel kiln scheme is relatively high, reaching more than 20 million yuan. This is mainly because the large-section tunnel kiln has a complex structure and high cost, and the price of the kiln car is also high. Not only that, because the kiln car is too large , The corresponding operating system must be set up to move these big guys smoothly, so the price of the entire operating system is also very high.

9. Operating costs

The power consumption of the first code burning is large, but the process links are few; the second code burning has many process steps, but the output is high; the first code burning has less labor, but the output is low, and the second code burning has more labor, but the output is high; the pass rate is also There are differences, the pass rate of the first code burning is slightly lower than that of the second code burning.         tunnel kiln

After the above analysis, the author made the following conclusions:

Advantages of one-time code burning: The production process is simplified, and the total investment in the construction of the factory is reduced by 10%-15% compared with the second code-burning; the labor quota is reduced, production management is convenient, and labor productivity is improved; The second code-burning process is omitted. The marshalling and unloading system, thus reducing the loss of blanks. Disadvantages are also very obvious: one-time sintering requires high raw material preparation and process. Generally, hard plastic and semi-hard plastic extrusion process is used, which is difficult to form, high extrusion pressure and high energy consumption.

The characteristics of secondary sintering: there are no special requirements for raw material preparation, and there are relatively few equipment in the process of crushing and stirring; in terms of brick molding, soft plastic extrusion process is mostly used, and the parameters such as moisture content, drying sensitivity and particle gradation of raw materials are affected. The requirements are relatively low; in terms of brick molding, the secondary firing increases the drying car, a small kiln operating equipment. Although it is an auxiliary equipment, it undoubtedly increases the operating cost of the enterprise.