1. Control of the mix ratio of grinding materials
The grinding materials are made of clinker, gypsum, and mixed materials in a certain proportion and ground into cement. Therefore, whether the mixing ratio between them is accurate will directly affect the quality of the cement and mainly depends on the measurement accuracy of the measuring equipment and the materials. The stability of the discharge amount and the sense of responsibility of the operators and on-site feeding personnel, therefore, strengthening the control of the mix ratio of the materials entering the grinding mill, calibrating the scale regularly, and ensuring that various materials are not mixed in the bin are to ensure that the cement quality is uniform and stable, and the cement quality is as planned. It is one of the important links in producing cement of various grades and is also the primary control link in cement production.
2. Grinding cement fineness and ratio control
There are three ways to express the fineness of cement: screen residue, specific surface area, and particle gradation. Increasing the fineness of cement has great benefits in improving the early strength of cement, and also has a certain impact on the later strength. When the quality and ratio of clinker and mixed materials are constant, the cement is ground finely, the specific surface area increases, and the reaction surface in contact with water when the cement is hydrated also increases, thus accelerating the hydration, setting and formation of the cement. hardening process. However, grinding cement too finely will undoubtedly reduce mill output and increase power consumption and product costs. The national standard controls the fineness to no more than 10%, the conch general standard controls no more than 6%, and our company controls no more than 2%.
3. Control of SO3 content of milled cement
The SO3 content in cement reflects the amount of gypsum added when grinding cement. Gypsum mainly plays the role of adjusting the setting time in Portland cement. Its inclusion can inhibit the rapid setting phenomenon caused by C3A in clinker. At the same time, an appropriate amount of gypsum can also improve some properties of cement. When the content in cement is insufficient, it cannot offset the rapid setting phenomenon caused by hydrated calcium aluminate. However, when the SO3 content in cement is too high, secondary crystallization will occur due to the rapid hydration rate of calcium sulfate, which will cause The setting reaction of cement becomes faster. Moreover, when the amount of gypsum is large, after the cement hardens, the excess gypsum will continue to react with calcium aluminate hydrate, and the reactants will cause expansion and damage the hardened cement stone structure (which is what we often say (affects the stability of cement), so the SO3 content in cement should be appropriate and strictly controlled. It affects the setting time and stability of cement. According to the national standard, SO3 is less than 3.5%, and our company controls 2.2±0.3%.
4. Control of the amount of mixed materials added
In cement production, due to the incorporation of mixed materials, on the one hand, certain properties of cement can be improved, on the other hand, increasing cement production can reduce cement costs. On the other hand, it can reduce environmental pollution and turn waste into treasure, which can not only improve economic benefits, but also improve social benefits. Our two-sided cement mill was built based on the fly ash project of Anqing Power Plant.
The amount of mixed materials added is related to the quality of the clinker and the quality of the mixed materials. If the quality of clinker is good, more mixing materials can be added. However, when the amount of mixing materials exceeds the limit, the strength of the cement will decrease significantly. The amount of mixing materials depends on the cement type, clinker quality and mixing properties.
5. Control of coagulation time
Cement setting time is a reflection of cement hydration speed and is related to the amount of gypsum added and the quality of clinker. The setting process is divided into two stages: initial setting and final setting. According to national standards, the initial setting time of the "five major" cements must not be earlier than 45 minutes, and the final setting time must not be later than 12 hours. Generally, the actual setting time is controlled within 1~ 3 hours, final setting time is 3~5 hours.
6. Cement stability control
Cement stability is a physical property that reflects the volume change of cement after hardening.
7. Control of the strength increase rate of milled cement at each age
Generally, the 28-day strength is calculated based on the 3-day strength rule (mainly determined by the strength increase rate of clinker)
8. Control of Cement Caking
One of the more common problems in cement storage is agglomeration. Whether in the warehouse or in packaged finished products, agglomeration will occur due to storage at higher temperatures for a longer period of time. Caking is caused by pre-hydration of cement. The hydration of cement mainly comes from two aspects. 1. Water vapor in the air; 2. Water brought into the gypsum. In addition, excessive moisture in the mixed material will cause excessive moisture in the grinding cement, which will also cause cement agglomeration. In order to prevent cement from agglomerating, the temperature and humidity of the ground cement should be reduced as much as possible and the storage period should be shortened.
9. Management of milled cement
In addition to strict control of milled cement according to various control indicators, the management of milled cement should also be strengthened to ensure the stability of the quality of milled cement. The main thing is to control the entry and exit of the milled cement into the warehouse. It is not allowed to go in and out from the top or bottom, and it is not allowed to be mixed in the warehouse. In addition, there must be a certain amount of storage for the milled cement.