Cement enterprises generally roughly divide grinding aids into "enhanced type" and "production increasing type". How to choose them? It is generally believed that if you want to increase strength, you should choose "enhanced" grinding aids, and if you want to increase production or save electricity, you should choose "increase production" grinding AIDS. This seems to be justifiable, but sometimes the results are not ideal.
In fact, as far as a grinding system is concerned, the strength, output and power consumption can be transformed into each other. If the cement is ground down a bit, the output and power consumption can be converted into strength. On the contrary, if the cement is ground coarse, the strength can be converted into output and power consumption.
Grinding aids can be divided into "high flow rate type" and "low flow rate type". We should first find out the weakness of the grinding system, and then choose the grinding aid suitable for the case to obtain better results. For example, if the capacity of the discharge hoist is not surplus, and the grinding aid with high flow rate is selected, the system will not only not increase production and save electricity, but also ensure the strength because of the bottleneck of increasing production.
As long as the grinding aid is helpful to make up for the deficiency of grinding system, it can obtain better enhancement or power saving effect. As for whether you want to enhance or want to increase production and save electricity, it can be transformed by fineness. In order to achieve the expected effect of grinding aids in cement production, it is necessary to consider the adaptability and pertinence of grinding aids.
1. Factors to be considered in selecting grinding aids
1) The adaptability of grinding aids to different clinker, different mixtures and their respective moisture content is different.
2) The adaptability of grinding aids to different grinding systems, mills of different specifications and even auxiliary machines of the system is different.
3) The composition and content of grinding aids directly affect the use effect of grinding aids, and too much or too little dosage will also affect the use effect.
4) There are many factors affecting the adaptability of grinding aids, which can not be considered so comprehensively. Therefore, it is necessary to emphasize the test, trial and timely adjustment before and during use.
5) After using some grinding aids in some grinding systems, some properties of cement may be affected, such as poor fluidity of mortar, low enhancement rate of 28d strength, prolongation or shortening of setting time, etc. some grinding aids will lead to poor compatibility between cement and concrete admixtures and affect the quality of concrete.
Although the use of grinding aids can improve production and save energy, it is needless to say that the excessive addition of grinding aids will lead to more concentrated cement particles and increase the porosity of particles accumulation, which is unfavorable to the concrete structure and has caused the aversion of the concrete industry. It is necessary to pay attention to the cement industry and grinding aid industry. We have the responsibility to find effective solutions Give.
If we want to reduce the concentration of particle distribution, the simple is to appropriately reduce the amount of grinding aids, in the play of grinding aids to save electricity effect, and we are not willing to. In order to adjust the adaptability of cement to concrete in foreign concrete industry, some auxiliary cementitious materials, namely mineral admixture, are often added in the preparation of concrete. One of its principles is to increase the fine aggregate of < 10 μ m, especially < 3 μ m, in the powder, so as to make the powder gradation closer to fuller gradation, so as to achieve the purpose of water reduction and densification, namely the so-called "micro aggregate effect".
That is to say, no matter what the composition of cement particles is, as long as there are corresponding admixtures and matching technologies, the unadaptability of cement particle composition can be made up and good concrete can be prepared; that is to say, as long as there are corresponding admixtures and their supporting technologies, the technical progress of cement grinding technology, including the use of grinding aids, can not be restricted by the composition of cement particles. This is the basic principle and development prospect of "separate grinding process" and "admixture correction process" in cement industry and concrete industry respectively.
Unfortunately, the "separate grinding process" of cement industry and the "admixture correction process" of concrete industry have not attracted enough attention of the two industries in China. The adaptability of concrete still depends on the original gradation of cement, which is the reality we are facing.
It is a pity that our cement industry only knows how to complain about the "nitpicking" of the concrete industry. Why can't we add certain mineral admixtures to improve our cement performance by using "micro aggregate effect"? Why can't we create conditions for adding ideal grinding aids?
Of course, "mineral admixture" is best added by the concrete industry, because the best mineral admixture not only depends on the cement, but also related to the performance and particle size distribution of other materials. However, when the concrete industry is not willing to do this work, the cement industry can try to do it first, because it is the cement industry that wants to add grinding aids, not the concrete industry.
The production and mixing of "mineral admixtures", although the cement industry does not play a complete role in the concrete industry, the cement industry can not replace the concrete industry, but the cement industry has incomparable production and mixing conditions than the concrete industry. The main beneficiaries of grinding aids are the cement industry, and the cement industry can take the initiative to take this responsibility.
Precautions for use of grinding aids
1) Keep the mixing amount of grinding aids and grinding materials stable. It is necessary to check the flow rate of grinding aids frequently to ensure the accuracy of the mixing amount. It is necessary to avoid adjusting the amount of grinding aids and increasing the production by a large margin. It should be adjusted gradually in stable production to avoid damaging the grinding condition.
2) Treatment of rough running or full grinding. In case of coarsening of product fineness and grinding fineness (closed-circuit mill), or excessive circulating load leading to full grinding, the amount of grinding aids should be appropriately reduced, or the phenomenon of full bin and coarse running should be adjusted by reducing the output.
3) The particle size and stability of the feed material. The particle size of the feed material should be controlled properly and kept stable. The frequent change of particle size will easily lead to unstable grinding in the mill and affect the use effect of grinding aids.
4) If the coarse bin is easy to be fully grinded and the fine bin is empty, it is generally due to the excessive increase of production, which leads to the insufficient crushing capacity of the coarse bin and the imbalance of the coarse and fine bin capacity. Therefore, the grading of the grinding body of the mill should be adjusted appropriately to increase the crushing capacity of the coarse bin.
5) It is necessary to adjust the operating parameters of the mill system timely and appropriately, such as the wind speed and air volume in the mill, the air volume and speed of the separator, the filling rate of each bin of the mill and the grading of the grinding body.
6) For the enhanced grinding aids, the grinding sound may be particularly loud after the adjustment of the feed materials (when the mixture is properly increased and the output is unchanged). The ventilation in the mill should be reduced to reduce the material flow rate, and the separator should be adjusted to increase the amount of return powder, so that the materials can be fully ground, instead of reducing the grinding sound by increasing the output.
3. Control the entrance of grinding aids
Grinding aids are generally transported and stored in bulk tank cars or barrels. For each batch of grinding aids entering the factory (each tank car is a batch; each batch of barreled grinding aids entering the factory is a batch according to varieties), the quality control personnel and production personnel of the user unit and the representative of grinding aid supplier (or the representative of grinding aid delivery personnel can be entrusted). Sampling requirements:
① Tank car: 2-3 times of random sampling in the unloading process, with a total volume of at least 1000ml;
② Barreled: 3-5 barrels per batch, with a total volume of at least 1000ml.
The sample is extracted into a plastic or glass container, mixed evenly, and divided into two parts. One sample was pasted with retention and sealing strips, and kept as a sealed sample for 90 days. The sample name, number (or batch), sampling time and sampler shall be indicated on the sample strip, and the sealing time and signature of the joint sealing person shall be indicated on the sealed sample strip.
The other sample was filled in for density, pH value detection and small grinding test, and the sample was kept for 40 days. Compared with the inspection results of the product qualification report, the density error is within 0.03g/cm3.
Small amount of additive can improve the stability
There is no doubt that the accuracy and stability of grinding aids have a great impact on its use effect and cost. Due to the difference of management requirements between large-scale cement production and low-dose addition of grinding aids, especially for small amount of grinding aids, the fluctuation of mixing amount is not large, but the relative value is not small, so it is more difficult to control the fluctuation.
Here is a simple and effective auxiliary method, which is to artificially "enlarge" the mixing amount. Through the communication between the supplier and the demander of grinding aids, a kind of low-cost and high-quality additive solution which does not affect the grinding aid and cement production is sought near the user. It is pre mixed into the grinding aid and stirred evenly, and the original grinding aid is used after the measurement is enlarged. In this way, when the original absolute value of fluctuation is unchanged, the relative value of fluctuation is reduced.