Application of high quality bentonite and coal powder in wet sand

one. Preface wet sand is the main additive bentonite, coal powder, its quality plays a vital role in the quality of wet sand. For many years, our factory has been using ordinary bentonite and coal powder, and castings often have defects such as scrapping and sticking sand. From the beginning of this year, after the use of high-quality bentonite and pulverized coal in our factory, the defects of castings and sand-bonding were reduced by more than 80%. Although high-quality bentonite and coal powder are used, the unit price is higher than that of ordinary bentonite and coal powder. However, due to the decrease in the amount of addition, the amount of new sand is reduced, the casting defects are reduced, and the casting cost is greatly reduced, which brings obvious economic benefits to the factory.
two. Production conditions and high-quality bentonite, pulverized coal and ordinary bentonite, coal powder performance comparison Production conditions The factory uses a high-efficiency double-rotor sand mixer S1420D sand mixer and a balance wheel type S124 sand mixer. The new sand uses 75/150 mesh Jiangxi Duchang sand, and the bentonite uses the high-quality bentonite Pda10 of Liaoning Jianping Dongming Mining Co., Ltd. The pulverized coal uses No. 15 high-efficiency coal powder of Henan Pingdingshan Xianghe Building Materials Co., Ltd.
The sand mixing process is as follows:
Add water, mix, mix, mix 5% new sand + old sand → 0.3% pulverized coal + 0.8 bentonite → adjust water → sand 5-10s 100-120s 5-10s
2. The performance of high-quality bentonite and ordinary bentonite The performance of high-quality bentonite and ordinary bentonite used in our factory is shown in Table 1.

3. Performance comparison between high quality coal powder and ordinary coal powder The performance of high quality coal powder and ordinary coal powder used in our factory are shown in Table 2.

three. Results and analysis Compared with high-quality bentonite and pulverized coal before and after the performance of sand, we have been using ordinary bentonite and pulverized coal. In order to ensure the certain strength and styling performance of the sand, reduce the occurrence of castings and sticking sand defects, it is necessary to increase bentonite and coal. The amount of powder added. For a long time, the mud content of the molding sand has risen sharply. Even if the moisture of the molding sand is as high as 6%, the compacting rate of the molding sand is low, the air permeability is low, the sand feel is still dry, the die-forming performance is poor, and it is not easy to repair. Castings are often scrapped in batches due to defects such as clamping and sticking. At the beginning of this year, after the high-quality bentonite and pulverized coal were used in our factory, the mud content of the old sand was greatly reduced, and the performance of the molding sand was significantly improved (see Table 3). In the first half of this year, compared with the second half of last year, the defects of castings and sand sticks decreased by more than 80%.

2. The effect of the quality of bentonite on the quality of wet sand As can be seen from Table 1, the amount of blue and swelling of high-quality bentonite is higher than that of ordinary bentonite. This is because the amount of blue absorbs the purity of bentonite, and the swelling value reflects the degree of bentonite. The higher the amount of bentonite is, the higher the purity of bentonite is, and the higher the wet adhesion of bentonite is. The higher the swelling value of bentonite is, the higher the degree of swelling of bentonite is, and the higher the heat-wet adhesion of bentonite is. The quality of bentonite concerned by wet sand foundry is mainly the wet cohesive force and the hot wet cohesive force. Therefore, only bentonite with high blue absorption and swelling value is the ideal additive for wet sand. In the experiment, I found that some bentonites have a high amount of blue absorption, which is more than 32g/100g, but the swelling value is very low, less than 36ml/3g, which indicates that the swelling is not fully sodiumized but the purity is high. Not suitable for wet sand. At the same time, some bentonites have a high swelling value of more than 701/3g, but the amount of blue is not less than 18g/100g, indicating that these sodium-based bentonites are not high in purity, but only after sufficient sodiumation, and are not suitable for wet sand. use. The author believes that only bentonite with a blue amount and a swelling value of “double high” can be called high-quality bentonite, which is suitable for wet sand production. Our factory standard stipulates that the amount of bentonite blue absorption is ≥32g/100g, and the swelling value is ≥70ml/3g.
3. The effect of the quality of pulverized coal on the quality of wet sand As shown in Table 2, the difference between high-quality pulverized coal and ordinary pulverized coal is that the former has low ash content; high volatile content and high grade of coke slag. If the ash content of the pulverized coal used in the wet sand is high, the mud content of the molding sand will increase, and the castings are prone to defects such as pores and sand holes. The pulverized coal should have a sufficiently high volatile content, which is necessary to form a reducing atmosphere in the mold and to produce bright carbon. The coke slag characteristics of pulverized coal have not been paid enough attention by many foundry manufacturers in the past. The pulverized coal with only 1-2 grades of coke slag has been used in large quantities on wet sand. In recent years, casting experts have used pulverized coal on wet sand. The slag characteristics opinion was agreed, and it is generally considered that the coke characteristics suitable for wet sand pulverized coal are applied to grades 5-6. Therefore, the pulverized coal standard of our factory should be less than 10% ash, the volatile content should be controlled between 30-38%, and the characteristic grade of coke slag is 5-6.
4. Economic benefits of using high-quality bentonite and coal powder When starting to use high-quality bentonite and coal powder, many manufacturers are often worried that the cost will rise. The opposite is true, mainly in the following three areas.
(1) The use of high-quality bentonite and coal powder will reduce the cost of raw materials due to the reduction in the amount of addition.
(2) Due to the use of high-quality bentonite and coal powder, the amount of added is reduced, and the amount of mud in the old sand is reduced. It is not necessary to add too much new sand to dilute the mud content of the sand, and only need to add new sand lost in the production process.
(3) After using high-quality bentonite and pulverized coal, the defects of the castings and the sand sticks are reduced.
four. Conclusion After using high-quality bentonite and coal powder, the mud content of the old sand decreased from 20-22% to 14-16% now; the moisture of the molding sand is greatly reduced, the wet compressive strength and air permeability are obviously improved, and the compacting rate of the sand is ideal. State; casting defects, sand-bonding defects decreased by more than 80%; production costs have not increased, and considerable economic benefits can be achieved.
It is recommended that the additives of wet sand should be selected from high-quality bentonite with a blue amount and a swelling value of “double high” to have high-quality coal powder with low ash content, moderate volatile content and coke slag grade 5-6.

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