Optimization and Application of Wear resistant material for Ball Mill in cement Industry

Date: 2019-07-10 Views:

According to the calculation of the consumption of high chromium ball in each mill calculated by a cement enterprise for several years in a row, the consumption of high chromium ball in each mill is 50g / t for raw meal, 80g / t for cement grinding, 150g / t for tons of cement, and 450t / t for cement enterprises with an annual output of 3 million t cement, plus 600t wear-resistant material consumption for mills such as liner, partition plate and unloading grate plate, which is calculated according to the current high chromium ball price of 6 500 yuan / t. The annual cost of wear-resistant materials is about 3 million yuan, and the cost of per ton of cement is about 1 yuan.

With the continuous expansion of the scale of cement industry in our country, the grinding of materials in the process of cement production has not been completely spherical. Although some new dry kiln grinding raw materials have been used in vertical grinding, most of the other materials, including cement grinding stations, still use a variety of ball mills for grinding, which consumes a large number of metal wear-resistant materials such as grinding body, partition board, liner and so on.

Development process of Metal Wear resistant Materials

The metal wear-resistant materials used in cement grinding have gone through three stages:

The first stage is the wear-resistant material represented by high manganese steel, which is used under the condition of high impact and strong wear, such as the jaw plate of large jaw crusher, the hammer head of large hammer crusher and so on.

The second stage: it is a wear-resistant material represented by nickel hard cast iron, which is still used in vertical grinding roller at home and abroad, but its application and popularization are limited because of its high carbide content, large brittleness, large amount of rare metal material nickel and high production cost.

The third stage: high chromium cast iron and all kinds of alloy steel as the representative of wear-resistant materials, such as ball mill liner, grinding ball, counterattack crusher plate hammer and so on. High chromium cast iron and alloy steel have replaced high manganese steel with excellent performance-price ratio.

Taking the mill liner as an example, high manganese steel was used in 1960s and replaced by alloy steel and high chromium cast iron after 1970s. The third generation wear-resistant materials have their own characteristics and are widely used under different working conditions. Medium manganese steel has higher working hardening ability by sacrificing toughness, which is used for mill liner and small hammer under medium impact condition. High chromium cast iron has many advantages.

The first, the Fe7C3 type carbide can be formed when the chromium content is 12%, the microhardness HV1300 to 1800, the micro-hardness HV800-1 100 of the Fe3C-type carbide in the common white-mouth iron is much higher, and the wear resistance is good;

Secondly, the shape of carbides has changed, which is in the shape of broken net and chrysanthemum, so the toughness of high chromium cast iron is higher than that of reticulated carbides. In addition, the matrix of high chromium cast iron can be obtained from all Austenite to all martensite through different heat treatment processes to expand its application range.

High manganese steel has been used in crushing and grinding equipment in cement industry of our country for many years. The characteristics of high manganese steel are as follows: the toughness is very high, and the work hardening can be produced under the condition of high impact load, which shows excellent wear resistance, but its yield strength is low, plastic deformation is easy to occur in use, arch concave and so on, and the hardness is very low, and the wear resistance is very poor when the impact load is not large enough. Therefore, alloy high manganese steel, medium manganese steel and ultra high manganese alloy steel have been developed on the basis of ordinary high manganese steel. Medium manganese steel is used in the liner of medium and small grinding machine, which increases the life of medium manganese steel by 50% and 80% compared with that of ordinary high manganese steel.

In the low, medium and high-chromium cast iron grinding balls in the late 1980s, the lining plate was put into use successively. The compartment plate made of high manganese steel has good toughness and no fracture, but it is easy to deform after impact, and the slit is narrowed.

For example, Φ 2.2 m&am p ≤ ti mes;6.5 m cement mill, the grate seam should be removed from 12 mm riveting to 3mm~5 mm, after wearing for a period of time, and gas cutting should be used in serious cases.

After the alloy steel liner is used, the grate plate does not deform, the grate joint remains unchanged, and the ventilation in the mill remains normal, but there is also a phenomenon of disconnection.

Existing problems and Solutions

Due to the continuous expansion of cement scale, the new cement grinding station is also springing up after a spring rain, especially some non-cement industry owners who have built new cement grinding station, have just entered the cement industry, lack of technical personnel, no experience, extensive management, unscientific management and use of grinding body, there are some problems, resulting in higher consumption of wear-resistant materials and rising cost in the process of cement grinding. In the management details are not fine, there are different materials of grinding body mixing, inaccurate measurement, supplementary grinding body is not timely, the amount is not calculated, the grinding inner gradation can not maintain a reasonable gradation, resulting in the grinding inner position is too high or too low. The process control is unreasonable.

1. Mixing of grinding materials

As the grinding medium in the process of cement grinding, the grinding body and related wear-resistant materials should be selected according to different grinding materials. Now some small cement enterprises have cast iron balls, low carbon alloy balls, low chromium balls, high chromium balls, some enterprises even own processing cast iron balls. The composition of various materials is different, and the wear resistance is also different. Because of the different processing technology of the grinding body of the same material, the physical properties and application effect of the grinding body are also quite different among different manufacturers. However, in the process of use, especially in the management of small and medium-sized enterprises is not strict enough, there is a mixed use of different materials of grinding bodies, especially the phenomenon of mixed use of grinding bodies of different materials. When the grinding body is supplemented, the grinding bodies of different materials are not purchased at a low cost due to the reasons of funds and the like, and a plurality of grinding bodies with different surface hardness and wear resistance are mixed in the same mill for use.

In the case of Shandong ZL cement plant, there are 5 raw materials and cement mills with a diameter of 2.2m and 6.5m. In 2005, due to the difficulty of capital, the enterprise has a short-term behavior, and a large number of self-refining grinding balls are adopted, although the price is lower, the performance of the grinding ball is poor. Because of the financial distress, the original high-chromium ball can not be added, and the grinding body in the mill can not be completely replaced, and the self-refining ball is completely added on the original high-chrome ball, so that the high-chromium ball and the cast iron ball are mixed and used, and the use effect is very poor. After one month, the grinding body is worn out after one month for each I-bin to be filled into the ball of the large-ball and the second-chamber hammer 50, such as 100,90,80, etc. If the diameter of the big ball is serious and the position is lowered, the diameter of the big ball to be added is 100 mm, and the diameter of the big ball to be added is 90 mm. After two months, the ball can only be used as the ball of the hammer 90 and the hammer 80, resulting in the confusion in the grinding level and the reasonable grading in the mill. The output of the mill is reduced, the consumption is increased, the power consumption is increased (as shown in Table 1), and the annual increase cost is RMB 1.8 million.

The price of self-refining cast iron is only 5000 yuan / t, at that time, the high chromium ball is 7,000 yuan / t, but the self-refining ball is processed by the waste iron of our factory, the material is different, the processing technology is different, the quality of the grinding body is difficult to guarantee: the surface hardness is not up to standard, the surface is different, the wear resistance of the grinding body is not wear-resistant in the course of use, and the wear of the grinding body is fast; in the casting process, there are trachoma in the ball. The self-refining ball and high chromium ball of different materials are mixed in the same silo, the surface and internal performance of the grinding ball are different, the concave shell appears inside, the circle is lost, and there are more cracks at the same time, resulting in large wear and tear of the grinding body. At the same time, cast iron ball and high chromium ball are used together in the same warehouse, and hard eating soft occurs. Phenomenon, low hardness grinding body wear fast, resulting in cement grinding ball consumption increased. This alone, the annual output of 300000 tons of cement costs increased by 1.815 million yuan.

(2) the grinding body does not match the liner, grate plate, etc.

The wear-resistant materials of cement grinding and raw material grinding include grinding body, liner, partition plate, grate plate, etc., which should be strictly matched in the process of use. Some enterprises do not pay attention to, just put into production according to the new design scheme assembly, the material basically matches, that is, the ball and the liner, the partition plate grate plate and so on the performance adapts, but in the later inspection repair adding ball process and the purchase grinding body takes into account the price factor, does not match from the material, such as the high chromium ball in the mill to add the ordinary ball, or the partition board Mn13 to the ordinary cast iron grate plate. In this way, there will be problems in the process of use. Because the grate plate does not match the grinding ball, the partition plate is worn out. Rapid, strength decrease, separator plate fracture, resulting in grinding body string silo, have to stop grinding and pour out all grinding balls, re-gradation, stop grinding time is long, affecting production. There are also lining plates that do not match the grinding body. For example, the lining plate of Mn13 is used in Bin II of Φ3m×9m cement mill of Shandong GF Company for 2~3 years, while ordinary cast iron lining plate is used to level the small corrugated plate only 3 months.

Incorrect metering of supplementary ball.

The supplementary ball of cement mill should be based on more comprehensive consumption statistics, but some enterprises often add ball only according to experience, or according to the estimation of grinding inner warehouse position, which can not guarantee the rationality of all kinds of grinding body gradation. Taking Φ 2.6 m × 13 m cement grinding ball as an example (Table 2), the average unit time output is 35 t / h, according to the ball consumption of 5%, 62500 t cement needs to be produced, the mill runs for 1 785 h, the calendar days are 74 d, and the grinding body needs to be added. This calculation is based on the data obtained under the long-term statistical situation. Different grinders, different technological conditions, different ball consumption, supplementary addition The running schedule of the ball is also different. Therefore, we should strengthen the management of process and technology, some do not measure in production, do not calculate, do not know how much should be made up, how many defects in the mill, how many specifications, only overall calculation, resulting in inaccurate calculation.

(4) the addition of grinding body is not timely.

Some enterprises do not have professional technical personnel to carry out technical data statistics, adding ball time according to the feeling, with the feeling of the mill, by listening to the grinding sound to estimate: feel the output is low, the grinding sound dark add the ball; hear a period of time the grinding sound is not brittle, suspected that the grinding body is insufficient, start adding the ball. This is unscientific. If the ball is not added for a long time, it will cause the grinding body to be insufficient for a long time, the grinding ability will decrease, and the output of the grinding machine will decrease, resulting in the increase of power consumption and cost of cement grinding. If the ball is added ahead of time, the load of the grinding body will be too large and the filling rate of the grinding machine will be high, which will affect the output and product quality of the grinding machine. Therefore, it should be based on the output. The running time is used to calculate the replenishment of the grinding body and to add it in time. In order to ensure the rationality of the grinding body gradation in the mill.

5 incomplete iron removal process

With the addition of industrial waste slag, the amount of slag, steel slag and power plant slag as cement mixture is increasing, especially the content of composite cement mixture reaches 40%. Due to the increase of the amount of mixed materials, the iron composition in raw materials increases. In the process of cement grinding, the grinding difficulty of cement grinding is increased, and the output of the mill is reduced. At the same time, the grinding of grinding body and iron material increases the consumption of grinding body and liner, and the consumption of wear-resistant material increases.

Therefore, the iron remover is installed at the feeding end of the grinding head, and the bulk iron material can be sucked out, and the iron chips, broken iron parts, broken grinding balls, broken liner screws, chains and other waste parts that fall into the process of equipment maintenance can also be sucked out; an iron remover can be added before the grinding material enters the powder separator, and the large pieces of iron can be broken and the small particles of iron material after grinding can be sucked out.

These measures can not only reduce the accumulation of materials in the mill, prevent blocks from blocking the partition plate and grate plate, ensure the ventilation in the mill and the flow rate of the material in the mill, but also avoid the circulation of iron parts in the mill system, wear the blade of the separator, and ensure the powder separation efficiency of the separator.

For example, Shandong DY Cement Plant is a grinding station with an annual output of 1,000,000t. Φ4.2m×13m cement mill is used with Φ1400~800 roller press. Iron separator is installed at the grinding head, but no iron removal device is installed at the end of the mill. The coarse powder separator is conveyed into the grinding head by air chute. As slag is used as the mixed material, there are many fine powder iron particles, which will not be blown up in the air chute, resulting in blocking the material. Each time, shutdown shall be shut down every time, which seriously affect the production.

6 broken ball and deformed ball are not picked out in time

In the grinding process, due to the uneven chemical composition of the grinding body and unstable processing technology, the hardness of the surface is different from that of the inner layer. There are deformed balls, ruptured hemispheres, etc., which will be stuck in the grate seam, the long-term honed surface will be sunken, and half of the irregular hemispheres will be found after inspection and selection. These broken balls, deformed balls accumulated in the warehouse to a certain amount should be picked out in time to prevent stuck in the grate seam, affecting the ventilation of the mill.

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