###### Analysis and solution of crack of ATOX50 raw material mill tie rod head

02/14/2021###### Cause analysis and solution of frequency conversion

02/15/2021**01 Existing problems**

The cement combined grinding system of a company is a “one drag two” coil flow process, the roller press is HFCG160×140, the mill is 3.2m×13m, ①3.0m×11m three mill each one, the main production of P•O42.5, P•S•A32.5 cement, the existing problems are:

(1) Over grinding phenomenon is serious. In order to ground the clinker fine, the 45μm sieve is controlled in 5% ± 1%, the specific surface area of 42.5 grade cement is 400m²/kg, the specific surface area of 32.5 grade cement is 450m²/kg, the laser particle size test particle size of 1μm below 10%, the particle size of 3μm below 22% in use, there are problems such as ball, paint non-stick wall and so on.

(2) Low output and high average power consumption when grinding table. In the design to P•O42.5 sets when the output of 150t/h to set, normal production when the production of 155 ~ 160t/h, P•S•A32.5 cement in 165 ~ 175t/h. After putting into production in 2013, the average annual power consumption is 33.4kWh/t, which is in the operation state of low station production and high power consumption.

(3) The roll gap of the roller press is large and the work done is small. HFCG160×140 roller press machine power 2× 1120KW, rated current 74A. In normal operation, the roll gap is about 40mm, and the working current of the motor is about 40A, accounting for only 54% of the rated current, which is far different from the working current of the same type of roller press of many manufacturers, 53 ~ 54A.

(4) It is difficult to build the stable flow silo of roller press. Roller press feeding adjustment of inclined insert plate is manual, because of the raw material particle size, moisture instability need to be adjusted often, time-consuming and laborious, difficult to adjust, cannot be stable warehouse. The feed bin pressure of roller press is not enough, the work fluctuation is large, the working current fluctuates between 32 ~ 58A, the power consumption is high, and the waste is large.

(5) The grinding process is not reasonable.

① Three silos, two double silos plate (with screening), grinding material sieve balance is shown in Table 1. According to the particle size of the grinding material, the whole grinding section is basically in the grinding state, and it is not necessary to divide into three silos. Double compartment plate takes up effective space and increases the mill load; Screening devices are meaningless and increase ventilation resistance. Double compartment plate also has uneven ventilation, uneven material, forced material, speed up the flow rate of the material in the mill, easy to form a “no material” powder grinding blind area after the compartment plate and other drawbacks.

**Table 1 Screen balance of grinding material**

(2) The function of activation liner is small. In the third warehouse of the mill, there are 4-ring frame activation liners with a height of 580mm. Compared with the mill, the type is perpendicular to the plane type of the cylinder. The activation power is low and there is no stopping function.

**02 Improvement Measures**

Through the analysis of the above problems, the following measures are taken:

(1) Add roller press separator. A TS4000 separator is added between the V separator and the cyclone cylinder to extract about 10% of the ultrafine powder directly into the finished product. The fineness of the ultrafine powder extracted is shown in Table 2. The specific surface area of finished cement was reduced to 350m²/kg for grade 42.5 and 400m²/kg for grade 32.5 with the same screen residual control. Laser particle size detection of less than 1μm content of 6%, 3μm content of 14%.

**Table 2 Fineness of ultrafine powder extracted**

(2) Internal transformation of grinding.

(1) To change three storehouses into two storehouses, remove the double storehouse plate for the single storehouse plate (see Figure 1), in the single storehouse plate before and after the end of the additional convex rib reinforcement, played four roles: one is to strengthen the strength of the single storehouse plate; The second is to protect the compartment plate, prolong the service life of the compartment plate; The third is to separate the grinding body to prevent blockage; The fourth is to strengthen the activation effect of the grinding body. The ventilation resistance in the mill is reduced after it is replaced with a single-layer compartment plate. The original fan draution of the two mills was 35 ~ 40Hz, but now it is reduced to 20Hz. Using the displaced space, 2T and 2.8T grinding bodies were added to the two mills.

**Fig. 1 single-layer compartment**

(2) Design and install a new all-area activation device. In 3m×11m mill installation height is 850mm with positive and negative Angle of 5° 6 ring activation lining plate, in 3.2m×13m mill installation 950mm high with positive and negative Angle of 5° 7 ring activation lining plate, activation lining plate is half cabinet type, the lower 400mm high fully enclosed, thickness 20mm. A series of auxiliary activation devices are installed on the activation lining plate to activate the grinding body in multidimensional and multidirectional ways, basically eliminating the “stuck” zone.

The grinding head is equipped with a material resistance device. A material resistance device for leakage and edge discharge is added at the feed slit of the grinding head, and the material is pushed into the grinding by the feed screw to eradicate “punching material”.

(4) Replace grinding end discharge grate plate. The grate plate at the end of grinding is replaced with an anti-blocking type, with a through hole rate of 5%, and the grate is changed from the original 4mm to 6mm. The grate plate is designed to enhance the activation effect of grinding body.

(3) Roller press feeding device. Purchase of electric inclined insert plate feeding device, completely eliminate the edge leakage. Stable storehouse construction, stable work done by roller press, reduce power consumption.

(4) Reduce the roll gap and increase the work done by the roller press. Through the corresponding measures, the roll gap is reduced from the original 40mm to the present 29mm, the working current of the roller press is stabilized at 53 ~ 54A, and the working current of the elevator of the double NSE1000 in the roller press system is reduced from the original 170A to about 145A (motor power is 132KW).

(5) Adjust the filling rate of the second warehouse of the mill. The original is 30%, and the filling rate of the grinding body in the second bin is adjusted to 26% through the analysis and summary after adding the activation device in the whole area. When the output of the original platform is guaranteed, the working current of the mill is reduced from 88A and 106A to 80A and 93A respectively.

**03 Effects**

Through the above measures, the 45μm sieve remaining is still controlled in 4% ~ 6%, the output of grinding machine is stable in P•O42.5 cement 195t/h, P•S•A32.5 cement 230t/h, the monthly average grinding power consumption 28.5kWh/t. The specific surface area decreased from the original 450m²/kg(32.5) and 400m²/kg(42.5) to 400m²/kg(32.5) and 350m²/kg(42.5), respectively. The particle content below 1μm was 6%, and the particle content below 3μm was 14%, which greatly improved the “over-grinding” phenomenon. It can be seen that the addition of semi-final grinding of the separator after V selection has obvious effect on eliminating the over-grinding phenomenon and improving the output and reducing the power consumption. Replacing double-deck spacer plate with single-deck spacer plate can improve the process condition in the mill and provide the possibility to increase the loading capacity. The whole area activation device and the corresponding operation mode can reduce the power consumption by about 10% when maintaining the output of the grinding machine. Reducing roll gap is an effective method to increase the work done by roller press.

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