01 Basic fault information
In November 2009, a company put into operation a clinker production line with a daily output of 5000t/d, which was designed by Tianjin Cement Industry Design and Research Institute and supported by the main engine. TCFC5500 grate cooler adopts technology imported from Danish company to manufacture four connecting rod support structure, as shown in Figure 1. The effective area of grate cooler is 128M ².

Figure 1: working principle of four connecting rods

The width of grate bed of TCFC5500 grate cooler of the company is 12 rows, each row width is 400mm, each row length direction is provided with 8 groups of support points, a set of four connecting rod device is provided with 10 GE35ES joint bearings. TCFC5500 grate cooler lower support bearings total 12×8×10=960 bearings, 960 lubrication points; Lubrication pipeline is complex, the oil quantity of each branch pipe is uneven, and the lack of oil is difficult to judge and deal with.

In the first year of operation, the grate cooler works well. In the second year, the four connecting rod mechanism fault gradually appeared: (1) the hydraulic cylinder seat open welding, broken cylinder head; (2) the four connecting rod bearing is worn and the grate bed elevation decreases; (3) walking beam deviation, sealing leakage; (4) The hydraulic cylinder is overloaded and forced to reduce production. The thin material layer runs and the wind blows through the material layer, resulting in lower secondary air temperature. At the beginning of each overhaul, 6 people should be specially arranged until the end of the overhaul. The maintenance time is ≥1400h/ time. The four connecting rod maintenance space is narrow, the cost is expensive, and the effect is not obvious.

02 Fault analysis of four connecting rod support mechanism

 (1) The working principle of the four connecting rod support mechanism is correct, and it is widely used in the clean air environment such as the dock loading/unloading machine in the harbor.

(2) In each air chamber under the grate bed of the grate cooler in the cement plant, 1-2 fans are used to blast ambient air near the kiln head. It is impossible for the kiln head cover and the seal of the kiln head to avoid dust leakage. The dust is absorbed by the negative pressure at the inlet of the fan and enters into each air chamber under the grate, and all air rooms are “positive pressure” environment.

(3) the grate under positive pressure air flow, containing dust or dust concentration is more and more big, although equipped with “high pressure lubrication system” by oil pressure to resist dust to enter, but nearly thousand “bearing group” in one damage, lubrication system of nearly one thousand line 1 but oil, GE35ES with seals on both sides is not the structure, the event with small probability events structure defects, dust into the bearing is inevitable.

(4) The four connecting rod mechanism is in the environment of positive pressure dust (especially the highly abrasive clinker dust), just like thousands of “woodpeckers” to attack the nearly one thousand bearings of the four connecting rod. Once the dust in the high-pressure airflow enters the four connecting rod bearing, it will lead to bearing abrasive wear.

(5) A group of four-connecting rod mechanism has 10 bearings. If any one of the bearings is worn, the four-connecting rod will lose its original design position and immediately destroy the working principle of the four-connecting rod, leading to a series of faults such as reduced grate elevation, deviation of the grate bed and increased additional load of the hydraulic cylinder.

(6) The company is located in a cold area with a long winter and the temperature at night is often below -40℃. The centralized lubrication system has nearly a thousand tubing and the smallest part is only about 4mm. The poor lubricant fluidity has a negative impact on the life of self-allocating plain bearings belonging to sliding bearings.

03 Installation and effect of roller support mechanism

Based on the above reasons, the leaders of the company made up their mind to dismantle the four connecting rod support mechanism in early 2014. We went into the grate for many times to measure, CAD drawing and assembly on the drawings, and prepared spare parts in advance. The “four connecting rod support mechanism” was removed by taking advantage of the seasonal shutdown in November, as shown in Figure 2. Install the “roller support mechanism” as shown in Figure 3.

Figure 2 four connecting rod support mechanism

Figure 3 roller support mechanism

 (1)TCFC5500 grate cooler, since the removal of the four connecting rod support mechanism in November 2014, was replaced with a roller support mechanism after only 15 days of construction. It has been in operation for nearly 9 years and has realized the “no maintenance” design.

(2) For TCFC5500 grate cooler, the comparison of parameters before and after the grate bed support mechanism renovation is shown in Table 1.

Table 1 Comparison of parameters before and after renovation of grate bed support mechanism TCFC5500

Item        Four connecting rod supporting mechanism     Roller support mechanism

Hydraulic cylinder pressure /MPa  18 (Clinker cannot be pushed away)  12

Clinker daily output /(td)       5000                         5800

Thickness of clinker layer /mm   700(thin layer)           800 (thick layer)

Secondary air temperature /℃    1100                          1190

Failure rate/%                5 Frequent Failures                 0

Annual maintenance cost/ten thousand yuan      50                  0

(3) As can be seen from Table 1, after the transformation, the hydraulic cylinder is no longer overloaded, the operation of thick material layer is realized, the secondary air temperature is increased by 90℃, the calcination capacity of the kiln system is significantly enhanced, and the clinker production is increased by 800t/d.

(4)The four connecting rods is replaced by the roller, the total investment is less than 1 million yuan, and the maintenance cost is saved 500,000 yuan per year. In addition, the economic benefits brought by clinker production increase and trouble-free operation of kiln system are less than one year.

04 Conclusions

As can be seen from the application effect of the company, the advantages of the roller support mechanism are as follows:

(1) The number of lubrication points is reduced by 10 times. The whole grate cooler TCFC5500 is equipped with 96 groups of rollers and 96 lubrication points, and the lubrication pipeline is extremely simple.

(2) The wheel and rail are made of forged low alloy structural steel, the surface is hardened to ensure the hardness HRC≥52 and the design life ≥13 years; Introduced the “no maintenance” design concept.

(3) After the roller installation, the maintenance space is spacious, easy to access and replace the roller components.

(4) The functions of “lateral deviation” and “vertical support” of the walking beam are endowed with rollers. After the integration of the two functions, the support structure is simpler.

(5) The roller base is provided with “high and low adjustable device”, convenient installation and maintenance.

(6) Japan TOPCON AT-B2 automatic level operation and alignment, error control is only 0.7mm/10m, which significantly improves the installation accuracy.

-END-