Application of the hottest wear-resistant ceramics

Application of wear-resistant ceramics in fan rotors of power plants

I. preface

the main fans used in thermal power plants are induced draft fans, powder exhausters and blowers. As one of the main auxiliary machines of the power plant, the induced draft fan and pulverized coal exhauster have seriously affected their output and brought frequent renewal and maintenance due to wear, which has become one of the hidden dangers of the safe operation of boilers in thermal power plants. For many years, although many surface strengthening methods have been used, including surfacing wear-resistant materials, thermal spray welding, surface coating with various polymer coatings, surface quenching, the effect is not very ideal. In view of the characteristics that the wear-resistant adhesive mainly uses the high bonding strength of the adhesive to bond the wear-resistant granular materials, and the wear-resistant force is provided by the wear-resistant materials, it is considered to use the adhesive to bond the wear-resistant ceramics for the wear-resistant and wear-resistant of the fan impeller. This technology has been applied in dozens of impellers of powder introduction and discharge fans. The longest service time has reached more than 3 years, and good economic benefits have been achieved

II. The feasibility of using ceramic sheets on fan impellers

ceramic sheets on fan impellers should first ensure that ceramics have excellent wear resistance, and then require ceramics and metal matrix to enjoy a preferential price: 1800 yuan/person good bonding performance, that is, the adhesive has good bonding strength and high temperature toughness

for the use of fan impeller, cold pressed sintered alumina ceramics are used. After measurement, its hardness can reach more than hra88, and its wear resistance is at least 5 times higher than that of high chromium cast iron, and more than 10 times higher than that of ordinary spray welding process. Therefore, the wear resistance can fully meet the requirements of general fan life. Because of the excellent wear resistance of ceramics, the thickness of ceramic sheet is generally only 1.5mm

the self-made adhesive is used, and the main performance indicators are as follows:

the tensile strength (metal metal) is 50MPa (room temperature) and 20MPa (150 ℃)

the shear strength is 28Mpa (room temperature) and 8Mpa (150 ℃)

when the induced draft fan works under the high temperature of nearly 180 ℃ and the high-speed scouring air flow with hard particles, it is required that the adhesive must have high temperature resistance, as well as certain shear strength and aging resistance. The coefficient of thermal expansion of ceramics is only half that of metals, so it also needs adhesives with good toughness. Relatively speaking, the rotating speed of the powder exhauster is up to 1500 R/min, and the ceramic sheets will be subjected to greater centrifugal force

after calculation, at 150 ℃, when the induced draft fan rotates at 960r/min, a piece of 100 × one hundred × The centrifugal force of 3 (mm) ceramic chips is 1.13mpa, and the shear resistance provided by the adhesive is 150MPa (150 ℃), which is 132 times the centrifugal force. It can be seen that the adhesive has a very high adhesive safety coefficient. For the powder exhauster, the adhesive force provided by the adhesive will also be more than 100 times the centrifugal force. It can be seen that the strength of adhesive has very high reliability

III. test conditions

the first test was carried out on unit 5 of Datong No. 1 power plant. This type of fan is a double suction structure with flat blades. The specific parameters are as follows: outer diameter Φ 2200, medium temperature 170 ℃, rotating speed 960r/min. There are 24 double row blades in total, with a blade thickness of 8mm. Another 10mm thick steel plate is used as the lining plate and connected with the blade with bolts. The service life of the lining plate is half a year (worn through). The thickness of the middle disc of the impeller is 20mm, and the service life is one year (a total of 12mm wear on both sides). The overall service life is one year, and it is replaced once a year

since this is the first time to conduct the test, for the sake of safety, 24 lining plates are reserved and only ceramic sheets are pasted on the outlet half with the most serious wear. The size of the ceramic blocks is 10 × ten × 3 (mm) and cured in a self-made oven. 3mm porcelain chips are pasted on both sides of the middle plate, which will cure naturally at room temperature

the fan was put into operation in May 1994 and tested in October 1995. The ceramics on both sides of the impeller hub were intact, without any falling off and blocking. The average wear was less than 0.1mm. According to the actual operation time, the maximum wear per year was 0.1mm. The wear amount is 1/30 of that before the ceramic tile. Among the 24 lining plates, 3 porcelain chips on the lining plates fell off during operation, and the rest were intact. After preliminary analysis, it is believed that the falling off of porcelain chips is caused by the gelatinization of the adhesive layer caused by local overheating (250 ~ 300 ℃) in the oven during drying and heating. Take advantage of the intermediate shutdown opportunity to continue to put into operation after repair, and there is no falling off phenomenon

by analyzing the wear of ceramic chips at different parts, it is found that the average wear of ceramic chips on the plane along the direction of air flow is less than 0.1mm. The closer it is to the outer circle of the impeller, the more serious the wear is, with an average wear of 0.2mm, which is significantly more serious than that at both sides of the hub of the middle disk. This is because the closer to the outer circumference of the impeller, the greater the air flow velocity, and the more serious the wear

compared with the direction along the air flow, the wear of porcelain chips along the vertical direction of the air flow is the most serious, up to 1 ~ 3mm. In fact, this is in line with the ceramic erosion mechanism, that is, the greater the incidence angle of the air flow, the more serious the wear. Moreover, due to the eddy current formed at the joint, the wear of the metal matrix along the joint is the most serious, and even the metal lining plate can be worn through, so that the ceramics are completely suspended, causing some porcelain chips to fall off at the windward joint

the tensile strength test was carried out on the lining plate and ceramic chips. The results showed that after one year of operation, the residual shear strength of the adhesive was still 10. The new standard of general Portland cement and the replacement method of cement glass capacity reduction MPa (150 ℃) were strictly followed. At this time, the centrifugal force is still 1.13mpa. According to the 10% annual aging rate, the residual strength of the adhesive after 5 years is 8.6mpa, which is still much higher than the centrifugal force

in order to further test the performance of the adhesive, two induced draft fans of the same model were pasted in May 1995, and the lining plate was removed and directly adhered to the blade. T-shaped porcelain chips were used on the windward side, further reducing the possibility of airflow scouring the bottom metal. After 600 days of continuous operation, the ceramic sheet is in good condition, the substrate does not fall off, and the average wear is less than 0.2mm

IV. usage in other power plants

1 Beijing Datang Gaojing Power Plant: because the electrostatic precipitator of the plant has not been put into operation, the dust removal efficiency is not high, resulting in serious wear of the induced draft fan impeller. The wear-resistant alloy coating with surface thermal spray welding hardness of more than HRC60 has a service life of only 4 months. Impeller diameter of this type Φ 2100, double suction so that a total of 24 blades are formed when releasing the profile roll. In October, 1996, the factory used ceramic adhesive technology to paste ceramic sheets directly on the thermal spray welding layer of the blade for anti-wear treatment. After nearly two years of operation, the wear was less than 0.2mm, but because it was directly pasted on the spray welding layer, some ceramic sheets fell off and were replaced. Through this test, the factory pasted ceramic sheets on the impellers of another four induced draft fans. At present, the operation has reached more than 3 years, and the service life has been increased by more than 5 times

2. Zhengzhou thermal power plant: the powder exhauster is a forward single suction impeller with impeller diameter Φ 1700, 16 blades in total. Due to serious wear, the method of spacer pile has been used as a wear-resistant measure for a long time, but the service life is always only 4 months. In 1996, ceramic was pasted on the impeller of a powder exhauster and put into operation. As a comparison, two sets of wear-resistant ceramic coatings were applied, and one set of surfacing a new type of wear-resistant electrode. After four months of operation, the inspection found that the wear of ceramic pieces is very slight among college students who are now studying in Colleges and universities, and they can hardly see any wear. Especially at the entrance, the part without sticking ceramic has been shortened by nearly 50mm, but one of the surfacing machines has been worn out and must be repaired before it can continue to operate. The one coated with wear-resistant ceramic coating is also close to wear through and must be repaired before it can continue to operate. Due to the good wear resistance of the pasted ceramics, the factory has pasted all the impellers of the powder exhauster with ceramics, which is expected to increase the service life by more than 6 times

3. Zhanjiang Power Plant: the impeller of the powder exhauster is a centrifugal impeller produced by Chengdu Electric Power Machinery Factory. Previously, the method of thermal spraying was used for anti-wear treatment, and its service life is only about one year. The replaced impeller can only be treated as waste. At the end of 1996, the factory pasted ceramics on the impellers (two old and two new) of four powder exhausters after investigation. In the spring of 1997, ceramic was pasted on the impeller of No. 7 fan (4 new and 3 old). In the past three years of operation, the ceramic wear on the surface of other impellers is very slight, except that some ceramics fall off due to the serious wear of the original matrix (the surface of the matrix has been uneven) on the impellers of two old fans. During the overhaul in October, 1999, four of them removed the impeller for other reasons. After inspection, only a small amount of ceramic chips fell off on one of them, and the other three were intact. After simple repair, it is expected to be used for at least another 3 years. In recent years, ceramic paste and wear-resistant treatment have been carried out for nearly 20 fan impellers of Zhanjiang Power Plant

the actual operation of dozens of fan impellers shows that pasting ceramic anti-wear is a reliable and effective measure. As long as the construction is careful and the process is strictly followed, the ceramic pieces can be guaranteed not to fall off. Due to the particularity of fan impeller, the successful application in fan impeller also provides a reliable reference value for the application in other parts, and provides another effective wear-resistant and wear-resistant measure for thermal power plants. (end)