Abstract: A ball mill is a grinding equipment that consumes a lot of energy. Every one percentage point reduction brings great benefits to the enterprise. The main sliding bearings at both ends of the ball mill have complex structures, difficult maintenance, and high energy consumption. Tianma Mining Company relies on a new product: large diameter rolling bearings to Φ two point seven × The transformation of the sliding bearing of the 3.6m ball mill into a rolling bearing has been estimated to save about 10% energy after one year of operation.
Keywords: ball mill; Large diameter rolling bearings; Babbitt alloy sliding bearings; Energy saving benefits
In order to reduce the consumption of mechanical and electrical energy in ball mills, reduce the operational resistance of ball mills, reduce employee labor intensity, and improve economic benefits, in December 2009, Tongling Nonferrous Metals Co., Ltd. Tianmashan Gold Mining Co., Ltd φ two point seven × The main sliding bearings at both ends of the 3.6m ball mill were renovated and replaced with large diameter rolling bearings. By comparing and analyzing the operating conditions and power consumption in the past three years after the renovation, it was found that maintenance costs were reduced, and the energy-saving effect was good, achieving the renovation effect.
Operation status of sliding bearings before using "babbitt alloy" in ball mill
The existing section of Tianmashan Gold Mining Company φ two point seven × The cylinder of the 3.6m ball mill falls onto two "Babbitt alloy sliding bearings" through the hollow shaft at the inlet and outlet ends. The centerline of the two main bearing seats is 4400mm, the installed power is 400KW, 6KV, the ball mill speed is 18 rpm, the processing capacity (converter slag) is 20-22 tons/h, and the operating load current is 35-38A. The original cooling lubrication "Babbitt alloy sliding bearing" oil tank, due to the wear and tear, aging, and dust pollution of the oil pipe seal, needs to add about 120kg of lubricating oil to the oil tank within about 2 months, and replace it all within 6-7 months. The annual cost of replacing the lubricating oil is about 25000 yuan. During the operation of the "Babbitt alloy sliding bearing", due to the difficulty in controlling the oil pressure and quantity, if there is a shortage or interruption of oil, in a short period of time, the "Babbitt alloy" will melt due to dry wear and heat, resulting in the failure of the sliding bearing and shutdown for maintenance. The sliding bearing needs to be recast with "Babbitt alloy". Before casting the babbitt alloy, all the steel balls inside the ball mill barrel should be poured out, and the ball mill should be lifted up with an oil jack to lift out the "sliding bearing" and remove the burnt babbitt alloy. Newly poured Babbitt alloy tiles need to be repeatedly scraped and ground until they meet the technical requirements before installation. Pouring and scraping are time-consuming, maintenance personnel have high labor intensity, and the ball stopping time is long, which affects production.
Installation of large diameter rolling bearings for ball mills
Pre installation conditions and inspection items for large diameter rolling bearings
Firstly, the centerline of the original inlet and outlet sliding main bearing seat of the ball mill remains unchanged. The diameter of the inlet and outlet hollow shaft of the ball mill is measured at four points on the 400mm contact surface between the sliding bearing and the axial front end, middle end, and rear end of the hollow shaft. This provides processing tolerance for the inner diameter of the tensioning sleeve used for installing large diameter rolling bearings.
2.2 Installation of Tensioning Sleeve for Large Diameter Rolling Bearings
Install the tensioning sleeve on the hollow shaft of the ball mill first, and the inner hole of the large diameter rolling bearing is installed on the outer circle of the tensioning sleeve. To ensure installation concentricity, the tensioning sleeve is processed into a 1:30 taper, and the inner ring of the large diameter rolling bearing is also processed into a 1:30 taper. The tightening sleeve requires a thickness of 25mm at the small end Z and a width of 280. Before installation, it can be disassembled. After installing the tensioning sleeve onto the hollow shaft, use 6 M16 screws on the symmetrically machined tensioning sleeve hole wall in advance × 70 internal hexagonal screws are used to connect the tensioning sleeve, and the rolling bearing is hot installed on the tensioning sleeve. To prevent the loosening of the internal hexagonal screws and the loosening of the tensioning sleeve connection, a half thickness clamp flange is used to connect the tensioning sleeve end face in a staggered manner.
2.3 Preparation for installation of large diameter rolling bearings
According to the size of the bearing, use a 10mm iron plate square oil basin, with 300kg of 220 # heavy-duty gear oil, a handheld thermometer, and sufficient dry wood preparation. A comprehensive inspection is required for lifting equipment with a lifting capacity of 2 tons to ensure lifting safety.
2.4 Installation of large diameter rolling bearings
Before installing large diameter rolling bearings, the Z-end position line of the rolling bearing should be marked on the tensioning sleeve. Firstly, it is necessary to ensure the axial centerline of the bearing seat in and out. Secondly, it is necessary to prevent installation misalignment. After heating and cooling the rolling bearing, the outer diameter of the taper tensioning sleeve is too large, which may cause cracking of the inner sleeve of the rolling bearing due to the small inner diameter of the rolling bearing.
Place the large diameter 120 ℃ bearing flat in an oil basin and add oil to the basin. The oil level should exceed the upper surface of the bearing by about 40-60mm. After measuring the oil surface temperature to 160 ℃ using a handheld infrared thermometer, stop heating and keep it warm for about 1.0 to 1.5 hours. When the oil cools to around 100 ℃, use a lifting device to lift the expansion rolling bearing and quickly install it onto the pre installed tensioning sleeve on the hollow shaft of the ball mill. The axial position is at the marking line of the tensioning sleeve. Then, wrap all the installed rolling bearings with a cloth and slowly cool the bearing temperature. Avoid expanding and cracking the inner ring of rolling bearings due to large temperature differences.
2.5 Inspection of large diameter rolling bearings after installation
After installing the rolling bearing onto two hollow shafts, it is required to check whether there are cracks on the inner and outer rings of the rolling bearing. After no cracks are found, before installing the new rolling bearing seat, check whether the axial centerline of the bearing seat is 5430mm, and check the horizontal height difference between the feed bearing seat and the discharge bearing seat, which is required to be controlled within 0-0.3mm. After the installation and positioning of the ball mill, check the clearance of the rolling bearing rollers and make original records. After the data meets the technical standards, inject about 20-22kg of molybdenum disulfide into the rolling bearing for trial operation. Firstly, conduct a 5-hour idle trial run of the ball mill. After the 5-hour idle run, add 40% of the specified full load ball material for half load operation. After running for 3 hours, add 40% of the full load ball material and continue running for 3 hours. After the above operations have no problems, stop the machine after running at full load for 12 hours and check if the bolts of the main bearing seats at the front and rear ends of the ball mill are loose. If there is no looseness, it can operate continuously. After two months of continuous operation, remove the lubricating grease of the rolling bearing, thoroughly clean the inner ring of the rolling bearing with diesel, blow it with high-pressure air, and then inject new lubricating grease of the same grade.
Comparison of sliding bearing and rolling bearing operation for ball mills
The sliding bearing of the original ball mill is prone to sand and water ingress, and its automatic centering ability is poor. The concentricity of the rotating body of the ball mill is not good, and it is easy to burn or stop production to replace the bearing. The time for grinding and replacing the bearing is long, and the labor intensity of the repair workers is high. Adopting rolling bearings, as they have good sealing and automatic centering function, the concentricity deviation is within the allowable range, ensuring normal operation. After the renovation, the mill cancelled the thin oil lubrication station, and there was no oil stain pollution. It effectively improved on-site cleanliness, resulting in synchronous improvement of economic and environmental benefits.
Energy saving benefits after the transformation of rolling bearings in ball mills
After φ2.7 × 3.6m the transformation of the sliding bearing of the ball mill into a rolling bearing, the motor current of the ball mill decreased by about 10%. The full load of the ball mill: processing 20-22 tons of converter slag per hour, the motor current of the sliding bearing is 32-34A, and the same processing capacity. After installing the rolling bearing, the motor current is 28-31A.
Before renovation Φ2.7 × 3.6m， the synchronous motor current of the ball mill is 32-34A, and after transformation, the motor current is 28-31A, which has a significant energy-saving effect. The specific calculation is as follows (calculated based on 330 days and 24 hours per day):
Annual electricity consumption before renovation: Electricity consumption=1.732×6000×34×330×24÷1000=2798400 degrees.
Annual electricity consumption after renovation:
Electricity level=1.732×6000×31×330×24÷1000=2551400 degrees
Energy savings before and after renovation:
279.84-255.14=24700 KWh (degrees)
The power saving rate is about 10%, and the electricity price is measured at Tianma Company's comprehensive electricity price of 0.66 yuan/KWh. The annual energy savings are:
24.70×0.66=16300 yuan.
After the use of the "large diameter rolling shaft" in the φ2.7×3.6m ball mill, the centralized oil supply station has been cancelled, and a manual pressurized pump with lithium grease lubrication has been used, with refueling once a quarter to improve the working environment and reduce oil pollution. The cost of lubricating oil and oil pumps has been greatly reduced. Based on comprehensive calculations, the annual comprehensive cost savings of using the "large diameter rolling shaft" in the ball mill are about 160000 yuan. The energy-saving effect is obvious, and the investment can be recovered within one and a half years. The transformation has achieved relatively ideal results.
More about Marginal Material Specification Sheet–MG-6:
Material specification sheet – MG-6 is Ball and roller bearing steel according to EN ISO 683-17. Ball and roller bearing steel for balls and rollers of any dimension,rings and discs up to 30mm effective thickness.
