Abstract: Ball mill is a grinding equipment with high energy consumption. Every percentage point reduction brings great benefits to the enterprise. The structure of the main sliding bearings at both ends of the ball mill is complex, difficult to maintain, and consumes a lot of energy. Tianma Mining Company relies on a new product: large-diameter rolling bearings, to transform the sliding bearings of the Φ 2.7 × 3.6m ball mill into rolling bearings. After one year of operation, it has been calculated that the energy saving is about 10%.

Keywords: ball mill; Large diameter rolling bearings; Babbitt alloy sliding bearings; Energy saving benefits

In order to reduce the energy consumption of the ball mill, decrease the operating resistance of the ball mill, reduce the labor intensity of employees, and improve economic benefits, in December 2009, Tongling Nonferrous Metals Co., Ltd. Tianmashan Gold Mining Company renovated the main sliding bearings at both ends of the φ 2.7 × 3.6m ball mill, replacing the existing sliding bearings with large-diameter rolling bearings. By comparing and analyzing the operating conditions and electricity consumption over the past three years after the renovation, the maintenance costs have been reduced, and the energy-saving effect has been better, achieving the renovation effect.

1. The operating status of the ball mill using "Babbitt alloy" front sliding bearings

Tianmashan Gold Mining Company currently has a section of ball mill cylinder with a diameter of 2.7 × 3.6m, which falls onto two "Babbitt alloy sliding bearings" through hollow shafts 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 revolutions per minute, the processing capacity (converter slag) is 20-22 tons/h, and the operating load current is 35-38A. The original cooling and lubrication "Babbitt alloy sliding bearing" oil tank needs to be replenished with about 120Kg of lubricating oil after about 2 months due to oil pipe seal wear, leakage, aging, and dust pollution. It will be replaced in 6-7 months, and the annual cost of replacing lubricating oil is about 25000 yuan. During the operation of the "Babbitt alloy sliding bearing", it is difficult to control the oil pressure and quantity. Once there is a shortage or interruption of oil, the "Babbitt alloy" will melt due to dry wear and heat, causing the sliding bearing to fail and stop for maintenance. The sliding bearing needs to be re cast with "Babbitt alloy". Before casting the new Babbitt alloy, all the steel balls in the ball mill cylinder should be poured out, and the ball mill should be lifted up through an oil cap. The "sliding bearing" should be lifted out to 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 ball stopping time is long, which affects production.

2. Installation of large diameter rolling bearings for ball mills

2.1 Pre installation conditions and testing items for large-diameter rolling bearings

Firstly, the centerline of the sliding main bearing seat of the ball mill remains unchanged, and the diameter of the hollow shaft of the ball mill's inlet and outlet is measured. Four points are measured on the 400mm contact surfaces between the sliding bearing and the front, middle, and rear ends of the hollow shaft, providing machining tolerances for the inner diameter of the tension 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 on the hollow shaft, connect the tensioning sleeve with 6 M16 × 70 hexagon socket screws on the symmetrically processed hole wall of the tensioning sleeve. The rolling bearing is hot installed on the tensioning sleeve to prevent the loosening of the hexagon socket screws and the loosening of the tensioning sleeve connection. Then, use a half thickness clamp flange to connect the end face of the tensioning sleeve in a staggered manner.

2.3 Preparation work for installation of large diameter rolling bearings

According to the size of the bearing, use a 10mm iron plate square oil basin, 300Kg of 220 # heavy-duty gear oil, a handheld thermometer, and sufficient dry wood preparation. The lifting equipment with a lifting capacity of 2 tons requires a comprehensive inspection to ensure lifting safety.

2.4 Installation of large diameter rolling bearings

Before installing large-diameter rolling bearings, it is necessary to mark the Z-end position line of the rolling bearing on the tensioning sleeve. This is to ensure the axial centerline of the bearing seat and prevent installation misalignment. After heating and cooling the rolling bearing, if the outer diameter of the tapered tensioning sleeve is too large, it 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 the oil pan, add oil to the oil pan, and the oil level should exceed the upper surface of the bearing by about 40-60mm. After measuring the oil surface temperature to 160 ℃ with a handheld infrared thermometer, stop heating and keep it warm for about 1.0-1.5 hours. When the oil cools down to about 100 degrees, use a lifting device to lift the expansion rolling bearing and quickly install it onto the hollow shaft of the ball mill. Install the expansion sleeve on the hollow shaft in advance, with the axial position marked by the expansion sleeve line. Then wrap all the installed rolling bearings with plain cloth and slowly cool the bearing temperature. Avoid causing the inner ring of the rolling bearing to swell and crack due to temperature differences.

2.5 Inspection of large diameter rolling bearings after installation

After installing the rolling bearing on two hollow shafts, it is required to check whether there are cracks on the inner and outer rings of the rolling bearing. If there are no cracks, 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 feeding bearing seat and the discharging bearing seat, which should be controlled within 0-0.3mm. After installing the ball mill, check the clearance between 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 bearings to prepare for trial operation. Firstly, conduct a 5-hour test run of the ball mill without load. After running for 5 hours without load, 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 another 3 hours. After running at full load for 12 hours without any problems, stop the machine and check whether 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 run continuously. After running continuously for two months, 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.

3. Comparison of the operation of ball mill sliding bearings and rolling bearings

The spherical sliding bearings of the original ball mill are prone to sand and water ingress, with poor automatic centering ability. The concentricity of the ball mill's rotating body is also poor, and it is easy to cause tile burning, production stoppage, and tile replacement. The time for tile research and replacement is long, and the labor intensity of repair workers is high. We use rolling bearings because they have good sealing and automatic centering function. The concentricity deviation is within the allowable range, which can ensure normal operation. After the renovation, the thin oil lubrication station of the grinding machine was eliminated, and there was no oil stain pollution, which effectively improved the site cleanliness and simultaneously improved the economic and environmental benefits.

4. Energy saving benefits of ball mill rolling bearings after renovation

After the transformation of the sliding bearing of the φ 2.7 × 3.6m ball mill into a rolling bearing, the motor current of the ball mill decreased by about 10%. The full load of the ball mill is to process 20-22 tons of slag per hour. The motor current of the sliding bearing is 32-34A. With the same processing capacity, the motor current after installing the rolling bearing is 28-31A.

Before the renovation, the synchronous motor current of the Φ 2.7 × 3.6m ball mill was 32-34A. After the renovation, the motor current was 28-31A, and the energy-saving effect was significant. The specific calculation is as follows (calculated based on 330 days, 24 hours per day):

Electricity consumption before the renovation: Electricity consumption=1.732 × 6000 × 34 × 330 × 24 ÷ 1000=2.7984 million kWh.

Annual electricity consumption after renovation:

Electricity consumption=1.732 × 6000 × 31 × 330 × 24 ÷ 1000=2.5514 million kWh

Energy saving before and after renovation:

279.84-255.14=247000 KWh (kWh)

The energy-saving rate is about 10%, and the electricity price is calculated based on the comprehensive electricity price of 0.66 yuan/KWh of Tianma Company. The annual energy savings are:

24.70 × 0.66=163000 yuan.

After the use of a "large-diameter rolling shaft" in the φ 2.7 × 3.6m ball mill, the centralized oil supply station was eliminated, and a manual pressure pump was used to lubricate with lithium grease. Oil was added once every season to improve the working environment and reduce oil pollution. The cost of lubricating oil and oil pump has been greatly reduced. According to comprehensive calculations, the annual comprehensive cost savings of using "large-diameter rolling shafts" in ball mills are about 160000 yuan, and the energy-saving effect is significant. The investment can be recovered in one and a half years, and the transformation has achieved a relatively ideal effect.

2026 August 3rd Week Marginal Product Recommendation

MG-TEX Steel with PTFE Fiber Fabric Bearings:

This new material uses the PTFE fibre fabric overlay on steel backing, the fabric is with high load capacity and much longer operating life comparing with conventional 3-layer bushes.The metal matrix provides the bearing with excellent load-bearing performance and can transfer the heat generated during the operation of the bearing in time, while PTFE woven material is designed to be used in completely dry friction conditions. It has a lower friction coefficient and excellent wear resistance. Compared with traditional bearings, in addition to high load performance, it can completely eliminate oil and eliminate process maintenance, and it slides smoothly. There will be no "sticky" phenomenon.

https://www.marginalbearings.com/steel-with-ptfe-fiber-fabric-bearings/mg-tex-steel-with-ptfe-fiber-fabric-bearings1.html