Centrifugal pump, as a rotating equipment for conveying materials, is particularly important for the production of metallurgical industry, especially for steelmaking production with strong continuity. Because the equipment management level of each manufacturer is uneven, the use of centrifugal pumps is also different. How to improve the utilization ratio and service life of centrifugal pumps has always been a major problem puzzling enterprise equipment management.

Structural Design of 1 Centrifugal Pump

There are many manufacturers of centrifugal pumps. Some centrifugal pumps are not standard in size and fit clearance is not the best value. The assembly errors will lead to the damage of components (including impellers, fasteners, bearings and mechanical seals). Although the balance hole on the back cover of impeller can reduce the efficiency of centrifugal pump, it can reduce the pressure on both sides of impeller and balance part of the axial thrust. Some manufacturers often neglect this problem, which will cause frequent damage to bearings and shorten their service life.

In order to prolong the service life of bearings and seals, improvement measures can be taken as follows: strengthening standardization and standardization of centrifugal pumps and parts; reducing assembly errors; improving design characteristics, such as reducing shaft length and increasing shaft diameter, adopting larger sealing chamber, applying large size bearings, and increasing bearing frame for improving lubrication environment. Material quality of overflow parts and seals is also very important. In the design and selecion, the physical properties of fluid should be fully considered to selec the appropriate material.

2 Centrifugal Pump Installation

The assembly accuracy of internal components of centrifugal pump must be carried out in accordance with the standard, including impeller, seal, bearing, etc. In the process of transportation, it is inevitable that the internal components of centrifugal pump will be loosened. Therefore, after the centrifugal pump is installed on the basis, it should be leveled and corrected. When the outlet and inlet of centrifugal pump are well connected with the pipeline, the stress will be generated, which will cause the deviation of the original alignment, so the centrifugal pump should be re-aligned. If the alignment is not good, it is easy to cause shock force, which will cause the radial movement of the shaft, the vibration of the shaft and the offset of the shaft in operation, increase the power consumption, wear and tear of bearings and seals, and shorten the service life of the shaft. Some studies have shown that when the coaxiality of the degree of axis separation is less than 0.005 mm, the life of the rotating machine is about 100 months; when the straightness of 25.5 mm is 0.007 6 mm, the life of the rotating machine is shortened to 10 months; and when the straightness of 25.5 mm is 1.27 mm, the life of the rotating machine is 2 months.

3 Correct Use and Maintenance

3.1 Accurate selecion of flow rate and head of centrifugal pump can ensure that the centrifugal pump is in the best performance state in the use process. If the centrifugal pump operates in a low flow state, it will cause circulation whirlpool and radial force in the centrifugal pump, which will make the impeller unbalanced, increase the bearing load, cause seal and bearing damage. Serious low flow can also make the fluid temperature rise, turbine and pump shell damage, and increase the deflection of the pump shaft, even make the pump shaft fatigue fracture. If the flow rate cannot be increased in production, the reflux can be increased from the process piping to achieve the purpose of regulating the flow rate.

3.2 To ensure good lubrication of centrifugal pumps

Most centrifugal pumps use rolling bearings, and the components of rolling bearings (rolling bodies, inner and outer raceways and retainers) are not all pure rolling. Due to the elastic deformation of parts under external loads, there are relative slides on the contact surface except for individual points. The contact area of each element of rolling bearing is small and the pressure per unit area is often very large. If lubrication is not good, the element is easy to bond, or because of friction heating too high, the rolling element tempers, which makes the bearing invalid, so the bearing must always be in the coating of oil film. Bearing lubrication is usually carried out by oil groove or oil mist. In order to ensure a certain thickness of oil film between rolling body and raceway contact surface, medium viscous turbine oil (ISO 68) is more suitable. In oil tank lubrication, the bearing part is immersed in oil, and the oil infiltration height should be 50% of the bearing bottom. If more than 50%, excessive oil eddy current will increase the oil temperature, which will accelerate the oxidation of lubricating brambles, thus reducing the lubrication performance; if less than 50%, the washing effect of oil on bearings will be reduced, and the lubrication effect is not good. In addition to temperature, water and pollutants are also important factors affecting the quality of lubricating oil. Studies have shown that only water is needed in pure mineral oils.