Stern bearing principle and key points

2019 - stern bearing principle and points 05 - 20 shaft system is an important part of ship propulsion system, bearing is the key component of shafting. End bearing fault, will affect the operation of the ship, but also increases the safety problems of the ship. Therefore, on all stages of design, construction and operation of the ship should be given enough emphasis on shafting. Shaft running, shaft and stern bearing produce relative motion and form wedge space, the lubricating oil in wedge space by rules of extrusion force, have a certain amount of force, and due to the viscosity of lubricating oil and so on between shaft and stern bearing form a layer of oil film, filling in between shaft and bearing the narrow wedge space. The existence of the oil film greatly reduce the contact force between the shaft and stern bearing, thereby reducing the friction and wear between two surfaces ( The figure below) 。 And with the long tail shaft, shaft and tail will produce large amounts of heat energy between bearing and passed to the lubricating oil, and the stern tube 'soak' in the cooling water tank, so the lubricating oil quantity of heat quickly taken away by the cooling water, remain the state of flow of cooling water, and oil heat not agglomeration, so the cooling of the lubricating oil to continue will be sufficient cooling of the stern bearing, so, under normal circumstances, the tail bearing temperature basically remained relatively stable. Stern bearing temperature is affected by three factors: the clearance between the shaft and bearing, bearing and the relative Angle of the shaft, the end bearing force. 1, the clearance. Shaft and bearing clearance are crucial factors in the shaft system with components, clearance whether appropriate, directly determines the oil film can be properly and fully established. The rules and regulations of the China shipbuilding quality standard 'and so on the various kinds of bearing in the different diameter of axle when the clearance value. Bearing gap is too small, the oil film can not fully established, and then between shaft and bearing 'dry grinding, lead to bearing high temperature. Bearing clearance is too large, when the shaft is moving left swinging, lubricating oil by irregular force, and the wedge space is too large, lubricating oil of its own gravity is greater than the adhesion, which also resulted in the oil film can not well established. No oil film lubrication effect is poor, between shaft and bearing force is unusual, and no oil film transfer heat efficiently in the oil pool, which generates heat, serious can lead to abnormal wear of bearing, melting, and even surface spalling. 2, relative Angle. Along with the development of the ship's large-scale, the weight of the propeller and gradually increase the length of the shaft system, after the stern tube bearing Angle is too large, the tail shaft and stern tube bearing contact area is reduced, resulting in bearing the local stress is too large. In order to make the front and rear bearing force uniform, wear uniform and prolong its life span, oblique boring and inclined bearing new design arises at the historic moment. Oblique bore the tail bearing bore, it is to point to by oblique boring stern tube bearing, makes them the center line of the hole and the center line of the bearing body tilt Angle. Bearing, the tail tilt into the stern tube bearing, shaft centerline and the center line of the bearing no relative Angle, usually dip tail pipe epoxy resin fixed within the stern, then install the stern bearing to the tail pipe. The ship adopts diagonal bore, according to the above design data and approved shafting alignment calculation shows that after the tail shaft and bearing the relative Angle of about 3. 5 x10rad to 3 of the rules and regulations of China classification society. 5 x10rad, thus using the boring. 3, the bearing stress analysis. Specification shall be specified on bearing length to diameter ratio, such as white metal bearing for 2 ~ 2. 5, acetate, rubber polymer bearing of 4. This is mainly in order to make the bearings on each point of local stress in line with the requirements of material. Tail shaft in the process of operation, the bearing contact with the shaft of arbitrary point, are caused by the gravity of the shaft, shaft rotational shear stress and axial shock when the irregular force, force is complex, so the existence of the oil film is crucial. Source: ( China survey)