Factors Affecting The Neutral Pair Of Double-bearing Generators

The input shaft position of the driving equipment assembled remotely is usually higher than the main shaft of the diesel generator. This compensates for vertical thermal expansion, flywheel droop and main bearing oil film enhancement of the spindle. These conditions cause the relative position of the spindle and the equipment input axis to change between the static and running state.

1. The rotor shaft of the bearing clearance generator and the crankshaft of the diesel generator rotate around their respective bearing centerlines, so their centerlines should be coincident. Alignment is carried out at rest, when the crankshaft is supported at the bottom of its bearings. The crankshaft is not in this position at the time of operation. Burst pressure, centrifugal force, and diesel engine oil pressure all try to lift the crankshaft so that the flywheel rotates around its true center. In general, the driven device uses ball bearings or roller bearings, which do not change their axis of rotation in static and operational conditions.

2. Flywheel drooping Diesel generator at rest, the net weight of the flywheel and coupling will bend the spindle. This effect must be compensated for in alignment because it can result in the guide hole or flywheel rotating od being lower than the actual centerline of the crankshaft bearing in the alignment process. Cummings therefore recommends that alignment be checked when coupling is installed.

3. the reverse torque of the diesel generator in the direction of relative axis rotation and the rotation trend of the driven device in the direction of axis rotation is the reverse torque. It will naturally increase with load, as well as cause vibration. This vibration is not felt at idle speed but can be felt at load. This is generally caused by the insufficient strength of the base under the anti-torque function, resulting in excessive deflection of the base, thus changing the center line alignment. This has the effect of side-to-side centerline deviation. The deviation disappears when the diesel generator is idle (no load) or shut down.

4. Thermal expansion When the diesel generator and generator reach the working temperature, thermal expansion or thermal expansion is produced. It expands vertically and horizontally at the same time. Vertical expansion occurs between the component mounting feet and their respective rotating centerlines. The size of this expansion depends on the material used, the temperature rise that occurs, and the vertical distance from the center of rotation to the mounting foot. Vertical compensation involves adjusting the centering device to a non-zero value. The horizontal thermal expansion of the spindle is delayed from the thrust bearing of the diesel generator to the other end. This thermal expansion is taken into account when the device is connected to this end of the diesel generator. 

This expansion use is slight if the drive is bolted to the diesel generator block, since the block and crankshaft expand at approximately the same rate. Horizontal compensation may be made by means of a coupling that permits sufficient relative motion between the drive and the driven device. When assembling the device, consideration should be given to horizontal thermal expansion into the working area of the coupling, not away from it. Otherwise, it will cause the thrust bearing of the main shaft to be overloaded, and or the coupling to be damaged. If the crankshaft still has end clearance when the diesel generator is detected in the hot state, enough clearance should be left in the cold state. With front crankshaft drive, the dial meter reading may show that the driven shaft is lower than the diesel generator. This is due to the fact that the dial meter is mounted on the driven shaft, not on the diesel generator, and due to the construction of the coupling, the dial meter reference point is reversed. Three, in the process of the main device are installed in the frame, it is necessary to carry out the final alignment work. The diesel generator should be filled with oil and water and in a state of ready operation. Misalignment between diesel generators and all mechanical driven equipment must be minimized. Many crankshaft and bearing failures are caused by inaccurate alignment of the drive. At operating temperature and under load, misalignment always causes vibration and/or stress loading. Because there is no accurate and feasible way to measure the alignment neutrality of diesel generators operating at the operating temperature of the diesel generator and operating under load, all Cummins alignment procedures must be performed when the diesel generator is stopped and the diesel generator and all driven equipment are operating at ambient temperatures. When the dial meter is not being read, place the driven device in its final position as far as possible. A minimum thickness of 0.76 mm and a maximum thickness of 3.2 mm shall be fitted under each mounting surface of the driven device. Use leveling and centering screws to move the driven device. For cold alignment, the generator is mounted slightly higher than the diesel generator to compensate for thermal expansion, bearing clearance and flywheel sagging. Four, the installation of the coupling in the maintenance, the flexible components of other coupling must be removed. The "rigidity" of the components can prevent accurate centering reading. After removing other couplings, the drive and driven elements of the coupling must be turned together during alignment inspection. This can prevent the end face or hole wall from parts, resulting in the error of the dial meter reading. When the elements are turned together, the dial meter reading will reflect only the device's misalignment. Five, the final alignment operation with two dial meter support to measure the hole and surface offset at the same time. Record the correct position of the neutral reading. Before reading the end face, ensure that the thrust acting on the crankshaft ends is always in the same direction. Set the two dial meters to zero at the top and take readings every 90O (1.5 radians). Turn the diesel generator to turn the whole system. When the moving generator reaches the requirement of accurate end face center, check the hole alignment and vice versa. Coupling alignment should be tested again after final gasket adjustment and bolt tightening. When the device reaches the operating temperature.

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