Tham khảo tài liệu 'handbook of shaft alignment part 3', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 70 Shaft Alignment Handbook Third Edition Before alignment After alignment DIDstrb P2-MIA Motor Inboard Axial DIDstrb P2-MIA Motor Inboard Axial 0 6000 12000 18000 2000 3000 0 6000 12000 18000 2000 3000 Frequency in cpm Frequency in cpm FIGURE Before and after axial vibration data on motor and pump. Gravitational force V-belt or chain tension Shaft misalignment Some types of hydraulic or aerodynamic loads Dynamic loads on shafts and bearings are caused by some of the following sources not a complete list by any means Out of balance condition . the center of mass is not coincident with the centerline of rotation Eccentric rotor components or bent shafts another form of unbalance Damaged antifriction bearings Intermittent period rubs Gear tooth contact Pump or compressor impeller blades passing by a stationary object Electromagnetic forces Simply stated vibration is motion. Vibratory motion in machinery is caused by forces that change their direction. For example a rotor that is out of balance and is not Detecting Misalignment on Rotating Machinery 71 rotating does not vibrate. As soon as the imbalanced rotor begins to spin it also begins to vibrate. This occurs because the heavy spot is changing its position causing the centrifugal force to change its direction. The rotor bearing support system being elastic consequentially begins to flex or move as these alternating forces begin to act on the machine. Another detectable vibration pattern exists in gears and is commonly referred to as gear mesh. Gear mesh can be detected as forces increase or subside as each tooth comes in contact with another. Other types of mechanical or electrical problems that can be detected through vibration analysis can be traced back to the fact that forces are somehow changing their direction. On the other hand when two or more shafts are connected together by some flexible or rigid element where the centerlines of each machine are not collinear the forces transferred from shaft to
