Gears & drives feeling the pulse
A mechanism consisting of toothed wheels that engage and transmit rotary motion, usually transforming angular velocity and torques. Gear drives are classified according to the relationship of the axes to the drives.
Gear drives are the most practical and widespread type of mechanical transmission. They are used to transmit power - from negligibly small values to tens of thousands of kilowatts-and to transmit circumferential forces of fractions of a gram to 10 mega newtons (1,000 tonnes-force). The main advantages of gear drives are their significantly smaller dimensions, high efficiency (losses in precision-made, well-lubricated drives are 1-2 percent, and, under especially favourable conditions, 0.5 per cent), longer life and greater dependability, lack of slippage, and small shaft loads. The disadvantages of gear drives include noisy operation and the need for precision manufacture. Shipping industry, power generating plants are the ones that deploy high to very high powered gear box and drives.
Gear drives are used in the form of simple single-stage drives and of various combinations of several drives built into machines or made as separate units. Gear drives are widely used to reduce angular velocities and increase the torque in reduction gears. Reduction gears usually operate in independent units of one, two, and three stages and with gear ratios of 1.6-6.3:1, 8-40:1, and 45-200:1, respectively. Two-stage reduction gears are the most common type (about 95 percent). Transmissions are used to produce various speeds of rotation of the final shaft while maintaining a constant speed of rotation of the drive motor.
There are typical three to four applications in cement industry where gear box and drives are commonly used. Those being kiln, ball mills and vertical roller mills. Just providing a good design of a gear box and drive is not sufficient. During operations it is necessary to monitor the health of the gear box and drive from time to time. Therefore condition monitoring of a gear box is extremely important specifically in large horse power gear boxes. Especially in the case of applications like VRM where DALOG is playing a significant role. Readers can refer to an article published by DALOG in the same issue elsewhere. There are good numbers of ways to know the condition of the machine but vibration analysis is the most popular and dependable.
Vibration analysis (VA)
As applied in an industrial or maintenance environment aims to reduce maintenance costs and equipment downtime by detecting equipment faults. VA is a key component of a Condition Monitoring (CM) programme, and is often referred to as Predictive Maintenance (PdM).
Just as the doctor examines his patient, the vibration specialist also checks out the machine when its condition worsens. The first signs appear with excessive vibration values, which are recorded during condition monitoring. The specialist uses high-performance analysers and suitable methods to find the root-cause of the increased vibrations in order to remedy the problem as soon as possible.
Vibration analysis consists in listening inside the machine. Each component vibrates differently and generates a characteristic noise that leaves a typical fingerprint in the spectrum in the form of a linear pattern. If damage is present, the pattern stands out from the noise floor. This allows the specialist to recognise, for example, whether the problem comes from unbalance, misalignment or bearing damage. In addition to an accurate diagnosis, it is generally also possible to determine whether urgent action is necessary or whether it can wait until the next scheduled servicing.
Benefits of VA
The bottom line is that VA benefits both the operator and the maintenance technician:
- Enables the identification of machine faults
- Provides information on root causes
- Localises the affected components
- Optimises spare parts logistics
- Allows early planning of maintenance measures.
- Vibration data analysis
Benefits of continuous vibration monitoring
The tools and methods of vibration analysis can be applied to quantitatively assess the condition and performance of equipment. Vibration data can reveal when equipment has broken welds or bolts, whether the rotor bars in a motor are intact, if the air gap between rotor and stator in the motor is non-concentric, etc. Vibration data can alert maintenance teams to structural or rotating looseness or the presence of resonance.
VA can be used to determine whether bearings have been properly installed. In a taper bearing, for example, the inner race has to be expanded to take up the clearance between the rotating element and the outer race. If that clearance is not removed, the bearing may wind up crooked or wobbling. This will introduce non-periodic features into the vibration signal. Phase analysis also can be used to check bearing concentricity.
VA also can be used to determine how well a machine is assembled. It can detect misalignment in a pump, for example, determining whether the rotating elements are binding, if the base is uneven, or if torsion exists between motor and pump.
Monitor critical assets: Vibration monitoring starts with critical assets, expensive equipment that would a represent substantial loss in the event of catastrophic failure. Historically, this type of equipment has been tracked using route-based vibration monitoring and, eventually, continuous online condition monitoring. Anomalies in the vibration spectrum can indicate issues such as lubrication breakdown and bearing defects sufficiently far in advance to permit timely repair, prolonging the lifetime of the asset.
Monitor troubled assets: Many plants operate around the clock, stopping once a month or once a quarter for scheduled maintenance. Unscheduled downtime reduces productivity and can cost from tens of thousands of dollars per hour to tens of thousands of dollars per minute. Online vibration monitoring provides a method for monitoring a troubled asset during the run-up to planned maintenance. If the condition of the equipment worsens, the line can be stopped before catastrophic failure occurs. With continuous online vibration monitoring, maintenance teams can receive immediate alerts when the condition of a troubled asset changes, enabling rapid response.
Monitor hard-to-reach assets: When it comes to maintenance, the most challenging assets are not necessarily the high-value ones but those located in hard-to-reach locations such as on rooftops, inside inaccessible cooling towers, high radiation or high-temperature environments, etc. Vibration monitoring makes it possible to understand how the various components of the system are working. Maintenance can detect problems early and take action when it is convenient to forestall unplanned downtime without putting personnel at risk unnecessarily.
In today's industrial environment, management, maintenance, and OEMs seek every tool possible to maximise availability. Online vibration monitoring is an essential tool for predictive maintenance, enabling asset owners to maximise productivity and minimise downtime while increasing worker safety. With economical online condition monitoring systems, organisations can take advantage of the benefits of online condition monitoring at a user-friendly price.
While many larger plants have excellent in-house VA capability, the answer for smaller plants, or those caught in the budget crunch, may be to out-source this highly technical function. Justification must consider the actual annual cost of downtime, the potential for savings in terms of lost productivity, as well as the cost of training and VA equipment. Before buying the equipment, make sure the management commitment is there to set up and train an effective preventive maintenance team.