Mechanical Troubleshooting: Chapter 4
Troubleshooting Power Transmission Components
In this module, we will learn about the failures of power transmission components in a machine. We’ll also learn about how to troubleshoot these failures. Skip to quiz!
Power Transmissions
Recall that we need energy to drive machines and equipment. The energy available is required to achieve the desired motion and work.
When energy is transmitted from input to output using mechanical elements, we call that mechanical power transmission.
The mechanical elements used in power transmission are:
Gears,
Belt and pulley systems, and
Chain and sprocket systems.
Gears
Machinery breakdowns are often the result of gear failure. The cause of gear failure can be:
Wear,
Overload, and
Misalignment.
Let’s discuss each of them in detail.
Wear is uniform metal removal from the surface of gear teeth. This condition is caused by metal-to-metal contact during operation.
The remedy to avoid wear failure in gears is to provide proper lubrication. Lubricant forms a thin film that prevents metal-to-metal contact between gears.
We often push our machines to their limits and beyond. For example, a two-seater bike designed for a capacity of two people is often driven with more than two persons sitting on it. This can result in excessive tooth loads on the gearbox inside our two wheeler.
When gears are loaded in this manner and subjected to stress, the gear tooth fails. To avoid this failure, we need to ensure that a machine is not overloaded.
Shaft misalignment is considered one of the common repeated problems in most rotating machinery. Misalignment leads to vibrations and additional load on a transmitting gear’s teeth.
A gear’s teeth will not mesh the way they were designed to, resulting in excessive loads on the weaker parts of the teeth. This will result in wearing of the gears and failure.
A gear must mesh properly to avoid gear failure.
We need to adjust a gear mesh by adjusting the location of the motor. Loosen the fasteners that lock the motor in position. Once the motor is loose, be sure it is free to move in the direction that would allow for gear mesh adjustment.
Belt and Pulley Drives
As belts, along with gears, are a critical component of power transmission, we often encounter their failures. Belt drive failure can result in a machine breakdown.
A belt drive system can have problems like:
Belt cracks,
Loud noises during startup, and
Pulleys that wear out prematurely.
If we notice any of these issues while examining our drive symptoms, then a possible cause could be improper belt tension.
A belt that’s too loose on a pulley will cause slippage, which leads to heat build-up from friction. This heat will damage our rubber belts and cause the belts to crack and break. A belt that’s too tight can add stress to our bearings leading to motor failure.
We need to make sure that our belts are correctly tensioned. This can help us prevent added costs associated with electric motor or belt failure.
We use a tension gauge to check belt tension. We need to measure a belt’s span length. Set a measured distance in the gauge by displacing the bottom O-ring. Set the top O-ring at zero position.
Next, press down on the belt in the approximate center of its span. We need to press down the belt until it deflects to the desired level on the O-ring. The desired level is compared with a reference belt or by aligning the bottom O-ring to the straight edge of the string.
Now that we have deflected the belt, the recommended amount for the top O-ring will have moved up the plunger. This will give us the tension measurement. We need to compare this with the force chart.
For example, for a speed range of 2501-4000 RPM, the recommended force of a new belt should be 7.6 lbs
Pulleys need to be appropriately aligned to prevent premature wear on belts and pulleys. Always check the alignment of pulleys after tensioning a belt because sometimes during tensioning the pulleys can move.
Chain and Sprocket Drives
Much like gear drives and belt drives, power can be transmitted by a roller chain. These chains are made up of several rigid links that are held together. A roller chain passes over a sprocket that pulls the chain.
Most often, a chain drive is susceptible to corrosion. A symptom of corrosion is surface pitting, and this is generally noticed on the sides of the links. To prevent corrosion, we will need to lubricate a chain often.
If we notice a roller chain is vibrating excessively, then the possible causes could be:
High speed,
Chain sag, and
Sprocket misalignment.
Let’s discuss each of them.
Any rotating piece of machinery has a critical speed, and roller chains are no exception. We need to ensure that a chain is running below critical speed to avoid vibration.
Excessive chain sag can cause vibration or excessive noise and prevent a chain from properly engaging its sprocket. This can prevent the chain from operating smoothly. On the other hand, an over-tightened chain can cause premature wear or elongation of the chain.
Sprocket alignment is also essential when we are first installing our chain drive. We need to ensure that both the drive socket and the drive sprocket tooth centerlines are straight to each other.
First, we will install the sprocket on the drive shaft. We need to make sure the ends of the chain are lined up with the sprocket. Now we’re ready to check the chain tension.
We can use the same tension gauge that we used when setting up a belt tension. We’ll place our straight edge or scale from sprocket to sprocket on the slack side of the chain drive.
From the straight edge, the distance of the O-ring gives sag present in the chain. A chain should be installed with sag from two to four percent of the sprocket center distance for most applications. If the chain sag is not within these limits, we need to remove the link of the chain.
The mechanical elements used in power transmission are:
Gears,
Chain and sprocket systems, and
Belt and pulley systems.
The cause of gear failure can be:
Wear,
Overload, and
Misalignment.
A belt drive system can fail due to:
Belt cracks,
Loud noises during startup, and
Pulleys that wear out prematurely.
If we notice a roller chain is vibrating excessively, then the possible cause could be:
High speed,
Chain sag, and
Sprocket misalignment.
Question #1: What are the elements of power transmission? (select all that apply)
Gears
Belt and pulley systems
Nuts and bolts
Chain and sprocket systems
Scroll down for the answer...
Answer: Gears
Belt and pulley systems
Chain and sprocket systems
Some external signs that indicate potential coupling failure include:
Abnormal noise,
Excessive vibration, and
Failed seals indicated by lubricant leakage.
Question #2: How can we avoid wear failure in gears? (select all that apply)
By spraying water on the gear
By lubricating gears
By using baking soda
By using wear pad
Scroll down for the answer...
Answer: By lubricating gears
The remedy to avoid wear failure in gears is to provide proper lubrication. Lubricant forms a thin film that prevents metal-to-metal contact between gears.
Question #3: How do we troubleshoot a gear that is not meshing properly?
By using multimeter
By checking centre distance
By adjusting the location of the motor
By measuring number of teeth on gears
Scroll down for the answer...
Answer: By adjusting the location of the motor
We need to adjust a gear mesh by adjusting the location of the motor.
Question #4: What could be possible symptoms of improper belt tension? (select all that apply)
Loud noises during startup
Bent pulleys
Pulleys that wear out prematurely
Belt cracks
Scroll down for the answer...
Answer: Loud noises during startup
Pulleys that wear out prematurely
Belt cracks
If a belt is not tensioned correctly, the belt drive system can have problems like:
Belt cracks,
Loud noises during startup, and
Pulleys that wear out prematurely.
Question #5: How do we check belt tension?
Using a multimeter
Using a slip gauge
Using a scale
Using a tension gauge
Scroll down for the answer...
Answer: Using a tension gauge
We use a tension gauge to check belt tension.
Question #6: What is the cause of excessive vibration of a roller chain? (select all that apply)
High speed
Rigid links
Chain sag
Sprocket misalignment
Scroll down for the answer...
Answer: High speed
Chain sag
Sprocket misalignment
If we notice a roller chain is vibrating excessively, then the possible causes could be:
High speed,
Chain sag, and
Sprocket misalignment.