What is a Coupling Hub?
It is necessary over the course of large-scale turbomachinery’s life to perform maintenance to ensure optimal performance. One such service may be the repair or replacement of a coupling hub that is joined between two pieces of machinery.
The coupling hub serves as a way for a motor to provide torque to a compressor or similar equipment. This makes it essential to the overall performance of the machinery.
Determining the appropriate method to safely disassemble the coupling hub will reduce the risk of damaging the hub and its mating equipment, as well as reducing the amount of time spent servicing the machinery.
Differences in Hub Design
Coupling hubs vary in design depending on the manufacturer, offering a number of ways in which it can be installed or removed.
There are two main designs that an end user can encounter: a straight bore hub and a tapered bore hub.
A tapered bore hub consists of a small internal diameter on one end that gradually increases across the length of the coupling hub. A tapered hub is installed to a mating tapered shaft end such that a pre-determined interference fit between the two surfaces is attained. This style of hub is easily installed and removed through the use of a hydraulic tool such as a Riverhawk hydraulic pusher.
A straight bore hub possesses a consistent internal diameter across the hub length and is typically shrink fit onto a shaft end to generate contact pressure. Unlike the tapered bore coupling hub, a straight bore coupling hub can be removed by a number of different methods depending on the discretion of the end user and the equipment that is available.
Methods of Removal
- Hydraulic Removal
The most common method of removing a straight bore coupling hub is through the use of a hydraulic removal tool such as the Riverhawk hydraulic puller.
The hydraulic removal tool typically consists of two main components: a cylinder and a piston.
The removal tool is attached to the hub face via tapped holes and utilizes hydraulic fluid to move the piston axially, which in turn will shift the hub axially in the opposite direction (off of the shaft end).
The primary benefits to this method of removal are speed and accuracy; installing and operating the hydraulic tool is simple and the user can accurately measure the amount of fluid injected into the tool and track the movement of the hub as it advances off of the shaft end.
This leads to less time spent on the job, which in turn translates to added cost savings for the end user.
There is a higher purchase cost associated with a hydraulic removal tool as a hydraulic pump and hose kit is required for operation, however this is offset by the decrease in time spent on the job and the repeatability of using said equipment.
- Mechanical Removal
Another conventional method of hub removal is through the use of a mechanical removal tool.
The mechanical removal tool typically consists of a claw or similar device, and a threaded piston.
The tool itself behaves similar to the hydraulic tool, in that it is secured to the hub face or flange and utilizes a piston to engage with the shaft end and shift the hub axially.
The primary difference is that the tool requires the end user to turn the piston via a wrench or similar mechanical input.
While the purchase cost of the mechanical tool is lower than that of a hydraulic removal tool, the added time and labor costs may prove this to be the less cost-efficient method.
Additionally, the mechanical device is limited by the amount of torque that the user can input when engaging the piston; the tool may not be able to generate sufficient force to fully remove the coupling hub.
3. Destructive Removal
The third method of hub removal is through the use of a plasma torch or similar device to remove material from the hub barrel with the intent to split the hub and relieve the contact pressure.
Caution should be taken when using this method as it is easy to remove too much material from the hub and begin to damage the shaft end.
Furthermore, the hub will release a substantial amount of force once separated, potentially causing injury to those in proximity.
As this method of removal will render the hub unusable, it should only be used when other removal options are not valid or if the hub is in severe disrepair and requires replacement.
Other Factors to Consider
- Proximity to Equipment – There may be limited space to install and operate a removal tool depending on the location of the coupling hub relative to its surrounding equipment.
- Environment – The coupling hub may be present in a hazardous environment that limits which method of removal to use.
- Dilation Assist – The end user may have access to different methods to dilate the coupling hub and reduce the contact pressure, be it hydraulic fluid or heat.
By reviewing the information above, you can significantly reduce the time spent identifying and selecting the appropriate method of removal for your coupling hub.
You may find other concerns that were not listed in this article. If that is the case, Riverhawk staffs a number of qualified engineers whom can address these concerns and help guide you in selecting which method is right for the job.
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David Albright is a Mechanical Engineer for Riverhawk who specializes in hydraulic tooling designed for coupling installation and removal. David holds a Bachelors of Science in Mechanical Engineering from Clarkson University, and has been with Riverhawk Company since 2017.