A perfect mechanical seal can be obtained between a tube and a hole by employing tube expansion systems. The seals obtained with these systems are tighter, leak proof and most reliable. They are widely employed in power plant equipment like tubes of boilers, condensers, heat exchangers, etc. The expansion system has to be chosen based on various factors like working conditions, type of application, dimensions of tubes and holes.
Principles of Tube Expansion:
- Incomplete expansion of the tube doesn’t result in a perfect fit of hole and tube. This is referred as under rolling.
- Tube can be damaged if over expansion takes place. This over expansion of tubes is known as over rolling.
- The tube holes have to be so prepared that it doesn’t result in leakage.
- The tube holes have to be coated with anti corrosive products to protect them from corrosion.
Components:
The components of the tube expander change with the type of expansion system and application. However, a few basic components are detailed below:
- Mandrel: The expander has a tapered pin at the center. Power is supplied through this pin which drives the roll against the tubes.
- Rolls: Rolls are tapered cylindrical structures. They are driven by mandrel and stays in contact with the tube.
- Cage: This holds the rolls and mandrel. The slots provide the required feed angle to the rolls
Types:
- Electric tube expansion systems: The torque can be applied accurately by making use of the digital torque setting. In comparison to most other systems, their design is compact and robust.
- Hydraulic tube expansion systems: They are really quiet in operation. They are widely used in boilers. As they develop high torque, they can be used effectively in heavy works.
- Explosive expansion: Explosive materials are used to generate high pressure inside the tubes. It is one of the most expensive methods and the operation is too noisy and risky.
Accessories:
Better performance can be achieved by employing various accessories as follows
- Telescopic shafts: Drives can be easily handled by incorporating these devices. These shafts absorb the torque produced during operation.
- Chucks and adaptors: Electric, hydraulic or pneumatic expansion systems can be used directly by using these chucks and adaptors.
- Torque controller: As the name suggests the range of torque can be easily adjusted. It has a longer life as it doesn’t have any moving parts in it.
- Grooving tool: They are used to make grooves in the tubes.
- Tube wall collapser: These devices can remove tube ends effectively. This device is used with a tube wall reducer.
Care:
- The expander has to be cleaned before operation.
- Electrical and hydraulic connections have to be checked thoroughly before operation.
- Periodical lubrication of the moving parts has to be done.
- The rolls have to be carefully inspected for chips and damages.
tubeexpanders 