Introduction of  Metal Bellows Expansion Joints

Metal Bellows Expansion Joints (they are also called compensators) are compensating elements for thermal expansion and relative movement in pipelines, containers and machines. They consist of one or more metal bellows, connectors at both ends, and tie rods that depend on the application. They are differentiated according to the three basic types of movement: axial, angular and lateral expansion joints.

Metallic Expansion Joins  are elastic vessels that can be compressed when pressure is applied to the outside of the vessel, or extended under vacuum. When the pressure or vacuum is released, the bellows will return to its original shape (provided the material has not been stressed past its yield strength).

Features of  Metal Bellows Expansion Joints

1. Reasonable structure, good elasticity, large range of compensation pipeline and little counterforce to the brackets of pipeline.

2. Shock absorption and noise decrease, heat and dust insulation, environmental protection and simple structure bracket.

3. The displacement can be deflected to prevent damagment caused by subsidence of connected brackets and equipment base. It can adapt itself to the centrifugal difference of pipeline installation to provide convenience to installation and maintenance.

4. Good resistance to milling, heat, aging and corrosiveness and long service life.

5. Little resistance and little weight. Each performance is better than the compensation device of other materials.

6. The temperature range of media is wide:-40–300oC

Manufacture of  Metal Bellows Expansion Joints

Welded Metal Bellows Expansion Joints  can be fabricated from a variety of exotic metals and alloys, whereas formed bellows are limited to alloys with good elongation – brass being a prime example. Welded bellows are not fabricated from brass because of its fundamentally poor weldability. Other advantages to welded bellows include compactness (higher performance in a smaller package), ability to be compressed to solid height with no damage, resistance to nicks and dents, and dramatically greater flexibility.

The welding of metal bellows is a microscopic welding process, typically performed under laboratory conditions at high magnification.

Hydroformed bellows are produced by forcing a metal tube to expand under hydraulic pressure inside a bellows-shaped mold, and assume the convoluted shape of the mold.

Electroformed bellows are produced by plating metal onto a bellows-shaped model (mandrel), and the subsequent mandrel removal by chemical or physical means.

Applications of  Metal Bellows Expansion Joints

Metal Bellows Expansion Joints -welded or convoluted (formed), are used in a large number of industrial applications:

Load cells; A load cell deforms if a certain load in the form of a pressure or a strain is imposed on it. This deformation is then detected by a strain gauge through which a low voltage direct current is flowing. The change in voltage is detected and made visible on a control panel. A bellows is mounted over the gauge to protect it from outside influences.

Vacuum interrupters; For the switching of very high voltages in transformer stations sparks should be avoided. To prevent any danger that the surrounding atmosphere will explode, oxygen has to be removed in the area where the sparks occur. This can be done by sealing the spark area completely. Bellows are used to seal such confined volumes and the inside of the bellows is evacuated or filled with an inert gas.

Mechanical Seals; These are mostly used to close the inside of a pump from the outside world to prevent leakage. For that purpose, a mechanical seal is mounted on the pump shaft. As the pump shaft is turning, there has to be a sealing element consisting of a stationary and a rotating ring. To enforce sufficient pressure on the two rings one is fitted with a spring. This spring can also have the form of a diaphragm (welded) bellow.

Pressure gauges: If the pressure of aggressive fluids or gases has to be measured, the gauge has to be isolated from the flow. For critical applications a diaphragm sealing is used instead of abourdon tube in the gauge. This gives more security that the aggressive media will not leak. The diaphragm is a self-contained sensor, transmitting the displacement to the measuring device.

Sensors: In this application diaphragm or convoluted bellows are completely sealed and filled with a certain gas. Two electrical poles are penetrating the inside of the bellows. By varying the current of those two poles the temperature inside the bellows can be regulated. The expansion or contraction of the bellows is used as an actuator to control a certain movement.

Valve Sealing: A bellows is used between the housing and the rising stem to seal the inside completely from the outside world. In Europe this is of particular importance as regulations such as TA Luft prohibit any leakage.

Couplings for stepper motors and servomotors: The flexible part, capable of compensating for misalignment is made by a bellows. It ensures that there is no angular positioning difference between the two coupling halves. This is essential if the positioning accuracy should be extremely precise.

Exhaust Bellows: Running engines cause self vibration. To compensate for those movements and temperature differences resulting in thermal expansion, bellows are used to connect the exhaust gas pipes to the funnel.

Piping expansion joint: In this application, bellows are formed in series to absorb thermal movement and vibration in piping systems that transport high temperature media such as exhaust gases or steam.

Metal bellows are also used in other products and market segments, including medical applications like implantable drug pumps, to industrial actuators, to aerospace applications such as altitudesensors and fluid management devices (accumulators, surge arresters, volume compensators, and fluid storage). Metal bellows are also found in space applications, providing reservoirs with potable water as well as accumulators to collect wastewater.