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What is a Rotary Union and How Can It Be Sealed Effectively? 
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What is a Rotary Union and How Can It Be Sealed Effectively?



A rotary union is a device which provides a seal between a stationary supply passage and a rotating part, thereby allowing the transfer of fluid. It goes by a multitude of names, somewhat dependent on industry and application. These include: Swivel joint, rotary coupling, fluid swivel, rotary manifold, etc. Regardless, the basic purpose of a rotary union remains the same: Deliver media from a stationary input to a rotating part.To get more news about rotary union, you can visit grandslipring.com official website.

A rotary union is engineered to take into consideration the media to be transferred, rotational speed, pressure and temperature, and number of flow paths. The basic components are as follow:Rotary unions are used across several markets including industrial automation, food and beverage, alternative energy, oil and gas, and aerospace and defense. In fact, they are used so extensively it is easy to overlook their impact on equipment and system functionality.

Coolant must be delivered to parts made of metal and other materials undergoing machining. This fluid prevents overheating, maintains dimensional stability, and clears away machined debris.

Operating parameters vary dependent on the specific application. Pressure can range from 0 to 20,000 psi and temperature from -150 to 400˚F. Rotational speeds generally fall in the range of 0 to 1000 rpm. Fluids may include water, oil, coolant or any other flowable media intended to be transferred. Flow passages may number from one (1) to ten (10) or more. A number of factors must be considered in the design of a rotary union, of which the sealing components may be the most important.

Material Selection in Rotary Seals
While acceptable for many static applications, traditional compression seals like O-Rings are not typically adequate for rotary sealing. Friction which causes wear and heat buildup can limit the life of rubber seals in direct contact with the shaft, and seal squeeze and stretch upon which compression seals depend can further exacerbate this issue. The images below show examples of O-Ring abrasion and compression set. These are due to excessive wear and potentially heat buildup, respectively, and both can lead to premature seal failure.
Friction is defined as the resistance of relative motion between two surfaces. The lower the coefficient of friction, the easier it is for surfaces to slide over one another. We want friction when walking in our shoes or driving in our car in order to maintain stability and control. However, friction in seals causes wear and tear and subsequently reduces life. Polytetrafluoroethylene (PTFE) is a thermoplastic material with an extremely low coefficient of friction. And it performs exceptionally in rotary sealing applications.

A spring energized seal (SES) consists of a jacket, typically machined from PTFE. A spring is inserted in order to energize the seals lips, thereby keeping them in contact with the seal gland and shaft. This provides a relatively low friction sealing solution. In addition to better dynamic life versus traditional compression seals, these low friction seals result in fewer stick slip issues and less motor power consumption. That relates to less wear and tear on equipment and systems. It should be noted that PTFE can be modified with fillers such as carbon, graphite, molybdenum disulfide, and polyimide to further accentuate certain characteristics.


16 maja 2023, 09:08
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