Everything you need to know about O-rings
Most mechanical and hydraulic systems, particularly engines, refrigerators, boilers, and many others, require seals to function correctly over time. However, the material used to make the seals determines how effective they will be. While different materials are used to make seals, there are several types of seals, the most common of which is the O-Ring. Discover what O-rings are, how they work, their benefits and drawbacks, the different types, etc.
What is an O-Ring?
An O-ring is a doughnut-shaped ring made of various materials including NBR, Fluoroelastomers, silicone and various other rubber compounds as well as other thermoplastic materials. It is used to close the path through which gas or liquid could escape and keep foreign components out of the machinery. The O-ring is inserted into a groove to keep it in place before being compressed between two surfaces. When you squeeze the O-ring, it seals the passageway through which the liquid and gas are trying to pass.
Under high pressure, the O-ring is squeezed against the opposing wall of the groove, resulting in a perfect seal. However, when the pressure is reduced, the O-ring, typically made of flexible materials, returns to its original size, resulting in a tight seal regardless of the pressure.
What is an O-Ring seal?
An O-ring seal is a device that prevents fluid and gas loss. It consists of an O-ring and a gland. The O-ring is a circular cross-sectional ring made of various materials (polymers and compounds). The gland, on the other hand, is a cut-out metal or other hard material that contains and supports the O-ring.
An O-ring seal’s other properties and performance characteristics include low friction, excellent dimensional stability, good insulating qualities, high-temperature sterilisation resistance, biocompatibility, durability, and inherent purity.
How does an O-ring work?
O-rings are like standard gaskets, but O-rings are specifically designed for industrial applications where they will be exposed to high temperatures and pressures, abrasive materials, and other foreign substances. O-rings are made of tough materials that can withstand extreme temperatures.
O-rings function by being inserted into the groove or gland between two components of machinery, which can be static or dynamic. When the two parts are pushed together, the O-ring conforms to the shape formed, resulting in a tight seal that will not allow water or even air to pass through. The greater the pressure applied to the O-ring, the tighter the seal.
However, the pressure applied to the O-ring mustn’t be excessive, or it will be damaged, and the seal will extrude. After the two compressed machinery components have been detached and the pressure applied to them has been released, O-rings can also return to their original round shape. As a result, they can be reused. However, they cannot be recycled indefinitely. They will become weak after several uses, and the pressure on them will eventually reduce their efficiency, necessitating their replacement.
O-ring features and characteristics
O-rings have a plethora of features and characteristics. These are the most important.
- O-rings can seal fluid pressures of up to 5 000 psi in static and cylinder cases. This pressure can be constant or variable.
- They can also form a seal between reciprocating pistons and cylinders at any fluid pressure up to 5 000 psi. However, there may be minor running leakage depending on the hydraulic medium’s ability to produce films
- A single O-ring will seal when pressure is applied alternately to one side and then to the other. When used in harsh environments or with heavy loads, the seal life can be extended by designing it so that each seal is only exposed to pressure on one side.
- The O-ring should be squeezed between the cylinder wall and the bottom of the seal groove for perfect sealing.
- Extrusion of the seal material into the piston-cylinder clearance is the most common cause of seal failure. Seal hardness and strength, fluid pressure, and piston-cylinder clearance are the primary causes of this.
- Abrasion against the piston walls or the cylinder causes some O-rings to fail. The contacting surfaces should be polished to ensure long seal life.
- How the seal groove is shaped makes no difference, provided it is correctly compressed between the groove’s underside and the cylinder wall and provides space for the compressed material to flow.
- O-rings can be installed in a groove carved into the cylinder wall rather than the piston surface without changing the seal design limitations.
- The chemical interaction between the seal and the hydraulic medium can have an impact on the seal’s durability, either positively or negatively. However, this is dependent on the seal material and fluid combination.
The benefits of using O-rings
- O-rings can seal under various pressure, temperature, and tolerance conditions.
- There is no need to retighten.
- Because no complex torque is applied while tightening, structural damage is unlikely.
- O-rings are small, portable, and take up little space.
- In contrast to non-elastic flat seals, an O-ring can be reused.
- When used for the appropriate application, the O-ring has the same lifespan as the O-ring material’s normal ageing period.
- O-ring failure happens gradually and is visible, alerting the user.
- O-rings are inexpensive.
O-ring use restrictions
Despite the numerous advantages that O-rings provide, they have some limitations. This includes:
- More than 1 500 feet per minute rotary speed.
- An unfavourable environment for O-ring material.
- Incompatibility in terms of chemical, temperature, and pressure.
Types of O-ring seals
Some options are ideal for your application, whether you require an O-ring seal for heavy-duty agricultural machinery, automotive cogs and pistons, or any other industry. These are a few of the various types of O–rings available.
Nitrile O-rings, also known as Buna-N or NBR, are a type of general-purpose seal. It has a good temperature range of -50°C and 120°C and excellent tear and abrasion resistance. Furthermore, nitrile is resistant to fluids, oils, and some hydraulic liquids. However, it is not resistant to automotive brake fluid, ketones, halogenated hydrocarbons, and nitro hydrocarbons. As a result, it can only be used for a limited number of applications in the agricultural, automotive, dairy, mining, plumbing, and railway industries.
Neoprene, a general-purpose elastomer, is unique in that it has moderate resistance to petroleum oils and weather elements such as ozone, oxygen, and UV. As a result, neoprene O-rings are ideal for some sealing applications that other types of O-rings cannot handle. It’s also resistant to flex cracking, has a high resilience and abrasion rating, and has a low compression set. In addition, neoprene has the same temperature range as nitrile and is frequently used to seal refrigerants in air conditioning and refrigeration systems.
Silicone O-rings have one of the broadest temperature ranges of any type of O-ring. Temperatures ranging from -100°C to 220°C can be tolerated. This tough O-ring is ideal for applications that require extremely high or low temperatures. However, it is prone to tears and abrasions despite its high flexibility and compatibility with water, steam, and petroleum. As a result, it is best suited for static applications rather than dynamic ones.
These are also known as FKM O-rings. They’re made of fluorocarbons and have a temperature resistance range of -40°C to 200°C, excellent mechanical properties, low gas permeability, and a low compression set. Viton O-rings are compatible with acids, petroleum and silicone fluids or gases, and halogenated hydrocarbons. However, they are incompatible with anime, low molecular weight esters, Skydrol, and hot hydrofluoric acids. Their application spans numerous industries, including aviation, automotive, chemical processing, and mechanical engineering plants.
PTFE machined parts with corresponding O-rings have numerous advantages that allow them to perform their functions optimally and for an extended period. O-rings have several benefits, including good wear, corrosion and abrasion resistance, non-permeability, chemical inertness, and low absorption. They can also operate at temperatures ranging from -73°C to 260°C. PTFE O-rings are commonly used in the manufacture of paint guns and steering devices in the automotive industry.
Basic O-ring components
These are the primary materials used in the manufacture of O-rings.
A polymer results from the chemical linking of molecules in a long chain-like structure. Polymers include both plastics and elastomers. Nitrile, neoprene, and PTFE O-rings are examples of polymer seals.
The term “synthetic rubber” was first applied to rubber-like compounds derived from sources other than rubber trees. This distinguishes them from natural gum rubber. However, rubber has since been defined to include both synthetic and natural materials with rubber-like properties.
The terms “elastomer” and “rubber” are often used interchangeably, but they are not the same. Any rubber material composed of long chain-like polymers that can return to their original shape after being significantly stretched is referred to as an elastomer.
A compound is a mixture of a base polymer and other chemicals that results in a finished rubber material. It is also referred to as a one-of-a-kind combination of chemical elements designed with specific properties to maximise operational performance.
These are just a few of the industries that use O-rings.
Transportation industries like automotive, aerospace and heavy-duty trucking necessitate the use of extremely high temperatures, chemical exposure, and vibrations, all of which can be mitigated by O-rings. They are also used in engines, brake systems, fuel systems, liquid rocket propellants, and other applications.
Several pieces of medical equipment rely on O-rings to function. Syringes, pumps, filtration devices, and connectors are among them.
Petroleum and natural gas
Because of the constant contact with aggressive media, high pressures, and a wide range of temperatures, chemicals, and additives, applications in the oil and gas industry are typically challenging. As a result, O-rings are used to withstand all challenging elements.
Installation of O-rings
The way an O-ring is installed determines its functionality in machinery. As a result, it is advantageous to know how to properly install an O-ring without damaging it or any other part of the machine. If O-rings are not correctly installed, it is only a matter of time before they begin to tear, creating a path for leaks and foreign materials to enter the machine.
To properly install an O-ring, you must follow a few basic steps.
Use the appropriately sized O-ring
Even though most O-rings are flexible and elastic, you must have the correct size to fit into the groove. If the O-ring is too small, it will tear due to stretching, and if it is too large, it will not provide a tight seal. Even if it works the first time, the O-ring’s lifespan will shorten, and it will begin to tear after a few uses.
Do not exceed the maximum elongation
Even though O-rings are mostly made of elastomeric materials and can be stretched to some extent, they should not be overstretched. This is because they become weak and vulnerable when stretched beyond their maximum rate. Therefore, stretching should be limited to 1% to 5%, with 2% being the most common.
When a thin layer of lubricant is applied to O-rings, they perform better and have a longer lifespan. This simple action protects the O-rings from damage. It also makes it easier for the O-rings to fit, avoids drying out, and reduces tension between the surfaces.
Don’t roll the O-ring
Instead of being rolled down, O-rings should be slid into place. When O-rings are rolled down the shaft, spirals form, reducing the rate at which they function. And an O-ring with a spiral wound is easily damaged, resulting in additional leakage. To avoid this, the O-ring should be properly lubricated to slide easily into place.
Cover sharp edges
Sometimes you must install an O-ring into a part with sharp edges that can damage the O-ring if not done carefully. In such cases, you should cover the edges with masking tape or another material and apply lubricants to them so that the O-ring can slide in easily.
Choosing an O-ring
These are the factors to consider when designing and selecting an O-ring type.
The first factor to consider is the compatibility of the O-ring with the fluid(s) that must be sealed. You must know whether there will be an immediate negative effect when the O-ring encounters harsh chemicals or if the effect will be gradual. When the O-ring comes into contact with more than one fluid, the sequence of exposure and the time of contact should be considered.
The system temperature may necessitate minor modifications to the gland design. For example, if the operation is only performed at high temperatures, the gland volume will need to be increased. This compensates for the O-ring’s thermal expansion. On the other hand, reduced gland depth will produce a better seal, ensuring that the contracted O-ring is properly squeezed for operations solely at low temperatures.
Pressure influences the design of O-ring seals because it influences the choice of compound shore hardness. At very low pressures, tight sealing with low durometer hardness is possible. However, the interaction of pressure and material shore hardness at higher pressures determines the maximum clearance that can be safely allowed.
Anti-extrusion (backup) devices can be used to prevent O-ring extrusion. These are small rings made of tough materials. They are inserted between the seal and the clearance gaps in the gland, providing no clearance.
O-ring lubrication is critical for proper static seal seating and the installation and operation of dynamic seals. The best time to apply lubricants to O-rings is during the installation process. Lubricants used on O-rings during this stage protect them from damage caused by cutting, pinching, or abrasion. In addition, lubrication allows for more accurate O-ring seating, faster assembly processes, and automated assembly line procedures.
Contact Fuzion Trading for details
Fuzion Trading manufactures and stocks a wide range of O-rings for industrial and commercial applications. Contact one of our representatives to learn more about our specialised range of O-rings. Alternatively, you can continue browsing our website for more information.