Oil Seals 101 – The Ultimate Guide | Dechengwang - PTFE
Oil Seals 101 – The Ultimate Guide | Dechengwang - PTFE
Lubricants applied between moving and stationary elements of mechanical equipment help to prevent damage. But when the equipment are under high pressure, the lubricants tend to escape, hence the need for oil seals to prevent the clashing of dry parts. Practically all mechanical equipment, including car engines, assembly machines, and PTFE machined parts use these oil seals to prevent harmful interaction that can result in damaged parts.
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In this guide, we will dwell deeply on oil seals and discuss everything that you need to know, such as what it is, how it works, why it fails sometimes, materials used in making it, factors to consider in choosing the right one for your application, and so on.
Oil seals, which are also referred to as radial shaft seals, rotary shaft seals, grease seals, or fluid seals, are used to close the gaps between fixed and moving parts of mechanical equipment. They are put between moving and stationary mechanical parts to make sure that moisture, contaminants, corrosive materials, and abrasives don’t cause any damage to these parts.
Oil seals are protective elements. They prevent the mixing of water and lubricants within a machine, thereby ensuring optimal machine functionality. Also, oil seals help to prevent lubricant leakage at high pressure like when the machine is working at an extremely high rate. Not only that, radial shaft seals stop foreign components from entering a machine. This is because they can contaminate the lubricant and even damage the machine.
Oil seals work by squeezing and retaining lubricant in a thin layer between the lip and the shaft. Perfect sealing is ensured by the hydrodynamic action of the rotating shaft, which in turn produces a slight pump action.
As earlier said, oil seals perform some functions that ensure the functionality of mechanical equipment and extend their lifespan. And how they do this is by retaining lubricants at all cost and not making them escape no matter how high the pressure of the machine is.
The other way oil seals work is by stopping outboard materials that can damage the machine or contaminate its lubricant. The outboard materials that the oil seal will need to stop depend on the application. However, the most common kinds are dirt, moisture, and the particles produced during manufacturing.
Standard petroleum oil has a lifespan of 30 years at 86 degrees Fahrenheit if it’s not
contaminated with moisture or any other particle. But the same oil will only last for a month at 212 degrees Fahrenheit if it’s contaminated with little water. This is why the function of an oil seal is very evident whenever it’s used.
Oil seals are always exposed to a lot of chemicals, both mild and harsh chemicals. The seals react by showing some signs like cracks, blisters, and discoloration especially when the chemical is harsh. This clearly shows that the chemical is not compatible with the seal, which goes as far as affecting its cross-link density (increase or decrease). When the cross-link density increases, the seal material becomes harder, but when it decreases, the seal material becomes softer.
When the oil seal material and the chemical are not compatible, there will be a chemical attack, which increases at high temperatures. The only way to remedy this is to select the right material for your application. If you’ll be dealing with harsh chemicals, choose oil seals that are made with reliable materials for their compatibility.
The major cause of extrusion and nibbling is stress caused by high pressure. This is commonly noticed when the oil seal has a chipped or nibbled look. In fact, in some cases, the surface of the seal tends to peel on its own, which makes it have a shaved look. What the stress does is that it increases the clearance gap between the mating edges, which causes the seal to get entrapped, and then leads to severe physical damage.
The perfect solution to this is to always use an oil seal that fits properly; the right size of the seal should be used. And in other cases, backup devices should be used to avoid the buildup of clearance gaps within the mating edges.
This is one of the frequent reasons for oil seal failure, and this is majorly because of the volatility of any of the elastomer’s constituents. These causative constituents may be part of the elastomer formulation, or gases that got entrapped in the elastomer during the molding process. The deceiving fact about this failure is that sometimes the oil seal won’t show any visual sign of out-gassing, however, sometimes when the out-gassing is extreme, they shrink.
The perfect remedy for this is to use oil seal materials that are rated for the temperature of your application. Also, ensure that the elastomer is free from volatile constituents like waxes, plasticizers, etc.
Nitrile is the most widely used rubber (elastomer) and it’s recommended as the best for almost all standard applications. This is solely due to the fact that nitrile has some intrinsic properties, such as low cost and compatibility with most environments. Some of the general applications of nitrile are non-latex gloves, automotive transmission belts, footwear, gaskets, synthetic leather, hoses, o-rings, and oil seals.
Nitrile is suitable for environments that have a temperature range of -30 degrees Fahrenheit to 250 degrees Fahrenheit. It is compatible with a variety of fluids, such as hot & cold water, silicone oil, animal & vegetable fat, hydraulic fluid, and gas oil. Nitrile is also a perfect material to use for any application that needs shock absorbers as it’s resistant to grease and abrasion.
However, it’s plagued with a few drawbacks, such as poor resistance to ozone, sunlight, and weather. It also has limited resistance to high temperatures and flames.
Polyacrylate oil seals are a perfect compromise between quality and cost. They perform well with high temperatures and chemicals, but not as well as Viton oil seals. Polyacrylate has a temperature range of -25 degrees Fahrenheit to 300 degrees Fahrenheit. Due to their outstanding resistance to hot oil and oxidation, they are commonly used in automobile transmissions and hoses; however, they are also used for shaft seals, gaskets, and o-rings.
Despite being a great substitute for more expensive high temperature resistant materials, polyacrylate has a problem of poor water compatibility and cold flexibility.
Silicone oil seals, which are also called VMQ, have strong resistance to temperature, which ranges from -140 degrees Fahrenheit to 392 degrees Fahrenheit. They are also resistant to ozone, light, and harsh weather conditions. Silicone is frequently used in hydraulics and pneumatics, as well as in the food and medical industries. Due to the material’s transparency and flexibility, it’s commonly chosen for the manufacturing of o-rings, molded parts, and flat seals, as well as electrical insulators.
Despite being incredibly flexible, silicone has some significant drawbacks. The toughness, resistance to wear, and abrasion of many silicone compounds are poor. If you seriously need an oil seal material with better strength and resistance to high temperature, the perfect option is Viton.
This is a specific type of synthetic rubber that’s commonly used in o-rings, gaskets, oil seals, sterile & chemical resistant gloves, and other molded items. Viton has a high density and it possesses the widest temperature range of -40 degrees Fahrenheit to more than 400 degrees Fahrenheit. This is why it’s highly preferred as the best material for higher temperature applications.
Also, Viton has the widest range of resistance to chemicals. It’s resistant to several chemicals like silicone oil & grease, mineral & vegetable oil, aliphatic, chlorinated hydrocarbons, methanol fuels, and so many more.
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Even though it’s better than other materials in terms of toughness and wear time, it is preferably used in dry-running applications. The salient demerit of this material is its cost.
Leather oil seals are commonly used for parts that are exposed to dirt and poor lubrication. The major advantage of this material is that it can function in cases where synthetic rubber cannot function. They are used for shafts that have rough surfaces that are more than what rubber seals can handle. This is because they are pre-lubricated and have the capacity to absorb liquids.
Leather oil seals have great running properties and are mostly used for abrasive applications.
O-rings, which are also referred to as oil seal rings or oil ring seals, are designed to join two parts and ensure that no air, moisture, or gas is allowed to pass through. They are usually inserted into a groove and manufactured to resist pressure. The resistance is what stops foreign elements from entering or leaving the joining.
O-rings are the most commonly used seals as they provide incredible value – very affordable, versatile, and efficient. They are made with several elastomer materials as to the application they will be used for, so it’s important that you know the materials an o-ring is made of before purchase.
Some of the uses of o-rings are pipes, plates, flanges, and cylinders. They can also be found in cameras, and scuba gear.
Spring seals are the perfect solution when regular seals are unable to produce a leak-proof mating surface. They are the best substitute for sealing applications involving machinery as they are capable of resisting more heat and pressure than other types of seals.
When they are subjected to hot & pressured oil, or hot & pressured gas, they will compress. These seals reduce in size and become more compact. Afterward, they store the mechanical energy generated by the heat and pressure, which is why they can maintain a leak-proof mating surface.
Lip seals are passive mechanical devices used to close the shaft exit points on electric motors and other rotating machinery. The seals are made to keep moisture and dust out of the machinery’s inner constructions while having little to no impact on how well they work.
Almost every lip seal is constructed to have a flexible inner part that creates a dynamic seal on the moving shaft, as well as a hard outer casing that statically matches the machine-end cover. The flexible part is made from different grades of rubber, while the hard part is made of light-gauge metal or strong plastic.
To increase the pressure around the shaft and maintain the seal’s integrity, certain lip seals have an extra spring looped into the flexible rubber part.
Seals perform best when they are lubricated, however, some machines quickly go on dry spells. So, in cases like this, choosing a leather or PTFE seal is the right decision to make as both of them can function with less lubrication than other types of seals.
Another factor you need to consider is the type of lubricants that are more suitable for the seals. Check for the appropriate viscosity of the lubricant that’s compatible with the seal material.
The functionality of oil seals in between machines cannot be emphasized. Apart from their primary function of preventing the entry and escape of elements that can damage the machines, they also help to elongate the machines’ lifespan.
In this article, we’ve discussed everything you need to know about oil seals, which are sometimes called radial shaft seals. Also, we’ve discussed the various types, their installation, and how to choose the right one for your application. With all these, you will be able to make an informed decision about the best oil seal for your needs.
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