Also known as grease seals, rotary shaft seals, or fluid seals, oil seals play a pivotal role in mechanical equipment. They are often overlooked because they are a small part of the machine, but when these oil seals fail, the consequences can be huge, like seal leakages that are costly to fix.
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From assembly machines to car engines, oil seals prevent any harmful damage from occurring, which is why you must choose the right oil seal with the highest quality. There are many kinds of oil seals, all of which have several uses.
This article will guide you through the most common factors you should look for when buying oil seals to help you choose the right one for the machinery you’re working on.
Improper installation and poor-quality oil seals are some of the reasons that pieces of machinery get damaged. When choosing an oil seal, consider the following factors.
The temperature range of the seal elastomer should match the temperature range of where you’ll install the seal. For example, high-temperature and high-pressure environments need more durable rubber, like Viton. If the oil seal is exposed to extreme temperatures outside of the elastomer’s range, the sealing lip may harden, break, and crack.
The oil seal’s material matters, as it can determine how well it performs depending on its use. Sealing elements can come in leather, silicone, synthetic rubber, Viton, nitrile, and polyacrylate. Nitrile is good for general purposes, as it’s flexible and resistant against oils, hot water, and gasoline. However, it doesn’t do well in extremely high temperatures. Meanwhile, silicone oil seals lessen wear and tear by absorbing lubricants. They have a wide temperature range and high thermal resistance, too.
Understanding the compression requirements of your components is important. Most ordinary oil seals are designed for very low-pressure applications (about 8 psi or less). If the intended application has high pressure, you should consider choosing an oil seal ideal for high pressure or changing to a pressure-free structure.
The oil seal shouldn’t suffer from spiraling or abrasions. As such, you should consider the maximum allowable shaft speed, runout, type of oil seal material, type of fluid being sealed, and housing bore and shaft concentricity before buying an oil seal.
Close shaft and bore tolerances should be present if you want the best seal performance. It would be best to consider the shaft’s vibration, eccentricity, and end play.
You must align bore and shaft centers because misalignment can shorten the oil seal’s life cycle due to the excessive wear concentrated on only one side of the sealing lip.
It would be best if you kept runout to a minimum. When the center of rotation moves, it’s usually caused by a shaft whip or bearing wobble. When you add misalignment, then you’ll face a greater problem. Contrary to common practice, installing flexible couplings won’t correct misalignment, which is why you need the right oil seal to prevent all these issues from arising.
The quality of the oil seal affects its service life. The higher the quality, the longer the lifespan, reducing wear and tear and increasing your ROI through lower maintenance costs. While wear and tear issues are inevitable, you should mitigate them by using materials that last long. Here, the first step to ensuring quality oil seals is purchasing from a reputable oil seal supplier.
When shafts have a Rockwell (RC) hardness of 30 or more, you can expect the oil seal to have a longer seal life. For shafts exposed to more abrasive contamination, your oil seal should handle RC 60.
You can tell that you have effective sealing if the shaft surface finish is in excellent condition. Sealing performance is greatly influenced by the spiral lead and the direction of the finish tool marks.
You’ll get the best sealing results when the shafts are ground or polished with concentric (no spiral lead) finish marks. If the shaft can’t help but have spiral finish leads, they should lead toward the fluid when the shaft rotates.
Oil or lubricants play a significant role in improving the oil seal’s performance. You should choose a lubricant compatible with the seal lip elastomer material and the right viscosity for the application. Incompatible lubrication can result in the wearing out of the oil seal.
An example of a lubricant you can use is Permatex Anti-Seize Lubricant, a highly refined blend of graphite, aluminum, and copper lubricants.
Different Types of Oil Seals
Are you looking to keep your machinery free from any unwanted leakages but aren’t sure which rotary shaft seal is right for your needs? This guide will provide you with everything you need to know in order to select the right one for your application.
Oil seals, which are also known as rotary shaft seals, fluid seals or grease seals, play an important role in closing down the gaps between moving and stationary elements of mechanical equipment.
By preventing lubricants from escaping, they protect key components of machinery from being damaged by leaks of various fluids. Everything from car engines to assembly machines use these oil seals to remain free from any harmful interactions that can cause serious and expensive damage to any of their critical parts.
There are a wide range of oil seals to select from for any number of uses, so this guide will break down the most common seals to help you choose the right one for whatever piece of machinery you are working on.
What are rotary shaft seals?
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Rotary shaft or oil seals are placed between moving and stationary pieces of machinery to ensure that contaminants, moisture, corrosive materials and abrasives do not damage the various components. They can also prevent unwanted mixing of fluids, including water and oil combining within a machine.
How are Oil Seals made?
First, an elastomer, most often nitrile, is vulcanised to a metal ring. This creates a stiffening effect that includes a specialised metal tension spring directly behind the sealing lip, keeping the oil seal firmly in place against the moving part.
Oil Seal Materials
There are many different materials used to manufacture oil seals.
Leather Oil Seals - Leather Seals, also known as Type L Oil Seals, are most common in components that are subject to dirt and poor lubrication. Since they come pre-lubricated and are able to absorb fluids, leather oil seals are able to provide sealing properties in conditions that synthetic rubber is unable to.
Synthetic Rubber Oil Seals - Styrene Butadiene Rubber oil seals, or just SBR oil seals, offer strong resistance to abrasions and lesions, making them an ideal seal for fast-moving machinery. With the ability to withstand extreme temperatures with its heat-aging qualities, they can be used in outdoor components. They are also seen as more cost-effective oil seals than natural rubber.
Nitrile Oil Seals - Nitrile oil seals, which is the commonly used term for acrylonitrile-butadiene rubber seals, is a very good general-purpose option due to the flexibility of use across a variety of components. The resistance is strong against fats, hot water, gasoline, mineral oils, grease and animal oils, making them the most often-used oil seals. They do not have a wide temperature range, making them a poor choice for machinery that can see extreme changes in temperature.
Viton Oil Seals - A synthetic rubber and fluoropolymer elastomer, Viton is used to make oil seals that provide resistance in both high temperature, up to 250°C and low compression set components. They also offer a high resistance to chemicals and abrasions, so they can be used in elements that regularly interact with petroleum and solvents.
Polyacrylate Oil Seals - Mostly selected for automotive and transmission uses, polyacrylate seals are able to withstand fuel, oil, ozone, sunlight and weather when used. With cars exposed to all these different fluids and elements, they are the perfect choice. However, they should not be used in low temperatures, as their flexibility weakens when cold.
Silicone Oil Seals - Designed to absorb lubricants in order to lessen wear and friction, silicone rotary shafts also offer high thermal resistance and a large temperature range. But, they do not handle abrasions well or interact with oxidized oils.
PTFE Oil Seals - A relatively new and exciting oil seal, the use of polytetrafluoroethylene means that they can withstand dry or unlubricated operations. With a massive thermal range of -130ºC to +200ºC and a strong resistance to chemicals, they are considered to be the future of rotary shaft seals.
How to Choose the Right Oil Seal
There are several key factors to consider when you are selecting the oil seals for your next project to ensure that you protect your machinery from immediate and long-term damage.
Pressure - Many oil seals can only withstand low-pressure applications, so understanding the compression set of your components is key.
Temperature - Just like pressure, the temperature that your oil seal will be operating in must be known so that you can choose one that can withstand the heat or cold. PTFE have the widest range of temperature, making them useful for machines who can see usage in extreme weather or elements.
Shaft Speed - Considering the speed that the shaft will be moving, the runout, the housing bore and the type of oil being sealed is vital to making sure you select an oil seal that will not suffer from abrasions or spiralling.
Fluid Types - Various oil seals are able to withstand interactions with oils, fuels, grease, water and more. Knowing what type of fluid the rotary shaft seal will be in constant contact with will ensure the longevity of the seal and surrounding components.
Lubricant Amount - Seals will always perform best when lubricated, however in some machines there are more likely to be dry spells. For these cases, selecting a leather or PTFE seal will be beneficial, as both can operate with less lubrication than others.
If you require any assistance in discovering the factors that lead to the right oil seal choices, the Simply Seals Team is happy to assist you!
Find the right Oil Seal for your needs with Simply Seals!
With dozens of specifically-designed oil seals made from a variety of materials, it can be very difficult to understand the best choice for their machinery.
That is why the Totally Seals team is always available to assist you with choosing the correct style, material, and size of oil seal for everything from commercial machinery to hobby car building.