Oil Seal Selection Guide: Common Types, Materials, and Real-World Specs

Lubricants are often used in machinery to keep it running smoothly. The issue is that if that lubricant begins to leak, it can cause damage, degradation, and destruction of the machinery, leading to delays and disruption.

Oil seals prevent the leakage of lubricants within automotive engines, hydraulic systems, and other industrial equipment. This protects the interior components from external contaminants.

But not all oil seals are made the same. Different types, materials, and even sizes offer a range of applications. From sealing rotating shafts to reducing dust entry, selecting the right oil seal is crucial to the correct functioning of the machine.

What are Oil Seals?

Oil seals (as the name suggests) are a sealing device used in machinery. They prevent leakage of sealed lubricants from inside and stop the entry of contaminants, like dust, dirt, water, or metal powder, from outside.

There are several different types of seals. Oil seals are a major contact-type sealing device. This refers to any mechanical seals where two or more components physically touch to prevent the passage of fluids or contaminants between the two areas.

How Oil Seals Work

Oil seals are more complicated than they first appear. The device can come in numerous shapes, sizes, and materials depending on the application.

Generally, they have a few features in common:

• Main Lip. This is the sealing edge that comes into contact with the shaft surface.
• Minor Lip. This prevents the entry of dust, dirt, and other contaminants into the interior.
• Sealing edge. The wedge-shaped part that makes contact with the shaft.
• Spring. Provides a tightening force to ensure a tight seal.
• Metal Case. Add rigidity to the seal and secure it within the housing.

Common Types of Oil Seals

Oil seals come in a staggering variety of options. If you're not familiar with the different varieties, it can be hard to know where to start.

The most important factor is in the structure of the seal. The different types also differ in the components. For example, a seal might have a spring or not have a spring, it might have no minor lip or be made of rubber.

There are two primary types:

• With Spring. Oil seals with a spring provide a tighter seal. These can either have a minor lip or no minor lip and have a rubber or metal case. There can also be a reinforcing inner metal wall. Every combination of these factors is available.
• Without Spring. Similarly, these can either have a rubber or metal casing wall or be with or without a minor lip.

The rubber or metal outer diameter surface can either provide a greater seal (as with rubber) or improve the fitting retention within the housing bore (as with metal). The reinforcing inner metal case protects the main lip if friction is a concern, and the presence of a minor lip is only relevant when contamination from the outside is a significant issue.

Seal Types

On the inner surface of the rubber oil seal, there is a specific type of groove. The groove pattern can provide a particular type of seal, either locking in the internal lubricants or offering a balance of sealing against the outside and inside.

Common seal types include:

• Helix Seal. The groove pattern faces in one direction on the air side, providing greater sealing performance.
• Perfect Seal. The groove pattern faces two directions on the air side, providing greater sealing performance in both rotational directions of the shaft.
• Super Helix Seal. Similar to the helix seal, the ribs are two-stepped, so that if one lip is worn out, the second lip comes into contact with the shaft.
• Seal with Side Lip. The pronounced side lip prevents entry of contaminants from the outside, e.g., dust or water.

Materials Used in Oil Seals

If you're already a little confused, that's okay. Just focus on the basics: springs increase the seal against the shaft, metal or rubber casings balance the seal against a secure fit, and the seal type balances the seal against friction and how the machine operates.

But there's another factor: the material the oil seal is made from.

Generally speaking, the metallic component is either galvanized or stainless steel:

• Galvanized steel is a cost-effective option that is coated in zinc to provide corrosion resistance. However, if the zinc is scratched or worn away, the underlying steel can rust. This makes it unsuitable for food-grade environments. Common in industrial or automotive settings.
• Stainless steel is corrosion-resistant and stronger than galvanised steel. It provides a smooth, low-rust seal that is suitable for food-grade environments. The downside is the higher cost.

The rubber oil seal is where the options become more varied. Most types of rubber are used, including:

• Nitrile. This low-cost option offers good oil resistance, moderate chemical resistance, and a wide effective temperature range.
• Viton®. High cost but offers excellent chemical and oil resistance.
• Silicone. High cost but good chemical and oil resistance. Suitable for food and pharmaceutical settings.
• PTFE. High cost for outstanding chemical resistance and excellent oil resistance. Used in chemical processing.
• ACM. Mid-cost, offering very good oil resistance and good chemical resistance. Common in auto transmissions.
• HNBR. Popular in modern engines due to mid-cost and excellent oil and chemical resistance.
• Polyurethane. Common in shock absorbers. Mid cost, moderate oil and chemical resistance. Not suitable for high temperatures.

There are also unusual examples like a polybenzimidazole-filled PTFE lip that enhances the lip's performance under high-speed and high-pressure conditions.

Real-World Specifications

Oil seals are found almost everywhere. They're used in everything from food and pharmaceutical production to automotive engines. If there's a lubricant used against a shaft, oil seals will be present to ensure the lubricant doesn't escape.

For example, a spring-loaded rubber lip seal is often used in engines against the crankshaft. The hot engine oil and high-speed rotation require a special type of seal. In contrast, hydraulic cylinders rely on a metal-cased oil seal. Here, the high pressure and potential for hydraulic fluid leakage mean there can be no risk of the seal slipping out of its housing.

Forever Seals is a trusted oil seal manufacturer, producing almost every kind of oil seal imaginable, from metal casings to rubber oil seals. We've got a solution for every machine. Browse our full selection of oil seals today, including industrial oil seals and automotive oil seals.

Frequently Asked Questions (FAQs)

How do I choose the right oil seal for my application?

That depends on the application environment. You'll need to consider the material type and the shape of the oil seal. If there's a risk of outside contamination, then a tighter seal with a minor lip is crucial. If this isn't such an issue, then these factors are necessary.

You'll also need to balance each material's pros and cons. For example, silicone is the preferred option for food and beverages as it is non-toxic. In contrast, PTFE is the only viable option in chemical processing due to its resistance.

What's the difference between rubber and metal-cased oil seals?

The primary difference is how well it fits into the outer casing. Rubber compresses slightly and provides a more forgiving fit. In contrast, metal provides greater strength and retention within the housing.

When should I replace an oil seal instead of reusing it?

The clearest sign is that something isn't going right. Often, you'll notice a slight oil leak around the seal, unusual noises from the machinery, or overheating. Don't wait. If you notice even the slightest signs of wear, e.g., cracks, tears, or deformation, replace the oil seal immediately.