Oil seal basics: how o-rings, seals are designed.

 

Tip: oil seal Basics

Most of you will already understand these basics of how an oil seal is designed but we wanted to put this tip out for people new to the field.

In an oil seal environment there is a shaft that is rotating inside a housing or bore. Because of friction, there must be some clearance between the shaft and the bore. The function of the oil seal is to stop whatever fluid is inside from leaking out the clearance between the shaft and housing. The seal may also be used to prevent outside materials, such as dirt, from moving in through the clearance.

"Dynamic sealing" is the relationship between the rotating shaft and the seal and is handled by the sealing element. A garter spring may used in the oil seal to increase the radial interference between the seal lip and contact point on the shaft. In order to achieve this interference, the oil seal's ID must be slightly smaller than the diameter of the shaft.

"Static sealing" is the relationship between the housing and the seal. In order to achieve this interference, the oil seal's OD must be slightly larger than the diameter of the housing or bore.

An oil seal normally consists of three basic components: the sealing element, the metal case and the spring. The purpose of the sealing element is to stop the fluid from leaking between the shaft and housing. The metal case will give rigidity and strength to the seal while it is being held in the bore or recessed groove. The spring will help make the sealing element more effective. All materials must be selected depending on the environment in which the oil seal will function.

 

Basic Things you Should Know About Oil Seals – Part 1

Basic Things you Should Know About Oil Seals – Part 1

 

Oil Seals

Mar 13, 2018

Oil seals play a crucial role in all rotating and moving part assembly as they act as a physical barrier to retain lubricants, whilst excluding dirt, moisture and other contamination. They are manufactured in a wide range of sizes and specifications to meet several demanding sealing applications across industries. This post, which has two parts, discusses some of the must know things about oil seals. Read on to understand the seals better!

 General Features of Oil Seals

Designed to offer optimum sealing performance, oil seals guarantee extreme durability even under high-peripheral speed. They are light-weight, compact, and exhibit high self-lubricating performance. As oil seals are manufactured using high-grade materials, they last long without showing the signs of any kind of hardening, softening or ageing.

 

Types of Oil Seals

As mentioned earlier, oil seals are available in varied designs to best match the applications. A few of the commonly available types include:

Type A single lip rubber coated w/spring

Type ADL double lip rubber coated w/spring

Type AO single lip rubber coated – no spring

Type AODL double lip

Type B single metal lip-metal case w/spring

Type BDL double lip

Type BO single lip – metal case

Type BODL double lip metal case

Type C single lip full metal case w/spring

 

Choosing the right seal is important as it determines the sealing performance by effectively preventing the leakage of lubricating oils and the ingress of contaminants.

 Materials of Choice

Oil seals are made from several materials. However, the material must be chosen considering several parameters including operating temperature, environment, pressure, and maximum shaft surface speed, among others. The most commonly used materials for oil seal construction are as follow:

PolyTetraFluoroEthylene (PTFE)

Fluoroelastomer ( Viton )

Silicon

Poly Acetal

Nitrile

General Purpose Polyurethane

Nitrile Buna Rubber

Fluorocarbon

Perfluoroelastomer

Polyacetal

Thermoplastic Elastomer

PTFE Filled Polyamid

Hot Water Resistant Polyurethane

Hodrogenated Nitrile

Ethylene Propylene

Fluoro-Silicone

Polyetheretherkeytone

Polyamid

Polytetrafluoroethylene*

Composites

Ultra High Molecular Weight Polyethylene

 Applications of Oil Seals

Oils seals find immense applications in agriculture, automotive, construction, material handling, mining, oil and gas, and so on. They are used in the assembly of:

Conveyors

Elevators

Engines

Grinding Mills

Pipelines

Wind Turbines

 So far, we have discussed features, types, materials used in the construction, and applications of oil seals. In the next post, we will discuss few more general things about oil seals.

Related Post

Oil Seals 101 – Part 1

What is an Oil Seal?

Oil seals, also referred to as shaft seals, are widely used to prevent the leakage of medium (such as oils and grease) along a rotating shaft. This leak prevention is primarily achieved by the sealing element which can be made from a wide range of materials that are chosen according to each application. They are commonly used in gearboxes, hydraulic cylinders, and related components.

Purpose of an Oil Seal

An oil seal is designed to perform three major functions: to prevent lubricants from leaking outside the seal even under high pressure, to act as a barrier to retain the lubricating oil, and to prevent dirt and other contaminants from entering the unit.

Shop for Oil Seals

 

Construction of an Oil Seal

Oil seals normally consist of three basic components: the sealing element, the metal case, and garter spring.

1. Sealing Element

The sealing element makes up the interior of the oil seal, and the materials commonly used are:

a. Nitrile Rubber (NBR) – this is the most commonly used material. It has good heat resistance properties and has good resistance to salt solutions, oils, hydraulic oils, and gasoline. Operating temperatures are recommended from -40 to 248⁰ F (-40 to 120 deg.C). Nitrile also functions well in a dry environment, but only for intermittent periods. The disadvantage of this material is poor chemical resistance.

b. Polyacrylate Rubber (PA) – also known as acrylic rubber, this material has better heat resistance than nitrile. PA is also recommended for a high surface speed environment. Operation temperatures are recommended from -4 to 302⁰ F (-20 to 150⁰ C). Polyacrylate rubber should not be used with water or in temperature below -4⁰ F (20⁰ C).

c. Silicone Rubber (SI) – these compounds operate effectively in a broad temperature range of -58⁰ F to 356⁰ F (-50 to 180⁰ C). Silicone rubber is a leading choice for its resistance to both low temperatures and heat. The high lubricant absorbency of the material minimizes friction and wear. These oil seals are usually used as crankshaft seals. Silicone has poor resistance to hydrolysis and should not be used in oxidized or hypoid oils.

d. Fluorocarbon Rubber (FKM) – is widely known under the Chemours (formerly Dupont™) trade name of Viton® and offers the best resistance to chemicals and superior performance to high temperatures.

2. Metal Case

The metal case is the exterior (or frame) of the oil seal, the principal function of which is to give rigidity and strength to the seal. The material of the case must be selected depending on the environment where the seals are to be used. Often the metal case is covered by the same rubber material used in the sealing element, which also helps seal the exterior of the oil seal in the housing bore. Common case material types are:

a. Carbon Steel – the most common material used in oil seals.

b. Stainless Steel – for applications that require resistance to water, chemicals, or corrosion. (Stainless steel metal cases are also recommended for many FDA applications.)

3. Garter Spring

The garter spring is located at the end of the primary sealing lip and used to apply pressure to the sealing lip against the shaft. Common garter spring material types are:

a. Carbon Steel – which is used in conjunction with regular lubricants.

b. Stainless Steel – which is used when resistance to water, seawater, and chemicals are involved.

Oil Seals From Global O-Ring and Seal

Global O-Ring and Seal carries a full line of oil seals in all industry standard sizes and has the ability to create custom oil seals. If you are a distributor or user of oil seals who may have need for our services, contact us today to speak with one of our team members, request a no-obligation quote, or place an order from our extensive inventory at GlobalOring.com.

Shop for Oil Seals

 

Want to learn more? Read “Oil Seals 101, Part 2”.

 

PRESIDENT/OWNER:
Bill has served in the sealing industry for more than 25 years, and founded Global O-Ring and Seal nearly 10 years ago.