The Ultimate Buyer's Guide for Purchasing high temperature oil seal

Seal High Temperature: A Comprehensive Guide

Seals are an integral part of many industrial types of machinery. It is the common opinion that high-temperature seals are tougher to manufacture when compared to low-temperature seals. This is because high-temperature resistant seals have to be manufactured from the most suitable material to withstand very high heat and pressure in given conditions.

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Not sure where to start when it comes to heat-resistant seals? Then this article is the right place for you! Read ahead to know more about seals that are used to seal high-temperature situations.

What Are High-Temperature Seals?

High-temperature seals are devices that are used for many purposes including preventing leakage, containing pressure, and avoiding contamination. The specialty of high-temperature resistant seals is that they are designed to prevent leakage across parts even when the machine is present in high-temperature situations. Usually, these devices can seal high temperatures up to ℃.

Due to their application in places like turbines, exhaust systems, and fuel cells, these seals need to be made of the most suitable material to minimize leakage and offer high resistance. As the seals endure extreme situations, they will eventually wear off if it is not made from the right material. 

Applications of High-Temperature Seals (about 470 words)

High-temperature seals find a wide range of applications in various fields because of their capability to withstand temperatures up to ℃. Manufacturers like Dechengwang employ expert designers who consider all the necessary factors before designing the seals that are used in high-temperature and pressure situations.

Aerospace

Fluoropolymer seals made of materials like PTFE are incredibly useful in the aerospace industry. These are high-temperature sealing parts that offer reliable protection during high-temperature situations that arise in many parts of the vehicle, from the engine to its surface. 

During re-entry into the atmosphere, the surface of the vehicle experiences immense levels of friction, leading to extreme temperatures. High-resistant seals can act perfectly in situations like these.

Automotive

Mainly used in the engine compartment, rubber seals help in absorbing extra heat and compression. High-temperature seals also find applications in various parts of a vehicle – for example, high-quality seals are an integral part of any transmission so as to avoid grime and other contaminants damaging the functioning of the transmission. Seals are also used for maintaining pressure within the compartment where the engine is placed.

Mechanical Engineering

Be it refineries, chambers, or turbines, high-temperature situations are inevitable in the mechanical engineering industry. When it comes to systems that regularly deal with extreme pressure and temperatures, it is important to choose a reliable high-heat seal that can offer effective sealing properties. 

If proper seals are not used to seal high-temperature situations, they might lead to leakage and corrosion, causing hazardous accidents.

Chemical Plant

Many chemical processes and reactions take place in extreme physical conditions like high or low temperatures. Seals used in chemical plants and industries need to be highly resistant because fluids of high temperature and pressure are transferred. 

Transfer of such fluids also eventually corrodes and wears off the mechanical parts used in the plants, so it becomes crucial to use high-quality high resistant seals and pumps.

Oil & Gas

The drilling of wells for oil and gas involves working in high-pressure, high-temperature situations. Both on and off the field for refineries, high-temperature sealing parts such as seals and O-rings are used to carry out the necessary processes smoothly. In these circumstances, only rubber and polymer seals can perform and retain their characteristics, thus offering long life and minimal issues.

Medical Engineering

Many people are not aware of the wide applications of seals in the medical engineering field. Rubber seals are used in many components like medical pumps, IV pipes, implant materials, lab equipment, and even temperature-controlling devices. 

Also, high-temperature-resistant seals find wide applications in this field – these components are an essential part of temperature-controlling and measuring devices.

Food Processing

When it comes to the food processing industry, purity, and stability are two important characteristics that one should look for in the devices used. PTFE is one of the best materials to use for high-tolerance seals when it comes to food processing and related industries. 

Since these seals come in contact with chemicals and other dangerous fluids of extreme temperatures and pressures, it is important to choose the right type of seal.

Factors to Consider When Choosing High Heat Seal Materials

It is of immense importance to choose the most suitable material for a high-heat seal. The wrong material can cause the seal to malfunction in extreme temperature situations, thus leading to potential hazards and damage. Here are some factors to consider while choosing materials for high-temperature seals:

Material Compatibility

High-heat seals are widely used in many industries. So, it goes without saying that throughout their life, seals come in contact with a variety of materials and fluids. Seals also come in contact with the environment and the other devices and components that are a part of the setup.

The material from which the seals are made should be compatible with the substances that they are going to interact with. For example, if a high-resistant seal is used in the chemical industry, it should be capable of withstanding corrosion as the seal will come in contact with dangerous chemicals.

Temperature Limit

The temperature limit of the material of the seal you are choosing is the most important factor to look out for. High-temperature seals will be employed in extreme situations, so they need to have high resistance to temperature and pressure. 

Often, extreme temperature and pressure can alter the characteristics of the material – this is not ideal for a seal. Also, the seals should be neutral to chemicals and other reactive materials.

PTFE material seals can be used in the temperature range of -180℃ to 260℃. This makes PTFE the best option to use in both extremely low and high temperatures.

Thermal Expansion and Contraction

The coefficient of thermal expansion is a material property that points out the extent to which a material will expand when it is heated. Elastomers in general have coefficients that are nearly ten times that of steel. In the case of PTFE, it has a high thermal coefficient, meaning that it expands when exposed to high temperatures.

When it comes to high-temperature seals, the coefficient of thermal expansion will determine the extent to which the sealing will grow or contract compared to its comparative metal components. High-quality PTFE seals like the ones offered by Dechengwang are capable of overcoming minor setbacks to perform a long life.

Resistance of Compression and Load

The compression set resistance of a material can be understood as its capability to revert back to its original shape after enduring resistance for a given time. This property of a seal is very important because it determines the capacity of a seal to withstand pressure and other external factors.

Many elastomers and fluorocarbon-based polymers have a great resistance-of-compression factor, making them a reliable choice of material for making products like gaskets, seals, and O-rings. 

Carbon-filled PTFE is one of the best materials in which highly resistant seals can be made – apart from excellent compressive strength, this material also exhibits resistance to corrosion.

Application Scenario

Another crucial factor to think about before choosing the material for a high-heat seal is the application of the seal. Depending on the industry in which the seals are to be used, the materials will differ. 

For example, seals made of fluorocarbon-based materials have high resistance to compression and can withstand extreme temperatures. This makes them a reliable choice for oil and gas industries.

If the application scenario involves a chemical plant, then manufacturers have to look for materials that are neutral to chemicals and can withstand corrosion. Thus to seal high-temperature situations in different scenarios, seals made of different materials might be needed.

Instructions for High-Temperature Sealing

To achieve perfect high-temperature sealing, one should follow a series of steps. The process starts with choosing the most suitable seal for a particular application and proceeding with the sealing methods and procedures. Also, it is important to conduct regular inspection checks to ensure that the seals are working properly.

Select Suitable Seals

There are many different factors one should consider before choosing a particular seal for an application. Some of the most important factors include:

Fluid pressure range – the range of pressure in which fluids will flow in a system

Temperature range – the maximum and minimum temperature sets in the system at which the seal will operate

Dimensions – the size and width of the pumps and cylinders will determine the size of the seal – the seal has to fit perfectly to avoid leakage.

Application – based on industrial application, the seal has to be chosen, as different applications demand particular characteristics.

Prepare the Sealing Surface

Now that the right seal is selected, it is time to work on a proper sealing surface. The sealing surface where the seal and the hardware of the machinery interact needs to be smooth – it is very important that this surface is clean and uniform.

Instructions for High Temperature Sealing

Choose the Appropriate Sealing Method

When handling high-temperature sealing, it is of great importance to pick the proper sealing technique. The most common kinds of sealing techniques for high temperatures one should be aware of are o-rings, sealants, gaskets, compression packings, and many more. 

For choosing the appropriate sealing method, it is best to pay attention to a wide variety of aspects, including pressure conditions, operating temperature conditions, kind of equipment used, chemical compatibility, etc. 

Follow Proper Sealing Procedures

Following proper high-temperature sealing procedures is essential for safety and credibility. Start with cleaning the surface of the sealing using safe-to-use cleaning elements. Paste the sealing material considering the operating pressure and temperature needs.

There are different types of procedures, like curing, compression, and torquing. Thus, do not go overboard with the pressure and temperature ranges during the sealing procedure. Prior to putting the sealing under high temperatures, it is best to leave the sealing material after applying it. 

Perform Regular Inspections and Maintenance

To make sure that the high-temperature seals are functioning properly, conducting routine inspections and maintenance is relatively vital. It is best to perform an inspection every now and then to check the seal’s condition and inspect for any damage such as leakage, wear and tear, etc. 

If any components are damaged, make sure to replace them as quickly as possible. Check the operating conditions such as pressure and temperature to ensure they do not deter the performance of the seals. 

6 Recommended Materials for Heat Resistant Seals

High-resistant seals are put under extreme temperatures and pressure. So, it is necessary for the seals to be made of materials that have a high coefficient of thermal expansion, and also are neutral to chemicals and extreme atmospheric factors. Here are some of the topmost recommended materials for high-temperature seals.

PTFE

Polytetrafluoroethylene (PTFE), also commonly known as Teflon, is a fluorocarbon-based polymer and is one of the most common materials from which rubber seals and gaskets are made. The color of the polymer is white. 

PTFE is a fluoropolymer that is well-suited for manufacturing high-temperature seals. Here are some of its properties.:

Temperature Range: The working temperature range of PTFE is from -180℃ to 260℃. Components made of this polymer function well at both extremely low and high temperatures.

Inertness: PTFE is biologically inert – it does not react to biological fluids, so it can be used in the medical field without any chance of mishaps. The material is also chemically resistant – it does not react to chemicals or does not deteriorate even when exposed to harsh chemicals.

Resistance to Compression: The polymer is highly resistant to compression, so it can retain its original shape easily.

Other Properties: The polymer is non-flammable. Teflon also has excellent insulating properties.

PTFE Compounds

There is a wide range of PTFE compounds like Carbon-filled PTFE, Glass-filled PTFE, Graphite-filled PTFE, etc. In general, all of the PTFE compounds exhibit excellent physical, thermal, and chemical properties that make them a suitable choice of material for making high-tolerant seals. Seals made of these materials also have reduced wear rates and friction coefficients when compared to virgin PTFE.

Carbon-filled PTFE: Contains up to 35% of carbon and the rest is PTFE. The color of the material is black. Parts made of this material exhibit improved resistance to load and electrical and thermal conductivity. The temperature range is from -269°C to 315°C. 

Glass-filled PTFE: Contains up to 40% of glass fiber. The color of the material is cream white. Properties include improved wear resistance, chemical resistance, and optimal performance in an oxidizing environment. The temperature range is from -260°C to 260°C.

Graphite-filled PTFE: Contains up to 25% of graphite. The color of the material is black. Properties include improved sliding properties against soft metals and chemical inertness. The temperature range is from -73°C to 204°C.

PEEK

Abbreviated as polyetheretherketone, this is a high-performance plastic that possesses impressive chemical resistance and mechanical strength. This material is highly recommended for manufacturing seals because they have high dimensional stability – the coefficient of thermal expansion for the material is high. The color of the plastic is light brown or black. 

Temperature Range: At very low temperatures, like below -70°C, the plastic is brittle. As for high temperature, it can withstand up to 260°C, making it a great choice for high-temperature seals.

Inertness: Chemically resistant to common chemicals including acids, oils, solvents, and salts. It’s also biocompatible.

Resistance to Compression: PEEK boasts high wear resistance and tensile strength. 

Other Properties: It’s a lightweight material. Considered to be the ideal replacement for stainless steel. The material also has excellent mechanical strength and stability.

Virgin PEEK is a common choice for making laboratory and medical equipment, thanks to its biocompatibility and chemical resistance.

PVDF

PVDF, which expands to polyvinylidene fluoride, is a fluoropolymer that has many special characteristics. For instance, the material is resistant to nuclear radiation, making it the perfect choice for use in nuclear reactors and related areas. 

PVDF also has high creep resistance – it can endure mechanical stress for a prolonged time in a given environment without losing its sealing properties. 

Temperature Range: PVDF has a wide temperature range: -50°C to 150°C. Due to this range, it is a reliable material for manufacturing high-resistant seals.

Inertness: PVDF has resistance against common chemical solvents like acids and oils.

Resistance to Radiation: PVDF is resistant to ultraviolet and nuclear radiation. This makes the material a great choice for use in the nuclear power industry.

Other Properties: This material has impressive dielectric properties. It also has low permeability.

PCTFE

Polychlorotrifluoroethylene (PCTFE) is a homopolymer of Chlorotrifluoroethylene (CTFE) and is a fluoropolymer that is known for its dimensional rigidity and stability. 

Translucent in appearance, this material is better than other fluoropolymers when it comes to mechanical properties and strength. PCTFE is also preferred for its low permeability.

Temperature Range: The working temperature of PCTFE is from -240°C to 150°C. While seals made of this material can be used in both low and high-temperature situations, it is usually employed in cryogenic applications.

Inertness: The material is resistant to all inorganic corrosive liquids.

Mechanical Properties: Impressive creep resistance, thus making it a great option for applications where there is a chance for high wear and tear. It retains dimensional stability over a wide temperature range.

Other Properties: PCTFE exhibits a great stress-crack resistance factor. It has really low gas permeability. Another specialty of this material is that it has near-zero moisture absorption.

PFA

Perfluoroalkoxy (PFA) also goes by the name vinyl ether. This is one of the few plastics that is suitable to employ in both extremely low and high temperatures. Apart from being used to make seals that seal high-temperature situations, this material is also used to manufacture pipes, fittings, and corrosion-resistant lining for vessels. 

Temperature Range: The working temperature of PFA is very impressive: it works in temperatures as low as -200°C and is also effective in extreme temperatures up to 260°C. 

Inertness: PFA is chemically inert to a wide range of chemicals including solvents and industrial chemicals.

Mechanical Properties: PFA is surprisingly stable at high processing temperatures. It has a low coefficient of friction and also a low dielectric constant. The material possesses impressive stress-crack resistance and creep resistance. 

Other Properties: The material is capable of resisting ignition, thus avoiding the spread of flame in case of an accident.

A Reliable High-Temperature Seals Services Provider: DECHENGWANG

When it comes to the manufacturing of seals used to seal high-temperature parts and situations, it is highly necessary to choose the right material for the seal and follow all the protocols during the manufacturing process. Dechengwang is one of the most trusted providers of high-temperature seals internationally and here are some reasons why: 

Offering Customized Design and Manufacturing

If you need to find a reliable seal manufacturer, Dechengwang is here to help you. We specialize in custom design and manufacturing of seals, O-rings, gaskets, and other machined parts. Our long experience in this field has helped us perfect our processes and achieve high-quality custom designs.

Providing A Wide Range of Sealing Materials

Dechengwang specializes in fluoropolymer materials and manufactures a wide range of products using the same. We use fluoropolymers for manufacturing machined components because of their excellent mechanical strength, chemical inertness, and resistance to corrosion. 

It should also be noted that these materials are the perfect choice for high-temperature sealing parts in applications that involve extreme temperature and pressure situations.

Available With No Minimum Order Quantity

Whether you are interested in placing a small order or big order, everything is possible with Dechengwang. We as manufacturers understand the needs and necessities of our clients and customers, so we do not keep a cap on the minimum order quantity. All of our products are available to order in any quantity the client requires – there are no delayed processes for generating the order either. 

Conclusion

When it comes to choosing high-temperature seals, there are many factors one should consider, ranging from temperature range to durability. The application of the seal also determines the material from which it should be made. PTFE, PEEK, and PVDF are some of the common materials from which high-resistant seals are made.

Looking for a reliable supplier for high-resistant seals? Dechengwang will be the best option. As one of the top-most manufacturers of fluorocarbon polymer components in China, we excel in a wide range of products including O-rings, bellows, and seals. Visit our website today to learn more about our products and services, and get an instant quote for your order!

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.

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.

11 Factors to Consider When Buying Oil Seals

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.

1. Temperature

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.

2. Material

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.

3. Pressure

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.

4. Shaft speed

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.

5. Shaft and bore tolerances

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.

6. Concentricity

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.

7. Runout

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.

8. Quality

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.

9. Shaft hardness

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.

10. Shaft surface finish

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.

11. Lubricant

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.

Oil Seals (Part 2): How to select the right oil seal

In Part 1, we explained the structure, functions, and types of oil seals.

Oil Seals (Part 1): The structure, functions, and types of oil seals

Oil seals come in various shapes to fit the machines and substances to be sealed.
For this reason, when designing a machine, it is important to select the oil seal that is right for that machine.

That's where this column comes in.
We will explain the key points for selecting the oil seal that is right for your machine.

1. Criteria for selecting oil seals

Oil seals come in a wide range of types, and they also have various sizes.
When selecting the right oil seal for your machine from among these many varied types of oil seals, the following two criteria are very important.

Criterion 1: It should be appropriate for the machine's usage environment and the operating condition that is being demanded of the oil seal

Criterion 2: It should be easy to acquire replacement oil seals and it should facilitate maintenance/inspection of the machine

Contact us to discuss your requirements of high temperature oil seal. Our experienced sales team can help you identify the options that best suit your needs.

If these criteria are met, damage of the machine can be reduced, the time needed to replace the oil seals when performing repairs can be shortened, and the machine can be used for a longer period of time.

In this way, selecting the appropriate oil seal will lead to machine design that is economically superior!

2. How to select the right oil seal

In general, oil seals should be selected in the order of priority indicated in Table 1.

However, when you actually select the oil seal to use, the most important factors are past success history and points of improvement, so it is not necessary to follow this order to the letter.
 

Table 1: The order of priority for selecting oil seals

No. Examination item 1 Seal type 2 Rubber material 3 Metal case and spring material

1) Seal type

Select your oil seal type according to Table 2.

Table 2: How to select the seal type

No. Examination item Flowcharts 1 O.D. (outside diameter) wall material Figure 1 2 Necessity of spring Figure 2 3 Lip type Figure 3

 

Table 3: Requirements

No. Requirements 1 Housing Made of steel, one solid design, housing bore surface roughness 1.8 μmRa 2 Substance to be sealed Grease 3 Pressure Atmospheric 4

Shaft surface speed

(peripheral speed)

6 m/s 5 Air-side condition Dusty

Table 4: Type of selected seal

Type 1 Type 2 O.D. wall material Rubber O.D. wall Metal O.D. wall Necessity of spring Spring required Spring required Lip shape Minor lip required Minor lip required
Type (type code)

For a more detailed discussion of seal types and type codes, please see the following:
 

2) Rubber material

The rubber material used in the oil seal should be selected based on the operational temperature and substance to be sealed.
Table 5 lists the major rubber materials along with their operational temperature ranges.
Note that it is necessary to check the compatibility with fluids.
＜N.B.＞
Extreme pressure additives are compounds added to the lubricant. They are activated by heat and chemically react against rubber, which deteriorates rubber properties. For this reason, it is necessary to check for compatibility with rubber materials.

Table 5: Major rubber materials and their operational temperature ranges

Rubber material
(ASTM*1 code) Grade Features Operational temperature range (°C) Compatibility with fluids

Nitrile rubber (NBR)

Standard type

Well-balanced in terms of resistance to abrasion and high and low temperatures

-30～

100

Necessary to check compatibility with fluids
(See *2)

Fluids
• Fuel oil
• Lubricating oil
• Hydraulic fluid
• Grease
• Chemicals
• Water

High- and low-temperature-resistant type Highly resistant to both high and low temperatures -40～

110

Hydrogenated nitrile rubber (HNBR)

Standard type

Compared with nitrile rubber, superior in resistance to heat and abrasion

-30～

140

Acrylic rubber (ACM)

Standard type High oil resistance and good abrasion resistance -20～

150

High- and low-temperature-resistant type Improved low temperature resistance and same level of heat resistance as the standard type -30～

150

Silicone rubber (VMQ)

Standard type Wide operational temperature range and good abrasion resistance -50～

170

Fluoro rubber (FKM)

Standard type The most superior in resistance to heat, and good abrasion resistance -20～

180

Notes
*1 ASTM: American Society for Testing and Materials
*2 For more details on fluid compatibility, please see the following:

Rubber materials, operational temperature ranges and their compatibility with fluids

3) Metal case and spring material

The metal case and spring material used in the oil seal should be selected based on the substance to be sealed.
Table 6 shows how to select the metal case and spring materials.

Table 6: Selection of metal case and spring materials

Substance to be sealed Material Metal case Spring

Cold rolled carbon steel sheet
(JIS* SPCC)

Stainless steel sheet
(JIS* SUS304)

High carbon steel wire
(JIS* SWB)

Stainless steel wire
(JIS* SUS304) Oil ○ ― ○ ― Grease ○ ― ○ ― Water × ○ × ○ Seawater × × ○ Water vapor × ○ × ○ Chemicals × ○ × ○ Organic solvent ○ ○ ○ ○

Notes
* JIS: Japanese Industrial Standard
✓: Compatible
✗: Incompatible
―: Not applicable

 
3. Shaft and housing design

Oil seals can show good sealing performance in combination with properly designed shafts and housings.

1) Shaft design

Table 7 shows the shaft design checklist.

Table 7: Shaft design checklist

No. Examination item Major points to confirm Remarks 1 Material Use one of the carbon steels for machine structural use, low-alloy steel, or stainless steel. Soft materials (brass and so on) are not suitable. 2 Hardness Shaft hardness should be at least 30 HRC. In usage conditions where wear can occur easily because of dust or contaminated oil, hardness should be 50-60 HRC. 3 Shaft diameter tolerance This should be h8 (seals are designed to suit shafts with a tolerance of h8). 4 Shaft end chamfer "Provide a chamfer on the shaft end.
(This prevents failure during mounting.)" See Figure 4. 5 Surface roughness and finishing The shaft surface to be in contact with the lip should be finished to
0.1 to 0.32 μmRa and 0.8 to 2.5 μmRz
and the lead angle to no greater than 0.05°. (There is a risk that the lead marks will impede the sealing performance of the oil seal: see Figure 5.)

Nominal shaft diameter
d1, mm d1-d2, mm を超え 以下 ― 10 1.5 min. 10 20 2.0 min. 20 30 2.5 min.

Figure 4: Shaft end chamfer

a) Good finished surface
(no lead marks) b) Undesirable finished surface
(visible lead marks)

Figure 5: Shaft surface with and without lead marks


 

2) Housing design

Table 8 shows the housing design checklist.

Table 8: Housing design checklist

No. Examination item Major points to confirm Remarks Material Steel or cast iron is generally used as the housing material.
Aluminum alloys and resin (materials with a large difference between the linear expansion coefficients) demand sufficient consideration (as there is a risk of failure due to the increased clearance with the oil seal at high temperatures). 2 Bore diameter tolerance 1. If the nominal bore diameter is 400 mm or less:
H7 or H8
2. If the nominal bore diameter exceeds 400 mm:
H7 3 Bore inlet chamfer Provide an appropriate chamfer with rounded corners.
(This facilitates mounting.) See Figure 6. 4 Shoulder diameter
(if the housing bore has a shoulder) Set appropriate shoulder diameter. See Figure 7. 5 Bore surface roughness 1. For metal O.D. wall type:
0.4 to 1.6 μmRa,
1.6 to 6.3 μmRz
2. For rubber O.D. wall type:
1.6 to 3.2 μmRa,
6.3 to 12.5 μmRz
(Firmly affixes the oil seal and prevents leakage through the seal O.D.)

Nominal seal width
b, mm

B1 min.
mm L
mm Over Up to ― 10 b + 0.5 1.0 10 18 1.5 18 50 b + 0.8

Figure 6: Recommended housing bore chamfers (shouldered bore)




 

Nominal seal O.D.
D, mm

F

mm Over Up to ― 10 D - 4 10 18 D - 6 18 50 D - 8

Figure 7: Recommended housing shoulder diameters

 

3) Total eccentricity

When the total eccentricity is excessive, the sealing edge of the seal lip cannot accommodate shaft motions and leakage may occur.
Total eccentricity is the sum of shaft runout and the housing-bore eccentricity.
Total eccentricity, shaft runout and housing-bore eccentricity are generally expressed in TIR (Total Indicator Reading).
 

A) Shaft runout
As shown in Figure 8, shaft runout is defined as being twice the eccentricity between the shaft center and center of shaft-center rotation trajectory.

Figure 8: Shaft runout

 

B) Housing-bore eccentricity
As shown in Figure 9, housing-bore eccentricity is defined as being twice the eccentricity between the housing-bore center and shaft rotation center.

Figure 9: Housing-bore eccentricity

 

4) Allowable total eccentricity

The allowable total eccentricity is the maximum total eccentricity at which the sealing edge can accommodate shaft rotation and retain adequate sealing performance. The oil seal's allowable total eccentricity is affected by the design of the oil seal, the accuracy of the shaft, and the operating conditions.

For details on shaft and housing design, please see the following:
Examples of allowable total eccentricity for oil seals

4. Seal characteristics

Oil seal performance is affected by not only the type and material of the selected oil seal, but also a variety of other factors, such as operating conditions, total eccentricity, rotational speed, the substance to be sealed, and lubrication conditions.
Figure 9 shows items relating to oil seal characteristics.
 

Figure 9: Items relating to oil seal characteristics

No. Item Content Major factors 1 Sealing property Lip pumped volume
(the volume of oil, etc., pushed back at the lip contact area per unit of time) • Shape
(hydrodynamic ribs)
• Rotational speed
• Oil viscosity, etc. 2 Oil seal service life Wear on the rubber material
Loss of lip sealing function • Operational temperature
• Total eccentricity
• Rotational speed
• Substance to be sealed
• Lubrication conditions, etc. 3 Lip temperature Temperature rise due to sealing edge friction heat because of the shaft rotation • Rotational speed, etc. 4 Allowable peripheral speed When shaft rotation is extremely fast, the sealing performance deteriorates. • Total eccentricity
• Rubber material
• Seal type, etc. 5 Allowable internal pressure Internal pressure is a factor that may deteriorate seal performance. • Total eccentricity, etc. 6 Seal torque The seal torque is large. • Lip radial load
• Lubricating oil
• Rotational speed
• Shaft diameter, etc.

For a more detailed discussion of seal characteristics, please see the following:
Seal characteristics

5. Conclusion

When selecting the oil seal that is right for your machine, it is important that the oil seal be appropriate for the requirements of the usage environment and that it be easily acquired for replacement.
In this month's column, "How to select the right oil seal," we conveyed the following points:

1) Oil seal shape and material should be selected based on the housing, substance to be sealed, pressure, rotational speed, total eccentricity, and air-side conditions.
2) Oil seals can show good sealing performance in combination with properly designed shafts and housings.
3) Oil seal performance is affected by not only the type and material of the selected oil seal, but also a variety of other factors, such as operating conditions, total eccentricity, rotational speed, the substance to be sealed, and lubrication conditions. For this reason, diligent care is required in oil seal selection.

In order for the sealing property of the oil seal you selected to really shine, attention needs to be paid to how it is handled.
In the event of seal failure, it is necessary to take effective countermeasures.

We will cover these points in the next column, "Oil Seals (Part 3)".

If you have any technical questions regarding oil seals, or opinions/thoughts on these "Bearing Trivia" pages, please feel free to contact us using the following form:

The Factors That Affect Seal Selection.

Factors Affecting Seal Selection

When lubricant begins leaking from hydraulic equipment, sumps or pumping systems, the chances are that the incorrect hydraulic seals were selected, installed poorly, maintained improperly or the wrong seals are being used for the application at hand.

However, the good news is that with an understanding of the factors that make for long seal life, most of these issues can be resolved. The other part of this is the importance of redefining the procedure for the selection of hydraulic seals.

Evaluating Factors when Selecting Seals

There are several variables to consider when oil seals need to be chosen. All need to be considered by maintenance engineers and designers.

Factors Involving the Shaft

The surface finish of the shaft onto which it will be installed will determine how effectively a seal can do its job. The best results in terms of sealing can be achieved when the shaft is ground or polished with concentric finish marks. The efficiency of the seal will be affected by the direction of finish marks, as well as the spiral lead. Any use of shafts with spiral leads should lead toward the fluid during rotation of the shaft.

The hardness of the shaft is another important factor. Shafts with RC hardness of 30 or more should expect longer seal life. Shaft hardness should be increased to RC 60 where the seal will be exposed to contamination considered to be abrasive.

Shaft speed is determined by the finish of the shaft and the amount of runout, as well as the concentricity of the shaft, housing bore and type of oil seal material as well as the type of fluid that the seal is preventing from leaking out of the equipment it’s installed on.

Additional Factors

Another factor is the temperature of the location where the seal is going to be installed. Care should be taken to ensure that the temperature at the site of installation will not exceed the range of the seal’s elastomer.

The pressure the seal will be placed under also affects which type of seal is chosen. Typically, most oil seals have been designed for very low-pressure applications of 8 psi or less. Any pressure higher than this will require the installation and use of some kind of pressure relief solution.

The centres of the bore and shaft need to be aligned. If they are not, this will result in the loss of seal life due to more wear on one side of the lip than on the other.

Continuous lubrication is one of the key factors to ensuring long seal life. Seals should be lubricated continuously using oil of the right viscosity for the application. But viscosity is not enough; the oil also needs to be compatible with the elastomer material of the seal’s lip. This is one of the most important ways to ensure a seal works as it should, and also involves the consideration of what kinds of additives will be used and whether or not a synthetic lubricant is being applied.

Where runout is concerned, as little as possible is the ideal if the goal is to extend seal life. When movement exists and the centre of rotation, shaft whip or bearing rotation is usually the cause. If misalignment is also present, this exacerbates the problem. There is also a myth that misalignment can be compensated for by installing flexible couplings. This will not fix the issue.

The presence of close tolerances of shaft and bore will ensure optimal seal performance. However, these are not the only factors; the vibration, eccentricity and end play of the shaft will also affect the performance of the seal.

When it comes time to purchase new seals, the importance of selecting the correct one cannot be underestimated, but this is what tends to occur more often than not, and what ultimately leads to premature and frequent seal replacement.

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?

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.

Are you interested in learning more about NBR Rubber OIL SEAL? Contact us today to secure an expert consultation!