Custom & Standard Rotary and Shaft Seals
Custom & Standard Rotary and Shaft Seals
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Machines with many moving parts often use oil to lubricate and protect mechanical components. However, when using oil, it’s important to take steps to prevent costly and potentially hazardous leaks. Oil seals offer a simple but effective solution, closing spaces between mechanical components to prevent lubricants from escaping. As an added benefit, oil seals also prevent moisture or chemical contaminants from breaching gaps in the machinery.
MSP Seals offers a full range of oil seals to prevent oil leaks and protect sensitive machinery from damage.
What Are Oil Seals?
Oil seals, alternatively known as rotary shaft seals or lip seals, are flexible rings of elastomer that secure the boundaries between stationary and moving components in a machine. These rings are flexible but durable, resisting wear from friction and exposure to oil. These properties allow oil seals to keep lubricants in a machine while keeping contaminants out. In doing so, oil seals prolong the working life of rotating shafts and precision bearings, ensuring that moving parts retain the lubrication they need for smooth performance.
MSP’s oil seals are designed to withstand extreme working environments, offering excellent durability and low friction properties to promote long working life. Our oil seals are lightweight and have a long shelf life, so they won’t become brittle or interfere with machine operation. Compared to standard seals, they offer improved performance in a convenient and easy-to-install form, making them the perfect solution for rotary shaft sealing.
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What Is The Best Material for an Oil Seal?
Oil seals can be made from several types of polymers, but one of the most effective is polytetrafluoroethylene, or PTFE. PTFE has exceptionally low friction, allowing it to resist abrasion and retain its integrity over time. PTFE is also resistant to high temperatures and chemical solvents, and it requires minimal lubrication, making it ideal for almost any operating environment.
Although PTFE is an excellent general-purpose oil seal material, using elastomers can also be appropriate, including silicone, nitrile, and EPDM. Materials are often chosen based on specific application requirements, such as the need to withstand specific chemicals. The mechanical properties of the rotary shaft, including shaft hardness and roughness, can also impact the selection of an oil seal elastomer. For instance, a softer metal shaft often requires a softer seal material than PTFE.
Why Does Rotary Shaft Roughness Matter for Oil Seals?
Although the physical properties of the seal are important, the properties of the rotary shaft can also affect performance and longevity. One primary consideration in this respect is rotary shaft roughness, which refers to the surface unevenness of the shaft. Rotary shafts can have different degrees of roughness based on their machined tolerance. Smoother shafts have more even surfaces with finer machined tolerances.
Rotary shafts with the appropriate surface finish promote even sealing and limit premature wear due to abrasion. Generally, oil seals perform better when they are paired with smooth, properly finished rotary shafts. However, some surface roughness is desirable as it allows a film of lubricant to flow between the seal and the shaft, extending the longevity of the oil seal.
A rotary shaft that is too smooth exerts extra friction on the oil seal since this lubricant film cannot form. By contrast, a rotary shaft that is too rough can abrade an oil seal, causing it to fail and leak oil.
Why Does Rotary Shaft Hardness Matter For Oil Seals?
Rotary shaft hardness refers to the shaft’s resistance to indentation, which is important to consider when selecting an oil seal elastomer. The seal must always be softer than the rotary shaft to avoid damaging or wearing down the metal, leading to mechanical failure. As mentioned above, this means that softer metals are not always compatible with PTFE, which has a higher hardness relative to other polymers. PTFE seals can erode softer metal components, despite their otherwise favorable performance characteristics.
In general, harder metals are preferable for rotary shafts than softer metals, since increased hardness usually corresponds to more durable shafts and seals. However, the ideal hardness depends on a number of application-specific variables like rotation speed and pressure.
The lowest speed and lowest pressure applications can handle softer metal shafts, but hardness should still be at least 35 on the Rockwell C scale with high lubrication. When speeds or pressures are higher, the ideal rotary shafts might have hardness levels of 60 or 70+ Rc. The ideal oil seal material changes accordingly.
Despite the overall performance advantages of hard shafts, one benefit of softer rotary shafts is that they offer more leeway when working with durable oil seals. A PTFE oil seal polishes underlying metals that have hardness levels below 45 Rc, refining the surface finish for a better seal and less friction.
At higher hardness levels, this polishing effect disappears, so excess surface roughness can be more problematic. Thus, the higher the hardness required for the application, the smoother the rotary shaft needs to be to protect the working life of the oil seal. Even with proper surface finishing, seals used with very hard rotary shafts may wear out faster simply because there is less room for imperfections in the surface finish.
Rotary Shafts & Oil Seals by MSP Seals
Whether your application uses harder metal shafts or softer ones, MSP Seals can help you identify the most appropriate oil seals for your application. Our personalized customer service team works with each client to determine your application’s key constraints, using these factors as a guide for material selection.
As experts in all manner of rotary and shaft seals, MSP offers a diverse range of oil seals and other sealing solutions, including:
- Grease Seals
- Shaft Seals
- Mechanical Seals
- V-Seals
- Braided Packing
We offer both standard and custom configurations for all of our sealing products, with standard and custom sizes measured in inches (SAE, ARP) and metric (JIS, DIN).
While PTFE is our preferred material for performance oil seals, we also offer seals from a wide variety of hard and soft materials. Some of our material capabilities include:
- Carbon
- Ceramic
- Nitrile Butadiene Rubber (NBR, Buna-N)
- EPDM (EP)
- Butyl Rubber (IIR)
- Fluorocarbon (V, FKM, FPM, FFKM, FFPM)
- Neoprene / Chloroprene (CR)
- Fluorosilicone (FSi)
- Polyacrylate (ACM)
- Silicone (Si)
- Polyurethane Rubber (AU, EU)
- PTFE
- Stainless Steel (304, 316, 316L, etc)
- Carbon Steel
- Brass
- Bronze
Our comprehensive sealing offerings include packaging, and labeling, as well as inventory and total cost management for clients seeking full-service sealing partners.
To learn more about MSP Seals, contact our team today. MSP is certified to ISO 9001:2015 and ISO 14001:2015. Our PTFE and sealing specialists are on hand to answer your questions and help you identify the best oil seals for your application.
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Oil Seals
The typical fundamental components of a shaft seal are:
2.1 Materials used for the sealing lip
The material used for the sealing lip is a mixture of one or more basic elastomers and a variety of ingredients, such as: reinforcing fillers, plasticizers, antioxidants, accelerators, etc. This is for the purpose of providing it with certain properties, such as:
- Compatibility with the fluid contacted
- High degree of elasticity
- Wear resistance
- Low friction coefficient.
A familiarity with the materials is essential to help the designing specialist make the proper selection of the most suitable materials for the application of interest. The main qualities of the compounds ROLF uses for producing its shaft seals are:
(acrylonitrile-butadiene)
(polyacrylate)
(polysiloxane)
(vynilidene-fluoridehexafluoropropene)
(acrylonitrile-hydrogenated butadiene)
(ethylene-propylene)
(Identification according to the ISO R 1629 standard of March, 1971).
NBR - Nitrile rubber
The most widely used elastomer in most current applications. It is particularly recommended in case of contact with:
- Paraffin-based (aliphatic) oils
- Mineral oils and fats (oils for engines, gearboxes, differentials, etc.)
- Hydraulic oils
- Water and aqueous solutions (lyes).
The temperature range varies from -30°C to + 120°C.
ACM - Polyacrylic rubber
This elastomer is recommend for use with:
- engine oils even if containing additives and sulfur
- transmission oils
- hydraulic oils.
The temperature range varies from -25°C to + 150°C.
MVQ - Siliconic rubber
Due to its chemical composition (high molecular weight chains of appropriately modified polysiloxanes), this series is particularly resistant toward atmospheric agents, light and ozone. It also exhibits an excellent high- and low-temperature resistance, so that its field of application covers a broad range. Despite its less than fully satisfactory tear and abrasion strength, its low friction coefficient amply compensates for the relative effect. It is recommended for:
- resistance to atmospheric agents, ozone, etc.
- mineral oils
- glycol-based fluids.
Never use with petrols.
The temperature range varies from -55°C to + 180°C.
FPM - Fluorinated rubber
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This elastomer has exceptional heat and chemical resistance. Its properties remain indefinitely stable up to about 200°C. It offers excellent performances in contact with:
- aliphatic hydrocarbons
- aromatic hydrocarbons (toluene, benzene, xylene)
- vegetable and mineral oils and fats, even if containing additives
- chlorinated solvents
- ozone
- light and atmospheric agents.
The temperature range is from -30°C to + 200°C.
HNBR - Hydrogenated nitrile rubber
The chemical structure of this elastomer (obtained by hydrogenating an appropriate type of NBR nitrile rubber) allows achieving, especially if vulcanized with a peroxide system, an average heat resistance 30°C above that of nitrile rubber, and an excellent abrasion resistance.
Its resistance to oils and solvents is on average slightly superior to that of nitrile rubber, except for special cases. It is therefore recommended for:
- heat resistance
- ozone resistance
- abrasion resistance.
The temperature range is from -40°C to + 150°C.
EPDM - Ethylene-propylene rubber
This rubber is based on ethylene-propylene plus a third (diene) monomer which allows its reticulation with sulphur. Due to its chemical structure, it has a peculiar resistance to fluids such as water and steam and environments such as ozone, which recommends its use for:
- water, up to boiling point
- steam
- particular hydraulic systems, such as braking systems
- ozone
- atmospheric agents
- bases
- polar solvents at ambient temperature.
The temperature range is from -50°C to + 150°C.
2.1.1 - Thermal expansion of elastomers
The thermal expansion coefficients of elastomers are decidedly superior to those of metals (see Table below). It is impossible, therefore, to merely consider the geometric shape of a shaft seal and its total radial load at ambient temperature, because its operating conditions and lifetime may substantially vary, depending on the change of the modulus of elasticity induced by a temperature change.
2.2 Metal case
Its function is to offer the shaft seal the necessary rigidity to enable a stable coupling with its relative housing seating. With reference to the elastomer, it may be of an inner (see par. 2.2.1), an outer (see par. 2.2.2) or a part-coated type (see par. 2.2.3).
2.2.1 - Inner metal case
This solution includes the following advantages:
- It eliminates the risk of corrosion
- It avoids damaging the seating, even if made of a light alloy, thus affording a better opportunity of substitutions without damages.
2.2.2 - Outer metal case
This type of case was designed for applications requiring high pulling forces and automated motions based on magnetic systems. In time, it has also been shown that in order to achieve a reliable seal, a ground outer finish and a finely machined seating was needed in addition to the use of sealing materials. Its cost was considerably higher than that of a coated type. It was therefore decided to use it only in combination with high-quality compounds, where most of the cost increase is compensated by the savings in elastomer materials.
At any rate, ROLF solved the problem by producing its seals with their outer surface coated only up to half of its height, as detailed below.
2.2.3 - Part-coated metal case
This solution involves coating the outer case up to about half of its height. This coating is a result of vulcanization and can be plain or corrugated to better fit the assembly forces required by the customers.
The resulting advantages are:
- excellent locking-in in the housing
- savings of high-quality materials
- ease of assembly
- safety in operation
This type of locking is advisable for projects requiring a particularly challenging application.
2.2.4 - Nature of the materials used for the case
In its standard version the metal case consists of a medium/deep draw steel sheet according to the UNI EN10130 or DIN 1624 standards, of a thickness commensurate with the size of the shaft seal. Where a resistance to corrosive fluids is required, it can be supplied as made from
- Stainless steel, to DIN 17440/tab. 1.54401 or AFNOR Z6 CND 17.11 standards (ex AISI 316)
- Brass, to UNI 4894 standards.
2.3 Spring
The spring has a function that is complementary to the fundamental action provided by the sealing lips. In fact, heat, mechanical deformation and chemical action of the fluids affect the original properties of the rubber. As a result, the original radial force exerted by the sealing element tends to decrease. The function of the spring is to counteract this tendency. The spring is a closely wound helical spring in toric form and possesses a calculated initial pre-loadinging force. This is supplemented by a stabilizing heat treatment performed at a higher temperature than the operating one, which makes it possible to achieve:
- at the design stage: the safety of using the most suitable radial force for the expected application,
- at the operating stage: a guaranteed stability of the radial force itself. The temperature effect actually determines, in the course of time, not merely an alteration of the rubber's original characteristics, but also a decrease of the mechanical properties of the steel constituting the spring.
2.3.1 - Nature of the materials constituting the spring
The choice of the materials constituting the spring depends on the type of fluid the Garter spring comes in contact with. In the standard version it consist of a phosphatized, high strength piano wire steel to UNI 3823 or DIN 17223 standards. The standard springs undergo a programmed bedding-in process which allows a precise evaluation of the radial force at the design stage. The use of springs of different material may be considered for particular applications. For instance, in cases requiring a seal against corrosive liquids such as seawater, detergent or acid solutions, a stainless steel spring can be employed, conforming to the following standards:
- DIN 17007 Table 2: 1,4300 or AFNOR Z10 CN 18.09 (ex AISI 302)
- DIN 17007 Table 2: 1,4401 or AFNOR Z6 CND17.11 (ex AISI 316)
- DIN 17007 Table 2: 1,4571 or AFNOR Z8 CNDT 17.12
The use of phosphorous bronze springs, while having the same chemical resistance as stainless steels, is not recommended because of the instability of its dimensional characteristics and the uneven decay of its load capacity.
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