One of the most used seals in technology is the oil seal. This is generally implemented as a zero pressure seal of lubricating oil and grease on a rotating shaft.
It is sometimes also used for other liquids and gases and for solids in the form of powder or granules. The seal keeps both the grease inside the application and any dirt outside of it with the addition of a dust lip.
The main causes of lubricant leaking from pumping systems, hydraulic machines or gearcases are the wrong selection,
improper application, inadequate installation and insufficient maintenance practices of sealing systems.
These problems can be avoided through a better understanding of the types of sealing materials available,
proper application and maintenance practices.
To help you easily select the right seal for your application, we have compiled in this article some useful tips and explanations of oil seals parameters.
For more information, please visit CDI.
When choosing an oil seal for an application, selecting the correct elastomer is important for maintaining good seal life and avoiding leakage or other damage. Consider the following points when making your purchase:
Be sure to also review the guidelines regarding hardware conditions such as shaft hardness and shaft roughness.
Oil seals are used in many manufacturing industries. With such a broad range of materials available, it can be tricky to select the appropriate material for a certain application. We have compiled the most important facts about different oil seals material so that the choice of the correct oil seal becomes easier for our customers.
In the standard construction, oil seals are made from oil and grease resistant rubber based on NBR (Perbunan). This material has very good running properties and excellent wear resistance. For high shaft speeds, large radialtolerances and good chemical resistance a range of other rubber materials is available at ERIKS.
Material overview for oil seals:
The different elastomers of oil seals are also different in their resistance to certian media. In the following table you can see which elastomer is suitable for which temperature ranges of the sealing medium:
- (minus in table) = For these media the elastomer is not resistant
* (star in table)= Within these groups, there are media which can be sealed by the elastomer in question. although these media could have a disadvantageous influence on the elastomer
For more information, please visit Oil Seal.
ERIKS oil seals are constructed with either a rubber case or a metal case.
Rubber-cased oil seals are the most common oil seal execution, used when a metal-cased seal has the potential to fail. In high temperatures and high pressures, fast expanding rubber can provide a tight fit and more stable sealability. Rubber-cased oilseals are frequently used as replacement for metal-cased oilseals in MRO applications because of easier installation. The most popular rubber-cased seal is Type R.
Metal-cased oil seals are used when installed to a housing bore made of the same material. This allows for equal contraction and expansion of the materials during operation, preventing leakage from occurring. Typically metal-cased seals are more cost efficient than rubber seals, but if the case material and housing bore material are not the same, a rubber seal should be used instead. The most popular metal-cased seal is Type M.
Springs can be made from different materials such as carbon steel or stainless steel including 304 and 316. Spring steel is often used as material name, refers to carbon steel, and is known for its pliability and strength.
An oil seal is principally intended for operating under normal atmospheric conditions. If however the peripheral speed does not exceed 8 metres per second, the oil seal is able to withstand a pressure of ca. 0,5 bar.
Oil seals with a large shaft diameter (500 mm) the pressure which the oil seal may be exposed to is 0,1 bar.The permissible pressure greatly depends on the operating conditions such as shaft speed, temperature and lubrication.
If the actual pressure exceeds the permissible maximum, the lip of the oil seal is forced against the shaft, resulting in a higher radial load, a higher level of friction, and excessive wear of shaft and seal.
To balance the pressure, oil seals can be provided with a supported sealing lip by using an easily fabricated metal support ring. Oil seals with a supported sealing lip can be used on small diameter shafts for pressures up to 6 bar if conditions are favourable (low temperatures, relatively low speed, good lubrication)
Oil seal sizes are typically specified by three common dimensions: the rotating shaft diameter (sometimes referred to as the inside diameter of the seal),
the housing bore diameter (also called the outside diameter of the seal), and the housing width (thickness) of the seal itself.
Because of an oil seal’s purpose, the right size is crucial.
The inside diameter of the oil seal must always be slightly smaller than the shaft diameter in order to seal lubricants inside and prevent harmful contamination.
In order to find the right oil seal, one needs to know parametres such as the diameter of the shaft and the housing or the width of the housing - these parametres are all measured in mm. The following images help to identify which part of the oil seals has to be measured to know these parametres.
This is the fastest speed the seal can support without potential failure.
The maximum allowable shaft speed is a function of the shaft finish, runout, housing bore and shaft concentricity,
type of fluid being sealed and the type of oil seal material.
When speed surpasses a seal's limit,
the sealing lip can experience excessive wear and tear due to the increased friction.
This wearing can negatively impact a seal's service life, and lead to oil leaks and machine downtime. The maximum shaft speed is measured in m/s.
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The SKF sleeve is looking like a very good option at 20mm width - thanks again.I believe you retain the standart seal size.Better confirm though.
http://www.barnwell.co.uk/catalog/product_info.php/products_id/55
It's looking tight to accomodate the sleeve's installation 'flange' inside the seal but I don't see a problem in fitting it the other way around - I'd just need to leave off outer rubber dust seal, which is what has caused the corrosion in the first place.
One follow-up question please: do you then use a standard oil seal over the sleeve or does it need a special slightly-oversize one from SKF?
It's looking tight to accomodate the sleeve's installation 'flange' inside the seal but I don't see a problem in fitting it the other way around - I'd just need to leave off outer rubber dust seal, which is what has caused the corrosion in the first place.
One follow-up question please: do you then use a standard oil seal over the sleeve or does it need a special slightly-oversize one from SKF?
I used one of these from Barnwell to repair the output shaft/flange on my PRM gearbox. Due to clearance issues and the need to get the new repair section further down the shaft I fitted it the wrong way round and once the installation flange was removed I then chamfered the lip on a lathe to remove any sharp edge to protect the new seal when fitting.
If you are careful and have no lathe access then the edge could be smoothed with fine wet and dry.
They are designed to be used with standard seal as the metal is extremely thin.
Had to rebuild the MS3B on my last boat. Couldn't find a manual so I wrote one - here if you want it ...
http://turbo36.files.wordpress.com//01/volvo-penta-ms3b-gearbox-overhaul-instructions.pdf
Yes I've already got your excellent manual, thanks. It isn't the same gearbox as mine though and there are some major differences e.g. your output seal was in a carrier held on by 4 bolts whereas mine fits directly into a recess in the gearbox end plate with no seperate carrier plus the seal dimensions are different. Also the water cooling arrangement is completely different, as is the slip clutch flange.I am sure it was an MS3B, as this was stamped on the dataplate. It was coupled to a TMD40A.
Are you sure yours wasn't an MS3 - which is what the exploded diagram in your document is entitled?
P.S. I found a Volvo workshop manual for the MS3B (in Norwegian!) here:
boatinfo.no/lib/gear/manuals/vp-ms3b-swe.html