News Seals-Shop GmbH
Jan 30 2019
How to Convert Imperial Units of O-Rings to Metric Sizes
Sometimes, this can be difficult if a part is metric and the only available seals have Imperial units dimensions, or vice versa. Still, this is not an insurmountable obstacle if an engineer knows the conversions involved. Here are some common seal units and the conversions between metric and imperial units for them.
There are several specifications that are essential to selecting the correct O-ring. The inside diameter, outside diameter and cross section define the dimensions of an O-ring. The inside and outside diameters are the distances from the center to the O-ring’s inside and outside surfaces, respectively. The cross section is the difference between the outer and inner diameters. All three dimensions are typically given in millimeters (mm) for metric O-rings and inches (in) for imperial O-rings.
One inch is equal to 25.4 mm, so when converting from an imperial dimension to a metric dimension, simply multiply by 25.4 mm/in. In order to convert from metric to imperial dimensions, multiply by the inverse of 25.4 mm/in, which is approximately 0.0394 in/mm. Imperial specifications are sometimes given as fractions (such as 1/3”) where the quote symbol after the fraction represents the imperial unit inch. In these cases, the first step is to always convert the fraction to a decimal, then perform the unit conversion. Thus, for example, 1/3” = ~0.33 in = 0.33 in x 25.4 mm/in = ~8.5 mm.
Another important O-ring specification is the maximum pressure rating. Generally, this tends to be expressed in megapascals (MPa) for metric O-rings. Imperial O-rings usually express this specification in units of pound-force per square inch (psi). One MPa is equal to approximately 145 psi. Therefore, to convert the required maximum pressure for an O-ring to imperial units, multiply by 145 psi/MPa. To convert an imperial maximum pressure to MPa, multiply by the inverse, equal to ~.007 MPa/psi. Occasionally, rather than MPa, maximum pressure will be given in bar. A bar is simply one-tenth of an MPa, so the conversion here is simple: 1 bar = 0.1 MPa = 14.5 psi.
Operating temperature range is another important specification that helps one understand whether an O-ring can withstand the environmental challenges of its application. It is therefore very important that a conversion is done correctly when comparing metric and imperial units. Metric O-rings have temperature ranges given in degrees Celsius. Imperial O-rings have operating temperature ranges given in degrees Fahrenheit.
To convert from Celsius to Fahrenheit, use the following formula:
T(°F) = T(°C) × 1.8 + 32
To convert from Fahrenheit to Celsius, use the following formula:
T(°C) = (T(°F) - 32) / 1.8
The specifications of inner diameter, outer diameter, cross section, maximum pressure and operating temperature range are critical to accurately identifying the correct O-ring for an application. Consequently, it is imperative, when confronted by metric or imperial units for these O-rings or their applications, that an engineer is able to convert between the two-unit systems for those specifications. Although the metric and imperial units don’t have to exactly agree, it is a good idea to try to get them as close as possible for optimal O-ring performance and part life.
Seals-Shop, the online shop of Trelleborg Sealing Solutions, offers a wide number of hydraulic, pneumatic and mechanical sealing products for a variety of applications available for immediate shipment in most cases. For more information, visit Seals-Shop.com.
Jan 8 2019
The correct selection of Radial Oil Seals
Choosing the right radial oil seal for virtually any application depends on operating conditions and the physical dimensions of the seal itself. While there are many considerations, here is a breakdown of the top four things you need to know when selecting a seal and why each is important.
The temperature within the seal’s environment is the main factor that dictates the radial oil seal materials. There is generally a stated temperature range that is optimal for that particular rotary seal. For example, there may be a stated range of 4 to 49° C. When the operating environment is too cold a seal may become brittle and at high temperatures the seal material may show greater elasticity. Increased temperature also accelerates the aging of the rubber. When axial cracks at the sealing edge are visible, the radial oil seal has been exposed to excessively high temperature, clearly out of its recommended range. An ambient air temperature increase of 10° C can halve the theoretical useful life of the rubber.
It isn’t just air temperature that can affect seals. Temperatures can fluctuate from:
- High-speed rotation that generates excess heat
- Insufficient lubricating and thermal management capabilities of the lubricant
- The circumferential velocity
- Applied pressure
Position or Size
Measurement is a key element for proper radial oil seal selection. The groove or the position into which the seal will be housed must be measured correctly so that there is as perfect fit as possible. This is critical because if your rotary seal does not fit, it will not be viable and leakage or contamination is a certainty.
Seal size is determined by the seal bore, the diameter of the hole in the housing where the seal will be fitted, seal outer and inner diameters (OD and ID) and seal width, which is the total width of the seal including inner and outer shells.
- Seal bore represents the diameter of the hole into which the radial oil seal will be seated.
- Seal OD: Measurements should be taken in at least three places equally spaced around the radial oil seal. The average of these readings can then be used as the OD.
- Seal width is a measurement of the radial oil seal height when laid on a level surface, which includes inner and outer shells.
- Shaft ID: A radial oil seal’s inner diameter can vary, so the shaft diameter is used as the inside dimension. If you don’t know the actual shaft diameter, you can estimate it by measuring the seal’s inside dimensions.
As the amount of pressure grows, the radial load and friction of the sealing lip increases as it contacts the shaft. Like temperature, recommended pressure for optimum performance is spelled out for each radial oil seal. Excess pressure causes seals to wear faster and shortens their life.
When a seal is under too much pressure, specified values of peripheral speed cannot be maintained but must be lowered relative to the magnitude of the pressure. At high pressures leakage between the seal’s periphery and the housing bore can be avoided by using radial oil seals with rubber-covered cases. When a seal is under pressure there is also a risk of axial movement in the housing bore, which is prevented by locating the seal against a shoulder with a spacer ring.
The speed at which a radial oil seal can effectively operate depends on such conditions as pressure, temperature, the lubricant or fluid involved, shaft finish and seal design. Lubrication between the seal lip and a moving surface reduces friction, an important seal degradant. The thickness of the lubricating film establishes the level of friction. Initially, when velocity increases, friction decreases as the lubricant is dispersed. Even at increased velocity, frictional forces will begin to climb, causing wear.
Various seal designs allow for a variety of maximum peripheral speeds. Higher peripheral speeds are appropriate for larger shaft diameters more than for smaller diameters, as cross-sectional area increases in proportion to the square of the diameter, thus increasing the heat dissipation capacity.
While higher speeds affect performance and seal life, speeds under and over the recommended range cause increased friction, impacting the seal material.
Common Causes of Radial Oil Seal Failure
While all seals eventually wear out, the most common causes of rapid failure include:
- Installation — damaged by handling, incorrect measurement, etc.
- Seal face open during operation, enabling particles to penetrate and affect seal fastening
- Improper radial oil seal selection
- Poor design
- Inadequate environmental controls
Not often considered is the chemical composition of the radial oil seal components, corrosion resistance, effects of compression, chemical attack, material choice and changing ambient conditions during use.
Today, there are interactive tools such as a Fits & Tolerances Calculator that allows you to determine lower and upper limit deviations and maximum and minimum interferences based on the selected tolerance classes for seal bore and shaft, which helps with the selection of the right radial oil seal.
The information in this article should provide the basics of selection. In addition, should a radial oil seal fail, look at the evidence, which should lead to the reason for the failure. Is the seal brittle or too elastic? The issue is temperature. Are particles getting through the seal? Check the rotary seal face opening.
Finding the best seal for your application does not need to be a larger-than-life exercise. For that best seal, begin here or try our Product Finder.
Company information Seals-Shop GmbH
Our customers come from all corners of the industry, including service and maintenance/repair, manufacturing and wholesale distribution. Our products are specifically intended to suit a variety of hydraulic applications, from light-duty linear hydraulic to heavy-duty rotary seals and static applications.
Our broad and diversified product range sets us apart from the rest, notably our extensive selection of FKM seals. On top of everything, all products are immediately available from stock (unless otherwise stated).
|Handelsregister||HRB 757821 Stuttgart|
|Legal form||Gesellschaft mit beschränkter Haftung|
|Type of company||Head Office|
|Fax||+49 711 78648879|
Turcon® is a perfluoroelastomer (FFKM) compound from Trelleborg Sealing Solutions which is matched to the needs of critical sealing environments, combining the media resistance of a PTFE with the elasticity of an elastomer.
Turcite® is dimensionally stable and wear resistant with excellent performance in dry and boundary lubrication.
The engineered plastic based sealing material Zurcon® provides outstanding wear resistance combined with good friction properties, making it suitable for reciprocating, slow rotating and oscillating applications.
HiMod®, a high modulus thermoplastic is suitable for custom molded components, reinforcing rings and Back-up Rings.
The composite bearing material Orkot® consists of technical fabrics impregnated with thermosetting resins and evenly dispersed solid lubricants gives unrivalled performance in dry running conditions.
Key figures Seals-Shop GmbH
Executives Seals-Shop GmbH
Herr Florent Guillomeau
CEO - Chief Executive Officer
Herr Jürgen Bosch
CEO - Chief Executive Officer (Geschäftsführung)
Activities Seals-Shop GmbH
- Service provider
- Moulded parts, rubber
- Rings and washers, rubber
- Diaphragms, rubber
- Packing rings, rubber
- O-rings, rubber
- Rings, rubber, for screw stoppers
- Rings, rubber cord, sealing
- Rings, cellular/foam rubber, sealing
- Rings, rubber, conical, sealing
- Rings, rubber, hexagonal, sealing
- Rings, rubber, flat, sealing
- Rings, rubber, square section, sealing
- Bushes, rubber
- Seals, rubber
- Seals, rubber, for bottles and jars
- Seals, rubber, dam and lock gate
- Rings, rubber, to customer specification
- Tapes and straps, plastic
- Jointings, packings and gaskets, plastic
- Gaskets, ethylene-propylene-diene monomer (EPDM)
- Gaskets, polyethylene (PE)
- Gaskets, polytetrafluoroethylene (PTFE)
- Gaskets, polytetrafluoroethylene (PTFE) filled
- Gaskets, polyvinyl chloride (PVC)
- Gaskets, plastic, for glazing and draught-proofing
- Packing rings, plastic
- Packing rings, vee type, plastic
- Packings, polytetrafluoroethylene (PTFE)
- Oil seals, plastic or synthetic rubber
- O-rings, polytetrafluoroethylene (PTFE)
- Seals, filled polytetrafluoroethylene (PTFE)
- Jointing materials, plastic
- Plastic products, industrial use
- Plastic products for the mechanical engineering industry
- Plastic products for the electrical and electronics industries
- Seals and gaskets, metal
- Packings, metal
- Internal combustion engine components NES
Other classifications (for some countries)
NACE Rev.2 (EU 2008) :
Manufacture of other rubber products (2219)
ISIC 4 (WORLD) :
Manufacture of other rubber products (2219)