An O-ring is a circle of rubber used as a mechanical seal. They are designed to be seated in a groove and compressed during assembly between two or more parts, creating a seal at the interface.
The joint may be static, or (in a few circumstances) have relative motion between parts and O-ring (rotating pump shafts and hydraulic cylinders, for example). Joints with motion usually require lubrication of the O-ring to reduce wear. This is often accomplished with the fluid being sealed.
O-rings are one of the most popular seals used in machine design because they are inexpensive and easy to make, reliable, and have simple mounting requirements. They can seal tens of megapascals (thousands of psi) pressure. In some cases, O-rings are used with back-up rings.
The O-ring was invented in 1936 by a then 72-year-old Danish-born man, Niels Christensen. During the second world war, the US government "bought" critical war-related patents after finding out the big businesses were in violation of Christensen's patent right. Christensen got a lump sum payment of US$75,000 for it.
THEORY AND DESIGN
Successful O-ring joint design requires a rigid mechanical mounting that applies a predictable deformation to the O-ring. This introduces a calculated mechanical stress at the O-ring contacting surfaces. As long as the pressure of the fluid being contained does not exceed the contact stress of the O-ring, leaking cannot occur.
The seal is designed to have a point contact between the O-ring and sealing faces. This allows a high local stress, able to contain high pressure, without exceeding the yield stress of the O-ring body. The flexible nature of O-ring materials accommodates imperfections in the mounting parts.
O-rings are available in a large number of standard sizes and materials. Manufacturers or reference books supply application and machining data for the mounting. O-rings are one of the most common and important elements of machine design.
O-ring selection is based on chemical compatibility, application temperature, sealing pressure, lubrication requirements, quality, quantity and cost.
TIPS & TRICKS (for getting optimal O-ring performance)
WHEN TO REPLACE O-RINGS
Over the years Services for Plastics, Inc. has seen many applications where O-rings have been used and performed without problems for years. However as a key to any preventative maintenance program and safety program replacement before failure is always the best.
While it is almost impossible to predict when an O-ring will fail, there are good rules of thumb to use. First is that when servicing an item that has an O-ring installed, look at the seal to determine if there is any cracking or hazing due to degradation or mechanical damage. In dynamic applications it is very important to look for wear patterns and material being removed from the seal during the movement.
Secondly, when servicing a item that contains a seal, if you can see it, you should replace it. This due diligence will do a long way to keep the machinery running longer. If the O-ring has been in service and 50% of its effective lifespan has been used, overlooking this can cause additional downtime later. And wouldn’t that be a waste of your time to tear the unit down again for something that you could have replaced in five minutes.
WHAT MAKES SFP O-RINGS BETTER THAN THE REST?
Because our O-ring suppliers are ISO-9001:2000 certified, you are purchasing O-rings that have proven chemical makeup along with consistent manufacturing and lot traceability. Don’t buy cheap foreign made O-rings that become brittle and fail when you can least afford it. Buy the best - SFP O-rings.
Click here for more information on O-rings
Manufacturers of High-Quality
Home | Request a Quote | Place an Order | Product Index | Online Catalog
SERVICES FOR PLASTICS, INC.
7925 N. Clinton St., Fort Wayne, IN 46825-3113, USA