Anyone who does maintenance and has repaired a pump or gearbox knows that one of the components that always needs to be replaced during repair is the lip seal. It is usually damaged when removed or disassembled. Perhaps it was the lip seal that caused the device to be taken out of service due to leaks. However, the fact remains that lip seals are important machine components. They trap oil or grease and help keep contaminants out. Lip seals can be found on almost any factory equipment, so why not take the time to learn how to select and install them correctly?
The main purpose of a lip seal is to keep contaminants out while maintaining lubrication. Essentially, lip seals work by maintaining friction. They can be used in a variety of applications, from slow moving equipment to high speed rotation, and in temperatures ranging from sub-zero to over 500 degrees Fahrenheit.
To function, the lip seal must maintain proper contact with its rotating part. This will be influenced by proper seal selection, installation and post-installation maintenance. I often see new lip seals begin to leak as soon as they are put into service. This usually occurs due to improper installation. Other seals will leak at first, but will stop leaking once the sealing material is seated on the shaft.
Maintaining a functional lip seal begins with the selection process. When selecting materials, consideration must be given to operating temperature, lubricant used, and application. The most common lip seal material is nitrile rubber (Buna-N). This material works well in temperatures ranging from -40 to 275 degrees Fahrenheit. Nitrile lip seals are suitable for most industrial applications, from new equipment to replacement seals. They have excellent resistance to oil, water and hydraulic fluids, but what really sets these seals apart is their low cost.
Another affordable option is Viton. Its temperature range is -40 to 400 degrees Fahrenheit, depending on the specific compound. Viton seals have good oil resistance and can be used with gasoline and transmission fluids.
Other sealing materials that can be used with petroleum include Aflas, Simiriz, carboxylated nitrile, fluorosilicone, highly saturated nitrile (HSN), polyurethane, polyacrylate, FEP and silicone. All of these materials have specific applications and precise temperature ranges. Be sure to consider your process and environment before selecting or changing seal materials, as the right materials can prevent costly failures.
Once the sealing material has been selected, the next step is to consider the seal structure. In the past, simple lip seals consisted of a belt on the wheel axle. Modern lip seals consist of many components that affect seal performance. There are different contact modes, as well as springless and spring-loaded seals. Non-spring seals are generally less expensive and are capable of retaining sticky materials such as grease at low shaft speeds. Typical applications include conveyors, wheels and lubricated components. Spring seals are typically used with oil and can be found on a variety of equipment.
Once the seal material and design have been selected, the lip seal must be installed correctly for it to operate effectively. There are many products on the market designed specifically for this task. Most look like bushing kits where the seal is installed directly into the hole. These tools can work well if chosen carefully, but most off-the-shelf versions are not as effective, especially when the shaft is already installed.
In these cases, I prefer to use a tube large enough to slide over the shaft and make good contact with the lip seal housing. If you can find something to hook the housing onto, you can prevent damage to the inner metal ring that connects to the lip seal material. Just make sure the seal is installed straight and at the correct depth. Failure to position the seal perpendicular to the shaft may result in immediate leakage.
If you have a used shaft, there may be a wear ring where the old lip seal used to be. Never place a contact surface on a previous contact point. If this is unavoidable, you can use some products that glide over the shaft to help repair the damaged surface. This is usually faster and more economical than replacing the shaft. Please note that the lip seal must match the size of the optional bushing.
When installing the lip seal, make sure the job is done correctly. I’ve seen people install seals using a punch so they don’t have to spend extra time finding the right tool. Accidental hammering may rupture the seal material, puncture the seal housing, or force the seal through the housing.
Be sure to take the time to install the lip seal and lubricate the shaft and seal well to prevent tearing or sticking. Also make sure the lip seal is the correct size. The hole and shaft must have an interference fit. Incorrect sizing may cause the seal to rotate on the shaft or become detached from the equipment.
To help your lip seal stay as healthy as possible, you should keep your oil clean, cool, and dry. Any contaminants in the oil can enter the contact area and damage the shaft and elastomer. Likewise, the hotter the oil gets, the more seal wear will occur. The lip seal should also be kept as clean as possible. Painting the seal or construction dirt around it can cause excessive heat and rapid deterioration of the elastomer.
If you pull out the lip seal and see grooves cut into the shaft, this may be due to particulate contamination. Without good ventilation, all the dust and dirt that gets into the equipment can damage not only the bearings and gears, but also the shaft and lip seals. Of course, it is always better to exclude contaminants than to try to remove them. Grooving can also occur if the fit between the lip seal and the shaft is too tight.
Elevated temperature is the main cause of seal failure. As the temperature rises, the lubricating film becomes thinner, resulting in dry operation. Elevated temperatures can also cause elastomers to crack or swell. For every 57 degrees Fahrenheit increase in temperature, the life of the nitrile seal is reduced by half.
Oil level can be another factor affecting lip seal life if it is too low. In this case, the seal will harden over time and will not be able to follow the shaft, causing leaks.
Low temperatures can cause seals to become brittle. Choosing the right lubricants and seals can help cope with cold conditions.
Seals can also fail due to shaft runout. This can be caused by misalignment, unbalanced shafts, manufacturing errors, etc. Different elastomers can withstand different amounts of runout. Adding a swivel spring will help measure any measurable runout.
Excessive pressure is another potential cause of lip seal failure. If you’ve ever walked by a pump or transmission and noticed oil leaking out of the seals, the oil pan was overpressured for some reason and leaked to the point of least resistance. This may be caused by a clogged respirator or an unventilated cesspool. For higher pressure applications, special seal designs should be used.
When checking lip seals, look for wear or cracking of the elastomer. This is a clear sign that heat is a problem. Also make sure the lip seal is still in place. I have seen several pumps with the wrong seals installed. When started, vibration and movement cause the seal to dislodge from the bore and rotate on the shaft.
Any oil leakage around the seal should be a red flag that requires further investigation. Worn seals can cause leaks, clogged vents, or damage to radial bearings.
When analyzing a lip seal failure, pay attention to the seal, shaft and bore. When inspecting the shaft, you can usually see the contact or wear area where the lip seal is located. This will show up as black wear marks where the elastomer contacts the shaft.
Remember: To keep the lip seal in good working order, the oil pan must be maintained in good condition. Before painting, close all seals, maintain proper oil levels, ensure the oil cooler is functioning properly, and select the correct seal design and materials. If you are actively rebuilding and installing your equipment, you can give your lip seals and equipment a fighting chance to survive.
NINGBO BODI SEALS is a professional manufacturer of oil seals and high-end sealing components .
Post time: Nov-29-2023