These are excellent analogues of the bearing buddy, but be prepared to install them using a classic mechanics technique. Prior to installation, place the protectors in the freezer and let them chill for an hour. This is a good time to enjoy a beer; I like Abita Amber.
We’re going back to the basics with your go-to guide for Bearing Installation.
When it comes to bearings, the quality of the overall performance, reliability and efficiency they yield, begins with the quality and precision of their installation. If there’s one thing to take away from this, it’s that nothing lasts forever and it’s up to YOU to maximize every last operational hour of your application parts.
Roller bearings play a vital role in rotating machinery by helping to: reduce friction, transmit loads and support shafts. However, 48 % of bearings fail before their natural death from being put in wrong or mishandled. Perfecting the art of bearing installation will ultimately prolong application service life and minimize downtime caused by unnecessary bearing failure.
1- ADOPT THESE GOOD PREPARATION HABITS
Although a bit tedious, this first stage is just as vital as those that follow it. Being lackadaisical this early on in the process could threaten the bearings’ chance for survival, well before the mounting begins.
First, all bearings should be stored flat in a cool, clean, low-humidity environment free of dust, shocks and vibrations. In addition, there are three good habits to get into, in preparing for bearing installation, to prevent from contamination and corrosion.
- Keep Bearings Clean – Leave them in their packaging up until they’re ready to be mounted. Once opened, handle the bearings with clean, dry hands or gloves. The fewer chances for dirt and contaminants to get into them, the better.
- Keep Surfaces Clean – Have a fresh piece of paper or plastic to work on, and never set the equipment anywhere outside it. All mounting and housing components should be clean, as well. Use either an Emory cloth to remove any dirt or other foreign bodies, or a fine file to get rid of any rust or burrs.
- Check Dimensions Carefully – Measure the shaft and housing diameters to make sure the bearing chosen is the correct size and that the shaft and housing are truly round. Do not use the bearing as a gauge to do this.
2 – DETERMINE THE BEST BEARING INSTALLATION PROCESS
Mechanical Mounting – Small-Sized Bearings
There are two types of mounting processes. Mechanical, or cold, mounting is the simpler option and is used for smaller bearings with an Internal Diameter (ID) of up to 4″/100 mm. This is often a more convenient mounting method, as the bearing can be mounted with no electricity right on the application itself.
It is important to check for proper seating of the bearing and use a special fitting tool to drive it onto the shaft. The tool should be complete with a sleeve, impact ring and dead-blow hammer.
Take special consideration to avoid applying force directly to the bearing’s: rings. cages. balls, rollers or seals. Start the bearing on the shaft with the rounder corner of the race going on first. Apply even, driving pressure, using smart, quick taps rather than heavy ones, while keeping everything square, supporting both the inner and outer race.
Hot Mounting – Medium-Sized Bearings
Induction Heater
For bearings with an ID that exceeds 4″/100 mm, the force needed to mount them increases considerably. This is best accomplished using heat in a process called hot mounting. The most vital factor in this method is the source of the heat. For example, techniques such as oil baths and exposure to open flames can harm and contaminate the bearings. Best results are attained using electric induction heaters, which allow for the easy regulation of heat.
The key here, is the temperature difference between the bearing and the shaft. Normally, a bearing temperature of about 150 F above that of the shaft is sufficient. Heating of the inner race and freezing of the outer race is the most common and recommended method. Required heat varies, though, so be sure to refer to the bearing manufacturer’s (OEM) heating guidelines.
Once hot, carefully slide the bearing onto the shaft, and when it cools, it will grip the shaft and work efficiently. Always wear proper Personal Protective Equipment and be careful not to overheat the bearing past 250 F (or 210 F for bearings with shields or seals). Extreme heat can cause the bearing’s metallurgy to change, which can alter bearing dimensions and/or hardness.
Hydraulic Mounting – Large-Sized Bearings
Hydraulic mounting is recommended when dealing with extra large bearings, or tapered shafts anywhere from 2 to 37 inches in diameter. It requires less manual effort and promotes greater operator safety. Hydraulic techniques allow for greater control and precision, as well, while minimizing the risk of damage to bearings and shafts.
Shafts with oil ducts and grooves can accept oil injected between the bearing bore and shaft surfaces, which creates a thin oil film. This reduces both the friction and the required force needed to mount the bearing. With an oil film applied, bearings can then be physically mounted using the hydraulic pump to drive them up the shaft. It achieves this by pumping oil into the hydraulic nut, which then pushes the piston out, ultimately exerting a force great enough to move the bearing into position. All the while, the pressure is being monitored by the pump for quality assurance.
The key objective in mounting bearings is finding the balance between minimum required force with maximum control. Determine the best bearing installation practice for your application and arm your workforce with the technologies and tools it takes to be successful.
3 – HANDLE WITH CARE
A lot of production falls on the accuracy of the bearings, and even though they are often made of steel, bearings are surprisingly delicate. “If you take the human hair and split it 10 times, that’s the precision that these bearings are made to have,” Tim Zerger, Bearings Business Group Director at IBT, says.
While you might not be able to see the damage, any mishandling of a bearing can end up costing you tremendously in production downtime. Even just by dropping a new bearing on the floor, Zerger says, “you don’t know the damage you could be doing. If that bearing costs $80 and it costs you $5,000 an hour for your production being down – and it takes an hour to put a new bearing in – its cheaper to throw that bearing away and install another new one.”
When engineers engineer a bearing, they calculate the life of how long it should last at a specific speed and load, and if you don’t put it on correctly, you cut that life down. “In all my years – almost 40 years now,” Zerger says, “I’ve never seen a failed bearing that’s come back, after we’ve sent it in to have it analysed, having failed because it was made wrong. It’s always the installation or lubrication issues.”
Take simple precautions in your bearing installation process and save yourself the money, the time and the headache of an unnecessary bearing failure.
A LEGACY YOU CAN COUNT ON
IBT Industrial Solutions was founded in 1949 with Industrial Bearings in mind. Since then, we have become a trusted source for industry knowledge and expertise when it comes to bearings. When you partner with IBT, you’re guaranteed access to the best service and brands in the business.
Looking for more information regarding bearing installation? Contact our team of experts!
Dust and water in bearings lead to early-life destruction. Therefore, protection methods against ingress are needed. This article introduces several protection methods and reviews shaft seal designs suited to contaminated conditions.
Machine Environment
Dusty surroundings are one of the most difficult environments for bearings. In equipment handling powders or in processes generating dust, the protection of bearings against contamination by fine particles requires special consideration.
Wet environments are even more difficult for bearings. Moisture in a bearing, whether it is water or a chemical, sits at the bottom of the race and emulsifies (mixes) with the oil.
The roller runs through and displaces the mixture, creating conditions for rolling element to race contact and their destruction. Instead of hydrodynamic gliding through the loading cycle, the element rubs or scrapes against the surface. Eventually the surface interaction leads to failure of the race or roller.
Bearing Housings
Bearings are contained within a housing from which a shaft extends. The shaft entry into the housing offers opportunity for dust and moisture to enter the bearing. The shaft seal acts to close the gap between the housing and shaft. Choosing the appropriate shaft seal and seal configuration to protect against dust and moisture ingress is critical to bearing life.
Figure 1. Shaft Bearing Housing Seals
Bearing housing seals for dusty environments are traditionally labyrinth or contact type (Figure 1). The labyrinth-type requires a straight shaft running true. Rubbing seals are the more common and allow for some flexing of the shaft. To prevent dust ingress when setting a lip seal into place, ensure the sealing lip faces outward.
Lip and Labyrinth Seals
The lip seal, while selected mainly for sealing the shaft to housing gap, is typically an unsatisfactory sealing device. Over time, the rubber used to make the lip is attacked by various oxidation catalysts, including oxygen, heat, wear metals and chemicals.
It then degrades, cracks, hardens or deforms, and the lip causes fretting corrosion of the shaft (the gouge seen under the lip when it slides off the shaft). Moisture on the shaft capillaries is drawn past the lip, and water sprayed directly at the lip seal blows past the seal and into the bearing.
Lip seals are rarely replaced in installed equipment although, as the seal is a perishable component, it should be routinely replaced.
If you have equipment with lip seals, and you want reliable long-life operation, you must replace the lip seal before it fails. To decide the replacement frequency, estimate the mean time (the middle time of the range of times for seal lives) between the seal failures on each particular type of equipment in the operation and schedule a replacement preventive maintenance work order to replace them at 70 to 80 percent of those mean time spans.
The labyrinth seal has a better reputation for shaft sealing than the lip seal if used with grease flush. The gaps between the two parts of the labyrinth must be sealed to keep out dust and water.
To improve bearing life for both labyrinth and lip shaft seals, use an automatic lubricator. Only a small quantity is necessary when slowly flushed into the bearing cavity to force dust and moisture away from the elements.
Grease flushing is not practical for oil-filled equipment. A better option is to replace shaft seals at a predetermined frequency just prior to failure.
Because of the inconvenience and high cost involved in caring for conventional shaft seals, there has been much development work to extend seal lifecycles. New designs and configurations are continually being developed and improved.
In situations of high dust contamination there may be a need to redesign the shaft seal arrangement for better dust protection than what is provided in standard housings. Some ideas which can reduce dust ingress into bearing housings include the following:
- Parallel seal configuration. Bearing housings can usually be purchased with combination seals as standard equipment.
- Design spring-loaded shaft-wiping devices to prevent dust ingress. The spring pushes the soft seal against both the shaft and the equipment wall to create a barrier. Figure 2 shows a conceptual design sketch. The assembly is installed in its own housing.
- Stand the bearing off the equipment to create a gap between the end of the equipment and the bearing housing, and install a stuffing box and packing at the housing interface. This approach usually leads to scoring on the shaft in materials-handling equipment; therefore, it is best to install a surface-hardened, replaceable sleeve for the packing to run against.
- Put in a felt seal wipe between the housing and the wall of the equipment to rub the shaft clean. This can be changed to a stuffing box and a packed gland if desired. It is best to install a hardened, removable sleeve on the shaft because the packing will eventually score the shaft.
- Install a grease barrier chamber between two seals. This barrier is separate from the bearing housing and acts as the primary seal for the bearing. Grease pumped into the chamber will flush out past the seals. Provide an auto-lube set with slow discharge for continuous purging.
- Replace the grease barrier chamber with an air purge (pressurized chamber).
- Install a shaft-wiping rubber shroud covering the bearing or the dust-emitting opening. The potential for overheating the bearing in a fully enclosed shroud limits its use to slowmoving bearings only.
- Purge grease through shaft seals or through a 15 mm hole (relief port) drilled in the housing. The hole must be on the side of the bearing opposite from the grease nipple, at the bottom of the bearing housing when in service and between the bearing and seal.
- Mechanical seals can be fitted to the shaft with the stationary seal sitting against the machine and the rotating seal mounted back along the shaft. Combinations of other seals and wipers can also be used in conjunction with the mechanical seal. Mount the auxiliary seals so that they encounter the dust/water first, and keep the mechanical seal as the last line of protection.
- In high-dust environments use a mechanical seal that has hard seal faces because the dust will score and scratch a soft seal face. An example is silicon carbide against silicon carbide.
- Spray-on flexible and elastic plastic coatings such as soft polyurethanes and ethylcellulose to cover the housing and a short length of the protruding shaft. The length of coating over the shaft acts like a long wiping shaft seal. Because of its length and continuous unbroken surface, it takes dust and moisture a long time to work their way up the shaft and into the housing.
The housing plastic coating does not prevent heat transfer because the coating is at the same temperature as the housing and still radiates and convects heat away.
Some conceptual examples of alternate shaft seal designs for dusty situations are shown in Figure 3.
Assembly
Bearing assembly must be spotlessly clean. If contamination occurs when the housing and element are joined, no amount of external protection will stop the bearing from premature failure. When assembling bearings into housings, take the following steps to ensure cleanliness:
- Wash your hands.
- Ensure there is no dust or powder in the air.
- Clear the work bench and wipe it clean.
- To prevent creating dust, ensure that there is no grinding or sweeping nearby during assembly.
- Use only fresh, clean grease (to the extent that you can control) to pack the housing.
- Clean components and remove all old grease, grime and solid buildup.
Breathers
A breather releases hot air out of a confined space and allows the air to return when the space cools. Enclosed bearings get hot during operation and cool to ambient temperature when not in use. The air drawn back into the space should be clean of dust and moisture. A poorly screened and filtered breather on a bearing housing or bearing housing enclosure allows ingress of moisture and dust into the bearings, causing premature life failure.
An inadequate breather should be replaced with a low-micron air filter that removes dust particles that are two micron and larger. Protect the breather or filter from water spray and damp conditions (for example, ban “hosing down” if possible) with a shroud or by using an extension tube going into a clean, safe environment. Make sure the breather extension tube cannot be crushed closed.
Editor’s Note:
Reprinted with permission of Mike Sondalini from Lifetime Reliability Solutions, www.lifetime-reliability.com. Related information is available from Feed Forward Publications at www.feedforward.com.au.
Reprinted with permission of Mike Sondalini from Lifetime Reliability Solutions, www.lifetime-reliability.com. Related information is available from Feed Forward Publications at www.feedforward.com.au.
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