Are you looking for a bearing housing for your application? Feeling overwhelmed by all of the different aspects of the decision making process? From pry slots to eye bolts, it can be easy to get lost in the world of mounted bearing selection. This article looks at features to consider so you can be confident in your bearing’s housing choice.
When it comes to choosing a mounted bearing unit, the bearing itself is going to be the main consideration. If you choose an SAF housing for your bearing, consider these factors:
Key Factors to Consider
- Material – Iron or steel?
- Finish – What sort of coating or paint is best suited for the operating environment?
- Seals and end plugs – Will an LER ring do the trick or is an upgrade needed?
- Zerks, drains, and access points – How often will you be performing maintenance?
- Eye bolts – For lifting and lowering those larger SAF housings.
- Pry slots – For optimal accessibility.
- Cap and base configurations – 2 bolts or 4?
Taking these factors into consideration when choosing a bearing housing for your application creates compatibility between your application and its environment. This ensures convenience during maintenance and repairs and helps minimize them as well.
Cast Iron (Gray Iron)
The most common material used in SAF housing blocks is cast iron. Cast iron bearing housings offer high quality strength while keeping costs affordable. The signature gray color that is often seen in the machined surfaces comes from the visible graphite in the iron. The graphite flakes in gray cast iron allow for better resistance to wear and corrosion.
Gray cast iron is also a popular choice for a bearing block because it absorbs vibrations and can withstand compression. It has high thermal conductivity which allows it to move heat more easily through metal. It can also withstand thermal cycling, going through high and low changes in temperature without strain.
For most applications, cast iron is a perfectly suited and economical choice for a bearing housing. However if your application is in an environment with extreme shock loads cast steel could be considered.
Cast iron is a great, economical choice for most bearing housings – with the exception of applications with extreme shock loads.
When extreme shock loads are involved, consider cast steel. The difference in cast iron vs. cast steel is the carbon content. Cast iron contains 2% carbon and cast steel has less than 2%. Cast steel is typically a more expensive material.
It has a high tensile strength and overall “toughness” that produces a fracture resistant mounted bearing housing. Cast steel is a popular choice for applications operating in an environment with extreme shock loads.
It could be worth the extra expense to have a cast steel housing in rough operating environments. The materials strength and flexibility could prevent expensive and possibly dangerous housing failures.
To choose the best material for your housing, think of your application and which of the physical properties will perform the best in your specific operating environment.
Most of the time, bearing housings are finished with a corrosion resistant paint but other finishes are sometimes offered for increased resistance in more harsh environments. With other finishes, stainless hardware including cap bolts, grease fittings, and seals are recommended.
Adding a corrosion resistant coating creates a bearing housing built to withstand particularly harsh environments. This is especially important for applications subjected to:
- Frequent washdowns
- Rain or humid environments
- Chemical exposure
- Extreme temperatures
- Salt water
- Heavy debris
There may not be many options as far as finish goes for bearing housings, but it is important to make sure yours is compatible with the environment your application operates in.
Seals and End Plugs
LER seal rings are considered to be the standard seal for SAF bearing block configurations. They utilize a non-contact labyrinth seal to prevent contaminants and debris from coming into contact with the bearing. Non-contact labyrinth seals are made up of layers of metal sealing plates forming a maze-like pattern. Some benefits of LER seals are: high reliability, long operating life, low friction, and easy installation.
The non-contact labyrinth LER seal can be upgraded to keep moisture or contaminants out of the housing. These upgraded seals often feature a rubber lip or element that contacts the housing to prevent contamination in more severe operating conditions. While these seals may do well to prevent contamination, they require the user to consider the seal drag and wear that are typical with contact seals.
End plugs are commonly used when the shaft ends inside the bearing housing. These are typically used to prevent foreign objects and debris from entering the housing. They are also good for protection against chemical exposure and high temperatures. Installing a cap and o-ring will further protect the bearing, however, expansion should be taken into consideration as the shaft should NOT make contact with the cap.
Seals and end plugs are often the bearings best defense against foreign contaminants and debris. They should always be considered when choosing a bearing housing.
Zerks, Drains, and Access Points
Zerks and drains are placed in different locations on a bearing housing depending on the manufacturer. Zerk fittings are used to feed lubricants (usually grease) into a bearing with a grease gun. Drains are used to purge excess grease or oil and equalize pressure.
Some housings have extra ports for testing equipment such as vibration readers, or ports to monitor oil temperature or levels. Make sure that the lubrication zerks, drains, and access points are located at points that are easily accessible.
Some manufacturers offer bearing housings with multiple dimpled locations – or tiny holes that haven’t been drilled all the way through. These dimples make drilling into the housing easier and ensures that the drilling locations are in ideal locations. These holes may be tapped to allow for the installation of zerks or monitoring equipment.
Zerks, drain holes, and access points should be considered to make maintenance and repairs of your application more convenient and less time consuming.
Some of the larger SAF bearing housings can weigh up to a thousand pounds and require a lifting mechanism for installation. Eyebolts screw into a hole (or holes) on the top of the housing cap and are designed to assist in the mounting and dismounting of the housing.
The included eyebolts are typically rated for the weight of only the housing and the installed bearing. Never attempt to lift additional weight using the installed eyebolts as it poses risk of eyebolt failure.
If a mounted bearing unit comes with two eyebolts, it is important to use both of them simultaneously when lifting and/or lowering the bearing block into position. Always make sure to screw the eyebolts in completely before use.
Eyebolts are key to when installing or removing SAF pillow block bearing housings when used properly. Make sure to take advantage of these convenient features when choosing a housing.
Pry slots are designed to create ease when separating the cap from the base of the bearing housing and accept most flat headed tools. They are usually located as conveniently as possible to allow for good leverage and to minimize the chances of accidental damage.
After hours upon hours of operation, the cap may become extremely hard to remove from the base by hand. It may feel as though you have forgotten to remove one or more of the fastening bolts. In these instances, pry slots become an essential feature. This simple and almost unnoticeable feature makes a big difference when it comes time to maintain or replace your bearing.
Although pry slots are often overlooked, these small features make a big difference during maintenance. Don’t forget to add them to the checklist when choosing a new bearing housing!
SAF bearing housings are available in a variety of two bolt and four bolt configurations. Two bolts for smaller housings and four bolts for larger housings.
The sizes falling in the “medium” range of these housings can have either two bolts OR four bolts. Four bolt housings falling in the mid range are categorized as FSAF.
- Smaller housings compatible with shaft sizes 2 inches and under are equipped with two base bolts and two cap bolts are categorized as SAF.
- Larger housings compatible with shaft sizes 3 15/16 inches and up are equipped with four base bolts and four cap bolts and are categorized as SAF.
- Housings compatible with shaft sizes ranging from 2 3/16 inches to 3 ½ inches have the option of 2 or 4 base bolts and cap bolts. For this range, SAF will have two base bolts and either two or four cap bolts. FSAF will always have four base bolts and four cap bolts.
The extra bolts make a secure connection between the base of the housing and the mounting surface and are mostly necessary for larger sizes of bearing blocks.
Configurations should be taken into consideration when selecting a new bearing housing especially if your selection is in the middle range where both options are available.
Knowing the operating conditions and environment that your bearing will be used in will help make the decision in finding the right bearing housing for your application. Keep the considerations and features mentioned above in mind when selecting a housing for your mounted bearing will help you when looking at your options. Remember, that the first thing to take into consideration is fitting the bearing’s needs and explore your options from there. Use this information to your advantage and choose the right bearing housing for your application today!
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