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Choosing between a journal bearing and roller bearing can be challenging. As mechanical engineers and designers with expertise in bearings, we know that the decision should not be taken lightly. The two options have distinct differences which must be considered before making an informed choice. In this article, we’ll break down the distinctions between these two types of bearings to help you decide which one is right for your project.
Journal bearings are comprised of a shaft rotating inside a housing or sleeve. This type of bearing does not use rolling elements like balls or rollers; instead, it works by rubbing against the inner surface of the housing. There are advantages to using this kind of simple design as well as challenges to consider when deciding whether it’s suitable for your application.
On the other hand, roller bearings make use of cylindrical rollers held together by spacers or cages in order to reduce friction and increase load capacity over journal bearing designs. These components provide superior performance characteristics but also come at a cost which needs to be weighed when choosing between them both.
We hope that after reading this article, you will have enough information to make an educated decision on whether a journal bearing or roller bearing is best suited for your specific application requirements.
Journal bearings offer a variety of advantages when compared to roller bearings. The first advantage is that they have high load capacity and can handle heavier loads without compromising performance, making them ideal for applications where other bearing types may fail due to their limited load capacities. Additionally, journal bearings are able to operate at higher rpm limits than roller bearings, allowing them to be used in more demanding applications. Finally, the selection criteria for journal bearings also tend to be simpler since they come in fewer shapes and sizes when compared with other types of bearings. This makes them easier to find the right size for any purpose. In terms of bearing selection criteria, journal bearings often prove superior in terms of both load capacity and rpm limits. Moving on from this section about the advantages of journal bearings, let’s now take a look at some disadvantages which could make it harder for you to decide if these are the best choice for your application needs.
Journal bearings are a veritable nightmare for mechanical engineers and designers. They can be an absolute catastrophe in terms of design, installation, noise, lubrication and cost. Here’s the lowdown on journal bearing disadvantages:
All in all, when considering whether or not journal bearings are worth pursuing for a given application one must weigh up the pros and cons carefully before making any decisions; however they remain popular solutions among many industries despite their drawbacks thanks largely in part to their versatility and relatively simple design components.
Roller bearings provide numerous advantages compared to traditional journal bearings, making them the preferred choice for many applications. They offer superior load-bearing capacity, higher speed capability and lower maintenance requirements than their counterparts. Additionally, roller bearings are more resistant to environmental conditions such as dust or temperature changes.
The above table illustrates the primary benefits of using a roller bearing over a journal bearing. When looking at longevity, roller bearings have far greater life expectancy; they also possess much higher load capacities while remaining capable of operating at high speeds with minimal maintenance needs. Furthermore, they are highly resilient against environmental factors like dust and temperature fluctuations which can cause significant damage to journal bearings in certain circumstances.
Overall, when choosing between journal and roller bearings it is important to consider all aspects of performance including durability, load capacity, high-speed capability and low-maintenance requirement along with any potential environmental influences that may arise in the application environment. These advantages make roller bearings an attractive option for most equipment designs where long service life and reliable operation are essential criteria for success.
The disadvantages of roller bearings can be likened to an unwelcome guest. They silently lurk in the background and make their presence known at the most inconvenient times – usually when you least expect it.
To begin, they are generally noisier than journal bearings. This is due to the higher friction between moving components that come with using roller bearing designs. Additionally, wear on these parts occurs more quickly over time due to this increased friction which leads to:
Finally, as a result of all these factors, choosing roller bearings should not be done lightly but rather after careful consideration of your specific application needs. Choosing the wrong type of bearing could lead to costly repairs in addition to downtime that may have been avoided had the right choice been selected from the start. The next section will discuss some important factors one must consider when selecting either a roller or journal bearing for any given project.
When choosing between a journal bearing and roller bearing, there are several factors to consider. Bearing type is the first factor that needs to be taken into account. Depending on the application, one type of bearing will work better than another. Load capacity should also be considered – both bearings have their own limits in terms of how much load they can handle before suffering mechanical failure or damage. Speed limits must also be assessed; any excessive speed may cause premature wear on certain components inside the bearing assembly. Temperature range is important too; some materials used for these types of bearings cannot operate within certain temperature ranges without being damaged over time. And finally, installation space should be examined as well – if the working area is cramped, this could restrict your choice of bearing size and design.
Overall, when selecting between journal and roller bearings, it’s best to assess each machine’s specific requirements related to the mentioned criteria so you can choose the right bearing for its intended purpose. Understanding all of these elements helps ensure that your selected bearing will function adequately throughout its entire lifespan with minimal maintenance required.
When choosing between a journal bearing and roller bearing, it is important to consider the load-bearing capacity of each. The following table provides an overview of key differences in load-bearing capacity:
Journal bearings are generally used for lighter loads that don’t require as much strength or weight support. Roller bearings, however, can handle heavier applications with larger amounts of weight and force. Depending on the size and type, some roller bearings have higher load capacities than others. Thus, depending on your application requirements, you may need to choose specific types of roller or journal bearings accordingly. Additionally, factors like ambient temperature, speed limits, and rotational speeds must be taken into account when making a decision about which type of bearing should be chosen.
Designing machines and equipment to accommodate rotating components often means selecting the correct bearing for the job. The choice between journal bearings or roller bearings can be made based on speed, load capacity, and operating temperature. Speed and RPM limits need to be taken into account when choosing a bearing type as well.
Journal bearings are generally recommended in applications that require low-speed rotations while still maintaining high torque ratings. These types of bearings have an unlimited maximum rpm limit but tend to work best in slower moving machinery with higher loads. On the other hand, roller bearings have a much lower torque rating, but they allow for greater speeds than journal bearings due to their ability to handle more rapid rotational movements without causing excessive wear on the bearing surfaces. Roller bearings typically have a maximum rpm limitation that should not be exceeded if extended life is desired from the product.
When considering both journal and roller bearing options, it’s important to consider machine-speed, maximum-rpm, rotational-speed, torque-rating, and expected bearing-life before making your selection. Factors such as these will help you determine which option is best suited for your particular application needs. Ultimately this decision will impact how successful your project is over time so take care when researching what solution works best for you!
Now that we have discussed the speed and RPM limits, let’s move on to operating temperature considerations when choosing between a journal bearing and a roller bearing. Temperature plays an important role in determining which type of bearing is best for your application. Bearing temperature must be kept within certain ranges as high temperatures can degrade performance or cause premature failure.
When selecting bearings, it is important to know the maximum-operating temperature rating of the bearings being considered. This information can usually be found in manufacturer product data sheets or catalogs. If this information is not available, you should contact the manufacturer directly. The manufacturer will also be able to provide specific temperature ratings based on their own testing results for each model they offer under different loading conditions. Generally, journal bearings can handle higher temperatures than roller bearings due to their larger surface area and better heat dissipation capabilities; however, this varies depending on lubrication requirements and other factors such as bearing size and material used.
It is also important to consider how the temperature range of the environment may affect bearing performance over time. You should make sure that any chosen bearing has enough margin in its rated temperature capacity versus expected operating temperatures for your application so that it does not reach its upper limit during normal operation or peak usage periods. Additionally, if extreme variations in environmental temperatures are anticipated (such as rapid changes from hot to cold), then more robust materials like stainless steel might need to be specified instead of softer metals like brass or aluminum alloys.
By understanding both speed/RPM limits and operating temperature requirements ahead of time, one can choose the right type of bearing with confidence knowing that it will perform optimally while meeting required specifications without exceeding its temperature rating limits. Therefore proper selection criteria upfront helps ensure optimum system performance throughout its lifetime with minimal maintenance requirements going forward.
When it comes to maintenance requirements, journal bearings and roller bearings differ significantly. Journal bearings require regular lubrication of the bearing surfaces and must be inspected regularly for signs of wear or damage. Roller bearings on the other hand typically need only periodic inspections since they are sealed units with their own lubricant supply that is usually sufficient throughout its service life. Additionally, installation of a journal bearing requires more attention than a roller bearing; alignment between components needs to be precise in order to ensure proper operation.
Conversely, installing a roller bearing is generally simpler because they are designed as self-aligning units. Bearing cleaning also differs; journal bearings often have crevices which can trap contaminants like dirt and dust particles, so thorough cleaning should be part of your maintenance routine when using this type of bearing. With roller bearings however, contaminant accumulation tends to be less of an issue due to the seals protecting the internal components from environmental conditions.
Considering these differences in terms of required care, one must weigh all factors before deciding whether a journal or roller bearing is suitable for their application. Size and installation space may further influence this decision…
When considering the maintenance requirements for a bearing, size and installation space are also key factors. Bearing size is affected by both the journal size and roller size, depending on which type of bearing you’ve chosen. For journal bearings, their longevity can be impacted if they aren’t sized correctly. Meanwhile, roller bearings require careful consideration when it comes to proper sizing for their axial or radial loads in order to prevent premature wear or failure.
The amount of space available in an application must also be taken into account when selecting a bearing. This will determine whether there is enough room to install the required bearing without issue. If not, then alternate solutions such as using split bearings may need to be considered instead.
In addition, considerations should be made regarding how easy it will be to perform regular inspections and lubrication with regards to any maintenance that needs doing on a particular bearing over its lifetime – especially where access is restricted due to tight spaces around the bearing installation area. Properly assessing all these factors prior to making your selection will help ensure that your choice of bearing meets all necessary requirements. With this information in hand, cost and availability can now come into play when deciding upon the ideal solution for a given application.
When it comes to making a decision between journal bearing and roller bearing, cost and availability are two of the most important factors. In one fell swoop, you can go from having an amazing project in your hands to being left with nothing but disappointment due to budget constraints or lack of stock availability – so let’s look at how these bearings compare on those fronts:
Overall then, there’s no clear winner across all categories when it comes to cost and availability – however knowing what your particular requirements are should help guide you toward selecting the right bearing for your job. With that in mind, we move on to looking at environmental conditions…
When considering a journal bearing versus roller bearing, environmental conditions are an important factor to consider. Many of these applications require long-term reliability and robust operation in extreme temperatures, humidity levels and vibration exposures. To ensure the correct application is chosen for each specific environment, it’s vital to assess the requirements against both types of bearings.
These features allow us to compare different materials and decide which one best meets our needs based on the environmental conditions we must operate within, ensuring reliable operation and minimizing downtime caused by component failure due to incorrect selection criteria being applied initially.
When it comes to choosing between journal bearings and roller bearings, quality assurance standards are an essential factor for consideration. Ensuring the necessary bearing performance requires a comprehensive approach to bearing quality assurance that covers all aspects of design, production, and operation. Bearing testing standards must be established at each stage which includes manufacturing, installation, operation, and maintenance in order to guarantee proper function.
Manufacturers should adhere to strict bearing manufacturing standards such as those outlined by leading industry organizations like ISO, ANSI/ABMA, or AGMA. This includes standardizing parts materials with clear specifications regarding hardness measurements and other characteristics related to strength and durability. All components must meet specific dimensional tolerances set by these guidelines and accepted practices before any assembly can begin.
Furthermore, the quality control process must involve thorough inspection throughout every step of the manufacturing process – from raw material selection through finished product delivery – using advanced visual assessment technologies such as optical microscopes or computed tomography scans (CT scans). The end goal is obviously to ensure that only high-quality products make their way into circulation but also have them live up to their designed purpose when put in use.
Once assembled correctly according to the highest possible quality assurance standards, one may confidently choose either journal or roller bearing depending on the requirements at hand. As we move forward into the next section about design considerations, it’s important that manufacturers understand how various factors influence optimal functioning so they can make informed decisions about what type of bearing best suits their needs.
When it comes to choosing between a journal bearing and a roller bearing, there are several design considerations that must be taken into account. Firstly, the installation requirements of each type of bearing can vary significantly. Generally speaking, journal bearings require more sophisticated installation techniques than roller bearings do. Secondly, lubrication is an important factor when selecting a bearing as different types require various amounts and types of lubricants in order to function correctly. Thirdly, load capacity is another key consideration; typically roller bearings have higher load capabilities compared to journal bearings. Finally, temperature limits should also be considered—roller bearings tend to operate better at higher temperatures when compared with journal bearings.
In terms of design considerations for selecting a bearing, proper installation technique is critical for ensuring optimal performance and longevity from the part. Furthermore, understanding the materials and lubrication requirements is necessary for achieving reliable operation over time. With regard to load capacities and temperature limits, it’s essential to consider these factors according to the specific application before making a selection. Ultimately, careful evaluation of these different elements will help ensure that you select the best possible solution for your needs.
In conclusion, when it comes to choosing between a journal bearing or roller bearing for your application, there are many factors to consider. Firstly, the cost and availability of each type must be taken into account as well as any environmental conditions they may encounter in their expected environment. Quality assurance standards should also be considered so that you can rest assured that whichever one you choose will have been produced with precision. Lastly, design considerations such as load capacity and speed requirements should be evaluated in order to make an informed decision about which type of bearing is best suited for your needs. By carefully weighing all these aspects we can ensure our projects run smoothly like clockwork – providing us peace of mind that our applications will deliver optimal results efficiently and safely.
Understanding Journal Bearings
Malcolm E. Leader, P.E. Applied Machinery Dynamics Co.
Durango, Colorado
This paper covers the basic aspects of journal bearings including lubrication, design and application. Descriptions of various types of journal bearings are presented. Guidance is given for choosing the proper bearing type and keeping your bearings healthy. A section on do’s and don’ts gives practical information.
Bearings are used to prevent friction between parts during relative movement. In machinery they fall into two primary categories: anti-friction or rolling element bearings and hydrodynamic journal bearings. The primary function of a bearing is to carry load between a rotor and the case with as little wear as possible. This bearing function exists in almost every occurrence of daily life from the watch on your wrist to the automobile you drive to the disk drive in your computer. In industry, the use of journal bearings is specialized for rotating machinery both low and high speed. This paper will present an introduction to journal bearings and lubrication. Lubrication technology goes hand-in-hand with understanding journal bearings and is integral to bearing design and application.
Since they have significant damping fluid film journal bearings have a strong impact on the vibration characteristics of machinery. The types of machinery we are concerned with range from small high speed spindles to motors, blowers, compressors, fans, and pumps to large turbines and generators to some paper mill rolls and other large slow speed rotors.
Not covered here is the topic of bearings for reciprocating machinery. While some of the same principals apply, engine bearings have special needs and design considerations and deserve a more complete study. Reciprocating machinery bearings tend to be simpler in geometry and much more complicated in application than turbomachinery bearings. For example, the typical turbomachinery journal bearing consists of a thin layer of babbitt on steel while a connecting rod bearing may have numerous different layers of copper, steel, nickel, or other metals with a thin layer of babbitt on top. This layering is done for fatigue resistance to the pounding loads encountered in such machinery. Engine bearings are often required to withstand peak specific loads in excess of 3,000 PSI or about ten times a typical motor or turbine bearing. Reciprocating machines rely primarily on the squeezing of the oil film for load support.
There are applications where anti-friction bearings are the best choice. Commonly, smaller motors, pumps and blowers use rolling element bearings. Paper mill rolls often use large specialized spherical roller bearings. Clearly, anti-friction bearings are best for these applications. However, once the size of a pump (or fan or motor, etc.) gets large enough and fast enough, a gray area is entered. Here you will still find rolling element bearings used successfully but as speeds increase and temperatures rise, rotor dynamics often become a concern and critical speeds are encountered. This is when damping is required and fluid film bearings become increasingly necessary. My experience is that turbomachinery designers (and users) should consider using fluid film bearings if running above 3,000 RPM or the machine exceeds 500 HP. In my opinion, at 1,000 HP and up, all machines except very special cases should be on journal bearings specifically designed for that service. There are exceptions of course, and the decision where to apply what type of bearing is ultimately done for every machine individually based on good engineering practice and experience. Unfortunately, this decision is sometimes based on economics which keeps maintenance engineers and consultants employed.
The primary advantage of a fluid film bearing is often thought of as the lack of contact between rotating parts and thus, infinite life. In a pure sense, this is true, but other complications make this a secondary reason for using these bearings. During startup there is momentary metal-to-metal contact and foreign material in the lubricant or excessive vibration can limit the life of a fluid film bearing. For these reasons, special care must be taken when selecting and implementing a lubrication system and special vibration monitoring techniques must be applied. The most important aspects of the health and longevity of a fluid film bearing are proper selection, proper installation, proper lubrication, and the alternating hydrodynamic loads imposed on the bearing surface by relative shaft-to-bearing vibration.
DO:
1. Always use the proper lubricant as determined by the manufacturer or engineering.
2. Understand the additive package in your lubricants to avoid potential conflicts with process fluids and/or component materials.
3. Provide proper cooling to the bearing and the lubricant.
4. If applicable, provide proper filtration to the lubricant.
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5. Implement a regular oil analysis program for all critical machinery. Monitor lubricants for viscosity changes, wear metals and contamination, especially water.
6. Stay within design guidelines on clearances. General rule is 1.5 mils (0. inches) per inch of shaft journal diameter. 3.0 mils/inch diameter is excessive clearance in most cases.
7. Handle bearings carefully. Babbitt surfaces are very soft and thin liners are easily distorted.
8. Inspect bearings under magnification or have a professional evaluation before reuse. Early fatigue damage is usually invisible and other damage like electrostatic discharge may not be readily apparent. Replace bearings if any doubt exists as to the serviceability of the used bearing. Tilting pad bearings may have back-of-pad and pivot wear and brinelling concerns.
9. Lubricate bearings during replacement with a heavy prelube oil such as an ISO 460 especially if a lot of shaft rotation will occur as during alignment.
10. Monitor bearing temperatures, preferably metal temperature with embedded thermocouples or resistance temperature detectors (RTD). Calibrate transducers before installation in the bearing. Install dual sensors in case one fails - leave the spare unconnected. Drain temperatures, while useful, will not give an early enough indication of heat problems.
11. Carefully protect the temperature device leads during handling and installation.
12. If a bearing is spherically mounted, ensure line-to- line contact or a slight crush. These bearings do not self align! The user must manually align these bearings.
13. Inspect all bearings and inspect the shops making or repairing your bearings. Many rebabbitting shops are not qualified to repair all types of bearings. Ask where they get their babbitt and what quality controls are used. Is babbitt welding and babbitt casting done?
14. Use common sense. Treat the bearing with respect and you will get good service. Follow the rules specified by API and the guidelines proposed in this
article.
15. Fix damaged shaft journals with submerged arc welding or plasma spray - NOT chrome plating.
16. If you find any lead babbitt bearing material replace it with type 2 high tin babbitt which is much stronger and environmentally friendly.
DON’T:
1. Never use unapproved substitute lubricants.
2. Never mix different lubricants unless the combination has been evaluated and approved - different additive packages may react. Never mix mineral oils and synthetic lubricants. Using synthetic oil in a system previously using mineral oil may loosen old deposits.
3. Never bypass oil filters or coolers.
4. Installing bearings too tight or too loose is a recipe for disaster. Never set clearances in a tilting pad bearing in the field - this must be done in a qualified shop.
5. Do not use automotive viscosity enhancers (e.g. STP) when fitting bearings.
6. Never hand scrape bearings for proper fit. Take the time to have bearing properly machined by a qualified shop. No pocket knives touching babbitt!
7. Never pry or hammer a bearing liner out or back into place.
8. Throwing a babbitt bearing into the parts bucket usually means you ruined it.
9. Never install temperature sensors in the babbitt, rather 0.030" behind in the steel backing. Those wires sticking out of the bearing are not used to carry the part!
10. Don’t use the low bid to buy or repair bearings. Reusing babbitt from old jobs or overflow is forbidden. Tiny contaminations can lead to early bearing failure.
11. If there is a choice, don’t use spherically seated bearings, use cylindrical fits.
12. Do not roll shafts in Teflon® strips or “V” blocks due to micro embedment. This could result in the shaft being unable to properly “wet” and causes failure.
13. Never let oil reservoir or sump temperature exceed 200°F.
14. Don’t expect thick babbitt (e.g. 0.060") to be better than “thin” babbitt (<0.015") The fatigue resistance of thin babbitt can be more than 10 times greater than thick babbitt.
15. Don’t use copper backed pads in the initial design unless there is no other option. This method of increasing capacity should be “held-back” in case additional capacity is needed in the future. It is easier than increasing bearing size.
16. Don’t ever disassemble a machine without measuring the bearing clearances “as-found”. This is the only chance you get to obtain this data which is an invaluable diagnostic tool.
17. NEVER coat a fluid film bearing journal with chrome. Use almost any other coating. Chrome is porous and water may get trapped behind the chrome and pop off the chrome layer causing catastrophic failure.
1. Machine Design, Part III by International Textbook Company,
2. Bearings and Their Lubrication by L. P. Alford, McGraw Hill, The American Machinist,
3. Lubrication of Industrial and Marine Machinery by
C. L. Pope and W. T. Everitt, John Wiley and Sons, , LC number 53-
4. Lubrication Fundamentals by J. George Wills, Marcel Dekker, Inc., , ISBN 0---7
5. Bearings and Lubrication by Joseph E. Shigley and Charles R. Mischke, a Mechanical Designer’s Workbook by McGraw Hill, , ISBN 0-07-- 2
6. Basic Lubrication Theory by Alistair Cameron. John Wiley & Sons, , ISBN -057-9
7. Machinery’s Handbook, 25th Edition, Industrial Press, Inc., , ISBN 0---5
8. Design of Film Bearings by Paul Robert Trumpler. The Macmillan Co., , LC number 66-
9. Bearing Design and Application by Donald F. Wilcock and E. Richard Booser, McGraw Hill, , 195, LC number 56-
10. Applied Tribology - Bearing Design and Lubrication by Michael M. Khonsari and E. Richard Booser, John Wiley and Sons, Inc., , ISBN 0-471- -9
11. Nicholas, J. C.,"Hydrodynamic Journal Bearings - Types, Characteristics and Applications," Mini Course Notes, 20th Annual Meeting, , The Vibration Institute, Willowbrook, Illinois, pp. 79-100.
12. Nicholas, J. C. and Allaire, P. E., , "Analysis of Step Journal Bearings - Finite Length, Stability," ASLE Transactions, 23 (2), pp. 197-207.
13. Nicholas, J. C., , "Stabilizing Turbomachinery with Pressure Dam Bearings," Encyclopedia of Fluid Mechanics, 2, Gulf Publishing Co.
14. Mehta, N. P. and Singh, A., , "Stability Analysis of Finite Offset-Halves Pressure Dam Bearings", ASME Journal of Tribology, 108 (2), pp. 270-274.
15. Lanes, R. F. and Flack, R. D., , "Effects of Three-Lobe Bearing Geometries on Flexible Rotor Stability", ASLE Transactions, 25 (3), pp. 377-385.
16. Nicholas, J. C., , "Stability, Load Capacity, Stiffness and Damping Advantages of the Double Pocket Journal Bearing," ASME Journal of Tribology, 107 (1), pp. 53-58.
17. Lund, J. W., , "Stability and Damped Critical Speeds of a Flexible Rotor in Fluid Film Bearings," ASME Journal of Engineering for Industry, 96 (2), pp. 509-517.
18. Newkirk, B. L. and Taylor, H. D., , "Shaft Whipping Due to Oil Action in Journal Bearing," General Electric Review, 28, pp. 559-568.
19. Gunter, E. J., , "Dynamic Stability of Rotor- Bearing Systems," NASA SP-113, pp. 153-157.
20. Nicholas, J. C., Gunter, E. J. and Barrett, L. E., , "The Influence of Tilting Pad Bearing Characteristics on the Stability of High-Speed Rotor B e a r i n g S y s t e m s , " R e p o r t N o . UVA//MAE81/141, School of Engineering and Applied Science, University of Virginia, Charlottesville, Virginia, pp. 30-32. Also in Topics in Fluid Film Bearing and Rotor Bearing System Design and Optimization, an ASME publication, April . pp. 55-78.
21. Theory and Practice of Lubrication for Engineers by Dudley D. Fuller, Wiley and Sons, , ISBN 0- 471--1
22. API Standards 612 (Special Purpose Steam Turbines), 617 (Centrifugal Compressors), 670 (Vibration and Temperature Monitoring) and RP684 (Rotordynamics) are available from the American Petroleum Institute in Washington, D.C. or from WWW.API.ORG
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