Fluctuating axial loads For “short periods of time” twice the value of Fap out of (1)/(2) can be permitted if it results in a temporary rise in bearing operating temperature of no more than 5°C. Depending on the bearing size, load and speed this “short period” covers only several seconds or can last a few minutes. As a rule of thumb, this “short period” can be considered as the time during which the axially loaded bearing runs 1,000 revolutions.

NOTE: Tailoring any change in grease to what came before will eliminate any potential conflicts within the mixture. Otherwise, bearings may need to be purged and cleaned.

Other criteria For slow running applications, in particular, it is not the frictional energy, respectively smearing in the flange contact, but the flange strength that puts the limit on the axial load carrying capacity of a cylindrical roller bearing. Easy-to-use formulas can be found in the SKF General Catalogue. However, for critical cases more precise calculations are recommended, e.g. by use of advanced FEA programs (fig. 7). SKF offers a consultancy facility through its application engineering services for this purpose.

Choosing a grease is entirely subjective to the application. Determine what you need, how to protect bearings and rolling elements best, and how lubricants will be delivered – as well as whether there are any environmental considerations, and so on.

Axial loadexample

Not unlike determining what grease is suitable for your application, deciding what greases are compatible will take research. The RPM of the bearing, operating temperatures, and resultant loads are all important factors in determining an appropriate grease.

Axial loadunit

As a result of this work, the current SKF catalogue formula for dynamic axial load carrying capacity has been reviewed and new insights, e.g. for oil flow cooling incorporated.

Some incompatibilities are more evident than others. Take, for instance, the NLGI grade. Having two different consistencies of grease will make it challenging to achieve a uniform distribution within a bearing. The same goes for the oil viscosity of the grease. When different, one oil may not be appropriate for the RPM or operating temperature of the application. High viscosity oils, when coupled with high speeds, will have trouble protecting the rolling elements.

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Summary and outlook With help of the reworked formula for the dynamic axial load carrying capacity of cylindrical roller bearings it is now possible to obtain a sufficiently precise estimation of the permissible axial load also for larger bearings with a heat conducting surface Ar > 50,000 mm². Operating conditions such as radial load, speed, lubrication, as well as internal geometry of SKF bearings and new friction models are taken into account. In addition, cooling by oil flow can be considered to calculate either the required oil flow for a given axial load or a permissible increase of axial load for a given oil flow. As SKF engineers are continuously aiming at improving profiles and materials, reducing friction, etc., these new formulas will also be continuously revised, presum-ably leading to even higher values in the future, which will have an impact of improved performance.

Mariner bearings use Mobil FM222 food-grade grease. An NLGI #2 aluminum complex grease that, according to Mobil, “helps provide superb equipment protection during frequent equipment cleaning operations.” Also an H1 category grease, it is intended for use in situations where there is incidental contact of grease with food or pharmaceutical products.

Generally, a handful of grease options will be entirely appropriate. But for those applications requiring extra care or extra thought, the time taken to select the right grease will benefit your application enormously.

For example: a NJ 2313 ECP bearing can withstand an axial load Fap.oil = 15 kN instead of Fap = 9 kN when it is cooled with s = 0.4 l/min oil flow through the bearing and the oil inlet temperature is  = 20°C below the bearing operating temperature for chosen reference conditions with Fr = 29 kN and n = 1,600 r/min.

The goal when lubricating something is protecting surfaces and separating them from one another through an oil film provided by the grease. Unfortunately, when two greases are incompatible, the situation can be similar to not using any grease at all. It can even go so far as damaging components, hastening a critical failure. This is a worst-case scenario, but an avoidable one.

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There is a small range of soaps and non-soaps available with a similar range of pros and cons. Lithium-based soaps have become the most prevalent because of good general performance as a thickener, but require specific additives to maintain this (such as anti-oxidizers) and have a lower maximum operating temperature. Polyurea-based thickeners will typically have higher temperature allowances but can have less pumpability in lubrication systems. Aluminum or calcium-based thickeners are found in food-grade greases, which have good water resistance but may also have lower temperature ranges.

In order to establishthe dynamic axial load carrying capacity of cylindrical roller bearings, different criteria compared with those used for the radial load carrying capacity need to be considered. Relevant are the application limitations to prevent wear, overheating and smearing in the flange contact, as well as flange fracture.

Not every element needs to be the same for two greases to be compatible. Although, if you are transitioning from one grease to another without flushing the bearing beforehand, the closer you can get to a complete match, the better the outcome will be for the bearing.

What is axial loadin civil Engineering

New developments The SKF catalogue formula (1) was developed in the 1980s and has proved to have an excellent agreement with experimental results and feedback from the field. In the past few years, however, following the rapid development of new larger-size and high power-density industrial gearboxes designs, especially for wind turbines, did the limitations of the current dynamic axial load carrying capacity of larger cylindrical roller bearings appear.

Food grade greases can complicate this even further. These greases must conform with significantly stricter guidelines as well as be able to handle a constant washdown environment and a barrage of cleaners, all the while minimizing contact with surroundings. Food grade greases typically include additional additives that help it perform in these areas.

What is axial loadon column

Thickeners are the part of the grease that keeps the oil contained within it. Incompatibility now becomes more problematic. If unsuitable for mixing, thickeners can change the entire consistency and cause the base oil and additives to bleed out from the grease. This situation leaves behind something wholly unrecognizable as a protectant and lubricant.

It might seem that finding an equivalent grease that is entirely compatible with what we’re replacing is a tall order. It can be. Impossible? Hardly.

It would be impossible to choose a grease without knowing the full scope of your application, but there are a few steps we can guide you through in determining what’s appropriate. Here’s a short list of selection factors you’ll want to address first:

This should be the first consideration on your list. As a general rule, high speeds require a low viscosity and slow speeds require high viscosity. Think of it this way – you want the oil in the grease to provide a film between any two surfaces. In a high-speed application, you want the oil to move out of the way of the rolling element quickly, while simultaneously filling in the space left behind.

Most published charts found online focus grease compatibility on only the thickener, disregarding several other important aspects of the grease – such as those listed above. While thickener is a critical component to consider, it hardly paints a complete picture. Calcium sulfonate and polyurea thickeners have moderate compatibility with others, whereas clay or aluminum complex thickeners allow less room for change. It is essential to consider the entire catalog of elements and measurements within a grease to find a compatible one.

What is axialloading of the spine

Comparison In larger industrial gearboxes cylindrical roller bearings in the NJ 23.. EC series are used and subjected to heavy axial loads. Fig. 6 shows a comparison of the dynamic axial load carrying capacity versus bearing size.

Dynamic axial load carrying capacity The dynamic axial load carrying capacity is a value for the permissible axial load that ensures a stable bearing operating temperature at 60°C above ambient temperature. That means that the frictional heat generated inside the bearing is equal to the heat dissipation via the shaft and housing at that temperature. This criterion has shown to be a good indication for safe operation without smearing at the flange contact, provided that lubrication conditions are adequate (viscosity ratio 2). The current SKF catalogue formula is based on a constant specific heat loss factor for all bearing sizes and a friction model taking into account SKF specific profiles and surface finishes:

An axial load between the inner and outer rings is transmitted between the flanges and the roller ends (fig. 2). The kinematic conditions in the flange contact always lead to a certain amount of sliding in the contact area (fig. 3), raising the total friction in the bearing. To improve this, SKF has continuously optimized the flange and roller end profiles. Nowadays the flanges have a slightly open design and roller ends are “blended” with an especially developed profile. This design ensures that the contact area is kept close to the flange undercut, so that even in case of roller skewing and tilting, the lubricant film build-up is realized. The result is reduced sliding friction and minimized stresses in the undercut.

Additional cooling In cases where the actual axial load exceeds the theoretical value derived by (1) or (2), additional cooling can increase the permis-sible axial load by a certain amount. For a constant oil flow through the bearing with a temperature difference between incoming and outgoing oil flow  [°C] and an oil flow volume through the bearing s [l/min], the permissible axial load Fap.oil [kN] becomes:

What is axialloading injury

Operating temperatures and types of load will influence viscosity requirements as well. One method of measuring viscosity is centistokes (cSt) at 40°c. Avoiding a scientific deep-dive, water is measured at 1 cSt, whereas some kinds of honey near 1,000 cSt. For general purpose greases in mounted ball bearings, 220 cSt viscosity will be widely found throughout the industry. Both Turner and Mariner use greases of this viscosity. Timken pillow block and food-safe greases are around 110 cSt. Dodge SC bearings (Unirex N2) and Polyrex EM (a widely used bearing grease) are both 115cSt.

Turner bearings come with Shell Gadus S2 V220. This grease is also an NLGI #2, but a lithium soap-based grease. This is a multi-purpose grease with extreme pressure, oxidation, and corrosion resistance additives.

With an abundance of lubricants supplied by numerous large and small manufacturers, it’s more important than ever to make sure that what we’re using is appropriate. Seriously incompatible greases will inevitably lead to failure. This is a foregone conclusion.

Axial loadformula

Demanding applications with larger size cylindrical roller bearings are the motivation behind studies on the dynamic axial load carrying capacity for this bearing type.

A constant specific heat loss factor for all bearing sizes now seems to be too optimistic for larger bearings. So, new factors based on experimental results and ISO 15312:2003 have been derived for bearings with a heat conducting surface Ar> 50,000 mm² with Ar =  . B . (D + d), see fig. 5. Inserted into (1) this leads to:

Design and applications of cylindrical roller bearings In many applications, cylindrical roller bearings are used for the non-locating bearing position (N and NU designs) to accommodate axial displacement between the shaft and housing within the bearing, e.g. resulting from thermal expansion of the shaft. These bearings can only take radial loads. Cylindrical roller bearings with flanges on both inner and outer rings can support axial loads additionally – NJ design bearings in one direction and NUP or NJ+HJ design bearings in both directions (fig. 1).

There is a potential that the grease hardens, becomes runny, or in the case of metal-based thickeners, leaves behind salt-like materials in whatever remains. It’s not hard to imagine what an abrasive similar to salt can do to your application. Think of petroleum jelly with fine grain sand as a parallel.

Axial loadbearing

Fap permissible axial load [kN] C0 basic static load rating [kN] Fr actual radial bearing load [kN] n rotational speed of the inner ring [r/min] d bearing bore diameter [mm] D bearing outside diameter [mm] B bearing width [mm] k1, k2 factors (=> table 1).

Application limits The radial load carrying capacity of cylin-drical roller bearings is based on “classical” sub-surface fatigue theory. For axially loaded cylindrical roller bearings, however, the following criteria need to be considered:

For bore diameters up to 85 mm , the current catalogue formula remains valid, but the permissible axial load can be further increased by oil flow cooling.

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For bearings in the NJ 23.. EC series with a bore diameter larger than 85 mm , it can be seen that the “former” formula gives rather high values (curve “A”), e.g. Fap = 274 kN for a NJ 2360 ECMA bearing at Fr = 400 kN and n = 285 r/min which could, according to (2) and (3), only be realized with an oil flow of s= 11 l/min and  = 20°C.

We cannot overstate how critical lubrication is in the power transmission industry. As a part of this community, you’ve most likely experienced first hand how improper lubrication has severely detrimental effects on rotating components. It is critical for all bearings – mounted or otherwise – to have not only the right grease applied, but applied in the correct quantities and on time as well.

Best practices primarily determined the NLGI grade throughout the power transmission industry over many years. NLGI grade 2 has the best performance in general mounted bearing applications. However, there are exceptions. Lower NLGI grades can better suit situations where you need increased pumpability for automatic lubrication or colder applications, which typically thicken and slow grease. Alternatively, use a higher NLGI grade for bearings or applications that require extra sealing or leak prevention.