The impact of rolling bearing design and manufacturing on bearing service life.

Jun 04, 2024

The world's renowned bearing brands, backed by their expert designers, have meticulously crafted high-quality designs for their products. These designers, each with their unique understanding of product applications, have created a diverse range of bearings. As a result, the working life of the bearings varies, yet many brands offer similar performance, a testament to the expertise of these designers.

The 'barrel effect' is a well-known concept that serves as an analogy in bearing design. Just as the shortest board in a barrel determines its water storage capacity, the weakest aspect in a bearing design significantly impacts its overall performance and service life. FV engineers believe that it's these weak aspects, not the advantages or average scores of a certain aspect, that truly affect the quality and final service life of the bearing.

1. Internal design of the bearing

Maximize the calculated load in a limited space. However, for the maximum load and the best solution, the bearing must be adapted to the actual application of mining; the working speed, limit speed, acceleration and deceleration, impact resistance, and brand interchangeability of the bearing, and many other factors will affect the design of the bearing. Of course, the bearing design must also consider the standardization of parts, manufacturing costs, and market returns. In general, the best design must consider many factors. Because FV bearings are more focused on roller neck bearings in the metallurgical industry, high-speed and high-load multi-row roller mill bearings are key products. Next, I will give an example to illustrate what I am talking about.

These two companies have different designs for the same model of bearing. The main differences are the thickness of the bearing outer ring inside the bearing and the number and size of rollers. Of course, there are many more differentiated designs on the market. The design load of these two designs differs by 6%. The number of rollers on the right is 30. Still, the diameter is 24mm larger, and the final calculated rated load is larger, so the design on the right is generally considered the optimal design. The working life of the bearing is also very good. So why are there different designs on the left on the market? 

FV engineers have found out through research that the following factors are the cause: 

1. After a long period of use, the roundness of the box hole of many users' bearing boxes is lost, or the diameter is out of tolerance. As a result, the outer diameter of the bearing cannot be installed well with the bearing box. The load zone angle of the bearing is greatly reduced or changed. In this case, the best way is for the user to repair or replace the new bearing box. But many users need the conditions to replace it. Then, some bearing designers will increase the cross-sectional thickness of the outer ring of the bearing to counteract this problem. Based on experience, designers believe that reducing a small amount of calculated load and giving more internal space to the outer ring will increase the outer ring's ability to resist deformation.

   
   

2. This roller with a diameter of 22 is the most economical choice with the largest inventory of manufacturers.

   
   

3. Because there is a big difference between the working load or speed in use and the theoretically calculated performance of the bearing, engineers have different tendencies in the maximum load and the limiting speed. Both designs can be used well by users, and the performance difference is very small. We FV bearing engineers believe that the design on the right should be given priority.

In addition to pursuing the maximum calculated load of the bearing, the 'limiting speed' is also a crucial consideration in bearing design. The 'limiting speed' refers to the maximum speed at which a bearing can operate without excessive heat generation or premature wear. Many bearings have rotating conditions of rapid acceleration or deceleration. Since the rollers are affected by centrifugal force and inertia, the performance and strength of the bearing cage should be emphasized. If the bearing does not rotate smoothly or the inside is not clean. Then, a strong enough cage should be selected. The material and weight of the cage also particularly affect the limiting speed of the bearing. Vibration and heat will accompany the rotation of the bearing. The volume of the cage occupies the space for grease, which is also worthy of attention by the bearing designers and users. The cage does not affect the calculated load of the bearing. It is one of the most important parts of the bearing. The cage is the protective cover of the heart of the bearing. If the cage is damaged, the inner and outer rings and rolling elements of the bearing will be quickly destroyed.

The size of each part of the bearing is like each plank of a wooden barrel. Instead of pursuing the highest performance in a single item, engineers need to focus their research and innovation on improving the weakest part of the bearing.

2. Internal manufacturing standards

Why are bearings produced by different manufacturers so different for the same design? Why are the quality of many 'Original Equipment Manufacturers' (OEMs) so different? Users usually only know the macroscopic size of the bearing, which is the basic size that affects the installation of the bearing, and the technical information shown on the general assembly drawing. However, users need to learn the detailed requirements of each part of the bearing and the assembly quality requirements. FV Bearing's engineers will give you an example to explain the differences in manufacturing standards.

These are two drawings of four-row tapered bearings. They are actually the same bearing, but different suppliers have different internal control requirements for quality.

Here, I will use a table from FV Bearing's internal training materials to show some of the main differences.

The main difference is the dimensional accuracy and rotational accuracy of the bearing. The fluctuation range of the internal clearance of the bearing and the difference between the clearances of the same batch. These factors greatly affect the quality and service life of the bearing. However, the standards in the industry are very loose. Only under more stringent internal manufacturing standards can more reliable bearings be manufactured.

3. Selection of bearing 'raw materials' and heat treatment

The prices of bearings of different brands vary greatly. I am not saying that Chinese brand bearings are much cheaper than European, American, and Japanese bearings. The price difference of bearings of different brands in China is also very large. The profit margin of Chinese bearings is relatively low. So, the main reason for this large price difference is the different raw materials used to manufacture bearings. There are many grades of steel, and the purity of steel is also different. Bearings for different applications should be made with more suitable raw materials. Do not abuse them. For example, the most commonly used bearing steel GCr15 bar is 850-1140$/ton. The G20Cr2Ni4(A) round bar used for medium and large rolling mill bearings in steel plants is priced at 2400-2850/ton. If the difference in raw materials exceeds one time, then the price of the finished bearing will be even greater. The value of bearings lies in their application. High-speed ball bearings and roller bearings with impact loads need to be manufactured with the right raw materials and heat treatment methods. We in the industry and users must always purchase bearings. It is gratifying that some high-quality and high-purity bearing steels from SKF, TIMKEN, and Sanyang Special Steel can also be used in China. It provides favorable support for FV to manufacture heavy-duty bearings with higher standards.

Heat treatment quality can improve the original performance to the strongest state, which is also the core technology of bearing quality. Put: good heat treatment needs to ensure the hardness of the bearing while also ensuring the microstructure of the metal structure. For example, there are many types of martensite with high hardness. Uniform and delicate needle-shaped martensite may be what we want most. Etc.

4. More reliable, improved design and innovative surface technology

Some bearing damages are caused by themselves, and some are caused by other bearings or parts installed with them.

FV engineer Kevin lists some typical cases for learning:

1. The working conditions of radial bearings and thrust bearings working together. If the radial bearing is frequently damaged, the thrust bearing (locating bearing) should be checked for damage or loss of function.

2. Pay attention to the parts that are closely installed with the bearing. If the matching tolerance is lost, the bearing will work under incorrect clearance. In addition, the reliability of the sealing system and whether the sealing type and sealing material can match the current working temperature and air/oil pressure. Users must install according to the installation specifications and conduct regular inspections and maintenance.

3. Bearing manufacturers can negotiate with users to give their improved solutions to make up for the shortcomings of users. For example, adding a sealing cover to a bearing only partially relies on the seals on the customer's bearing box. The bearing is protected by its seal. Protected grease. Thus extending the working life of the bearing.

4. Application of new technologies, in order to prevent the bearing and raceway surfaces from being eroded by moisture, and to improve the oil film adhesion ability of the raceway, improve the wear resistance of the raceway. Reduce friction. FV bearings have provided new solutions with surface coating technology for many large steel mills in China. Manganese phosphating coating technology is the most commonly used coating in the metallurgical and heavy industry fields. The life of the bearing is extended.

5. Changes and upgrades in grease

Many users only know that filling grease can protect bearings, but they rarely study the types and properties of grease. Regarding oil lubrication, appropriate anti-wear protective agents (Organic molybdenum friction improver) can be added to greatly improve the anti-wear performance of the oil, which can effectively reduce the wear of the bearing surface and each valve body. Regarding grease lubrication, the most popular No. 2 lithium-based grease is not a panacea. There are many industry-specific greases on the market. In the Chinese market, extreme-pressure lithium-based grease with molybdenum disulfide and graphite additives is widely used in high-speed wire mill bearings. Calcium sulfonate composite grease is also widely used in the field of medium and large metallurgical bearings, and its performance is very excellent. Polyurea grease is widely used in continuous casting machine bearings due to its excellent high-temperature resistance. Therefore, if industrial bearings want to extend their service life, they need to select the type and viscosity of lubricating grease scientifically.