Precautions for purchasing four row cylindrical roller bearings

Aug 30, 2021

This is the first article in the "Kevin Words Bearing" column.  Mr Kevin will continue to update valuable experience every week and share them with you. 

Four row cylindrical roller bearing is the most popular high-speed bar mill bearing in the world. But it is true that steel mills encounter many strange troubles in the procurement process. Our application engineers maintain long-term communication with users. Now summarize the following precautions to customers and give our solutions.

1. Application and material selection:

At present, small and medium-sized four row cylindrical roller bearings are most widely used in the field of long mill, and the inner diameter of the bearing is usually ≤ 340mm in China. The raw materials of this type of bearing are GCr15, GCr15SiMn and a small amount of GCr18Mo. The heat treatment of bearing parts is usually martensite hardening, bainite hardening and composite hardening. The hardness of the bearing is usually HRC 59-62. The four row cylindrical roller bearing made of this material and heat treatment process can be well used in hot-rolled bar and threaded steel mills. The price is very good.

Quality difference points: 1. Purity and oxygen content of steel    2. Heat treatment quality, conversion rate of martensite and bainite     3. Cage Quality 

Solution: confirm the raw material certificate, heat treatment certificate and hardness test report

2. Manufacturing accuracy of bearing

The bearing used in high-speed long strip mill usually has better rotation and dimensional accuracy than p6. Better rotation accuracy can improve the service life of the bearing and the quality of rolled steel bar. High precision bearings play a positive role in the reliability of the whole rolling mill system. However, the market is full of rolling mill bearings with accuracy lower than P6, P0 grade bearings and poor quality bearings.

Quality difference points: 1. Overall dimension accuracy      2. Rotation runout accuracy    3. (Rollers Quality *)

Solution: our engineers suggest to buy rolling mill bearings with accuracy better than p6.  Although the price is slightly more expensive, it has a longer working life. More competitive.

3. Internal clearance and interchangeability of bearing

The most special property of four row cylindrical mill bearings is their interchangeability. In the process of rolling steel, workers need to change rolls regularly. The inner ring of the bearing needs to be replaced together with the mill roll. This is a problem that breaks out frequently. The inner ring and outer ring components of four row cylindrical roller bearings can be separated. And the internal clearance is determined by the parts together. Please refer to the figure below, and I will give you an example (Model: 313812 C4 fou-row cylindrical roller bearing), which will help us understand the important line of this problem.  

International general standards:   Fw=202 (+0.025, 0) ; Raceway diameter of inner ring = 202 (-0.170 , -0.195)  Then the internail radial clearance 0.170 ~ 0.220mm    RIC=C4;

Some unknown brands have their own standards:   Fw=202 (+0.110, +0.085) ;  Raceway diameter of inner ring =  202 (-0.085, -0.110). Then the internail radial clearance also  0.170 ~ 0.220mm  RIC=C4 also;

If the user purchases bearings of different standards, there will be bad trouble: 
Case 1:   202 (+0.025, 0)   &   202 (-0.085, -0.110),  then the RIC= 0.085 ~ 0.135 mm   RIC=CN,  this clearance is too small.  

Case 1:   202 (+0.110, +0.085)   &   202 (-0.170, -0.195),  then the RIC= 0.255 ~ 0.305 mm   RIC=C5,  this clearance is larger than C4. 

Both cases may reduce the working life of the rolling mill bearing,  We need attention and control.

International standard for Inner Ring Interchange：

Difference: it is not necessary to follow the interchange tolerance of ISO standard. Different manufacturers may have different standards.

Solution: strictly confirm the drawings before purchasing. The inner ring raceway diameter tolerance and the outer ring roller lower end diameter tolerance shall be confirmed. Confirm that it meets the exchange standard of the bearing currently in use before determining the purchase.

4. Bearing design details

There are many manufacturers of rolling mills or rolling mill bearing housings in the world. The lubrication system of the bearing housing must match the bearing. The number, position and size of lubrication holes or grooves on the bearing outer ring or inner ring shall be correct. At present, whether the outer diameter and four end faces of small four row cylindrical roller bearings need lubrication grooves. This will affect the service life of the bearing.

Does the cage material and interior of the bearing need improved design? Generally, the most common is the turning solid copper / steel cage. At present, there will be some upgraded designs on the market to change the diameter, length and quantity of internal rollers. The bearing can be added with a certain load rating, such as the solid window cage design. Improved design does not necessarily apply to all users. The customer needs to try before deciding.

Difference:  whether there is correct lubrication / disassembly lubrication groove. Is it in line with the original design?

Solution: the mechanical maintenance engineer shall carefully check the original drawings and the design of the bearing housing. Ensure that grease can be smoothly injected into the bearing. Ensure that the maintenance engineer needs these lubrication grooves.

5. Professional suppliers and manufacturers

There are thousands of bearing brands in the world. There are more than tens of thousands of bearing models. Not every bearing brand focuses on rolling mill bearings. Rolling mill bearings are only a small series in the bearing family. Many bearing brands do not understand the application of bearings. They don't understand the above 1-4 problems. These bearing brands may not know more about these rolling mill bearings than customers. Do not ask the price before purchasing all rolling mill bearings. Please be sure to ask the supplier if they know about rolling mill bearings.  Does the supplier have its own professional rolling mill bearing catalgue and samples.  I believe users should ask some professional questions to test the professional ability of bearing suppliers. 

Difference: is it a professional rolling mill bearing supplier

Solution: it is recommended that steel mill users contact China FV bearing company, or SKF, Timken and other international brands. Because FV not only supplies bearings, but also helps users solve many difficult problems in the production process. FV is a knowledge-based industrial bearing brand.

FV have shown bearing model list of wire rod mill that FV can supply.     Please collect and share.