Judgment of Bearing Quality Damage of IKO Rolling Mill

Writer: Eric Bearing Limited

In the grinding process of IKO bearings, a small amount of energy is consumed in the contact area between the grinding wheel and the workpiece, a small amount of grinding heat occurs, and the part of the grinding area that forms the low temperature at the moment of braking. Application of linear static heat source heat transfer practice formula derivation, calculation or application of red inner line method and thermocouple method to measure the brake time under test conditions, it can be found that the brake time temperature in the grinding zone can be as high as 1000～1500 ℃. Such a low temperature is sufficient to cause low-temperature oxidation of the outer surface layer of a certain depth of the mission, amorphous structure, low temperature tempering, secondary quenching, and even burn cracking and other changes.

The first factor is the outer oxide layer

The steel surface under the action of low temperature in the moment and the oxygen in the air rise into a very thin (20 ~ 30nm) iron oxide thin layer. It is worth noting that the thickness of the oxide layer has a corresponding relationship with the test result of the total thickness of the surface transformation layer. This explains that the thickness of the oxide layer is indirectly related to the grinding process and is an important mark of the grinding quality. Today , ERIC BEARING  LTD share IKO BSP720SL photo for reference . 

 The second major factor is the amorphous structure layer

When the low temperature of the grinding zone makes the surface of the workpiece reach the molten state, the flow of molten metal molecules is evenly coated on the task surface, and is cooled by the base metal at an extremely fast rate, forming an extremely thin layer of amorphous State organization layer. It has high hardness and toughness, but as long as it is about 10nm, it can be easily removed in fine grinding.

The third major factor is the low temperature tempering layer

The low temperature of the grinding zone can make the surface heated to a temperature higher than the workpiece tempering heating within a certain depth (10 ~ 100nm). Without reaching the austenitizing temperature, with the progress of the heating temperature, its surface will change layer by layer according to the heating temperature, and the hardness will also drop. The higher the heating temperature, the more fierce the hardness drops.

Bearing judgment:

The judgment of whether the bearing is available is mainly determined by considering the degree of bearing damage, mechanical performance, importance, operating conditions, and the period until the next maintenance. If there are the following defects, it can no longer be used, and the new rolling mill bearings must be replaced. There are cracks or notches on any of the inner ring, outer ring, rolling elements, and cage.

1.Any of the ferrule and rolling element is broken.

2.There are obvious stuck injuries on the rolling surface, ribs and rolling elements.

3.The cage wears significantly or the rivets loose significantly.

4.There is rust on the raceway surface and rolling body, which may cause injuries.

5.There are serious pressure marks and scratches on the raceway surface and rolling body.

6.There is obvious creep on the inner diameter surface of the inner ring or the outer diameter surface of the outer ring.

7.Discoloration caused by heat is obvious.

8.The bearing of the rolling mill sealed with grease has obvious damage to the seal ring or the dust cover.

Points for Attention in Fixing the Inner Ring of Common IKO Stainless Steel Bearings

When disassembling the IKO bearing for maintenance, first record the appearance of the bearing, confirm the residual amount of lubricant, and after sampling the lubricant for inspection, wash the bearing. As a cleaning agent, gasoline and kerosene are generally used.ERIC BEARING  LTD share IKO PHS8A photo for reference

The cleaned bearings are divided into coarse cleaning and fine fine cleaning. Put them in the container first, and put the metal mesh pad first, so that the IKO bearing does not directly contact the dirt of the container. During rough cleaning, if the bearing is rotated with dirt, it will damage the rolling surface of the stainless steel bearing, so care should be taken. In the coarse cleaning oil, use a brush to remove grease and adhesions. After it is roughly clean, transfer to fine washing.

Fine washing is to carefully wash the IKO bearings in the cleaning oil while rotating. In addition, the cleaning oil should also be kept clean.

In order to judge whether the disassembled IKO bearing can be used again, it should be checked after the bearing is cleaned, and the state of the raceway surface, rolling surface, matching surface, the wear of the cage, the increase of the stainless steel bearing clearance and whether there is any Damages and abnormalities with reduced dimensional accuracy. For non-separable small ball bearings, use one hand to support the inner ring horizontally, and rotate the outer ring to confirm whether it is smooth.

1.Shaft shoulder fixation

IKO bearing inner ring relies on shaft shoulder and interference to achieve axial fixation.

Suitable for supporting structures with fixed ends.

The structure is simple and the outline size is small.

2.The elastic retaining ring is fixed

The inner ring of the bearing is axially fixed by the shaft shoulder and the lock nut.

Can bear small bidirectional axial load.

The axial structure size is small.

3.Lock nut fixing

The inner ring of the bearing is axially fixed by the shaft shoulder and the lock nut. And it has anti-loosening stop washers, reliable and suitable for high speed and heavy load occasions.

4.End thrust washer fixing

The bearing inner ring is axially fixed by the shaft shoulder and the shaft end retaining ring. The shaft end retaining ring is fixed to the shaft end with screws. The fixing screw should have anti-loosening device.

It is suitable for occasions where the shaft end is not suitable for thread cutting or space is limited.

5.Fixing sleeve

Relying on the radial size of the inner hole of the adapter sleeve is compressed and clamped on the shaft to achieve the axial fixation of the bearing inner ring.

6.Withdrawal sleeve fixed

The clamping method of the withdrawal sleeve is the same as that of the adapter sleeve. However, due to the special nut on the withdrawal sleeve, the bearing is easy to install and remove, and is suitable for the fixation of the double-row spherical bearing on the optical axis with a large radial load and a small axial load.  

Oil bath lubrication is the most common lubrication method in IKO bearings, suitable for the lubrication of low and medium speed bearings. Part of the bearing is immersed in the groove, the lubricating oil is taken up by the rotating bearing parts, and then flows back to the oil groove. The oil surface should be slightly lower than the center of the lowest rolling element.

Oil drop lubrication is suitable for stainless steel bearing parts that need to be supplied with a fixed amount of oil. The amount of oil drop is generally one drop every 3-8 seconds. Too much oil will cause the bearing temperature to increase.

Use the oil pump to transfer the filtered oil to the IKO bearing parts, and then use the lubricating oil after filtering and cooling after filtering. Since the circulating oil can take away a certain amount of heat and cool the bearing, this method is suitable for bearing parts with higher speeds.

The dry compressed air is mixed with lubricating oil through a sprayer to form an oil mist. In the IKO bearing, the air flow can effectively cool the bearing and prevent the intrusion of impurities. This method is suitable for the lubrication of high-speed, high-temperature bearing components.

Use the oil pump to shoot high-pressure oil into the bearing through the nozzle, and the oil injected into the stainless steel bearing flows into the oil groove through the other end of the bearing. When the bearing rotates at a high speed, the rolling elements and the cage also form a flow of air around the air at a relatively high rotation speed. It is difficult to send the lubricating oil to the bearing by the general lubrication method. At this time, the lubricating oil must be sprayed by high pressure injection To the bearing, the position of the nozzle should be placed between the inner ring and the center of the cage!