In order to better serve LT and assist lt to achieve the purpose of energy saving and consumption reduction in bearing application, DMD actively invited to the LT site to carry out on-site measurement, interactive communication, actual mapping and other measures to improve the service life of bearings. The details are as follows:

Bearing structure and performance

The main characteristics of this type of bearing are higher radial bearing capacity, higher limit speed, higher machining accuracy and higher separability (inner and outer rings can be separately installed) the inner ring fits with the shaft in the form of interference fit, and the outer ring assembly matches with the bearing housing hole clearance, which has the functions of high interchangeability and easy disassembly If the bearing does not have the ability of aligning, it is more sensitive to misalignment. Any misalignment will easily lead to bearing eccentric load and torque load.

Measurement of bearing pedestal

Therefore, the type bearing does not have the pick-up performance, that is, the bearing seat hole must have high accuracy, so the ellipse and taper must be within the required tolerance range.

On site inspection, there are two lower roller bearing seats using fcd5678275p6c3 bearing;

1. Bearing pedestal:

Load area: 390 (+ 0.12 + 0.08 + 0.12 + 0.12)

Non load area: 390 (+ 0.05 + 0.04 + 0.05 + 0.05)

2. Bearing pedestal:

Load area: 390 (+ 0.08 + 0.12 + 0.12 + 0.08)

Non load area: 390 (+ 0.04 + 0.05 + 0.02 + 0.03)

According to the data analysis, the accuracy of the bearing seat does not meet the accuracy requirements of the bearing. Under the impact force produced when the rolling mill passes through the steel, the excessive cylindricity will inevitably cause the outer ring reciprocating elastic deformation. If the outer ring is subjected to excessive reciprocating elastic deformation, the surface and subsurface cracks (bearing area) will appear on the outer ring, causing the bearing outer ring to peel off and damage in advance.

It is necessary to restore the bearing seat to the standard tolerance of Ф 390 H7 (+ 0.057 0), and the ellipse and taper of the bearing seat shall not exceed 2 / 3 of the bearing seat tolerance.

Lining plate and lug

In addition, according to the on-site inspection, both sides of the fcd5678275 bearing block of your company are not lined, that is, both sides of the bearing block are directly matched with the lining plate on the mill housing. From the view of the wear degree of the outside, it can be judged that the wear on both sides is uneven, and the lug of the box body on the operation side is bumped, deformed and bumped.

This is bound to cause eccentric displacement of bearing housing hole, resulting in different wall thickness on both sides of bearing pedestal. After running on the machine, the cross of roll system will be caused, resulting in axial load, i.e. torque load, which will cause damage to a row of bearings close to the roll body. Therefore, it is suggested that the machine tool or special measuring tool on the bearing pedestal should measure and correct the eccentric displacement of the seat hole center, and the lug should be polished and corrected. 

Bolt tightening

After the installation of the roller system, there is bolt leakage. The screw thread is mostly sliding or there are many foreign matters. The bolt leakage will lead to the axial locking of the positioning bearing, which will cause the inclination misalignment of the inner and outer rings, and lead to the bearing fatigue damage in advance, especially the cage wear, copper powder dropping and edge curling.

Therefore, it is necessary to align the bolts according to the operation standards, fix the bolts evenly in place, and re tap the thread mouth of the sliding thread.

Bearing life and adjustment

Since there is no other spare parts related to the bearing, the service life of fcd5678275 bearing can only be given theoretically from the ideal state.

Theoretical design rated dynamic load: 3600kn; rated static load: 7000kN; theoretical rated life value: L10 = 106 / 60N * (CA / P) 10 / 3 ≈ 5641 hours ≈ 8.0 months

In theory, the service life that can fully meet the requirements of rolling mill equipment is analyzed. However, due to the fact that the working conditions of the rolling mill are not ideal, such as large tolerance of bearing pedestal (including ellipse and taper), unqualified roll diameter accuracy (straightness and interference tolerance), etc. Therefore, DMD will adjust the structure and material of the bearing to be supplied to meet the requirements of on-site operation.

1. Section thickness adjustment of bearing outer ring

The thickness adjustment can enhance the overall strength of the outer ring and reduce the damage to the outer ring due to impact and bearing seat hole out of tolerance.

2. Adjustment of rolling element crown

Increasing the crown value of the rolling element can slow down the damage of the edge stress to the outer ring bearing area.

3. Adjustment of bearing hardness

Adjust the hardness coordination between the rolling element and the inner and outer rings to improve the impact load and material toughness on the premise of ensuring the hardness.

4. Cage wrapping rate and thickness adjustment

It can increase the ratio of cage teeth higher than the length of rolling element, increase the wrapping of rolling element in radial direction by thickening cage, and put an end to the problems of cage tooth breakage and deformation. 

5. Increase grinding capacity

Add 0.05-0.1 grinding amount to the inner ring. After installing the inner ring, your company must grind again to ensure the concentricity of the inner ring and the roller. The concentricity between the inner ring and the roller is not more than 0.01mm. The diameter difference of the inner ring at both ends of the roller is not more than 0.02mm. The surface roughness of the inner ring of the bearing after grinding is not greater than ra0.30 

Disassembly and installation site

The installation shall follow the following procedures:

(1) When installing labyrinth ring (waterproof sleeve), the matching between labyrinth ring and roll neck is generally tight dynamic fit, and it needs to be tapped in with copper rod during installation. Both ends of labyrinth ring must be parallel and closely fit with shaft shoulder and bearing inner ring.

(2) Before installation, ensure the integrity, flatness and cleanliness of the parts, such as shaft shoulder and box hole, must remove the sharp burr, the dimension tolerance of the hole shall conform to: H7, the bearing tolerance shall comply with: p6.

(3) When installing the inner ring, the inner ring of the four row cylindrical roller bearing and the roller neck are interference fit, and the inner ring should be heated to 90-100 ℃ before installation. Do not exceed 120 ℃ to prevent the inner ring from retracting completely after cooling. Heating method can be oil tank heating can also be used induction heating, do not use open fire heating. The increase of inner diameter when heated by oil tank is calculated according to the following formula:

△d＝12.5×10-6△t.d

Where: △ D - increase of inner diameter of inner ring after heating (mm)

Δ T - the difference between oil temperature and room temperature (℃), the room temperature standard is 20 ℃.

D - inner diameter of inner ring (mm)

When installing FCD type double inner rings, it is necessary to make the inner ring and inner ring, inner ring and labyrinth ring face close to each other along the axial direction during the cooling process of the inner ring, and the feeler gauge shall be used for inspection.

(4) Generally, the outer ring of the four row cylindrical roller bearing with outer ring is in transition fit with the inner hole of the bearing seat. The copper rod can be used to tap the outer ring, roller and cage into the bearing seat.

(5) After installing the sleeve, rotate it to ensure smooth rotation. In case of any jamming, it should be disassembled immediately to check and find out the cause.

(6) It is important to check the service condition of the sealing ring, such as lip fracture and skeleton deformation, which needs to be replaced immediately.

(7) The gland of bearing box and the end face of box shall be locked with corresponding rubber pad to prevent pressure relief and external emulsion and foreign matters from invading into the bearing.

After sale and service

After the modified bearing enters the site, DMD will assign technicians and engineers to assist LT bearing installation and off-line inspection to ensure that the bearing can reach the expected service life safely and stably. DMD will provide 24-hour telephone service and 12-hour on-site service.