Experience sharing

The clearance size of tilting pad sliding bearings directly affects the operating condition of the bearings, and there are many cases of bearing damage caused by improper adjustment of bearing clearance. Senior technician at Liaoyang Petrochemical, Yue Jingchun's experience in teaching solutions is a rare secret for frontline technicians.

Clearance of tilting pad sliding bearings

Sliding bearings have the advantages of smooth operation, impact load resistance, simple structure, small size, high precision, and low vibration, so they are widely used in oil refining and chemical machinery. Especially for tilting pad type sliding bearings, the pads can freely swing and move synchronously with the shaft neck, always forming a Z-shaped oil film when the working conditions change. The oil film is stable, has good anti vibration performance, and is not prone to vortex and oil film oscillation, which can increase the stability of the rotor. Therefore, it is widely used in various major units of chemical plants. However, the clearance size of tilting pad sliding bearings directly affects the operating condition of the bearings, and there are many cases of bearing damage caused by improper adjustment of bearing clearance.

Examples of damage to tilting pad sliding bearings

In May 2008, the Mechanical Maintenance Department of Liaoyang Petrochemical discovered fatigue damage to the radial bearing of the steam turbine during the maintenance of a nitrogen compressor unit at Jilin Fertilizer Plant (as shown in Figure A). After analysis and verification, the cause of the bearing damage was fatigue damage caused by excessive adjustment of the bearing clearance.

In June 2008, the mechanical maintenance department of Liaoyang Petrochemical was inspecting a compressor unit in the ethylene workshop of Zhongyuan Ethylene Chemical Plant. During the disassembly of the speed reducer, it was found that the radial bearing of the high-speed shaft was severely burned (as shown in Figure B). After analysis and verification, the reason for the damage to the bearing was due to the high temperature burning caused by the adjustment of the bearing clearance too small.

Figure A Radial Bearing Fatigue Damage of Steam Turbine

Figure B: The radial bearing shell of the high-speed shaft of the accelerator is burnt out

As can be seen from the above, measuring and adjusting the clearance of radial tilting pad sliding bearings is of utmost importance for the installation and maintenance of rotating equipment.

Comparison of several methods for measuring the clearance of radial tilting pad sliding bearings:

1. Lead compression method

The operation method is to directly remove the upper half of the radial sliding bearing from the body, evenly place the lead wire on the upper half of the shaft neck, and then reinstall the upper half of the sliding bearing. Use the bearing shell and shaft neck to flatten the lead wire, and then measure the thickness of the lead wire being squeezed to obtain the bearing clearance value. Its advantage is that it is easy to operate and can measure bearing clearance without removing the entire bearing from the body. Its disadvantage is that when measuring tilting pad sliding bearings, due to the free swinging of the pads, the measurement values are uneven and the errors are large, making it impossible to measure the coaxiality of a single pad in the bearing body.

2. Shaft lifting method

The operation method is to gently lift the rotor shaft neck with a hoist or manual hoist without disassembling the bearing until it is completely in contact with the bearing upper tile (never use a crane to operate directly), then lower the shaft neck and fully in contact with the lower tile. Use a dial gauge to measure the distance difference between these two positions, which is the bearing clearance. Its advantage is that it is easy to operate, without disassembling the bearings, and the bearing clearance can be measured directly in the machine body. Its disadvantage is that it requires lifting the entire rotor, and the operation method is cumbersome, which can easily cause damage to the equipment itself; If the measurement of the internal structure of the bearing is complex and the measurement data is inaccurate, it is not possible to measure the coaxiality of a single tile in the bearing body.

3. False axis method

The operation method is to first make a fake shaft with the same basic dimensions as the rotor shaft neck, remove the entire bearing, install it on the fake shaft, and use a dial gauge to measure the bearing clearance by pushing and pulling. Its advantage is accurate measurement and the ability to simultaneously measure the coaxiality of a single tile relative to the entire bearing body. Its disadvantage is that the measurement is slightly more complex and requires a certain amount of computing power.

4. Shaft gauge method

The operation method is to first make several fake shafts with a diameter interval of 0.02mm, and then use the principle of the pass stop gauge to pass the fake shafts through the bearings in sequence. The bearing can be measured as the inner diameter of the bearing on which fake shaft it feels neither loose nor able to rotate.

Taking a bearing with a basic size of Φ 80mm as an example, assuming that the clearances between bearings Z small and Z large are 0.12mm and 0.16mm, respectively, the designed inner diameter of the bearing should be between Φ 80.12mm and Φ 80.16mm. Firstly, we need to make three fake shafts with a diameter spacing of 0.02mm, namely one fake shaft with a diameter spacing of Φ 80.12mm, one fake shaft with a diameter spacing of Φ 80.14mm, and one fake shaft with a diameter spacing of Φ 80.16mm. Then, the fake shafts are sequentially inserted into the bearing. If the fake shaft with a diameter of Φ 80.12mm cannot pass through the bearing, it indicates that the diameter of this bearing is smaller than that of Φ 80.12mm and the bearing clearance is too; If the false shaft with a diameter of Φ 80.16mm can easily pass through and there is still clearance, then if the bearing diameter is larger than Φ 80.16mm, the bearing clearance will be too large and also unqualified; If the false shaft with a diameter of 80.14mm is inserted into the bearing, and the bearing is not loose and can rotate on the false shaft, then the bearing clearance meets the standard.

In order to save materials, multiple fake shafts can also be sequentially made on one shaft to form a stepped shaft, which is similar in shape to the combat weapon of the cold weapon era - whip, called whip shaft. The advantages of this method are simple operation, accurate measurement, and the ability to measure the coaxiality of a single tile in the entire bearing with a dial gauge. The disadvantage is that making fake shafts or whip shafts requires a certain amount of cost. From the above comparison, it can be concluded that the false axis method is an economical and accurate measurement method.

The above is a summary of the experience in repairing tilting pad sliding bearings over the past decade, which is written here for discussion with everyone. In my personal opinion, measuring the clearance of tilting pad sliding bearings is an important task for the maintenance and installation of rotating equipment. Each of the above methods has its own advantages, mainly because the staff should choose the appropriate operation method according to the actual situation and accurately measure it to ensure the quality of equipment installation and maintenance.

2025 December 2nd Week Marginal Product Recommendation:

Material Specification Sheet–MG-6:

Material specification sheet – MG-6 is Ball and roller bearing steel according to EN ISO 683-17. Ball and roller bearing steel for balls and rollers of any dimension,rings and discs up to 30mm effective thickness.