Methods to Prevent Early Damage of Diesel Generator Bearing

The sliding bearings used in diesel genset are usually divided into two types: one is the lining thin wall bearing, which is commonly known as the bearing bush in the form of tiles; The other is bushing, also known as copper sleeve, which is hollow cylinder. The lining thin wall bearing is mainly used to support the crankshaft and connecting rod of the engine; Bushing is mainly used to support camshaft journal and piston pin. During the normal use of the bearing, it is difficult to avoid such natural damage due to gradual wear until it loses its working capacity and ends its service life. Early damage of sliding bearing is much more common than bearing burning, so it is important to prevent early damage of sliding bearing. So what methods can effectively prevent the early damage of diesel generator set bearings?

1. Improve the design and manufacturing process of bearings

When designing or selecting bearings, the thermal balance of bearings shall be considered to control the temperature rise.

Because the bearing works under the friction state, the success consumption is caused by the internal friction (viscosity) of the lubricating oil liquid, which is converted into heat and causes the bearing temperature rise, the viscosity of the lubricating oil decreases, and the clearance changes, which will soften the babbitt alloy of the bearing, and even cause the bearing burning and shaft holding accident in serious cases.

Therefore, in the structural design, the oil inlet hole should be opened from the top of the upper bearing pad (non load bearing area) of the bearing, so that the lubricating oil can be introduced from the non load bearing area. The inner surface of the bearing pad is provided with oil grooves along the longitudinal or transverse direction with the oil inlet hole as the center, which is conducive to the uniform distribution of lubricating oil on the journal to control the temperature rise.

According to the working conditions of the bearing, the bearing materials must have the following properties: small friction coefficient; Good thermal conductivity, small thermal expansion coefficient; Strong wear resistance, corrosion resistance and adhesive resistance; It shall have sufficient mechanical strength and plasticity. Therefore, babbitt can be selected as the bearing pad material. Babbitt alloy can work well under stable load, but it is easy to cavitate under unstable load, so it should not be used in high-power engine.

The high tin lead base alloy and low tin lead base alloy have higher strength and hardness, stronger anti fatigue and anti cavitation ability, and have better application effect in high-power engines.

In recent years, aluminum alloy containing 20% tin or pure tin was coated on the nickel grid on the surface of copper lead bearing by the splash plating method of physical vapor deposition in foreign countries, with good results. In addition, the whole round oil groove bearing bush is changed into semicircular oil groove or partial oil groove bearing bush, which can not only improve the lubrication state of the engine sliding bearing, but also improve its bearing capacity.

2. Improve the maintenance and assembly quality of bearings

Improve the hinge fitting quality of the bearing, ensure that the back of the bearing is smooth and spotless, and the locating bump is intact; The self spring opening is 0.5-1.5 mm, which can ensure that the bearing bush fits closely with the bearing seat hole with its own elasticity after assembly; Each end of the upper and lower bearing pads installed in the bearing pedestal shall be 30-501 higher than the plane of the bearing pedestal μ m. The height can ensure that the bearing and the bearing seat are closely matched after the bolts of the bearing cover are tightened according to the specified torque, generating sufficient friction self-locking force, preventing the bearing from loosening, with good heat dissipation effect, and preventing bearing ablation and wear; The working surface of the bearing cannot be measured by the scraping method to reach 75% - 85% of the contact mark. The fitting clearance between the bearing and the journal shall meet the requirements when the bearing is not scraped.

In addition, the processing quality of crankshaft journal and bearing shall be checked during assembly, and the repair process specification shall be strictly implemented to prevent incorrect installation and uneven torque or inconformity of bearing bolts due to improper installation method, which will lead to bending deformation and stress concentration, leading to early damage of bearing.

3. Select and fill lubricating oil reasonably

The lubricating oil with low oil film surface tension shall be selected during use to reduce the impact of oil flow when bubbles collapse, which can effectively prevent bearing cavitation; The viscosity grade of lubricating oil shall not be increased at will to avoid increasing the coking tendency of bearing; The lubricating oil level of the engine must be within the standard range, and the lubricating oil and refueling tools must be clean to prevent any dirt and water from entering, while ensuring the sealing effect of all parts of the engine. Check and replace lubricating oil regularly; The place where lubricating oil is injected shall be free from pollution and sandstorm to prevent the invasion of all pollutants; It is prohibited to mix lubricating oils of different quality, viscosity grades and types of use. The settling time of lubricating oil before filling shall not be less than 48h.

4. Use and maintain the engine correctly

When installing the bearing, the moving surface of the shaft and bearing shall be coated with clean oil of the specified brand. After the engine bearing is reassembled, the fuel switch shall be turned off before the initial start, and the starter shall be used to drive the engine to idle for several times. When the engine oil pressure gauge shows, the fuel switch shall be turned on and turned on, and the accelerator shall be set to the medium and low speed position, and the engine shall be started for operation observation. The idling time shall not exceed 5min. Do a good job in running in of the new engine and the engine after overhaul. During the running in period, it is prohibited to work under the condition of rapid load increase and decrease and high speed for a long time; After the engine has been working at full load for a long time, it cannot be stopped immediately. The engine must be allowed to run at medium low speed with no load for 15 minutes before it can be stopped. Otherwise, the internal heat cannot be dissipated.

The above are some methods that Dingbo Power has arranged for you to effectively prevent the early damage of diesel generator set bearings. It is the most effective way to timely check and adjust the technical conditions of crankshaft and bearings. If you have any other question, please contact us by email dingbo@dieselgeneratortech.com.