Talking about the causes of bearing failure in turbochargers

The turbocharger is an exhaust gas-driven type, which uses the high-temperature and high-pressure exhaust gas discharged from the diesel engine to drive the turbine as power, and compresses the air through the compressor wheel to improve the intake efficiency of the diesel engine and greatly improve the output power of the diesel engine. It adopts axial arrangement, the middle of the volute is water-cooled, and the bearing structure is adopted at both ends of the main shaft. Due to the large axial load, the BS adopts a double-row radial thrust ball bearing at the compressor end, and an aluminum alloy cage is used to reduce the bearing size. Radial and axial shock-absorbing springs are also arranged for radial and axial vibration; the turbine end TS adopts a single-row radial roller bearing and a copper alloy cage; the BS bearing is the main axial force end, and the TS bearing is The support end is only subjected to radial loads.

Damaged BS double-row bearings, the aluminum alloy retainer of one bearing has been completely broken, the other bearing still has a small amount of aluminum alloy retainer, the steel ball is intact, and the inner ring and radial damping spring are partially blue. Oxidized color. Inspection of its radial and axial shock-absorbing springs found that its positioning flange was torn by impact, and its fracture was shear fracture. This is because the supercharger main shaft rotates eccentrically at high speed, and the gap between the moving parts is out of control. The shock-absorbing spring in the total stroke of the BS bearing has not lost its function, and there is a lubricating oil film on the surface of the spring plate. A dismantling inspection of the TS bearing showed that although 8 of the 12 balls were heavily worn, the copper alloy cage was intact. From the more than 200 grams of debris and debris collected in the BS bearing oil cavity, fragments of aluminum alloy cages can be clearly found.

The triangular fragments of the larger BS bearing aluminum alloy cage and the new bearing aluminum alloy cage as random spare parts were cut and two samples were taken for material analysis. Scanning Electron Microscopy (SEM) was used to observe the cage fragments and the new bearing cage samples. The testing instrument was a JXA-840A electron probe microanalyzer made in Japan. The results are as follows.

(1) The material of the bearing cage is Al-Cu-Fe-Ni alloy, which has the characteristics of high strength and heat resistance.

(2) Electron microscope observation shows that there are serious micro-cracks on the surface of the end face of the cage fragment A, and the loose defects of the aluminum alloy can be observed on the edge of the fragment; Under the action of alternating stress, the expansion of micro-cracks on the end face of A will lead to the fatigue fracture of the cage.

(3) The electronic fracture morphology of the cage fragments is a typical dimple, indicating that the material has good plastic toughness, and its final fracture zone is a ductile fracture.

(4) There are also more inclusions and looseness in the new cage material.

The BS bearing bears a large axial alternating load, and there are many inclusions in the aluminum alloy cage material of the bearing, and micro-cracks are formed under the action of alternating stress, and the expansion of micro-cracks eventually leads to the fatigue fracture of the cage; Casting porosity in the material also reduces the fatigue strength of the material. The technical function of the BS oil pump is normal. Analysis of the structural characteristics of the oil pump and the surface condition of the parts shows that the oil pump is not in a state of oil shortage. The fatigue fracture of the aluminum alloy cage caused the failure of the BS bearing, which eventually led to the serious wear of the main shaft of the turbocharger.

Precautions for use of one-way bearings and selection of matching load

Precautions for the use of one-way bearings:

The heavier load uses a larger overwind, and the overwind between the ring and the shaft or housing depends on the size of the load. A lighter load with a smaller overwind will also increase the wear of the one-way bearing, and keep the one-way bearing and its surrounding environment clean. Even the invisible smile dust enters the one-way bearing. vibration and noise.

Strong punching is not allowed, be careful when using the device. It is not allowed to hit the one-way inlet bearing directly with a hammer, and it is not allowed to transmit pressure through the rolling elements.

Use special tools as much as possible, and use suitable and accurate installation tools. Try to avoid the use of things like cloth and short fibers.

When the one-way bearing is directly taken by hand, the one-way bearing is prevented from being corroded. To fully wash the sweat from the hands, and apply high-quality mineral oil before operating, especially in the rainy season and summer, pay special attention to rust prevention.

Load selection for one-way bearing fit:

The level of fit between the outer ring and the seat hole can only be achieved by controlling the tolerance of the journal and the tolerance of the seat hole. The matching between the inner ring of the one-way bearing and the shaft adopts the base hole system, and the inner diameter and outer diameter of the rolling one-way bearing are manufactured according to the standard tolerance of the inner ring and the shaft of the one-way bearing. The cooperation between the outer ring of the one-way bearing and the seat hole adopts a machine shaft system.

It is necessary to know the actual load conditions of the one-way bearing and choose the right fit. Working temperature and other requirements are actually very difficult. Therefore, in most cases, the size of the load is selected according to the use of fine grinding.