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How to prevent early damage of diesel engine sliding bearing

Creation:HOORAY Source:Hooray Machinery Release Time:2016-11-14 20:09

Abstract:Use on the engine of the sliding bearing is usually divided into two kinds: one kind is a thin-walled bearing bushing type, shape of tiles commonly known as bearing shell; The other is a liner, is also called copper sets, for hollow cylinder shape. Bushin
Use on the engine of the sliding bearing is usually divided into two kinds: one kind is a thin-walled bearing bushing type, shape of tiles commonly known as bearing shell; The other is a liner, is also called copper sets, for hollow cylinder shape. Bushing type is mainly used for thin wall bearing retainer engine crankshaft and connecting rod; Bushing is mainly used for bearing CAM shaft neck and piston pins. This article main narration is bushing type thin wall bearing (bearing).

1, the form of the early damage

Bearing in the process of normal use, due to the gradual wear and tear until the end of the last loss of working ability, its service life, the natural damage is difficult to avoid. But if an engine assembly improper adjustment, lubricating oil quality is bad or use conditions and other factors caused the bearing wear or prematurely appear all sorts of injury, early damage is man-made. Early damage not only greatly reduce the service life of bearing, at the same time also can affect the normal work of the engine. According to the maintenance experience of diesel engine is found for a long time, the common form of early damage of the sliding bearing has a mechanical damage, bearing hole corrosion, pitting corrosion fatigue, corrosion, etc.

(1), the mechanical damage
Sliding bearing mechanical damage refers to bearing alloy surface appear different degree of the trench, serious when in contact with the surface of metal strip and a massive disorderly cut; Under normal circumstances, the contact surface damage and ablation phenomenon exist at the same time. Bearing mechanical damage is the main reason of the difficult to form the oil film bearing surface or oil film were severely damaged.

(2), bearing the cavitation
Sliding bearing in cylinder pressure under the action of repeated impact load), surface plastic deformation and cold work hardening, local loss of deformation ability, gradually formed and expanded, and then with the shedding of wear debris, formed in the surface layer loaded cavity. The cavitation, general bearing shell pits is first appeared, and then gradually expand the pits of the interface crack, and lead to an alloy layer along the interface crack parallel to the direction of extension, until it is peeling off. Sliding bearing is the main reason of the cavitation, due to structural elements such as oil groove and oil hole of the cross sectional sudden change flow caused by strong disturbance, in the vacuum area of the flow disorder form bubbles, then because of the pressure, generate cavitation bubble breaking. Cavitation occurs commonly in high load bearing, such as the crankshaft main bearing on the lower bearing.

(3), fatigue pitting
Bearing fatigue pitting refers to, because the engine to work overtime and make bearing overheating and bearing clearance is too large, central bearing fatigue damage and fatigue pitting or fall off. This kind of damage is mostly to overload, bearing clearance is too large, or lubricating oil is not clean, and mixed with caused by foreign bodies. Therefore, when using, should pay attention to avoid bearing overload work don't too low or too high speed operation; To adjust the engine to idle speed stable state; To ensure the normal bearing clearance, prevent engine speed too high or too low; Check, adjust the performance of the cooling system, to ensure that the engine working at a comfortable temperature.

(4), bearing alloy corrosion
Bearing alloy corrosion is generally area for the lubricating oil is not pure, lubricating oil in the stage of chemical impurities (such as acid oxide) make bearing alloy oxidation and acid generated, cause bearing alloy parts fall off, forms the rule of no small hiatal or small pits. Bearing alloy corrosion is the main reason of the improper selection, bearing lubricating oil material corrosion resistance is poor, or the engine work violent, the temperature too high.

(5), bearing burning fuse
Between journal and bearing friction pair have tiny bumps on metal surface, direct contact form local high temperature, in the case of insufficient lubrication, cooling, make or local burning-out bearing alloy were black. This failure is often caused by journal and bearing with tight; Insufficient pressure lubricating oil is easy to make the bearings burned.

(6), cylindrical bearings
Just go bearing cylindrical bearing hole with relative rotation here. Cylindrical bearing go after, not only affect the heat dissipation of bearing, easy to make alloy bearing inner surface ablation, but also can make the bearings on the back of the injury, serious when burning bearing. The main reason is that the bearing are too short, tenon damage, processing or installation does not conform to the specifications, etc.

2, the preventive measures,

Sliding bearing early damage is more common than bearing burning, so to prevent sliding bearing early damage is very important. The correct maintenance of the sliding bearing is an effective way to reduce early bearing damage, is also the reliable guarantee for extend bearing life. Therefore, in the daily maintenance and repair of the engine, must pay attention to the bearing surface of the alloy, the back end and the appearance of edge angles in shape, if there is any abnormal or half signs of wear and tear, to seriously investigate the cause, and take appropriate measures to improve the bearing of the working conditions, pay much attention to the prevention of early damage of the sliding bearing.

(1), improve the bearing design and manufacturing process
Design or choose bearing, want to consider the heat balance to control the temperature rise of bearing. Because work bearing under friction condition, caused by oil liquid internal friction (viscosity), power consumption is converted into heat caused by temperature rise, change, lubricating oil viscosity reduction, clearance will soften the babbitt bearing, serious when produce tile burning accident holding shaft. On structure design, therefore, should from the bearing bush (non load-bearing area) at the top of the oil hole in, make the lubricating oil from the bearing area introduction; Within the bearing surface of the oil hole centered along the longitudinal or transverse groove, conducive to uniform distribution of lubricating oil on the shaft neck to control the temperature.
According to the requirements of the bearing working condition, bearing materials must have the following properties: small friction coefficient; Good thermal conductivity, thermal expansion coefficient; Wear-resisting, corrosion resistance and bonding ability; To have enough mechanical strength and plasticity. Therefore, optional babbitt bearing materials. Babbitt can work well in stable load, but under the unsteady load easily happened cavitation, so should not be used in high power engine. High tin lead alloy and low tin lead alloy with high strength and hardness, fatigue resistance and cavitation resistance is stronger, it is better to use in the high power engine. Appeared in recent years, foreign by physical vapor deposition coating method in copper lead bearing surface nickel plating on the grid containing 20% sn or pure tin plating of aluminum alloy, the effect is very good. In addition, the entire round groove bearings instead of semicircle groove or part of the oil groove bearings, such not only can improve the engine sliding bearing lubrication state, but also improve its carrying capacity.

(2), improve the quality of bearing maintenance and assembly
Improve the quality of bearing hinge distribution, to ensure smooth and no spots on the back of the bearing, positioning bumps intact; Amount of bounce off its 0.5 1.5 mm, this guarantees that after assembly bearing with the aid of its elasticity and bearing hole joint closely; In bearing in the upper and lower two pieces of each end bearing shall be higher than that of bearing seat plane 30-501 microns, the higher quantity can ensure torque tighten bearing cap bolts by the regulation after the bearing and the bearing seat close coordination, generate enough force of friction self-locking, bearing is not loose, good heat dissipation effect, prevent bearing ablation and wear; Bearing of the working face can't scrape contact pattern match method reached 75% - 75% for measure, should be not scraping makes fitting clearance of bearing and shaft neck up to par.
In addition, to pay attention to check the crankshaft journal and bearing assembly processing quality, the strict repair technology standard, prevent the installation is not straight caused by improper loading method and uneven bearing bolt torque or do not conform to the regulations, resulting in a bending deformation and the stress concentration, lead to early damage of the bearing.

(3), reasonable selection and filling lubricating oil
In use process want to choose the lubricating oil, the oil film surface tension small, make the formation of air bubbles breaking the corresponding impact of oil flow is reduced, the bearing can effectively prevent cavitation; Lubricating oil viscosity grade, not increased at lest increase bearing coking tendency; Engine oil level of lubricating oil must be within the scope of the standard, lubricating oil and gas with tools must be clean and prevent the entry of any dirt and water, at the same time ensure that the sealing effect of the various parts of the engine. Pay attention to the regular inspection and replacement lubricating oil; Place for filling lubricating oil should be no pollution, no dust, prevent the intrusion of all pollutants; Different quality, different levels and different types of viscosity lubricating oil mixture, lubricating oil filling the settling time before the general should not be less than 48 h.

(4), proper use and maintenance of the engine
When installing bearings, should be in the movement of shaft and bearing surface coated with grades clean engine oil. After refitted engine bearing, before starting the first should be shut off fuel switch, with the starter to drive the motor ticking over several times, when the engine oil pressure gauge, open the fuel to switch after I have a show, and the gas in low speed, start the engine running. Idle running time is not more than 5 min. Be new and overhaul engine break-in period, after the ban surge vastly decrease in load for a long time period and high speeds; End of the engine full load for a long time after work, can't stop immediately, must let the engine to idle after 15 min in a low speed to stop, or internal heat is not to go out.

Strengthen the oil filter, crankcase ventilation equipment cleaning and maintenance work, according to the specifications timely replacement filter; Guarantee the normal work of the engine cooling system, control the engine to normal temperature, prevent the radiator boiled, prohibit driving without cooling water; Correct use fuel, accurately adjust with gas phase and the ignition timing and so on, to prevent abnormal combustion engines; To have the condition of crankshaft and bearing technology inspection and adjustment work.

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