Dear crew members, hello everyone! Today we are going to talk about a part that may not be usually inconspicuous, but is related to the health of the "heart" of the ship - the starter motor and the flywheel ring gear.
Event recap
On the morning of July X, 2024, when the law enforcement officers of the Industrial Port Law Enforcement Brigade of the Wuhan Maritime Safety Bureau conducted a security inspection of the mission ship "B", they tested the main engine of the ship in combination with the special action to prevent the failure of the ship's mechanical and electrical equipment. After inspection, the main engine on the right side of the ship failed to start. When asked about the ship's chief engineer, the chief engineer replied: "This engine has been like this a lot lately, sometimes good and sometimes bad!" Need to try a few more times! ”
Basic Information
Fault profile
1. In the process of starting the right host, it is observed that the pressure in the starting cylinder is 1.5Mpa, and after the adjustment of the pressure reducing valve, the pressure is stabilized to 0.6Mpa, which meets the preset starting pressure requirements.
2. When checking the air filter, confirm that there is no obvious dirt inside, and at the same time, it is found that there is a slight dirty blockage in the gas pipeline, but this situation does not affect the normal start of the main engine.
3. The gas cylinder produces a large amount of oil and water in the process of discharge, however, when checking the operation of the solenoid valve, it is confirmed that it can operate normally, and the function of the solenoid valve is not affected by the preliminary judgment.
4. When starting the main engine, there is an abnormal sound between the driving gear and the flywheel end of the main engine, and after inspection, it is confirmed that there is a small range of cracking in the meshing part of the air starting motor of the main engine and the flywheel end gear, which is the main reason for the instability of the main engine.
What is a starter motor?
At present, there are two main starting modes for medium-speed diesel engines used in the marine field, one is the starting motor mode, and the other is the cylinder head distributor mode, both of which require the external air cylinder to provide 3MPa high-pressure air. For European brand diesel engines, such as Germany's MAN, Finland's Wärtsilä, Japan's Yanmar and domestic diesel engine manufacturers produced by medium-speed engines, the starting mode is the starting motor method, while the Niigata and Daihatsu diesel engines in Japan use the cylinder head distributor method.
How it works
The starting motor has the characteristics of wide application, simple structure, convenient operation, easy maintenance, low cost, etc., and is currently widely used in marine medium-speed diesel engines, and the pneumatic starting motor used in the ship is Yantai Kalent AST825, which is a turbine form of motor, which drives the small gear ring through the piston inside, thereby driving the diesel engine to rotate. Of course, this starting device also includes pressure reducing valves, starting solenoid valves and other equipment. When the starting solenoid valve is opened, the 3MPa high-pressure air supplied by the outside world passes through the pressure reducing valve configured by itself, and the air is reduced to about 1MPa, and the air flows into the gearbox of the starter motor through the bypass pipeline, which drives the pinion to slowly stretch out and engage with the flywheel gear ring, when it is completely meshed, the high-pressure air of the main circuit begins to enter the inside of the starting motor, drives the piston inside, drives the pinion gear through the piston drive the turbine impeller inside, and the pinion drives the meshing flywheel gear ring. Thus helping the diesel engine to start successfully. When the speed of the diesel engine is greater than 150rpm/sec, the solenoid valve is closed, and the pinion is automatically retracted.
The question is, why do they break?
Common causes of failures
reason
1. The correct starting procedure of the diesel engine should be a single start, if the start fails, the second or continuous start is prohibited before the diesel engine has not stopped rotating, and the next start can only be carried out after the diesel engine completely stops rotating, otherwise the pinion or flywheel ring of the starting motor may be damaged.
Due to operator negligence, the most common problem is continuous starting. When the first start fails, due to the tension factor, involuntarily carried out the re-start operation, at this time the diesel engine has not completely stopped rotating, the pinion of the starter motor rotates and stretches out again, and it is more difficult to mesh with the flywheel ring gear that has not stopped rotating, and in the case of this unfavorable factor, it is very easy to cause the flywheel gear ring and the starting motor to be damaged. Due to the softness of the flywheel ring gear compared to the starting motor gear, most of the time the flywheel ring gear is damaged first when it is difficult to mesh.
2. In the case that the starting motor is not loaded and the speed is high, if the continuous rotation is greater than 6 seconds, the internal operation of the motor is reduced due to overtime and high-speed operation, the lubrication condition is reduced, the oil film layer is damaged, and the dry friction is formed to produce high temperature, which may lead to the small piston cylinder of the starting motor due to poor lubrication and wear and other failures. The flywheel ring gear or starter motor continues to operate even though it has been damaged, resulting in a more serious failure of the flywheel ring gear or starter motor.
3. The quality of compressed air quality is also an important factor, such as the air contains moisture, which erodes the starting system for a long time, or the air is not clean, and some fine particles and dust enter the solenoid valve in the starting motor, causing the solenoid valve to fail to close, resulting in the failure of the starting motor.
4. The overall quality of the diesel engine is guaranteed by the standardized processing and assembly of each part. It may be because of a small mistake, it will also affect the overall operation. Therefore, the processing process of parts and components should be guaranteed in strict accordance with the technical requirements, as well as the assembly process, so as to reduce the occurrence of accidents.
The meshing gap is too small: If the motor works for too long and the speed increases due to operation error or starting motor. In this case, there may be no gap or interference between the teeth due to the thermal expansion effect caused by the small mesh gap and high-speed friction, and the starter motor pinion may be damaged when it is squeezed outward in the flywheel ring gear, resulting in failure.
The meshing gap is too large: if the meshing gap is too large, with the increase of frequency, the lubrication effect will become worse, and even dry friction will occur, and the damage to the ring gear will be great. If the hardness of the ring gear is lower than the standard, the gap will be too large, and the scratching damage of the surface of the ring gear will be increased by the active tooth top during the meshing process, and when the gap between them is too large, the gear will be squeezed out, and the operation at this time will lead to serious consequences of damage to both the motor and the ring gear.
Day-to-day management
Due to the high reliability and low failure rate of the pneumatic starting motor, many crew members are very familiar with its use, but they are very unfamiliar with its internal structure and working principle, and they are often in a hurry when there is a problem. Therefore, it is recommended that the wearing parts of the air motor on the ship be equipped with a set of spare, in case of failure, you can rest assured that they can be dismantled and replaced. (Suggested spare parts: starting solenoid valve, axial main starting valve, relevant sealing ring of pre-meshing piston, bearing of transmission mechanism) during daily use, pay attention to the quality of compressed air, try to discharge, keep the air dry. Maintain the proper starting air pressure and adjust the pressure reducing valve if the pressure is found to be too high. Every time you start, pay attention to the sound of the starter motor, and check the abnormality in time to avoid more serious accidents.
Relevant requirements:
Technical Rules for Statutory Survey of Inland River Vessels (2011)
Chapter 4.3.1.1(6): Confirm that the main propulsion unit, including the main propulsion machinery, gear transmission and shafting, as well as the pumps and piping systems serving the main propulsion unit, are maintained and in good working order.
Source: Yangtze River Maritime Release
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