JPH0151549B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a spark erosion prevention device for a ship, and more specifically, in a ship that uses a diesel engine as the main propulsion engine, spark erosion occurs due to a potential difference between the propeller shaft, which is the propulsion shaft, and the ship's hull. The present invention relates to a device for preventing.

The spark erosion described above refers to cloudy marks that appear on the sliding surface of the main diesel engine crankshaft, especially on the sliding surface with the main bearing, and roughness on the white metal surface.This phenomenon rarely occurs on ships equipped with a shaft grounding device. The white turbidity corresponds to the crank angle at which the oil film thickness on the main bearing is at its thinnest, and as a result of microscopic observation, what appeared to be melting traces due to electrical discharge was discovered on the white metal surface. It has been determined that spark erosion is caused by a potential difference between the hull (main bearing) and the propeller shaft (crankshaft).
In other words, it is thought that the electrical potential difference between the hull and the propeller causes current to pass through the seawater to the propeller, and when the oil film becomes thinner during one rotation of the crankshaft, it is discharged from the crank journal to the white metal of the main bearing, causing spark erosion. .

By the way, this spark erosion was discovered in bits and pieces in Japan around 1978, but at first it did not have such an impact that it was considered a problem, but recently the main engines have become more powerful and have longer strokes, and the hull paint The spark erosion phenomenon has become more severe due to improvements in propeller performance, larger diameter propellers, lubricant additives, etc., and countermeasures have become necessary.

According to the research results, the hull is negative.
600mV, propeller is -200mV, 400m
It is spark erosion due to the potential difference of V,
On ships equipped with shaft earthing devices up to now,
It has been reported that spark erosion hardly occurs when the propeller shaft-hull potential is 80 mV or less, and it is currently desired to maintain the potential difference to 50 mV or less using a shaft grounding device.

The conventional shaft grounding device described above forms a closed circuit that grounds the propeller shaft and the ship's hull, and uses zinc as a sacrificial anode on the ship's hull side. Specifically, it connects a brush to the rotating crankshaft to ground it. In order to reduce contact resistance and reduce contact resistance, we use silver carbon for the brushes and a silver band for the sliding ring fitted to the propeller shaft, so the contact sliding surfaces must be cleaned at least twice a day. In order to maintain performance, labor-intensive maintenance is required. This is because it has recently been pointed out that spark erosion occurs even on ships equipped with the above-mentioned shaft grounding device.
Additionally, unstable fluctuations were observed in the actual measurement results of contact resistance, confirming the need for frequent maintenance.

On the other hand, as long as the contact resistance is small, the potential difference between the propeller shaft and the hull is kept low, but this causes a large current to flow and the consumption of the zinc increases more than necessary, so the amount of zinc must be significantly increased. It won't happen.

Therefore, there is a contradiction in that while the contact resistance is low, zinc is consumed rapidly, and if maintenance is neglected, spark erosion will occur due to an increase in the contact resistance.

In view of the above, an object of the present invention is to provide a novel spark erosion prevention device that can prevent the occurrence of spark erosion without requiring a large amount of maintenance, and can also reduce the consumption of zinc within a range of low contact resistance. shall be.

In order to achieve such an object, the present invention connects a propeller shaft and a diesel engine crankshaft via an electrically insulating joint in a ship using a diesel engine as a main propulsion engine, and also connects the propeller shaft and the ship's body. A shaft grounding device is interposed therebetween, and a variable resistance is provided between the brush that contacts the propeller shaft of this grounding device and the hull.

An embodiment of the present invention will be described below with reference to the drawings.

In the schematic diagram shown in FIG. 1, 1 is a ship body including a main diesel engine 2, 3 is a propeller, and a propeller shaft 4 and a crankshaft 5 are connected via an electrically insulating joint 6, which will be described later. Further, 7 is a sacrificial anode (zinc), and 8 is a shaft grounding device that connects the propeller shaft 4 and the hull 1 in front of the electrically insulating joint 6.

The electrical insulation joint 6 has a cross-sectional configuration shown in FIG. 2, and a flange plate portion 9 formed at the shaft end of the propeller shaft 4 and a flange plate portion 10 formed at the shaft end of the crankshaft 5 are made of FRP. - They are butted together with an insulating spacer 11 made of epoxy resin or the like sandwiched between them, and a plurality of circumferential parts of both plate parts 9 and 10 are connected by fastening members made of insulating bolts 12, insulating washers 13 and 14, and nuts 15. . This insulating bolt 12 has a threaded portion 1 at its tip as shown in FIG.
An insulating coating layer 16 made of polyphenylene sulfide resin, fluorine resin, etc. is formed on the circumferential surface except for 2a. Electrical conduction between the plate parts 9 and 10 is prevented. The insulating washers 13 and 14 are made of an insulating material such as FRP or epoxy resin, and when the nuts 15 are screwed onto the bolts 12 and both flange plate parts 9 and 10 are tightened,
Bolt head 12b, flange plate 9, nut 15
and the flange plate portion 10 are electrically insulated. Thus, the propeller shaft 4 and the crankshaft 5 are electrically insulated at the joint portion by an insulating spacer 11, an insulating bolt 12, and insulating washers 13 and 14.

As shown in FIG. 4, the shaft grounding device 8 has a sliding ring (silver band) 16 tied to the propeller shaft 4, and a holder 18 for a brush 17 in contact with the sliding ring (silver band) 16.
A ground wire 19 is led from the holder 18 to the hull 1, and a variable resistor 20 is installed in the middle of the ground wire 19, and the resistance value of the variable resistor 20 is set between the sliding ring 16 and the brush 17. For example, when the contact resistance increases, the resistance value of the variable resistor 20 is lowered and the shaft grounding device 8
Constructed to improve the flow of anti-corrosion current to the sides.

In the prevention device configured in this way, the current that attempts to flow from the propeller shaft 4 to the crankshaft 5 due to the potential difference between the propeller shaft 4 and the hull 1 is blocked by the insulating joint 6, and therefore the crankshaft Spark erosion in 5 is prevented. By the way, if the insulation is done by the insulating joint 6, the current will stray and there is a possibility that electrolytic corrosion will occur at a new location.
However, because of the shaft grounding device 8, the current flows through the propeller shaft 4 → sliding ring 16 → brush 17 → ground wire 19 to the hull 1, which prevents the current from straying. 4 corrosion protection was also achieved.

Furthermore, if the contact resistance increases at the contact portion between the sliding ring 16 and the brush 17, the earth current on the hull 1 side will naturally be suppressed, causing wear and tear on the members 16 and 17 as described at the beginning. However, as mentioned above, the variable resistor 2 connected to the ground wire 19
If the resistance value of 0 is lowered, contrary to the increase in contact resistance, the overall resistance value will remain the same or will decrease, allowing the earth current to flow smoothly, and thereby increasing the resistance of members 16 and 17. There is little wear and tear, and even if the maintenance effort required to replace this member is greatly reduced, no problems will occur. Furthermore, due to the presence of the variable resistor 20, there is no need to reduce the contact resistance between the sliding ring 16 and the brush 17 more than necessary, so that consumption of zinc as a sacrificial anode can be prevented.

As can be understood from the above explanation, according to the present invention, since the propeller shaft and the crankshaft are electrically insulated at their joint, there is no flow between them based on the potential difference between the propeller shaft and the hull. This current is cut off at the joint and does not flow to the crankshaft, which prevents electrical discharge from the crank journal to the white metal of the main bearing, or spark erosion. Moreover,
The current that strays due to the electrical insulation described above is guided to the shaft grounding device and flows to the hull, so there is no possibility of galvanic corrosion occurring in new areas, and the variable resistor inserted between the brush hulls prevents the brush portion from being damaged. Since the anti-corrosion current can be controlled by following fluctuations in contact resistance, the amount of zinc used as a sacrificial anode can be reduced, unnecessary wear and damage caused by excessive corrosion protection can be prevented, and the labor required for maintenance can be reduced. This can be significantly reduced.

[Brief explanation of drawings]

The drawings show one embodiment of the present invention, in which Fig. 1 is a schematic diagram of a ship equipped with a spark erosion prevention device, Fig. 2 is a partially cutaway side view of an electrically insulating joint, and Fig. 3 is an insulating FIG. 4, which is a partial sectional view of the bolt, is a schematic diagram of the shaft grounding device. 1...hull, 2...diesel engine, 4...
... propeller shaft, 5 ... crankshaft, 6 ... electrical insulation joint, 8 ... shaft grounding device, 17 ... brush,
20...variable resistor.

Claims (1)

[Claims] 1. In a ship whose main propulsion engine is a diesel engine, the propeller shaft and the diesel engine crankshaft are connected via an electrically insulating joint, and a shaft grounding device is interposed between the propeller shaft and the hull, and this grounding device A spark erosion prevention device for ships, which includes a variable resistance between the brush that contacts the propeller shaft and the ship's hull.