BÀI GIẢNG TRANG TRÍ hệ ĐỘNG lực CHƯƠNG 2(ENGLISH)

Chapter 2 SHAFTING AND ITS COMPONENTSIN THIS CHAPTER WE HAVE FOLLOWING UNIT: UNIT 2.1 ARRANGEMENT OF SHAFTING UNIT 2.2 PROPELLER SHAFT UNIT 2.3 STERN TUBE UNIT 2.4 STERN BEARING UNIT 2.5

Chapter 2 SHAFTING AND ITS COMPONENTS

IN THIS CHAPTER WE HAVE FOLLOWING UNIT:

UNIT 2.1 ARRANGEMENT OF SHAFTING

UNIT 2.2 PROPELLER SHAFT

UNIT 2.3 STERN TUBE

UNIT 2.4 STERN BEARING

UNIT 2.5 STERN TUBE SEALING

UNIT 2.6 REQUIREMENTS FOR COOLING AND LUBRICATING STERN BEARING

UNIT 2.7 INTERMEDIATE SHAFT AND BEARING

UNIT 2.8 THRUST SHAFT AND THRUST BEARING

UNIT 2.1 ARRANGEMENT OF SHAFTING

8- Thrust bearing 9- Double bottom tank

2 Installation principle of the shafting.

There is one or more shaft line depending on kind of ships In almost cargo ships, the shafting has only one propeller and one shaft line is used Normally, a shaft line is placed parallels with the keel of the ship; in some case the shaft line is placed unparallel with the keel It makes with basic line

an angle α, α ≤ 5 o (α- angle is formed by the shaft line and the keel of the ship in vertical section).

In a propulsion plant with two shaft lines, they are normally installed symmetrically and parallel to the vertical keel section of the ship In some cases, they make with the vertical keel section angles β (β- angle is formed

by the shaft line and the ship vertical keel section), β ≤ 3 o If α > 5 o , β > 3 o

then thrust force of propeller will be decreased However, in some special cases α is permitted till 15 o

To reduce cost and total weight of the propulsion plant; to economize

on metal and increase transmission efficiency, the shafting should be shortened.

β

β

β β

3 Position of shaft bearings.

Shaft bearings are usually positioned near bulkhead or keel of the ship where ship's hull structure is strongest Position of the shaft bearings relates to vibration of the shafting.

According to the rule of Russia Register:

Where: D - Diameter of a shaft

L - Distance between shaft bearings.

UNIT 2.2 PROPELLER SHAFT (TAIL SHAFT)

Taper Key

Shaft

Figure 2.2: Structure of the propeller shaft and the propeller boss

UNIT 2.3 STERN TUBE

There are many differences in structure of stern tube depending on individual ship and kinds of stern bearing Its function is to place bearing for supporting of propeller and propeller shaft With heavy load, so its structure must be strong enough to withstand the acting forces At the aft end of stern tube is provided with lock nut to secure stern tube to stern frame The fore end of stern tube is secured to bulkhead by bolts and nuts.

1

2

34

5

67

8

9

10

1112

Figure 2.3: Stern tube

1- Propeller shaft 2- Stern tube

3- Metal bush

4, 5- Stern bearing 6- Stern frame 7- Stern tube nut 8- Retaining ring 9- Gland cover 10- Packing 11- Aft peak bulkhead 12- Water pipe

UNIT 2.4 STERN BEARINGS

Special wood and synthetic rubber bearings are lubricated and cooled

by water while lubricating oil (L.O) is used for white metal bearings.

The propeller shaft is supported by stern bearings There is one or more bearing for each of the propeller shaft depending on the structure of the ship and length of the propeller shaft Stern bearings withstand too heavy working conditions; it is very difficult to inspect and repair (unless on dry dock) So its structure must be strong enough to ensure safe operation of the ship

There are some kinds of materials for making stern bearings such as:

- Special wood (lignum vitae)

- Synthetic rubber

- White metal

1 Special wood bearing (lignum vitae bearing).

a Structure.

The traditional propeller shaft or stern bearing is lubricated by water It consists of a number of lignum vitae staves located in longitudinal grooves in a metal bush Lignum vita is a kind of hard wood with very good wear characteristics and it is compatible with water

The staves with against the grain are used in lower part of the bearing They have a higher longevity than staves with the grain These staves are closely placed and secured by brass plate The length of secured plate is equal to length of the staves and thickness of this plate is about 60% of the staves Two or three brass plates can be used to secure the staves When the bearing is working with water-cooling, the staves will expand boundary and create pressing force to each other

The metal bushes in which the staves are mounted are pressed into cast iron stern tube At the after end of the metal bush is provided with a shoulder and it

is secured by a lock nut on the stern tube Generally, two staves bush are fitted in the stern tube The aftermost bush has a length about 4 times the diameter of the shaft and it is the main bearing unit The forward bush is short and acts mainly as a guide The center (unbushed part) of the stern tube is connected to a seawater service line, which, together with ingress of water between the shaft and aft bush, provides lubrication

To increase longevity of the propeller shaft, the brass sleeves must be fitted

Clearance of fitting: D1 = 1.003D + 1.0 (mm)

Where D1 is inside diameter of the bearing, D is outside diameter of the shaft (including brass sleeve)

1- Propeller shaft 2- Brass sleeve 3-Lignum vitae 4- Metal bush 5- Screw

6- Secured plate

5

1

2 6

Figure: Lignum vitae bearing

b Advantages of lignum vitae bearing.

- This kind of bearing is very suitable for propeller shaft, which has a big diameter and low speed.

- It is safe in operation.

- Absorb vibration of the propeller shaft.

- Maintain clearance between shaft and bearing if optimum cooling and lubricating.

- Longevity is high (about 10 years)

2 Synthetic rubber bearing (Rein forced rubber).

a Structure.

There are some differences in structure of synthetic rubber bearings but basically, the rubber staves are positioned in a metal bush A groove is made between two staves to let water flow in for lubricating The metal bush is fixed to the stern tube by screws (metal bush must not rotate) The same with special wood, brass sleeves must be inserted to propeller shaft in case of rubber bearing The friction coefficient between rubber bearing and brass sleeves in water is about 0.02 ÷ 0.007 depends on kinds and shapes of rubber bearing.

1- Stern tube 3- Rein forced rubber stave 2- Metal bush 4- Brass sleeve 5- Propeller shaft

5

Hard rubber Soft rubber

Figure 2.5: Synthetic rubber bearing

3 White metal bearing.

a Structure

1 2

3 4

5

Figure: White metal bearing

1- Propeller shaft 2- Stern tube 3- White metal 4- White metal liners 5- Oil groove

A typical analysis of white metal is 3% copper, 7.5% antimony the remain is tin The thickness depends on requirement of registry Lloyd’s register recommends the thickness

of 3.8 mm for shaft 300 diameters, up to 7.4 mm for shaft 900 diameters The bearing clearance can be calculated: D1 = 1.001D + 0.5 (mm)

Where: D1 - Inside diameter of the bearing, D - Outside diameter of the shaft.

White metal liner must be fixed to the stern tube otherwise it will be turned together with shaft and be soon damaged The white metal bearing must be lubricated by lubricating oil.

1

2

34

5

67

8

9

1011

12

UNIT 2.5: STERN TUBE SEALING

FUNCTION:

• Its function is to prevent leakage of seawater through, or loss

of oil from, the stern bearings

• Shaft seals are very important during operation of the shafting;

they maintain good condition of the stern bearings and protecting marine pollution.

• Nowadays, there are two common types of shaft seal are used

widely on board ships They are:

* Gland packing

- Aft seal

- Forward seal

1 Gland packing seal type.

structure:

• It consists of simple stuffing boxes filled with packing material; usually rove cotton imbrued

with tallow or graphite as a lubricant In the case of high duty packing the material may be white metal clad

• These packing are tight to the shaft that make the sealing function

• Gland packing can be lubricated by water or lubricating oil

• Gland packing are adjusted by tightening or loosening gland cover (4).

3- Gland packing 4- Gland cover 5- Metal bush

• Advantages:

- Simple and cheap.

• Disadvantages:

- Water always penetrates to the engine room.

- Longevity of the packing is low.

- Force of loosing and tightening must be suitable.

- Gland packing have to assembly onboard the ship…

• Application:

- This kind of shaft seal is only used onboard the small and

the former ship.

2 Simplex shaft seal

•The four sealing rings are numbered by No.1, No.2, No.3, and No.3S from the seawater side Seawater penetration is tightly protected by No.1 and No.2 sealing rings

• No.1 sealing ring, in particular, has an additional function to

protect the inside of the stern tube from extraneous substances

in seawater

• The oil pressure in the chamber between two (No.3 and No.3S)

sealing rings located at forward is usually adjusted to be the same pressure as stern tube pressure, which is 0.2 - 0.3 kg/cm2

higher than sea water pressure Therefore, there is no pressure loaded on No.3S sealing ring on the above conditions Normally, lubricating oil in the stern tube is sealed by No.3 sealing ring.

• However, if much oil leakage from No.3 and No.3S chamber

would be found, No.3S sealing ring could be used to protect the above leakage instead of No.3 sealing ring by the easy valve operation handle inboard.

Propeller boss

No.3 No.3S

Propeller shaft

No 2 No.1

Figure 2.8: Aft simplex seal

1- Cover ring

2- Sealing ring (No.1, 2, 3, 3S)

3- Inter mediate rings

4- Oil inlet

6- Packing 7- Stern tube 8- Stern frame 9- “O” ring

b Forward seal

* The forward seal is of a construction almost similar to the aft seal, except that it is composed of two sealing rings.

* The sealing rings are numbered No.4 and No.5 from the side of stern tube

* No.4 sealing ring seals tight the lubricating oil inside the stern tube while No.5 sealing ring seals tight the lubricating oil in the oil chamber between No.4 and No.5 sealing rings The forward liner is tightened with bolts to the split - type clamp ring mounted to the propeller shaft

Propeller shaft

No.5 No.4

1 2

4 5

6 7 10

UNIT 2.6: REQUIREMENT FOR COOLING AND

LUBRICATING STERN BEARING

Why do we have to lubricate and cool stern bearing?

To lubricate and cool the stern bearings, lubricating oil or water can be used If the bearings are lacked lubricating, dry friction will be created and the shaft and the bearings will be damaged soon.

♣ For the bearings made from white metal, ball bearing,

lubricating oil is used to lubricate.

♣ Lignum vitae, rubber used water for lubricating.

Transfer line

Gravity tank low

Gravity tank high

Stern tube cooling tank

Venting pipe

Three-way cock

T P

Needle valve

Figure 2.10: Stern bearing lubricating oil system

1 Requirements for the bearings lubricated and cooled by water.

♫ Lignum vitae, synthetic rubber bearing uses water for lubricating and cooling Seawater

outside the ship or water pumped from engine room can be used for these purposes.

♫ These kinds of the bearings need enough capacity of water for lubricating and cooling If lack of water, the bearings temperature increases then the bearings and shaft sleeve will be damaged The best temperature for lignum vitae bearing is smaller than 50oC.

♫ For synthetic rubber bearing, when lack of water the friction coefficient of the bearing increases then bearing temperature will be fast increased and both shaft and bearing will

be stuck to each other.

♫ The best water for lubricating and cooling is the pressured water pumped from the engine

room after cleaned by a strainer The flow of pressured water will clean sand and dirt from working surface of bearings when the ship sailing at shallow and dirty water area.

♫ The water lines must be provided with pressure gauges, sight glasses, thermometer to

monitor the lubricating and cooling condition of the bearings Water pressure ≤ 2.5 Kg/cm2, temperature ≥ 20oC

♫ Cooling and lubricating water for the bearings must be supplied before trying the main

engine.

2 Requirements for the bearings lubricated and cooled by lubricating oil.

♫ Oil for lubricating of this type can be supplied by a pump or a gravity

tank After lubricating the bearing, the oil must be cooled by water in a cooler Pressure gauges, sight glasses, thermometer must be provided to monitor the lubricating condition

♫ If the gravity tank is used for lubricating, they must be installed above the

highest water level of the ship Level gauge and low-level alarm must be fixed to this tank.

♫ For this type of the lubricating, the sealing condition is very important if

the after sealing ring damaged, oil may be leaked or seawater may come into lubricating oil, so attention must be paid when operating The best way is to follow instruction of the maker.

UNIT 2.7: INTERMEDIATE SHAFT AND BEARING

☻ Depending on arrangement of engine room, marine propulsion plant may

have intermediate shaft or not If engine room is arranged in midship, the shaft line may have two or more intermediate shaft, but almost ship engine room is placed at the aft of the ship and there is only one intermediate shaft Steel is material to make the intermediate shaft.

♥ - Flanges are arranged at the both ends of the shaft to connect the intermediate shaft to the propeller shaft and the thrust shaft.

♥ - Normally, each intermediate shaft has one bearing Figure 2.12 illustrates

structure of the intermediate bearing Oil is used to lubricate for the bearing White metal is material to make the bearing When operating, attention must be paid to the bearing such as oil temperature, oil level, oil quality, and condition of sealing ring.

UNIT 2.8: THRUST SHAFT AND THRUST BEARING

1.Thrust shaft

The thrust shaft is installed between of crankshaft and intermediate shaft and together with this shaft; it transmits power of the main engine to the propeller Thrust shaft made of forged steel, has one or two collars In medium or high-speed engines, it is installed in the reduction gear, which is located in the after part of the main engine

2 Thrust bearing

Thrust bearing is designed to absorb thrust force from the propeller and transmits it to the hull of the ship There are three kinds of thrust shaft bearing corresponding to the thrust shafts, these are:

a Tapered roller bearing

A tapered roller bearing is normally installed on small ships in a reduction gear This kind of bearing has light weigh, small size and small friction coefficient, but for the big ships it is difficult to inspect, repair and change the roller bearing