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

Chapter 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 Arrangement of the single shafting 1- E/R bulkhead 2- Stern tube 3- Water tank 4- Propeller shaft 5- Intermediate shaft M/E 6- Intermediate bearing 7- Thrust shaft 8- Thrust bearing 9- Double bottom tank 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 ≤ 5o (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 ≤ 3o If α > 5o, β > 3o then thrust force of propeller will be decreased However, in some special cases α is permitted till 15o To reduce cost and total weight of the propulsion plant; to economize on metal and increase transmission efficiency, the shafting should be shortened α β β β β 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: 12D < L < 22D Where: D - Diameter of a shaft L - Distance between shaft bearings If D < 100 mm, L is calculated: Lmax = 91 D UNIT 2.2 PROPELLER SHAFT (TAIL SHAFT) Key Taper Shaft Figure 2.2: Structure of the propeller shaft and the propeller boss UNIT 2.6: REQUIREMENT FOR COOLING AND LUBRICATING STERN BEARING Why 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 Gravity tank high Venting pipe Stern tube cooling tank Gravity tank low T P Three-way cock Needle valve Transfer line Figure 2.10: Stern bearing lubricating oil system 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 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 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 b Thrust bearing (with multi- collars thrust shaft): ♪ This is a traditional type used in the past such as old steam ship Because one collar could not withstand heavy thrush force from the propeller so two, three or more collars are provided to transmit thrush force to bearings, which are fixed tightly to hull of the ship Because big size in structure and difficulty in repairing so it is rarely used nowadays c Thrust bearing (with one collar thrust shaft) ♪ Due to dimension of the thrust with many collars is so large, so the change in design of thrust bearing was developed with one collar thrust bearing Its structure is shown in the Figure 2.11 When shaft rotating, between surface of the collar and surface of the pad creates an oil wedge Because of that, the oil firm is always maintained between two surfaces and this kind of bearing can withstand heavy thrush force ♪ When shaft working, L.O temperature is increased To maintain the temperature in the bearing case lower 70o C, a L.O cooler must be fitted Besides that, a heater also is installed to reduce viscosity of L.O in cold weather Effect of a worn-out thrust bearing ♣ Misalignment of the thrust shaft system, a too small space between the collar and its bearing or a shortage of oil in the quantity may result in heating up and wearing out With a worn-out thrust bearing, the crankshaft will be approached forward in ahead turning and afterward in astern turning, thus cause the following problems: ♣ - Heat will be produced by friction between webs and the crank pin metals or the side face of the main bearings ♣ - Slant movements of the piston will increase wears of the piston and the cylinder liner in fore and aft direction The misalignment of the connecting rod will increase the temperature of the piston pin and crank pin metal FINISH CHAPTER QUESTION 1: Please write about the distinctions of gland packing and simplex shaft seal? QUESTION 2: Please write about the differences between three kinds of stern bearing?