Piston forming the lower part of the combustion chamber: The diesel engine is a type of internal combustion engine which ignites the fuel by injecting it into hot, high-pressure air in a combustion chamber. In common with all internal combustion engines the diesel engine operates with a fixed sequence of events, which may be achieved either in four strokes or two, a stroke being the travel of the piston between its extreme points. Each stroke is accomplished in half a revolution of the crankshaft.
Piston forms the lower part of the combustion chamber. It seals the cylinder and transmits the gas pressure to the connecting rod. The piston absorbs heat of combustion and this heat must be conducted away if the metal temperature is to kept in safe limits. The Piston comprises of two pieces; the crown and the skirt.
The crown is subject to the high temperatures in the combustion space and the surface is liable to be eroded/burnt away. For this reason the material from which the crown is made must be able to maintain its strength and resist corrosion at high temperatures.
The crown is subject to the high temperatures in the combustion space and the surface is liable to be eroded/burnt away. For this reason the material from which the crown is made must be able to maintain its strength and resist corrosion at high temperatures.
Steel, alloyed with chromium and molybdenum is used, and some pistons have a special alloy welded onto the hottest part of the crown to try and reduce the erosion caused by the burning fuel. The crown also carries the 4 or 5 piston ring grooves which may be chrome plated.
The cast iron skirt acts as a guide within the cylinder liner. It is only a short skirt on engines with an exhaust valve (known as uniflow scavenged engines), as unlike a trunk piston engine, no side thrust is transmitted to the liner (that’s the job of the crosshead guides).
The stresses to which a piston is subjected to are as follows:
(mechanical & thermal stresses) Compressive and tensile stress caused by bending action due to gas pressure Inertia effect – movement up and downwards
Thermal stresses – rapid temperature change
The crown of a piston is subjected to a very high gas pressure which will subject the top surface of the crown to compressive loading and the lower surface of crown will be under tensile loading. The piston crown will be like a uniformly loaded beam
As the piston moving upward, towards the end of its stroke its velocity will be reducing.The inertia effect will tend to cause the piston to bow upwards, so that the surface of the crown along with sides will be under tensile loading and lower surface of the crown will be under compressive loading When the piston is retarded on its approach downwards to BDC, the inertia effect will be reversed
The thermal stresses set up in a piston are caused by the different temperature across a section.The free expansion of the hot side is restricted by the cooler surface of the piston. Maximum safe temperature at the three most critical zones for alluminium-alloy piston are Crown 370 degree to 400 degree C. Top ring groove and gudgeon pin bosses 200 degree to 220 degree C.
Mechanical and thermal stresses should be considered to gather as they tend to be complimentary to each other. Top and sometimes 2nd ring grooves is tapered up to 2 times normal axial clearance thus:
i) Clearance allows for carbon deposit
Clearance avoids piston crown edge touching liner due to thermal stress
If the crown temperature exceeds 400 degreeC, failure will probably occur from cracking. If the top ring groove temperature exceeds 220 degreeC, for any length of time, trouble may be expected from: i)Stuck piston rings ii) Formation of carbon at the bottom of the ring groove, causing the ring to be packed out
Cracking of crown – due to thermal and mechanical stresses. Cracking through piston wall especially in way of top ring groove – due to fluctuating gas load, excessive thermal stresses. Crack starts from inside wall. Cracking may take place due to the following reasons apart from the reasons mention above:
i) Unsuitable material for the rating of the engine or inadequate machining ii) Excessive scaling on the cooling side, cavitaion erosion iii) High coolant temperature iv) Local impingement v) Poor atomization, high penetration of fuel vi) High water content in fuel
Cooling of ships engine – how it works , requirement of fresh water & sea water cooling system
Cooling of engines is achieved by circulating a cooling liquid around internal passages within the engine. The cooling liquid is thus heated up and is in turn cooled by a sea water circulated cooler. Without adequate cooling certain parts of the engine which are exposed to very high temperatures, as a result of burning fuel, would soon fail.
Cooling enables the engine metals to retain their mechanical properties. The usual coolant used is fresh water: sea water is not used directly as a coolant because of its corrosive action. Lubricating oil is sometimes used for piston cooling since leaks into the crankcase would not cause problems. As a result of its lower specific heat however about twice the quantity of oil compared to water would be required.
Water carried in pipes is used to cool machinery. The main engine is cooled by two separate but linked systems: an open system (sea-to-sea) in which water is taken from and returned to the sea (seawater cooling), and a closed system where freshwater is circulated around an engine casing (freshwater cooling).
Freshwater is used to cool machinery directly, whereas seawater is used to cool freshwater passing through a heat exchanger. The particular feature of an engine cooling system is continuous fluid flow. Fluid in motion causes abrasive corrosion and erosion. To reduce the effects of turbulent flows, seawater systems incorporate large diameter mild steel pipes, the ends of which open to the sea through sea chests where gate valves are fitted.
If a seawater cooling pipe bursts, both suction and discharge valves will have to be closed to prevent engine room flooding. In order to make sure the valves operate correctly when you need them to, open and close them at regular, say monthly, intervals. Seawater pipes are usually mild steel, but galvanised steel, copper or copper alloy are also used. Freshwater cooling pipes are generally made of mild steel.
Fresh water cooling system
A water cooling system for a slow-speed diesel engine is shown in Figure . It is divided into two separate systems: one for cooling the cylinder jackets, cylinder heads and turbo-blowers; the other for piston cooling.
The cylinder jacket cooling water after leaving the engine passes to a sea-water-circulated cooler and then into the jacket-water circulating pumps. It is then pumped around the cylinder jackets, cylinder heads and turbo-blowers. A header tank allows for expansion and water make-up in the system. Vents are led from the engine to the header tank for the release of air from the cooling water. A heater in the circuit facilitates warming of the engine prior to starting by circulating hot water.
The piston cooling system employs similar components, except that a drain tank is used instead of a header tank and the vents are then led to high points in the machinery space. A separate piston cooling system is used to limit any contamination from piston cooling glands to the piston cooling system only.
Sea water cooling system
The various cooling liquids which circulate the engine are themselves cooled by sea water. The usual arrangement uses individual coolers for lubricating oil, jacket water, and the piston cooling system, each cooler being circulated by sea water. Some modern ships use what is known as a ‘central cooling system’ with only one large sea-water-circulated cooler. This cools a supply of fresh water, which then circulates to the other Individual coolers. With less equipment in contact with sea water the corrosion problems are much reduced in this system.
A water cooling system for a slow-speed diesel engine is shown in Figure . It is divided into two separate systems: one for cooling the cylinder jackets, cylinder heads and turbo-blowers; the other for piston cooling.
The cylinder jacket cooling water after leaving the engine passes to a sea-water-circulated cooler and then into the jacket-water circulating pumps. It is then pumped around the cylinder jackets, cylinder heads and turbo-blowers. A header tank allows for expansion and water make-up in the system. Vents are led from the engine to the header tank for the release of air from the cooling water. A heater in the circuit facilitates warming of the engine prior to starting by circulating hot water.
The piston cooling system employs similar components, except that a drain tank is used instead of a header tank and the vents are then led to high points in the machinery space. A separate piston cooling system is used to limit any contamination from piston cooling glands to the piston cooling system only.
Sea water cooling system
The various cooling liquids which circulate the engine are themselves cooled by sea water. The usual arrangement uses individual coolers for lubricating oil, jacket water, and the piston cooling system, each cooler being circulated by sea water. Some modern ships use what is known as a ‘central cooling system’ with only one large sea-water-circulated cooler. This cools a supply of fresh water, which then circulates to the other Individual coolers. With less equipment in contact with sea water the corrosion problems are much reduced in this system.
A sea water cooling system is shown in Figure . From the sea suction one of a pair of sea-water circulating pumps provides sea water which circulates the lubricating oil cooler, the jacket water cooler and the piston water cooler before discharging overboard. Another branch of the sea water main provides sea water to directly cool the charge air (for a direct-drive two-stroke diesel).
The upper sea suction valve is used while in port to prevent any mud or sand entering the cooling system. Its also used while sailing in shallow waters. The lower sea suction valve is used when sailing in deep water to avoid air entering the cooling system while the ship is rolling or pitching.
Central cooling system
In a central cooling system the sea water circuit is made up of high and low suctions, usually on either side of the machinery space, suction strainers and several sea water pumps. The sea water is circulated through the central coolers and then discharged overboard.
A low-temperature and high-temperature circuit exist in the fresh water system. The fresh water in the high-temperature circuit circulates the main engine and may, if required, be used as a heating medium for an evaporator. The low-temperature circuit circulates the main engine air coolers, the lubricating oil coolers and all other heat exchangers. A regulating valve controls the mixing of water between the high-temperature and low-temperature circuits. A temperature sensor provides a signal
The advantages of a central cooling system are;
Less maintenance, due to fresh water system having cleaned treated water
fewer salt water pumps with attendant corrosion and fowling problems
simplified and easier cleaning of coolers higher water speeds possible with a fresh water system,
resulting in reduced pipe dimensions and installation costs
the number of valves made of expensive material is greatly reduced, also cheaper materials can be used throughout the system
constant level of temperature is maintained, irrelevant of seawater temperature, also no cold startings, reduced cylinder liner wear, etc.
การขึ้นภาษีนำเข้าสินค้าจากประเทศจีนสู้ประเทศสหรัฐอเมริกานั้นทำให้ผู้ประกอบการที่ต้องพึ่งพิงการผลิตที่มีต้นทุนถูก เช่น iPhone จาก Apple Inc. เริ่มกระจายความเสี่ยงและให้ความสนใจในการลงทุนในกลุ่มประเทศเอเชียตะวันออกเฉียงใต้ด้าน Capacitors แผงวงจร Hard-Drive และชุด Bluetooth Headset
Starrag UK ได้เพิ่มจำนวนเครื่องจักรในแหล่งผลิตของพวกเขาที่สวน Advanced Manufacturing Park ด้วยเครื่องกลึง CNC แนวเส้นตรง ซีรี่ย์ Bumotec s191 แบบ 7 แกน โดยถูกติดตั้งที่ AMRC ด้วยเครื่อง Boeing Center
Dr. David Curtis ผู้ร่วมงานทางเทคนิคที่ AMRC ด้วยระบบ Boeing Center อธิบายว่า “Bumotec s191 ให้โอกาสพวกเราในการพัฒนาการปฏิวัติกระบวนการแมชชีนนิ่งสำหรับวัสดุ และภาคส่วนต่างๆ ใหม่ ในตอนนี้พวกเรากำลังมองไปที่โครงงานในอนาคตที่พวกเราสามารถนำอุปกรณ์ชิ้นเล็กๆ ที่มีความซับซ้อน และพัฒนาโซลูชั่นประหยัดต้นทุน และประสิทธิภาพที่เพิ่มมูลค่าแก่อุตสาหกรรมของสหราชอาณาจักร”
MM INFOStarrag Group คือ ผู้จัดหาเทคโนโลยีเครื่องแมชชีนที่มีความแม่นยำสูงระดับโลกสำหรับงานกัด กลึง เจาะและเจียรชิ้นงานที่เป็นวัสดุโลหะ คอมโพสิตและเซรามิก
EXECUTIVE SUMMARY
Starrag UK has expanded the number of machines it has in-situ at the Advanced Manufacturing Park with a seven-axis Bumotec s191 linear CNC turn-mill centre being installed at the AMRC with Boeing Centre.
According to Starrag, the Swiss-built machine has linear drives and high-level thermal stabilisation that achieves machining accuracies of 2.5 microns in the six-sided single set-up machining of even the most complex workpieces within the X, Y and Z axes capacity range of 400 mm, 200 mm and 410 mm, respectively.
Dr David Curtis, Technical Fellow at the AMRC with Boeing Centre, explains: “The Bumotec s191 gives us opportunities to develop revolutionary new machining processes in any material and for any sector. We are now looking for projects where we can take small, complex components and develop optimised, cost-saving solutions that add value to UK industry.”
MFM engineering Main engine and generator engine maintenance service, boiler cleaning and survey ,pump and compressor repairing, heat exchanger cleaning ,hydraulic system repairing , tank cleaning ,other machinery on vessel
แต่สิ่งสำคัญในการบริหารงานบำรุงรักษา คือ การสร้างสมดุลระหว่างค่าใช้จ่ายบำรุงรักษากับผลตอบแทนเพื่อไม่ให้เกิดการลงทุนที่เกินความจำเป็น ดังนั้น การเพิ่มสมรรถนะเครื่องจักรและลดค่าใช้จ่ายบำรุงรักษาเป็นประเด็นหลักของระบบสารสนเทศ ซึ่งประสิทธิผลจะเกิดขึ้นก็ต่อเมื่อระบบสารสนเทศงานบำรุงรักษาสามารถยืดช่วงเวลาเฉลี่ยการเกิดความเสียหายหรือ MTBF และสามารถลดเวลาเฉลี่ยการซ่อมแซม (Mean Time To Repair) หรือ MTTR โดยทั้ง MTBF และ MTTR เป็นปัจจัยชี้วัดประสิทธิผลการสร้างความน่าเชื่อถือและความพร้อมระบบ (Availability)
EXECUTIVE SUMMARY
Proactive maintenance is a method that focus on preventive maintenance and predictive maintenance to take an action before the system failed or broke. Not only prevent routine problem, the method will analyze the major problem with systematic to take action and prevent the same problem to be occurred recently. This method created reliability for the manufacturing system but it will be effective when the organization applied lean and TPM continuously, and also assign every member to cooperation in the identification of waste’s activity
One of the Total Productive Maintenance Goals for production line development is the Zero Breakdown.
If installed air-conditioning system can be well maintenance, the goal of TPM for Zero Breakdown will definitely be achieved, which shall allow efficient operation for the production line of the factory, and save energy very well. In addition, new installed cooling system or recent repaired one should undergo the running test, and fix all defects before the prior normal operation, while during the daily normal operation of the cooler, some operating checks must be carried on as follows
Temperature of coolant or cooling air.
Temperature of cooler’s components, cylinder block, and cylinder of compressor, condenser and bearing.
Sound of operation and vibration.
Electrical pressure, and electrical current of cooler, cool water making tower, water pump, etc.
Pressure and temperature of lubricant in compressor.
Pressure and temperature of refrigerant flowing in cooling making cycle.
Designated temperature for opening expansion valve.
