1、 1 专业外文翻译材料原文 Engines Cylinder Block The cylinder block is the largest past of the engine.Its upper section carries the cylinders and pistons.Normally,the lower section forms the crankcase,and supports the crankshaft.It can be cast in one piece from grey iron.Or it can be alloyed with other metals l
2、ike nickel or chromium. The iron casting process begins by making up the shapes of what will become water jackets and cylinders as sand cores which are fitted into moulds.The stops there parts becoming solid iron during casting.Molten iron is poured into sand moulds that are formed by patterns in th
3、e shape of the block. After casting,core sand is removed through holes in the sides and ends,leaving spaces for the cooling and lubricant passages.There holes are sealed with plugs.The casting is then machined.Cylinders are bored and finished,surfaces smoothed,holes drilled and threads cut.All cylin
4、der blocks are made with ribs,web and fillets to provide rigidity but also keep weight to a minimum. Cylinder Block Construction As more manufacturers try to make vehicles lighter and more fuel efficient,more and more engine blocks are being cast from aluminium.A block made of aluminium alloy is lig
5、hter than if it were made of cast iron.So if two engines are generating the same power,the alloy version would have a better weight-to-power ratio than the cast alloy version.Aluminium alloy blocks are made by various casting processes,including pressure casting.Another method is gravity casting,whe
6、re the molten metal is poured into molds. Cast iron liners are usually used in the cylinders of aluminium blocks,and sometimes in cast-iron blocks.Some sleeves are cast into the block.Grooves on the outside form a key that stops any movement in the cylinder.They also increase surface area to assist
7、heat transfer from the sleeve to the block. Some blocks dont need liners.They can be made of wear resistant material that makes a hard-wearing surface for the pistons and piston rings.Or the cylinder bore may have some sort of surface treatment to make it hard-wearing. When the cylinders,block and c
8、rankcase are all cast together,it is called a monoblock construction.A horizontally-opposed block has a split crankcase.The two 2 engine blocks are joined together by the flanges of the crankcase. In air-cooled engines,the cylinders are usually made as separate parts,then bolted to the same crankcas
9、e.Each cylinder has cooling fins.Theyre often machined to give uniform thickness and allow free flow of air. Pistons The piston,with its connecting rod and bearing,transfers the force of the combustion and expansion of the power stroke to the crankshaft.The piston itself,its rings,and the piston pin
10、,also known as the gudgeon pin,are together called the piston assembly.The cutaway shape on this piston allows it to clear the counterweights on this rotating crankshaft. The connecting rod connects the piston to crankshaft. It is fastened to the piston at its little end,by a piston or gudgeon pin.T
11、he big end of the connecting rod has a detachable cap,and carries 2 halves of the big end bearing.The big end is attached to the crankshaft at the crankpin journal. Cylinder Sleeves Cylinder sleeves are used in engine blocks to provide a hard-wearing material for pistons and piston rings. The block
12、can be made of one kind of iron thats light and easy to cast,while the sleeve uses another kind that is better able to stand up to wear and tear. There are three main types of sleeves-dry,flanged dry,and wet. The dry sleeve can be cast in or pressed into a new block, or used to recondition badly-wor
13、n or damaged cylinders that cant easily be re-bored.Its a pressed fit in its bore in the cylinder blocks.Its wall is about 2mm thick.Its outer surface is in contact with the block for its full length.Its top finishes flush with the top of the block and can hardly be seen.Once in place,dry sleeves be
14、come a permanent part of the cylinder block. A flanged,dry sleeve is like a normal dry sleeve,but a flange at the top fits into a recess in the surface of the engine block.Its not a tight fit and it can be replaced if its worn. With a wet sleeve,the outer surface is part of the waterjacket around th
15、e cylinder.Its called wet because it has coolant against its outer surface.This helps speed up heat transfer between the sleeve and coolant.The sleeve is sealed at the top to prevent coolant leaks.This stops coolant entering the combustion chamber,and the bottom of the crankcase.A flange at the top
16、of the sleeve fits into a recess in the block.The lower end has 1 or 2 neoprene sealing rings. 3 With coolant in direct contact with the cylinder sleeve,corrosion can be a problem.It can even insulate the sleeve from the coolant,which reduces the main advantage of having a wet sleeve at all. The wal
17、ls on wet sleeves are thicker than on dry sleeves.They dont have the same support from the block as dry sleeves so they depend on their wall thickness to stop distortion. In diesel engines,vibration caused by combustion can cause cavitation.This damage appears similar to corrosion and it can eventua
18、lly destroy the cylinder. Grey Iron Grey iron is a form of cast iron.There are many different kinds of cast iron,depending on the particular materials they contain.Grey iron is a cast iron that contains carbon in the form of graphite,plus silicon,manganese and phosphorus.The fractured surface of a c
19、ast iron with graphite appears grey,hence the name.It is brittle and cannot absorb shocks.It resists heat and corrosion,and can be cast into many different shapes.It is used for many components. Cylinder Head The cylinder head bolts onto the top of the cylinder block where it forms the top of the co
20、mbustion chamber.In-line engines of light vehicles have just one cylinder head for all the cylinders.Larger in-line engines can have two or more.V-type and horizontally- opposed engines have a separate cylinder head for each bank of cylinders. Just as with engine blocks,cylinders heads can be made o
21、f cast of cast iron,or aluminium alloy.A head made of aluminium alloy is lighter than if it were made of cast iron. Aluminium also conducts heat away more quickly than iron.So with an aluminium-alloy head, the heat of combustion can be conducted away into the coolant more quickly . Manufacturing the
22、 head is similar to manufacturing the block.A casting mold is made.Sand cores are put in to form any hollow areas. Depending on the engine,these can be for coolant and lubricant passages,and inlet and exhaust ports. Air-cooled engines have cooling fins cast into the cylinder head. The underside of t
23、he head is shaped to form the combustion chamber. Molten metal is poured in,and allowed to cool. The cores are broken out and removed,and the cylinder head cleaned of any sand. After casting comes machining.Surfaces that must seal are machined flat.Holes are drilled and tapped for attaching blots and studs.
