模具毕业设计论文外文翻译

Injectio n Moldi ng

The basic concept of inject ion mold ing revolves around the ability of a therm op lastic material to be softe ned by heat and to harde n whe n cooled .In most op erati ons ,gra nu lar material (the p lastic res in) is fed into one end of the cyli nder (usually through a feeding device known as a hopper ),heated, and softe ned( plasticized or pl asticated),forced out the other end of the cyli nder,while it is still in the form of a melt,through a nozzle into a relatively cool mold held closed under pressure.Here,themelt cools and hardens until fully set-up.The mold is then open ed,the pi ece ejected,a nd the seque nee rep eated.

Thus,the sig nifica nt eleme nts of an injectio n moldi ng machi ne become :1)the way in which the melt is p lasticized (softe ned) and forced in to the mold (called the inject ion un it); 2)the system for opening the mold and clos ing it un der p ressure (called the cla mping uni t);3)the type of mold used;4)the mach ine con trols.

The part of an injectio n-moldi ng machi ne,which con verts a p lastic material from a sold p hase to homoge neousse ni-liguid p hase by rais ing its temp erature .This unit main tai ns the material at a p rese nt temp erature and force it through the injectio n unit no zzle into a mold .The plun ger is a comb in ati on of the injection and p lasticiz ing device in which a heati ng chamber is moun ted betwee n the plun ger and mold. This chamber heats the pl astic material by con ducti on .The plun ger,o n each storke; pu shes unm elted p lastic material into the chamber ,which in turn forces p lastic melt at the front of the chamber out through the no zzle

The part of an injectio n moldi ng mach ine in which the mold is moun ted,a nd which pro vides the moti on and force to open and close the mold and to hold the mold close with force duri ng injectio n .This unit can also p rovide other features n ecessary for the effective functioning of the molding operation .Moving plate is the member of the cla mping un it,which is moved toward a stati onary member.the movi ng secti on of the mold is bolted to this movi ng plate .This member usually in cludes the ejector holes

and moldmounting pattern of blot holes or “ T”slots .Stationary plate is the fixed

member of the clamping unit on which the stationary section of the mold is

bolted .This member usually includes a mold-mounting pattern of boles or “ T”

slots.Tie rods are member of the cla mping force actuati ng mecha nism that serve as the

tension member of the cla mp whe n it is holdi ng the mold closed.They also serve as a

gutde member for the movable plate .Ejector is a pro visi on in the cla mping unit that

actuates a mecha nism within the mold to eject the molded p art(s) from the mold .The

ejecti on actuat ing force may be app lied hydraulically or pn eumatically by a cyli nder(s) attached to the moving plate ,or mechanically by the opening storke of the moving

plate.

Methods of melting and injecting the plastic differ from one machine to another

and are con sta ntly being imp rored .couve nti onal machi nes use a cyli nder and p ist on to

do both jobs .This method simp lifies mach ine con struct ion but makes con trol of

injectio n temp eratures and p ressures an in here ntly difficult p roblem .Other machi nes

use a p lastcat ing extruder to melt the p lastic and p isto n to inject it while some hare

bee n desig ned to use a screw for both jobs :Nowadays,sixty p erce nt of the mach ines

use a rec ip rocati ng screw,35% a plun ger (concen trated in the smaller machi ne

size),a nd 5%a screw pot.

Many of the problems connected with in jection molding arises because the

densities of polymers change so markedly with temperature and pressure.Athigh

temp eratures,the den sity of a polymer is considerably cower than at room

temp erature ,p rovided the pressure is the same.Therefore,if modls were filled at

atmos pheric p ressure, “shrinkage ” would make the molding deviate form the shape of the mold.

To compen sate for this poor effect, molds are filled at high p ressure.The p ressure

comp resses the poly mer and allows more materials to flow into the mold,shri nkage is

reduced and better quality moldi ngs are p roduced.Cludes a mold-m oun ti ng p attern of

bolt holes or “ T”slots.Tie rods are members of the clamping force actuating