英语翻译Injection molding machines are manufactured in many size

英语翻译
Injection molding machines are manufactured in many sizes.These are rated according to size by the amount of material which can be injected in one cycle,which ranges from a fraction of an ounce in the small laboratory models to many pounds in large production equipment .Laboratory models are used in the research and development of new polymers and molding techniques.
There are two basic units to an injection molding machine; one for injecting the heated plastic and one for opening and closing the mold.The first unit includes a feed hopper,heated injection cylinder ,and an injection plunger or screw system.The second unit comprises a hydraulic operated moving platen and a stationary platen on which the halves of the mold are mounted.Injection molding machines are also available in vertical models.
There are many variations in injection molding machine design,however,the basic machines are of either the screw-ram,or plunger type.The main difference between these types is the method in which the plastic material is delivered from the hopper to the nozzle of the machine.Machines of the reciprocating-screw type are used more because of the material.
The injection molding machine has a variety of instrumentation used for the clamping unit,mold,and injection molding machine.Fig.2.1.1 shows the most important possibilities of the instrumentation.In fact ,there is no known direct method for in-line checking of the condition of the mold.
A typical laboratory injection molding machine,will vary in shot capacity from a few grams to about one-half ounce.It will have a clamping device that is usually hand operated with a cam action and an injection system operated manually or by compressed air.The injection system exerts very high pressure on the mold,from 5000 to 20000 psi.It is therefore necessary for the mold to be clamped together with a greater pressure than the injection pressure or the mold halves will be forced apart and flash(squeeze out of resin at the parting line of the mold)will result.
The loading chute and the heating cylinder make up the other major components of the machine.Most of the laboratory size machines are of the plunger type.
Injection molding is especially suitable for high production runs,most machines produce several thousand products an hour.Virtually all thermoplastic resins can be injection molded,however,some are more difficult to process and require specialized equipment.From a knowledge of polymer structure,it becomes evident that resins with wide melting range mold easier than those with a sharp or narrow melting point,Other factors to consider are the molding temperature requirements,moisture absorption of the resin,and the necessary properties required for the product.For example,acetal resin has a sharp melting point,turning quickly to a liquid,which requires exacting temperature controls.