模具专业英语电子教案

(271页)

'模具专业英语电子教案'
1. The injection molding Injection molding is principally used for the production of the thermoplastic parts, although some progress has been made in developing a method for injection molding some thermosetting materials. The problem of injecting a melted plastic into a mold cavity from a reservoir of melted material has been extremely difficult to solve for thermosetting plastics which cure and harden under such conditions within a few minutes①. The principle of injection molding is quite similar to that of die-casting. The process consists of feeding a plastic compound in powdered or granular form from a hopper through metering and melting stages and then injecting it into a mold②. After a brief cooling period, the mold is opened and the solidified part ejected. Injection-molding machines can be arranged for manual operation, automatic single-cycle operation, and full automatic operation. The advantage of injection molding are: (i) a high molding speed adapted for mass production is possible; (ii) there is a wide choice of thermoplastic materials providing a variety of useful properties; (iii) it is possible to mold threads, undercuts, side holes, and large thin sections.2. The injection-molding machine Several methods are used to force or inject the melted plastic into the mold. The most commonly used system in the larger machines is the in-line reciprocating screw, as shown in Figure 1-1. The screw acts as a combination injection and plasticizing unit. As the plastic is fed to the rotating screw, it passes through three zones as shown: feed, compression, and metering. After the feed zone, the screw-flight depth is gradually reduced, forcing the plastic to compress. The work is converted to heat by shearing the plastic, making it a semifluid mass. In the metering zone, additional heat is applied by conduction from the barrel surface. As the chamber in front of the screw becomes filled, it forces the screw back, tripping a limit switch that activates a hydraulic cylinder that forces the screw forward and injects the fluid plastic into the closed mold③. An antiflowback valve prevents plastic under pressure from escaping back into the screw flights. The clamping force that a machine is capable of exerting is part of the size designation and is measured in tons. A rule-of-thumb can be used to determine the tonnage required for a particular job. It is based on two tons of clamp force per square inch of projected area. If the flow pattern is difficult and the parts are thin, this may have to go to three or four tons. Many reciprocating-screw machines are capable of handing thermosetting plastic materials. Previously these materials were handled by compression or transfer molding. Thermosetting materials cure or polymerize in the mold and are ejected hot in the range of 375℃~410℃. Thermoplastic parts must be allowed to cool in the mold in order to remove them without distortion. Thus thermosetting cycles can be faster. Of course the mold must be heated rather than chilled, as with thermoplastics. New words and Expressionsinjection molding 注射模 principally [5prinsipli] adv.主要地thermoplastic [7WE:mE5plAstik] n. 热塑性,热塑性塑料 thermosetting [ 7WE:mEu5setiN] n. 热固性plastic [5plAstik, plB:stik] n.塑胶,塑料 melted vt.(使)熔化,使软化cavity [5kAviti] n. 型腔 reservoir [5rezEvwB:] n. 容器,储存器extremely [iks5tri:mli] adv极端地,非常地 principle [5prinsEpl] n. 法则,原则,原理die-casting 压力铸造 compound [5kCmpaund] n. 混合物,复合的,混合powdered [5paudEd] vt. 弄成粉的,粉状的 granular [5^rAnjulE] adj. 由小粒而成的,粒状的hopper [5hCpE] n. 加料漏斗 metering[5mi:tEriN] vt. 测量(法),计[配]量,测定eject [i5dVekt] vt. 逐出,喷射 solidify [sE5lidifai] vt.(使)凝固,(使)团结manual [5mAnjuEl] adj.手的,手动的,手工的 automatic [ 7C:tE5mAtik] adv自动的,机械的property [5prCpEti] n.性质,特性 thread [Wred] n.螺纹undercut [5QndEkQt] n.侧向分型,底切 reciprocating screw 往复螺杆plasticize [5plAstisaiz] vt.使成可塑体 compression [kEm5preF(E)n] n.浓缩,压缩screw-flight螺杆的螺纹 convert [kEn5vE:t] vt. 使转变,转换shear [FiE] vt.剪, 剪切 semifluid [9semi`flU:id, 9semai~] adj.半流质,半流质的barrel [5bArEl] n.桶 chamber [5tFeimbE] n.室,房间trip [trip] vt.松开棘爪而开动;使跳闸;切断 switch [switF] n.开关,转换,转变hydraulic [hai5drC:lik] adj.水力的,水压的 cylinder valve 气缸阀clamping force锁紧力 exert [i^5zE:t] vt.尽(力),施加(压力)rule-of-thumb单凭经验的方法 transfer molding 传递模塑法,转送成形polymerize [5pClimEraiz] vt.(使)聚合 distortion [dis5tC:FEn] n.扭曲,变形 plunger
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