专业模具英语.docx

1、专业模具英语专业模具英语1. The injection molding and machine 1.1The 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 me

2、lted 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 minutes. The principle of injection molding is quite similar to that of die-casting. The process consists of f

3、eeding a plastic compound in powdered or granular form from a hopper through metering and melting stages and then injecting it into a mold. After a brief cooling period, the mold is opened and the solidified part ejected. Injection-molding machines can be arranged for manual operation, automatic sin

4、gle-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 materials providing a variety of useful properties; (iii) it is possible to mold threads, undercuts, side holes,

5、 and large thin sections.1.2 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 . The screw acts as a combination injection and plasticizing unit. As the p

6、lastic is fed to the rotating screw, it passes through three zones: 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 z

7、one, 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 mold. An antif

8、lowback 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 .The injection-molding machine ,the reciprocating-screw injection system and is measured in tons. A rule-of-thumb can be us

9、ed 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 thermosetti

10、ng 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 375410. Thermoplastic parts must be allowed to cool in the mold in order to remove them without distortion. Thu

11、s thermosetting cycles can be faster. Of course the mold must be heated rather than chilled, as with thermoplastics.Machines are available for molding sandwich parts. One cylinder and plunger injects measured amount of skin material into the die, and then a second cylinder squirts the filler inside

12、the mass. Finally, a final spurt from the first cylinder clears the core material from the sprue. The aim is to produce composites with optimum properties. Either case or core may be foamed.2.Feed system It is necessary to provide a flow-way in the injection mould to connect the nozzle (of the injec

13、tion machine) to each impression. This flow-way is termed the feed system. Normally the feed system comprises a sprue, runner and gate. These terms apply equally to the flow-way itself, and to the molded material which is removed from the flow-way itself in the process of extracting the molding.A ty

14、pical feed system for a four-impression, two plate-type mould. It is seen that the material passes through the sprue, main runner, branch runners and gate before entering the impression. As the temperature of molten plastic is lowered while going through the sprue and runner, the viscosity will rise

15、; therefore, the viscosity is lowered by shear heat generated when going through the gate to fill the cavity. It is desirable to keep the distance that the material has to travel down to a minimum to reduce pressure and heat losses. It is for this reason that careful consideration must be given to t

16、he impression layout and gates design.Sprue A sprue is a channel through which to transfer molten plastic injected from the nozzle of the injector into the mold. It is a part of sprue bush, which is a separate part from the mold.Runner A runner is a channel that guides molten plastic into the cavity

17、 of a mold.Gate A gate is an entrance through which molten plastic enters the cavity. The gate has the following functions: restricts the flow and the direction of molten plastic; simplifies cutting of a runner and moldings to simplify finishing of parts; quickly cools and solidifies to avoid backfl

18、ow after molten plastic has filled up in the cavity.Cold slug well The purpose of the cold slug well, shown opposite the sprue, is theoretically to receive the material that has chilled at the front of the nozzle during the cooling and ejection phase. Perhaps of greater importance is the fact that i

19、t provides positive means whereby the sprue can be pulled from the sprue bush for ejection purposes.The sprue, the runner, and the gate will be discarded after a part is complete. However, the runner and the gate are important items that affect the quality or the cost of parts.3 .RUNNER The runner i

20、s a channel machined into the mould plate to connect the sprue with the entrance to the impression. The wall of the runner channel must be smooth to prevent any restriction to flow. Also, as the runner has to be removed with the molding, there must be no machine marks left which would tend to retain

21、 the runner in the mould plate. There are some other considerations for the designer to bear in mind: (i) the shape of the cross section of the runner, (ii) the size of the runner ；(iii) the runner layout.Runner cross-section shape The cross-sectional shape of the runner used in a mould is usually o

22、ne of four forms: fully round, trapezoidal, modified trapezoidal and hexagonal.The criterion of efficient runner design is that the runner should provide a maximum cross-section area from the standpoint of pressure transfer and a minimum contact on the periphery from the standpoint of heat transfer

23、. The ratio of cross-sectional area to periphery will, therefore, give a direct indication of the efficiency of the runner design; the higher the value the greater the efficiency. Runner layoutThe layout of the runner system will depend upon the following factors: (i) the runner of impression, (ii)

24、the shape of the components, (iii) the type of mould, (iv) the type of gate.When designing a runner system there are two main considerations. The runner length should always be kept to a minimum to reduce pressure losses, and the runner system should be balanced.Runner balancing means that the dista

25、nce the plastic material from the sprue to the gate should be the same for each molding. This system ensures that all the impressions will fill uniformly and without interruption providing the gate lands and the gate areas are identical. Runner layout It is not always practicable, however, to have a

26、 balanced runner system and this particularly applies to moulds which incorporate a large number of differently shaped impressions. In these cases（as shows examples ） balanced filling of the impression can be achieved by varying the gate dimensions that is by balanced gating.4 .GATES The gate is a c

27、hannel or orifice connecting the runner with the impression. It has a small cross-sectional area when compared with the rest of the feed system. This small cross-sectional area is necessary so that: i) The gate freezes soon after the impression is filled so that the injection plunger can be withdraw

28、n without the probability of void being created in the molding by suck-back. ii) It allows for simple degating and in some mould this degating can be automatic.) After degating only a small witness mark remains.) Better control of the filling of multi-impressions can be achieved.) Packing the impres

29、sion with material in excess of that required to compensate for shrinkage is minimized.The size of the gate can be considered in terms of the gate cross-sectional area and the gate length, the latter being known as gate land. The optimum size for a gate will depend on a number of factors including (

30、i) the flow characteristics of the material to be molded (ii) the wall section of the molding, (iii) the volume of material to be injected into the impression, (iv) the temperature of the melt (v) the temperature of the mould.No theoretical size exists for the ideal gate. The gate size chosen in pra

31、ctice for a particular component is normally based on past experience. However, the reader may not have this experience upon which to base a decision and, therefore, a guide to the dimensions for each gate type is given. To the general case of a molding with a wall section between 0.75mm and 4 mm. F

32、igure 4-1 Types of gateType of gate To obtain the optimum filling conditions the type of gate must be carefully chosen. On most occasions, however, the choice will be obvious as only one type of gate will meet the particular requirements for the molding on hand. The types of gate (see Figure 4-1) commonly used are: sprue gate(f), edge gate(n), overlap gate(a), fan gate(b), diaphragm gate(g), ring gate(h), film gate(c), pin gate(d), submarine gate(m) and tab gate(e).5. Parting surfaceThe parting surfaces of a mould are those portion of both mould plates, adjacent to the impressions, which butt