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Tiếng Anh Ngành Kỹ Thuật [K1] - Unit 2: Processes

Chủ nhật - 07/02/2016 15:32
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Recorder 4
Good moming, everyone. This is the last in our series of short talks about the plastics industry. Last week we looked at the process of extrusion blow moulding. Today, I'm  going to explain how vacuum moulding works. This is also called vacuum forming , or vacu-forming.
Vacuum forming is a process of making a shape out of a thermoplastic sheet. A thermoplastic sheet is a material that becomes soft when you heat it , and later on it becomes hard after you   cool it. In vacuum forming , as in other processes of plastic moulding, heating and cooling are important parts of the process.
As  its name suggests, with vacuum forming , we have to create a vacuum in the mould in order to produce the moulded object. As  you remember,a vacuum occurs when we suck the air out of a container. So sucking air out, or suction, is an important part of the process, and we use a simple air pump for this purpose.
Now, I've given you a printed handout with some diagrams. As  you can see in figure 2 on your handout, there are some air-exhaust holes at the bottom of the mould. These are for sucking the air out.
But let's start with the first stage, which is heating. As  Figure  1 on your handout illustrates, the heaters are situated above the machine and heat the thermoplastic sheet below them.
The next stage is positioning. As  can be seen  in Figure 2, the thermoplastic sheet is moved to a position directly above the vacuum  mould .
The third stage is illustrated in figure 3.  Here , the thermoplastic sheet is stretched  over the top part of the mould. Here you can see that the plastic material is stretching and becoming thinner. This is the stretching stage.
The fourth and final stage is shown in figure 4.  Here the pump on the right-hand side of the machine is sucking the air out of the mould, and this suction is creating a vacuum. Finally in this vacuum forming stage, as  figure 4 clearly show , the plastic sheet is sucked down over the mould. 
Recorder 5
close, closure
compress,  compression
eject, ejection
expand, expansion
extrude, extrusion      
heal, healer
inflate, inflation
inject, injection
mould,  mould
rotate, rotation
transfer I (verb), transfer (noun)

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