Reheat blow

Regulatory systems, environmental impact assessment, 10 232-233 Rehalogenating bleaches, 19 261 Reheat blow-molding process, 20 47 Rehm-Weller equation, 19 112 Rehydration bonded alumina, 2 395, 396-397... 

The two-stage PET stretch blow molding system is usually referred to as the reheat blow molding... 

Soft-drink bottles made from poly(ethylene terephthalate) (PET) are usuady made by stretch-blow mol ding in a two-step process. Eirst, a test-tube-shaped preform is molded, which is then reheated to just above its glass-transition temperature, stretched, and blown. Stretching the PET produces biaxial orientation, which improves transparency, strength, and toughness of the botde (54,56). A one-step process is used for many custom containers that are injection stretch-blow molded. 

Reheat and blow moulding in which parisons are bought from an external furnisher and are blown on an in-house machine. 

When the molten mixture cools, it produces a transparent, rigid mass that softens when it is reheated. While it is hot and soft, the glass can be shaped by blowing, rolling, or molding it into the desired shape. The glass used most often in windows, sometimes called flat glass, is of the soda-lime type. 

Injection blow molding utilizes an injection molder to produce the preform to be blown. In the example we will consider here, a hollow preform resembling a test tilbe is made by conventional injection molding (top diagram of Figure 14-64). The preform is then transferred to a second mold where it is reheated and blown into final shape, as shown in Figure 14-64. 

PET resin is converted into three basic forms a fibre a film or sheet and some form of container. Each of the processes for manufacture of the finished article needs a preform of some type, i.e., the processes are all twofold. Eibres are made first with a continuous fibre which is cooled, then reheated and stretched at a fixed temperature (see Eig. 20.2). Eilm is first extruded into a sheet, cooled, then reheated and stretched in two directions (see Eig. 20.3). Einally a bottle is formed from the reheating of a preform or test-tube-like object and stretched in two directions by physical pushing and by blowing with high pressure air (see Eig.20.4). 

Proceed as in the previous exercise to the stage indicated by Fig. 6.20d. With the same flame reheat the small bulb and blow it to the shape shown in Fig. 6.20i. Allow the glass to cool slightly, then reheat at the end of the bulb, flattening it to the shape (Fig. 6.20j) by melting. 

The blister must be kept under close observation while it is being blown up. If blowing is overdone a shape such as that shown in Fig. 6.29b results, and difficulties of making a T-tube will be increased. The top of the blister is reheated and blown up as in Fig. 6.29c. The blister is again reheated and blown out (Fig. 6.29d). 

Adjust the air and gas to give a small pointed flame and melt the centre of the test-tube end. Blow out a small bulb, then reheat and open the bulb as in sketch. The hole should be slightly smaller than 8 mm diameter (Fig. 6.31 c). 

Some care must be taken to avoid blowing too large a bulb although it is fairly easy to reheat a bulb and blow it up slightly, it is much more difficult to re-melt and re-blow to a smaller diameter. It is not easy to judge bulb diameters by eye. A good plan is to use the tube diameter as a unit, and to remember the ratio of the bulb diameter to the mbe diameter. 

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