Billow forming

Like the snap back process, billow forming is a sheet pre-stretch process used with a male mold. The sheet is clamped across a pressure chamber and is billow pre-stretched by applying a low magnitude positive air pressure to the chamber. The male mold is then moved into the stretched sheet until the clamp seals on the mold periphery. Contact between the mold and controlling the rate at which the pressure chamber is vented to compensate for the advancing mold can regulate the sheet. 

This version of the billow forming method is used with grained or polished stock on a male mold to preserve the surface finish. The... 

Figure 10.7 Billow forming with plug assist (reprinted with permission from [1 ])...

If billow forming is used, it is usually combined with plug-assist. Why is this the case ... 

Billow forming n. A variant of thermoforming, in which the hot plastic sheet is clamped in a frame and expanded upward with mild air pressure against a male plug or female die as the plug or die descends into the frame. The process is suitable for thin-walled containers with high draw ratios. 

Methylphenazinium methyl sulphate [299-11-6] M 306.3, m 155-157° (198°dec by rapid heating). It forms yellow prisms from EtOH. Solubility in H2O at 20° is 10%. In the presence of aqueous KI it forms a semiquinone which crystallises as blue leaflets from EtOH. [Wieland and Roseen B 48 1117 1913 Voriskova Coll Czech Chem Commun 12 607 1947 Billow B 57 1431 1924]. 

Vacuum (or pressure) is used both to billow pre-stretch and to form the sheet. The heated sheet is first clamped across a vacuum box or chamber, which is then partially evacuated, causing atmospheric pressure to billow and stretch the sheet. A male mold is then advanced into the billowed sheet, and forming is completed by drawing a vacuum (or pressure) on the mold while venting the vacuum chamber to the atmosphere. The process is a takeoff to drape forming but with the advantage of sheet pre-stretch, which produces a much more uniform distribution of wall thickness. 

To meet different formed products with different processable plastics different variations of this basic process are used. An example is a heated sheet clamped over a billow box (enclosed) chamber. Air pressure in the chamber is used causing the sheet to billow. 

The air slip process uses a positive pressure billow sheet pre-stretch that is generated by the movement of a male mold towards the heated sheet that is clamped across a pressure chamber. The mold platen acts as a piston in the chamber and drives a volume of air ahead of it that serves to billow the sheet. At the full extent of its forward travel, the mold periphery seals against the sheet frame, and forming is completed by drawing a vacuum through ports in the mold. 

This view runs into difficulties that have only recently been completely resolved. The principal one is that the pseudopotential form factor happens to be very small for this particular diffraction. In Fig. 18-4 is sketched the pseudopotential form factor for silicon obtained from the Solid State Table the form factor that gives the [220] diffraction is indicated. Because it lies so close to the crossing, it is small and the diffraction is not expected to be strong. Heine and Jones (1969) noted, however, that a second-order diffraction can take an electron across the Jones Zone this could be a virtual diffraction by a lattice wave number of [lll]27j/a billowed by a virtual diffraction by [llT]27c/a. (Virtual diffraction is an expression used to describe terms in perturbation theory it can be helpful but is not essential to the analysis here.) This second-order diffraction would involve the large matrix elements associated with the [11 l]27c/a lattice wave number indicated in Fig. 18-4, and Heine and Jones correctly indicated that these are the dominant matrix elements. 

FRA Franco, T.T., Galaev, I.Yu., Hatti-Kaul, R., Holmberg, N., Billow, L., and Mattiasson, B., Aqueous two-phase system formed by thermoreaetive vinyl imidazoleAfinyl eaprolaetam eopolymer and dextran for partitioning of a protein with a polyhistidine tail, 5iotec/z o/. Techn., 11,231, 1997. 

You may also think of the first law of thermodynamics in the billowing manner When it comes to ener, the best you can do is to break even. You cannot get more energy out of a system than the amount you put into it. For example, if you put 100 J into a system as work, you can get 100 J out of the system in the form of change in internal, kinetic, or potential eneigy of the system. As you learn more about eneigy you vtill also learn that accoidii to the second law of thermodynamics, unfortunately you cannot even break even, because there are always losses associated with processes. We will discuss the eflfect of losses in terms of performance and efficiency of various systems later in this chapter. 

Fig. 5-6. Forming with a billow snapback is recommended for parts requiring a uniform, controllable wall thickness.

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