Читать книгу Encyclopedia of Glass Science, Technology, History, and Culture - Группа авторов - Страница 96

The continuous double‐roll process was developed in the United States in an effort led by the Ford Motor Company to meet a growing demand from the automotive industry. As delivered from the forehearth, the molten glass was pressed to a given thickness, cooled rapidly by a water‐cooled pair of rotating rolls, and then conveyed into a horizontal annealing lehr. The thickness was determined mainly by the gap between the rolls, whereas the output was fixed by the rotating speed of the rolls.

As made by Pilkington Brothers in the 1920s, this process was then improved to manufacture plate glass through online grinding after annealing, followed by polishing of the cut plates. The process was further developed by Saint‐Gobain in the 1950s to grind and polish on line the glass ribbon (Chapter 10.9). Along with a waste of about 20% of the glass, very high investment and operating costs were major disadvantages of these mechanical methods, however, which in fact prompted Pilkington to develop the float process as described in Section 5.

Figure 4 Sketch of the Pittsburg Pennvernon process in cross section. The molten glass is drawn upward from the free surface right above the drawbar immersed below the glass surface [3].

Figure 5 Sketch of the Asahi process in cross section. The rotatable Asahi blocks are immersed into molten glass instead of the débiteuse, and enable the parting line to be renewed where devitrification takes place [6].

Because the float process was not designed at all for patterned and wire‐reinforced glass, the continuous roll out process, with which these products have been produced since the 1920s, has escaped oblivion (Chapter 10.9). Thanks to its versatility and facility for customization, it has even found new special applications, for instance, to make cover glasses for solar cells with excellent light diffusion through patterned textures on the surface. Usually the pattern is impressed on the lower surface by the lower roll, which is engraved. Generally the thickness range is 2–7 mm for the patterned and 8–25 mm for the polished glass.

As to wire‐reinforced glass, it is produced in two ways depending on whether the wire is simply inserted into a molten glass (single‐pass process, Figure 6) or sandwiched between two glass layers (double‐pass process). Although more complex, the latter process has advantages over the former in terms of larger output, wider width, and higher quality, and better suitability for subsequent conversion into polished wired glass because the wire mesh is always precisely located at the center in the thickness direction [1, 3–8].