tailieunhanh - IELTS Academic Reading Sample 109 - Sheet Glass Manufacture The Float Process

Luyện tập với IELTS Academic Reading Sample 109 - Sheet Glass Manufacture The Float Process giúp các bạn hệ thống kiến thức đã học, làm quen với cấu trúc đề thi, đồng thời rèn luyện kỹ năng giải đề giúp bạn tự tin đạt kết quả cao trong kì thi sắp tới. Mời các bạn cùng tham khảo. | You should spend about 20 minutes on Questions 1-13 which are based on Reading Passage 109 below. Sheet glass manufacture the float process Glass which has been made since the time of the Mesopotamians and Egyptians is little more than a mixture of sand soda ash and lime. When heated to about 1500 degrees Celsius C this becomes a molten mass that hardens when slowly cooled. The first successful method for making clear and flat glass involved spinning. This method was very effective as the glass had not touched any surfaces between being soft and becoming hard so it stayed perfectly unblemished with a fire finish . However the process took a long time and was labour intensive. Nevertheless demand for flat glass was very high and glassmakers across the world were looking for a method of making it continuously. The first continuous ribbon process involved squeezing molten glass through two hot rollers similar to an old mangle. This allowed glass of virtually any thickness to be made non-stop but the rollers would leave both sides of the glass marked and these would then need to be ground and polished. This part of the process rubbed away around 20 per cent of the glass and the machines were very expensive. The float process for making flat glass was invented by Alistair Pilkington. This process allows the manufacture of clear tinted and coated glass for buildings and clear and tinted glass for vehicles. Pilkington had been experimenting with improving the melting process and in 1952 he had the idea of using a bed of molten metal to form the flat glass eliminating altogether the need for rollers within the float bath. The metal had to melt at a temperature less than the hardening point of glass about 600 C but could not boil at a temperature below the temperature of the molten glass about 1500 C . The best metal for the job was tin. The rest of the concept relied on gravity which guaranteed that the surface of the molten metal was perfectly flat and horizontal. .