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, 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. Consequently, when pouring molten glass onto the molten tin, the underside of the glass would also be perfectly flat. If the glass were kept hot enough, it would flow over the molten tin until the top surface was also flat, horizontal and perfectly parallel to the bottom surface. Once the glass cooled to 604°C or less it was too hard to mark and could be transported out of the cooling zone by rollers. The glass settled to a thickness of six millimetres because of surface tension interactions between the glass and the tin. By fortunate coincidence, 60 per cent of the flat glass market at that time was for six- millimetre glass.
Pilkington built a pilot plant in 1953 and by 1955 he had convinced his company to build a full-scale plant. However, it took 14 months of non-stop production, costing the company £100,000 a month, before the plant produced any usable glass. Furthermore, once they succeeded in making marketable flat glass, the machine was turned off for a service to prepare it for years of continuous production. When it started up again it took another four months to get the process right again. They finally succeeded in 1959 and there are now float plants all over the world, with each able to produce around 1000 tons of glass every day, non-stop for around 15 years.
Float plants today make glass of near optical quality. Several processes – melting, refining, homogenising – take place simultaneously in the 2000 tonnes of molten glass in the furnace. They occur in separate zones in a complex glass flow driven by high temperatures. It adds up to a continuous melting process, lasting as long as 50 hours, that delivers glass smoothly and continuously to the float bath, and from there to a coating zone and finally a heat treatment zone, where stresses formed during cooling are relieved.
The principle of float glass is unchanged since the 1950s. However, the product has changed dramatically, from a single thickness of 6.8 mm to a range from sub-millimetre to 25 mm, from a ribbon frequently marred by inclusions and bubbles to almost optical perfection. To ensure the highest quality, inspection takes place at every stage. Occasionally, a bubble is not removed during refining, a sand grain refuses to melt, a tremor in the tin puts ripples into the glass ribbon. Automated on-line inspection does two things. Firstly, it reveals process faults upstream that can be corrected. Inspection technology allows more than 100 million measurements a second to be made across the ribbon, locating flaws the unaided eye would be unable to see. Secondly, it enables computers downstream to steer cutters around flaws.
Float glass is sold by the square metre, and at the final stage computers translate customer requirements into patterns of cuts designed to minimise waste.
- Giải thích từ vựng
- Mixture (n) /ˈmɪks.tʃər/ hỗn hợp
Eg: The mixture of flour, water, and yeast is then left in a warm place for four hours.
Their latest cd is a mixture of new and old songs.
- Molten (a) /ˈməʊl.tən/ nóng chảy
Eg: A two-dimensional molten aluminium droplet is of finite extent and is surrounded by a passive gas.
- Unblemished (a) /ʌnˈblem.ɪʃt/ không có vết nhơ, không tỳ vết
Eg: His reputation was unblemished in 1996, when he was simply the best high school player in the nation.
What i’m after is smooth, unblemished skin.
- Labour intensive (a) /ˌleɪ.bər.ɪnˈten.sɪv/ cần nhiều lao động, dùng nhiều lao động
Eg: A lot of farming techniques have been abandoned because they were too labour intensive.
- Squeeze (v) /skwiːz/ ép, vắt, nén, siết chặt
Eg: As she waited to go into the exam, he squeezed her hand and wished her good luck.
- Virtually (adv) /ˈvɜː.tʃu.ə.li/ hầu như, gần như
Eg: Their twins are virtually identical.
That wine stain on my shirt has virtually disappeared.
Một số từ đồng nghĩa:
- Almost we need to hurry up – it’s almost time to go.
- Nearly it’s nearly midnight.
- Near he was near tears (= almost crying).
- About are you about ready to leave?
- All but the concert was all but over by the time we arrived.
- Well-nigh it was well-nigh impossible to get a person on the phone these days.
- Non-stop (a, adv) /ˌnɒnˈstɒp/ xuyên suốt, liên tục, không ngừng
Eg: It felt like we had travelled non-stop for the entire week.
It rained non-stop all week.
Một số từ đồng nghĩa:
- Always the power plant is always running.
- For ever i will love you for ever.
- Permanently his reputation was permanently ruined by the scandal.
- Eternally evildoers shall be eternally condemned.
- Uninterruptedly stocks have risen uninterruptedly for the last three months.
- Polish (v) /ˈpɒl.ɪʃ/ đánh bóng, làm cho láng
Eg: Polish your shoes regularly to protect the leather.
He polished the hardwood floor.
- Rub (v) cọ, chà xát, làm mòn
Eg: The wheel is rubbing on the mudguard.
Their perpetually wet clothes rubbed against their skin.
- Altogether (adv) /ˌɔːl.təˈɡeð.ər/ hoàn toàn, tất cả, toàn bộ
Eg: The government ought to abolish the tax altogether.
She wrote less and less often, and eventually she stopped altogether.
- Gravity (v) /ˈɡræv.ə.ti/ trọng lực, trọng lượng
Eg: Gravity pulls objects together.
- Guarantee (v) /ˌɡær.ənˈtiː/ bảo đảm, bảo hành, cam đoan
Eg: European airlines guarantees its customers top-quality service.
Journalists may enter the danger zone but unfortunately we cannot guarantee their safety.
- Horizontal (a) /ˌhɒr.ɪˈzɒn.təl/ ngang, nằm ngang
Eg: Draw a horizontal line across the bottom of the page.
Keep the patient horizontal with the feet slightly raised.
- Parallel (a) /ˈpær.ə.lel/ song song
Eg: Hills road is parallel to mill road.
The road runs parallel with the coast.
Collocation
- Parallel to/with something
- Tension (n) /ˈten.ʃən/ sức ép, áp lực
Eg: We need more tension in the wires, so pull them tighter.
The surface tensions are functions of the local extension ratios, which depend on the global deformation of the membrane.
- Coincidence (n) /kəʊˈɪn.sɪ.dəns/ sự trùng khớp ngẫu nhiên, sự trùng hợp
Eg: You chose exactly the same wallpaper as us – what a coincidence!
Meeting you here in rome is a remarkable coincidence.
- Pilot (a) /ˈpaɪ.lət/ thử nghiệm
Eg: If the pilot scheme is successful, many more homes will be offered the new television service.
The pilot episode of the series had the biggest viewing numbers of the year.
- Usable (a) /ˈjuː.zə.bəl/ có thể dùng được, sử dụng được
Eg: The specific software is also usable in other areas of research.
- Optical (a) /ˈɒp.tɪ.kəl/ (thuộc) quang học
Eg: The glowing cloud was an optical effect.
Her eye tests revealed that she has no optical defects.
- Simultaneously (adv) /ˌsɪm.əlˈteɪ.ni.əs.li/ đồng thời, xảy ra cùng một lúc, làm cùng một lúc
Eg: The network was broadcasting four games simultaneously across the country.
The opposing units opened fire simultaneously at close range and a 15-minute firefight ensued.
- Coating (n) /ˈkəʊ.tɪŋ/ lớp phủ ngoài, lớp mạ
Eg: The goggles have a laser-protection coating.
Apply a thin coating of glue to the surface.
- Relieve (v) /rɪˈliːv/ làm nhẹ bớt, giảm bớt
Eg: If china and other asian economies let their currencies rise, this will relieve pressure on the euro.
- Dramatically (adv) /drəˈmæt.ɪ.kəl.i/ đột ngột
Eg: The economic power of many asian countries has grown dramatically in recent years.
Environmental awareness has increased dramatically over the past decade.
- Mar (v) /mɑːr/ làm hư, làm hỏng, làm hại
Eg: Sadly, the text is marred by careless errors.
- Inspection (n) /ɪnˈspek.ʃən/ sự kiểm tra, sự thanh tra
Eg: Her passport seemed legitimate, but on closer inspection, it was found to have been altered.
Collocation
-
- Carry out/make an inspection normally you will carry out an inspection of the goods as soon as possible after delivery.
- A close/detailed/thorough inspection
- On closer/close inspection the goods looked fine, but, on closer inspection, several items were found to be faulty.
- Refine (v) /rɪˈfaɪn/ lọc, lọc trong, luyện tinh, tinh chế
Eg: Crude oil is industrially refined to purify it and separate out the different elements, such as benzene.
Sugar and oil are refined before use.
- Upstream (a, adv) /ˌʌpˈstriːm/ngược dòng, ngược tuyến
Eg: Rowing upstream was hard going.
They are working upstream to try and prevent such a situation happening again.
Từ trái nghĩa:
Downstream
- Unaided (a) /ˌʌnˈeɪ.dɪd/ không có sự trợ giúp
Eg: Since his accident, he hasn’t been able to walk unaided.
Một số từ đồng nghĩa:
- (all) by yourself i don’t think i can fix the car alone – can you help?
- (all) on your own i learnt the song all on my own.
- Single-handedly she single-handedly saved the company from bankruptcy.
- Unassisted after years of using a cane, intensive physio enabled her to walk unassisted.
- Independently the charity helps people to live independently.
- Steer (v) /stɪər/ lái, dẫn hướng
Eg: She carefully steered the car around the potholes.
- Specific (a) /spəˈsɪf.ɪk/ đặc trưng, riêng biệt, cụ thể
Eg: The regional editions of the paper contain specific information for that area.
They nailed him down to a specific time and place.
- Invest (v) /ɪnˈvest/ đầu tư
Eg: The institute will invest five million in the project.
He’s not certain whether to invest in the property market.
Một số từ đồng nghĩa:
- Spend how much do you intend to spend on a house?
- Pay when you bought the tickets, how much did you pay?
- Splurge we’ve just splurged on new kitchen appliances.
- Blow we won a £15 million settlement in court and we blew it all in six years.
- Instant (a) /ˈɪn.stənt/ ngay tức khắc, lập tức
Eg: This type of account offers you instant access to your money.
Contrary to expectations, the film was an instant success.
- Detect (v) /dɪˈtekt/ dò ra, tìm ra, khám phá ra, phát hiện ra
Eg: Some sounds cannot be detected by the human ear.
Financial experts have detected signs that the economy is beginning to improve.
Detectable (a)
Detection (n)
- Luyện tập
Bài 1: Chọn từ trong khung để hoàn thành các câu bên dưới
| relieving | non-stop | horizontal | gravity | usable |
| dramatically | molten | coincidence | simultaneously | coating |
- The ……………………………………….. zone acts as an electrical conductor with normal conductivity and heat is generated throughout its volume.
- They talked …………………………………………….. about the play.
- On this graph, time is on the …………………………………………. X-axis, and distance is on the vertical Y-axis.
- She was cooking a meal while …………………………………………….. holding a business meeting via her mobile phone.
- The cost of the project has increased ………………………………………. since it began.
- The campaign has fallen short of its goal of …………………………………………… the burden of unsustainable debt on the poorest countries.
- Frost formed a white …………………………………………. on the windows.
- Aquatic organic matter is subject to a hard-water error and is therefore not …………………………….
- By some extraordinary …………………………………………, I sat down right opposite your mother in the train.
- The building leans so much that it seems to defy ……………………………………..
Bài 2: Chọn đáp án đúng để điền vào chỗ trống
- Some people call English a mongrel language because it is a ………………………. of old German and French. A. coincidence B. mixture
- The river is ………………………………………………… to Green Street. A. parallel B. horizontal
- She ……………………………… her hands together in effort to warm them. A.polished B. rubbed
- Torn apart by war, its economy ……………………………… destroyed, this country now faces a very uncertain future. A. virtually B. horizontally
- The service sector is more labour …………….. and less productive than manufacturing. A. intensive B. molten
- You’d never guess that boyish, ……………………………… face spent so much time outdoors. A. parallel B. unblemished
- Adjust the string ………………………. of your tennis racket to suit your style of playing. A. tension B. coincidence
- The electricity company …………………………………. connection within 24 hours. A. relieves B. guarantees
- The staging of the play included some incredible ……………………….. tricks. A. optical B. usable
- From the ………………………….. episode, this looks to be one of the best new shows we’ll see this fall. A. specific B. pilot
- I tried to …………………………….. the boat away from the bank. A. steer B. invest
- Some of the children have ………………………….. learning difficulties. A. instant B. specific
- The alarm should go off automatically as soon as smoke is ……………………… A. invested B. detected
- I hope the fact that Louise isn’t coming won’t …………………….. your enjoyment of the evening. A.mar B. refine
- The customs officials made us go through the whole rigmarole of opening up our bags for ………………… A. coating B. inspecting
- The process of ……………………………….. oil produces several useful chemicals. A. refining B. steering
- The nearest town is about ten miles ……………………………. A. upstream B. optical
- The two explorers attempted an …………………………….. walk across the South Pole. A. unblemished B. unaided
- Once he had finished cleaning the floor, he ………………………… the cloth out. A. squeezed B. rubbed
- She decided to ……………………….. the ring up and find out who it belonged to. A. polish B. rub
- It’s all right working with him, but living with him would be a different matter ………………………… A. simultaneously B. altogether
- Following a need for ……………………. results, more health care providers are starting to offer online access. A. instant B. specific
- You have all …………………….. significant amounts of time and energy in making this project the success that it is. A. steered B. invested
Bài 1:
1.molten 2. non-stop 3. horizontal 4.simultaneously 5. dramatically
- relieving 7. coating 8.usable 9.coincidence 10. gravity
Bài 2:
1.B 2.A 3.B 4.A 5. A
6.B 7.A 8.B 9.A 10. B
11.A 12.B 13. B 14.A 15.B
16.A 17.A 18.B 19.A 20. A
21.B 22.A 23.B
