Unit 1 glass
- 1. UNIT V - GLASS Glassis an inorganic,homogeneousandamorphoussubstanceobtainedthroughthe cooling of a molten mass. Its main qualitiesare the transparency andhardness.The glasshasuncountable applicationsinthe mostvariedindustries, given itsinalterabilitycharacteristics,hardness,resistance andthermal,optical and acoustic properties, becoming one of the fewmaterials yet irreplaceable, being every time more present in the technological development researches for the well-being of the man. Composition of Glass - it’s not a single compound and its difficult to give it a particular chemical formula - commonly expressed as combination of alkali oxides, metal oxides and silica dioxides aX2O, bYO, 6SiO2 Where, a, b are no. of molecules; X is an atom of an alkali metal i.e. Na, K etc. Y is an atom of a bivalent metal i.e. Ca, Pb etc. For example, Soda-lime Glass - Na2O, CaO, 6SiO2 Potash-lead Glass - K2O, PbO, 6SiO2 Important properties of glass 1. Absorbs, refracts and transmits light 2. Amorphous substance having no definite crystalline structure – which makes it easy to fuse it and mould it as many times as possible 3. No sharp melting point 4. Does not react with water and other atmospheric agents – but is affected by alkalis 5. Characteristics,bothphysical and chemical, vary considerably with addition of other materials (B2O3, if added with glass makes its alkali resistant) 6. Excellent electrical insulator at elevated temperatures 7. Easy to clean and maintain it from stains 8. Easy to add colour to glass 9. Considerablecompressive strengthuptocertainpointbutdoesnotdeformbutbreaks – highlybrittle substance 10. Thermal conductivity is less Manufacturing of Glass
- 2. Stage I – Collection of raw materials depending on the type of the glass: Say, Soda-lime Glass preparation needs Chalk (CaO), Soda ash (Na2O) and Clean sand (SiO2) Culletinthe formof waste glassor brokenglassis addedto increase the fusibilityaswell as to prevent the loss of alkali through volatilisation. Decolourisers are also added to eliminate the yellowish tint of Ferric Oxides and greenish tint of Ferrous Oxides – Antimony Oxide, Arsenic Oxide, Cobalt Oxide, Manganese Oxide, Nickel Oxide are the most commonly used decolourisers. Stage II – Preparation of batch - By adding ingredients in correct proportion, and mixing them uniformly. Stage III – Melting in furnace - In potfurnace or tank furnace dependingonthe scale of operation – small scale in pot and large scale in tank furnace - Refractory lining of fire clay. Stage IV – Fabrication of glass Float Glass – makes the molten glass float over liquid tin; Plate Glass – rolled over either two layers of roller or combination of plate and rolled Cast glass – cast by pouring molten glass or pressing them in moulds. Stage V – Annealing of glass - It’s of process of making glass objects cool down gradually from a very high temperature - Due to highthermal insulationof glassrapid cooling creates thermal stress between inner and outer layers of glass – leading to a state of strain - Makes glass highly vulnerable to minor shocks and disturbances – thus annealing is a crucial process Flue methodof annealing– glassobjectsbeingpassedthroughaflue withvaryingtemperature allowingittocool down gradually – a constant process applied for large scale annealing. Oven method of annealing – temperature variation achieved by cooling the oven itself from high temperature – an intermittent process suitable for small scale annealing.
- 3. Test for waviness - Apply a coating of silver on one surface protected by metallic copper film (similar to making of mirror out of glass) - Sketch comprising broad straight bands at 45˚ to the horizontal in a rectangle waved in front of the mirror which should be vertically placed. - Image of bands free from distortion means that the glass is free from waviness or ‘distortion free’. TREATMENT OF GLASS
- 4. USES Glass is used in the following non-exhaustive list of products: Packaging (jars for food, bottles for drinks, flacon for cosmetics and pharmaceuticals) Tableware (drinking glasses, plate, cups, bowls) Housing and buildings (windows, facades, conservatory, insulation, reinforcement structures) Interior design and furnitures (mirrors, partitions, balustrades, tables, shelves, lighting) Appliances and Electronics (oven doors, cook top, TV, computer screens, smart-phones) Automotiveand transport(windscreens,backlights,lightweightbutreinforced structural components of cars, aircrafts, ships, etc.) Medical technology, biotechnology, life science engineering, optical glass Radiation protection from X-Rays (radiology) and gamma-rays (nuclear) Fibre optic cables (phones, TV, computer: to carry information) Renewable energy (solar-energy glass, windturbines) TYPES OF GLASS Glass block: When it comes to designing and building with glass, one of the simplest yet most versatile ways of utilising glass is in the form of glass blocks. Glass blocks can be used both internally and externallyandwhereverthey are placed the way in which they transmit and refract light allows the designer to maximise the sense of light and space creating beautiful and alwaysunique livingandworkingspaces.Where privacyisparamountopaque glassblocks can be selected, retaining light and vibrancy whilst protecting privacy. Glassblocksare suitable forbothcommercial andresidential purposesandcanbe usedto fill windowopenings,form dividingwalls,externalwalls,inthe creationof showercubicles,bars,terraces,anddesks.Infactthe designpotential for the use of glass blocksinanyconstructionislimitedonlybyyourimagination. Block Glass is hollow sealed made by fastening together two halves of pressed glass. It is used for making partitions. Glass Blocks - glass blocks typically have compressive strength in the range of 3-4 MPa - can be either hollow (made of two pressed glass shapes fused together into a single unit at an elevated temperature with the air trapped inside dehydrated and partially evacuated) or solid - chemical composition similar to the glass used in door/window panels - can have various colours, textures, transparency and dimension - usedmostlyaspartitionwallswhere lighttransmission,insulationandglare control are of majorimportance - mortar used in glass block masonry is cement – lime mortar where cement in 1 part, lime in 0.5 part and sand in 3 parts are used The foamed glass aggregate is produced from cleaned recycled glass. The product is especially suited for usage in the construction of roads, as frost-heave insulation as well as a bulk lightening material. It is also excellent as an all-round building insulator (foundation and frost heave insulator, flat roof insulator in the
- 5. structure of invertedroofs),aswell asa bulklighteningmaterial forfoundations.Crushedfoamed glass can also be used as a capillary blocker. Float Glass The floatglassis a transparent,colorlessorcoloredglass,withuniformthicknessandhomogeneousmass. It is the ideal glass for application that demand perfect visibility, as it does not present optical distortion and has high light transmission. It constitutesthe rawmaterial forthe processingof all the otherflatglasses,beingapplied to different segments and it can be: laminated, tempered glass, curved, screen-printed glass and used in double glazing. It is used in automotive industry, of household appliances, civil construction, furniture and decoration. Casted Glass Glasscasting is the processinwhich glassobjectsare cast bydirectingmoltenglass intoamouldwhere it solidifies.The technique hasbeenusedsince the Egyptianperiod.Moderncastglassisformedbya varietyof processessuchas kilncasting,orcastingintosand,graphite or metal moulds. Solar control Solar control glassis glass designed to reduce or prevent solar heating of buildings. There are two approaches that c an be used: the glass is either tinted (coloured) throughout the material (called a "body tint"), or else it has a microscopically thin and transparent coating on one side. In the body tint approach,the colour causes the glass to absorb solar energy, which is then re-radiated back out and away from the building. Coated glasses immediately reflect the heat away. These technologies reduce the solar heating that tends to take place in large buildings, and thus reduce the need for air conditioning. It is therefore an energy-saving technology. In dwellings it helps prevent uncomfortable overheating in conservatories and other rooms with large areas of glazing, and it can also reduce irritating glare from direct sunlight. Solar control glass can becombined with many other features for multifunctional glazing, such as thermal insulation, self cleaning, noise reduction, decorative glass and enhanced safety and security. Decorative Glass Glass can transform living spaces and work environments. A wide range of effects, patterns and colours allows interior designers endless possibilities in look and atmosphere. Glass can be combined wi th stone, wood or metal for a strong visual and tactile effect. In offices and other professional settings, glass offers a fresh, light yet serious aesthetic and has the advantage of being a material that wears exceptionally well and is impervious to moisture and most cleaning products. Laminated Glass is made by sandwiching a layer of polyvinyl butyral between two or more layers of plate or sheet glass. It is also lso known as safety glass. The examples are heat proof glass, sound proof glass and bullet proof glass. Heat and sound proof glasses Two or more glass plates are sandwiched by a tinted plastic inner layer. It provides high resistance to heat and glare. By increasing the thickness of plastic layer the glass can be made more sound resistant. Bullet proof glass is produced by placing vinyl plastic and glass in several alternate layers and pressing them with outer
- 6. layers of glass. It is used in banks, jewellery stores and display windows. lnsulatingglass is composed of two glass plates into which a layer of 6–13 mm thick dehydrated air is sealed. The roundedges areformed by fusing together the twoglass plates. These glasses reduce the heat transmission by 30–60 per cent. Wired Glass is produced by embedding wire nets 0.46 to 0.56 mm into the centre of sheet glass during casting. The minimum thickness of wired glass is 6 mm. When broken it does not fall into pieces. It has higher melting point than ordinary glass. Wired glass is used for fire resisting doors and windows, for sky lights and roofs. Aspecial example of this is wired-refrax glass which transmits 100 per cent more light than the other glasses. Fire resistance A range of fire-resistantglass types is availablethatoffers increasinglevels of protection, which is measured in defined time periods (30, 60, 90, 120, 180 minutes). Fire-resistant glass must meet strict levels of integrity and insulation, or integrity only which are set down by European CE standards. Fire-resistant glass must always be specified as part of a tested and approved glazing system and installed by specialists to be sure of reaching expected fire performance, if required. Structural Glazing Structural glazing is a system of bonding glass to an aluminium window frame utilizing a high-strength, high performance silicone sealant. It uses the adhesive qualities of silicone sealants to retain the glass in the frame by adhesion without the necessity of any mechanical retention such as beads, clips or bolt fixings. Structural glazing with sealants allows perfectly uniform large glazed surfaces, not interrupted by traditional frames or any other supporting or fitting system projecting out of the frame. Instead of being fitted in a frame, the glass is fixed to a support, which in turn is attached to a structural element of the building, the tightness of the whole system being obtained by a siliconeseal.Theglass is fixed on its support by means of a silicone seal along the edges of the internal surface. The glazing is prepared in a factory by mounting a structural seal support frame onto the glass, complete with appropriate setting blocks, location blocks and distance pieces. On site, the support frame is attached to the building structure by mechanical means and the gaps between the glazings are sealed. APPLICATION OF GLASS IN DOOR AND WINDOW SHUTTERS Transparent or translucent glass sheets, clear or tinted are used as door and window shutters in various sizes Classification of transparent glass used as door/window glazing 1. AA Quality or Special Selected Quality (SSQ) – for safety glass in door/window or wind shields. 2. A Quality or Selected Quality (SQ) – for selected glazing and wind shields. 3. B Quality or Ordinary Quality (OQ) – for general purpose glazing and framing. 4. C Quality or Greenhouse Quality (GQ) – For green house glazing but varied suitably for doors and windows.
- 7. Glazing and energy conservation measures. In the late1980s Pilkington achieved its biggestadvance in floattechnology sinceits invention three decades earlier,when it announced success with continuous on-linecoatingto make low-emissivity glasses atup to 1km per hour. The Group now has a complementary suiteof low-E products,includingtheoff-linecoated thin silver-based product PilkingtonOptitherm™,and the on-linemanufactured Pilkington K Glass™ and Energy Advantage™. The on-lineproducts are based on a semi-conductingcoatingof tin oxide doped with fluorineatoms. The coating,0.3-0.4 micron thick, has the unusual property of transmittingalmostall visiblelight,whilerejectingheat waves (infrared) at room temperature. It is deposited in a few seconds by a chemical vapour deposition (CVD) process applied to the hot glass whileitmoves through the manufacturingprocess.The coatingis hard,coherent and adheres well to the glass duringcuttingand handling,becauseitis deposited at high temperature. A low-E coatingis normally used on the cavity-facingsurfaceof the inner pane of a double-glazingunit.Its job is significantly to reduce radiativeheatloss into the cavity and then to the outsideair. Floatglass itself strongly absorbsinfrared and warms up,but the low-E coatingradiates poorly into the cavity. Doped tin oxide films havelong been known in the industry but Pilkington research nowfocuses on fine-tuning their optical properties by better understandingof high-speed, atmospheric pressureCVD chemistry and of the interaction of n-type dopants such as fluorinewith the tin oxidelatticeatoms. also be used as a capillary blocker.