Finishing Operations on Glass Asst. Lect. Shireen Hasan LECTURE 8 Finishing Operations on Glass By Asst. Lect. Shireen Hasan

Finishing Operations on Glass Operations include grinding, polishing, and cutting. Glass sheets often must be ground and polished to remove surface defects and scratch marks and to make opposite sides parallel. In pressing and blowing with split dies, polishing is often used to remove seam marks from the product

Other Finishing Operations Decorative and surface processes performed on certain glassware products include: 1- Mechanical cutting and polishing operations; and sandblasting 2- Chemical etching (with hydrofluoric acid, often in combination with other chemicals) 3- Coating (e.g., coating of plate glass with aluminum or silver to produce mirrors). Glass containers typically receive two surface coatings, one at the hot end, just before annealing and one at the cold end just after annealing.

At the hot end a very thin layer of tin oxide is applied either using a safe organic compound or inorganic stannic chloride. At the cold end a layer of typically, polyethylene wax, is applied via a water based emulsion. This makes the glass slippery, protecting it from scratching and stopping containers from sticking together when they are moved on a conveyor. 4- Secondary processing, Sometimes container factories will offer services such as labelling. Several labelling technologies are available. This is screen-printing of the decoration onto the container with a vitreous enamel paint, which is then baked on. An example of this is the original Coca-Cola bottle.

8- QUALITY CONTROL of Glass Glass containers are 100% inspected; automatic machines, or sometimes persons, inspect every container for a variety of faults. During the process of melting and shaping of the glass (preparation of mixture, transportation, hot molding), different faults can occur in the glass. Quality of the glass is defined with maximum allowed number of faults and their size. Possible faults: stones, bubbles, vind.

Tones Hard bright dots inside the product, caused by : irregularities during the preparation of the mixture (white dots), crystallization during the melting process, disintegration of fireproof materials from the furnace structure (white, brown, red dots), fall of the agitator shaft into the workspace (dark dots). All these faults occur locally on some products. In case of an irregularly melted glass mixture, faults can be noticed on all workspaces and products, accompanied with small bubbles and vind.

Bubbles Bubbles can be formed as a result of bad melting of the mixture- If they are result of bad melting, bubbles occur on all products. They are of small in size and spread throughout whole product. They can also be the result of the reboil process. Bubbles are considered as a fault, when their size is over 1mm and they can be found only on one part of the product.

Vind Is a line or an area on the product with different angles of refraction. Vind faults are caused by: ● a new furnace- reaction between glass and fireproof materials of the furnace (can happen with old furnaces also), ● Fault during mixture preparation, ● Inadequate temperature regime of melting,

Stones Foreign inclusions called stones which are pieces of the refractory brick lining of the melting furnace that break off and fall into the pool of molten glass, or more commonly oversized silica granules (sand) that have failed to melt and which subsequently are included in the final product.

9- Packaging and Marketing Glass containers are packaged in various ways for marketing. Popular in Europe are bulk pallets with between 1000 and 4000 containers each. This is carried out by automatic machines (palletisers) which arrange and stack containers separated by layer sheets. Other possibilities include boxes and even hand-sewn sacks.

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