Cement and Glass Industries Questions and Answers

Answer: C

The first two are correct. The third is inverted, since a reducing atmosphere is essential to prevent tin oxide forming and marking the glass surface. The ribbon is annealed in a lehr before cutting. Tin oxide on the bath would mark the lower face.

Answer: D

Correct answer: remove internal stress by slow cooling

A formed article cools unevenly, so the outside solidifies while the inside is still contracting, leaving locked-in stress that can crack the piece spontaneously or on the slightest scratch. Annealing reheats it just below the softening point and cools it slowly through the stress range, letting the glass relax. It is the opposite of toughening, which deliberately imposes a stress pattern.

Answer: A

Once tempered, any cut releases the stored stress and the whole sheet shatters, so all cutting and drilling must be done first. The other three are precisely what makes it a safety glass. Toughened panes are sized before they are treated.

Answer: B

The compressive surface layer stores energy, and breaking through it destroys the whole pane. This is why every hole and edge must be finished before the sheet goes into the tempering furnace. Any later cut destroys the whole pane at once.

Answer: C

Both are true and the reason gives the mechanism: glass fails from surface flaws in tension, and putting the surface into compression means the flaws are held closed until the applied load is large. Annealed glass has no such protection at its surface.

Answer: D

Correct answer: a much lower thermal expansion

Boric oxide substituted for much of the soda gives an expansion coefficient about a third that of soda lime glass, so a borosilicate article develops far smaller stresses when heated or cooled unevenly and resists thermal shock. That is why it is used for laboratory ware and for cookware. It is also less dense and has a *higher* softening temperature, not a lower one.

Answer: A

Correct answer: the rotary kiln for clinker

The rotary kiln belongs to cement manufacture, not to glass. The other three are all glass forming processes at very different scales: the float process for flat glass, blow and blow for containers, and drawing through a die for optical fibre. The two industries share raw materials and high-temperature furnaces, which is why they are treated together, but their forming operations have nothing in common.

Answer: B

Correct answer: press and blow, or blow and blow

A gob of molten glass is delivered to a blank mould and formed into a parison - by a plunger in press and blow, or by air in blow and blow - and the parison is then transferred to the finish mould and blown to shape. Press and blow gives better wall thickness control and so lighter bottles; blow and blow is used for narrow necks.

Answer: C

Correct answer: 1 and 2 only

Statements 1 and 2 describe the two products correctly: continuous filament is drawn through platinum bushings and wound, while insulation wool is made by flinging or blowing the melt into short fibres. Statement 3 is wrong - fibres are so fine that they cool essentially instantly and uniformly, so no stress gradient develops and no lehr is needed. Annealing is for articles thick enough to cool unevenly.

Answer: D

Seventy-two divided by fourteen is a little over five. The ratio is worth remembering because it fixes the melting behaviour of the batch more than any single component does. Real batches also carry alumina and magnesia.