V. Write a short summary of the text. IV. Compare different

IV. Compare different

I. Read the sentences and say if they are true or false. If they are false, correct them.

II. Find the equivalents of the following terms:

a)

b)

c)

d)

e)

f)

g)

h)

i)

j)

k)

l)

m)

n)

o)

p)

q)

r)

s)

t)

III. Fill the gaps using the following words:

Text 3 The paper machine

A paper machine has to produce from this very dilute aqueous fibrous suspension a uniform 'mat' of fibres exhibiting uniform dimensional, physical and visual characteristics. The magnitude of this task, can be illustrated by considering a fibre 2-3mm (0 • 787 - 0 • 1181 in) in length and 40 microns wide in a 0 • 3 per cent aqueous suspension being presented to a machine of up to 6 metres (approximately 20 feet) in width and weighing thousands of tons and producing paper at a speed of 1,000 metres (approxi­mately 3,280ft) per minute,

The pulp is fed from a 'head box' through a slice aperture on to a continuous moving wire (a wire mesh), at what is called 'the wet end' of the paper making machine. Slice setting, consistency of stock and the rate of flow of the furnish on to the wire, controls the 'substance' (unit weight) of the paper. The wire may vibrate from side to side in order to help maintain random fibre orientation. Water drains through the mesh, aided by foils and vacuum boxes beneath the wire. Sheet consolidation and watermarking may be achieved by the use of a 'dandy roll'. A dandy is a mesh covered roll, which rotates on the partially formed paper sheet. It carries wire marks called 'electros' and/or 'embossings' which compress the sheet and produce areas of light and shade due to changes in sheet density. These watermarks can be used to identify branded papers or be used as security features.

During the Fourdrinier manufacturing process, one side of the sheet is in contact with the wire. As a result a very fine impression of this wire may be detectable on this side of the final product — it is called 'the wire side of the sheet' and its characteristics may be slightly different to those of the top side, particularly in relation to print quality. Twin wire papers overcome this characteristic by effectively laminating two sheets together immediately after the sheet formation stage to leave the smoother top sides (the 'felt') available for printing.

At the end of the wire section, the fibrous web is still 92/93 per cent water, but it has matted together sufficiently for it to 'jump' into the press section where it is transported by felt through a series of granite and rubber composition presses, The press section removes more water by its 'mangle action' and also imparts polish to the wet sheet.

The remaining water is removed by passing the paper around several large, metal drying cylinders heated by super-heated steam. Before the paper making process is complete, however, the web may pass through a size press and/or coating station in order to further control or alter the final characteristics of the sheet. Size, m the form of starch solution, gelatin or other surface sealants may be applied, usually by roll coating, to both sides of the sheet, the added weight being only a few grammes per square metre (fractions of an ounce per ten square feet). This application supplements any earlier 'internal sizing' and helps to seal off loose fibres in the surface, controls ink receptivity, any tendency to feather at the touch of pen and ink, or adds a specific characteristic to the sheet such as colour, slip, release properties, moisture/vapour permeability or security features.

After further drying by a second group of cylinders the paper may be 'calendered' on the machine. Calendering imparts a smooth finish by passing the paper through a vertical stack of polished steel rolls, the temperatures and pressure of which may be varied. Finally, the paper is wound to form a very large 'jumbo' reel, which on wide modern machines may weigh up to 10 tonnes (11 short tons) or more.

Exercises :

Дата добавления: 2014-12-23