1. Read the text below, entitle it, desipher the abbreviations and speak about d. Mendeleyev and his periodical table.

Valency stands for "strength of joining" (combining capacity) that divides the elements into classes; the reason for the varying weights of the same element in different compounds.

Sometimes more than one set of atoms go to make up a molecule, e. g. methane: hydrogen is valency 1, carbon is valency 4, so the formula must be CH₄; four atoms of H to one of C. And the recipe will be:

Hydrogen Carbon CH4 Methane

(at. wt. 4x1) + (at. wt. 12x1) →

4 parts by weight 12 parts by weight 16 parts by weight

The molecular weight of hydrogen fluoride is 40, yet the atomic

weight of hydrogen is 1 and of fluorine 19, so HF would equal 20. This means the formula must be written (HF) or H F — there are two sets of atoms in the molecule.

2. Fill in the gaps with the introductory and connective words and examplify the information.

Today plastics are referred ____ materials of great importance, for no

other group of materials is able to offer ____ a unique combination ____ properties. By alloying, modifying ____ well as ____ changing the structure

of polymers, chemistsand technologists are able toproduce different kinds of plastics. Plastics can be mass produced ____ a lower cost compared with metal parts. ____ plastics do not possess the high strength of steel they are suitable ____ many purposes. Plastics can be reinforced ____ incorporating fibrous materials such ____ glass fiber, nylon and, at last, pure carbon fibers. The carbonplastics are known to open up vast new possibilities ____ the engineering field. Some plastics are able to withstand much higher temperature than metals. There exist plastics ____ have high mechanical syrength and are able to withstand the extremes of pressures. It gives them a great advantage ____ metals.

3. Arrange a scientific conference on the following topics. Use the gerunds, as well as the introductory and connective words.

1. The composition and properties of metals. 2. Alloys and metalloids.

3. Metals application. 4. Metals substitutes.

Text 3

1. Scan the text for metal-forming operations. Read and

translate the text.

Metal Forming

The formability of metal is based on atomic structure. In each

crystal or grain of the metal are slip planes that allow relative movement. As slip is induced by outside forces, the metal will yield because of the sliding action. Forming can be devided into forging, pressing and bending, drawing, extruding, casting, powder metallurgy,

and spinning.

Shearing. Shearing produces separation in the metal by localized

forces applied in opposite directions that are beyond the tensile strength of the material. One of the most common shearing operations is done by stamping dies.

Pressing. Pressing usually refers to the press-working of metals between dies in a press. The most common method is that of forming metal between matched dies. The part may first be blanked out and then formed, or the part may be formed from a larger sheet and then cut to exact size by the use of trimming dies. Embossing is a process of deforming metal between matched dies without changing its thickness. Common examples of this process are decorative brass or copper plates and medallions.Coining is a pressworking process in which the thickness of the metal is changed. The most common example of this process is in the production of coins. The metal must be made to flow into the die to produce different designs on each side of the metal. High unit forces are required, three to five times the compressive strength of the metal.

Forging. Forging is the localized plastic work­ing of metal by means of compressive forces ap­plied by manual or power hammers, presses, or special forging machines. The process may be done hot or cold; however, the hot process is im­plied because cold forging has other names such as cold heading or upsetting. Forging produces very strong products.

Extrusion. Metal is extruded by placing it in a chamber and forcing it through a die. This method is used in making long bars of many

familiar shapes such as tubes, aluminium door and window frames.