METALSMETALS The metals, which are used in construction, mainly divided into

two groups.

FERROUS METALS– Cast Iron– Wrought Iron– Steel

NONFERROUS METALS– Aluminium– Copper– Lead– Zinc– Tin

METALSMETALSIron is an ancient material known probably

since 3000 B.C. In the 19th century the industrial revolution

brought metals into wide use to make machinery.

Iron in both cast and wrought forms begun to be employed for bridge building, for columns in mill structures and then as a major structural material for the frames of train sheds, market halls and other utilitarian buildings.

Iron is one of the most abundant materials in the earth’s crust. About 5 % of it is iron.

It is a reasonably tough and silver – white looking metal. It is ductile (capable of being drawn out into very thin wires) and malleable ( capable of being hammered or rolled into shape).

But iron readily oxidizes (rust) when left exposed to air.

The differences in appearance, strength, brittleness, and workability of various irons depends to great extend on the percentage of carbon alloyed with the pure iron.

As steel was discovered, iron began to be replaced by stronger steel in building many types of large and tall buildings.

The high strength and moderate cost of steel made it an ideal material for railroad rails, engines and other machines and ship building.

Towards the end of the 19th century, it was recognised as the best available material for the structural frames of tall buildings.

Steel structural members are cut and drilled at the mill and assembled on site with rivets, welding, or bolts and nuts.

While steel will not burn, the heat of a fire can soften it enough to structural failure.

Therefore, in multi - story buildings steel is always fireproofed by covering it with masonry, concrete, or in modern practice, sprayed insulating material.

In addition to forming a cage like frame construction, steel can be used to make roof trusses to span wide openings.

It is also the material for other types of constructions, including domes, space frames, roof structures in which many small members create a grid using the rigidity of triangular forms to provide high strength with minimal material.

Steel is a key material for suspended structures using steel cable to support roofing as well as for suspension bridge carrying roadway over a wide open space.

 

Steel is currently used for the structure of variety of buildings, especially to form the roof structures of garages, shops, warehouses and factories.

In small houses, steel may be used in the form of single floor beams or tubular columns to support the beams.

MANUFACTURE OF STEELMANUFACTURE OF STEEL

Iron is normally extracted from iron ore with the help of coke ( coal) and a flux (limestone).

Coke is light, porous material made from coal.

To remove impurities from the iron ore crashed limestone combines with the impurities to form slag.

Slag is lighter than iron. It floats on top of the molten iron and is removed.

There are normally two different holes of outlet for either of these two different materials in the blast furnace, one for slag, normally at a higher level, and the other for molten iron, at the bottom.

The molten iron which is called pig iron, is removed from the furnace by allowing it to flow into large ladles.

In the next step, some contents of the molten metal is removed while certain other elements are added to it.

The sulphur and phosphorus contents must be lowered to an acceptable level. Meanwhile, carbon and other elements are added to it.

Most steel is made by adding scrap steel to the pig iron melt. In the USA 50 % of the raw material is made up of recycled, scrap iron.

The output of the furnace is teemed into ingot moulds.

Later, these ingots are held in soaking pits until they reach a uniform temperature.

When the iron ingot has reached the desired temperature, it is conveyed to the blooming mill.

The blooming mill is set of rollers made of steel, chilled to produce a hard exterior.

The product of blooming mill is usually a large steel slab, ranging from 15x15 cm or 29x39 cm.

The initial rolling operation reduces the size of the ingot so that the second set of rolls can give it a final shape.

Structural mill produces wide-flange structural shapes. It uses both horizontal and vertical rolls to produce desired shapes.

Cast IronCast IronCast iron is essentially an alloy of iron,

carbon, and silicon.It can contain 2 to 4% carbon.It is quite brittle and it has relatively low

tensile strength, so it is not used where high stresses or impact loads are found.

It is widely used to make castings and machinery parts, window frames, bath basins.

Wrought IronWrought Iron

The wrought iron of ancient times had some advantages.

It had less tendency to corrode (rust) and it had a fibrous quality that gave it a certain toughness.

During the production process most of the carbon are removed. It contains less carbon.

It is used for iron work such as railings for stairways and for the production of pipe and other products subject to deterioration by rusting.

SteelSteel

Steel is obtained from pig iron by reducing carbon and impurities in it.

Steel refers to iron alloys that contain less than 2% of carbon and also some manganese.

CLASSIFICATION OF STEELSCLASSIFICATION OF STEELS A- Carbon Steels:

This type of steels are usually classified according to their carbon content, as more carbon means more hardness for the steel. As the carbon content increases, the steel also becomes less ductile (elastic) and more brittle.

  Very mild carbon steel: (0.05 to 0.15% carbon)

Soft, very easy to work with and preferred for sheets, wire, rivet (perçin), pipe and fastenings.

  Mild structural Carbon Steel: ( 0.15 to 0.25%

carbon)Strong, ductile and used for buildings, bridges, boats and bailers (tanker).

Medium Carbon Steels: (0.25 to 0.35% carbon)Stronger and harder than mild structural grade. Used for machinery, ship building, and general structural purposes.

  Medium Hard: (0.35 to 0.65% carbon)

Used in locations subject to wear and abrasion.  Spring: (0.85 to 1.05% carbon)

Used for manufacturing spring.  Tool: (1.05 to 1.20% carbon)

The hardest and strongest of the carbon steels, used for tools and cutting edges.

B- Alloy Steels

An alloy steels is one in which certain alloying elements have been added to the molten mix in excess of those elements allowed in carbon steel. Alloying elements such as manganese, nickel, chromium, vanadium and copper are used to provide steel with extra properties that are unobtainable in carbon steels. For example, copper alloys have improved resistance to corrosion and are used for products that are subject to moisture. Chromium increases strength and acts as a hardener.

1. Weathering steels:These alloy steels offer corrosion resistance and strength up to 40 % higher than structural carbon steel. They also provide a protective oxide film that seals the surface against further corrosion. The protective oxide film gradually assumes a pleasing texture and darkness to a colour ranging from brown to warm purple.

2. Stainless steels:The corrosion resistance of iron is greatly improved when the quantities of chromium are increased. At 11.5 % there is sufficient chromium to form an inert film of chromic oxide over entire metal surface. This steel is considered stainless.

GALVANIZINGGALVANIZING

Steel sheets may be protected against rust and corrosion by a galvanized zinc coating.

Galvanizing serves as a double protection.

It forms a mechanical barrier against moisture and prevents oxidation or rusting of the steel base.

Hot dipping:Hot dipping: To coat steel with zinc, cleaned steel is immersed in a bath of molten zinc.

The zinc adheres to the base metal in a smooth, even cover, usually of crystalline appearance.

Galvanized sheet may be formed, rolled, shaped or assembled with little damage to the coating.

However, if edges are trimmed or welded, the area must be treated for protection.

ALUMINIUMALUMINIUM

The light weight and the resistance to rusting are the two main characteristics of aluminium. For these characteristics it is a popular material for many architectural details, such as store fronts, window frames, exterior wall cladding, partition wall finishing, exterior door sash board and suspended ceiling boards.

It can be made into continuous ribbons of varied form by the process of extrusion (squeezing through a die that determines cross – sectional shape). Detail elements such as handrails and hardware items are often made of aluminium. 

Surfaces will develop a grey oxide surface unless finished by anodising (a form of plating) or with other coating. Anodising can produce a colour tone while preserving the metallic glitter of aluminium surfaces.

COPPERThe special orange metallic colour of

cooper is well known for its decorative possibilities.

Copper must be protected with a lacquer coating if it is not to turn a green oxide colour, frequently seen as the tone of roofing.

Interior uses in hoods over fireplaces, stoves or bar counters are not uncommon.

ZINCZINC

Zinc is lighter and stiffer then lead but is affected by acids and has a high coefficient of expansion.

Rolled sheet zinc is sometimes used for roofing and flashing, but zinc has a much wider application as a coating for steel roofing sheets.

LEADLEAD

  A principle source of lead is ore containing galena, lead sulfide. Lead is a soft, plastic malleable metal used primarily in sheet form. It is used as flashing in curtain wall panels, and as roofing material. Lead is used to cover sheets of steel and copper. It is highly resistant to acids. 

 

TINTIN

Because of its resistance to corrosion, tin is used largely to coat iron and steel roofing sheets.