Non Ferrous Metals & It’s Alloys

Non-ferrous metals are those which do not contain iron as the base material. The most commonly used non-ferrous metals in wokshop are aluminium, copper, lead, tin, nickel and zinc. They also form very useful alloys amongst themselves, known as non-ferrous alloys, which possess very significant characteristics like high resistance to corrosion, conductivity of heat and electricity, lightness in weight and of being non-magnetic. These properties enable these metals and alloys to be preferred over iron, steel and their alloys where these characteristics stand as the primary considerations. Non- ferrous metals and alloys can also be cast and machined without any appreciable amount of difficulty, but they are more expensive as compared to the ferrous products. However, apart from the cost factor, there are some inherent disadvantages associated with non-ferrous metals, when compared with ferrous metals, such as high shrinkage, hot shortness and lower strength at elevated temperatures.

Use of non-ferrous metals in engineering offers the following advantages :

1. Very good electrical and magnetic properties.

2. Good castability.

3. Good formability

4. Ability to be easily cold worked.

5. High resistance to corrosion.

6. Attractive appearance.

7. Lower density.

Aluminium

Aluminium ore is found as a hydrated aluminium oxide, called bauxite. The impurities present in it are oxide of iron, silicon and titanium. The first process, therefore, is to separate aluminium oxide from these impurities. For this purpose, bauxite is fused in an electric furnace and carbon is added to reduce the impurities, which form a sludge and can be removed. As a result of this refining, pure aluminium oxide is separated from the impurities. Then an electrolytic bath is used to reduce aluminium from its oxide. As the electrolytic process proceeds the oxygen escapes through the bath and molten aluminium collects at the bottom (cathode), from where it is periodically tapped off. This mineral is mainly available in our country in Bihar, Maharashtra, Madhya Pradesh, Karnataka and Tamil Nadu.

Properties and uses

1. High electrical conductivity. Used for heavy conductors and busbar work.

2. High heat conductivity. Used in various domestic tensile and other heat conducting appliances.

3. Good resistance to corrosion. Used in manufacture of containers for chemical industry and window frames etc.

4. It can be readily worked, extruded, rolled, drawn and forged.

5. It has high ductility and is extremely light in weight. Widely used in aircraft industry.

6. Its corrosion resistance can be considerably increased by anodising.

7. It becomes hard by cold working and ,therefore, needs frequent annealing.

 8. Its low tensile strength can be sufficient improved by adding 3 to 4 percent copper.

Copper

It is not available in pure form under the earth. It is extracted from its ores through a series of processes. A couple of locations where copper ores are found in India are Khetri in Rajasthan and Ghatsila in Bihar. Copper pyrites are the main ores used for extracting copper.

The copper ore is first roasted to drive out water, CO2 and sulphur. It is followed by melting in a reverberatory furnace of the type used for wrought iron . Silica is added to the charge to form slag with impurities like iron and alumina, etc. The molten metal is tapped and transferred to a converter where air is blown through it to burn the impurities. This results in the production of a crude form of copper, known as blister copper, containing 68% purity. Final refining is done by an electrolytic process, pure copper depositing on the cathode. This gives a highly pure (99.9%) copper which is remelted and cast into suitable shapes.

Properties and uses

1. High electrical conductivity. Used as electrical conductor in various shapes and forms viz., sheet and contacts etc.

2. High heat conductivity. Used in heat exchangers and heating vessels and appliances.

3. Good corrosion resistance. Used for providing base coating on steel prior to nickel and chromium plating.

4. High ductility. Can be easily cold worked, ruled, drawn and spun. Loses ductility in cold working, requiring annealing.5. Light in weight. Used in various appliances where light weight with good corrosion resistance is desired.

Magnesium

Principal sources for obtaining magnesium are natural salt brines, sea water, water liquors obtained from potash industry and ores. The principal ores are magnesite, dolomite and carnallite. Various processes have been developed for its extraction, but the most popular and widely used one is the electrolytic process. Properties and uses

1. It is the lightest of all metals, weighing about two-third of aluminium.

2. It may be sand, gravity and pressure die-cast.

3. Its castings are pressure tight and obtain good surface finish. A few examples of magnesium castings include motor car gear box differential housing and portable tools.

4. It may be easily formed, spun, drawn, forged and machined with high accuracy.

5. Additions of 10% aluminium and small amounts of zinc and manganese improve its strength and casting characteristics.

6. Additions of 2% Mn helps in its easy forming into plates and sheets and extrusion work.

7. In finely divided form it is likely to burn, and adequate fire protection measures should be strictly observed.

Zinc

The zinc ore is first concentrated through a suitable process. This concentrate is fed into a retort with a suitable amount of carbonaceous material (say coal). Several retorts are housed in one furnace and their temperature raised to 11000 C. Zinc emerges as vapor and is passed through a condenser, where it is collected as a liquid. The impurities are given out as gases and burn at the mouth of the condenser. By rapid cooling the zinc vapour may be quickly converted into powered zinc.

Properties and uses

1. High corrosion resistance. Widely used as protective coating on iron and steel. It may be coated either by dip galvanising, electroplating or sheradising. The coating can also be provided through painting or hot spraying.

2. Low melting point and high fluidity. Make it the most suitable metal for pressure die-casting, generally in the alloy form.

Lead

Lead ores are generally found as oxides or sulphides. Other impurities present in the ores are iron, copper and zinc etc. The prepared ore concentrate, together with the flux (lime and silica), is fed into a small blast furnace where the temperature is raised to about 10100 C. The lead is melted and a liquid slag formed of the impurities. Both slag and molten lead are tapped at intervals. Further refining is carried out in a reverberatory furnace, where an oxidising atmosphere is maintained to burn out the impurities.

Properties and uses

1. Good corrosion resistance. Used for water pipes and roof protection.

2. Good resistance to chemical action. Used for acid baths and containers in chemical industry.

3. It is soft, heavy and malleable, can be easily worked and shaped.

4. It is used as an alloying element in making soft solders and plumber’s solders.

5. It is also alloyed with brass and steel to impart them free cutting properties.

Tin

The most prominent tin ore is cassiterite. It also carries compounds of copper, iron, lead, antimony, bismuth and zinc etc. As usual an ore concentrate is prepared. This concentrate is roasted to drive off excess arsenic and sulphur. The roasted ore is transferred to a reverberatory furnace, where it is heated. Anthracite is added to the charge which reacts chemically to separate tin, the latter sinking to the bottom of the furnace. From there it is tapped at intervals. This crude tin is remelted and refined further. For obtaining high purity tin the electro-deposition method is used.

Properties and uses

1. Good resistance to acid corrosion Used as coating on steel containers for food.

2. It is soft, has good plasticity and can be easily worked.

3. It can be easily rolled into thin foils, but cannot be drawn due to low strength.

 4. It is used as an alloying element in soft solders, bronzes bearing metals.

Nickel

Its extraction process consists of first roasting the ore, followed by smelting in a small blast furnace. Limenstone and quartz are added as flux. They form slag with impurities. Coke is used as fuel. Crude molten nickel is tapped off periodically from the bottom of the furnace. This crude metal is further refined in a bessemer converter followed by treating with sulphuric acid to extract pure nickel. Copper is separated as copper sulphate.

Properties and uses

1. It has a good resistance to both acid and alkali corrosion. It is, therefore, widely used in food processing equipment.

2. It has high tensile strength and can be easily worked cold and hot.

3. It is plated on steel to provide a corrosion-resistance surface.

4. It is an important alloying element with steel. Its higher proportions are advantageously used in the production of stainless steel like monel and inconel.