Lesson 10

Read the text: The crucible furnace. The puddling furnace

Crucible furnace

The crucible way is the oldest one used for making high carbon steel and special steels. High carbon steel is made by melting scrap steel in a crucible about 20 inches high and one foot in diameter, made of graphite which can stand great heat. The percentage of carbon the scrap steel contains must be known. The amount of carbon wanted is then placed on top of the steel. A cover is placed over the top and a number of these crucibles are placed in a hot furnace. The melted iron mixes with the carbon, thus making steel containing any percentage of carbon necessary. The melted steel is then poured into forms. Special steels are made the same way, but some additional materials are also put in the crucible. Crucible steel is a higher grade, stronger and more expensive steel than either the Bessemer or open-hearth ones. Crucible steel is used for pens, knives and some machine parts where very high hardness and strength are needed.

Crucible process

High grade tool steels and some alloy steels are still made by the crucible process, although the electric furnace is now capable of making steel equal in quality to crucible steel. In the crucible process, wrought iron, or good scrap, together with a small amount of high purity pig-iron, ferro-manganese, the necessary alloying metals, and slagging materials are placed in a day or clay-graphite crucible, covered with an old crucible bottom and melted in a gas-or-coke-fired furnace. After the charge is entirely molten, with sufficient time allowed for the gases and impurities to rise to the surface, the crucible is withdrawn, the slag removed with a cold iron bar, and the resulting fifty or one hundred pounds of steel poured into a small ingot which is subsequently forged to the desired shape. The crucible process differs from other steel-making in that little or no refining is included; the purity of the metal depends almost entirely upon the purity of the materials charged. The chief advantage of the process is that it removes most of the impurities, including oxygen and entangled particles.

The Puddling Furnace

Puddling furnace is the simplest type of furnace. It is used to make wrought, iron. It has the fire at one end and is separated from the hearth by a wall. When the flame passes over the hearth its heat is thrown back from the roof of the furnace on to the metal, which is placed on the hearth. Through, an opening in the side wall the puddler stirs the metal with a long rake called a rabble. In this way impurities and carbon are burned away. And the metal is little by little made into a paste that looks like boiled rice. From time to time flux-is thrown in to collect ash and impurities. The puddler collects the granules into a ball. He rolls it back and forth over the hearth. And finally he takes it out at exactly the right moment. This ball is then passed through squeezers; or it is worked under the hammer into bars.

In 1783 Peter Onion of Wales, patented a puddling furnace. A few years later Henry Cort greatly improved it. The puddling furnace was of the type we call the reverberatory furnace. It is a furnace in which the flame passes over the charge but does not come in contact with it. The charge in the reverberatory furnace is placed on a hearth. The heat comes from the fire at one end of the furnace. The flame is directed against the arched roof over the hearth. When the flame passes along the arch its heat is thrown downward. It melts out the iron as it falls on it and burns away the impurities. Along the sides of the furnace are openings through which the molten metal is stirred with rabbles. The finished iron is removed in balls weighing about one hundred pounds apiece.

1. Match the left part with the right:

1. The metal is little by little made into a paste	a) that looks like boiled rice.
2. The puddler stirs	b) then placed on top of the steel.
3. The amount of carbon wanted is	c) than either the Bessemer or open hearth ones.
4. Crucible steel is a higher grade, stronger and more expensive steel	d) the metal with a long rake called a rabble.

2. Complete the sentences with the suggested words: metal, separated, passes, furnace, wrought

Puddling furnace is the simplest type of _______. It is used to make _______, iron. It has the fire at one end and is _______ from the hearth by a wall. When the flame _______ over the hearth its heat is thrown back from the roof of the furnace on to the _______, which is placed on the hearth.