Vertical continuous casting

Steels are commonly cast ……(1) vertical continuous casting machines. Molten metal is continuously supplied …….(2) the ladle …..(3) the intermediate ladle (tundish) …..(4) which it is continuously poured ……(5) the mold …..(6) a controllable rate keeping the melt level ……(7) a constant position. The water-cooled copper mold (primary cooling zone) extracts the heat of the metal causing its solidification. The mold oscillates in order to prevent sticking ……(8) the casting. When the casting goes out from the mold it is cooled …..(9) the secondary cooling zone ……(10) water (or water with air) sprayed ……(11) the casting surface. Most of vertical continuous casting machines are equipped …….(12) strand guide units bending the casting and changing its configuration ……(13) vertical ….(14) horizontal. The casting is continuously extracted …….(15) the mold by the withdrawal unit followed …….(16) a cut-off unit. The casting process begins with inserting a dummy (primary) bar ……(17) the mold. Then a molten metal is poured …..(18) the mold where it solidifies and grips …..(19) the end of the dummy bar. The dummy bar is disconnected …..(20) the casting after passing the withdrawal unit. Direct Chill (DC) casting method is used for vertical semi-continuous casting of non-ferrous metals (Aluminum alloys, Copper alloys, Magnesium alloys).

8. Read the text and find English equivalents to the following Ukrainian words and word-combinations: розчинятися, розплавлений метал, погіршувати, щільність, рознімна модель, верхня опока, нижня опока, ливарний стрижень, лінія рознімання, загострювати, обтиснення, під тиском, ківш, литник, газовий різак, стрічкова пилка, відрізний різець, кувалда (ковальский молот), змінювати, охолодження, гаряча штамповка, зварювання, прилипати, процес дуття, дробоструминний пристрій, відбивність, дробоструминне оброблення (очищення), піскоструминне оброблення (очищення), дробострумінне зміцнення, шліфування.

Casting processes

Degassing

In the case of aluminium alloys, a degassing step is usually necessary to reduce the amount of hydrogen dissolved in the liquid metal. If the hydrogen concentration in the melt is too high, the resulting casting will be porous as the hydrogen comes out of solution as the aluminium cools and solidifies. Porosity often seriously deteriorates the mechanical properties of the metal.

An efficient way of removing hydrogen from the melt is to bubble argon or nitrogen through the melt. To do that, several different types of equipment are used by foundries. When the bubbles go up in the melt, they catch the dissolved hydrogen and bring it to the top surface. There are various types of equipment which measure the amount of hydrogen present in it. Alternatively, the density of the aluminium sample is calculated to check amount of hydrogen dissolved in it.

Mold making

In the casting process a pattern is made in the shape of the desired part. This pattern is made out of wax, wood, plastic or metal. Simple designs can be made in a single piece or solid pattern. More complex designs are made in two parts, called split patterns. A split pattern has a top or upper section, called a cope, and a bottom or lower section called a drag. Both solid and split patterns can have cores inserted to complete the final part shape. Cores are used to create hollow areas in the mold that would otherwise be impossible to achieve. Where the cope and drag separates is called the parting line.

When making a pattern it is best to taper the edges so that the pattern can be removed without breaking the mold. This is called draft. The opposite of draft is an undercut where there is part of the pattern under the sand making it impossible to remove the pattern without damaging the mold. The molds are constructed by several different processes dependent upon the type of foundry, metal to be poured, quantity of parts to be produced, size of the casting and complexity of the casting.

Pouring

In a foundry, molten metal is poured into molds. Pouring can be accomplished with gravity, or it may be assisted with a vacuum or pressurized gas. Many modern foundries use robots or automatic pouring machines for pouring molten metal. Traditionally, molds were poured by hand using ladles.

Shakeout

The solidified metal component is then removed from its mold. Where the mold is sand based, this can be done by shaking or tumbling. This frees the casting from the sand, which is still attached to the metal runners and gates – which are the channels through which the molten metal traveled to reach the component itself.

Degating

Degating is the removal of the heads, runners, gates, and risers from the casting. Runners, gates, and risers may be removed using cutting torches, bandsaws or ceramic cutoff blades. For some metal types, and with some gating system designs, the sprue, runners and gates can be removed by breaking them away from the casting with a sledge hammer or specially designed knockout machinery. Risers must usually be removed using a cutting method but some newer methods of riser removal use knockoff machinery with special designs incorporated into the riser neck geometry that allow the riser to break off at the right place.

Heat treating

Heat treating is a group of industrial and metalworking processes used to alter the physical, and sometimes chemical, properties of a material. The most common application is metallurgical. Heat treatments are also used in the manufacture of many other materials, such as glass. Heat treatment involves the use of heating or chilling, normally to extreme temperatures, to achieve a desired result such as hardening or softening of a material. It is noteworthy that while the term heat treatment applies only to processes where the heating and cooling are done for the specific purpose of altering properties intentionally, heating and cooling often occur incidentally during other manufacturing processes such as hot forming or welding.

Surface cleaning

After degating and heat treating, sand or other molding media may adhere to the casting. To remove this the surface is cleaned using a blasting process. This means a granular media will be propelled against the surface of the casting to mechanically knock away the adhering sand. The media may be blown with compressed air, or may be hurled using a shot wheel. The media strikes the casting surface at high velocity to dislodge the molding media (for example, sand, slag) from the casting surface. Numerous materials may be used as media, including steel, iron, other metal alloys, aluminium oxides, glass beads, walnut shells, baking powder among others. The blasting media is selected to develop the color and reflectance of the cast surface. Terms used to describe this process include cleaning, bead blasting, and sand blasting. Shot peening may be used to further work-harden and finish the surface.

Finishing

The final step in the process usually involves grinding, sanding, or machining the component in order to achieve the desired dimensional accuracies, physical shape and surface finish. Removing the remaining gate material is usually done using a grinder or sanding. These processes are used because their material removal rates are slow enough to control the amount of material. These steps are done prior to any final machining.