1 Define the main idea of the text.

a) Sand casting is more expensive than die and investment casting.

b) Sand casting is the most expensive of all the casting processes.

c) Sand casting is the cheapest of all the casting processes.

d) Sand casting is the most important of all the casting processes.

2 Answer the question:

Why is it necessary to taper the edges when making a pattern in the sand casting process?

a) The pattern is made in the shape of the desired part.

b) The pattern can be removed without breaking the mold.

c) The pattern can have cores inserted.

d) The pattern is made larger than the cast.

BUSINESS ACTIVITY

Complete the dialogue.

Manager: “Your promotion has been declined”.

Employee: “_______________”.

Don’t say that!

But I work so hard.

You must be kidding me.

Sorry to hear that, but thank you for the information.

Text 3 The Pressure Die Casting Process

Pressure die casting with zinc-based alloys is one of the most efficient and versatile high-production methods that can be used for the manufacture of strong, accurate, complex and intricately shaped metal components. The process is carried out in an automatic machine suitable to withstand the high pressure under which molten metal is pushed by a hydraulically actuated plunger into a two-piece steel die containing one or more cavities, each an exact inverse replica of the part or parts to be produced.

Because of the quick chill and rapid freezing that takes place when molten metal comes in contact with the relatively cool steel die and because of the fine metallurgical grain structure that results, the mechanical properties of pressure die castings are generally superior to castings produced by other methods. Zinc pressure die castings, for example, are stronger than sand cast 356-T6 aluminum, SAE 40 bronze and class 30 cast iron. Also, pressure die cast components produced using the ZA alloys are stronger than pressure die cast aluminum alloy 380.

1 Complete the sentence according to the text.

Pressure die casting is carried out …

a) under the high pressure.

b) in an automatic machine.

c) by other methods.

d) using the ZA alloys.

2 Answer the question:

What is the reason of metal rapid freezing?

a) It is pushed by a hydraulically actuated plunger.

b) It comes in contact with the relatively cool steel die.

c) It has the fine metallurgical grain structure.

d) It is strong, accurate and complex.

BUSINESS ACTIVITY

Put the parts of the business letter in the correct order.

a) Dear Prof. Green:

b) Yours sincerely,

c) RockwayApartments

Northtown, MI 22221

d) Thank you for your invitation to the conference. We appreciate your care and

consideration.

e) Dept. of English

Idaho State College

Boise, ID 99999

f) A. Springer

g) 10 April 2013

Text 4 Casting and Titanium Alloys

The pouring of molten metal into a mold in which solidification takes place is termed casting. Although the term casting has been applied to ingot production, and certain components such as welds have a cast structure, it is intended to deal with the casting of finished or semi-finished products.

The difficulties of casting titanium stem from inherent characteristics, such as its high chemical reactivity, and the flow properties of the molten metal. Conventional methods which employ such refractoriness as silica, magnesia, or alumina and which have been successfully applied to other metals are not practical with titanium.

Since titanium will likewise attack the furnace crucible material during melting of the metal prior to casting, it has been found necessary to prevent the impingement of the molten metal on the crucible wall. This has been accomplished by using skull melting techniques.

The method requires the maintenance of a solid layer of titanium metal between the crucible wall and the molten metal. This is accomplished by directing the arc at the center of the charge, and the careful maintenance of a temperature gradient between the molten metal and the wall.

As in ingot production, the molten metal and, in turn, the hot casting are susceptible to atmospheric contamination. To prevent this contamination an argon atmosphere is sustained in the crucible and the mold. To further eliminate the contamination, the furnace is designed to allow tapping of the melt at the bottom or side, and the sealing of the mold to the furnace over these vents. Thus, the pouring of the casting is also accomplished under an inert atmosphere.

This method of casting requires some skill in its operation. Not only does the skull technique require careful control in the melting, but ventilation must also be supplied simultaneously with pouring to allow escape of the gases present to minimize gas porosity. At present it is the only satisfactory technique for casting titanium.

A second difficulty, one which is peculiar to titanium, is in the maintenance of good flow over severe changes of dimension or direction within the mold. This requires, in many instances, the redesign of the mold or the cast component. Fillets or tapers, where dimensional or directional changes occur, have proved quite satisfactory in minimizing the difficulty.

Shell casting. Shell casting or shell molding utilizes the bonding of a refractory with a thermosetting plastic resin to form the mold. Stepwise, the procedure consists of forming two metal cavities, usually from aluminum, which are patterns of the part to be cast. One pattern coincides with one half of the part and the other pattern with the other half. These patterns, of course, must contain the necessary gates and risers.

One of the patterns is heated and clamped on top of a dump box or hopper, which contains the resin-refractory mixture. The refractory material can be cither graphite or zirconium, and the resin any one of several commercial phenolic casting materials. The mesh size of the refractory is variable, as is the ratio of resin to refractory, and is experimentally determined for the shape being cast.

In general the amount of resin employed should be slightly higher than that employed in the shell castings of iron alloys. When the pattern has been securely fastened lo the dump box, the hopper and pattern arc inverted for 30 to 60 seconds, after which time they are returned to their original position. The pattern which is coated with the resin-refractory mixture is removed and placed in a furnace for curing.

The curing time and temperature are dependent on the resin employed. After curing, the mold is stripped from the pattern. The other half of the mold is prepared in a similar manner using the second pattern.

Investment casting. Investment casting, also termed precision casting or lost wax casting, like shell molding is employed to cast small parts. This method is not as adaptable to assembly line speed as shell molding, but it is capable of producing the intricate shapes not possible with the shell technique.

To prepare an investment mold, a pattern with the necessary gates and risers is formed in the image of the component to be cast. The material used to form the pattern should be something which can be melted, volatilized, or burned off, such as wax or plastic. This pattern is coated with slurry consisting of the refractory and a binding agent. For titanium, zirconium is used as the refractory, and a silicate or zirconium compound such as zirconium nitrate serves as the binder.

The coated pattern is further built up by backing with coarse-mesh zirconium and the investment is then air-dried. The air-dried investment is recoated with slurry of coarse zirconium, the binder, and a hardening agent. The investment is again air-dried, after which it is heated to remove the pattern. The mold is fired at 1500 to 1600°F (810 to 870°C) for one to two hours and air-cooled.

Some work has also been carried out with graphite as the refractory. This method omits the backing and uses lower firing temperatures. Results are inconclusive, and the superiority or inferiority of graphite to zirconium is not readily evident.

In either case the mold is sealed to the furnace and the casting poured and allowed to solidify and cool. As in shell molding, the mold is expendable and is stripped from the Casting, after which the necessary machine work is performed.

Titanium end products have been produced by this method and have been found to possess good mechanical properties.