XI Международная студенческая научная конференция Студенческий научный форум - 2019

Modern molding machines successfully perform a consider­able amount of work that was done by hand.

Those molding machines that are used primarily for pack­ing sand in flasks can be classified as squeezer machines, jar (or jolt) machines, jolt squeezers, and sand slingers. Other types of machines employed in molding are pattern-draw ma­chines (stripping-plate machines and stripper machines) roll­over machines, combination machines, vibrators, and others.

The squeezer machine rams sand into the flask, which is placed between the machine table and an overhead plate, thus obtaining uniform density of the sand contained in the flask.

The jar or jolt machine consists of a rugged base cylinder and piston which is attached to the machine table. The table is lifted by air pressure directed against the piston from below, and is then permitted to drop. This action produces a jar which rams the molding sand evenly in the flask. The operation is very rapid, and some of the jolt machines used for small flasks give more than a hundred blows per minute.

The jar-squeezer machine, also called the jolt-squeezer ma­chine, combines the operating principles of the jolt machine and the squeezer machine. A complete mold, drag and cope, is produced by means of this machine.

Machines called sand slingers are sand-filling and ramming devices used in the rapid molding of large castings. These machines can be used in combination with other molding de­vices such as the roll-over machine and the pattern-draw ma­chine.

Machines of various kinds have been developed for the purpose of drawing pattern out of the mold. There are two types of pattern-drawing machines: the stripping-plate machine and the stripper.

In the stripping-plate machine, the pattern is fitted through a plate that fits accurately around the pattern. The patterns are drawn through the plate, either by moving the pattern supports down with a lever or by raising the plate and the mold half up, free from the pattern. The stripping-plate machine is best adapted to that class of work which offers difficulties in drawing the pattern from the sand.

A stripper is a machine that either lifts the mold away from the pattern or lifts the pattern away from the mold.

CASTING METALS

Cast Iron.— The term cast iron is applied to ferrous alloys. Among the ferrous metals, cast iron occupies first place and is recognized as one of the cheapest materials used in the manufacture of everyday life products. Cast iron is not con­sidered a very strong or tough structural material, but it is the most economical. Its low melting point, low shrinkage, good fluidity, and machinability are properties that recommend its use.

Pig Iron.— The chief raw material for cast iron is pig iron, which is produced in a blast furnace by smelting iron ore with coke and a flux (substances promoting fusion) such as limestone. The final analysis of the pig iron is substantially determined by the kind of iron ore used in the smelting pro­cess.

Pig iron got its name from the shape of the molds in which metal from the blast furnace was cast. Originally, the pigs were cast in sand molds.

Modern large-volume production of pig iron is carried out by casting blast-furnace metal by means of a large machine, which is in principle an endless conveyer chain of pig molds.

Some pig irons are used in gray-iron foundries, and are called foundary pig irons. Pig iron used for making steel by the acid Bessemer process or the acid open-hearth process is known as Bessemer pig iron. Basic pig iron is used for the basic open-hearth process.

Non-Ferrous Metals. — The non-ferrous metals used in the foundary are usually alloys of two or more metals. Non-fer­rous castings include those composed of copper-base alloys (brass and bronze), aluminium-base alloys, zinc-base alloys, tin-base alloys, lead-base alloys, bearing metals, and some special alloys composed of magnesium or nickel and other metals.

THE CUPOLA FURNACE

The cupola is the oldest type of furnace and the most econo­mical. It may be obtained in different sizes and can be operated for as long a time as may be required to produce a given amount of melted metal. It is difficult to produce metal of precisely uniform quality in the cupola as compared to furnaces in which uniformity of the molten material can be con­trolled by frequent and pe­riodic tests and adjustment. Cupola capacities vary from 1 to 15 tons of metal per heat (the amount of metal melted at one time).

The cupola is a cylindric­al shell constructed from boiler plate and lined with firebrick. The main furnace structure is usually support­ed on cast-iron legs, and the opening at the bottom of the furnace may be closed by cast-iron doors, which swing up into position and are held closed by an iron upright at the center. Refractory sand protects these doors during the melting of the charge, which is placed over the layer of sand. At the end of the melting operation, the doors swing out of the way and materials remaining from the charge drop downthrough the opening.

On one side of the cupola, level with the bottom, is the breast opening for lighting the fire. This opening is also used as the tap hole. Opposite the tap hole, and somewhat higher, is the slag hole. The charging door is located approximately halfway up the vertical shell. The top of the cupola is open except for a metal shield.

A single row of openings or tuyeres is arranged around the circumference of the shell's interior at its base as a means of introducing air to the coke bed. A wind box, externally circling the cupola at the level of the tuyeres, supplies the air.

Cupola Zones. — A foundry cupola is generally divided into a number of zones: the crucible zone, tuyere zone, combustion zone, melting zone, preheating zone, and the stack zone.

The crucible zone is located at the bottom of the cupola; it is situated in the space between the sand bottom of the furnace and the bottom of the tuyere openings. Molten iron and slag accumulate in this space between the burning pieces of coke.

The tuyere openings are above the cruicible and take up a space from 3 to 6 inches in depth depending upon the size of furnace.

The combustion zone is that section of the cupola which extends from the bottom of the tuyeres to the top of the coke bed.

The melting and preheating zones extend from the top of the combustion zone to the charging door. The location of the charging door depends upon the size of the cupola. High charg­ing doors, however, are recommended for large cupolas which are run all day, since greater fuel efficiency can be gained from the use of such charging doors.

The purpose of the stack, which is another zone of the cupola, is to carry off the waste gases. It is located above the charging door. A roof hood is usually fastened to the stack to prevent leaks around the cupola.

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