Compound Steam Engine | Classification Compound Steam Engines

CLASSIFICATION OF COMPOUND STEAM ENGINE

The compound steam engines are usually classified into two types:

1. Tandem compound steam engine

2. Cross compound steam engine

TANDEM COMPOUND STEAM ENGINE

In this type of engine, the two cylinders usually will have a common piston rod and fixed in tandem, working on the same crank shaft. These cylinders may be observed as having crank at zero degree to each other.

01 - tandem engine - type of compound engine

Steam generated in the boiler is supplied to one side of the piston of the high pressure(H.P) cylinder. On the other side of the high pressure piston exhaust takes place simultaneously and this exhaust steam now acts on the piston of the low pressure (L.P) cylinder. The valves should be functioned in such a way that there should be continuous admission of steam in the high pressure as well as low pressure cylinder simultaneously. After the steam supply is cut off in the high pressure cylinder, the steam expands and after the high pressure exhaust steam is admitted to low pressure cylinder upto cut-off point, it further expands to the condense pressure if the engine is considering or to the atmosphere for non-condensing engines.

Since usually the steam engines are double acting, the steam flow takes place during the return stroke as shown by thin arrow heads.

As the cycle of H.P and L.P cylinders are in phase the maximum turning moment on the crank-shaft, due to each and every cylinder, will certainly act at the same instant. This is the disadvantage of this type of compound engine, since a large flywheel is consequently required.

CROSS COMPOUND STEAM ENGINE

1. Woolfe type compound steam engine

2. Receiver type compound steam engine

WOOLFE TYPE COMPOUND STEAM ENGINE

01 - WOOLFE TYPE COMPOUND STEAM ENGINE - COMPOUND STEAM ENGINE

In this type of two cylinder compound engine, the crank of the cylinder are at an angle of 180 to each other. The cylinders are arranged in a side by side manner, and exhaust steam from H.P cylinder passes directly into the L.P cylinder, the expansion is, therefore, continuous during the stroke. As the crank are at an angle of 180° the two cycles are in the phase and causes a large variation in the turning moment on the crankshaft; this is the same disadvantage as in the tandem type of compound steam engine.

RECEIVER TYPE COMPOUND STEAM ENGINE

In this type, the steam from one cylinder is not directly discharged into the next cylinder but it is discharged into a chamber known as ‘receiver’. So receiver is nothing but a reservoir of steam from where the steam is admitted into the L.P cylinder during its admission stroke. In this arrangement, the crank angle will be less than angle of 180°. In a two cylinder compound engine the angle is 90°.This type of engine can start in any position. It can also be run at reduced loads, with one cylinder in operation.

01 - RECEIVER TYPE COMPOUND STEAM ENGINE - COMPOUND STEAM ENGINE

There is always an unavoidable pressure drop in the receiver due to condensation of steam but it can be reduced by steam jacketing the receiver. The reservoir should be large enough to keep the pressure in it fairly constant; its volume should be about 1.5times the H.P cylinder volume.

According to number of expansion stages, the compound steam engine may also be classified as follows.

1. Double expansion

2. Triple expansion

DOUBLE EXPANSION

In double expansion engine the expansion of steam takes place in two cylinders. First the steam expands in high pressure cylinder and then it is discharged into the low pressure cylinders. Finally, it is exhausted into the condenser.

TRIPLE EXPANSION

In this type of engine, the expansion of steam is completed in three cylinders. The steam from the high pressure cylinder is exhausted into intermediate pressure cylinder and then the steam is discharged into the low pressure cylinder. The steam from the low pressure cylinder is discharged into the condenser.

Electro Chemical Grinding | Non-Traditional Machining Process

Electro Chemical Grinding (ECG)

Electro chemical grinding is also called electrolytic grinding. Metal is removed from the surface of the work piece by electro chemical action and also by abrasive action of a grinding wheel. 90% of metal is removed by electro chemical action and 10% of metal is removed by the abrasive action of the grinding wheel.

01 - WORKING OF ECG - UNCONVENTIONAL MACHINING PROCESS

The equipment has a metal bonded grinding wheel. Brass, bronze and copper are bonded with abrasive grains in the grinding wheel. Diamond abrasive is used for grinding tungsten. Aluminium oxide abrasive is used for other metals.

The wheel is held in a horizontal spindle. The spindle is supported on insulated bearings. The work piece is held in a fixture against the grinding wheel. A gap of about 0.01mm is maintained between the wheel and the surface of the work piece. The work piece is connected to the positive terminal of a D.C. supply. The grinding wheel is connected to the negative terminal. 4 to 16V, 300 to 1000 Amps D.C supply is applied. A mixture of sodium chlorite, sodium chlorate or sodium nitrate and water is used as the electrolyte. The electrolytic solution is made to flow between the work piece and the grinding wheel. Electro chemical action takes place. Metal from surface of the work piece is removed in small particles. In addition to this, the rotating grinding wheel also removes metal from the work surface by abrasion. The small particles of metal removed from the work piece are carried away by the electrolyte. The electrolyte is collected in a reservoir. It is filtered and recirculated by a pump. Electrolyte also acts as coolant. The work piece is slowly fed towards the grinding wheel maintaining a constant gap between the work piece and the grinding wheel.

01 - CONSTRUCTION OF ECG - NON TRADITIONAL MACHINING PROCESS

Applications:

· Used for machining hard materials which are conductive to electricity

· Used for grinding of tungsten carbide tool tips and hard steels.

·  Used to grind thin section.

· Cylindrical grinding, form grinding, plunge grinding and surface grinding operations are done using this process.

· Used for machining refractory materials, high strength steels, nickel and cobalt base alloys etc.,

Advantages:

· Very fine finish is obtained

· Suitable for machining very hard materials like carbides. Carbides are difficult to machine by other processes.

· No heat is generated during the process.

· No distortion to the work piece

· No burrs are produced.

· Fast operation

· Thin materials can be ground without deflection as the grinding wheel does not press the work piece.

· Wheel wear is drastically reduced.

· No heat is generated so there is no danger of burning or heat distortion.

Disadvantages:

· This process can be used to machine only metals which are conductive.

· Sharp corners of the work piece cannot be machined.

· Electrolytic solution is corrosive.

· Initial cost of the equipment is high when equipped with larger power supplies.

· Intricate shapes may not be formed.