Q.1.What is advantage of Podwer Metallurgy ?

ADVANTAGES OF POWDER METALLURGY:

1. The processes of powder metallurgy are quite and clean.
2. Articles of any intricate or complicated shape can be manufactured.
3. The dimensional accuracy and surface finish obtainable are much better for manyapplications and hence machining can be eliminated.
4. Unlike casting, press forming machining, no material is being wasted as scrap and the process makes utilizes full raw material.
5. Hard to process materials such as diamond can be converted into usable component and tools through this process.
6. High production rates can be easily achieved.
7. The phase diagram constraints, which do not allow an alloy formation between mutually insoluble constituents in liquid state, such as in case of copper and lead are removed in this process and mixtures of such metal powders can be easily processed and shaped through this process.
8. This process facilitates production of many such parts, which cannot be produced through other methods, such as sintered carbides and self-lubricating bearings>
9. The process enables an effective control over several properties such as purity, density, porosity, particle size, etc., in the parts produced through this process.
10. The components produced by this process are highly pure and bears longer life.
11. It enables production of parts from such alloys, which possess poor cast ability.
12. It is possible to ensure uniformity of composition, since exact proportions of constituent metal powders can be used.
13. The preparation and processing of powdered iron and nonferrous parts made in this way exhibit good properties, which cannot be produced in any other way.
14. Simple shaped parts can be made to size with 100 micron accuracy without waste.
15. Porous parts can be produced that could not be made in any other way.
16. Parts with wide variations in compositions and materials can be produced.
17. Structure and properties can be controlled more closely than in other fabricating processes.
18. Highly qualified or skilled labor is not required. in powder metallurgy process.
19. Super-hard cutting tool bits, which are impossible to produce by other manufacturing processes, can be easily manufactured using this process.
20. Components shapes obtained possess excellent reproducibility.
21. Control of grain size, relatively much uniform structure and defect such voids and blowholes in structure can be eliminated.

LIMITATIONS OF POWDER METALLURGY:

1. Powder metallurgy process is not economical for small-scale production.
2. The cost of tool and die of powder metallurgical set-up is relatively high.
3. The size of products as compared to casting is limited because of the requirement of large presses and expensive tools which would be required for compacting.
4. Metal powders are expensive and in some cases difficult to store without some deterioration.
5. Intricate or complex shapes produced by casting cannot be made by powder metallurgy because metallic powders lack the ability to flow to the extent of molten metals.
6. Articles made by powder metallurgy in most cases do not have as good physical properties as wrought or cast parts.
7. It may be difficult sometimes to obtain particular alloy powders.
8. Parts pressed from the top tend to be less dense at the bottom.
9. A completely deep structure cannot be produced through this process.
10. The process is not found economical for small-scale production.
11. It is not easy to convert brass, bronze and a numbers of steels into powdered form.

Q.2.What is advantage of Shielded Metal Arc Welding (SMAW) or Manual Metal Arc Welding (MMAW)?

Shielded Metal Arc Welding (SMAW) or Manual Metal Arc Welding (MMAW):

Advantages:

1. . Shielded Metal Arc Welding (SMAW) can be carried out in any position with highest weld quality.
2. MMAW is the simplest of all the arc welding processes.
3. This welding process finds innumerable applications, because of the availability of a wide variety of electrodes.
4. Big range of metals and their alloys can be welded easily.
5. The process can be very well employed for hard facing and metal resistance etc.
6. Joints (e.g., between nozzles and shell in a pressure vessel) which because of their position are difficult to be welded by automatic welding machines can be easily accomplished by flux shielded metal arc welding.
7. The MMAW welding equipment is portable and the cost is fairly low.

Limitations:

1. Due to flux coated electrodes, the chances of slag entrapment and other related defects are more as compared to MIG and TIG welding.
2. Duo to fumes and particles of slag, the arc and metal transfer is not very clear and thus welding control in this process is a bit difficult as compared to MIG welding.
3. Due to limited length of each electrode and brittle flux coating on it, mechanization is difficult.
4. In welding long joints (e.g., in pressure vessels), as one electrode finishes, the weld is to be progressed with the next electrode. Unless properly cared, a defect (like slag inclusion or insufficient penetration) may occur at the place where welding is restarted with the new electrode.
5. The process uses stick electrodes and thus it is slower as compared to MIG welding.

Applications:

1. Today, almost all the commonly employed metals and their alloys can be welded by this process.
2. Shielded metal arc welding is used both as a fabrication process and for maintenance and repair jobs.
3. The process finds applications in
   (a) Building and Bridge construction
   (b) Automotive and aircraft industry, etc.
   (c) Air receiver, tank, boiler and pressure vessel fabrication
   (d) Ship building
   (e) Pipes and
   (f) Penstock joining
   

Q.3.What is advantage and disadvantage of WELDED CONNECTIONS?

ADVANTAGES AND DISADVANTAGES OF WELDED CONNECTIONS:

The advantages and disadvantages of welded connections over riveted connection are given below :

Advantages:

1. The welded structure are comparatively lighter than corresponding riveted structure.
2. The welded joint has greater strength as compared to the riveted joint.Hence efficiency of a welded joint is more than that of a riveted joint.
3. Addition and alternations can be easily made in the existing welding structure more easily than in riveted structure.
4. A welded structure has a better finish and appearance than a corresponding riveted member. The maintenance and painting cost for a welded structure is less than for the riveted structure.
5. Welding takes less time than riveting.
6. In welded connections the tension members are not weakened as in the riveted joints.
7. Members of such shapes, which are difficult for riveting, can be easily welded.
8. It is possible to weld any part of a structure at any point. But riveting requires enough clearance.

Disadvantages:

1. Welding requires skilled labour and supervision.
2. As there is an uneven heating and cooling during welding, the members may get distorted or additional stresses may develop.
3. Testing a weld joint is difficult. An X-ray examination alone can enable us to study the quality of the connection.

Q.4.What is advantage and disadvantage of reciprocating internal combustion engines over external combustion engines?

Advantages of reciprocating internal combustion engines over external combustion engines :

Reciprocating internal combustion engines offer the following advantages over external combustion engines :

1. Overall efficiency is high.
2. Greater mechanical simplicity.
3. Weight to power ratio is generally low.
4. Generally lower initial cost.
5. Easy starting from cold conditions.
6. These units are compact and thus require less space.

Advantages of the external combustion engines over internal combustion engines :

The external combustion engines claim the following advantages over internal combustion engines 

1. Starting torque is generally high.
2. Because of external combustion of fuel, cheaper fuels can be used. Even solid fuels can be used advantageously.
3. Due to external combustion of fuel it is possible to have flexibility in arrangement.
4. These units are self-starting with the working fluid whereas in case of internal combustion engines, some additional equipment or device is used for starting the engines.

Q.5.What is advantage and disadvantage of T- Combustion chamber,I-head (or overhead valve) combustion chamber,F-head combustion chamber?

Advantages of T- Combustion chamber 

1. Valve mechanism simple and easy to lubricate.
2. Detachable head easy to remove for cleaning and decarburising.
3. Valves of larger sizes can be provided.

Disadvantages :

1. More surface-to-volume ratio and therefore more heat loss.
2. Longer length of flame travel.
3. Valve size restricted.
4. Thermal failure in cylinder block also. In I-head engine the thermal failure is confined to cylinder head only.

3. I-head (or overhead valve) combustion chamber. 

This type of combustion chamber has both the inlet valve and the exhaust valve located in the cylinder head. An overhead engine is superior to side valve engine at high compression ratios.

Advantages :

1. Reduced pumping losses.
2. Higher volumetric efficiency (since the larger valves and larger lifts can be accommodated).
3. Less prone to detonation (since the path of flame travel is reduced).
4. Less force on the head bolts and therefore less possibility of leakage of compression gases or jacket water.
5. Lower surface-volume ratio and, therefore, less heat loss and less air pollution.
6. Easier to cast.

4. F-head combustion chamber

N In such a combustion chamber one valve is in head and other in the block. This design is a compromise between L-head and I-head combustion chambers.N One of the most perfect F-head engines (wedge type) is the one used by the Rover company for several years. Its advantages are :

1. High volumetric efficiency .
2. Maximum compression ratio for fuel of given octane rating .
3. High thermal efficiency .
4. It can operate on leaner air-fuel ratios without misfiring.