lathe Machine

          A lathe  is a machine tool which rotates the workpiece on its axis to perform various operations such as cutting, sanding, knurling, drilling, or deformation with tools that are applied to the workpiece to create an object which has symmetry about an axis of rotation.

Lathes are used in woodturning, metalworking, metal spinning, and glassworking. Lathes can be used to shape pottery, the best-known design being the potter’s wheel. Most suitably equipped metalworking lathes can also be used to produce most solids of revolution, plane surfaces and screw threads or helices. Ornamental lathes can produce three-dimensional solids of incredible complexity. The material can be held in place by either one or two centers, at least one of which can be moved horizontally to accommodate varying material lengths. Other workholding methods include clamping the work about the axis of rotation using a chuck or collet, or to a faceplate, using clamps or dogs.

Examples of objects that can be produced on a lathe include candlestick holders, gun barrels, cue sticks, table legs, bowls, baseball bats, musical instruments (especially woodwind instruments), crankshafts and camshafts.

Welding

Welding:

          Welding is the process of joining two metals either those metals are similar or dissimilar, with or without the application of pressure and with or without the use of filler metal.

Weldability:

          In is the property of metal which indicates the ease with which two similar or dissimilar metals are joint together.

Advantages of welding:

1. Strength is more.

2. Takes less time.

3. Weight of welding joints is less.

4. Smooth appearance.

5. Less wastage of material.

6. Efficiency is Maximum which not possible in other types of joints.

7. Complicated shape can be easily welded.

8. It can be done at any point of structure.

Disadvantages of welding:

1. Skilled workers are required.

2. It is permanent joint.

3. Jigs and fixtures are required.

4. Preparation of edges.

5. Personal protective equipments.

INGREDIENTS OF MOULDING SANDS

PRINCIPAL INGREDIENTS OF  MOULDING SANDS :
          The principal ingredients of moulding sands are given below :
(1)    Silica sand grains
(2)    Clay
(3)    Moisture
(4)    Miscellaneous materials
>> SILICA  SAND GRAINS :
          Silica in the form of granular quartz, itself a sand, is the chief constituent of moulding sands.silica sand contains from 80% to 90% silicon dioxide and is characterized by a high softening temperature and thermal stability.it is a product of the breaking up of quartz rocks or the decomposition of granite, which is composed of quartz and feldspar.
>> CLAY :
          Clay is defined as those particles of sand ( under 20 microns in diameter ) that fails to settle at a rate of 25mm per minute, when suspended in water. Clay consists of two ingredients : FINE SILT and TRUE CLAY. Fine silt is the sort of foreign matter or mineral deposit and has no bonding power. It is the true clay which imparts the necessary bonding strength to the mould sand, so that the mould does not lose its shape after rimming. Most moulding sands for different grades of work contain 5% to 20% clay.
>> MOISTURE :
          Moisture in requisite amount, furnished the bonding action of clay. When water is added to clay, it penetrates the mixture and forms a microfilm which coats the surface of flake-shaped clay particles. The bonding quality of clay depends of the maximum thickness of water film it can maintain. The bonding action is considered best if the water added is the exact quantity required to form the film. The water should be between 2% to 8% .
>> MISCELLANEOUS MATERIALS :
          Miscellaneous materials that are found, in addition to silica and clay in moulding sand are oxide of iron, limestone, magnesia, soda, and potash. The impurities should be below 2% .

Types of Moulding Sands

Types of Moulding Sands :

1: Green sand :
The sand in its natural or moist state is called green sand. It is also called tempered sand. It is a mixture of sand with 20 to 30 percent clay, having total amount of water from 6 to 10 percent. The mould prepared with this sand is called green sand mould, which is used for small size casting of ferrous and non-ferrous metals.
2: Dry Sand :
The green sand moulds when baked or dried before pouring the molten metal are called dry sand moulds. The sand of this condition is called dry sand. The dry sand moulds have greater strength, rigidity and thermal stability. These moulds used for large and heavy casting.
3: Loam Sand :
A mixture of 50 percent sand grains and 50 percent clay is called loam sand. It is used for loam moulds of large Grey iron casting.
4: Facing Sand :
A sand which is used before pouring the molten metal, on the surface is called facing sand. It is specially prepared sand from silica sand and clay.
5: Backing or Floor Sand :
A sand used to back up the facing sand and not used next to the pattern is called backing sand. The sand which have been repeatedly used may be employed for this purpose. It is also known as black sand due to its color.
6: System Sand :
A sand employed in mechanical sand preparation and handling system is called system sand. This sand has high strength, permeability and refractoriness.
7: Parting Sand :
A sand employed on the faces of the pattern before the moulding is called parting sand. The parting sand consists of dried silica sand, sea sand or burnt sand.
8: Core Sand :

The cores are defined as sand bodies used to form the hollow portions or cavities of desired shape and size in the casting. Thus the sand used for making these cores is called core sand. It is sometimes called oil sand. It is the silica sand mixed with linseed oil or any other oil as binder.

Properties of Moulding Sands

Properties of Moulding Sands :

1: porosity or permeability :
It is the property of sand which permits the steam and other gases to pass through the sand mould. The porosity of sand depends upon its grain size, grain shape, moisture and clay components are the moulding sand. If the sand is too fine, the porosity will be low.
2: Plasticity :
It is that property of sand due to which it flows to all portions of the moulding box or flask. The sand must have sufficient plasticity to produce a good mould.
3: Adhesiveness :
It is that properties of sand due to it adheres or cling to the sides of the moulding box.
4: Cohesiveness :
It is the property of sand due to which the sand grains stick together during ramming. It is defined as the strength of the moulding sand.
5: Refractoriness :

The property which enables it to resist high temperature of the molten metal without breaking down o r fusing.

6: Chemical Stability :

The property of sand to resist chemical reaction with molten metal is termed as chemical stability.