So for large quantity production along with low cost the majority will prefer sand. But in cases of small quantity precision products lost wax. On those cases the precision is the main factor and the factor of cost is ruled out .
What is Sand Casting ?
Sand casting is a metal casting process which involves the use of natural sand along with adequate proportion of clay (as a binder material) to keep the sand grains together or it can use the silica sand and artificial binder pair. The mixture is then contained in a moulding flask or moulding box consisted of two matching parts . The mixture in the box is compressed by hand or mechanical ramming is done around the pattern. A parting sand is used between the two halves of the moulding flask. When the these boxes are separated after establishing the sprue system by patterns and the dowels a negative mould shape is left behind in the moulding sand. The molten metal is then poured into that hollow section or cavity. These are the basic steps of sand casting used for metal casting.
Different sand casting processes and their pros and cons
Sand casting process involves the use of different types of sands and binder pairs. There are
different types of molding sand in a casting process. And the quality of the casting depends on the
properties of various natural and synthetic molding sands. Below the main types of sand casting processes are discussed with there advantages and limitations along with comparisons.
Green Sand Moulding
This process involves the use of natural sand which already have a small percentage of clay. The green sand casting process involves the following basic steps.
- Adequate amount of water is added to the sand.
- After adding water the green or natural sand is thoroughly conditioned and mixed with the help of rollers. The clay and water works as binder which holds the sand grains together.
- The sand is compressed around the pattern and rammed so that it becomes compact and tight. And this is known as 'Green Strength'.
Advantages of green sand moulding
1. Appropriate for long production runs
2. Very low cost process.
3. Materials are available in all around the world.
4. The process is versatile
5. The sand is reusable.
Disadvantages of green sand moulding
1. It needs skilled workers and craftsmen.
2. Intricate Patterns are not very suitable.
3. Surface Finishing is not good. Needs additional machining.
Dry sand casting process
The main concentration of dry sand casting process is on Iron casting. Major features are
- This mixture is rich in clay.
- The rammed sand is more compact.
- It needs well ventilation with the appropriate use of venting rod.
- Sand must dried before pouring the molten metal into the mould.
Advantages of dry sand casting
1. Dry sand moulding gives a closer and finer grain structure which is suitable for large and heavy castings. (typically for iron castings buy not exclusively). In heavy castings natural sand has the tendency to become weaker when baked and dried.
2. Dry sand controls excessive gassing and porosity as a result gives a better dimensional accuracy.
Disadvantages of dry sand casting
1. Sand needs meticulous blending and preparation.
2. To unleash the trapped gases dry sand moulding needs ample and thorough venting.
3. Kiln and fuel is needed because the mould is needed to be baked.
Carbon dioxide-silica sand moulding
In comparison to CO2 - Silica moulding process, sometimes the green sand process seems obsolete. In this process -
- Sand grains are bound together with the use of Sodium Silicate and it is hardened by the use of Carbon dioxide gas.
Advantages of carbon dioxide-silica sand moulding
1. Semi-skilled worker can do the work.
2. It is a very versatile process.
3. It produces very good surface finish.
4. Used for long production runs
5. The distortion is negligible.
Disadvantages of carbon dioxide-silica sand moulding
1. It is a expensive process.
2. Thorough mixing of the materials is very necessary.
3. Gathering all the materials is not easy.
4. It needs careful mixing which involves the use of mechanical means.
5. A common fault is poor surface finish because of over gassing.
6. If sand reclamation plant is not present then the sand cannot be reused.
Synthetically bonded sand casting process
- This process uses silica sand.
- Synthetic resin is used as a binder. These binders can be air set, or thermo set or can use catalysts.
Floor Moulding process
- This process is used mainly for large castings alone.
Advantages of floor moulding
1. Materials are readily available.
2. Suitable for huge castings.
Disadvantages of floor moulding
1. The application of floor moulding is very limited .
2. It needs very experienced workers.
Loam Moulding Process
Used for large one-off casting processes which may involve "oil bonded sand". Here a vegetable oil is used for oxidizing or drying the sand.
Advantages of loam moulding process
1. A great method for casting a single piece or a small number of heavy and large castings.
2. Most of the times motor casings, bells and fly wheels are cast by this process which means that this process is very much suitable for casting cylindrical, conical and domed shape materials.
3. The caster can use a strickle as a substitute of large and costly patterns.
Disadvantages of loam moulding process
1. Not suitable for large quantity production.
2. This process is almost died out. These days it is used merely in the bell foundries. This process also needs great technical skills.
These are the main sand casting processes which are useful in different fields. A well experienced blacksmith or caster would well utilize the advantages and disadvantages of all the sand casting processes. There are also processes like die casting, lost wax casting, centrifugal castings, lost mercury process and lost polystyrene process which all are useful in different fields,
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