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Applications, Advantages and Disadvantages of Shell Moulding

🔗How shell moulding is done? Application of shell moulding Shell moulding is suitable for mass production of thin-walled casting in any met...

Applications, Advantages and Disadvantages of Shell Moulding

Application, Advantages and Disadvantages of Shell Moulding

🔗How shell moulding is done?


Application of shell moulding

  • Shell moulding is suitable for mass production of thin-walled casting in any metal having the size of 20kg. Most commonly used includes iron, bronze and aluminium alloy casting.
  • The shell moulding is economical when a large number of thin-walled shell items with reasonable sharp corners and projection.
  • The casting of small mechanical parts that requires high level of precision. E.g., Cylinder head, connecting road, gear housing.
  • Production of high precision moulding cores. E.g., Engine block water jackets.
  • Other applications include refrigerator valve late, cast tooth bevel gears, automobile transmission parts, chain seat brackets etc.


Advantages of shell moulding

  1. The process of shell moulding can be automated entirely for mass production
  2. Short lead time possible
  3. High productivity and low labour cost
  4. Low tooling and equipment cost.
  5. Many materials option
  6. Very little scrap is generated. The sand can be recycled.
  7. Excellent collapsibility as resin binder burns out in heat generated by molten metal, which makes shaking out of product is easy. So it requires a lower draft angle, which saves the material and subsequent machining costs.
  8. High permeability, varying wall thickness to be made without any venting difficulties. So, there is no need for a complex system of risers.
  9. Shell casting is more dimensionally accurate than sand moulding. Fewer restrictions in casting design.
  10. Complex shapes of fine details can be produced with excellent tolerance and a smooth surface finish. Smoother surface achieved by finer grain size.
  11. Thin wall of the shell rapidly heats up as molten metal is poured in it, preventing the chilling of metal as it is poured. It helps to the rapid flow of metal through runners allowing the filling of complex moulds and preventing possibility of a cold shut.
  12. Excellent tolerance and dimensional stability. Dimensional tolerance is as close as +.075mm. It helps to reduce machining costs.
  13. Excellent surface finish is obtained, and the surface is free from fins and blemishes associated with the green sand moulding.
  14. Since the sand has good strength, the mould can be designed to have an internal cavity directly with shell mould, thus eliminating the need for a mould core.
  15. The shell mould can be stored indefinitely for future use.


Disadvantages of shell moulding

  1. The pattern is expensive. Since the entire mould is formed from pattern, the pattern must include a gating system. It is economical only in mass production.
  2. High labour cost if it is done manually.
  3. High initial cost for specialized equipment.
  4. Dimensional limitation, a minimum thickness of cast is 4mm.
  5. Resin binders are expensive.
  6. Permeability of mould may decrease due to fine grains; there may be a chance of gas inclusion.
  7. Shrinkage can be a problem.

What Is Meant By Shell Moulding? Process Of Shell Moulding

Shell moulding process


What is shell mould casting?

Shell moulding is a variation of sand casting in which a relatively thin mould is made around heated metallic patterns. The shells are firm, so it is easy to handle them. Shell moulding has many advantages over green sand moulding. It can be produced by hand or automatic machine more quickly and cheaply than green sand mould. This improved process of sand casting is capable of giving good surface finish, dimensional accuracy and tolerance. The highly precise casting may not require further processing. This method is used for making cylinder heads, gear housing, engine block etc.

Comparison Between Injection Moulding And Extrusion Moulding


Injection moulding and extrusion moulding

Injection moulding and extrusion moulding are popular plastic manufacturing processes. At an initial glance, it may appear to be similar. Both injection moulding and extrusion have their own purpose and advantages.

Injection Moulding Application Advantages and Limitations

injection moulding application

The term injection moulding normally used in conjunction with thermoplastic material. Simply it is the process of melting the thermoplastic and inject it into the mould.


Read: Injection Moulding Machine Working Principle and The Process

Injection Moulding Machine Working Principle and The Process

injection moulding


What is plastic injection moulding?

Injection moulding is one of the most commonly used processes to produce thermoplastic plastic parts. It is a cyclic process of mould filling followed by cooling and ejection. It is very economical in mass production. In fact, the feedstock need not be plastic; it can be plastic and non-plastic material. However, the machine should be configured to the feedstock material, and material must be plasticized before injection.

What Is Carbon Dioxide (CO2) Moulding Process? Application Advantages and Disadvantages

Gassing CO2

🔗 Types of mould material - green sand, dry sand, skin dried, loam, metal mould

🔗 Comparisonbetween green sand moulds and dry sand moulds


How Carbon dioxide moulding is done? The principle behind it

CO2 moulding (Carbon dioxide moulding) is a unique moulding process. This is essentially a quick moulding process. Here liquid sodium silicate is used as a binder instead of clay in the conventional sand moulding. The principle behind the CO2 moulding process is that when CO2 passes through a sand mix containing liquid sodium silicates binder for two-three minutes, it immediately gets hardened by silica gel formation. The silica gel (SiO2.x.H2O) is formed by the chemical reaction between sodium silicate and carbon dioxide. This silica gel gives the strength sufficient to eliminate baking/ drying of mould.



The sand used must be dry and free from clay. GFN of sand grains is in the range of 55 to 85. The sand is mixed with 3-5% of sodium silicate. Some other additives, such as coal powder, wood floor, Dextrin, iron oxide, aluminium oxide etc., are also added to obtain specific properties. Dextrin, coal powder and wood flour improve collapsibility. Aluminium improves the hot strength of sand at 800°C. Iron oxide helps to prevent the deformation of cores, and it produces a smooth interface between mould and metal, thus helping to get a good surface finish.


co2 Gassing method


The gassing of co2 into the mould can be carried out in different ways (gassing with a probe, gassing with a hood) depending essentially on the mould’s size. The flow rate, time of gassing and pressure of CO2 gas depends on the depth of penetration required. Usually, gassing time is within 15 to 30 seconds. The mould must be used within 12hours; otherwise, it starts to absorb water from the atmosphere and deteriorate.



The chemical for this reaction is given below


Na2O . mSiO2 . xH2O + CO2 —> Na2CO3 + mSiO2 . xH2O

 

After passing carbon dioxide, the pattern is removed, and the mould is ready to pour molten metal immediately into it. This eliminates the headache of foundrymen's need for greater skill and caring during mould-making and baking.



Application of carbon dioxide moulding

  • Nowadays, it is used to make cores for conventional mould instead of complete mould.
  • Production of heavy and thick-walled steel casting. There is no weight limit.
  • Production of cast iron, steel, aluminium, and copper-based alloy casting.
  • For making of larger cores of heavy ferrous casting.
  • Used for making parts of valves engine, machine tools railway casting, gear casting wheel casting



Advantages of carbon dioxide moulding


  1. The method is versatile. It can be used in small and large foundries for light and heavy casting and ferrous and non-ferrous foundries alike.
  2. Does not require core drier or baking process. It saves time and cost for heating and floor space.
  3. Withdrawal Pattern is facilitated since the mould immediately hardened.
  4. Less mould cracking and deformation. Low mould rejection.
  5. Since it does not involve any distortion due to baking, better dimensional accuracy can be achieved.
  6. Machining allowance can be reduced.
  7. It has high strength, so it does not require other reinforcement.
  8. Semi-skilled operator is required compared to dry sand moulding
  9. Process good strength and hardness.
  10. The process can be mechanized for mass production.
  11. Molten metal can be immediately poured in to mould and hence reduce the production time



Disadvantages or limitation of carbon dioxide moulding


  1. The mould is expensive
  2. One of the main disadvantages of CO2 moulding is that used sand mixture cannot be recovered easily. An expensive and difficult reclamation process is necessary.
  3. CO2 moulding is less suitable for non-ferrous casting and thin-walled casting.
  4. The life of the mould is short. Mould should use within 12 to 24hr.
  5. Poor collapsibility.
  6. CO2 cores are susceptible to moisture.