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GREEN SAND

Introduction: A commonly used form of sand casting, green sand casting gets its name because wet sand is used in the molding process. A variety of additives like pitch, cellulose and silica flour are used in this process. The aggregate of sand mold consist of mixture like silica, clay, water and other materials are taken for bank sands or lake sands. The main advantage of green sand casting is that the sand can be used any number of times after adjusting the composition. Raw sand are obtained and processed to provide a consistent distribution of grain sizing. A variety of additives such as pitch, cellulose, and silica flour are used in the process.

Molds for sand casting: In green sand casting process lake or bank sand is used as the aggregate and different kinds of additives are used like pitch, cellulose and silica flour. A sand mixture is made of sand, grains, clay, water and other material according to the casting requirements. The patterns is then mounted on a mold board and a suitable fask in placed around it.
Green sand mold is rammed around the pattern and when the pattern is removed there will be a suitable mold cavity. The sand mixture is rammed around the pattern and sometimes automated machines are used to vibrate the sand in the mold. In the mold the molten metal is poured and when it solidifies the cast is removed from the mold. Mold release agents can be used, but commonly the mold is broken to remove the cast. The moud can be again processed and reused in the next castings.

Application: Green sand casting is used largely for heavy casting like casting bells, where the casting are to be cleaned and polished for fine surface finish.

Advantages:

  • A reasonably priced process, green sand casting enables great flexibility in the choice of molds and patterns.
  • This is an environmental friendly process where there mold aggregated can be treated and repeatedly used.
  • This process enables speedy, economical and expeditious execution of the casting process
  • asily adaptable to automated and semi-automated machines for some process.
  • The aggregate and adhesives are readily available at reasonable rates.

NO - BAKE SAND

Introduction: Also known as air-set mold, No bake casting is the most sophisticated casting techniques of the modern times. In this process a strong chemical bond is created in the mold that is made from a mixture of sand, quick-setting resin and catalyst. Air set molding, which is a cold setting process, was developed in response to the increasing demand for castings by customers worldwide. Though is an expendable mold, this mold is largely favored because this strong molds, can stand on it own, without the used of mold boxes and therefore mold of any size can be made.

Process: Graded Kiln dried sand is manually mixed in a mixer with the chemical binder like urethane and catalyst. When the sand mix leaves the mixer it forms a strong mixture. The presence of resin in the mixture, helps to keep the sand to remain strongly bound at room temperature. This strong and hard non-reusable sand mixture is then packed around the pattern or multiple patterns made of wood, metal or plastic. This process is known as the compaction process. Now when the casting mold is set the pattern removed by the roll over process. In the mold cavity, molten metal in poured from the crucible guided by the sprure and the gating. Shrinkage during the solidification in compensated by the use of risers.

After casting, the molded sand is taken away from the casting. Sand can be reclaimed to some extend by thermal means. No bake sand mixture can be used not only to make mold but also to make cores for internal passages.

Reclamation of Sand: No bake sand casting is an expendable process where the mold cannot be reused. The Sand used for the mold cannot be reused as in other sand casting process. But some techniques are developed by which the sand can be broken down, cooled and filtered to be reused. The reclaimed sand is then mixed with a large amount of fresh sand in order to make a new no bake sand mold.

Application: Widely favored for high precision casting in brass, bronze, aluminum and iron alloys, this process ensures accurate production of complicate designs. No bake process is an ideal process for high value, heavy and critical castings. Casting of large size can be done with perfection, since the mold can stand on it own without the need for flasks or other supports.

Advantages:
A simple method that required less manual labour // Reduced production cost // More number of cast can be produced // Complicated designs and excellent surface finish can be casted compared to other sand casting techniques // Less time for mold setting // Most efficient and advanced sand casting techniques currently available // Big castings can be casted in a single mold. // Large, heavy, intricate, castings can be produced


Co2 SAND

Introduction: Co2 Casting is a kind of sand casting process. In this process the sand molding mixture is hardened by blowing gas over over the mold. This process is favoured by hobby metal casters because a lot of cost cutting can be done. In addition, one can be sure of getting dimensionally accurate castings with fine surface finish. But, this process is not economical than green sand casting process.

Process: The Mold for Co2 Casting is made of a mixture of sand and liquid silicate binder which is hardened by passing Co2 gas over the mold. The equipment of the molding process include Co2 cylinder, regulator, hoses and hand held applicator gun or nozzle. Carbon di oxide molding deliver great accuracy in production.

Any existing pattern can be used for the molding purpose which can be placed in the mold before the mold is hardened. This method helps in producing strong mold and cores that can be used for high end applications. If the process is carefully executed then casting can be as precise as produced by the shell casting method.

Carbon di oxide casting is favored both by the commercial foundrymen and hobbyist for a number of reasons. In commercial operations, foundrymen can assure customers of affordable castings which require less machining. The molding process which can be fully automated is generally used for casting process that require speed, high production runs and flexibility. In home foundries this is one of the simplest process that improves the casting quality .

Applications: Co2 casting process is ideal where speed and flexibility is the prime requirement. molds and cores of a varied sizes and shapes can be molded by this process.

Advantages: This process has many advantages in comparison to other forms of castings some of them are as follows:
  • Compared to other casting methods cores and molds are strong
  • Reduces fuel cost since gas is used instead of to other costly heating generating elements
  • Reduces large requirement for number of mold boxes and core dryers
  • Provides great dimensional tolerance and accuracy in production
  • Moisture is completely eliminated from the molding sand
  • This process can be fully automated.