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Gating System In Sand Casting

Gating System In Casting

When molten metal is poured into the mould during the casting process it requires a proper system to allow molten metal to flow in each section of the mould to make proper casting. 

This process is carried out by a system called a gating system which consists of multiple elements namely a pouring basin. runner, sprue, gate, and risers which allow molten metal to flow into the mould cavity, ensuring proper directional solidification, removal of slag and maintaining the proper velocity of molten metal in the system.

The majority of casting processes such as sand casting, die casting, investment casting, vacuum die casting, gravity die casting or permanent mould casting have the gating system included for molten metal to smoothly flow in the mould cavity and riser.

Few casting processes such as slush casting, continuous casting and centrifugal casting do not have a complex gating system such as sand casting and die casting.

Gating System

What is a gating system in casting?

A gating system in casting is a combination of various gating elements such as a pouring basin, sprue, sprue base well, runner, runner extension, gate, ingate and riser used to fill the mould cavity with molten metal to manufacture sound casting eliminating defects.

Gating System

The function of the gating system is to fill the mould cavity keeping in mind the temperature gradient, the flow of molten metal, directional solidification, feed rate of molten metal, slag and dross in metal and casting defects.

I have covered the function of the gating system in detail below in the article.

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Function Of Gating System

What is the function of the gating system in casting?

• Molten metal should enter the mould cavity with less turbulence.
• Erosion of sand in mould should be the least.
• Slag, dirt, dross, oxides and impurities trapping system should trap the unwanted substance and prevent it from entering the mould cavity.
• Directional solidification should be achieved by a gating system to avoid casting defects with a proper thermal gradient.
• Uniform feeding of molten metal should be fed to the sections of casting with different thicknesses.
• There should be a smooth flow of molten metal in the mould cavity through ingates.
• Air aspiration and turbulence of molten metal should be avoided in gating elements.
• The time taken to fill the mould cavity should be minimal.
• Optimum casting yield should be achieved with the gating system in the casting process.
• Travel of molten metal should be less which can be achieved by keeping runners, sprue and gates of shorter length.
• Unwanted gases, steam and vapour should be exhausted from the mould cavity through the riser.
• The gating system should achieve continuous feeding of molten metal.
• There can be multiple mould cavities in the sand-casting process. The gating system should ensure the filling and distribution of molten metal equally.
• Removing and breaking the gating system from the final casting should be easy.
• The gating system should be economical in cost to make.
• Molten metal should fill the gating system fully and then start freezing or solidifying.
• The gating system should not cause mould and core erosion.
• The gating system should have proper control over filling the mould cavity with molten metal.
• The pouring basin and sprue should be full all the time reducing air aspiration and turbulence during the flow of molten metal.
•  The runner should be connected to all gates supplying molten metal uniformly to all sections of the casting.
• The riser as a gating element should feed the mould cavity continuously resulting in uniform solidification and shrinkage of the casting.

Factors Controlling The Function Of The Gating System

What are the factors controlling the function of the gating system?

Factors controlling the function of the gating system in sand casting are as follows:

• Location of pouring basin, in-gates, sprue, runner and riser.
• The rate at which molten metal flows in a mould cavity.
• Pouring temperature of the molten metal.
• Rate of solidification of molten metal.
• The temperature at which molten metal enters the mould cavity.
• Fluidity and thermal gradient of molten metal.
• Pouring basin, furnace and types of equipment.
• Location of runner, in-gate, sprue and riser.
• Cost of making gating system and economical aspect behind it.
• The thermal gradient is to be achieved during solidification.
• Turbulence, vortex, air aspiration and sand erosion in the mould cavity.
• Shape, size and length of gating elements such as pouring basin, sprue, gate, runner and riser.
• Type of metal used for making a casting.

Types Of Gating Elements In Casting

What are the types of gating elements?

Types/elements of the gating system are as follows:

• Pouring basin.
• Sprue.
• Sprue base well.
• Runner.
• Gate.
• Riser.

Pouring Basin

The pouring basin in casting is a reservoir located in the cope section of the mould to reduce vortex, and turbulence during the pouring operation in the casting process.

I have written a detailed article on pouring basin in casting discussing function, working, design and types of pouring basins with diagrams.

Sprue

Sprue in the casting process is a vertical channel that connects the pouring basin to the runner.

I have discussed in detail the article on sprue in casting process working, types, design, and the formula with diagrams.

Sprue Base Well

Sprue base well is at the base of the sprue to absorb molten metal flowing at a higher velocity.

Runner

A runner is a common horizontal channel that connects the sprue and gate together. The function of a runner is to allow molten metal to connect to multiple gates and ensure a uniform flow of molten metal into each gate.

Another important function of the runner is to trap slag, oxides, sand and molten metal impurities from entering the final casting.

I have discussed runners with types, functions, designs and diagrams in a detailed article on runner in casting.

Gate and Ingate

The gate connects the runner with the ingate. Molten metal flowing from the runner enters the mould cavity through the gate and in-gate.

Gate and ingate should fill the mould cavity fully maintaining a constant flow of molten metal.

I have discussed gate in casting article with types, functions and diagrams in detail.

Riser

A riser in casting is used to compensate for liquid shrinkage and solidification shrinkage during the solidification process.

The riser is the last element in the gating system that supplies molten metal to the mould cavity during the solidification process.

I have written a riser in casting article explaining types, function, working, and design with diagrams.

Design Of Gating System

• Step 1: Calculate the pouring time of the molten metal.
• Step 2: Calculate the sprue choke area.
• Step 3: Select the gating ratio suitable for the casting.
• Step 4: Select the location of the gating elements such as sprue, runner, in-gate and riser.
• Step 5: Calculate runner, in-gates and runner sizes.

Precautions Taken During Designing Gating System

• Avoid any sharp turns, edges, or corners which may cause sand erosion and turbulence.
• The gating system should maintain the required temperature and pressure throughout the casting process.
• The gating system should not interrupt with chills, padding, cores and chaplet instead should accommodate the use of it.
• The required amount of molten metal should be supplied to all sections of the casting section.
• The system should be strong enough to take care of the metastatic force present during the process.
• The gating system should be economical to make.
• The system should be less time-consuming to make during the mould-making process.
• After the casting is taken out solidified gating system should be easy to separate from the final casting.
• The dry strength of the gating system should be higher to sustain the high temperature of molten metal.
• The gating system should be able to exhaust gases induced during the flow of the molten metal.