The gating system refers to all passageways through which molten metal passes to enter into the mould cavity.

Objective of the Gating System

The objective of the gating system are:

1. To minimise turbulence, which tends to promote absorption of gases, oxidation of the metal, and erosion of the mould.
2. To get enough metal into the mould cavity before the metal starts to solidify.
3. To avoid shrinkage.
4. Establish the best possible temperature gradient in the solidifying casting so that the shrinkage if occurs must be in the gating system not in the required cast part.
5. Incorporates a system for trapping the non-metallic inclusions.

Elements of Gating System

Various elements of gating system are:

1. Pouring Basin
2. Sprue
3. Sprue-Base Well
4. Runner
5. Runner Extension
6. In-Gate

While designing the gating system the following factors should be taken into consideration:

1. Flow of Metal in Gating System
2. Pouring Time
3. Choke Area
4. Gating ratio

Flow of Metal in Gating System

The molten metal flowing through the gating system follows the Bernoulli’s theorem, which states that the total energy head remains constant at any section (ignoring the frictional losses). The Bernoulli’s equation is:
\[ h + {\frac{P}{\rho g}} + {\frac {V^2} {2g}} = constant \]
Where:
h = height of the liquid
P = static pressure
V = metal velocity
g = Acceleration due to gravity 
\(\rho\) = Fluid density

Bernoulli's theorem helps us to understand the metal flow in the gating system. To avoid turbulence in the metal flow the gating system must be designed in such a way that the system always runs full with the liquid metal, and avoid sharp corners. Any changes in direction or cross sectional area should make use of rounded corners.

As suggested earlier to avoid the aspiration the tapered sprues are designed in the gating systems. A sprue tapered to a smaller size at its bottom will create a choke which will help keep the sprue full of molten metal.

We can get exact tapering by using continuity equation as below
\[ A_1 V_1 = A_2 V_2 \]
or
\[ A_2 = A_1 {\frac{V_1}{V_2}} \]
Since velocity is proportional to the square of the potential head:
\[ A_2 = A_1 {\sqrt{\frac{h_1}{h_2} }} \]

The square root suggests that the profile must be parabolic,but making parabolic profile is not so convenient and straight  taper is preferred.

Pouring Time

Pouring time is defined as the time required for complete filling of the mould cavity. The objective of the gating system is to fill the mould cavity as fast as possible. Too long pouring time requires higher pouring temperature and too less pouring time may create turbulence in the flow of metal. Thus an optimum pouring time is to be known for a given casting.

The pouring time depends on the casting material, size, and complexity. Since steel loses heat at a faster rate, the pouring time should be less. For non-ferrous metals, since they lose heat slowly and also form dross if poured quickly, a longer pouring time is required.

Choke Area

Choke area is the place in the gating system which regulates the flow of molten metal. Generally, the bottom portion of the sprue is considered as choke area. The main advantage of having sprue base as choke area is that proper flow characteristics are established early in the mould.

Gating ratio

The gating ratio is the relative cross-sectional area of sprue, runner and in-gates. Based on gating ratio the gating systems are grouped into two categories.

• Non Pressurised
• Pressurised

Non pressurised gating system has runner and in-gates areas higher than the sprue area (Choke area). In this system, there is no pressure existing in the metal flow which helps in reducing the turbulence. On the other hand, this system requires careful design to ensure complete filling of the mould and large size runners and gates which reduces the casting yield.

Non pressurised system is used for the drossy alloys such as aluminium and magnesium alloy. The ratios used are 1:2:2, 1:3:3 or 1:4:4.

In pressurised gating system generally, the in-gates area is kept smallest which builds back pressure in the gating system. The gating ratios such as 1:0.75:0.5, 1:2:1 and 2:1:1 is used. This system keeps itself full of metal, thus minimises the problem of aspiration. This system requires smaller runner and gating system which increases the yield of the casting. On the other hand, high velocity of metal flow may cause turbulence and associated dross formation. This system is suitable for ferrous metals and brass.

The riser is a source of extra metal which flows from the riser to mould cavity to compensate for shrinkage which takes place in the casting when it starts solidifying. Without a riser, heavier parts of the casting will have shrinkage defects (voids), either on the surface or internally. These defects are termed as a hot spot since they remain hot until the end.

Risers are normally placed at that portion of the casting which is last to freeze. A riser must stay in liquid state at least as long as the casting and must be able to feed the casting during this time. If the reverse were true, liquid metal would flow from the casting toward the solidifying riser and the casting shrinkage would be even greater. Hence, castings should be designed to produce directional solidification that sweeps from the extremities of the mould cavity toward the riser.

Risers are known by different names as a metal reservoir, feeders, or headers.

Functions of Risers

• Provide extra metal to compensate for the volumetric shrinkage
• Allow mould gases to escape
• Provide extra metal pressure on the solidifying mould to reproduce mould details more exact
• Produce directional solidification

Riser placement

 Risers should be located so that directional solidification occurs from the extremities of the mould cavity back toward the riser. Since the thickest regions of a casting will be the last to freeze, risers should feed directly into these locations.

As mentioned in earlier, the larger the solidification modulus, the longer the solidification time. If a casting section has a larger modulus than all of the surrounding casting sections, it will still be solidifying after the surrounding sections are completely solidified. The last region to solidify in such a casting section is termed a hot spot. Once the hot spots in a casting are identified, a riser must be placed adjacent to each hot spot. This ensures that feed metal will be available to feed each hot spot until solidification is complete.

Types of Risers

A riser is categorised based on three criteria:

1. Based on position
2. Whether it is open to the atmosphere
3. How it is filled

Depending on the position of the riser it can be classified into two categories as below:

• Top Riser
• Side Riser

Top Riser

The top riser is positioned on the top of the casting. Since they are placed on the top of the casting, top risers will have shorter feeding distance and will occupy less space within the flask. The designers will have more freedom for the layout of the pattern and gating system.

Side Riser

Side risers are located adjacent to the mould cavity, displaced horizontally along the parting line.

Depending on whether it is open to the atmosphere or not the risers can be classified into two categories as below:

• Open Riser
• Blind Riser

Open Riser

If the top of the riser is open to the atmosphere it is called as an open riser. The open risers convenient to make, but the position where it can be placed is limited. Since the top of the riser is open to atmosphere, the heat loss will take place faster as compared to the blind riser.

Blind Riser

If the riser is contained entirely within the mould, it is known as a blind riser. It can be located more conveniently than the open risers. Since it is surrounded by moulding sand the heat loss will be slow and it will be more effective.

And lastly depending on how it is filled risers can be classified as below:

• Live Riser or Hot Riser
• Dead Riser or Cold Riser

Live riser or Hot Riser

Live risers receive the last hot metal that enters the mould and generally does so at a time when the metal in the mould cavity has already begun to cool and solidify. Risers that are part of the gating system generally live risers. Live risers are usually smaller than dead risers.

Dead Riser or Cold Riser

If the riser fills with material that has already flowed through the mould cavity it is known as a dead riser or cold riser. Top risers are almost always dead risers.

Feeding Aids

There are feeding aids that can be implemented to promote directional solidification and to reduce the number and size of risers, thereby increasing the yield of casting. These techniques generally work by either speeding the solidification of the casting (chills) or retarding the solidification of the riser (sleeves or toppings).

Use of Chills

When casting having combination of thick and thin sections and, directional solidification is not possible, by providing only risers, chills are used to increase the cooling rate and obtain directional solidification. Chills can be of two types:

• External Chills
• Internal Chills

External Chills

External chills are placed in the mould wall at any required position. They are made in a different shape to match the mould contour. External chill may be of a direct or indirect type. The direct type comes in contact with molten metal whereas indirect type is placed behind the mould wall and will not have direct contact with molten metal.

Internal Chills

Internal chills are placed within the mould cavity, and finally becomes an integral part of the final casting. The metal of internal chill should be the same as or compatible with the alloy being cast.

Use of Sleeves

Riser sleeves which are either purely insulating or mildly exothermic may be used to reduce the heat transfer through the wall of the riser, which keeps riser in a molten state for a longer duration. These are made of fire clay – sawdust for ferrous materials, Plaster of Paris is generally used as an insulator for non-ferrous metals.

Use of Exothermic Materials

Exothermic materials help in achieving directional solidification by the generation of heat. Due to its contact with molten metal, a chemical reaction takes place, which produces a substantial amount of heat to keep riser in a molten state. The exothermic material can be added to the sand in the riser wall or it can be added to the top surface of the molten metal in the riser. When added to the top of riser would give out heat and act as an insulator to the atmosphere.

The exothermic material is a mixture of the oxide of the metal to be cast and aluminium metal in powder form.

The exothermic material can also be used as a core in the mould at desired position to achieve directional solidification. The core retains the shape after the reaction and provides heat insulation to the metal. Another method of using exothermic material is to mix it with facing sand and apply the mixture to those portions of the casting where more heat is required.

All castings are made with the molten metal. Ideally, the molten metal should be available in an adequate amount, at the desired temperature, with the desired chemistry and minimum contamination. A number of furnaces can be used for melting the metal. The choice of furnace depends on the type of metal to be melted. Some of the furnaces used in metal casting are as follows:

1. Crucible furnaces or indirect fuel-fired furnaces
2. Cupola
3. Electric arc furnace
4. Induction furnace
5. Direct Fuel-Fired Furnaces Or Reverberatory Furnaces

The melting furnace should have following characteristics:

• Holding material for an extended period of time without deterioration of quality.
• Economical to operate.
• And should not pollute the environment.

Selection of the most appropriate furnace depends on the factors listed below

• Minimum temperature requirement.
• Desired melting rate.
• Alloy being melted and the form of available charge material.
• The desired quantity of molten metal.
• Fuel used in the furnace and cost of fuel.
• Whether melting is to be batch or continuous.
• Environmental restrictions.
• The cost of the furnace.

Steel castings and ingots (used as raw material for remelting) or sometimes slabs, for working, are generally cast directly from the refining furnace in which the steel is made. In certain cases, there may be a separate melting and alloying stage. In the cast iron foundry, the pigs cast at the blast furnace are remelted and any extra alloying carried out. Pure copper ingots for working are cast directly from the refining furnace. For copper and other non-ferrous metals, usually, the refined metal is cast into notched bar ingots of suitable sizes. These ingots are remelted, alloyed as required and cast into final shapes or ingots for working. Clean scrap of known composition is often incorporated at the melting stage. The chemistry of scrap material can be adjusted through alloy additions in the form of either pure materials or master alloys that are high in a particular element but are designed to have a lower melting point than the pure material and a density that allows for good mixing. Preheating the metal being charged is another common practice, and it can increase the melting rate of the furnace by as much as 30%.

Crucible Furnaces or Indirect Fuel-Fired Furnaces

Crucible furnaces are small capacity typically used for small melting applications. It is suitable for the batch type foundries where the metal requirement is intermittent. The metal is placed in a crucible which is made of clay and graphite, silicon carbide, cast iron, or steel. The energy is applied indirectly to the metal by heating the crucible by coke, oil or gas.

Stirring action, temperature control, and chemistry control are often poor, and furnace size and melting rate are limited. Nevertheless, these furnaces do offer low capital and operating cost.

Better control of temperature and chemistry can be obtained, however, if the crucible furnaces are heated by electrical resistance heating.

Cupola

Cupola furnaces are tall, refractory-lined cylindrical furnaces used to melt iron and ferrous alloys in foundry operations.
  
Alternating layers of coke (carbon), iron (pig iron and/or scrap), and limestone or other flux, and possible alloy additions are charged and melted under forced air draft. A schematic diagram of a cupola is shown in Figure. This diagram of a cupola illustrates the furnace's cylindrical shaft lined with refractory and the alternating layers of coke and metal scrap. The molten metal flows out of a spout at the bottom of the cupola.

Cupolas are simple and economical, can be obtained in a wide range of capacities, and can produce cast iron of excellent quality if the proper raw materials are used and good control is practised. Control of temperature and chemistry can be somewhat difficult. Since it is difficult to control the chemistry inside of the furnace, the final chemistry adjustments are often performed in the ladle, using the various techniques of ladle metallurgy.

Working of Cupola

• There is a charging door through which coke, pig iron, steel scrap and flux is charged.
• The blast is blown through the tuyeres.
• These tuyeres are arranged in one or more row around the periphery of the cupola.
• Hot gases which ascend from the bottom (combustion zone) preheats the iron in the preheating zone.
• Cupolas are provided with a drop bottom door through which debris, consisting of coke, slag etc. can be discharged at the end of the melt.
• A slag hole is provided to remove the slag from the melt.
• Through the tap hole, molten metal is poured into the ladle.
• At the top conical cap called the spark arrest is provided to prevent the spark emerging to outside.

Electric Arc Furnace

An electric arc furnace used for steel making consists of a refractory-lined vessel, usually water-cooled in larger sizes, covered with a retractable roof, and through which one or more graphite electrodes enter the furnace Figure . The furnace is primarily split into three sections:

• The shell, which consists of the side walls and lower steel bowl
• The hearth, which consists of the refractory lines of the lower bowl
• The roof, which may be refractory-lined or water-cooled, and can be shaped as a section of a sphere, or as a frustum (conical section). The roof also supports the refractory delta in its centre, through which one or more graphite electrodes enter.

The top of the furnace is first lifted or swung aside to permit the introduction of charge material.

After charging the top is then repositioned, and the electrodes are lowered to create an arc between the electrodes and the metal charge. The path of the heating current is usually through one electrode, across an arc to the metal charge, through the metal charge, and back through another arc to another electrode. Oxygen is blown into the charge for combusting or cutting the steel and extra chemical heat is provided by wall-mounted oxygen-fuel burners. Both processes accelerate the charge meltdown. Supersonic nozzles enable oxygen jets to penetrate foaming slag and reach the liquid bath.

Fluxing materials are usually added to create a protective slag over the pool of molten metal. Slag usually consists of metal oxides, and acts as a destination for oxidised impurities, as a thermal blanket (stopping excessive heat loss) and helping to reduce erosion of the refractory lining. Reactions between the slag and the metal serve to further remove impurities.

Induction Furnace

An induction furnace is an electrical furnace in which the heat is applied by induction heating of metal. Induction furnace capacities range from less than one kilogram to one hundred tonnes capacity and are used to melt iron and steel, copper, aluminium and precious metals.

The heating by the induction method occurs when an electrically conductive material is placed in a varying magnetic field. Induction heating is a rapid form of heating in which a current is induced directly into the part being heated. Induction heating is a non-contact form of heating.

There are two basic types of induction furnaces.

• The high-frequency, or coreless units, shown schematically in
• Low-frequency or channel-type induction furnaces, shown schematically in Figure

Direct Fuel-Fired Furnaces Or Reverberatory Furnaces

Direct fuel-fired furnaces, also known as reverberatory furnaces, are metallurgical or process furnace that isolates the material being processed from contact with the fuel, but not from contact with combustion gases. As illustrated in Figure, a fuel-fired flame passes directly over the pool of molten metal. The heat being transfer to the metal takes place through both radiant heating from the refractory roof and walls and convective heating from the hot gases

As soon as the molten metal is in the mould, it begins to cool. When the temperature drops below the freezing point (melting point) of the material, solidification starts. Solidification involves a change of phase of the material and differs depending on whether the material is a pure element or an alloy. A pure metal solidifies at a constant temperature, which is its melting point (freezing point). For alloys, the solidification occurs over a temperature range depending upon the composition.

Solidification takes place in two stages as given below:

• Nucleation
• Growth

For sound casting, it is important to control both of these stages.

Nucleation

Nucleation is the process of formation of tiny stable solid particles from the liquid (generally 50-60 atoms of 1-2 nm diameter). When molten metal reaches a temperature below its melting point, the liquid state will have more energy than solid state and as a result, internal energy is released. At the same time, a solid-liquid interface must be created, which requires energy. Thus in order for nucleation to occur, there must be a net reduction or release of energy. As a result, nucleation takes place at a temperature below the equilibrium melting point (the temperature where the internal energies of the liquid and solid are equal). The difference between the melting point and the actual temperature of nucleation is known as the amount of undercooling. Larger the extent of undercooling, greater will be the number of nuclei formed.

Growth

In this stage, nuclei grow and then aggregate, which occurs as the heat of fusion is extracted from the molten metal. Direction, the rate of growth, and type of growth can be controlled by the manner of heat removal. Various techniques are as below:

• Directional solidification
• Movement of solid-liquid interface opposite to the direction of heat flow.
• Modify heat flow direction

The relative rates of nucleation and growth control the size and shape of the resulting crystals. Faster rates of cooling generally produce products with finer grain size and superior mechanical properties.

Cast Structure

The final solidified casting may have as many as three distinct regions or zones as follows:

• Chill zone
• Columnar zone
• Equiaxed zone

Chill zone

When a melt comes to the contact with a wall of the cold metallic mould, the rapid nucleation takes place and a narrow band of randomly oriented small chill crystals (equiaxed grains) form at the surface of the casting.

Columnar zone

As the latent crystallization heat, liberating from the crystallizing metal decreases the undercooling of the melt and depresses the fast grains growth. At this stage some of the small grains, having favourable growth axis, start to grow in the direction opposite to the direction of heat flow. As a result columnar crystals (columnar grains) form. The length of the columnar grains zone is determined by the constitutional undercooling. When the temperature of the melt, adjacent to the solidification front, increases due to the liberation of the latent heat, constitutional undercooling will end and the columnar grains growth will stop.

Equiaxed zone

Further cooling of the molten alloy in the central zone of the ingot will cause the formation of spherical, randomly oriented crystals, known as the equiaxed zone. Low pouring temperatures, alloy additions, and the addition of inoculants can be used to promote the formation of this region, whose isotropic properties (uniform in all directions) are far more desirable than those of columnar grains.

Different cooling rates and solidification times can produce substantial variation in the structure and properties of the resulting casting. Die casting, for example, uses water-cooled metal moulds, and the faster cooling produces higher-strength products than sand casting, where the mould material is more thermally insulating. Even variations in the type and condition of sand can produce different cooling rates. Sands with high moisture contents extract heat faster than ones with low moisture.

Fluidity of molten metal

The ability of a metal to flow and fill a mould, its runniness, is known as fluidity. Pure metals will have good fluidity. This term consists of two basic factors:

1. Characteristic molten metal and
2. Casting parameters.

The following characteristics of molten metal influence fluidity.

Viscosity

As viscosity and its sensitivity to temperature (viscosity index) increase, fluidity decreases.

Surface tension

A high surface tension of the liquid metal reduces fluidity. Oxide films developed on the surface of the molten metal thus have a significant effect on fluidity. For example, the oxide film on the surface of pure molten aluminium triples the surface tension.

Inclusions

As insoluble particles, inclusions can have a significant adverse effect on fluidity and will greatly reduce the fluidity of pure elements, thus easily accounting for the fact that further alloying appears to reduce the fluidity. This effect can be verified by observing the viscosity of a liquid such as oil with and without sand particles in it; the former has higher viscosity.

Superheat

All investigations of fluidity have confirmed that the fluidity increases linearly with the superheat (defined here as the excess of metal temperature over liquidus temperature).  This effect of superheat is valuable in itself.  In addition, however, it can help us to understand the special fluidity properties of eutectics.  

Freezing Rang of Alloy

Fluidity is inversely proportional to the freezing range. Thus the shorter the range (as in pure metals and eutectics), the higher the fluidity becomes. Conversely, alloys with long freezing ranges (such as solid-solution alloys) have lower fluidity.

Latent Heat of Solidification of Alloy

The latent heat of solidification will affect the fluidity of metals simply by affecting the solidification time. Greater the solidification time, the further metal will run before freezing.

Tests for fluidity

Although none is accepted universally, several tests have been developed to quantify fluidity. One such test is shown in Figure, where the molten metal is made to flow along a spiral channel at room temperature. The distance of metal flow before it solidifies and stops is a measure of its fluidity. Obviously, this length is a function of the thermal properties of the metal and the mould, as well as the design of the channel. Such tests are useful and simulate casting situations to a reasonable degree.

Several types of defects may occur during casting, which is caused by irregularities in the moulding process. These defects considerably reduce the total output of the casting and increase the cost of the production. Therefore, it is most important to understand the causes of these defects.

Based on the cause of defect the casting defects can be classified into five major categories as follows:

• Defects Caused by Moulding Material
• Defects Caused by Gas
• Defects Caused by Pouring metal
• Defects Caused by Shrinkage
• Mould Shift
• Metallurgical Defects

Defects Caused by Moulding Material

These defects are caused by the characteristics of the moulding material. These defects occur mostly because either moulding material is not of required properties or ramming is improper. Following are the defects caused by moulding material:

• Cuts and Washes
• Metal Penetration
• Fusion
• Buckles and Rat Tails
• Swell
• Inclusions
• Drop

Defects Caused by Gas

A condition existing in a casting caused by the trapping of gas in the molten metal or by mould gases evolved during the pouring of the casting. The defects in this category can be classified into following categories:

• Blowholes
• Pinhole porosity

Defects Caused by Pouring metal

The likely defects in this category are

1. Mis-runs and Cold shut.
2. Slag Inclusions.

Defects Caused by Shrinkage

These are caused by liquid shrinkage occurring during the solidification of the casting. To compensate for this, proper feeding of liquid metal is required. For this reason, risers are placed at the appropriate places in the mould. Sprues may be too thin, too long or not attached in the proper location, causing shrinkage cavities. It is recommended to use thick sprues to avoid shrinkage cavities. Shrinkage defects can be split into two different types:

• Open shrinkage defects and
• Closed shrinkage defects.

Mould Shift

The mould shift defect occurs when cope and drag or moulding boxes have not been properly aligned.

Metallurgical Defects

There are two defects in this category

• Hot Tears
• Hot Spots

After the solidification of the casting, the mould is knocked out and solidified casting is taken out of the moulding sand. At this juncture, the cast product is attached with risers and gates. Many times the moulding sand also gets adhered to the casting as some of the sand gets fused with the molten metal. The cleaning of castings refers to the removal of gates, risers and sand. Also, cleaning may involve machining or abrasive finishing of the cast product. The cleaning operations usually performed on a casting are given below:

1. Removal of gates, in-gates, riser, feeder etc.
2. Surface cleaning
3. Trimming
4. Finishing

Removal of gates, in-gates, riser, feeder etc.

There are various methods of removal of unwanted metallic parts from the solidified cast product. In the case of brittle material, the gates, risers, and feeder can be removed by the impact force. These are usually done in shake out or knock out devices. Other processes that may be used to cut off the metallic parts include band saws, grinding machine, shearing machine, cutting torches, etc.

Surface cleaning

As the temperature of the molten metal is usually high, sand particles near the surface of the casting get fused and adhere to the surface of the casting. The cleaning of the surfaces both interior and exterior thus becomes necessary. There are several methods to remove the adhered sand from the castings. Some of the most common methods of removal of sand are tumbling, and sand or metallic shot blasting. Tumbling is done in a barrel like machine called as tumbling mill which helps to remove the sand by rubbing action of the cast parts with each other. Whereas, in blasting, abrasive particles are thrown on the surface of the casting in a carrying medium. Air is the most common medium used in this process. Sometimes, metallic shots are thrown on the surface of the castings to remove the unwanted material. Blasting processes include air blasting, centrifugal blasting, hydro-blasting etc. Other methods to clean the cast surface include wire brushing and buffing.

Trimming

Trimming operations involves the removal of fins, gates and risers appendages, metallic chaplets, etc. These unwanted material is removed by using hammer and chisel called as chipping process, or by pneumatic chipping hammers or by the use of grinders.

Finishing

The finishing at this stage refers to the final cleaning. The castings, after the removal of gates, risers, fins, chaplets, adhered sand, is washed and then depending upon the requirements of the end product final finish is provided by machining, polishing, buffing, chemical treatment etc.

Inspection and testing of castings encompasses five main categories:

1. Surface finish
2. Dimensional accuracy
3. Mechanical properties
4. Chemical composition
5. Casting soundness

Surface Finish

The surface finish of a metal casting can be influenced by the type of pattern or moulding sand, mould coating, and method of cleaning. The surface finish of a casting can be measured by perthometer, roughness tester, and by using profilo-meter. Usually, Root mean square values are measured.

Dimensional Accuracy

Variation in the dimensions of a casting can be the result of:

• Mould cavity expansion caused by the heat and head pressure of molten metal and
• The contraction of the metal as it cools and heat treatment

Mechanical Properties

Mechanical testing gives an evaluation of the metal and the casting to determine whether the properties are in compliance with the specified mechanical requirements. Following are common mechanical tests used in metal casting facilities.

Chemical Composition

The chemical composition of an alloy has a significant bearing on its performance properties. Chemical composition can be further affected by minor alloying elements added to the material. Casting alloys are typically specified according to ASTM, SAE and AMS alloy specifications. Depending on how susceptible an alloy is to the variation of its chemical composition, chemical analysis may be required to verify the proper composition is present to achieve a certain set of properties.

Chemical analysis often involves a sample of molten metal poured into a special mould and evaluated by spectrographic atomic absorption or x-ray fluorescence analysis. Many metal casting facilities check the chemical composition of the alloys they are pouring throughout the course of a day, so melt shop personnel can make required adjustments to the alloy composition as needed.

Casting Soundness

The performance of metal components can be notably affected by internal and surface defects that can not be detected through the regular course of the visual inspection. Several non-destructive methods can be employed to inspect castings for these “invisible” flaws. Non-destructive tests determine the integrity of a casting without causing physical damage, so once it passes the tests; it can be used for its intended application. Below is a detailed list of non-destructive tests.

Non-Destructive Testing Methods

• Visual Inspection
• Dimensional Inspection
• Dye Penetrant and Fluorescent Powder Testing
• Magnetic Particle Inspection
• Ultrasonic Testing
• Radiographic Inspection
• Eddy Current Inspection
• Pressure Leak Testing