Casting Manufacturing Process, Basic Steps in the Casting Process, Metal Casting Process Steps Home » Casting Process » Casting Process: Basic Steps Casting Process: Basic Steps Industrial Process Description The metal casting process has been divided into the following five major operations: Obtaining the Casting Geometry : The process is referred as the study of the geometry of parts and plans, so as to improve the life and quality of casting. Casting Patternmaking : In pattern making, a physical model of casting, i.e. a pattern is used to make the mold. The mold is made by packing some readily formed aggregated materials, like molding sand, around the pattern. After the pattern is withdrawn, its imprint leaves the mold cavity that is ultimately filled with metal to become the casting. n case, the castings is required to be hollow, such as in the case of pipe fittings, additional patterns, known as cores, are used to develop these cavities. Coremaking & Molding : In core making, cores are formed, (usually of sand) that are placed into a mold cavity to form the interior surface of the casting. Thus the annul space between the mold-cavity surface and the core is what finally becomes the casting.

Molding is a process that consists of different operations essential to develop a mold for receiving molten metal. Alloy Melting and Pouring : Melting is a process of preparing the molten material for casting. It is generally done in a specifically designated part of foundry, and the molten metal is transported to the pouring area wherein the molds are filled. Casting Cleaning : Cleaning is a process that refers to the different activities performed for the removal of sand, scale, and excess metal from the casting. However, all the operations may not apply to each casting method but such processes play an important role to comply with environmental guidelines. Casting Process Foundry |authorSTREAM - by Kishore09331A0396 Metal Casting Introduction: : Introduction: Metal Casting is one of the oldest materials shaping methods known. Casting means pouring molten metal into a mold with a cavity of the shape to be made, and allowing it to solidify. When solidified, the desired metal object is taken out from the mold either by breaking the mold or taking the mold apart. The solidified object is called the casting. By this process, intricate parts can be given strength and rigidity frequently not obtainable by any other manufacturing process.

The mold, into which the metal is poured, is made of some heat resisting material. Sand is most often used as it resists the high temperature of the molten metal. Permanent molds of metal can also be used to cast products. Foundry: : Foundry: ” Foundry or casting is the process of producing metal/alloy component parts of desired shapes by pouring the molten metal/alloy into a prepared mould (of that shape) and then allowing the metal/alloy to cool and solidify. The solidified piece of metal/alloy is known as a CASTING”. Casting Terms: : Casting Terms: 1. Flask: A metal or wood frame, without fixed top or bottom, in which the mold is formed. Depending upon the position of the flask in the molding structure, it is referred to by various names such as drag - lower molding flask, cope - upper molding flask, cheek - intermediate molding flask used in three piece molding. 2. Pattern: It is the replica of the final object to be made. The mold cavity is made with the help of pattern. 3. Parting line: This is the dividing line between the two molding flasks that makes up the mold. Slide 5: 4.

Core: A separate part of the mold, made of sand and generally baked, which is used to create openings and various shaped cavities in the castings. 5. Pouring basin: A small funnel shaped cavity at the top of the mold into which the molten metal is poured. 6. Sprue: The passage through which the molten metal, from the pouring basin, reaches the mold cavity. In many cases it controls the flow of metal into the mold. 7. Runner: The channel through which the molten metal is carried from the sprue to the gate. Slide 6: 8. Gate: A channel through which the molten metal enters the mold cavity. 9. Chaplets: Chaplets are used to support the cores inside the mold cavity to take care of its own weight and overcome the metallostatic force. 10. Riser: A column of molten metal placed in the mold to feed the castings as it shrinks and solidifies. Also known as feed head. 11. Vent: Small opening in the mold to facilitate escape of air and gases.

Basic Features: : Basic Features: Pattern and Mould A pattern is made of wood or metal, is a replica of the final product and is used for preparing mould cavity. Mould material should posses refractory characteristics and with stand the pouring temperature. When the mold is used for single casting, it made of sand and known as expendable mold. When the mold is used repeatedly for number of castings and is made of metal or graphite are called permanent mould. For making holes or hollow cavities inside a casting, cores made of either sand or metal are used. Slide 8: Melting and Pouring: Several types of furnaces are available for melting metals and their selection depends on the type of metal, the maximum temperature required and the rate and the mode of molten metal delivery. Before pouring provisions are made for the escape of dissolved gases. The gating system should be designed to minimize the turbulent flow and erosion of mould cavity.The other important factors are the pouring temperature and the pouring rate. Slide 9: Solidification and Cooling: The properties of the casting significantly depends on the solidification time cooing rate.

Shrinkage of casting, during cooling of solidified metal should not be restrained by the mould material, otherwise internal stresses may develop and form cracks in casting. Proper care should be taken at the design stage of casting so that shrinkage can occur without casting defects. Slide 10: Removal, Cleaning, Finishing and Inspection: After the casting is removed from the mould it is thoroughly cleaned and the excess material usually along the parting line and the place where the molten metal was poured, is removed using a potable grinder. White light inspection, pressure test, magnetic particle inspection, radiographic test, ultrasonic inspection etc. are used Schematic diagram of casting mould: : Schematic diagram of casting mould: Steps involved in making a casting: : Steps involved in making a casting: Make the pattern out of Wood , Metal or Plastic. Prepare the necessary sand mixtures for mould and core making. Prepare the Mould and necessary Cores. Melt the metal/alloy to be cast. Pour the molten metal/alloy into mould and remove the casting from the mould after the metal solidifies. Clean and finish the casting. Test and inspect the casting. Remove the defects, if any. Relieve the casting stresses by Heat Treatment.

Again inspect the casting. The casting is ready for shipping. Advantages of metal casting: : Advantages of metal casting: Casting is one of the most versatile manufacturing process. Casting provides the greatest freedom of design in terms of shape, size and the product quantity. Casting imparts uniform directional properties and better vibration capacity to the cast parts. Casting produces machinable parts. Shapes difficult and uneconomic to obtain otherwise may be achieved through casting process. ( Contd..) Slide 15: A product may be cast as one piece, there by eliminating the need of metal joining processes. Very heavy and bulky parts which are otherwise difficult to get fabricated may be cast. Metals (like cast iron) dificult to be shaped by other manufacturing processes may be cast. Casting can be designed for equal distribution of loads and for minimum stress concentration in order to achieve more strength and increased service life. Casting process can be mechanised and usefully employed for mass production of components. Slide 16: Limitations of casting: Dimensional accuracy and surface finish of the castings made by sand casting processes are a limitation to this technique. Many new casting processes have been developed which can take into consideration the aspects of dimensional accuracy and surface finish.

Some of these processes are die casting process, investment casting process, vacuum-sealed molding process, and shell molding process. The metal casting process is a labor intensive process Applications of Casting: : Applications of Casting: Transportation vehicles Turbine vanes Power generators Railway crossings Agricultural parts Aircraft jet engine parts Sanitary fittings Communication, Construction and Atomic Energy applications, etc.. Different Sections in Foundry: : Different Sections in Foundry: Pattern making Sand mixing & preparation Mould and core making Mould assembly & handling Melting Pouring Shaking out Fettling & finishing Heat treatment Inspection & testing Raw Materials for Foundry: : Raw Materials for Foundry: Metals and alloys. Fuels (for melting metals). Fluxes. Metals and alloys commonly used in Foundries: : Metals and alloys commonly used in Foundries: 1. Ferrous 2. Non-Ferrous FERROUS: Cast irons Steels NON-FERROUS: Copper alloys Aluminium alloys Magnesium alloys Zinc alloys Nickel alloys Fuels for Melting Metals: : Fuels for Melting Metals: Coal Coke Gas Oil electricity Fluxes: : Fluxes: A flux is a low melting point material.

When heated up, it melts and combines with ash, viscous slags, sand, metallic oxides etc., and makes a fluid and easy flowing slag. This slag being lighter comes on to the surface of the molten metal from where it can be easily skimmed, tapped or removed before pouring the metal into the mould. Slag protects molten metal from furnace atmosphere. Refractories: : Refractories: Refractories are heat resistant materials. They can withstand high temperatures without being fused. Crucibles and furnace sides and bottoms containing molten metal are made up of refractories. These are used as ladles for pouring metal into the mould. Refractories constitute furnace walls and roof and thus minimize heat losses. Core and core prints: : Core and core prints: Castings are often required to have holes, recesses, etc. of various sizes and shapes. These impressions can be obtained by using cores. So where coring is required, provision should be made to support the core inside the mold cavity. Core prints are used to serve this purpose. The core print is an added projection on the pattern and it forms a seat in the mold on which the sand core rests during pouring of the mold.

The core print must be of adequate size and shape so that it can support the weight of the core during the casting operation. Depending upon the requirement a core can be placed horizontal, vertical and can be hanged inside the mold cavity. Pattern having core prints. : Pattern having core prints. Pattern Making: : Pattern Making: A Pattern is a model or the replica of the object to be cast. Except for the various allowances a pattern exactly resembles the casting to be made. A pattern is required even if one object has to be cast. Functions of Patterns: : Functions of Patterns: A Pattern prepares a mould cavity for the purpose of making a casting. A Pattern may contain projections known as core prints if the casting requires a core and need to be made hollow. Patterns properly made and having finished and smooth surfaces reduce casting defects. Properly constructed patterns minimize overall cost of the casting. Selection of Pattern Materials: : Selection of Pattern Materials: The following factors assist in selecting proper pattern material: No. of castings to be produced. Dimensional accuracy & surface finish. Shape, complexity and size of casting. Casting design parameters. Type of molding materials. The chance of repeat orders. Nature of molding process.

Slide 30: The pattern material should be: Easily worked, shaped and joined. Light in weight. Strong, hard and durable. Resistant to wear and abrasion . Resistant to corrosion, and to chemical reactions. Dimensionally stable and unaffected by variations in temperature and humidity. Available at low cost. Materials for making patterns: : Materials for making patterns: Wood Metal Plastic Plaster Wax. 1. Wood Patterns: : 1. Wood Patterns: Advantages: Inexpensive Easily available in large quantities Easy to fabricate Light in weight Thay can be repaired easily Easy to obtain good surface finish Limitations: Susceptible to shrinkage and swelling Possess poor wear resistance Abraded easily by sand action Obsorb moisture, consequently get wraped Cannot withstand rough handling These are used where the no. of castings to be produced is small and pattern size is large. 2. Metal Patterns: : 2. Metal Patterns: Advantages: Do not absorb moisture More stronger Possess much longer life Do not wrap, retain their shape Greater resistance to abrasion Accurate and smooth surface finish Good machinability Limitations: Expensive Not easily repaired Ferrous patterns get rusted Heavy weight These are employed where large no.

of castings have to be produced from same patterns. 3. Plastic Patterns: : 3. Plastic Patterns: Advantages: Durable Provides a smooth surface Moisture resistant Does not involve any appreciable change in size or shape Light weight Good strength Wear and corrosion resistance Easy to make Abrasion resistance Good resistance to chemical attack Limitations: Plastic patterns are Fragile These are may not work well when subject to conditions of severe shock as in machine molding (jolting). 4. Plaster Patterns: : 4. Plaster Patterns: Advantages: It can be easily worked by using wood working tools. Intricate shapes can be cast without any difficulty. It has high compressive strength. Plaster may be made out of Plaster of paris or Gypsum cement. Plaster mixture is poured into a mould made by a sweep pattern or a wooden master pattern, in order to obtain a Plaster pattern. 5. Wax patterns: : 5. Wax patterns: Advantages: Provide very good surface finish. Impatr high accuracy to castings. After being molded, the wax pattern is not taken out of the mould like other patterns; rather the mould is inverted and heated; the molten wax comes out and/or is evaporated.

Thus there is no chance of the mould cavity getting damaged while removing the pattern. Wax patterns find applications in Investment casting process. Types of Patterns: : Types of Patterns: Single piece pattern. Split piece pattern. Loose piece pattern. Match plate pattern. Sweep pattern. Gated pattern. Skeleton pattern Follow board pattern. Cope and Drag pattern. (a)Split pattern(b) Follow-board(c) Match Plate(d) Loose-piece(e) Sweep(f) Skeleton pattern : (a)Split pattern(b) Follow-board(c) Match Plate(d) Loose-piece(e) Sweep(f) Skeleton pattern 1. Single piece (solid) pattern: : 1. Single piece (solid) pattern: Made from one piece and does not contain loose pieces or joints. Inexpensive. Used for large size simple castings. Pattern is accommodated either in the cope or in the drag. Examples: Bodies of regular shapes. stuffling box of steam engine. Fig: Single piece pattern : Fig: Single piece pattern 2. Split piece pattern: : 2. Split piece pattern: Patterns of intricate shaped castings cannot be made in one piece because of the inherent difficulties associated with the molding operations (e.g. withdrawing pattern from mould).

The upper and the lower parts of the split piece patterns are accommodated in the cope and drag portions of the mold respectively. Parting line of the pattern forms the parting line of the mould. Dowel pins are used for keeping the alignment between the two parts of the pattern. Examples: Hallow cylinder Taps and water stop cocks etc., Fig: split piece pattern : Fig: split piece pattern 3.Loose piece pattern: : 3.Loose piece pattern: Certain patterns cannot be withdrawn once they are embedded in the molding sand. Such patterns are usually made with one or more loose pieces for facilitating from the molding box and are known as loose piece patterns. Loose parts or pieces remain attached with the main body of the pattern, with the help of dowel pins. The main body of the pattern is drawn first from the molding box and thereafter as soon as the loose parts are removed, the result is the mold cavity. 4. Match plate pattern: : 4. Match plate pattern: It consists of a match plate, on either side of which each half of split patterns is fastened. A no. of different sized and shaped patterns may be mounted on one match plate.

The match plate with the help of locator holes can be clamped with the drag. After the cope and drag have been rammed with the molding sand, the match plate pattern is removed from in between the cope and drag. Match plate patterns are normally used in machine molding. Fig: Match plate pattern : Fig: Match plate pattern 5. Sweep pattern: : 5. Sweep pattern: A sweep pattern is just a form made on a wooden board which sweeps the shape of the casting into the sand all around the circumference. The sweep pattern rotates about the post. Once the mold is ready, Sweep pattern and the post can be removed. Sweep pattern avoids the necessity of making a full, large circular and costly three-dimensional pattern. Making a sweep pattern saves a lot of time and labour as compared to making a full pattern. A sweep pattern is preferred for producing large casting of circular sections and symmetrical shapes. 6. Gated pattern: : 6. Gated pattern: The sections connecting different patterns serve as runner and gates. This facilitates filling of the mould with molten metal in a better manner and at the same time eliminates the time and labour otherwise consumed in cutting runners and gates.

A gated pattern can manufacture many casting at one time and thus it is used in mass production systems. Gated patterns are employed for producing small castings. castings : castings Gating system 7. Skeleton pattern: : 7. Skeleton pattern: A skeleton pattern is the skeleton of a desired shape which may be S-bend pipe or a chute or something else. The skeleton frame is mounted on a metal base The skeleton is made from wooden strips, and is thus a wooden work. The skeleton pattern is filled with sand and is rammed. A strickle (board) assists in giving the desired shape to the sand and removes extra sand. Skeleton patterns are employed for producing a few large castings. A skeleton pattern is very economical, because it involves less material costs. 8. Follow board pattern: : 8. Follow board pattern: A follow board is a wooden board and is used for supporting a pattern which is very thin and fragile and which may give way and collapse under pressure when the sand above the pattern is being rammed. With the follow board support under the weak pattern, the drag is rammed, and then the fallow board is with drawn, The rammed drag is inverted, cope is mounted on it and rammed.

During this operation pattern remains over the inverted drag and get support from the rammed sand of the drag under it. Follow boards are also used for casting master patterns for many applications. 9. Cope and Drag patterns: : 9. Cope and Drag patterns: A cope and drag pattern is another form of split pattern. Each half of the pattern is fixed to a separate metal/wood plate. Each half of the pattern(along the plate) is molded separately in a separate molding box by an independent molder or moulders. The two moulds of each half of the pattern are finally assembled and the mould is ready for pouring. Cope and drag patterns are used for producing big castings which as a whole cannot be conveniently handled by one moulder alone. Fig: Cope and drag pattern : Fig: Cope and drag pattern Pattern Allowances: : Pattern Allowances: A pattern is larger in size as compared to the final casting, because it carries certain allowances due to metallurgical and mechanical reasons for example, shrinkage allowance is the result of metallurgical phenomenon where as machining, draft, distortion, shake and other allowances are provided on the patterns because of mechanical reasons.

Types of Pattern Allowances: : Types of Pattern Allowances: The various pattern allowances are: shrinkage or contraction allowance. Machining or finish allowance. Draft of tapper allowances. Distortion or chamber allowance. Shake or rapping allowance. 1.Shrinkage Allowance: : 1.Shrinkage Allowance: All most all cast metals shrink or contract volumetrically on cooling. The metal shrinkage is of two types: 1. Liquid Shrinkage: it refers to the reduction in volume when the metal changes from liquid state to solid state at the solidus temperature. To account for this shrinkage; riser, which feed the liquid metal to the casting, are provided in the mold. 2. Solid Shrinkage: it refers to the reduction in volume caused when metal loses temperature in solid state. To account for this, shrinkage allowance is provided on the patterns. Slide 58: Almost all cast metals shrink or contract volumetrically after solidification and therefore the pattern to obtain a particular sized casting is made oversize by an amount equal to that of shrinkage or contraction. Different metals shrink at different rates because shrinkage is the property of the cast metal/alloy.

The metal shrinkage depends upon: The cast metal or alloy. Pouring temp. of the metal/alloy. Casted dimensions(size). Casting design aspects. Molding conditions(i.e., mould materials and molding methods employed) Slide 59: Rate of Contraction of Various Metals : 2. Machining Allowance: : 2. Machining Allowance: A Casting is given an allowance for machining, because: Castings get oxidized in the mold and during heat treatment; scales etc., thus formed need to be removed. It is the intended to remove surface roughness and other imperfections from the castings. It is required to achieve exact casting dimensions. Surface finish is required on the casting. How much extra metal or how much machining allowance should be provided, depends on the factors listed below: Nature of metals. Size and shape of casting. The type of machining operations to be employed for cleaning the casting. Casting conditions. Molding process employed Machining Allowances of Various Metals: : Machining Allowances of Various Metals: 3. Draft or Taper Allowance: : 3. Draft or Taper Allowance: It is given to all surfaces perpendicular to parting line.

Draft allowance is given so that the pattern can be easily removed from the molding material tightly packed around it with out damaging the mould cavity. The amount of taper depends upon: Shape and size of pattern in the depth direction in contact with the mould cavity. Moulding methods. Mould materials. Draft allowance is imparted on internal as well as external surfaces; of course it is more on internal surfaces. Table 2 : Draft Allowances of Various Metals: : Table 2 : Draft Allowances of Various Metals: Fig: taper in design : Fig: taper in design 4. Distortion or cambered allowance: : 4. Distortion or cambered allowance: A casting will distort or wrap if : It is of irregular shape, All it parts do not shrink uniformly i.e., some parts shrinks while others are restricted from during so, It is u or v-shape, The arms possess unequal thickness, It has long, rangy arms as those of propeller strut for the ship, It is a long flat casting, One portion of the casting cools at a faster rate as compared to the other. 5. Shake allowance: : 5.

Shake allowance: A patter is shaken or rapped by striking the same with a wooden piece from side to side. This is done so that the pattern a little is loosened in the mold cavity and can be easily removed. In turn, therefore, rapping enlarges the mould cavity which results in a bigger sized casting. Hence, a –ve allowance is provided on the pattern i.e., the pattern dimensions are kept smaller in order to compensate the enlargement of mould cavity due to rapping. The magnitude of shake allowance can be reduced by increasing the tapper. Pattern Layout: : Pattern Layout: Steps involved: Get the working drawing of the part for which the pattern is to be made. Make two views of the part drawing on a sheet, using a shrink rule. A shrink rule is modified form of an ordinary scale which has already taken care of shrinkage allowance for a particular metal to be cast. Add machining allowances as per the requirements. Depending upon the method of molding, provide the draft allowance. Pattern Construction: : Pattern Construction: Study the pattern layout carefully and establish, Location of parting surface. No. of parts in which the pattern will be made. Using the various hand tools and pattern making machines fabricate the different parts of the pattern.

Inspect the pattern as regards the alignment of different portions of the pattern and its dimensional accuracy. Fill wax in all the fillets in order to remove sharp corners. Give a shellac coatings(3 coats) to pattern. impart suitable colors to the pattern for identification purposes and for other informations. Pattern Colours: : Pattern Colours: Patterns are imparted certain colors and shades in order to: Identify quickly the main body of pattern and different parts of the pattern. Indicate the type of the metal to be cast. Identify core prints, loose pieces, etc., Visualise the surfaces to be machined, etc. Moulding Materials : Moulding Materials Major part of Moulding material in sand casting are 70-85% silica sand (SiO2) 10-12% bonding material e.g., clay cereal etc. 3-6% water Requirements of molding sand are: Refractoriness Cohesiveness Permeability Collapsibility The performance of mould depends on following factors: Permeability Green strength Dry strength Molding Material and Properties: : Molding Material and Properties: A large variety of molding materials is used in foundries for manufacturing molds and cores.

They include molding sand, system sand or backing sand, facing sand, parting sand, and core sand. The choice of molding materials is based on their processing properties. The properties that are generally required in molding materials are: 1. Refractoriness: : 1. Refractoriness: It is the ability of the molding material to with stand high temperatures (experienced during pouring) with out Fusion, Cracking, buckling or scabbing, Experiencing any major physical change. Silica sand have high refractriness. 2. Permeability: : 2. Permeability: During pouring and subsequent solidification of a casting, a large amount of gases and steam is generated. These gases are those that have been absorbed by the metal during melting, air absorbed from the atmosphere and the steam generated by the molding and core sand. If these gases are not allowed to escape from the mold, they would be entrapped inside the casting and cause casting defects. To overcome this problem the molding material must be porous. Proper venting of the mold also helps in escaping the gases that are generated inside the mold cavity. 3. Green Strength: : 3.

Green Strength: The molding sand that contains moisture is termed as green sand. The green sand particles must have the ability to cling to each other to impart sufficient strength to the mold. The green sand must have enough strength so that the constructed mold retains its shape. Green strength helps in making and handling the moulds. 4. Dry Strength: : 4. Dry Strength: A mould may either intentionally be dried, or a green sand mould may lose its moisture and get dried while waiting for getting poured or when it comes in contact with molten metal being poured. The sand thus dried must have dry strength to Withstand erosive forces due to molten metal, Withstand pressure of molten metal, Retain its exact shape,and Withstand the metallostatic pressure of the liquid material. 5. Hot Strength: : 5. Hot Strength: As soon as the moisture is eliminated, the sand would reach at a high temperature when the metal in the mold is still in liquid state. The strength of the sand that is required to hold the shape of the cavity is called hot strength. In the absence of adequate hot strength, the mold may enlarge break, erode or get cracked. 6. Collapsibility: : 6.

Collapsibility: Collapsibility determines the readiness with which the molding sand, Automatically gets collapsed after the casting solidifies, and Breaks down in knock out and cleaning operations. If the mould or core does not collapse, it may restrict free contraction of solidifying metal and cause the same to tear or crack. 7. Flowability: : 7. Flowability: It is the ability of the molding sand to get compacted to a uniform density. Flowability assists molding sand to flow and pack all-around the pattern and take up the required shape. Flowability increases as clay and water contents increase. 8. Adhesiveness: : 8. Adhesiveness: It is the property of molding sand owing to which, it Sticks with the walls of molding boxes, Sticks with gaggers, and Thus makes it possible to mold cope and drag. 9. Fineness: : 9. Fineness: Finer sand mould resist metal penetration and produce smooth casting surfaces. Fineness and permeability are in conflict with each other and hence they must be balanced for optimum results. Molding Sand Composition: : Molding Sand Composition: The main ingredients of any molding sand are: Base sand, Binder, and Moisture 1.

Base Sand: : 1. Base Sand: Silica sand is most commonly used base sand. Other base sands that are also used for making mold are zircon sand, Chromite sand, and olivine sand. Silica sand is cheapest among all types of base sand and it is easily available. 2. Binder: : 2. Binder: Binders are of many types such as: Clay binders, Organic binders and Inorganic binders Clay binders are most commonly used binding agents mixed with the molding sands to provide the strength. The most popular clay types are: Kaolinite or fire clay (Al2O3 2 SiO2 2 H2O) and Bentonite (Al2O3 4 SiO2 nH2O) Of the two the Bentonite can absorb more water which increases its bonding power. 3. Moisture: : 3. Moisture: Clay acquires its bonding action only in the presence of the required amount of moisture. When water is added to clay, it penetrates the mixture and forms a microfilm, which coats the surface of each flake of the clay. The amount of water used should be properly controlled.

This is because a part of the water, which coats the surface of the clay flakes, helps in bonding, while the remainder helps in improving the plasticity. A Typical Composition of Molding Sand: : A Typical Composition of Molding Sand: Effect of moisture, grain size and shape on mould quality : Effect of moisture, grain size and shape on mould quality Classification of casting Processes: : Classification of casting Processes: Casting processes can be classified into following FOUR categories: 1. Conventional Molding Processes Green Sand Molding Dry Sand Molding Flask less Molding 2. Chemical Sand Molding Processes Shell Molding Sodium Silicate Molding No-Bake Molding 3. Permanent Mold Processes Gravity Die casting Low and High Pressure Die Casting 4. Special Casting Processes Lost Wax Ceramics Shell Molding Evaporative Pattern Casting Vacuum Sealed Molding Centrifugal Casting 1.Green Sand Molding: : 1.Green Sand Molding: Green sand is the most diversified molding method used in metal casting operations. The process utilizes a mold made of compressed or compacted moist sand. The term "green" denotes the presence of moisture in the molding sand. The mold material consists of silica sand mixed with a suitable bonding agent (usually clay) and moisture.

Advantages: Most metals can be cast by this method. Pattern costs and material costs are relatively low. No Limitation with respect to size of casting and type of metal or alloy used Disadvantages: Surface Finish of the castings obtained by this process is not good and machining is often required to achieve the finished product. 2.Dry Sand Molding: : 2.Dry Sand Molding: When it is desired that the gas forming materials are lowered in the molds, air-dried molds are sometimes preferred to green sand molds. Two types of drying of molds are often required. Skin drying and Complete mold drying. In skin drying a firm mold face is produced. Shakeout of the mold is almost as good as that obtained with green sand molding. The most common method of drying the refractory mold coating uses hot air, gas or oil flame. Skin drying of the mold can be accomplished with the aid of torches, directed at the mold surface.

3.Shell Molding Process: : 3.Shell Molding Process: It is a process in which, the sand mixed with a thermosetting resin is allowed to come in contact with a heated pattern plate (200 oC), this causes a skin (Shell) of about 3.5 mm of sand/plastic mixture to adhere to the pattern.. Then the shell is removed from the pattern. The cope and drag shells are kept in a flask with necessary backup material and the molten metal is poured into the mold. This process can produce complex parts with good surface finish 1.25 µm to 3.75 µm, and dimensional tolerance of 0.5 %. A good surface finish and good size tolerance reduce the need for machining. The process overall is quite cost effective due to reduced machining and cleanup costs. The materials that can be used with this process are cast irons, and aluminum and copper alloys. 4.Sodium Silicate Molding Process : 4.Sodium Silicate Molding Process In this process, the refractory material is coated with a sodium silicate-based binder. For molds, the sand mixture can be compacted manually, jolted or squeezed around the pattern in the flask.

After compaction, CO 2 gas is passed through the core or mold. The CO 2 chemically reacts with the sodium silicate to cure, or harden, the binder. This cured binder then holds the refractory in place around the pattern. After curing, the pattern is withdrawn from the mold. The sodium silicate process is one of the most environmentally acceptable of the chemical processes available. Slide 95: The major disadvantage of the process is that the binder is very hygroscopic and readily absorbs water, which causes a porosity in the castings.. Also, because the binder creates such a hard, rigid mold wall, shakeout and collapsibility characteristics can slow down production. Some of the advantages of the process are: A hard, rigid core and mold are typical of the process, which gives the casting good dimensional tolerances; good casting surface finishes are readily obtainable; Cntd.. : Sculptureworks, Inc.

The Story of Sculpture: From Clay to Bronze Introduction: The Art of the Lost-Wax Process The earliest known “lost-wax” castings date from the early dynasties of Egypt, nearly 7,000 years ago, when metal was poured into “investments” of fired clay that had been shaped with the help of wax that was melted, or “lost”. Then, sometime between 4,000 and 3,000 B.C., bronze was discovered, probably by accident, as being a metal that was harder than copper or tin alone. Thus began the era known as the Bronze Age. Ancient “lost-wax” bronze castings have withstood the centuries, visually telling the tale of past cultures, their religions, and their social structures. For example, Chinese bronzes depicted ceremonial images; Indian and Egyptian castings symbolized deities; Africans cast images of nature; and the Greeks recreated the human form. Many of these cultures have since grown obsolete, their religions have evolved and societies have changed. Elements of the “lost-wax” process have been refined. Yet today, bronze casting is essentially the same as it was in 2,000 B.C.

during the Akkadian period. Bronze is an alloy of 95% copper, 4% silicon and 1% manganese with traces of other elements such as iron. Silicon bronze has been the bronze of choice for fine art castings since its development in the 1920s. It is corrosion-resistant, strong, resilient, formable and weldable. Also known as "hot-cast" bronze, a fine art "lost-wax" casting of silicon bronze is created through many labor-intensive steps. Sculptor Tuck Langland works on the clay for his sculpture "Kenyan Dancer". 1. Making the Original Clay Sculpture To begin the process of making a bronze sculpture, most sculptors choose to make an original out of clay. There are multitudes of different clays available for the sculptor. The three main categories of clay used for sculpture are water-based clay, oil-based clay, and self-hardening/low-fire clay. Choosing the proper clay for a particular project may simply be a matter of preference. Experience, however, is perhaps the best teacher when deciding what type of clay to use.

Most of the artists with Sculptureworks prefer to work with oil-based clay (also known as plasticene, plastilene, or plastilina). The main reason for working with oil-based clay is because it never dries or hardens. It can always be softened and reworked if a change needs to be made. The main concern with using oil-based clay is how to have the clay soft enough to build the sculpture rapidly and yet at the same time have the clay hard enough to produce good detail. The usual solution is to choose a clay that is hard enough for detail work and then just use heat to soften the clay for buildup. Very small sculptures are often modeled directly in wax which, though more difficult to model, allows for maximum detail. 2. The Use of Armatures An armature in a sculpture is a material used for supporting the weight of the clay. An armature is usually necessary when portraying a figure in motion or in a standing posture. The armature serves as the underlying support to the sculpture. In some cases, a skeletal formation can be made out of wire, or other materials such as pipe or aluminum, that will help hold the clay in place, so that the clay can be worked and detailed.

When working with large sculptures, weight is an important issue. Thus, after the initial armature is constructed, sculptors often use “fillers” such as styrofoam or aluminum foil to “fill out” the form and reduce the amount of clay being used. If most of the mass of the armature can be made with filler, then the clay on top will be just a thin skin instead of a huge thick mass that risks falling off. Once the armature is built, the clay sculpture can then be formed around and on the armature. The armature holds the parts of the sculpture in place, allowing the sculptor the freedom to move the clay along the armature to get the form that he or she wants. For bas reliefs, an armature can be constructed which consists of a grid of screws connected with wires to prevent the clay from sliding. Sculptor Blair Buswell made this larger-than-life armature to support his monumental sculpture of basketball legend Oscar Robertson. Blair covered this steel armature with foam before adding the clay. Sculptor Paul Oestreicher makes finishing touches to the clay version of his sculpture of painter Alfred Levitt. 3.

Finishing the Clay in Preparation for Molding Once the final touches have been made to the original clay sculpture, the final procedure before molding is touching up delicate details and smoothing the surface of the clay to perfection. This is quite important because any error or imperfection in the clay would be copied in the molding process and would appear in every subsequent stage. Thus, the smoother the clay, the less work will be needed on the wax replica and the finished bronze casting itself. Hook tools, or rake tools, are often used to cut the clay down to a new contour and to leave small raised ridges on the surface. For smoother surfaces, rubber or metal kidney tools can be used. For really fine surfaces, a brush and a solvent are used to whisk away all tool marks. Once the desired smoothness has been achieved, the piece should be allowed to dry thoroughly before continuing to the molding process. 4. Making a Mold of the Clay Original When the clay sculpture is completely smooth and finalized, a mold must be made of the original clay. Excellent surface replication of the original can be achieved with a polyurethane mold compound or a high-quality silicon rubber. The most common material used to produce a mold today is a material known as Smooth On.

It is a latex rubber that is very carefully formulated to be able to pick up the minutest details in a work. The rubber mixture is applied directly to the surface of the clay, using a brush to actually “paint” it onto the surface. Special attention needs to be given to avoidance of air bubbles that may be trapped within the rubber mixture. Once the first coat of rubber has been applied to the surface, it must be allowed to thoroughly dry (usually for 24 hours) before the next coat is applied. All of the details from the original clay are now picked up within the rubber material that has been painted on. A mold most generally consists of three to five coats of rubber (applied over the course of several days). Once the final coat of rubber has dried, a firm outer "jacket" is made to help retain the shape of the more flexible rubber mold for pouring the wax replica. This “jacket” is usually made out of plaster, Hydrocal, resin, or epoxy, and is called the “mother mold”.

When all of this is complete and it is all dry, the outer "jacket" is removed, and the rubber is then cut away from the clay, on what is called a parting line (simply the division line for the mold). The sculpture has now gone from a positive form to a negative form. If the sculpture is large or complex, it will usually have to be divided into smaller pieces, with each piece needing its own individual mold. The pieces will be rejoined later, after the sculpture is cast in bronze, to make the complete sculpture whole again. The learning process for making an excellent multiple piece rubber mold can take years. A novice should hire a professional, or make a plaster waste-mold of the original and make a plaster cast (a positive). From this solid positive a rubber mold can be made without risk of "losing" the original. The highest quality mold will save much time and money in production. Above: Sculptor Tuck Langland applies the first coat of rubber by brush to make the mold of his sculpture "Dawn". Above: Sculptor Tuck Langland applies the third coat of rubber by spatula.

Above: Sculptor Tuck Langland applies the top plaster "jacket", or "mother mold", to hold the form of the mold. A worker pours melted wax into the "mother mold" through a hole in order to make a wax positive. 5. Pouring a Wax Replica From the Mold With the “mother mold” complete, positive forms can now be generated by pouring a wax replica. Pouring a wax is usually done in four stages or coats. The first coat is applied by heating the wax to a temperature of approximately 220 degrees Fahrenheit. While the wax is quite hot, the mold is rotated about, in an attempt to coat the entire internal surface of the mold with the melted liquid wax, which is poured into the “mother mold” through a hole. The second coat of wax is applied slightly cooler, at around 200 degrees. The final two coats go on at approximately 180 to 185 degrees. A completed wax should be approximately 1/4” thick, or just slightly thinner. When the wax cools and the mold is removed, a wax positive of the sculpture emerges.

If the sculpture is a bas relief, or if it has a large mold that opens wide, it is usually much easier to brush on the wax. Following the same temperature guidelines per coat as above, the wax must be brushed on beginning in the deepest hollows of the mold to avoid any drips. 6. Wax Chasing "Wax chasing" is the procedure of repairing all of the imperfections that were created during the pouring process of the wax to maintain the original details within the mold. There will most always be a few air bubbles, seams, and mold lines which will need to be removed from the surface of the wax positive. "Wax chasing" is usually performed at the foundry by a professional "wax chaser". However, if the sculptor prefers, they can do the "wax chasing" themselves. The "wax chasing" procedure is done with small, delicate tools for scraping, and with a hot tool for filling in the imperfections within the wax. Once the wax is back to a perfectly finished state, the sculptor inspects the wax. If the wax receives the sculptor's approval, it is ready to go to the foundry for spruing.

A wax chaser at Schaefer Foundry in Arlington, TX, works on the wax with small tools to remove any imperfections. Photograph by Elizabeth Loggins. A diagram of the sprue system by Sculptor Tuck Langland . 7. Spruing a Wax The finished wax is a positive replica of the original clay. A network of wax rods, called sprues and gates, are next attached to the positive wax model. These sprues will serve as a type of channel system, which will feed the molten metal to all of the areas of the sculpture, as well as allow gases and air to escape. Also, a wax funnel (called a pouring cup) is attached to the gates for use during pouring. A worker at Schaefer Foundry in Arlington, TX, attaches a sprue system to a wax portion. Photograph by Elizabeth Loggins. During the spruing process, special care is given to areas such as the tips of a rabbit ear, or the fingers of a frog, to ensure that these fine areas will not “short pour”. Once the spruing is completed, the wax is ready to go on to the shelling process. 8.

Ceramic Shell (Investment Casting) The ceramic shell process requires a series of dipping the wax positive into a mixture called slurry to create a hard shell. This ceramic shell, once dry, becomes a hard, durable shell around the entire sculpture that is going to receive, hold, and shape the molten metal to produce the bronze figure. The wax is first dipped into a solvent, which cleans any loose particles or debris from the surface of the wax. The shell process is about to begin. The clean wax is dipped into a solution called prewet, followed by two coats of a very fine grained slurry. This is known as the primary coating. This is where all of the fine detailing in the piece is picked up. It is almost like grained silicon flour. The shell then progresses through the slurry process, into different slurry mixtures, which are various grades, gradually becoming courser with each coating. Each time the wax is coated with the ceramic slurry mixture, it is allowed to dry thoroughly. Each coat adds support to the overall strength of the shell. The ceramic shell process consists of seven to nine coats of slurry mixture.

Once all of the coats have dried, the ceramic shell is then sent to be “dewaxed”. 9. Melting/Burning Out the Wax When the ceramic shell is complete, it is placed in a high pressure sealed oven, known as an autoclave. High temperatures (1500 to 1800 degrees Fahrenheit) and pressure force the wax from the shell and the wax melts out, thus becoming "lost". This is where the name “Lost-Wax Process” has been derived. The wax has now left the shell, leaving the detailed impression within the shell, which will soon become filled with the molten bronze. This step also hardens the ceramic shell in order to prepare the shell for the extreme temperature of the molten bronze which it is about to receive. The workers at Schaefer Foundry in Arlington, TX, carefully lift up the crucible, containing the molten bronze, out of its heating furnace. Photograph by Elizabeth Loggins. 10. Casting/Pouring the Bronze When the ceramic shell is empty of wax, it is then re-fired and made ready to have the molten bronze poured into it.

All of the hot ceramic shells are taken to the pouring floor, where they are either placed in sand to stand by themselves, or they are wired to a support frame to be held in place. The solid blocks of bronze, meanwhile, are heated to a temperature of approximately 2250 degrees Fahrenheit so that liquid bronze is created. The liquid bronze is stirred and prepared for the pour. When the molten bronze is ready, the foundry workers very carefully lift the crucible, containing the liquid bronze, out of its heating furnace. The workers must wear protective face shields, clothing, gloves, and boots. Moving quickly and very precisely, the foundry workers pour the liquid bronze into each awaiting ceramic shell. When the ceramic shells are all full with the poured bronze, they are then left to cool for several hours. The negative space within the ceramic shells have now become positive bronze castings. Right: A worker at Schaefer Foundry in Arlington, TX, pours the molten bronze into ceramic shells. Photograph by Elizabeth Loggins. Sculptor Tuck Langland breaks apart a cooled shell to separate the metal inside from the shell. 11.

Break Out Once the bronze and ceramic shell has cooled, the ceramic shell is broken off to separate the bronze metal from the shell. This is done with hammers, tools, power tools, and sand blasters. This process needs to be done very cautiously, though, in order not to cause unwarranted damage to the metal surface. Once the entire ceramic shell has been removed, the sprues (which have now become metal) must also be cut away or sawed off. At this stage, the uncovered bronze is considered a "raw metal". 12. Metal Chasing "Metal chasing" is the process of finishing the metal back to the appearance of the original. This process usually involves a fair amount of welding with a high frequency welder. Grinders are often used to remove sprues. Angle grinders with a variety of different grades of Roloc pads are used to finish the surface of the bronze. Always start out with a courser pad and then work your way down to a very fine pad when chasing the metal. It may also be necessary to retexture some areas of the bronze. This can be done with a tool known as a pencil grinder.

This tool uses a variety of high-speed burrs, some of which are quite similar to those used by a dentist, to perfect the final bronze. A metal chaser at Schaefer Foundry in Arlington, TX, works on the metal with small tools to remove any imperfections in the final bronze. Photograph by Elizabeth Loggins. 13. Metal Welding/Assembly If the sculpture being created was rather large or complicated, it might have been cut into pieces during the mold stage. This is necessary in order to be able to make molds that would be small enough to pour bronze into evenly. That is, instead of one big mold for a large piece, the piece may have been broken up into five or ten different smaller pieces, each piece with its own mold. Each smaller mold would thus be a different part of the whole sculpture, so that when all of the pieces have been poured and chased, they can then be fit back together to create the whole piece. If this is the case, all of the separate bronze pieces must be welded together to create the whole sculpture again. A metal welder will use a high frequency welding torch to carefully weld the sculpture together.

After the sculpture is welded back to one piece, all of the weld lines must also be chased away so that they disappear and it looks as though the sculpture was all one piece to begin with. A welder at Schaefer Foundry in Arlington, TX, carefully welds a bronze bird to a branch. The bird's wings need to be added as well. Photograph by Elizabeth Loggins. A worker at Schaefer Foundry in Arlington, TX, uses the sand-blasting cabinet. Photograph by Elizabeth Loggins. 14. Sand-Blasting the Bronze When the final piece is all welded together and chased to perfection, the bronze is next sand-blasted (or bead-blasted) to make it very smooth and shiny. Using a sand-blast cabinet is the most convenient way to sand-blast a sculpture. The sculpture is placed inside of the cabinet and the lid is closed securely. A worker can insert their arms into the cabinet through holes on the side of the cabinet which have gloves attached to protect the worker's arms. Wearing these protective gloves, the worker can then operate the sand-blasting compressor while monitoring the progress through a window in the cabinet.

After the sculpture is sand-blasted, the sculptor once again inspects the piece for accuracy. Now that the bronze has been sand-blasted, its true gold-like color, almost like glowing platinum, is visible. The sand-blasting also makes the surface of the bronze more porous, allowing the top surface to be more open to penetration of the patina in the next stage. 15. Patinazation The "patina" is the color of the bronze. "Patinazation" is the process whereby a calculated chemical reaction between bronze, acidic chemicals, and high temperatures oxidize the surface of the metals. Certain chemicals will produce certain predictable colors when they are sprayed on the bronze and then heated up. The patina process begins by heating (usually with a torch) the surface of the bronze to a temperature of approximately 450 to 475 degrees Fahrenheit. The surface will have a nice golden appearance when it is ready. A wide variety of techniques can then be used for chemical application, the most common being done with natural bristle brushes. Chemicals can also be applied with spatter guns, spray bottles, and airbrushes. J.D.

uses a blow torch to heat a bronze in preparation to apply the patina. Photograph by Elizabeth Loggins. The bare metal, before the patina is applied, of "Head of Dawn" by Sculptor Tuck Langland . "Head of Dawn" by Sculptor Tuck Langland after the final patina is applied (with ferric nitrate over liver of sulfur). The chemicals applied to the bronze will interact with the metal, creating a colored or textured appearance to the surface of the bronze. The patina has become quite an art in itself, and many beautiful combinations can be achieved. Browns, golds, and reds are typically produced through the use of Ferric Nitrate. Greens and blues can be produced with Cupric Nitrate. Whites and beiges can be produced with Bismuth Nitrate and Zinc Nitrate. Silver Nitrate is very expensive, but if applied very hot and with persistence and expertise, it can create a beautiful silvery-gray patina. The ancient Asians would bury their bronzes to naturally oxidize them, sometimes for years, in order to create patinas. Today, the oxidation and coloring of bronze sculpture can take place within a matter of hours.

But it is still a delicate process that should be performed with caution and with the proper equipment, preferably by a trained patineur. After the patina is applied, the patineur and the sculptor decide between two sealants to protect the patina. The traditional method of protection is to apply several thin coats of clear paste wax to the surface, which is then lightly buffed with a soft, clean, cotton cloth. This patina should last indefinitely indoors. However, if people repeatedly touch certain areas, the bronze may be expected to eventually shine through. Because today's outdoor atmosphere is more corrosive and carries a higher content of manmade pollutants, a more durable lacquer, metal protectant is recommended for any sculptures placed outdoors. Incralac™ is one such sealant designed specifically for copper and its alloys. Since Incralac™ produces a plastic-looking, high-gloss finish, the sculpture must be waxed to create the soft look of a traditional patina. 16. Completion: The Finished Sculpture After the completion of all of the above steps, a unique bronze sculpture will have been produced and can now be sold.

Of course, if this piece sells and the sculptor wants to make another one, that sculptor will then have to return to the “mother mold” and go through all of the steps again in order to make another bronze sculpture. One of the main things to keep in mind when viewing sculpture is that the "lost wax" process creates truly unique sculptures. Although the sculptors examine each of the waxes, and double check each finished metal, due to the handmade nature of this process, each cast and each patina will be similar but still distinctively unique. Right: The finished sculpture "Kenyan Dancer" by Sculptor Tuck Langland . Left: "From Clay to Bronze: A Studio Guide to Figurative Sculpture" by Sculptor Tuck Langland . 17. Summary: The Lost-Wax Process Volumes have been written on the subject of the "lost-wax" process as well as the procedures of mold-making, casting, and patinazation. We hope you have found this overview of the "lost-wax" process interesting and enlightening.

For further information about the art of the “lost-wax” process, Sculptureworks recommends the book From Clay to Bronze: A Studio Guide to Figurative Sculpture (pictured at left) by Sculptor Tuck Langland , one of our Sculptureworks artists. Also, the below diagram from Tuck's book gives a visual summary of the complex "lost-wax" process. Right: Diagram by Sculptor Tuck Langland showing a summary of the “lost-wax” process (from clay to bronze) with solid, or traditional, investment. Top row, left to right: the original clay sculpture, the rubber mold with shell (or "mother mold"), pouring wax into the mold, the hollow wax cast, and adding the sprue system. Bottom row, left to right: the wax with investment, burning out the wax, pouring the bronze, and breaking the cast. The above diagram is found in Sculptor Tuck Langland 's book "From Clay to Bronze: A Studio Guide to Figurative Sculpture". The "lost-wax" process explained above is primarily used for casting sculptures in bronze. Other options, however, for casting sculpture include bonded bronze, bonded marble, and pewter.

Bonded bronze (AKA "cold-cast" bronze) is primarily resin. The surface is a skin of resin into which bronze powder has been blended. Bonded marble is resin with marble powder. With a low-luster white surface, it is subtle and quite beautiful. Bonded bronze and bonded marble are hand-cast, hand-finished, lighter-weight and less-expensive alternatives to bronze. Pewter, an alloy of nickel and silver, is another less-costly alternative. Also, if you are interested in creating a sculpture using the "lost-wax" process, it is important to note that shrinkage will occur in any casting process. The mold shrinks. The wax shrinks. The metal shrinks. A sculpture which in clay was 26" long may be 25" long in metal. 18. Care for Bronze Sculpture All bronze sculpture is an investment which must be properly cared for. For indoor bronzes, the bronze should be wiped with a clean, soft rag once a year. Use a soft brush and apply a coat of Johnson's Paste Wax or Tree Wax to the sculpture. Allow it to sit for an hour or so and then buff it with a soft brush or rag.

This will protect your bronze from the oil of human hands, dust, and grease. Outdoor bronzes should be treated twice a year by cleaning and waxing the metal. Generally, this cleaning should be performed right before and right after summer. Waxing the bronze right before summer is especially important because this will protect it during the hot summer months. Copyright © 2001 - 2014. Sculptureworks, Inc. All rights reserved. Induction heating for the metal and foundry industry - EFD Induction Videos Induction heating for the metal and foundry industry Our very first equipment items were designed and built for the Metal and Foundry—and over the past five decades we have led the way in developing time- and money-saving solutions for the sector. Our solutions for Metal and Foundry are mainly to be found in the following areas: Forging of billet heaters and horizontal/vertical bar end heaters Melting of metal and glass Plasma heating of titanium and silicon Plasma Metal and Foundry Forging EFD Induction has no fewer than three groups of equipment designed specifically for forging applications . Each range offers compact, easy-to-install solutions that include capacitor banks and converters with full control panels.

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Question: A foundry is specifically involved in what metal process?
Answer: Casting