Chapter 7 Pouring Molten Metals Parts after Machining

Chapter 7 Pouring Molten Metals Parts after Machining Automated Molding Line Castings during Machining Process Chapter 7: Casting and casting processes - IE 252 11/3/2020 Casting and casting processes 1

2 Chapter 7: Casting and casting processes - IE 252 11/3/2020

7. 1 Introduction History : Casting is the oldest known process to manufacture metallic and nonmetallic complements. For example, it is applied for metals, plastic, porcelain, . . etc. Definition: A "foundry" term usually applied to the collection of necessary material, tools and equipments required to produce castings. Definition: "foundryman" term also applied to people produce. Chapter 7: Casting and casting processes - IE 252 As secondary basic processes: Usually machining and drifting allowances are also considered in mold design. 11/3/2020 Definition (Basic process): In casting process, the liquid material is poured into a cavity (mold cavity) that corresponds to the desired geometry. The shape obtained in liquid state is stabilized usually by solidification and then removed from the mold as solid-state component. 3

7. 1 Introduction 7. 2 Classification of major casting processes Chapter 7: Casting and casting processes - IE 252 11/3/2020 Major casting processes are grouped into: ØSand casting group, ØPermanent metallic mold casting group, ØPrecision casting group, ØCentrifugal casting group. 4

7. 1 Introduction 7. 2 Classification of major casting processes Melting using industrial furnaces Chemical composition check Pouring liquid material in mold cavity Chapter 7: Casting and casting processes - IE 252 Drawing, allowances, tolerances, 11/3/2020 Manufacturing stages involved in the casting process. The dashed lines in the drawing represent feedback and corrections. Removing component from mold cavity Checking dimensions, quality, heat treatment Fig. 7. 1 The main operations of producing components by casting process. 5

ØRaw material: usually selected by the costumers. ØMelting: usually carried out through industrial melting furnaces. Controlling the chemical composition is carried during melting process, where elements are added and removed as necessary, to correct the composition before pouring process. ØMold production: mold production usually carried out through traditional and nontraditional machining processes, when metallic mold is used. Both in metallic and nonmetallic molds, riser and runner designs have to be considered in mold production. . The mold production is usually subjected to many corrections even after initial mold production. This can be done after initial casting batch through poring and solidification stages. Chapter 7: Casting and casting processes - IE 252 ØComponent specification: cover component geometry drawing, material, tolerances, final properties (e. g. surface finish), number of components produced. 11/3/2020 7. 1 Introduction 7. 2 Classification of major casting processes 6

ØMelting temperature must be controlled. Pouring at lower temperatures will freeze metal before filling mold cavity which result in defect casings. Pouring at higher temperature will result in reaction between mold walls and molten metal, which also results in mold damage and generation of gases that results in defect castings. ØFurnaces must prevent metal contamination, this can be achieved by lining the furnace with the proper refractory materials. This will protect molten metal from oxidation and gas generation which also results in defect casings. Two furnace lining are common; acidic (e. g. quartz) and base (e. g. limestone). ØUsing slug lining on the top of molten metal of pouring crucible will protect the molten metal from: atmosphere (O 2, N 2, ) and combustion product (Co 2, Co, H 2 O. ). Chapter 7: Casting and casting processes - IE 252 ØFor efficient casting process, chemical composition of metal must be controlled before the pouring process. This can be achieved by adding or/and removing elements and minimizing the dissolved gases that may result in defect casing. 11/3/2020 7. 1 Introduction 7. 2 Classification of major casting processes 7. 3 Melting and control of composition 7

7. 1 Introduction 7. 2 Classification of major casting processes 7. 3 Melting and control of composition 7. 4 Classification of mostly used industrial melting furnaces [7. 1] E A 11/3/2020 *Melt cast iron (and sometimes copper/copper alloys). *It is charged continuously by a layer of coke and layer of pig iron (or scarp). * 8 -10 Ton per hour per square meter of furnace crosssection area 7. 4. 2 Open-hearth furnace (Fig. 7. 2 B) *Mainly used in steel foundries to produce steel castings. *Natural gas, or oil-fired are commonly. *The capacity ranges from 25 -350 Ton per charge/8 Hr F B 7. 4. 3 Rotary furnace(Fig. 7. 2 C). *Usually used to melt cast iron and non-ferrous metals. *Natural gas or oil-fired are commonly used as a fuels for this type of furnace. *Furnace capacity ranges from 0. 5 to 10 Tons per charge C Chapter 7: Casting and casting processes - IE 252 7. 4. 1 Cupola furnace (Fig. 7. 2 A) G D Fig. 7. 2 Commonly used industrial melting furnaces. 8

7. 1 Introduction 7. 2 Classification of major casting processes 7. 3 Melting and control of composition 7. 4 Classification of mostly used industrial melting furnaces [7. 1] E A 11/3/2020 *Oil-fired or natural gas are used as fuel for this type of furnace. *Electric resistance or induction coils are also used to heat the furnace crucible mounted around the external walls of the crucible. *Capacity 0. 5 kg to 500 Kg 7. 4. 5 Arc furnace(Fig. 7. 2 E) *Two types are common: direct and indirect arc furnaces. *The arc is generated between charge and the graphite electrodes in case of direct arc furnaces. *In indirect arc furnace, the arc is developed between graphite electrodes, where heat is transmitted to the charge by radiation, conduction and convection. *Arc furnaces are most commonly used to melt cast iron and steel. *Direct arc furnace capacity ranges from 2 - 30 Tons, while indirect arc furnace used for lower capacities due to its low efficiency. F B C Chapter 7: Casting and casting processes - IE 252 7. 4. 4 Crucible furnace(Fig. 7. 2 D) G D Fig. 7. 2 Commonly used industrial melting furnaces. 9

7. 1 Introduction 7. 2 Classification of major casting processes 7. 3 Melting and control of composition 7. 4 Classification of mostly used industrial melting furnaces [7. 1] E 11/3/2020 A *Two types : low frequency (60 -180 Hz), channel type, Fig. 7. 2 F) and high frequency (1000 -30000) Hz, crucible type, Fig. 7. 2 G). *The high frequency type is commonly used for melting cast iron and steels, while non-ferrous metals are melted using low frequency types. Capacity 0. 5 Ton to 10 Ton F 7. 4. 7 Resistance furnace *Electric resistance furnaces are commonly used for melting non-ferrous metals and they are of the crucible type. *Electric resistance coils are mounted around the crucible and used as heating elements. *The capacity of these furnaces, range between 0. 5 to 500 Kgs. B C Chapter 7: Casting and casting processes - IE 252 7. 4. 6 Induction furnace (Figs. 7. 2 F and G) G D Fig. 7. 2 Commonly used industrial melting furnaces. 10

Chapter 7: Casting and casting processes - IE 252 11/3/2020 7. 5 Charge balance in melting furnaces 11

Chapter 7: Casting and casting processes - IE 252 11/3/2020 7. 5 Charge balance in melting furnaces e. g. Charge balance in Cupola furnace/ Estimate furnace weight and composition / 12

Chapter 7: Casting and casting processes - IE 252 11/3/2020 7. 5 Charge balance in melting furnaces e. g. Charge balance in Cupola furnace/ Estimate furnace weight and composition / 13

Chapter 7: Casting and casting processes - IE 252 11/3/2020 7. 5 Charge balance in melting furnaces e. g. Charge balance in Cupola furnace/ Estimate furnace weight and composition / 14

Chapter 7: Casting and casting processes - IE 252 11/3/2020 7. 5 Charge balance in melting furnaces e. g. Charge balance in Cupola furnace/ Estimate furnace weight and composition / 15

ØInternal shapes in castings are obtained by placing backed core/cores consisting of silica sand a binder in the mold cavity. ØThe molten metal is poured into the pouring basin and flows to the mold cavity through a gate or system of gates. ØAfter filling the mold cavity, the melt enters the risers, which act as a reservoir of excess metal to compensate for shrinkage during solidification. A new mold must be made for each casting. ØThe mold box can be designed to manufacture multiple components to increase productivity. Chapter 7: Casting and casting processes - IE 252 Definition: ØIn sand casting the molten metal is poured into a pre- prepared sand mold, dimensioned, and contoured to match the desired casting. 11/3/2020 7. 5 Charge balance in melting furnaces 7. 6 Casting processes [7. 2]. 7. 6. 1 Sand casting process 16

Molding sand consists of : Sand material (resist the high temperature and permeability), commonly used are silica (Si. O 2) or quartz sand (cheaper). Olivine sand also used for steel castings(manganese steel and non-ferrous castings), Zircon (investment casting)and synthetic sands also used but more expensive. The binder (give the strength), e. g. Clay (bentonite, kaolin, . ), Cement, Sodium silicate (for Co 2 process), Oil, Resin (shell molding). Additives (gives collapsibility). Water 4 -8% (to activate the binder). Sometimes the mold is baked in oven 100 -300 C, for several hours to obtain dry sand that helps reduce gas holes, blows or porosity in castings. Chapter 7: Casting and casting processes - IE 252 Molding sand: The fundamental requirements of sand is to resist high temperature, strength to retain the mold shape, withstanding the mechanical load from liquid metal, permeability (to permit the escape of gases, and collapsibility (to permit shrinkage). 11/3/2020 7. 5 Charge balance in melting furnaces 7. 6 Casting processes [7. 2]. 7. 6. 1 Sand casting process 17

Chapter 7: Casting and casting processes - IE 252 Sand mold production: the common method of producing a sand mold is through using a top flask (called cope), and a bottom flask (called drag). To improve productivity of this molding technique, different molding machines were developed to provide vibration compression and shaking on both cope and drag of sand mold to produce uniform mold strength. Fig. 7. 3 shows the traditional molding technique using cope and drag and a split patterns. 11/3/2020 7. 5 Charge balance in melting furnaces 7. 6 Casting processes [7. 2]. 7. 6. 1 Sand casting process 18 Fig. 7. 3 Traditional sand molding techniques using cope/drag and split pattern system.

Chapter 7: Casting and casting processes - IE 252 Sand mold production: the common method of producing a sand mold is through using a top flask (called cope), and a bottom flask (called drag). To improve productivity of this molding technique, different molding machines were developed to provide vibration compression and shaking on both cope and drag of sand mold to produce uniform mold strength. Fig. 7. 3 shows the traditional molding technique using cope and drag and a split patterns. 11/3/2020 7. 5 Charge balance in melting furnaces 7. 6 Casting processes [7. 2]. 7. 6. 1 Sand casting process Fig. 7. 4 Flaskless molding technique for used to increase the production of sand molds. 19 Fig. 7. 3 Traditional sand molding techniques using cope/drag and split pattern system.

Chapter 7: Casting and casting processes - IE 252 Applications: ØSand casing is a common method of producing relatively cheap complements made of steel, casting, brass, aluminum, . . etc. ØNumerous molding techniques employ sands to produce sand molds, e. g. green sand molding (commonly used), dry sand molding (similar to green sand molding but baked sand), core sand molding, shell sand molding, . . etc. ØThe typical component weight is in the range of 500 grams to 50 Kg or even several tons e. g. machine tool frames. Wall thickness generally between 5 to 50 mm. ØExample products are engine blocks, crankshafts, connected rods, machine bed, turbine housing, . . etc. ØSand casing produce rough surfaces, and lower dimensional accuracy compared to other casting processes, hence, machining is required for those castings. ØMachining and drift allowances must be considered in pattern design. 11/3/2020 7. 5 Charge balance in melting furnaces 7. 6 Casting processes [7. 2]. 7. 6. 1 Sand casting process 20

Chapter 7: Casting and casting processes - IE 252 Machinery: ØEquipment consists of pattern, which usually manufactured form wood (low production batch), plastics (e. g. thermosetting plastic) and metals (for long live pattern and high production rate). ØFlask and flaskless molding techniques are used to manufacture sand mold. ØCore equipment also used to produce cores for the internal shape of components. 11/3/2020 7. 5 Charge balance in melting furnaces 7. 6 Casting processes [7. 2]. 7. 6. 1 Sand casting process 21

Resin Coated Sand for engine casting, aluminum casting, main mold component, hollow core, solid core Chapter 7: Casting and casting processes - IE 252 Definition: In shell mold casting, which is a type of sand mold casting, the mold produced from dried silica sand (fine and sharp) mixed with a thermosetting resin (phenolic). 11/3/2020 7. 5 Charge balance in melting furnaces 7. 6 Casting processes [7. 2]. 7. 6. 1 Sand casting process 7. 6. 2 Shell mold casting 22

Chapter 7: Casting and casting processes - IE 252 Shell mold preparation: • An accurate metal pattern is heated to 150 -250 C, and the sand mixture is dumped on the pattern, which is placed in mold box. After a few minutes, a layer of the sand mixture is cured, and the excess mixture is removed by inverting the mold box. • The pattern and the partially cured shell are baked in an oven for a few minutes to complete the curing process. • The pattern and shell are now separated, and the mold halves assembled with clamps, glue, or other devices. The shell mold is placed in a pouring jacket and backed up or supported by shot or sand sometimes using supported pins. • After mold production, molten metal is poured in the mold and the metal solidified. The component is obtained by breaking the mold. For high production multiple pattern plate may design to have multiple patterns. Furthermore, for high production the pattern plate is designed to have gating and sprue system. 11/3/2020 7. 5 Charge balance in melting furnaces 7. 6 Casting processes [7. 2]. 7. 6. 1 Sand casting process 7. 6. 2 Shell mold casting 23

Shell molding used to manufacture cores Chapter 7: Casting and casting processes - IE 252 Applications: ØShell mold casting offers greater dimension accuracy and better surface finish than the green sand casting process. Also, it offers sharp corners, internal shape contour, small holes, . . etc. ØHence, accurate castings can be produced using this method. Sometimes, cores are produced using shell molding while the mold is produced using green sand mold technique, to obtain accurate internal shapes of castings, e. g. water pump and compressor casing components. ØThe disadvantage of this molding technique, is the initial cost of the tooling system. Fore example, air-cooled combustion engines are produced using shell mold casting. An average weight of the components range between 10 to 20 Kg. Machinery: Equipment consists of metal pattern mounted on the pattern plate including runner, gate and sprue system. Heating oven, flask and metal or sand shot. Sometimes, electric heating elements are inserted in the pattern plate to control the temperature driven using temperature controller system, also automatic injectors may be used to automate the process and increase productivity. 11/3/2020 7. 5 Charge balance in melting furnaces 7. 6 Casting processes [7. 2]. 7. 6. 1 Sand casting process 7. 6. 2 Shell mold casting 24

Chapter 7: Casting and casting processes - IE 252 11/3/2020 7. 5 Charge balance in melting furnaces 7. 6 Casting processes [7. 2]. 7. 6. 1 Sand casting process 7. 6. 2 Shell mold casting 7. 6. 3 Investment casting 25

Chapter 7: Casting and casting processes - IE 252 Mold preparation: ØBefore casting the pattern is melted by warming the mold and then inverted to allow the wax to flow out. ØProduction of master pattern (from metal or wood), which is required to produce the master die for wax pattern. ØProduction of wax patterns by pouring or injection of wax into the master die. ØAssembling the pattern assembly with a thin layer of investment material (dipping in a thin slurry of fine-grained silica). ØProduction of final investment by placing the coated pattern assembly into flask and pouring investment material around. 11/3/2020 7. 5 Charge balance in melting furnaces 7. 6 Casting processes [7. 2]. 7. 6. 1 Sand casting process 7. 6. 2 Shell mold casting 7. 6. 3 Investment casting 26

Chapter 7: Casting and casting processes - IE 252 Mold preparation: ØDrying and hardening for several hours. Melting the wax pattern assembly by warming the mold and inverting it to allow the wax to flow out. ØHeating the mold to higher temperatures ( 850 -1000 C), to drive off moisture. ØPreheating the mold to 500 -1000 C to assist the flow of molten metal to thin sections and to obtain accurate part geometry. ØPouring the molten metal, either by gravity, or pressure. ØRemoval of castings after solidification by breaking the mold. 11/3/2020 7. 5 Charge balance in melting furnaces 7. 6 Casting processes [7. 2]. 7. 6. 1 Sand casting process 7. 6. 2 Shell mold casting 7. 6. 3 Investment casting 27

Chapter 7: Casting and casting processes - IE 252 Applications: ØIn investment casting no draft allowance is required and very complex shape, e. g. pump impellers, compressor diffusers, turbine plates or wheels, etc. , are common components produced using investment casting. ØPart complex geometry is limitless in case of investment casting process. Investment casting applied for both ferrous and non-ferrous Metal plate metals also used to manufacture metals Resin plate difficult to machine or un-machineable metals e. g. radioactive metals. ØAn accurate components are produced with tolerances of +/-0. 075% for components having dimensions up to 15 mm. ØLow surface roughness is obtained using investment casting (1. 5 -3 Ra). 11/3/2020 7. 5 Charge balance in melting furnaces 7. 6 Casting processes [7. 2]. 7. 6. 1 Sand casting process 7. 6. 2 Shell mold casting 7. 6. 3 Investment casting 28

Machinery: Equipment for producing the ceramic mold consists of slurry tank, baking oven. The equipment for making the wax pattern are also needed. Metal plate Resin plate Chapter 7: Casting and casting processes - IE 252 11/3/2020 7. 5 Charge balance in melting furnaces 7. 6 Casting processes [7. 2]. 7. 6. 1 Sand casting process 7. 6. 2 Shell mold casting 7. 6. 3 Investment casting 29

7. 6 Casting processes [7. 2]. 7. 6. 1 Sand casting process 7. 6. 2 Shell mold casting 7. 6. 3 Investment casting 7. 6. 4 Permanent mold casting In permanent mold casting the molten metal is poured into a permanent (reusable) metallic mold and distributed in mold cavity under the gravity force. The process is similar to sand casting mold, however, the mold design is to be used many times and usually manufactured from cast iron or steel. Furthermore, the mold is heated (using chemical torch or electric resistance coil) to provide better mechanical properties for the casting components. Two half mold design is common which simples mold structure including gate, runner, sprue and riser system 11/3/2020 Fig. 7. 7 Permanent mold gravity casting process. Chapter 7: Casting and casting processes - IE 252 • Gravity mold casting 30

7. 6 Casting processes [7. 2]. 7. 6. 1 Sand casting process 7. 6. 2 Shell mold casting 7. 6. 3 Investment casting 7. 6. 4 Permanent mold casting Chapter 7: Casting and casting processes - IE 252 Aluminum permanent mold casting, or gravity die-casting, is the casting of molten aluminum in a reusable metal mold or die. The die material is most commonly cast iron or steel. Tilt pouring is one variation of the permanent mold process. 11/3/2020 • Gravity mold casting 31

7. 6 Casting processes [7. 2]. 7. 6. 1 Sand casting process 7. 6. 2 Shell mold casting 7. 6. 3 Investment casting 7. 6. 4 Permanent mold casting Chapter 7: Casting and casting processes - IE 252 Applications: ØThe permanent mold casting process can produce a wide verity of parts such as automobile parts (water pump, gear transmission box body, dynamo brackets, car wheels frames. . etc), also electric motor covers, water taps, toys, . . etc. Aluminum, zinc, magnesium and copper/copper alloys are common materials cast using permanent mold casting. ØMold high cost is the main disadvantage of this process. However, the accuracy and tolerances are more than sand casting process. ØSurface finish is also better when compared to sand casting (25 -100 Ra). Sometimes the mold walls are coated by refractory material to resist the heat and increase live of the mold. 11/3/2020 • Gravity mold casting 32

7. 6 Casting processes [7. 2]. 7. 6. 1 Sand casting process 7. 6. 2 Shell mold casting 7. 6. 3 Investment casting 7. 6. 4 Permanent mold casting Chapter 7: Casting and casting processes - IE 252 Machinery: ØThe simple mold may consist of two half or even a single part. ØThe mold includes gate, runner and pouring basin system in its internal cavity. Alignment pins, an injection system and clamps are also included. ØThe process can be manual or automatic using special machines having hydraulic slides. The gravity casting machines usually built to meet customer requirements and produced parts. Furthermore, the machine is equipped with mold tilting mechanism to allow air escaping and easily metal filling of mold cavity. 11/3/2020 • Gravity mold casting 33

7. 6 Casting processes [7. 2]. 7. 6. 1 Sand casting process 7. 6. 2 Shell mold casting 7. 6. 3 Investment casting 7. 6. 4 Permanent mold casting 11/3/2020 • Gravity mold casting. • Low pressure casting Chapter 7: Casting and casting processes - IE 252 Definition: In low pressure permanent mold casting, the mold is mounted above an induction or resistant furnace, while the molten metal, inside the furnace, is forced into die cavity through low pressure of inert gas. The mold is made of graphite or metal (e. g. cast iron). The pressure varied from 0. 12 to 0. 2 Mpa. 34 Fig. 7. 8 Low-pressure permanent mold casting.

7. 6 Casting processes [7. 2]. 7. 6. 1 Sand casting process 7. 6. 2 Shell mold casting 7. 6. 3 Investment casting 7. 6. 4 Permanent mold casting 11/3/2020 • Gravity mold casting. • Low pressure casting Chapter 7: Casting and casting processes - IE 252 Applications: Fine products and accurate dimensions are obtained using this casting process. Castings like car wheels, appliance panel covers, motor covers, . . etc are common products for this casting process. 35 Fig. 7. 8 Low-pressure permanent mold casting.

Definition: ØIn high pressure permanent mold casting (commonly called die casting in industry), the molten metal is forced or injected to the mold cavity under high pressure varied between 2 to 300 MPa. ØThe molten metal is solidified and then injected from the mold cavity as solid metal part using steel injector pins mounted inside the mold structure. ØThis results in a more uniform part, generally of high surface finish and dimensional accuracy. For many parts, post-machining can be totally eliminated, or very light machining may be required to bring dimensions to size. Chapter 7: Casting and casting processes - IE 252 • Gravity mold casting. • Low pressure casting. • High pressure die casting. 11/3/2020 7. 6 Casting processes [7. 2]. 7. 6. 1 Sand casting process 7. 6. 2 Shell mold casting 7. 6. 3 Investment casting 7. 6. 4 Permanent mold casting 36

Die casting processes: Two die casting processes are common in industry. 1 -Cold chamber die casting process : Here the molten metal is ladled into the cold chamber for each shot. There is less time exposure of the melt to the plunger walls or the plunger. This is particularly useful for metals such as Aluminum, and Copper (and its alloys) that alloy easily with Iron at higher temperatures. Fig. 7. 9 Die casting process: cold-chamber die cast process. Chapter 7: Casting and casting processes - IE 252 • Gravity mold casting. • Low pressure casting. • High pressure die casting. 11/3/2020 7. 6 Casting processes [7. 2]. 7. 6. 1 Sand casting process 7. 6. 2 Shell mold casting 7. 6. 3 Investment casting 7. 6. 4 Permanent mold casting 37

7. 6 Casting processes [7. 2]. 7. 6. 1 Sand casting process 7. 6. 2 Shell mold casting 7. 6. 3 Investment casting 7. 6. 4 Permanent mold casting 11/3/2020 • Gravity mold casting. • Low pressure casting. • High pressure die casting. 2 -Hot chamber die casting process : Here the pressure chamber is connected to the die cavity which is immersed permanently in the molten metal. The inlet port of the pressurizing cylinder is uncovered as the plunger moves to the open (un-pressurized) position. This allows a new charge of molten metal to fill the cavity and thus can fill the cavity faster than the cold chamber process. The hot chamber process is used for metals of low melting point and high fluidity such as tin, zinc, and lead that tend not to alloy easily with steel at their melting temperatures. Chapter 7: Casting and casting processes - IE 252 Die casting processes: Two die casting processes are common in industry. Fig. 7. 9 Die casting process: hot chamber die, air activated; plunger activated; 38

Fig. 7. 10 Centrifugal casting process (Vertical and horizontal rotating axis Chapter 7: Casting and casting processes - IE 252 Definition : ØIn centrifugal casting, the molten metal is forced to mold cavity by centrifugal forces. ØWhere permanent or non-permanent mold is forced to rotate during metal solidification, ØAn example for this process is pipe casting. The process is nearly limited for symmetrical components. 11/3/2020 7. 6 Casting processes [7. 2]. 7. 6. 1 Sand casting process 7. 6. 2 Shell mold casting 7. 6. 3 Investment casting 7. 6. 4 Permanent mold casting 7. 6. 5 Centrifugal casting 39

7. 8 Pouring system in mold Chapter 7: Casting and casting processes - IE 252 ØFor higher quality and thinner sections, high pressure pouring technique is recommended. ØThe molten metal is poured initially in pouring basin (common for large mold to prevent slag getting in) through the sprue in case of gravity pouring technique. Ø No pouring basin is required for high pressure pouring technique, which is replaced by an injection channel system. ØThe molten metal will flow from spur to runner, then to gating system and finally to mold cavity and riser. ØIt is worth noting that poor design of runner; gating and riser systems may result in defect castings. ØSprue is usually tapered by 2 º at the end bottom of mold for higher flow and reduction of air aspiration. ØMore than one gate may required in mold gating system design especially with large castings. As a general design rule, the sprue cross-sectional area should be sized 20% larger than the total cross-section areas of the gate/gates system. 11/3/2020 ØOne important factor that effect obtaining castings without defects, pouring system in mold design either in permanent or non-permanent mold. Pouring molten metal in mold cavity achieved either at high pressure (2 -15 Mpa), low pressure (0. 12 to 0. 3 Mpa), or without pressure (gravity) technique. 40

Chapter 7: Casting and casting processes - IE 252 ØWhen designing mold cavity and gating system, metal shrinkage must be considered in mold cavity design. ØFor example, the solidification shrinkage is between 6 -7% for aluminum, while it is between 1. 9 to 2. 5% for cast iron, for more information on mold gating design refer to literature [7. 2]. ØFrom cooling curve of metal and alloys background, there is a single melting point when metal is poured, while there are melting ranges in case of alloys. Ø Volume shrinkage is not important for both liquid and solid metals, while it becomes serious for mixed solid and molten metal (during the solidification range), which result in cracks in castings. 11/3/2020 7. 9 Riser consideration in mold design 41

7. 9 Riser consideration in mold design Chapter 7: Casting and casting processes - IE 252 11/3/2020 ØTo compensate for shrinkage during cooling from the pouring temperature to solidification, a reservoir of molten metal should be attached to casting (riser). ØFor shrinkage compensation, the reservoir or riser must be solidified after component solidification. ØSolidification procedure of cube of molten metal with and without reservoir (riser) of molten metal. 42

For proper riser design, the following requirement must be achieved: ØSolidification time of riser is greater than the solidification time of casting (triser>tcasting). Chapter 7: Casting and casting processes - IE 252 11/3/2020 7. 9 Riser consideration in mold design ØEnough feed of metal. ØProper location (near the thickest section). 43

7. 10 Simplified riser design based on solidification time ts Solidification time of a component. K : Molding condition constant (depend mold, die casting mold, …etc) Vol : Component volume. Sa : Component surface area. on mold material e. g. sand Chapter 7: Casting and casting processes - IE 252 11/3/2020 ØA scientist called Chrorinor stated that the solidification time of any metal component is function of its volume, surface area and molding method. ØThe solidification time is given in the following equation: 44

7. 10 Simplified riser design based on solidification time Definition: Component modulus : can be define as the ratio between casting volume to its surface area and is given as follows: Chapter 7: Casting and casting processes - IE 252 OR 11/3/2020 As illustrated previously, to obtain good castings without defects, riser solidification must be occur after cast components, i. e. 45 Hence, for any casting component:

7. 10 Simplified riser design based on solidification time Hence, for any casting component: Example 7. 3 Calculate the modulus of a cylinder, given: a) Diameter = height (D=H), b) Diameter = 0. 5 height (D=1/2 H). Solution: a) For D=H: Volume= Surface area= Modulus= D H Chapter 7: Casting and casting processes - IE 252 11/3/2020 As a design rule, we could define riser modulus as follows : 46

7. 10 Simplified riser design based on solidification time Volume= Surface area= b) For D=1/2 H : Volume= H Modulus= Chapter 7: Casting and casting processes - IE 252 Solution: a) For D=H: D 11/3/2020 Example 7. 3 Calculate the modulus of a cylinder, given: a) Diameter = height (D=H), b) Diameter = 0. 5 height (D=1/2 H). Surface area= 47 Modulus=

a) For cube: l b) For plate: a Bar a l a t w Plate Chapter 7: Casting and casting processes - IE 252 Example 7. 4 Calculate the modulus of the following geometries: a) Cube, b) Plate, a a Cube c) Bar 11/3/2020 7. 10 Simplified riser design based on solidification time c) For Bar: ( w=t=a) 48

7. 10 Simplified riser design based on solidification time Chapter 7: Casting and casting processes - IE 252 11/3/2020 Example 7. 5 The solidification time of a cube having 10 cm edge length is 6 min. , calculates the solidification time of another cube with 15 cm edge length and a cylinder having the same volume and equal height and diameter (H=D) and molded with same condition? 49

7. 10 Simplified riser design based on solidification time 7. 10. 1 Riser design procedure Example 7. 6 Based on the design rule given above, find out riser geometry required to mold a plate having an overall dimensions of 100 x 50 x 10 cm, assume Dr=Hr for riser geometry? Solution: Plate volume Vol=100(50)(10)=50000 cm 3 Riser Plate surface area Sa=2(50)(100)+2(100+50)(10)=13000 cm 2, Plate Modulus Mc=50000/13000=3. 85 cm Dr=Hr=6 Mr=27. 6 cm Plate Chapter 7: Casting and casting processes - IE 252 • Calculate the casting modulus Mc. • Calculate riser based on design rule Eq. 7. 6 (Mr=1. 2 Mc). • Calculate riser diameter as Dr=6 Mr (Assume Dr=Hr for riser geometry). 11/3/2020 Based on design rule Eq. 7. 6 and Modulus definition, riser design based on solidification time is given as follows: • Assume Dr=Hr for riser (if not stated), then Mr=1. 2 Mc=1. 2(3. 85)=4. 6 cm 50

7. 10 Simplified riser design based on solidification time 7. 10. 1 Riser design procedure Example 7. 7 30 All dimensions in cm. . ø 15. ø 10 . ø 20 . 12 Fig. 7. 13 Chapter 7: Casting and casting processes - IE 252 a) Calculate the solidification time for the part shown in Fig. 7. 13? b) Design a riser for the casting shown in Fig. 7. 13 based on the simplified solidification time method, assume Dr = Hr for riser? c) Make net sketch of sand molding for the given casting showing; riser and its position, cope, drag, parting line, and core/cores (if required). 11/3/2020 The solidification time of a cylinder with outer diameter of 10 cm and length of 18 cm is 2. 582 Min. . 8 51

7. 10 Simplified riser design based on solidification time 7. 10. 1 Riser design procedure 30 Example 7. 7 All dimensions in cm. . 12 Fig. 7. 13 . 8 b) Riser design rule given in section 7. 10. 1, will be used: Riser modulus Mr=1. 2 Mc=1. 2 (2)=2. 4 cm. < Then riser diameter Dr=Hr=6 Mr=6(2. 4)=14. 4 cm << c) Fig. 7. 14 shows a neat sketch for the sand molding of the given casting. In Fig. 7. 14, two molding techniques are shown; vertical and horizontal configuration. Vertical molding technique required two cores, one core used to obtain the external surfaces, while the other is for internal surfaces. 11/3/2020 . ø 20 Chapter 7: Casting and casting processes - IE 252 . ø 15. ø 10 52

7. 10 Simplified riser design based on solidification time 7. 10. 1 Riser design procedure Chapter 7: Casting and casting processes - IE 252 11/3/2020 Example 7. 7 53

7. 10 Simplified riser design based on solidification time 7. 10. 1 Riser design procedure Chapter 7: Casting and casting processes - IE 252 11/3/2020 Example 7. 7 54

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Chapter 7: Casting and casting processes - IE 252 End Chapter 7 59 11/3/2020