Gating system & casting Processes LECTURE :- 9 UNIT 2 Gating system & casting Processes DTEL 1

CHAPTER 2:- SYLLABUS Pouring basin, Sprue, choke, runner, ingrate 1 Function Trap contaminants Regulate flow of molten metal Control turbulence To establish directional solidification . 1 2 3 4 5 DTEL DTEL 2 2

CHAPTER- SPECIFIC Objective / course outcome The student will be able to: Understand the gating design. 1 furnaces.. 2 DTEL DTEL DTEL 3 3 3

Design of gating system LECTURE :- 9 Design of gating system Design of gating system Pouring cup Cut into cope Large enough to keep the sprue full Skim core to provide clean metal DTEL 4

Gating and Riser design LECTURE :- 10 ELEMENTS Gating and Riser design Vena cotracta Molten metal h1 h2 mold Aspiration at point 2 Vacuum generation Pseudo Vena contracta Prevents vacuum DTEL 5

Rise ring LECTURE :- 9 DTEL Cube Plate Solidification time for steel castings different shapes in green sand Cylinder is insulated at ends Risering a cube and plate Both castings have equal freezing times yet the riser which is adequate to feed the cube is not adequate to feed the plate Riser is 4” in dia. Cube is 4” side and plate is 8”x8”x2” DTEL 6

Riser design: Caine’s Method LECTURE :-9 Riser design: Caine’s Method Relative riser and casting geometry to obtain sound steel castings DTEL 7

LECTURE :-10 DTEL Riser 1.00 Riser on Plates and large A/V casting Sound 4.5 t Vr/Vc t Defective 0.00 8 16 24 32 (l+w)/h 4 t t DTEL 8

Furnaces for Casting Processes LECTURE :-11 Furnaces for Casting Processes Apart from the type of alloy being produced, selection of equipment for melting and casting must depend upon economic factors. These include the balance between cost and quality requirements for particular classes of casting, and the nature of the demand for molten metal as determined by the pattern of production. There are numerous types of furnaces used for Casting Processes, however, the most commonly furnaces used in foundries are: − Cupolas − Crucible furnaces − Electric-arc furnaces − Induction furnaces DTEL 9

Cupola Furnace LECTURE :- Vertical cylindrical furnace equipped with tapping spout near base used only for cast irons, and although other furnaces are also used, largest tonnage of cast iron is melted in cupolas The "charge," consisting of iron, coke, flux, and possible alloying elements, is loaded through a charging door located less than halfway up height of cupola DTEL 10

(c) tilting-pot furnace LECTURE :- 12 Crucible Furnaces Metal is melted without direct contact with burning fuel mixture Sometimes called indirect fuel-fired furnaces Container (crucible) is made of refractory material or high-temperature steel alloy Used for nonferrous metals such as bronze, brass, and alloys of zinc and aluminum Three types used in foundries: (a) lift-out type, (b) stationary, (c) tilting Three types of crucible furnaces: (a) lift-out crucible, (b) stationary pot, and (c) tilting-pot furnace DTEL 11

Electric-Arc Furnaces LECTURE :- 13 Electric-Arc Furnaces Charge is melted by heat generated from an electric arc High power consumption, but electric-arc furnaces can be designed for high melting capacity. Used primarily for melting steel DTEL 12

Metal Casting Processes LECTURE :- 14 Casting defects &foundary mechanizing Metal Casting Processes Introduction Sand casting Shell-Mold Casting Expendable Pattern Casting Plaster-Mold Casting DTEL 13

Die Casting Examples LECTURE :- 15 DTEL A permanent mold casting process in which molten metal is injected into mold cavity under high pressure. Pressure is maintained during solidification, then mold is opened and part is removed Molds in this casting operation are called dies; hence the name die casting Use of high pressure to force metal into die cavity is what distinguishes this from other permanent mold processes Fig 11.1 (a) The Polaroid PDC-2000 digital camera with AZ91D die-cast, high purity magnesium case. (b) Two-piece Polaroid camera case made by the hot-chamber die casting process DTEL 14

Hot-Chamber Die Casting LECTURE :- Hot-Chamber Die Casting Figure 11.13 Cycle in hot‑chamber casting: (1) with die closed and plunger withdrawn, molten metal flows into the chamber DTEL 15

Advantages of Hot Chamber Die Casting LECTURE :-16 Advantages of Hot Chamber Die Casting Improved productivity Superior surface finish High tolerance Intricate shapes with thin walls can be easily produced Limitations Only low melting alloys (such as Zn, Sn, Pb) are cast Small castings weighing less than 4.5 kg can be cast DTEL 16

Cold‑Chamber Die Casting LECTURE Cold‑Chamber Die Casting Figure 11.14 Cycle in cold chamber casting: (1) with die closed and ram withdrawn, molten metal is poured into the chamber DTEL 17

LECTURE 1:- NUMBER SYSTEM Cold chamber die casting suitable for casting of Aluminum alloy Mg alloys Brass etc Pressure applied in cold chamber die casting method can be as high as 2000 atmospheres Advantages high temperature metals and alloys can be cast large parts (weighing around 25 kgs) can be cast high surface finish ( 1 m) and dimensional tolerance better mechanical properties of the casting because of the fine grains large cycle time metal sometimes looses the superheat and cause defects such as “cold shut” DTEL 18

Shell-Mold Casting LECTURE 1:- 16 Developed in the 1940’s (b) Pattern and dump box rotated (c) Pattern dump box in position for the investment (d) Pattern and shell removed from dump box Developed in the 1940’s Produces close dimensional tolerances Good surface finish Low cost process Common methods of making shell molds. (a) Pattern rotated and clamped DTEL 19

Advantages of Shell Mould Casting LECTURE :- 16 Advantages of Shell Mould Casting Good surface finish (Ra 1.25 to 3.75 microns) High dimensional tolerance Amenable towards automation Castings weighing up to 450 kgs can be cast by this process Thin sections (up to 0.25 mm) can be cast by this process Limitations Patterns are expensive Castings weighing more than 450 kgs cannot be made Highly complicated shapes cannot be made Applications Cast iron, Aluminum and copper alloys are cast by this process DTEL 20

LECTURE 16 Investment Casting A refractory material (investment) is poured around or built up on a pattern The investment is hardened by drying or heating The pattern is removed by melting or burning Metal is poured into the resulting cavity DTEL 21

LECTURE 16 Investment Casting DTEL 22

Applications of Investment Casting LECTURE 16 Applications of Investment Casting Intricate shaped objects like jewelry Cylinder heads cam shafts gas turbine blades Advantages of Investment Casting Process Complicated and intricate shaped products can be easily cast High dimensional tolerance achievable Surface finish is excellent Additional machining not required as it is a net shape process All types of metals and alloys can be cast by this process Limitations A relatively expensive process Size of the casting is limited (max. around 5 kg) DTEL 23

LECTURE 16 Centrifugal Casting A family of casting processes in which the mold is rotated at high speed so centrifugal force distributes molten metal to outer regions of die cavity The group includes: True centrifugal casting Semicentrifugal casting Centrifuge casting DTEL 24

True Centrifugal Casting LECTURE 16 True Centrifugal Casting Figure 11.15 Setup for true centrifugal casting. DTEL 25

Semicentrifugal Casting Process LECTURE 16 Semicentrifugal Casting Process (a) Schematic illustration of the semicentrifugal casting process. DTEL 26

LECTURE 16 Centrifuge Casting Mold is designed with part cavities located away from axis of rotation, so that molten metal poured into mold is distributed to these cavities by centrifugal force Used for smaller parts Radial symmetry of part is not required as in other centrifugal casting methods DTEL 27

LECTURE 16 blow Surface Defects scar drop scab penetration Classification of casting defects blow scar drop scab penetration Surface Defects Internal Defects blow/gas holes porosity pin holes inclusions and dross hot tear shrinkage mold shift core shift Visible Defects rat tail swell misrun cold shut DTEL 28

DEFECTS IN CASTINGS LECTURE 16 Surface and internal defects DTEL Molding sand too too fine or heavily rammed Sand erosion Low permeability Poor venting, high moisture Hydrogen inclusion Buoyancy of liq. metal Inadequate packing High fluidity Poor mold strength Surface and internal defects DTEL 29