MOULDING SAND cont... COMPOSITION: BASE SAND (upto 85%) – Mainly SILICA GRAINS (SiO 2 ) – Main source is river sand – Zircon, Chromite, Olivine Sand SILICA GRAINS ZIRCON SAND CHROMITE SAND OLIVINE SAND

MOULDING SAND COMPOSITION BINDER (upto 11%) – Provides REQUISITE STRENGTH – CLAY is generally used Kaolinite Bentonite : absorbs more water MOISTURE (upto 4%) – Activates the CLAY helps in bonding

TYPES OF SAND MOULD CASTING (i) CONVENTIONAL MOLDING PROCESS (a)Green sand mold. (b)Dry sand mold, (ii) CHEMICAL SAND MOLDING PROCESS 1. Shell molding 2. Sodium Silicate Molding 3. No-Bake molding (iii) PERMANENT MOLD CASTING 1. gravity die casting 2.pressure Die casting

(iv) SPECIAL CASTING PROCESSES 1.Centrifugal casting 2.Investment casting 3.Vacuum sealed casting 4.Slush casting 5.Squeeze castingetc.

Green sand moulding The term “green” denotes the presence of moisture in the molding sand. Composition + + MOISTURE Advantages a.Most metals can be cast by this method. b.Pattern costs and material costs are relatively low. c.No limitation with respect to size of casting & type of metal or alloy used.

DISADVANTAGES POOR SURFACE FINISH OF THE CASTING. Machining is required to achieve the finished product. Improper properties of moisture and cclay result in casting defects. Unclean environment.

DRY SAND MOLDING Need for dry Sand Molding - to avoid pinholes - to increase the strength of the mold Types of dry Sand Molding 1. Skin drying (using torches,infrared lamps,hot air etc.) 2. Complete mold drying ( by using large ovens)

SHELL MOLDING FEATURES:  Metallic pattern is used  Molding material: Fine sand + Thermosetting resin (Phenol-formaldehyde)(5kg of phenol- formaldehyde in 100 kg of sand)  Heating arrangement for the pattern

TYPES OF SAND MOULD CASTING contd… Shell Moulding POINTS TO REMEMBER: A cope-drag metal pattern heated at 200 – C Dump box containing sand mixed with thermosetting resin inverted for 30 sec Shell skin about mm Oven for heating the shell for 60 sec at 3150C temp Gap between clamped shell and Moulding Flask, backing sand gravel, coarse sand or metal shot

Shell Moulding Applications: Valves bodies, Bearing caps, Gears, Very suitable for like petrol engine cylinder..\Video\Shell Moulding.wmv Advantages:  Excellent surface finish  Good dimensional accuracy of order of to mm  Molds can be stored  Suitable for Mass production  Sand metal ratio relatively low  Less Skill-ness required Limitations:  High initial cost  Specialized equipment  Expensive Resin binder  Limited for small size  Cost not justified for small scale productions

Need for Sodium Silicate molding poor strength of green sand mold (for cores) Poor surface finish of green sand mold Inability of green sand mold to retain small details

SODIUM SILICATE Molding cont… MOLDING MATERIALS: Fresh silica sand Sodium silicate (binder) Hardener (CO2 gas, portland cement, blast furnace slags, etc) Types: 1. Self hardened Hardener: portland cement, blast furnace slags, ferro-silicon, etc Setting time: hours 2.CO2 hardened Hardener: CO2 gas Setting time: few minutes

TYPES OF SAND MOULD CASTING contd… Carbon-dioxide moulding Points to Remember:  Mould material: Dry silica sand (no clay) + (3-5%) sodium silicate + moisture (<3%)  CO2 at kg/cm2 forced for about 20 to 30s  CO2 head or probe or curtain is used  CO2 reacts with the sodium silicate to cure, to form hard silica gel Na2SiO3 +CO2 ————— → Na2CO3 + SiO2.xH2O (Silica Gel)

Carbon-dioxide moulding Applications: Aluminum cylinder; Pump, Compressor Impeller, casing; Parts of Diesel engine Advantages:  Quick & simple operation  Requires semi-skilled worker  accommodates a wide range of core and mold sizes  When used for making cores, the process can be automated for long durations &speedy productions runs  Good dimensional tolerance  Good casting surface Limitations:  Recovery of used sand difficult  Binder is hygroscopic and absorbs water  collapsibility slows down production..\Video\Sodium Silicate & CO2 Core Making.(ipad).mp4