TYPE of PATTERNING Choice of pattern depends on: Configuration of casting Number of casting required Types : 1..  Easiest to fabricate  Most inexpensive  May be entirely in the drag

 Used for high depth casting or, to eliminate withdrawal problem  Split along the parting surface  Must be aligned properly  Eliminates withdrawal problems for complex patterns 2.

SPLIT PATTERN contd…

 Two halves of the pattern are mounted on a match plate  Mould preparation  May be with gating and risering  Made up of metal (usually Al)  Large production rate, higher dimensional accuracy  Expensive but additional cost is justified with the increase of productivity 3.3.

USE OF MATCH PLATE PATTERN EXPLAINED

4. Gated Pattern  used for mass production  joins patterns with gates and common runner

5. Sweep Pattern  Used for large axi-symmetric or, prismatic shapes  Reduces cost of 3D pattern  Sweep is a template having a desired contour

6. Loose-Piece Pattern  used when withdrawal is very difficult  Obstructing part held as a loose piece  high skilled job, and generally expensive

7. Skeleton Pattern  Used for small number of large and heavy castings  Ribbed construction of wood which forms an outline  Desired shape obtained by strickle  Making of complete pattern is not economical

 Similar to split pattern  Along with gating and risering system  Cope and Drag may be prepared by two moulders  Generally used for heavy casting 8.

SAND PROPERTIES 1.FLOWABILITY 2.REFRACTORINESS – Ability to avoid fusion with metal 3.PERMEABILITY – Ability of flow of gas passing through a specimen under a standard pressure 4.GREEN STRENGTH – Ability to cling to each other to impart sufficient strength 5.DRY STRENGTH – Ability to retain the shape of the mold cavity in dry condition 6.HOT STRENGTH – strength of the sand that is required to hold the shape in hot condition 7.COLLAPSIBILITY - Ability to provide no resistance during contraction of solidified casting 8.ADHESIVENESS 9.COHESIVENESS 10.DURABILITY

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.Continuous casting 4.Vacuum sealed casting 5.Slush casting 6.Squeeze castingetc.

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 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  Evolution of gases reduced  Good dimensional tolerance  Good casting surface Limitations:  Recovery of used sand difficult  Binder is hygroscopic and absorbs water  collapsibility slows down production  Generally used for high- production runs Sodium Silicate & CO2 Core Making.(ipad).mp4