SAND CASTING
PRESENTED BY
GROUP 1 ANG PHEI CHEE CHUNG YU NING
PRESENTED BY
GROUP 1 ANG PHEI CHEE CHUNG YU NING
CONTENTS INTRODUCTION THE SAND EQUIPMENTS GATING SYSTEM THE PROCESS FLOW CHART OF PROCESS CYCLE
PRODUCTS OF SAND CASTING
bronze cast model
cast model
INTRODUCTION Sand casting, the most widely used casting process, utilizes expendable sand moulds to form complex metal parts that can be made of nearly any alloy. The sand casting process involves the use of a furnace, metal, pattern, and sand mould.
MATERIALS Sand casting is able to make use of almost any alloy. An advantage of sand casting is the ability to cast materials with high melting temperatures, including steel, nickel, and titanium. The four most common materials that are used in sand casting are shown below, along with their melting temperatures.
Materials
Melting temperature
Aluminum alloys
1220
Brass alloys
1980
Cast iron
1990-2300 1260 C)
Cast steel
2500
F
(660 C)
F
(1082 C)
°
°
°
°
F
°
(1088-
°
F
°
(1371 C) °
ADVANTAGES Can produce very large parts Can form complex shapes Many material options Low tooling and equipment cost Scrap can be recycled Short lead time possible
DISADVANTAGES Poor material strength High porosity possible Poor surface finish and tolerance Secondary machining often required Low production rate High labor cost
THE SAND Different types of sand are used in sand casting; Petro-bond This is a mixture of quality sand and oil or synthetic resin. Green sand A mixture of sand, clay, water and sometimes other additives. It is called green sand because it is re-usable. The right amount of water has to be added to prevent porosity. Sand mixed with water glass can be hardened with CO2 gas . (This transforms the sand into a solid mould, which can be used after the cope & drag are removed.)
CHARACTERISTICS OF SAND FLOWABILITY
The ability to pack tightly around the pattern. PLASTIC DEFORMATION
Have the ability to deform slightly without cracking so that the pattern can be withdrawn. GREEN STRENGTH
Have the ability to support its own weight when stripped from the pattern, and also withstand pressure of molten metal when the mold is cast.
PERMEABILITY
This allows the gases and steam to escape from the mold during casting. THERMAL STABILTY
Ability to resist damage, such as cracking, from the heat of the molten metal. REUSABILITY
Ability of the sand to be reused for future sand molds.
EQUIPMENTS CASTING FLASK ± Consists of the cope (top halve) and the drag (bottom halve) to receive the pattern.
The drag (left) and cope (right) of a casting flask
PATTERN ± Model of products, made of wood, plastic or metals.
CORE ± To produce cavities within the casting, made of plaster, metals and ceramics.
Left:- Corebox, with resulting (wire reinforced) cores directly below. Right:- Pattern (used with the core) and the resulting casting below (the wires are from the remains of the core)
STRAIGHT EDGE BAR ± To level the sand above or below the casting flask, made of metals.
RAMMER ± Consists of 2 different ends, an wedge-shaped end and a flat shape end. Use to compress the sand.
PARTLING SAND ± Put on the pattern to make it easier to remove.
LADLE ± Use to melt the metals and pour into the mould.
GATING SYSTEM This picture shows the cross section of a sand casting mould.
DEFINATIONS POURING CUP ± This is where the metal is poured into the mold.
SPRUE ± The vertical channel from the top of the mold to the gating and riser system. Also, a generic term used to cover all gates, runners and risers.
RUNNER ± The portion of the gate assembly that connects the sprue to the casting in gate or riser.
GATE ± The end of the runner in a mold where molten metal enters the mold cavity.
RISER ± A reservoir of molten metal provided to compensate for the contraction of the metal as it solidifies.
MOLD CAVITY ± The impression in a mold produced by the removal of the pattern. When filled with molten metal it forms a casting.
COPE ± Upper or top most section of a flask, mold or pattern.
PARTING LINE ± A line on a pattern or casting corresponding to the separation between the parts of a mold.
DRAG ± Lower or bottom section of a flask, mold or pattern.
THE PROCESS
A wooden pattern of the required casting shape is made. A metal or plastic can also be used.
A metal or wooden flask is used to contain the sand.
The pattern is placed in the flask and packed in with sand.
The other half of the mould is placed on top, again staring with a wooden or metal frame.
Sand is added around the pattern through a sieve, so that it packs together better.
The sand is then packed around the pattern using the wedge-shaped end of a rammer.
More sand is added, this time not sieved.
The sand is then rammed in firmly using a peen or the flat end of the rammer.
The sand is then leveled off, and the excess removed.
A piece of pipe is carefully pushed through the sand to the pattern to create a runner, and some risers.
Small holes are created in the surface of the sand, and CO2 gas is passed through to harden the molding sand mixed with the water glass.
The 2 halves of the mould are then separated and the pattern removed.
The entrance to the mould ( the runner ) is then connected to the mould cavity, and the other half mould is hardened with CO2.
The 2 halves of the mould are placed back together, ready to make the casting.
Molten metal is poured through the runner until it fills the mould and starts to flow up the risers.
The metal is left to cool and solidify, and then the mould is broken apart to reveal the casting.
The metal is left to cool and solidify, and then the mould is broken apart to reveal the casting.
The runner and risers can then be cut off, and the casting polished to give a better surface finish.
PROCESS CYCLE
MOULD MAKING
CLAMPING
POURING
TRIMMING
REMOVAL
COOLING
PROCESS CYCLE
