Sand Casting

Sand Casting

It is a process in which molten metal flows by gravity into a mold where it solidifies into the shape of mold cavity.
It has advantages and disadvantages too which are stated respectively:

• Internal and hollow sections can be made in single step.
• It has big application like in making propelliar.
• It has limitation in mechanical properties like porosity, poor dimensional accuracy, poor surface finish. 

Terms Related To Casting

Terms related to casting are described below:

• Riser     →     It is a reservoir used into metal casting mold to prevent cavities due to shrinkage.
• Pouring Cup     →     It is a basin through which molten metal is poured into mold.
• Sprue     →     It is a passage through which molten metal is introduce into mold.
• Core     →     It is a full scale model of the interior surfaces of the part.
• Chaplets     →     Parts which hold the core in its position in the mold cavity during pouring.
• Cope     →     The lower portion of mold from parting line.
• Drag     →     The upper portion of mold from parting line.
• Flask     →     A container in which cope, drag and mold cavity are surrounded by sand.
• Parting Line     →     A line which separates cope and drag of mold.

Pattern & it's Types:

A full sized model of the part enlarged to account for shrinkage and machining allowance in the final casting.

There are 4 types of pattern which are discussed below:

1. Solid or One Peice Pattern:

• It has same geometry as casting and can be adjusted in size for shrinkage and machining.
• Addition of gating system is left to worker.
• Location of partition line between two halves of mold is a big problem.

2. Split Pattern:

• Pattern is divided into two segments along a single parting line.
• Addition of gating system is left to worker.
• Tapered pins in the cope align with holes in drag for proper positioning.

3. Match Plate Pattern:

• Two pieces of split Pattern are attached to opposite sides of wood or metal plate.
• Holes in the plate allow the cope and drag sections of the mold to be aligned accurately.

4. Cope & Drag Pattern:

• Cope and drag halves of spilt pattern are attached to separate match Plate to produce cope and drag pattern.
• Used for large castings.

Pattern Allowance:

Modifications that are incorporated into a pattern due to solidification shrinkage and machining is called Pattern Allowance.

Some pattern allowance like shrinkage, draft, machining are diccussed in the video given below:

Sand Conditioning:

Conditioning of sand is required to fulfill the following properties:

1. Strength:

The molds ability to maintain its shape and resist erosion caused by the flow of molten metal.

2. Permeability:

Ability to permit gases to escape through the voids in the sand.

3. Thermal Stability:

Ability of sand at the surfaces of the mold cavity to resist cracking.

4. Collapsibility:

Ability of mold to shrink without cracking the casting.

5. Reusability:

Ability of sand to be use multiple times to make other molds.

If you want to know about future or nowaday technology for sand conditioning.

Types of Sand Molds:

There are three types of sand molds which are discussed below:

1. Green sand mold  ↣  Mold which contains moisture at the time of pouring.
2. Dry sand mold   ↣   Mold which contains no moisture because it is baked in oven at temperature of about 150 to 300°C.
3. Skin Dried sand mold   ↣   Mold which is partially achieved by drying the surface of green sand mold upto 15mm by using heating lamps.

Reference:

• University Notes 
• Book Fundamental of Modern Manufacturing 6th Edition by Mikell P. Groover
• Videos from youtube and Google 
• Images from google images