Types of Pattern
Patterns are of various types, each satisfying certain casting requirements.
Single Piece Pattern
The one piece or single pattern is the most inexpensive of all types of patterns. This type of pattern is used only in cases where the job is very simple and does not create any withdrawal problems. It is also used for application in very small-scale production or in prototype development. This type of pattern is expected to be entirely in the drag and one of the surface is is expected to be flat which is used as the parting plane. A gating system is made in the mold by cutting sand with the help of sand tools. If no such flat surface exists, the molding becomes complicated. A typical one-piece pattern is shown in Figure 6.
Figure 6: A Typical One Piece Pattern
Split or Two Piece Pattern
Split or two piece pattern is most widely used type of pattern for intricate castings. It is split along the parting surface, the position of which is determined by the shape of the casting. One half of the pattern is molded in drag and the other half in cope. The two halves of the pattern must be aligned properly by making use of the dowel pins, which are fitted, to the cope half of the pattern. These dowel pins match with the precisely made holes in the drag half of the pattern. A typical split pattern of a cast iron wheel Figure 7 (a) is shown in Figure 7 (b).
Figure 7 (a): The Details of a Cast Iron Wheel
Figure 7 (b): The Split Piece or Two Piece Pattern of a Cast Iron Wheel
Classification of casting Processes
Casting processes can be classified into following FOUR categories:1. Conventional Molding Processes
2. Chemical Sand Molding Processes
3. Permanent Mold Processes
4. Special Casting Processes
Green Sand Molding
Green sand is the most diversified molding method used in metal casting operations. The process utilizes a mold made of compressed or compacted moist sand. The term "green" denotes the presence of moisture in the molding sand. The mold material consists of silica sand mixed with a suitable bonding agent (usually clay) and moisture.
Sand Mold Making Procedure
The procedure for making mold of a cast iron wheel is shown in (Figure 8(a),(b),(c)).
Figure 8 (a)
Figure 8 (b)
Figure 8 (c)
Figure 8 (a, b, c): Sand Mold Making Procedure