Types of Pattern

• Solid pattern or Single piece pattern.
• Split pattern.
• Loose piece pattern.
• Gated pattern.
• Match plate pattern.
• Sweep pattern.
• Skeleton pattern.
• Cope and drag pattern.
• Segmental pattern.
• Follow board pattern.

Solid Pattern/Single Piece Pattern: A single piece pattern is used for a simple casting. In this pattern, no joint or partition is used. It can be moulded in a single moulding box as shown in Figure 20.4.

Figure 20.4 Single Piece Pattern

Split Pattern: If design of the pattern is not simple, it is difficult to withdraw as a single piece from mould. The pattern is made into two pieces or into a split form and joined together by dowels, which is shown in Figure 20.5.

Figure 20.5 Split Pattern

Loose Pieces Pattern: Some single piece patterns are made to have loose pieces in order to enable their easy withdrawal from the mould. These pieces form an integral part of the pattern during moulding (Figure 20.6). After the mould is complete, the pattern is withdrawn leaving the pieces in the sand, which are later withdrawn separately through the cavity formed by the pattern.

Figure 20.6 Loose Piece Pattern

Gated Pattern: In a mass production, where many castings are required, gated pattern may be used. Such patterns are made of metal to give them strength and to eliminate any warping tendency. The connecting parts between the patterns form the gates or runners for the passage of molten metal into the mould cavity, are the integrated parts of this pattern (Figure 20.7).

Figure 20.7 Gated Pattern

Match Plate Pattern: Match plates provide a substantial mounting for patterns and are widely used with machine moulding. In the figure, a match plate is shown upon which patterns are mounted for two small dumb bells. It consists of a flat metal or wooden plate to which the patterns and gates are permanently fastened. On either end of the plate, there are holes to fit into a standard flask (Figure 20.8).

Figure 20.8 Match Plate Pattern

Sweep Pattern: Sweeps can be used for preparing moulds of large symmetrical castings of circular cross-section. The sweeping equipment consists of a base, suitably placed in the sand mass, a vertical spindle, and a wooden template, called sweep. The sweep may have different shapes of casting desired. The sweep is rotated about the spindle to form the cavity (Figure 20.9). Then the sweep and spindle are removed. The filling sand patches the hole of spindle. Cores are fitted as required.

Figure 20.9 Sweep Pattern

Skeleton Pattern: Skeleton pattern requires large amount of wooden work. It is used for large size casting. A pattern consists of a wooden frame and strips, called skeleton pattern. It is filled with loam sand and rammed properly, and surplus sand is removed. Both halves of the pattern are symmetrical as shown in Figure 20.10.

Figure 20.10 Skeleton Pattern

Cope and Drag Pattern: Cope and drag pattern is used for heavy casting which is difficult to handle in a single piece. This pattern is made in two parts in cope and drag and finally assembled together to form a complete mould cavity (Figure 20.11).

Figure 20.11 Cope and Drag Pattern

Segmental Pattern: Segmental pattern is used for large ring-shaped casting (Figure 20.12). A vertical central spindle is firmly fixed near the centre of a drag flask. The bottom of the mould is then rammed and swept level with a sweep. Now, with the segmental pattern is properly fastened to the spindle and in a starting position, moulding sand is rammed up on the inside and outside of the pattern but not at the ends. After the surplus sand has been levelled off from its top, the segmental pattern is unfastened from the spindle, rapped, and drawn. The next position for the segmental pattern will be adjoining its last position with sufficient overlap to ensure continuity. The process is continued until a complete ring-shaped mould cavity has been made. The mould may be closed with a cope or with cover cores. Sweeps and segmental patterns are widely used for making large gears, wheels, and sheaves. Cores made in one core box may be set together on a level surface to form spokes and inside surfaces of the rim and the hub. A large cast gear can be moulded with a segmental pattern having only three or four teeth.

Figure 20.12 Segmental Pattern

Follow Board Pattern: Follow board is a wooden board, which is used to support a thin section pattern. The pattern may have a cavity shape or projection shape. Due to thin section during ramming there is chance of breaking of pattern, therefore a support of same shape follow board is required which is shown in Figure 20.13.

Figure 20.13 Follow Board Pattern

Colour Codes Used in Pattern

Following colour codes are used on pattern for various purposes as given below:

• Red: Surface is to be machined.
• Black: Surface is to be left unmachined.
• Yellow: Core print is to be used.
• Black strips or Yellow base: Stop offs.
• Clear or no colour: Parting surface.