Pattern types in casting
Solid or single piece pattern
This is one piece pattern. This pattern is the cheapest but its use can be done to a limited extent of production only since its molding involves a large number of manual operations like Gate cutting, providing runner and riser and the like.
Two-piece or split pattern.
Many times the design of casting offers difficult in mold making and withdrawal patterns if a solid pattern is used. For such casting split or two-piece pattern are employed. They are made in two parts which are joined at the parting line by means of the dowel. While molding one part of the pattern is contained by the drag, and others by the cope.
Casting has a more complicated design than above required the pattern in more than two parts in order to facilitate an easy molded and withdrawal of pattern. Their pattern may consist of three or four or more parts depending upon their design.
Match plate pattern
These patterns are used where the rapid production of small and accurate casting is a desire on a large scale. This pattern is made in two pieces, one piece mounted on one side and the other piece on the other side of the plate is called a match plate pattern.
They are also used in mass production of small casting for such casting multi-cavity mold is prepared is single sand mold carries in a number of cavities. The pattern for these casting is connected to each other by means of gate former which provides a suitable channel or gate in the sand for feeding the molten metal to these cavities. Only one runner can be used for feeding the molten metal. This enables a considerable saving in a molding time and a uniform feeding of molten metal.
A pattern consisting of a wooden frame and strips with made called a skeleton pattern. It is filled with loam sand and rammed. The surplus sand is removed by means of strickle. The core can be prepared separately either with the help of a core box or another skeleton made by made for that and assembled in position in the mold.
The sweep can be advantageously is used for preparing the mold for a large symmetrically casting, particularly of circular cross-section. This effect in a large saving in time labor and material. The full equipment consists of the base suitable placed in a sand mass a vertical spindle and wooden plates called a sweep. The outer end of the sweep carries the contour corresponding to the shape of the desired casting. The sleep is rotated about the spindle to the form of the cavity. The hole made by the removal of the spindle is patched up by filling the sand.
Pattern with loose pieces
Some pattern usually single piece is made to have a loose piece in order to enable their easy withdrawal from the mold. These pieces form an integral part of a pattern during molding. After the mold, it completes the pattern is withdrawn leaving the piece in the sand which are later withdrawn separately through the cavity formed by the pattern.
Cope and drag pattern
When the very large casting is to be made the complete pattern becomes too heavy to be handled by a single operator. Such a pattern is made in two parts which are separately molded in different molding boxes. After completion of the mold, the two boxes are assembled to form the complete cavity of which one part is contained by drag and the other is cope. Thus in a way, it is nothing but it two-piece or split pattern of which both the pieces are molded separately instead of being mold in the assembled position
Follow Board pattern
A follow board is a wooden board used to support a pattern during molding. It acts as a sheet for the pattern. Such a single piece pattern that has an odd-shaped or very thin wall requires a follow board. In the former case, the following board is provided with a cavity corresponding to the shape of the pattern in which the pattern is seated for molding. In the latter case, the following board carries a projection conforming to the inside shape of the thin-walled pattern to support it during molding. If such a sport does not provide the pattern may sag or get broken due to less wall thickness during ramming.
These patterns are used for preparing the mold for large circular casting avoiding the use of a solid pattern of the exact size. If the principal they work like a sweet but the difference is that the sweep is given a continue revolving motion to generate the desired shape where the segmental pattern is a portion of the solid pattern itself and the mold is prepared in part by it. It is mounted on a central pivot and after preparing the part mold in one position, the segment is a move to the next position. The operation is repeated until the complete mold is ready.