CORE AND CORE BOX
Cores are compact mass of core sand that when placed in mould cavity at required location with proper alignment does not allow the molten metal to occupy space for solidification in that portion and hence help to produce hollowness in the casting. The environment in which the core is placed is much different from that of the mold. In fact the core (Fig. 10.12) has to withstand the severe action of hot metal which completely surrounds it. Cores are classified according to shape and position in the mold. There are various types of cores such as horizontal core (Fig. 10.13), vertical core (Fig. 10.14), balanced core (Fig. 10.15), drop core (Fig. 10.16) and hanging core (Fig. 10.17).
There are various functions of cores which are given below
1. Core is used to produce hollowness in castings in form of internal cavities.
2. It may form a part of green sand mold
3. It may be deployed to improve mold surface.
4. It may provide external under cut features in casting.
5. It may be used to strengthen the mold.
6. It may be used to form gating system of large size mold
7. It may be inserted to achieve deep recesses in the casting
1. Core Box
Any kind of hollowness in form of holes and recesses in castings is obtained by the use of cores. Cores are made by means of core boxes comprising of either single or in two parts. Core boxes are generally made of wood or metal and are of several types. The main types of core box are half core box, dump core box, split core box, strickle core box, right and left hand core box and loose piece core box.
1. Half core box
This is the most common type of core box. The two identical halves of a symmetrical core prepared in the half core box are shown in Fig. 10.17. Two halves of cores are pasted or cemented together after baking to form a complete core.
2. Dump core box
Dump core box is similar in construction to half core box as shown in Fig. 10.18. The cores produced do not require pasting, rather they are complete by themselves. If the core produced is in the shape of a slab, then it is called as a slab box or a rectangular box. A dump core-box is used to prepare complete core in it. Generally cylindrical and rectangular cores are prepared in these boxes.
3. Split core box
Split core boxes are made in two parts as shown in Fig. 10.19. They form the complete core by only one ramming. The two parts of core boxes are held in position by means of
clamps and their alignment is maintained by means of dowel pins and thus core is produced.
4. Right and left hand core box
Some times the cores are not symmetrical about the center line. In such cases, right and left hand core boxes are used. The two halves of a core made in the same core box are not
identical and they cannot be pasted together.
5. Strickle core box
This type of core box is used when a core with an irregular shape is desired. The required shape is achieved by striking oft the core sand from the top of the core box with a wooden piece, called as strickle board. The strickle board has the same contour as that of the required core.
6. Loose piece core box
Loose piece core boxes are highly suitable for making cores where provision for bosses, hubs etc. is required. In such cases, the loose pieces may be located by dowels, nails and dovetails etc. In certain cases, with the help of loose pieces, a single core box can be made to generate both halves of the right-left core. Copied from Introduction to Basic Manufacturing Processes and Workshop Technology by Rajender Singh.