The Casting Process
Complicated castings such as for example chain links with many undercuttings can either be made using a sand mould or via a waxmelting process. The latter is specially suitable for producing smal parts. The principles of the manufacture are as follows:
1. The objekt with the form of the required casting is connected to one or serveral melt-flow-leads. Hereafter this object is encased in silicon. After the silicon is completely hardened it is carefülly cut open and the objekt removed.
2. The silicon form is closed. Wax liquified at ca. 70° C is injected into the form using little pressure. After hardening the wax model is removed. This step is repeated as often as required. The wax models are cleaned, inspected an connected to each other so as to form a casting-system (-tree). This system is placed into a box that is heat-resistant. Applying vacuum the free space in the box is completely filled with a special type plaster of paris.
3. The box with the contents is held at ca. 730° C for eleven hours. The wax and the water content of hte plaster evaporate.
4. Using vacuum liquid brass having ca. 1000° C is poured into the casting system.
5. The castings are freed from plaster, cleaned and the melt-flow-leads removed.
The exected yield is ca. 90 %.
Advantages of the Casting Process:
- Nearly all types of shapes can be produced - even those with many undercuttings. In consequence this process is especially suited for the produktion of chain-links.
- For small series this casting process is also the method of choice because the costs involved to make the form are small in contrast to other casting methods.
- The process is labour intensiv. Each article needs two casting steps: The wax- and the metal form production. Also the multiple wax forms of an article must have wax connections as a prerequsite for the the thereafter metal-casting.
- The process is also cost-intensive because a special type of plaster of paris is needed, that can only be used once, also disposal fees a charged. The wax is costly.
- The process involves a fair amount of time. For example, the plaster moulds need a minimum calcination time of elven hours to guarantee the complete removal of wax residues as well as a flawless casting.