Metal casting entails filling molten metal into a mould at high pressure and temperature to produce a finished product. Several castings can be produced using this process in a short period. However, defects can occur because of various reasons, including operator skills, choice of equipment, and quality assurance. Defects refer to undesirable imperfections that arise during a casting process such as fusion, gas porosity, shrinkage, and swells. This article examines common casting defects and how to prevent them. Beginners should be mindful of such defects since they can ruin the aesthetics and functionality of finished metal cast products.
Fusion is the process whereby grains of sand, which is the common mould type, fuse with molten metal. The fusion occurs under very high temperature as the molten metal is pressed into a mould. Also, since sand has low refractoriness, fusion occurs, leading to a thin glassy-looking crust that attaches to a casting. Beginners can avoid the fusion problem or control it by reducing the temperature of molten metal just before pouring. Besides, there is a need to improve the refractoriness of moulding material.
One common problem with casting is porosity. Gas porosity occurs when molten metal traps gases, such as oxygen, hydrogen, and nitrogen. Therefore, the trapped gases lead to gas bubbles that form as the molten metal cools. Furthermore, pouring molten material very quickly can cause turbulence, which introduces unwanted gases into a casting process. Gas bubbles can cause circular and rounded cavities or holes, which diminish the surface of a finished product. One way of preventing defects caused by porosity is to dry the cavities and cores before pouring molten metal. You can also increase the rate of solidification of metal by reducing its temperature. Besides, increasing the permeability of sand and introducing fluxes can help in reducing porosity.
Dimensional or geometrical inconsistencies is another common defect that beginners must look out for during casting. A slight shift in mould can cause inaccuracies in dimension. When a mould shifts during casting, the top and bottom parts might misalign, thereby leading to dimensional errors. Other common causes of such inaccuracies include problems with fitting the core, wear and tear, problems with the pattern used, and inaccuracy of metal shrinkage. Inconsistencies in dimensions can be resolved by using a proper mould design and pattern. You can also incorporate metal weights to hold a mould firmly in place to avoid shifting during a casting process.
For more information, contact a die casting service in your area.