The casting Print

Mechanical properties depend on casting technique and on cooling time: a quick cooling, like in continuous, centrifugal or die casting strengthens mechanical properties. And as casting thickness influences the cooling, the project managers have to correctly estimate that a thickness increase causes mechanical properties’ decrease (on yield point, tensile strength, hardness, etc.). Sand casting allows production of a wide range of sizes, shapes and product complexity; by this technology propellers weighing up to 70 Ton can be produced. It is probably the most versatile technique, aimed to produce pumps, valves, bearings, filters, joints, pickling equipment, machinery for paper production and so on.The casting

Permanent mould casting produces pieces which require a better finish and a deeper dimensional precision such as rotors of centrifugal pumps. Huge quantities of small objects without inner core are produced through lost-wax casting. It is a high automatized process. Die casting is suitable to small pieces with complicated shapes, produced in large quantities and low dimensional tolerances. An alloy which is widely used with this technique is CuAl10Fe3 as it has an excellent fluidity in liquid state and resistance to wear, impact and effort: for this reason it is used where repeated impacts are involved such as in components of car gears. Surface quality can furthermore be improved by following machining: for example toothed wheel’s surface hardening improves anti-wear characteristics of the product.

Centrifugal casting is suitable to cylindrical pieces with length between 150 and 2000 mm, included roughly shaped wheels and bearings. One important advantage in using this technique is directional solidification: the external part cools down first, with a small crystalline grain structure, leaving possible imperfections only in the inner part. It is ideal for pieces subjected to wear on their external surface. Continuous or semi-continuous casting is a simple method to produce billets or bars meant for further machining. To sum up solidification method is chosen depending on elements like product dimensions, quantity, dimensional tolerance, finish and costs. During casting operations three risks have to be considered: oxides integration, gas porosity and shrinkage cavities; the first two depend mainly on casting techniques while the third element depends on shape geometry and production method.


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