Durability, reliability and good mobility of structures and machines depend to a large extent on the materials from which they were made and their properties. The choice of material from which potential castings will be made is one of the first steps in ensuring the highest quality of components and installations, as well as a satisfactory final result. Want to know how to choose a casting material?
In order to design a foundry product, it is worth first defining what functional functions it is to fulfill. For this purpose, it is worth specifying the specificity of the product in the most specific way possible.
The following questions will help with this:
It can be, for example, transport, construction machinery, shipbuilding.
Thanks to this question, we can determine how many and what sizes of castings we need.
Will the system using casts work under high temperature, will it come into contact with water or chemicals, or will it work as part of a moving structure?
Already at the design stage, it is necessary to consider what material the object will be made of in order to obtain its optimal parameters.
The above questions should be clarified using the criteria according to which the material is selected. These criteria are:
Not all of these criteria must always be considered useful, and it is not always reasonable to include them in a complete set. For example, when the casting is to be an internal structural element of a construction machine, uniform color or other eye-friendly properties will not be important. However, precision and accuracy will still count.
Let's take a closer look at these criteria.
The construction criteria provide appropriate properties of the finished casting, guaranteeing its functionality and durability.
The technological criterion is what makes it possible to make a casting using a material that will have the desired properties, so as to avoid a time-consuming, energy-wasting and production-wasting process.
The economic criterion boils down to the use of the material that will be the cheapest and most available among the materials that meet the relevant requirements.
The ecological criterion is a criterion according to which the material with the longest life is selected, taking into account the phase of the product's life cycle (i.e. production, distribution and use), including the possibility of utilization and management (including reuse) of the generated waste.
The aesthetic criterion, important for example in industrial design, takes into account aesthetic aspects such as shape, color, surface texture, proportion, style of execution, possibility of forming and resistance to external factors.
After specifying our needs and taking into account all of the following individual criterias, we move on to the last - and most important - stage of selecting casting materials –their properties. Among the parameters for the selection of casting materials, we distinguish:
What exactly are these properties?
| Physical properties | Chemical properties | Mechanical and technological properties | Technical (utility) properties |
Physical properties include, for example:
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Chemical properties include:
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technological properties | Technical (utility) properties include:
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| tensile properties | |||
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It is worth presenting the mentioned properties wider.
Density is the ratio of the mass of a homogeneous body to the volume, expressed in kg/m3 or g/cm3. Alloys and light metals, such as lithium, sodium, magnesium, aluminum and their alloys, are characterized by low density. On the other hand, heavy metals, such as iron, nickel, copper, tungsten, platinum and their alloys, have a high density.
The melting point of metals and their alloys is described in degrees Celsius (°C). All metals are fusible, but their melting point varies within very wide limits. For this reason, they are divided into easily fusible, hardly fusible and very fusible. Metals have a constant melting point, while the melting point of most alloys falls within certain temperature ranges.
Specific Heat Capacity simply means the amount of heat given off or absorbed by 1g of a given substance when the temperature changes by 1°C. The specific heat depends on the type of substance, temperature and method of heating. It is
Thermal conductivity can be defined as the rate at which heat is transferred by conduction through a unit cross-section area of a material, when a temperature gradient exits perpendicular to the area. As one of the characteristic features of metals and alloys the measure of thermal conductivity is presented as the amount of heat that flows through a 1 m long conductor with a cross section of 1 m2 in 1 hour at a temperature difference of 1°C.
The electrical conductivity of metals and alloys is the ability to conduct electricity.
The magnetic properties of metals and alloys rely on their ability to become magnetized.
Thermal expansion is the ability of certain material to change its shape, area, volume, and density in response to a change in temperature. Thermal expansion of metals and alloys manifests itself in an increase in linear dimensions and volume under the influence of temperature increase and contraction during cooling. The phenomenon of thermal expansion is of great practical importance and must be taken into account in the construction of bridges, devices operating in variable temperatures and heat engines.
Mechanical properties determine the resistance of the metal to external factors.
The technological properties of metals are a way to determine their suitability when processed.
Knowing the theoretical side of the issue, it is worth looking at its practical aspect. In this part of our small guide, we will show the properties and applications of exemplary materials used in foundry, on the example of cast iron and cast steel castings.
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